GB2535745A

GB2535745A - Glow plug resistance measurement circuit and method

Info

Publication number: GB2535745A
Application number: GB1503185.9A
Authority: GB
Inventors: Nieddu Stefano
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2015-02-25
Filing date: 2015-02-25
Publication date: 2016-08-31
Anticipated expiration: 2035-02-25
Also published as: GB2535745B; GB201503185D0

Abstract

A method for measuring the resistance RGP of a glow plug 360 comprises (a) connecting at least one resistor 510, 550 of known resistance RSH Rref to the glow plug to create a voltage divider 600 between a feeding node 535 and a ground node 365, an intermediate node 515, 520 being provided between the glow plug 360 and the at least one resistor (510, 550); (b) integrating over time alternatively a first, a second and a third voltage signal VI, V2, V3 as input signal VINT,in to obtain an output signal VINT,out (c) comparing the output signal VINT,out with a low threshold value VL and a high threshold VH for generating a pulse width modulated signal VPWM (d) selecting the voltage signals VI, V2, V3 as input signal VINT,in in step (b), on the basis of a variation over time of the pulse width modulated signal VPWM and (e) determining the resistance value RGP of the glow plug on the basis of the known resistance value RSH Rref and of a variation over time of the pulse width modulated signal VPWM.

Description

GLOW PLUG RESISTANCE MEASUREMENT CIRCUIT AND METHOD

TECHNICAL FIELD

*** The present invention relates to a circuit and a method for measuring the resistance value of a glow plug, in order to determine an actual operating temperature value of it. BACKGROUND * n * *** * ** e* It is known that Diesel engines are provided with ceramic or metallic glow plugs for * * * * 15 allowing cold-start of the engine and for optimizing combustion performance during engine operation.

Glow plugs are located in a combustion chamber of the engine and are electrically connected to a voltage power source, for example a battery of the vehicle, by means of an electric switch controlled and driven by an electronic control unit (ECU).

During operation of the engine the temperature of glow plugs must be accurately controlled to keep the operating temperature in a predetermined operating range. Indeed, an excessive heating of the glow plugs can stress them, shortening their service life, while a too low temperature can lead to an increase of polluting substances in the environment.

The temperature of a glow plug is controlled by monitoring its electrical resistance since the temperature depends on the electrical resistance of the glow plug. * to* * ** * * e * * e* * * *

According to a known prior art the electrical resistance of a glow plug is determined by measuring directly both current and voltage of the glow plug and calculating the resistance by means of the Ohm law, i.e. by using a volt-amperometric measurement.

The measurement precision of the electric current is strictly depending on the technical implementation and usually is insufficient to be compliant with the accuracy requirements, therefore a compensation at the end of the line of production is needed, which increases the production cost.

Additionally, the measurement accuracy can be negatively influenced during the life-cycle of the vehicle, in particular due to aging.

In any case the determination of the electrical resistance of a glow plug made according to the prior art can have, as an optimistic case, a tolerance equal or greater of * * * ** * the 4%, which involves a temperature tolerance of ± 60°C, considering a glow plug working ** * * temperature of 1250°C. * ***

Current developments in the engine components management via the electronic * * * ( * control unit (ECU) aims at providing a design rationalization of the ECU, and in some cases * -** * to the design of in-house electronic control units. * * *

* * The implementation of a measurement circuit into an ASIC (application-specific * * integrated circuit), and in general to a separate component, dedicated to the glow plugs management could save costs for the ECU.

But this is a challenge for the silicon technologies used in automotive field, in fact, low offset operational amplifiers cannot be implemented into high voltage CMOS chips because the minimum offset achievable is about 2,5 mV.

Additionally, the glow plug measurement signal is very low, in fact, the minimum operating value is 25mV. Therefore, the offset is comparable with the signal range and this inevitably causes a measurement error of 10%, which is too high and practically not

acceptable.

In view of the above, an object of an embodiment of the present invention is to improve the resolution accuracy of the determination of a resistance value of glow plugs (in particular of ceramic glow plugs) to allow an efficient temperature control of the glow plugs.

Another object of an embodiment of the present invention is to provide a direct measurement of the resistance value of the glow plug, wherein the measured resistance value is independent from the offset of the electronic components of the circuit.

Another object is that of accomplish the above-mentioned goals with a simple, rational and rather inexpensive solution, which can be implemented into an ASIC dedicated to the glow plugs management.

SUMMARY

* * * * * * * * * * * *These and other objects are achieved by the embodiments of the invention as defined * * * * * 15 * * * *** ° * * * * * * * * * . * * * * * * * in the independent claims. The dependent claims include preferred and/or advantageous aspects of said embodiments.

An embodiment of the invention provides a method for measuring a resistance value of a glow plug having an on state and an off state. The method comprises the steps of: a) connecting at least one resistor, having a known resistance value, to the glow plug to create a voltage divider between a feeding node and a ground node, wherein the feeding node is arranged between a free end of the at least one resistor and a voltage power source and the ground node is arranged between a first end of the glow plug and a ground pole, an intermediate node being provided between the glow plug and the at least one resistor; b) integrating over time alternatively a first, a second and a third voltage signal, as input signal to obtain an output signal, wherein the first, second and third voltage signals are defined respectively as the difference between a reference voltage value and the voltage value at the feeding node, the difference between the reference voltage value and the voltage value at the ground node and the difference between the reference voltage value and the voltage value at the at least one intermediate node between the glow plug and the at least one resistor; c) comparing the output signal obtained during the step b) with a low threshold value and a high threshold for generating a pulse width modulated signal on the basis of said comparison, d) selecting said first, second, and third signal as input signal in said step b), on the basis of a variation over time of the pulse width modulated signal, e) determining the resistance value of the glow plug on the basis of the resistance value of the at least one resistor and of a variation over time of said pulse width modulated * ** signal.

* * * *** * Advantageously, the integration of at least three voltage signals, and in particular of * * ** ** * * * * * advantageously providing a measured value of the glow plug resistance that is ** * independent from the offset effects. * * *

* * * Additionally, it is possible to improve the measurement accuracy, in fact, the ** * measured resistance value of the glow plug will be dependent on the tolerance of the at * * least one resistor that is connected to the glow plug. More in detail, the error in determine the resistance value of the glow plug can be of the order of 1%, in fact, the tolerance of the at least one resistor connected to the glow plug is lower than 1%. This advantageously leads to an accuracy of the temperature evaluation of the glow plug that is of the order of 1%, i.e. ± 15°C, considering a glow plug working temperature of 1250°C.

It has to be also noted that the degradation of the accuracy of the resistor connected to the glow plug can be neglected, in fact, the resistor is stable and is substantially not a first, a second, and third voltage signals allows to compensate the offset effects, thus * * * affected by aging effects.

* * * According to an aspect of the invention, in the step a) a reference resistor and a shunt resistor are connected to the glow plug. The shunt resistor is selectively connected and disconnected to/from the glow plug, and in particular the shunt resistor is connected to the * * * * 5 glow plug during the on state of the glow plug and the shunt resistor is disconnect from the glow plug during the off state of the glow plug.

More in detail, during the on state of the glow plug both the shunt resistor and the reference resistor are connected to the glow plug, while during the off state of the glow plug only the reference resistor is connected to the glow plug, the shunt resistor being disconnected from the glow plug.

This aspect of the invention allows to carry out the measurement of the glow plug resistance value during both the on state and the off state of the glow plug.

It has to be noted that according to an aspect of the invention, the reference resistor is permanently connected to the glow plug.

It has to be also noted that according to an aspect of the invention, the shunt resistor is connected to the glow plug to provide the on state of the glow plug and the shunt resistor is disconnect from the glow plug to provide the off state of the glow plug. According to an aspect of the invention, the third voltage signal is defined as the difference between a reference voltage value and the voltage value at a second intermediate node between the glow plug and a shunt resistor during the on state of the glow plug, and the third voltage signal is defined as the difference between the reference voltage value and the voltage value at a first intermediate node between the glow plug and a reference resistor during the off state of the glow plug.

An advantage of this aspect, is to allow the measurement of the glow plug resistance value during both the on state and the off state of the glow plug in a simple way, by using * * * * * * * ** * * * * * * * * * * * * * * * * * * * different resistors connected to the glow plug and thus using different voltage signals to be integrated over time during the on state and during the off state of the glow plug. Additionally, the use of different voltage signals in the on state of the glow plug and in the off state of the glow plug allows to provide at least three voltage signals in both the on state and the off state of the glow plug, to be integrated in said step b).

According to another aspect of the invention, in the step d) of selecting said first, second, and third voltage signals as input signals is carried out according to at least one sequence in which the first, second and third voltage signals have alternatively positive and negative values.

Thanks to this aspect, the sequence of voltage values used as input signal on the basis of the selection made in said step d), allows to provide an alternation of voltage * ** * * * signals having opposite values (positive/negative) used to provide a modification pulse * * * * * width modulated signal during the comparison of said voltage signals with a low threshold * * ** ** ** * * * According to an aspect of the invention, the step of integrating over time alternatively * * * a first, a second and a third voltage signal as input signal comprises four integrations. More * * * ** * ** in detail, said first, second and third voltage signals are integrated one time, and * * * * additionally a further integration of at least one of said first, second and third voltage signal is carried out for a second time (i.e. twice). In other words, at least one of said first, second and third voltage signal is integrated two times, thus four integrations can be carried out.

As it will be disclosed later in greater detail, according to an aspect, the step d) of selecting the first, second, and third voltage signals as input signal is carried out according to at least one sequence comprising at least four voltage signals as input signal. More in detail, the sequence comprises each of said first, second, and third voltage signals and one of said first, second and third voltage signal is repeated two times in the sequence.

value and a high threshold.

According to an aspect of the invention, the step d) of selecting the first, second, and third voltage signals as input signal is carried out according to at least one first sequence during the on state of the glow plug and according to at least one second sequence during the off state of the glow plug.

Advantageously, this aspect allows to provide different sequences of the selected voltage signals as input signal to be integrated over time, during the on state of the glow plug and during the off state of the glow plug.

According to still another aspect of the invention, the at least one sequence during the on state of the glow plug comprises the following succession: V2, V3, V2, VI, and at least one sequence during the off state of the glow plug comprises the following succession: V2, VI, V3, Vi, wherein V, is defined as the difference between a reference * * * voltage value and the voltage value at the feeding node, V2 is defined as the difference * ** *** * * between the reference voltage value and the voltage value at the ground node, and V3 is ** * * * * * at least one intermediate node between the glow plug and the at least one resistor. *

* * * * An advantage of this aspect is to provide a simple and effective way to measure the * * * * * * resistance value of the glow plug in both the on state and the off state of the glow plug, * * * * * * while providing a measured value which is not affected by offset effects.

According to an aspect of the invention, the at least one sequence of voltage signals is synchronized with the pulse width modulated signal generated during said step c).

Thanks to this aspect, it is possible to provide a modification of the voltage signal to be integrated and thus to determine the time interval need for selecting another voltage signal as input signal used for the measurement of the resistance value of the glow plug.

According to an aspect of the invention, the resistance value of the glow plug during the on state of the glow plug is determined by the equation: defined as the difference between the reference voltage value and the voltage value at the RsH * Rref tup (t0 tdwn) RGp = (RsH Rref) tdwn (rD tup) wherein tdvin is the time interval needed for the output signal to pass from said low threshold value to said high threshold value during integration of said second voltage signal; to is the time interval needed for the output signal to pass from said high threshold value to said low threshold value during integration of said third voltage signal; top is the time interval needed for the output signal to pass from said high threshold value to said low threshold value during integration of said first voltage signal; RsH and Rrer are the resistance values of a shunt resistor and of a reference resistor connected to the glow plug during the on state of the glow plug.

Advantageously, this aspect provides a simple and reliable way to measure the resistance value of the glow plug as a function of time intervals (and in particular on the * * * * * * variation over time of said pulse width modulated signal) and of the known resistance * * * * * * . values of the resistors connected to the glow plug. Advantageously, the measured * * * * resistance value of the glow plug is not affected by offset effects and it is also accurate, ** * * * * 15 being the tolerance of the resistors connected to the glow plug lower than 1%. * * *

According to an aspect of the invention, the resistance value of the glow plug during * * * * * * * * * * the off state of the glow plug is determined by the equation: * tup (t3 taunt) * * RGp -Rref lawn (ts tup) wherein town is the time interval needed for the output signal to pass from said low threshold value to said high threshold value during integration of said second voltage signal; is is the time interval needed for the output signal to pass from said low threshold value to said high threshold value during integration of said third voltage signal; tin, is the time interval needed for the output signal to pass from said high threshold value to said low threshold value during integration of said first voltage signal; and Ref is the resistance 2 5 value of a reference resistor connected to the glow plug, preferably permanently connected to the glow plug.

This aspect provides a simple and reliable way to measure the resistance value of the glow plug also in the off state of the glow plug. The measured resistance value is calculated as a function of time intervals (and in particular on the variation over time of said pulse width modulated signal) and of the known resistance value of a reference resistor, preferably permanently connected to the glow plug. Advantageously, the measured resistance value of the glow plug is not affected by offset effects and it is also accurate being the tolerance of the resistor connected to the glow plug lower than 1%.

According to still another aspect of the invention, said step e) provides to evaluate a weighted average of the resistance value of the glow plug measured during the on state, and/or during the off state, of the glow plug on the basis of the time duration of said on * ** * * * state and/or of said off state of the glow plug. *** *

* An advantage of this aspect is to increase the accuracy of the measurement taking * * * * * * * * * which the measurement of the resistance value is carried out. More in detail, the weighted average of the resistance value of the glow plug measured during the on state, and/or * * * * * * during the off state, can be advantageously calculated on the basis of the duty cycle of a * * * * * switch configured to turn on and turn off the glow plug, i.e. a switch intended to modify the state (on/off states) of the glow plug.

The method of the invention can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of a computer program product comprising the computer program. The method can be also embodied as electromagnetic signals, said signal being modulated to carry a sequence of data bits which represent a computer program to carry out all steps of 2 5 the method.

into account the time duration of the on state and/or of the off state of the glow plug during Another embodiment of the invention provides for a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a memory system associated to the Electronic Control Unit (ECU) and a computer program comprising a program-code for carrying out all the steps of the method described above, the computer program being stored in the memory system.

Another embodiment of the invention provides for a circuit for measuring a resistance value of a glow plug. The glow plug is provided with a first end connected to a ground pole and a second end connectable to a voltage power source by means of at least one resistor. The at least one resistor is connectable to the glow plug for creating a voltage divider between a ground node, arranged between a free end of the glow plug and a ground pole, and a feeding node arranged between a free end of the at least one resistor and the voltage *rther provided with at least one intermediate node between the glow plug and the at least one resistor. The circuit further comprises a input selector and a voltage integrator connected to the input selector, the input selector being configured to alternatively connect the voltage integrator to the feeding node, or to the * * * * ground node, or to the at least one intermediate node to select a first, a second, and a third ** * * * * * * * * * * * * * voltage signal as input signal of the voltage integrator. The voltage integrator is provided Oil * * * with an output line for providing an output signal indicating the integral over time of the input signal. The circuit further comprises a comparator and a logic unit, said comparator being connected to the output line of the voltage integrator for providing a pulse width modulated signal to the logic unit for evaluating said resistance value of said glow plug and for controlling said input selector.

An advantage of this embodiment is to provide a circuit for measuring the resistance value of the glow plug that is accurate and at the same time independent from the voltage signal supplied to the circuit. * * * ** * ** * *

Moreover, the accuracy of the measured resistance value of the glow plug is very high, being dependent on the resistance value of the at least one resistor connected to the glow plug.

Additionally, the circuit according to an embodiment of the invention allows to measure the resistance value of the glow plug by using three voltage signals which are selected and integrated over time, thus allowing a compensation of the offset effects.

Additionally, the circuit can be advantageously implemented on in-house developed electronic control unit (ECU) via an ASIC or a discrete component.

According to an aspect of the invention, the circuit comprises a shunt resistor having a known resistance value, and a reference resistor having a known resistance value. The reference resistor has a first end connected to the feeding node and a second end * ** * * * connected to a first intermediate node of the voltage divider arranged at a second end of *** * 9 the glow plug. The shunt resistor has a first end connected to the feeding node and a * * * * * arranged between the shunt resistor and the glow plug, preferably between the first and * ** * * second intermediate nodes, to selectively connect and disconnect the shunt resistor * * . * * * to/from the glow plug. Advantageously, according to this aspect a shunt resistor is ** * * * * AI selectively connected and discontented to/from the glow plug respectively during the on state and the off state of the glow plug.

By doing so, it is possible to carry out the measurement of the glow plug resistance value during both the on state and the off state of the glow plug.

It has to be noted that the reference resistor is preferably permanently connected to the glow plug during both on and off states.

According to an aspect of the invention, the switch arranged between the shunt resistor and the glow plug, preferably between the first and second intermediate nodes, is * ** ** second end connected to a second intermediate node of the voltage divider. A switch is configured to modify the operating state of the glow plug, i.e. to provide the on/off states of the glow plug. It has to be noted that the switch arranged between the shunt resistor and the glow plug is preferably arranged between the shunt resistor and the first intermediate node, where the reference resistor is connected to the glow plug.

In general it has to be noted that the glow plug is provided with an on state and an off state, and a switch preferably controlled and driven by an electronic control unit (ECU) is used to modify the operating state of the glow plug, i.e. to provide the on/off states of the glow.

According to an embodiment of the invention, the resistance value of the reference 1c) resistor is much greater than the resistance value of the glow plug, and the resistance value of the shunt resistor is much less than the resistance value of the glow plug. *

** * An advantage of this embodiment is that when the glow plug is in the off state the * *** * * reference resistor is practically connected in series with the glow plug, at the same time a ** ** ** * * * ** reference resistor, which can be used as input signal to be integrated. * ** * *

An advantage of this embodiment is that when the glow plug is in the on state the ** * * * * shunt resistor is practically connected in series with the glow plug, and at the same time a ** ** * * voltage value is present at the second intermediate node between the glow plug and the shunt resistor which can be used as input signal to be integrated. It has to be noted that, according to a possible embodiment, in the on state of the glow plug the shunt resistor is in parallel with the reference resistor, and both these resistors are connected to the glow plug.

Another embodiment of the invention provides an internal combustion engine comprising at least one glow plug and a circuit described herein for measuring the resistance value of the glow plug. I. *

voltage value is present at the first intermediate node between the glow plug and the Still another embodiment of the invention provides an automotive system comprising an engine provided with at least one glow plug, the automotive system further comprising a circuit described herein for measuring the resistance value of the glow plug.

Still another embodiment of the invention provides an automotive system comprising an engine provided with a glow plug and at least one resistor, having a known resistance value, connected to the glow plug to create a voltage divider between a feeding node and a ground node, wherein the feeding node is arranged between a free end of the at least one resistor and a voltage power source and the ground node is arranged between a first end of the glow plug and a ground pole, an intermediate node being provided between the glow plug and the at least one resistor, further comprising: * means for integrating over time alternatively a first, a second and a third voltage signal, * ** * -* as input signal to obtain an output signal, wherein the first, second and third voltage ** * * signals are defined respectively as the difference between a reference voltage value S. * * and the voltage value at the feeding node, the difference between the reference * * 4 II * 15 voltage value and the voltage value at the ground node and the difference between the reference voltage value and the voltage value at the at least one intermediate node * * ** * between the glow plug and the at least one resistor; * * * means for comparing the output signal with a low threshold value and a high threshold * P for generating a pulse width modulated signal on the basis of said comparison, * means for selecting said first, second, and third signal as input signal on the basis of a variation over time of the pulse width modulated signal, * means for determining the resistance value of the glow plug on the basis of the resistance value of the at least one resistor and of a variation over time of said pulse width modulated signal.

BRIEF DESCRIPTION OF THE DRAWINGS * *

Other features, advantages and details appear, by way of example only, in the following detailed description of embodiments, with reference to the accompanying drawings, in which: * Figure 1 schematically shows an automotive system belonging to a motor vehicle; * Figure 2 is the section A-A of an internal combustion engine belonging to the automotive system of figure 1; * Figure 3 is a scheme of a circuit for measuring a resistance value of a glow plug according to an embodiment of the invention; * Figures 4 and 5 show the variation over time of some signals used in an embodiment of the invention respectively during the on state of the glow plug and during the off state of the glow plug. DETAILED DESCRIPTION * * * Some embodiments may include an automotive system 100, as shown in Figures 1 ** *- and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 ** ** * *** ** * 15 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145. *

A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.

* GPIs * . * *** * l* * * * ^ ** A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and * * - ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140.

2 0 The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

In the combustion chamber 150 is located a glow plug 360 which is a heating element which is electrically activated for cold starting of the engine and also for improving the combustion performance within the combustion chamber.

The glow plug 360 is electrically connected to a voltage power source 530, for example a battery of the automotive system, and is controlled to have an on state and an off state. According to a possible embodiment, the on/off states of the glow plug 360 are controlled by an electronic control unit (ECU) intended to control a switch. As it will disclosed in more detail later, according to a possible embodiment, a switch 540 can be * ** * * provided to control the on/off states of the glow plug 360. *

* * * * * The air may be distributed to the air intake port(s) 210 through an intake manifold 200. *

* * * * * * * * 15 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air * * * * * into the manifold 200. In still other embodiments, a forced air system such as a * * * * * * turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be ** * * provided. Rotation of the compressor 240 increases the pressure and temperature of the * * air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may 2 0 reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

An air intake duct 205 may provide air from the ambient environment to the intake manifold The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300. * * *

* * * The automotive system 100 may further include an electronic control unit (ECU) 450 * * * * ****** in communication with one or more sensors and/or devices associated with the ICE 110. * *

The ECU 450 may receive input signals from various sensors configured to generate the * * * * ** * * manifold pressure and temperature sensor 350, a combustion pressure sensor that may * * * * be integral within the glow plugs 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR valve 320, the VGT actuator 290, and cam phaser 155 and the glow plug 360. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors ** ** * * * * * signals in proportion to various physical parameters associated with the ICE 110. The * * * * * sensors include, but are not limited to, a mass airflow and temperature sensor 340, a and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system 460, and send and receive signals to/from the interface bus. The memory system 460 may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices.

The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

The program stored in the memory system 460 is transmitted from outside via a cable * * * * . * or in a wireless fashion. Outside the automotive system 100 it is normally visible as a ** * * * computer program product, which is also called computer readable medium or machine * * readable medium in the art, and which should be understood to be a computer program * * * * * * transitory in nature.

** * * * * * An example of a transitory computer program product is a signal, e.g. an electromagnetic signal such as an optical signal, which is a transitory carrier for the computer program code. Carrying such computer program code can be achieved by modulating the signal by a conventional modulation technique such as QPSK for digital data, such that binary data representing said computer program code is impressed on the transitory electromagnetic signal. Such signals are e.g. made use of when transmitting computer program code in a wireless fashion via a WiFi connection to a laptop.

In case of a non-transitory computer program product the computer program code is * * * * * * * * code residing on a carrier, said carrier being transitory or non-transitory in nature with the * * * * * consequence that the computer program product can be regarded to be transitory or non-embodied in a tangible storage medium. The storage medium is then the non-transitory carrier mentioned above, such that the computer program code is permanently or non-permanently stored in a retrievable way in or on this storage medium. The storage medium can be of conventional type known in computer technology such as a flash memory, an Asic, a CD or the like.

With reference to figures 3, 4 and 5, a possible embodiment of a circuit and a method for measuring the resistance value Rcp of the glow plug 360 will be now discussed.

More in detail, Figure 3 illustrates a possible embodiment of a circuit 500 for measuring a resistance value RGP of the glow plug 360.

The glow plug has a first end 360a connected to a ground pole 370 and a second end 360b connectable to a voltage power source 530 by means of at least one resistor 510, * * * 550. * * *

* * * * A ground node 365 is arranged between the first end 360a of the glow plug 360 and ** ** * * * * * According to a possible embodiment, the at least one resistor 510, 550 is connectable * * * * * * arranged between a first end 360a of the glow plug 360 and a ground pole 370, and a * * * * feeding node 535 arranged between a free end of the at least one resistor 510, 550 and * * the voltage power source 530.

As for example shown in Figure 3, the glow plug 360 is connectable to a voltage power source 530 (having a voltage value Vsat) by means of a shunt resistor 510, having a known resistance value RsH, and a reference resistor 550, having a known resistance value Rrer, for creating a voltage divider 600 between the ground pole 370 and the voltage power source 530.

The voltage divider. 600 is provided with at least one intermediate node 515, 520 * * the ground pole 370. *

* * * * to the glow plug 360 for creating a voltage divider 600 between a ground node 365, that is between the glow plug 360 and the at least one resistor 510, 550.

More in detail, as for example shown in figure 3, a first intermediate node 515 is provided between the reference resistor 550 and the glow plug 360, preferably in correspondence of the second end 360b of the glow plug 360.

A second intermediate node 520 is provided between the shunt resistor 510 and the glow plug 360.

More in detail, the reference resistor 550 is provided with a first end connected to the feeding node 535 and a second end connected to a first intermediate node 515 of the voltage divider 600, that is arranged at a second end 360b of the glow plug.

The shunt resistor 510 is provided with a first end connected to the feeding node 535 and a second end connected to a second intermediate node 520 of the voltage divider ** * 600.

* * * ** * * * A switch 540 is arranged between the shunt resistor 510 and the glow plug 360, * * preferably between the first and second intermediate nodes 515, 520 to selectively connect * * * * ** * * **** is and disconnect the shunt resistor 510 to/from the glow plug 360. * * * * **

In particular, see for example figure 3, the shunt resistor 510 has a first end connected * * * * * * to the voltage power source 530 at a feeding node 535 and a second end connectable to * * * * the second end 360b of the glow plug by means of a switch 540. * *

The switch 540 is controlled by the ECU 450 for turning on and off the glow plug 360, preferably with an adjustable duty cycle. When the switch 540 is closed, the glow plug is turned on (on state of the glow plug), vice versa when the switch 540 is open, the glow plug is turned off (off state of the glow plug).

The switch 540 is connected between the shunt resistor 510 and the glow plug 360, respectively at a first intermediate node 515 and second intermediate node 520 of the voltage divider 600.

* * * * * 5 * * .* * 10 ** * * .. * * is * * * *** * * * * * * * * * ** * * * * According to an aspect of the invention, the reference resistor 550 is connected to the glow plug 360 and the shunt resistor 510 is selectively connected and disconnected to/from the glow plug 360. More in detail, the reference resistor 550 is connected in series to the glow plug 360 during the off state of the glow plug and the shunt resistor 510 is connected to the glow plug during the on state and it is discontented from the glow plug during the off state.

According to an aspect of the invention, the reference resistor 550 is connected in series to the glow plug 360 during the off state of the glow plug and the shunt resistor 510 and the reference resistor 550 are both connected to the glow plug 360 during the on state of the glow plug.

More in detail, during the on state of the glow plug 360 (e.g. when the switch 540 is closed) the shunt resistor 510 is arranged in parallel with the reference resistor 550.

According to an aspect, the resistance value RsH of the shunt resistor 510 is much less than the resistance value Asp of the glow plug, and the resistance value Rref of the reference resistor 550 is much greater than the resistance value Rcp of the glow plug. Typically, the resistance value RGP of the glow plug is in the range of a few ohms (Cl) thus, the resistance value RsH of the shunt resistor can be chosen in the range of few milliohms the of (mfg) and resistance value IRre the reference resistor in the range of kilo-ohms (kf2). * .

The circuit 500 comprises an input selector 575, a voltage integrator 710, a comparator 720 with hysteresis and a logic unit 800.

The voltage integrator 710 is connected to the input selector 575, and the input selector is configured to alternatively conned the voltage integrator to the feeding node 535, or to the ground node 365, or to at least one intermediate node 515, 520 to select a first, a second, and a third voltage signals VI, V2, V3 as input signal VINT,IP of the voltage integrator 710.

More in detail, according to a possible embodiment, the input selector 575 is movable in at least three positions (indicated in figure 3 as 1, 2, 3a and 3b) in correspondence of which the voltage integrator 710 is respectively connected with the feeding node 535, to the ground node 365, and to at least one intermediate nodes 515, 520.

It has to be noted that according to a possible embodiment, as for example show in figure 3, the input selector 575 is movable in four positions (indicated in figure 3 as 1, 2, 3a and 3b) in correspondence of which the voltage integrator 710 is respectively connected with the feeding node 535, to the ground node 565, and to two intermediate nodes 515, 520.

As mentioned above, the movement of the input selector 575 in said at least three positions, allows to select a first, a second, and a third voltage signals Vi, V2, V3 as input signal VINT,tri of the voltage integrator 710.

The voltage integrator 710 is provided with an output line 710c for providing an output signal VINT,out indicating the integral over time of the input signal VoTrio.

According to a possible embodiment, the voltage integrator 710 comprises an * * * * * operational amplifier integrator, wherein the non-inverting input 710a is connected to a ** * * * * voltage reference value Vo and the inverting input 710b is connected to the input selector * ** * * 575. The voltage reference Vo is preferably selected to be an average voltage value * * * between the voltage value Voo at the feeding node 535 and the voltage value Vow, at the ground node 365.

The input selector 575 is controlled by the logic unit 800 for connecting alternatively the voltage integrator, and in particular the inverting input 710b of the of the voltage integrator 710, to the feeding node 535, or to the ground node 365 or to the first or second intermediate nodes 515, 520.

The offset voltage value of the operational amplifier integrator 710, indicated as SV * * * * 5 * * * * 10 ** * * ** ** * is * * * * * (see figure 3) is added to the voltage reference value Vo at the non-inverting input 710a of the integrator 710. It has to be noted that in the present disclosure, reference will be made to the voltage reference value Vo alone to indicate also the correspondent offset voltage value (BV) of the operational amplifier integrator 710 that is added to the voltage reference value Vo.

Indicating with VINT,in the input signal of the integrator, and with VINT,out the output signal of the integrator, it follows that: VINT,out = RCf VINT,in dt wherein R and C are known values of the resistor and the capacitor of the voltage integrator, as for example shown in figure 3, and VINT., is the difference between the * * **** voltage reference value Vo (including the offset voltage value 8V) and the voltage value at *** * the inverting input 710b that can be alternatively connected, by means of the selector 575, * * ** to the feeding node 535, or to the ground node 365 or to the first or second intermediate * * * * * * * nodes 515, 520. ** * *

The output signal VINT,Out of the voltage integrator indicates the integral over time of * * * * * * . the difference between the reference voltage value Vo (including the offset voltage value ** * 8V) and the voltage value at the inverting input 710b.

As already mentioned above, the circuit 500 further comprises a comparator 720 and 2 0 a logic unit 800, and the comparator 720 is connected to the output line 710c of the voltage integrator 710 for providing a pulse width modulated signal Vpwm to the logic unit 800 for evaluating the resistance value Rol. of the glow plug and for controlling the input selector 575.

The comparator 720 is preferably a Schmidt trigger with the input connected to the output line 710c of the voltage integrator 710.

In particular, when the input selector 575 connects the inverting input 710b to the feeding node 535 having a voltage value Vup, the input signal VINT,in is equal to a first voltage signal Vi defined as: VINT.in = VI = V0 SV -Vup This input signal can be reached when the input selector 575 is arranged in the position 1 (see figure 3).

When the input selector 575 connects the inverting input 710b to the ground node 365, having a voltage value Vown, the input signal VINT,r, is equal to a second voltage signal V2 defined as: = V2 = Vo + SV -Vdwn This input signal can be reached when the input selector 575 is arranged in the position 2 (see figure 3).

When the input selector 575 connects the inverting input 710b to one of the intermediate nodes 515, 520 having a respective voltage value VD, Vs, the input signal VINT,in is equal to a third voltage signal V3 defined as: Vinrr,in = V3 = V0 + 8V -VD (during the on state of the glow plug) * ** * * * *** * * * * * * * * * * * * 15 * f** * * * * * * * * * * * and * * VINT,in = V3 = Vo + SV -Vs (during the off state of the glow plug) The input signal Vs = Vo + SV -VD can be reached when the input selector 575 is arranged in the position 3a (see figure 3).

The input signal Vs = Vo + SV -Vs can be reached when the input selector 575 is arranged in the position 3b (see figure 3).

The logic unit 800 controls the input selector 575 according to a first sequence when * i* * * * ** * * * * * * * * w * * * * * *11. * * * * * * *

the glow plug 360 is turned on (i.e. during the on state), and according to a second sequence when the glow plug 360 is turned off (i.e. during the off state).

The first and the second sequences are synchronized with the pulse width modulated signal at the output of the comparator 720. It has to be noted that the comparator 720 has a low voltage threshold VL and a high voltage threshold VH.

When the output signal VINT,ow of the integrator 710 reaches the low voltage threshold value VL or the high voltage threshold value VH, the output signal Vpwm of the comparator 720 switches from a low voltage value (a logic zero '0") to a high voltage value (a logic one "1") or vice versa, and the logic unit 800 commands the commutation of the input selector 575 according the first sequence (during the on state of the glow plug) or the second sequence (during the on state of the glow plug).

In general, it has to be noted that the output signal Viw,out obtained during the integration over time of the input signal VINT,in is compared with a low threshold value VL and a high threshold VH for generating a pulse width modulated signal Vpwm on the basis of said comparison.

The variation over time of said pulse width modulated signal VPWM is used, preferably by means of the logic unit 800, to select the first, second, and third voltage signal VI, V2, V3 as input signal VINT,in.

Figure 4 illustrates the variation over time of the input and the output signals of the integrator 710 when the glow plug 360 is turned on (during the on state of the glow plug).

The logic unit 800 controls the input selector 575 so that the input signal VINT,n being integrated according the sequence comprising the following succession: V2, V3, V2, V1.

Advantageously the sequence is selected so that the voltage signals V1, V2, V3 have alternatively positive and negative values.

According to the sequence V2, V3, V2, V1, the input signal VINT,in = V2 is integrated over time until the output signal VINT,oui reaches the high voltage value VH of the comparator 720 then, the logic unit 800 commands the commutation of the input selector 575 so that the input signal VINT,in is V3.

It has to be noted that in the on state of the glow plug 360 the input signal Vs is V3 = Vo + SV -Vo, obtained by moving the input selector to connect the voltage integrator 710 with the second intermediate node 520, e.g. by moving the input selector 575 in correspondence of the position 3a (see figure 3).

When the output signal VINT.out reaches the low voltage value VL of the comparator 720, the logic unit 800 commands the commutation of the input selector 575 so that the input signal VINTin is V2.

V2 is integrated over time until the output signal VINT,00t reaches the high voltage value * * ** * VH then, the logic unit 800 commands the commutation of the input selector 575 so that *** * * ** **** the input signal VINT., is V, that it is integrated until the output signal VINT.out reaches the * * low voltage value VL of the comparator 720.

RGp = RGH * Rref tit), (t9 taws) (Rs/4 Rrei) tliWYI (tD rap) In other words, the logic unit by knowing the resistance value RsH of the shunt resistor ** * * * * * * * By defining taw, as the time interval needed for the output signal VINT.out to pass from *** * * the low threshold value V1 to the high threshold value VH during integration of the second * * * * * * voltage signal V2, to as the time interval needed for the output signal Vinmpul to pass from * the high threshold value VH to the low threshold value VL during integration of the third * * voltage signal V3 (wherein V3 = Vo SV -VD), and tup as the time interval needed for the output signal VINT.out to pass from the high threshold value Wito the low threshold value VL during integration of the first voltage signal VI, the resistance value RGP of the glow plug 360, during the on state of the glow plug, is determined by the logic unit 800 using the following equation: and the resistance value Rres of the reference resistor, by determining the above cited time intervals to, tup, tdw. (for example by means of a counter), can evaluate the resistance value RGP of the glow plug 360 with an accuracy depending only by the shunt resistor and reference resistor accuracies (that can be minor than 1%).

It has to be noted that the time intervals to, t" P, tdw. indicates the variation over time of the pulse width modulated signal VPWM.

The measure of the resistance value of the glow plug is also independent from the offset of the operational amplifier.

In fact, by solving the integral over time during the tem time interval when VINT,111 is V2, follows that: * tclwn * * * * * (70 SV -Vd") * RC = (VH -VL) * * * * * * . .. * * * By solving the integral over time during the to time interval when VINT,In is Va, follows * * * * * tD (V0 + 8V -VD) * -= (VH VL) RC * * * * * * * ** * * By solving the integral over time during the tup time interval when VINT.M is VI, follows rCup (vs + ay -14, ) * R--(141 -With an algebraic combination of the preceding equations the offset can be compensated obtaining the following two equations: (VD -Yawn) = (Vii -VO * (1+ RC tD Ldwn and * * * * * that: * * that: (Vup -Vdwn) RC = (VH -Vt) * (1 -+ tup tdwn From the ratio of the above two equations follows that: (VD -Vawn) -Vdwn) tE, (tup td,,",") Because the first member of the above equation is the voltage ratio of the voltage divider 600, i.e.: (VD -Vdwn) = RGp (Vup Vdwn)RGH *Ikr f RGP RSH Rreil * * * The resistance value RAP of the glow plug 360 can be evaluated from the above * * * equation obtaining the equation: RSH * Rref) Cup (tD tdwn)** * * RGp *** * RSH Rref tdwn (tD tup) * * * ** The logic unit 800 can also evaluate the resistance value Rop of the glow plug 360 * * when it is turned off (i.e. during the off state of the glow plug). * *

* * * **.* " 15 Figure 5 illustrates the variation over time of the input and the output signals of the * * integrator 710 when the glow plug 360 is turned off (during the off state of the glow plug). According to a possible embodiment, the logic unit 800 controls the input selector 575 so that the input signal ViNtie being integrated according to a sequence comprising the following succession: V2, V1, V3, V1.

Also in the off state of the glow plug, the sequence is selected so that the voltage signals V1, V2, V3 have alternatively positive and negative values.

Thus, the input signal Viumn, with VINT,in = V2 is integrated over time until the output signal VINteet reaches the high voltage value VH of the comparator 720 then, the logic unit 800 commands the commutation of the input selector 575 so that the input signal VINT,in is tut, (tD + tdwn) v,.

Analogously, when the output signal VINT,out reaches the low voltage value VL of the comparator 720, the logic unit 800 commands the commutation of the input selector 575 so that the input signal VINT,in is V3.

V3 is integrated over time until the output signal VINT.out reaches the high voltage value VH then, the logic unit 800 commands the commutation of the selector 575 so that the input signal ViNtin is Vi that it is integrated until the output signal VINT,out reaches the low voltage value VL of the comparator 720.

It has to be noted that in the off state of the glow plug 360 the input signal Va is V3 = Va + 5V -Vs, obtained by moving the input selector to connect the voltage integrator 710 * * * * * * *** * with the first intermediate node 515, e.g. by moving the input selector 575 in * * * correspondence of the position 3b (see figure 3).

** ** By defining tdwn as the time interval needed for the output signal VINT,out to pass from * a ** * * * the low threshold value VL to the high threshold value VH during integration of the second * * * voltage signal V2, ts as the time interval needed for the output signal to pass from the low threshold value VL to the high threshold value VH during integration of the third voltage signal V3 (wherein V3=V0 + SV -Vs), and tip as the time interval needed for the output signal VINT,out to pass from the high threshold value VH to the low threshold value VL during integration of the first voltage signal V,, the resistance value Rep of the glow plug 2 0 360, when it is turned off, is determined by the logic unit 800 using the following equation: tup(r5 -tdwn) The logic unit by knowing the resistance value of the reference resistor Bre( and by determining the above cited time intervals ts, tup, tdwn (for example by means of a counter), can evaluate the resistance value Rep of the glow plug 360 with an accuracy depending only by the reference resistor accuracy (that can be minor than 1%).

* * * * * 15 * * * * * * RCP = Rref tdwn (tS tap) * * * * 5 * * * 10 ** * * * is * * * ** * ** ** ** * * * It has to be noted that the time intervals ts, t t dwn indicates the variation over time of the pulse width modulated signal Vpwm.

Also in this case the measure of the resistance value of the glow plug is also independent from the offset of the operational amplifier.

The offset compensation during the off state of the glow plug can be demonstrated in an analogous manner illustrated above for the evaluation of the resistance value of the glow plug when it is turned on.

According to an aspect, the resistance value RAP of the glow plug 360 can be evaluated as a weighted average of the resistance value RAP of the glow plug 360 measured during the on state, and/or during the off state, of the glow plug, on the basis of the time duration of said on state and/or of said off state of the glow plug.

More in detail, according to a possible embodiment, the resistance value RGp of the glow plug 360 can be also evaluated as the weighted average of the values of said glow plug during the on and/or off states of the glow plug on the basis of the duty cycle of the switch 540 intended to turn on and off the glow plug 360. **

* *** * It has to be noted that the measured resistance value RGP of the glow plug 360 is used * * to determine the temperature of the glow plug 360, preferably according to its physical properties. The determined temperature value of the glow plug 360 can be then used, for example by the ECU, to carry out a comparison with a target temperature value that can be correlated to the engine operating conditions. On the basis of the comparison of the determined temperature value of the glow plug with a target temperature value, the ECU controls the activation/deactivations (i.e. control the on/off state) of the glow plug to reach the target temperature. As mentioned above, the switch 540 can be controlled by the ECU to control the on/off states of the glow plug 360.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, s applicability, or configuration In any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. * * * * * .

* ** * * * It* * * * * * * * * * * * * * * * * . * **

REFERENCES

1, 2, 3a, 3b positions of the input selector motor vehicle automotive system internal combustion engine engine block 125 cylinder cylinder head camshaft * ** 140 piston * * * *** * 145 crankshaft * * 15 147 gearbox ** ** 148 clutch ** * * 150 combustion chamber **** *** * 155 cam phaser * * 160 fuel injector * * * * * *** n 170 fuel rail * * 180 fuel pump fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 exhaust port 225 exhaust manifold 230 turbocharger 3 0 240 compressor 250 turbine 260 intercooler 305 350 360a * * * . 360b * 365 *** * * * 370 ** * * * 380 * * 400 * * ** ** . * : 20 430 * * 440 500 535 aftertreatment system exhaust pipe VGT actuator exhaust gas recirculation system EGR conduit EGR cooler EGR valve throttle body mass airflow and temperature sensor manifold pressure and temperature sensor glow plug first end of glow plug second end of glow plug ground node ground pole coolant and oil temperature and level sensors fuel rail pressure sensor cam position sensor crank position sensor speedometer EGR temperature sensor accelerator pedal position sensor

ECU

memory system circuit shunt resistor first intermediate node second intermediate node voltage power source feeding node switch reference resistor 575 input selector 600 voltage divider 710 voltage integrator 710a non-inverting input 710b inverting input 710c voltage integrator output 720 comparator 800 logic unit VINT,1 input signal of the voltage integrator VINT,out output signal of the voltage integrator VpwM pulse width modulated signal Vo voltage value at the second intermediate node Vs voltage value at the first intermediate node * * * * * * *** * VL low threshold VH high threshold * Vo reference voltage value ** * * **** * * * V1 first voltage signal ** * V2 second voltage signal * V3 third voltage signal * °. *.T 20 6,V offset voltage value * Vim voltage value at the feeding node * * W.n voltage value at the ground node Vs., voltage value of the voltage power source Rep resistance value of the glow plug Rsry resistance value of the shunt resistor Rref resistance value of the reference resistor R resistor of the voltage integrator C capacitor of the voltage integrator to time interval for passing from VH to VL during integration of V3 = Vo + 8V -Vo is time interval for passing from VL to VH during integration of Vs =Vo + 8V -Vs tup time interval for passing from VH to VL during integration of V1 td,,,,, time interval for passing from VL to VH during integration of V2

Claims

CLAIMS1. A method for measuring a resistance value (R3p) of a glow plug (360) having an on state and an off state, comprising the following steps: a) connecting at least one resistor (510, 550), having a known resistance value (RsH, Rreo, to the glow plug (360) to create a voltage divider (600) between a feeding node (535) and a ground node (365), wherein said feeding node is arranged between a free end of said at least one resistor (510, 550) and a voltage power source (530) and said ground node (365) is arranged between a first end (360a) of said glow plug (360) and a ground pole (370), an intermediate node (515, 520) being provided between the glow plug (360) and said at least one resistor (510, 550); * ** * * * *** * * * * ** ** 15 * * * * * * *** * ** * * * * ** * * * 20 b) integrating over time alternatively a first, a second and a third voltage signal (V1, V2, Vs) as input signal (Vinr.ip) to obtain an output signal (VIwpm) wherein, said first, second and third voltage signals (V1, V2, V3) are defined respectively as the difference between a reference voltage value (Vo) and the voltage value (V" p)at said feeding node (535), the difference between the reference voltage value (Vo) and the voltage value (Vdwo) at said ground node (365) and the difference between the reference voltage value (V0) and the voltage value (Vs, VD) at said intermediate node (515, 520) between the glow plug (360) and said at least one resistor (510, 550), c) comparing the output signal (VINtout) obtained during the step b) with a low threshold value (VI.) and a high threshold (VH) for generating a pulse width modulated signal (Vpwm) on the basis of said comparison, d) selecting said first, second, and third voltage signal (V1, V2, V3) as input signal 25 (VINT,in) in said step b), on the basis of a variation over time of said pulse width modulated signal (Vpwin), e) determining the resistance value (Rep) of the glow plug (360) on the basis of the resistance value (RsH, Rm.° of said at least one resistor (510, 550) and of a variation over time of said pulse width modulated signal (Vpwm).
2. The method according to claim 1, wherein in said step a) a reference resistor (550) is connected to the glow plug (360)and a shunt resistor (510) is selectively connected and disconnected to/from the glow plug (360), the shunt resistor being connected to the glow plug during the on state of the glow plug and the shunt resistor being disconnected from the glow plug during the off state of the glow plug.
3. The method according to claim 1 or 2, wherein said third voltage signal (Vs) is defined as the difference between said reference voltage value (Va) and the voltage value (VD) at a second intermediate node (520) between the glow plug (360) and a shunt resistor (510) during the on state of the glow plug, said third voltage signal (V3) being defined as the difference between said reference voltage value (Va) and the voltage value (Vs) at a first intermediate node (510) between the glow plug (360) and a reference resistor (550) during the off state of the glow plug.The method according to any previous claim, wherein said step d) of selecting said first, second, and third signal (Vi, V2, Va) as input signal ( \Amt.-0 is carried out according to at least one sequence in which the voltage signals (V1, V2, V3) have alternatively positive and negative values.The method according to any previous claim, wherein said step d) of selecting said first, second, and third signal (V1, V2, V3) as input signal (VINT,m) is carried out according to at least one first sequence during the on state of the glow plug and according to at least one second sequence during the off state of the glow plug.

The method according to claim
4 or 5, wherein at least one sequence during the on state of the glow plug comprises the following succession: V2, V3, V2, V1, and at least one sequence during the off state of the glow plug comprises the following succession: V2, V1, V3, V1.

The method according to any claim 4 to 6, wherein said at least one sequence is synchronized with the pulse width modulated signal generated during said step c).

The method according to any previous claim, wherein the resistance value (Rep) of * * * 15 4. * * *

*** * * * * **** * ** * *** * * * * * * * * *
5.

* 11.* * * . 2 0
6.
7.
8.the glow plug (360) during the on state of the glow plug is determined by the equation: RGp = RsH Ryer tup (ti tdwn) (RSH ff ref) trim, (tD tup) * * * * 15 * * * * 20 * * * * * . * * * *** * * * * * * *** * * * * * * * * ° * * * * * wherein: tdym is the time interval needed for the output signal (Wrotaii) to pass from said low threshold value (VL) to said high threshold value (VH) during integration of said second voltage signal (V2); to is the time interval needed for the output signal (Viiimiii) to pass from said high threshold value (VH) to said low threshold value (VI.) during integration of said third voltage signal (V3); tap is the time interval needed for the output signal (Vinmoui) to pass from said high threshold value (VH) to said low threshold value (VI.) during integration of said first voltage signal (Vi); Rre and RsH are respectively the resistance value of a reference resistor (550) and the resistance value of a shunt resistor (510) connected to the glow plug (360).
9. The method according to any previous claim, wherein the resistance value (Rsp) of the glow plug (360) during the off state of the glow plug is determined by the equation: to pass from said low threshold value (VL) to said high threshold value (VH) during integration of said third voltage signal (V3); Li, is the time interval needed for the output signal (Wmciiii) to pass from said high threshold value (VH) to said low threshold value (Vt.) during integration of said first voltage signal (Vi); and Rref is the resistance value of a reference resistor (550) connected to the glow plug (360).wherein: taw', is the time interval needed for the output signal (Vmoiii) to pass from said low threshold value (VL) to said high threshold value (VH) during integration of said second voltage signal (V2); is is the time interval needed for the output signal (Wr,oui) RCP = Rref tup (ts -tan) tdwn (t5 tup)
10. The method according to any previous claim, wherein said step e) provides to evaluate a weighted average of said resistance value (RGP) of said glow plug (360) measured 25 during the on state, and/or during the off state, of the glow plug on the basis of the time duration of said on state and/or of said off state of the glow plug. * .. * * **0 * * * 15 * * ** * * * * * * * * ** * ****20 * ** * * *
11. A circuit (500) for measuring a resistance value (RGP) of a glow plug (360) having an on state and an off state, said glow plug having a first end (360a) connected to a ground pole (370) and a second end (360b) connectable to a voltage power source (530) by means of at least one resistor (510, 550), said at least one resistor (510, 550) being connectable to said glow plug (360) for creating a voltage divider (600) between a ground node (365), arranged between a first end (360b) of said glow plug (360) and a ground pole (370), and a feeding node (535) arranged between a free end of said at least one resistor (510, 550) and the voltage power source (530), said voltage divider (600) being provided with at least one intermediate node (515, 520) between the glow plug (360) and said at least one resistor (510, 550), said circuit (500) comprising a input selector (575) and a voltage integrator (710) connected to said input selector, the input selector being configured to alternatively connect the voltage integrator to said feeding node (535), or to said ground node (565), or to said at least one intermediate node (515, 520) to select a first, a second, and a third signal (V1, V2, V3) as input signal (Vinrr,n) of the voltage integrator (710), said voltage integrator having an output line (710c) for providing an output signal (Vmout) indicating the integral over time of the input signal (VINT.), said circuit further comprising a comparator (720) and a logic unit (800), said comparator (720) being connected to the output line of said voltage integrator (710) for providing a pulse width modulated signal (Vpwm) to said logic unit for evaluating said resistance value (RGp) of said glow plug and for controlling said input selector (575).
12. The circuit according to claim 11, comprising a shunt resistor (510), having a known resistance value (RGH), and a reference resistor (550), having a known resistance value (Rre0, said reference resistor (550) having a first end connected to said feeding node (535) and a second end connected to a first intermediate node (515) of the voltage divider (600) arranged at a second end (360b) of the glow plug, said shunt resistor (510) having a first end connected to said feeding node (535) and a second end connected to a second intermediate node (520) of the voltage divider (600), a switch (540) being arranged between the shunt resistor and the glow plug to selectively connect and disconnect the shunt resistor (510) to/from the glow plug (360).
13. The circuit according to claim 12, wherein the resistance value (R.1)of said reference resistor (550) is much greater than the resistance value (RGP) of said glow plug (360), and wherein the resistance value (RsH) of said shunt resistor (510) is much less than the resistance value (RGP) of said glow plug (360).
14. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1 -10.
15. A computer program product on which the computer program according to claim 14 is stored. * *** . * *** * * * * ** ** * * * * * S* * * * * * * * * * ** * *