EP3046395B1

EP3046395B1 - Heating apparatus, temperature estimation apparatus and heater control apparatus

Info

Publication number: EP3046395B1
Application number: EP15202744.7A
Authority: EP
Inventors: Masanori Otsubo; Yohei Kan
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2015-01-16
Filing date: 2015-12-24
Publication date: 2017-06-21
Anticipated expiration: 2035-12-24
Also published as: JP2016134212A; JP6433304B2; EP3046395A1

Description

The present invention relates to heating.
A glow plug is widely used as an auxiliary heat source of a compression-ignition-type internal combustion engine (e.g., a diesel engine or the like). A known method of estimating the surface temperature of a glow plug utilizes the electrical resistance of a heating element which constitutes the glow plug. This method utilizes the phenomenon that the electrical resistance of the heating element depends on the temperature of the heating element, see for example
US-A-5,922,229 which discloses a glow plug with a heater and an ion-sensing electrode, on which the precharacterizing portion of claim 3 is based.
The above-described prior art technique premises that a fixed relation exists between the electrical resistance of the heating element and the surface temperature of the glow plug. However, in actuality, the electrical resistance of the heating element also varies with the coolant temperature of an engine, the temperature of engine oil, the temperature within a combustion chamber, etc. Therefore, complex correction in which the above-described factors are taken into consideration is needed for accurate estimation of the surface temperature of the glow plug. Further, the relation between the electrical resistance of the heating element and the temperature of the heating element is apt to receive the influence of a production-related variation. Because of these factors, the above-described prior art technique has a room for improvement of the accuracy of temperature estimation. Such a problem is not limited to glow plugs but is common among all heaters using a heating element. An object of the present invention is to improve the accuracy in estimating the temperature of a heater or to accurately control the temperature of the heater.

[Means for Solving the Problem]

The present invention, which solves the above-described problem, can be realized as the following aspects.

(1) According to one aspect of the present invention, there is provided a temperature estimation apparatus as defined in claim 1. Since the substrate is formed of ceramic, the electrical resistance of the substrate strongly varies with the temperature, and a portion of the substrate having a higher temperature has a smaller electrical resistance. Therefore, the electrical resistance of a portion of the substrate between the conductor and the heating element, which portion has the highest temperature, becomes the dominant factor of the electrical resistance of the substrate between the conductor and the heating element (hereinafter referred to as the "substrate resistance"). Temperature estimation performed on the basis of the electrical resistance of such a local portion mitigates the influence of an external environment in which the heater is disposed, the influence of a production-related variation, etc., whereby the accuracy in estimating the temperature of the heater improves.
(2) According to another aspect of the present invention, there is provided a heater control apparatus as defined in claim 3. As described above, a strong correlation exists between the substrate resistance and the temperature of the heater. Therefore, the temperature of the heater can be controlled accurately by controlling the substrate resistance.
(3) The obtainment section may obtain the electrical resistance on the basis of a potential difference between the conductor and the heating element, and a value of current flowing between the conductor and the heating element. The electrical resistance can be obtained easily.

The present invention can be realized in various forms other than the above-described forms. For example, the present invention can be applied to an apparatus which includes no heater. Namely, the present invention may be realized as a temperature estimation apparatus or a heater control apparatus. Alternatively, the present invention may be realized, for example, as a temperature estimation method, a heater control method, a computer program which realizes the temperature estimation method or the heater control method, or a non-temporary storage medium which stores the computer program.
The invention will be further described by way of examples with reference to the accompanying drawings, in which:-

[FIG. 1] Schematic diagram of a heating apparatus.
[FIG. 2] Partially sectioned view of a glow plug.
[FIG. 3] Sectional view of a forward end of the glow plug and its vicinity.
[FIG. 4] Flowchart showing temperature control processing.
[FIG. 5] Graph approximately showing the relation between the highest surface temperature of a substrate and the resistance of the substrate.

FIG. 1 schematically shows the configuration of a heating apparatus 100. The heating apparatus 100 is mounted on a diesel engine vehicle and heats a combustion chamber of a diesel engine. This heating is performed so as to assist the ignition of fuel injected from an injector 459.
The heating apparatus 100 includes a glow plug 1 and a control section 50. The glow plug 1 is a ceramic glow plug. As shown in FIG. 1, the glow plug 1 is attached to a cylinder block 45 by screwing an external thread portion of a housing 4 into the cylinder block 45. As a result, the glow plug 1 is attached in a state in which a forward end portion of the glow plug 1 is exposed to a combustion chamber of the cylinder block 45.
The control section 50 includes an ECU 52, a glow relay 53, a battery 54, and a glow relay 531. The glow relay 53 is disposed between the positive terminal of the battery 54 and an external lead wire 233 of the glow plug 1.
The negative terminal of the battery 54 is connected to the cylinder block 45 through the glow relay 531. When the glow relay 53 is on, the negative terminal of the battery 54 electrically communicates with the cylinder block 45. Since the potential of the cylinder block 45 is the ground potential, when the glow relay 531 is on, the negative terminal of the battery 54 is grounded.
The ECU 52 supplies the electrical power of the battery 54 to the glow plug 1 through the external lead wire 233 by turning on the glow relay 53 and the glow relay 531. By this supply of the electrical power, the ECU 52 causes the glow plug 1 to generate heat. The ECU 52 controls the heat generation of the glow plug 1 by controlling the ratio between the on time and off time of the glow relay 53. The glow relay 531 is always maintained in its on state during a period during which heating is performed, and is turned off when heating is stopped.
The control section 50 further includes a DC power supply 51, a relay 55, a resistor 521, and a potentiometer 522. The relay 55 is disposed between the resistor 521 and an external lead wire 333 of the glow plug 1. The relay 55 allows and prohibits the supply of electricity from the DC power supply 51 to the glow plug 1 through switching operation.
The negative terminal of the DC power supply 51 is connected to the cylinder block 45, whereby the negative terminal of the DC power supply 51 is grounded. The resistor 521 is disposed on the positive terminal side of the DC power supply 51. The potentiometer 522 measures a voltage (drop voltage) by which the voltage of the DC power supply 51 drops at the resistor 521.
The ECU 52 estimates the temperature of the glow plug 1 by using these circuit configurations. The ECU 52 utilizes the estimated temperature for the above-described control of heat generation of the glow plug 1 (which will be described later together with FIGS. 4 and 5). The ECU 52 further utilizes values obtained from a water temperature sensor 525 and an engine speed sensor 526 for the above-described control of heat generation. The water temperature sensor 525 measures the temperature of engine cooling water. The engine speed sensor 526 measures the rotational speed of the engine. The above-described temperature estimation and heat generation control will be described later together with FIGS. 4 and 5.
FIG. 2 is a partially sectioned view of the glow plug 1. FIG. 3 is a sectional view of a distal end of the glow plug 1 and its vicinity, and shows the state in which the glow plug 1 is attached to the cylinder block 45. Below, the glow plug 1 will be described with reference to FIGS. 2 and 3.
As shown in FIG. 2, the glow plug 1 includes the housing 4, a heater 10, a terminal portion 23, a terminal portion 31, an internal lead wire 33, an internal lead wire 231, a connection terminal 232, the external lead wire 233, a connection terminal 332, the external lead wire 333, and a rubber bush 421. These members are assembled along the axial line O of the glow plug 1. Notably, in the present specification, the side of the glow plug 1 where the heater 10 is located will be referred to as the "forward end side," and the side opposite thereto will be referred to as the "rear end side."
As shown in FIG. 2, the housing 4 includes an outer tube 41, a protection tube 42, and a metallic shell 47. The protection tube 42 is an approximately cylindrical member extending along the axial line O and has openings on the forward end side and rear end side thereof. A forward-end-side opening portion of the protection tube 42 is attached to the rear end of the metallic shell 47. The rubber bush 421 is inserted into a rear-end-side opening portion of the protection tube 42. The rubber bush 421 is a circular columnar member made of rubber. The rubber bush 421 inserted into the protection tube 42 seals the space located forward of the rubber bush 421. The outer tube 41 is disposed on the forward end side of the protection tube 42. The metallic shell 47 has an external thread portion 43. The external thread portion 43 is used to attach the glow plug 1 to the cylinder block 45 of the engine.
As shown in FIG. 3, the heater 10 has a generally rod-shaped member which has a hemispherical forward end portion and extends along the axial line O. The heater 10 is fixed within the housing 4 via the outer tube 41. The outer tube 41 is a ring-shaped member made of metal. The heater 10 has an electro-heating element 2, an electrode 3, a substrate 11, and a pair of lead wires 21 and 22. The electro-heating element 2, the electrode 3, and the lead wires 21 and 22 are embedded in the substrate 11 and are held. The substrate 11 is formed of a ceramic which contains Si₃N₄ (silicon nitride) as a main component.
As shown in FIG. 2, the external lead wires 233 and 333 extend through the rubber bush 421 and reach the interior of the glow plug 1. The external lead wire 233 is connected to the terminal portion 23 through the connection terminal 232 and the internal lead wire 231. The terminal portion 23 is disposed on the outer circumferential surface of the substrate 11 with a gap formed between the terminal portion 23 and the inner circumferential surface of the housing 4. As will be described later, the terminal portion 23 electrically communicates with the housing 4 through the heater 10. The housing 4 is fixed to the cylinder block 45 as described above, whereby the housing 4 electrically communicates with the cylinder block 45 which is the ground potential. As described above, the cylinder block 45 is connected to the negative terminal of the battery 54. Therefore, when the glow relays 53 and 531 are turned on, a closed circuit is formed.
As shown in FIG. 3, the lead wire 21 is connected to the terminal portion 23. The lead wire 21 extends through the interior of the substrate 11 and is connected to one end of the electro-heating element 2 having a U-like shape. The other end of the electro-heating element 2 is connected to the outer tube 41 through the lead wire 22. Therefore, when the glow relays 53 and 531 are turned on, the voltage of the battery 54 is applied to the electro-heating element 2, and a current flows through the electro-heating element 2 embedded in the substrate 11. The electro-heating element 2 is formed of a ceramic which is smaller in electrical resistance than the substrate 11. When the voltage of the battery 54 is applied to the electro-heating element 2, a portion of the electro-heating element 2 near the forward end of the heater 10 generates heat.
Next, a circuit for the above-described temperature estimation will be described. As shown in FIG. 2, the external lead wire 333 is connected to the terminal portion 31 disposed at the rear end of the substrate 11 through the connection terminal 332 and the internal lead wire 33. As shown in FIG. 3, the electrode 3 is connected, at one end thereof, to the terminal portion 31 and extends along the direction of the axial line O within the substrate 11. The other end of the electrode 3 is disposed near the forward end of the electro-heating element 2.
The electrode 3 is formed of an electrically conductive ceramic and is embedded in the substrate 11 such that the electrode 3 is separated from the electro-heating element 2. Therefore, when the relay 55 is turned on and the DC power supply 51 electrically communicates with the electrode 3, a potential difference is generated between the electrode 3 and the electro-heating element 2. This potential difference is utilized in temperature control processing which will be described next.
FIG. 4 is a flowchart showing the temperature control processing. The temperature control processing is repeatedly executed by the ECU 52 during a period during which the generation of heat by the glow plug 1 is required.
First, the ECU 52 obtains a drop voltage V₅₂₁ at the resistor 521 through use of the potentiometer 522 (step S610). Subsequently, the ECU 52 calculates a substrate resistance R₁₁ (step S620). The substrate resistance R₁₁ refers to the electrical resistance of the substrate 11 between the electro-heating element 2 and the electrode 3.
The substrate 11 is formed of ceramic and has an electrical resistance on the basis of which the substrate 11 is generally classified as an insulator. However, since the electrical resistance of the substrate 11 is naturally finite, when a high voltage is applied to the electrode 3, a slight current flows through the substrate 11. This current flows to conductors embedded in the substrate 11 and conductors in contact with the substrate 11, and finally flows to the cylinder block 45. The conductors disposed in the substrate 11 are the electro-heating element 2, the lead wire 21, and the lead wire 22. The conductors in contact with the substrate 11 are the terminal portion 23, the terminal portion 31, and the outer tube 41.
However, the greater part of the current flowing through the substrate 11 flows from the vicinity of the forward end of the electrode 3 to the vicinity of the forward end of the electro-heating element 2. This is because a portion of the the substrate 11 having a higher temperature has a smaller electrical resistance as will be described later. Since the electro-heating element 2 generates heat in the vicinity of the forward end thereof as described above, a portion of the substrate 11 near the forward end of the electro-heating element 2 has a higher temperature as compared with other portions.
In view of the above, the current flowing to the conductors other than the electrode 3 is ignored in the calculation of the substrate resistance R₁₁. Further, since the electrical resistance of the electro-heating element 2 is smaller than the substrate resistance R₁₁, the electrical resistance of the electro-heating element 2 is ignored in the calculation of the substrate resistance R₁₁. Namely, in the present embodiment, the electro-heating element 2 is treated as a conductor.
In the case where the above-described premise is employed, the substrate resistance R₁₁ is calculated by the following expression (5). In the following expressions (1) to (5), V₁₁ represents the potential difference between the electro-heating element 2 and the electrode 3, I represents the current flowing through the resistor 521, and V₀ represents the voltage of the DC power supply 51. $R_{11} = V_{11} / I \dots (1), V_{11} = V_{0} - V_{521} \dots (2), I = V_{521} / R_{521}$
When the expressions (2) and (3) are substituted into the expression (1), the following expression (4) is obtained. $R_{11} = (V_{0} - V_{521}) / (V_{521} / R_{521})$
Since V₅₂₁ << V₀ in the present embodiment, the following expression (5) is obtained from the expression (4). $R_{11} = V_{0} \times R_{521} / V_{521}$
Subsequently, the ECU 52 estimates the highest surface temperature of the substrate 11 (step S630). The highest surface temperature of the substrate 11 refers to the highest value among the surface temperatures of the substrate 11. The substrate 11 has different surface temperatures in different portions thereof, and normally, a portion near the forward end of the electro-heating element 2 has the highest surface temperature.
FIG. 5 is a graph approximately showing the relation between the highest surface temperature of the substrate 11 and the substrate resistance R₁₁. This graph is a semilogarithmic graph which shows the substrate resistance R₁₁ in logarithm scale. This relation was obtained in advance by an experiment in which the substrate resistance R₁₁ was actually measured while the highest surface temperature of the substrate 11 was changed, and is stored in the ECU 52.
As shown in FIG. 5, the highest surface temperature of the substrate 11 changes only slightly with a change in the substrate resistance R₁₁. For example, as shown in FIG. 5, when the substrate resistance R₁₁ changes from a value A to a value 1000 times the value A, the highest surface temperature of the substrate 11 only changes from 1200°C to 600°C.
Next, the ECU 52 determines a target temperature (step S640). The target temperature refers to a target value of the highest surface temperature of the substrate 11. The target temperature is determined on the basis of the input value from the water temperature sensor 525, the input value from the engine speed sensor 526, and other values relating to the engine (e.g., the temperature of intake gas).
Subsequently, the ECU 52 determines a target resistance (step S650). The target resistance refers to the substrate resistance R₁₁ corresponding to the target temperature determined in step S640. This determination is made on the basis of the relation shown in FIG. 5.
Finally, the ECU 52 controls the energization of the heater 10 (step S660). Specifically, the ECU 52 controls the ratio between the on time and off time of the glow relay 53 such that the substrate resistance R₁₁ approaches the target resistance. After that, the ECU 52 ends the temperature control processing.
According to the above-described embodiment, at least the following effects can be obtained.

(a) The highest surface temperature of the substrate 11 can be estimated accurately. Conceivably, this effect is obtained mainly for the following reasons (a-1), (a-2), and (a-3).
- (a-1) In the case of an estimation method based on the substrate resistance R₁₁, as described above, the estimated value of the highest surface temperature is insensitive to a change in the substrate resistance R₁₁. As a result, even when the measurement of the substrate resistance R₁₁ involves some error, the estimated value of the temperature does not change greatly. Therefore, the above-described estimation accuracy improves.
- (a-2) Since the electrical resistance of the substrate 11 decreases greatly when its temperature increases, the electrical resistance of a portion of the substrate 11 between the electro-heating element 2 and the electrode 3, which portion has the highest temperature, becomes the dominant factor of the substrate resistance R₁₁. Namely, the substrate resistance R₁₁ is a parameter which strongly reflects the value of the highest temperature. The value of the highest temperature is considered to approximate the highest surface temperature of the substrate 11. Therefore, the substrate resistance R₁₁ is an excellent parameter for estimating the highest surface temperature of the substrate 11.
- (a-3) Since the substrate resistance R₁₁ is a parameter which strongly reflects the state of a local portion as described above, it is less likely to be affected by a variation in the production of the glow plug and disturbances. The disturbances refer to the cooling water temperature of the engine, the temperature of engine oil, the temperature of the combustion chamber, etc.
(b) The obtainment of the substrate resistance R₁₁ can be realized easily by the above-described simple circuit.
(c) Since the temperature estimation of the present embodiment is less likely to be affected by disturbances as described above, complex correction processing or the like in which disturbances are taken into consideration becomes unnecessary.
(d) Since the highest surface temperature can be estimated accurately as described above, the highest surface temperature can be controlled accurately.

The present invention is not limited to the above described embodiments, examples, and modifications and may be embodied in various other forms without departing from the scope of the invention which is defined in the claims. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in the modes described in "SUMMARY OF THE INVENTION" can be appropriately replaced or combined to solve some of or all the foregoing problems or to achieve some of or all the foregoing effects. A technical feature which is not described as an essential feature in the present specification may be appropriately deleted. For example, the followings are exemplified.
The highest surface temperature of the substrate is not required to be controlled. Namely, the above-described temperature control processing may be modified to execute steps S610 to S630 without executing the steps (steps S640 to S660) for controlling the highest surface temperature of the substrate. Namely, a portion of the temperature control processing may be executed as temperature estimation processing.
The highest surface temperature of the substrate is not required to be estimated. Namely, in the above-described temperature control processing, estimation of the highest surface temperature of the substrate (step S630) may be omitted. The steps (steps S640 to S660) for controlling the highest surface temperature of the substrate can be performed without estimating the temperature of the substrate.
The material of the substrate may be changed to other ceramics. For example, the material may be titanium diboride or a mixture of silicon nitride and titanium diboride. Alternatively, the material may be alumina, sialon, or the like.
The configuration of the circuit for obtaining the substrate resistance may be changed. For example, the circuit may be configured to apply a voltage between the pair of external lead wires and measure the value of current. Since this configuration allows accurate grasping of the voltage applied between the electro-heating element and the electrode, the accuracy in measuring the substrate resistance improves.
The present invention may be applied to ceramic heaters other than those of the glow plugs. For example, the present invention may be applied to heating appliances, heat sources for soldering irons, douche-quipped toilet seats, heat sources for semiconductor manufacturing apparatuses, heat sources for measuring equipment, and components of science equipment.

DESCRIPTION OF REFERENCE NUMERALS

1:: glow plug
2:: electro-heating element
3:: electrode
4:: housing
10:: heater
11:: substrate
21:: lead wire
22:: lead wire
23:: terminal portion
31:: terminal portion
33:: internal lead wire
41:: outer tube
42:: protection tube
43:: external thread portion
45:: cylinder block
50:: control section
51:: DC power supply
52:: ECU
53:: glow relay
54:: battery
55:: relay
100:: heating apparatus
231:: internal lead wire
232:: connection terminal
233:: external lead wire
333:: external lead wire
421:: rubber bush
521:: resistor
522:: potentiometer
525:: water temperature sensor
526:: engine speed sensor
531:: glow relay

Claims

A temperature estimation apparatus for estimating a temperature of a heater (10) including a conductor (3), a heating element (2) which generates heat when electricity is supplied thereto, and a substrate (11) which is formed of ceramic and in which the conductor (3) and the heating element (2) are separately embedded and held,
characterized by:
the temperature estimation apparatus comprising:
an obtainment section (S610, S620) which obtains an electrical resistance (R₁₁) of the substrate (11) between the conductor (3) and the heating element (2); and

an estimation section (S630) which estimates a temperature of the substrate (11) on the basis of the electrical resistance (R₁₁) obtained by the obtainment section (S610, S620).
A heating apparatus (100) comprising:
a heater (10) including a conductor (3), a heating element (2) which generates heat when electricity is supplied thereto, and a substrate (11) which is formed of ceramic and in which the conductor (3) and the heating element (2) are separately embedded and held; and

an energization section which supplies electricity to the heating element (2) so as to cause the heater (10) to generate heat,

the heating apparatus (100) further comprising:
a temperature estimation apparatus as defined in claim 1.
A heater control apparatus for a heater (10) including a conductor (3), a heating element (2) which generates heat when electricity is supplied thereto, and a substrate (11) which is formed of ceramic and in which the conductor (3) and the heating element (2) are separately embedded and held,
the heater control apparatus comprising:
an energization section which supplies electricity to the heating element (2) so as to cause the heater (10) to generate heat;

characterized by:
an obtainment section (S610, S620) which obtains an electrical resistance (R₁₁) of the substrate (11) between the conductor (3) and the heating element (2),

wherein the energization section (S660) controls the supply of electricity to the heating element (2) such that the electrical resistance (R₁₁) obtained by the obtainment section (S610, S620) becomes equal to a predetermined value.
A heating apparatus (100) comprising:
a heater (10) including a conductor (3), a heating element (2) which generates heat when electricity is supplied thereto, and a substrate (11) which is formed of ceramic and in which the conductor (3) and the heating element (2) are separately embedded and held; and

a heater control apparatus as defined in claim 3.
A heating apparatus (100) according to claim 2 or 4, wherein the obtainment section (S610, S620) obtains the electrical resistance (R₁₁) on the basis of a potential difference between the conductor (3) and the heating element (2) and a value of current flowing between the conductor (3) and the heating element (2).