GB2328295A

GB2328295A - Regulating the fuel pressure in an internal combustion engine

Info

Publication number: GB2328295A
Application number: GB9817300A
Authority: GB
Inventors: Christof Hammel; Udo Schulz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-08-16
Filing date: 1998-08-07
Publication date: 1999-02-17
Anticipated expiration: 2018-08-07
Also published as: DE19735561B4; GB2328295B; FR2767358B1; JPH11153054A; DE19735561A1; GB9817300D0; FR2767358A1

Abstract

Controlling a high-pressure fuel supply installation in an internal combustion engine, in particular an engine with a common fuel rail system 130, comprises the steps of conveying fuel by pumps 110 and 125 from a low-pressure region into the high-pressure region including the rail 130, detecting the fuel pressure P in the rail 130 using a pressure sensor 140, and then regulating the pressure in the rail 130 in dependence on a target value PS. Regulation is performed by a control device 150 which controls the coil 136 of a regulating valve 135. Pressure detection for controlling pressure regulation takes place only at predetermined time intervals which lie outside the periods when fuel is supplied to the engine. Therefore the pressure fluctuations which occur during injection are not allowed to influence the pressure regulation. Pressure detection for controlling the drive signals A to the injectors 131 can take place at different predetermined time intervals (figure 2).

Description

1 2328295 METHOD OF AND CONTROL MEANS FOR CONTROLLING AN INTERNAL

COMBUSION ENGINE The present invention relates to a method of and a control means for controlling an internal combustion engine.

A method and a device for the control of an internal combustion engine are described in DE 195 48 278, in which regulation of the fuel pressure in a fuel storage device in a common rail system is described. The drive control duration of the injectors in such common rail systems is usually preset in dependence on the quantity of fuel to be injected and the pressure in the storage device. For this purpose, the pressure in the storage device is detected synchronously with the engine rotational speed. The pressure regulation takes place in a fixed time raster. For this purpose, the rail pressure detected synchronously with the rotational speed is scanned synchronously with time. This can, under unfavourable operational states, lead to appreciable dead times during the pressure regulation, which causes the pressure regulator having to be applied very slowly. This is an undesired boundary condition from the viewpoint of rapid regulating-out of interference magnitudes.

It would thus be desirable to minimise the dead time in fuel pressureregulation for the purpose of control of an internal combustion engine.

According to a first aspect of the present invention there is provided a method for the control of an internal combustion engine, especially an engine with a common fuel rail system, wherein at least one pump conveys fuel from a low-pressure region into a pressure storage device and pressure values, which characterise the fuel pressure in the pressure storage device, are detected by a pressure sensor, and wherein a drive control signal for a pressure-regulating means is presettable starting from the detected pressure values and a target value, characterised in that the pressure values are detected at preset time intervals, no pressure values being detected during an injection of fuel.

Preferably, a detection, synchronised in angle, of pressure values takes place in addition. The detection, synchronised in angle, of pressure values can take place directly before the beginning andlor the end of the injection. For preference, the pressure values ascertained during the detection synchronised in angle are used for the control of the injection.

2 Expediently, a sliding mean value formation is carried out over every at least two detected pressure values.

According to a second aspect of the invention there is provided control means for the control of an internal combustion engine, especially an engine with a common rail system, wherein at least one pump conveys fuel from a low-pressure region into a pressure storage device, with a pressure sensor which detects pressure values characterising the fuel pressure in the pressure storage device, and with a pressure regulator which presets a drive control signal for pressure-regulating means starting from the detected pressure values and a target value, characterised in that means are provided which detect the pressure values at preset time intervals, no pressure values being detected during an injection of fuel.

The dead time in the case of a fuel pressure regulating loop may be able to be substantially reduced by a method exemplifying the invention An example of the method and embodiment of the control means of the present invention will now be more particularly described with reference to the accompanying drawings, in which:

Fig. 1 is a block diagram of control means embodying the invention; Fig. 2 is a diagram showing fuel pressure entered as a function of the time and the instants of pressure measurement by the control means; Fig. 3 is a block diagram of pressure detection means of the control means; Fig. 4 is a flow chart illustrating steps of a method exemplifying the invention; and Fig- 5 is a flow chart illustrating further steps of the method.

Referring now to the drawings, there is shown in Fig. 1 a fuel supply system of an internal combustion engine with high-pressure injection, the illustrated system usually being known as a common rail system.

3 The installation comprises a fuel supply container 100, which is connected with a first filter 105, a regulable preliminary conveying pump 110 and a second filter 115. The fuel passes from the second filter 115 by way of a duct to a valve 120. The connecting duct between the filter 115 and the valve 120 is connected with the container 100 by way of a lowpressure limiting valve 145. The valve 120 is connected with a rail 130 by way of a highpressure pump 125. The rail represents a storage device and is connected with injectors 131 by way of fuel ducts. The rail 130 is connectible with the container 110 by way of a pressure-regulating means, in particular a pressure-regulating valve 135 controllable by means of a coil 136.

The ducts between the exit of the high-pressure pump 125 and the entry of the pressureregulating valve 135 represent a high-pressure region, in which the fuel stands under high pressure. The pressure in the highpressure region is detected by means of a sensor 140. The ducts between the tank 100 and the high-pressure pump 125 represent a lowpressure region.

A control device, denoted by 150, acts on the injectors 131 by a drive control signal A and controls the coil 136 of the pressure-regulating valve 135 in drive. For this purpose, an output signal P of the pressure sensor 140 and output signals of further sensors, for example a rotational speed sensor, are evaluated.

The control device 150 comprises a pressure computation block 151, to which the output signal of the pressure sensor 140 is conducted. The pressure computation block 151 applies signals to a quantity computation block 152 and to a first input of an interlinking point 154. An output signal PS of a target value presetting device 153 is present at a second input of the interlinking point 154. The target value presetting device 153 processes the output signal N of a rotational speed sensor 160 and of the quantity computation block 152. The quantity computation block acts on the injectors by drive control signals A and the pressure computation block by a signal QK, which indicates that an injection takes place. A pressure regulator 155 is acted on by the output signal of the interlinking point 154 and in turn controls the coil 136 of the pressureregulating valve 135.

In use, fuel from the container, is conveyed by the conveying pump 110 through the fitters 105 and 115. At the exit of the pump 110, the fuel is acted on by a pressure between 1 and about 3 bar. When the pressure in the low-pressure region of the fuel system has 4 reached a presettable pressure, the valve 120 opens and the entry of the high-pressure pump 125 is acted on by a certain pressure. This pressure depends on the construction of the valve 120. Usually, the valve 120 is arranged so that it frees the connection to the high-pressure pump 125 at a pressure of about 1 bar.

If the pressure in the low-pressure region rises to an impermissibly high value, the lowpressure limiting valve 145 opens and frees the connection between the exit of the pump 110 and the container 100. The pressure in the low-pressure region is kept at values between about 1 and 3 bar by means of the valve 120 and the low-pressure limiting valve 145.

The high-pressure pump 125 conveys the fuel from the low-pressure region into the highpressure region. The high-pressure pump 125 builds up a very high pressure in the rail 130. Usually, pressure values of about 30 to 100 bar are achieved in systems for applied ignition engines and pressure values of about 1000 to 2000 bar in compression ignition engines. The fuel can be injected under high pressure by way of the injectors 131 to the individual cylinders of the engine.

The pressure in the rail or in the entire high-pressure region is detected by means of the sensor 140. The pressure in the high-pressure region can be regulated by means of the pressure-regulating valve 135, which is controllable by a coil 136. The pressure-regulating valve 135 opens for different pressure values in dependence on the voltage present across the coil 136 or the current flowing through the coil 136.

Further setting members can also be employed for the regulation of the pressure P in the high-pressure region. These are an electrical preliminary conveying pump adjustable in respect of the conveyed quantity, or a controllable high-pressure pump. In addition to the pressureregulating valve 135, a pressure-limiting valve can also be provided, which at a preset pressure frees the connection between the high-pressure region and the lowpressure region.

The block 151 prepares the signal provided by the pressure sensor 140 and supplies it to the quantity computation block 152 on the one hand and the comparison point 154 for pressure regulation on the other hand. The quantity computation block 152 computes, in dependence on the pressure P and the desired quantity of fuel to be injected, the signals A for action on the injectors 131.

The target value presetting device 153 computes, starting from different operating parameters, such as the rotational speed N of the engine and the quantity of fuel to be injected, a target value PS for the fuel pressure in the storage device 130. This target value PS is compared in the interlinking point 154 with the actual value M, which is made available by the block 151. In dependence on this comparison, the pressure regulator 155 computes the drive control signal for action on the pressure-regulating valve 135.

The computation of the drive control signals in dependence on the pressure P is carried out before each injection and thus takes place in dependence on rotational speed with a variable time interval. The interval between these computations greatly depends on engine speed. The computation of the control signal A in the pressure-regulator 155 takes place in a fixed time cycle. This time cycle is chosen so that the regulator can react immediately to changing target values PS and the new target value have effect as rapidly as possible.

The pressure for the actual value detection is detected synchronously in time with a very short time cycle preferably of about 10 milliseconds. The pressure values are detected at preset and preferably fixed time intervals. The evaluation, synchronously with angle or rotational speed, of the pressure for the computation of the drive control signal A takes place parallelly thereto. It is a problem, however, that as illustrated in Fig. 2, the pressure P fluctuates significantly during the injection. The pressure P is entered as a function of time t in Fig. 2. A respective injection cycle begins at each of the instants M, t2 and t3. This leads to the pressure dropping rapidly and subsequently rising again to its original value. The injection ends respectively at the instants tV, t2' and tX.

The fluctuations of the pressure during the injection cannot readily be compensated for by the pressure regulation. When these fluctuations are taken into consideration for the actual value detection, this results in the output signal of the pressure regulator being subject to undesired strong fluctuations. To avoid this, no pressure values for the pressure regulation are detected in the time spans between tl and tV, between t2 and t2' or between t3 and tX.

6 The instants of the time-synchronous pressure detection, at which the pressure detection for pressure regulation takes place, are marked by circles in Fig 2. The instants for anglesynchronous pressure detection, at which the pressure detection takes place in order to compute the drive control signals A for the injectors, are marked by crosses.

In the case of the illustrated example, the value during the pressure detection directly before the injection is used for pressure regulation as well as for control of the injectors.

An embodiment for realisation of this procedure is illustrated in Fig. 3. Elements already described in Fig. 1 are denoted by corresponding reference symbols. The components 400, 410 and 420 represent the significant parts of the pressure detection block 151, which provides the value PI. The output signal P of the pressure sensor 140 is passed by way of first switching means 400 to change-over switching means 420. The output signal of the change-over switching means 420 is passed as the actual value PI to the interlinking point 154.

The switching means 400 is controlled in drive by a clock pulse transmitter 410 at a preset clock pulse frequency. During each cycle, the switching means 400 is closed and its input is passed to the output. The switching means 420 is, as a rule, in its closed state. This means that the signal P of the sensor 140 is passed on as the actual value PI to the interlinking point 154 at the time intervals preset by the pulse generator 410.

When the block 152 delivers a signal A, which indicates an injection, the switching means 420 is switched into its second position. This has the effect that the output signal of the switching means 420 remains at its old value. The signal QK is present between the instants tl and tV, t2 and tZ and t3 and tX.

An example of the procedure is illustrated by the flow diagram of Figure 4. A time counter t is set to 0 in a first step 500. In a subsequent step 510, the time counter t is increased by a value At. An interrogation step 520 checks whether the time counter t has a value greater than St. This value St determines the interval between the measurement value detection. If this is not the case, the step 510 is repeated, but if this is the case an interrogation step 530 checks whether a drive control signal A for the injectors is present. If this is not the case, the value P2 is detected in a step 540 and used as the actual value PI.

7 It is particularly advantageous if a sliding mean value formation takes place each time over at least two pressure values detected synchronously in time. This means that, apart from the value P2 actually detected in the step 540, the old value P1, which was detected in the previous program sequence, is additionally taken into consideration. The value P used for pressure regulation is computed in a step 550 by mean value formation from the values P1 and P2. Subsequently, the old value P1 is written over by the new value P2 in a step 560. This is illustrated by way of example by the blocks in dashed lines in Fig. 4. It is advantageous if averaging is carried out over more than two measurement values.

Fig. 5 illustrates steps for detection of the pressure for presentation to the quantity computation. Firstly, an angle value W is set to 0 in a first step 600. The angle value W is increased by AW in a subsequent step 610. Subsequently, an interrogation step 620 checks whether the angle W is greater than a threshold value SW. This threshold value SW is chosen so that it corresponds with the revolution of the crankshaft since the last computation. If this is not the case, the step 610 is repeated. If this is the case, the pressure value P is detected in a step 630 and passed on to the quantity computation block. The threshold value SW is chosen so that this angle-synchronous detection of the pressure values takes place directly before the beginning andlor before the end of the injection. Preferably, the threshold value is preset appropriately in dependence on the operating conditions.

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Claims

1. A method of controlling an internal combustion engine, comprising the steps of conveying fuel from a low-pressure region of a fuel supply installation of the engine to storage means for storing fuel under pressure to be supplied to the engine, detecting fuel pressure in the storage means at predetermined time intervals lying outside the periods in which fuel is supplied to the engine, and determining a control signal for fuel pressure regulating means in dependence on an actual value indicative of the detected pressure and a target value for the pressure.

2. A method as claimed in claim 1, comprising the further step of detecting fuel pressure in the storage means in synchronism with engine crankshaft angle.

3. A method as claimed in claim 2, wherein the detection of fuel pressure in synchronism with angle is carried out directly before, directly after or directly before and after a cycle of fuel supply to the engine.

4. A method as claimed in claim 2 or claim 3, comprising the step of using values indicative of detected fuel pressure in synchronism with angle for control of fuel supply to the engine.

5. A method as claimed in any one of the preceding claims, comprising the step of subjecting the values indicative of detected pressure to a sliding mean value formation.

6. A method as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

7. Control means for controlling an internal combustion engine, comprising conveying means for conveying fuel from a low-pressure region of a fuel supply installation of the engine to storage means for storing fuel under pressure to be supplied to the engine, detecting means for detecting fuel pressure in the storage means at predetermined time intervals lying outside the periods in which fuel is supplied to the engine, and determining means for determining a control signal for fuel pressure regulating means in dependence on an actual value indicative of the detected pressure and a target value for the pressure.

9

8. Control means as claimed in claim 7, wherein the storage means is a common fuel rail of a fuel injection system.

9. Control means substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows -to- 1. A method of controlling an internal combustion engine, comprising the steps of conveying fuel from a low-pressure region of a fuel supply installation of the engine to storage means for storing fuel under pressure to be supplied for combustion in the engine, detecting fuel pressure in the storage means at predetermined time intervals lying outside the periods in which said fuel supply takes place, and determining a control signal for fuel pressure regulating means in dependence on an actual value indicative of the detected pressure and a target value for the pressure.

3. A method as claimed in claim 2, wherein the detection of fuel pressure in synchronism with angle is carried out directly before, directly after or directly before and after a cycle of said fuel supply.

4. A method as claimed in claim 2 or claim 3, comprising the step of using values indicative of detected fuel pressure in synchronism with angle for control of said fuel supply.

7. Control means for controlling an internal combustion engine, comprising conveying means for conveying fuel from a low-pressure region of a fuel supply installation of the engine to storage means for storing fuel under pressure to be supplied for combustion in the engine, detecting means for detecting fuel pressure in the storage means at predetermined time intervals lying outside the periods in which said fuel supply takes place, and determining means for determining a control signal for fuel pressure regulating means in dependence on an actual value indicative of the detected pressure and a target value for the pressure.

1 8. Control means as claimed in claim 7, wherein the storage means is a common fuel rail of a fuel injection system.