GB2327777A

GB2327777A - Regulating the fuel pressure in an internal combustion engine

Info

Publication number: GB2327777A
Application number: GB9816003A
Authority: GB
Inventors: Christof Hammel
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-07-25
Filing date: 1998-07-22
Publication date: 1999-02-03
Anticipated expiration: 2018-07-22
Also published as: DE19731995A1; FR2766520A1; JPH11101148A; DE19731995B4; GB2327777B; GB9816003D0; FR2766520B1; JP4276718B2

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 setting the pressure to a target value using a regulator. The regulator comprises a control device 160 which acts on the coil 136 of a pressure regulating valve 135. The valve can be arranged so that it discharges a certain quantity of fuel back into the low pressure region in dependence on the control signal A and the coil 136. The control device processes signals from various sensors 165 representing operational states of the engine, such as rotational speed, and then the transmission behaviour of the regulator is set depending on these sensed parameters. For example, the values of the proportional and integral constants of the regulator can be varied.

Description

2327777 1 METHOD OF AND CONTROL MEANS FOR CONTROLLING AN INTERNAL

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

A method and a control device for the control of an internal combustion engine are described in DE-OS 195 48 278, in which regulation of the fuel pressure in a common rail system is described. The fuel is conveyed by means of a pump from a low-pressure region into a storage device, in which the fuel pressure is detected by means of a sensor. A regulator determines a drive control signal for action on a pressure-regulating valve in dependence on the difference between a target value and an actual value.

The amplification and dynamic behaviour of the regulating path formed by the pressureregulating valve and storage device is greatly dependent on the engine operating state. In certain operational states, a rapid pressure rise takes place. In other operational states, the pressure rise is slow. Moreover, oscillations and instabilities arise in the case of large and small regulating differences.

It would thus be desirable to be able to ensure a stable regulation of fuel pressure, especially for an internal combustion engine with a common rail system in all operational states.

According to a first aspect of the present invention there is provided a method for the control of an internal combustion engine, especially for an internal combustion engine with a common fuel rail system, wherein at least one pump conveys the fuel from a lowpressure region into a storage device and the fuel pressure in the storage device is detectable by a pressure sensor, the pressure being settable to a target value by a regulator, characterised in that the transmission behaviour of the regulator is presettable in dependence on operating parameters.

Preferably, regulating parameters which determine the transmission behaviour of the regulator are presettable in dependence on a pressure build-up quantity available for pressure build-up in the storage device. The regulating parameters may also be presettable in dependence on a rotational speed andlor a magnitude which corresponds 2 with the quantity of fuel injected into the internal combustion engine, andlor in dependence on the sign andlor amplitude of a regulation deviation of the regulator.

For preference, in the case of high values of the pressure build-up quantity, the regulating parameters are presettable in such a manner that high values result for the proportional amplification and/or the integration constant of the regulator, whereas for small values of the pressure build-up quantity the regulating parameters can be presettable in such a manner that small values result for the proportional amplification andlor the integration constant of the regulator.

According to a second aspect of the invention there is provided control means for the control of an internal combustion engine, especially for an internal combustion engine with a common fuel rail system, wherein at least one pump conveys the fuel from a lowpressure region into a storage device, a pressure sensor detects the fuel pressure in the storage device and a regulator sets the pressure to a target value, characterised in that means are provided to preset the transmission behaviour of the regulator in dependence on operating parameters.

Due to the presetting, which is dependent on operating parameters, of the transmission behaviour of the regulator, a rail pressure regulation can be achieved, which operates in stable manner and with dynamically good behaviour in all operational states.

An example of the method and an embodiment of the control means of the 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; Figs. 2a to c are diagrams of signal courses in the control means; and Fig. 3 is a block circuit diagram of a regulator in the control means.

Referring now to the drawings there is shown in Fig. 1 a fuel supply installation 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 by way of a first filter 105 and a preferably regulable preliminary conveying pump 110 with 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 low-pressure limiting valve 145. The valve 120 is connected with a rail 130 by way of a high-pressure pump 125. The rail represents a storage device and is connected by way of fuel ducts with fuel injectors 131. The rail is also connected with the container 100 by way of a press u re-regu lati rig 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 160 includes a pressure regulator and acts on relevant setting members, such as the coil 136 of the pressure-regulating valve 135, by a drive control signal A. The control device 160 processes different signals from different sensors 165, which signals characterise the operational state of the internal combustion engine andlor of a motor vehicle fitted with the engine. Such an operational state is, for example, the rotational speed of the engine.

The regulator is preferably constructed as proportional-integral regulator which has at least proportional-integral behaviour. The regulator can also have other components, for example differential components.

In use, fuel from the container 100 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 bars. When the pressure in the low-pressure region of the fuel system has reached a presettable value, the valve 120 opens and the entry of the highpressure 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.

4 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 into the individual cylinders of the engine by way of the injectors 131. The pressure in the rail 130 or in the entire highpressure region is detected by means of the sensor 140. The pressure in the highpressure region can be regulated by means of the press ure-reg ulating valve 135, which is controllable by the coil 136. The pressure-regulating valve 135 opens at different pressure values in dependence on the voltage across or the current flowing through the coil 136.

The pressure-regulating valve 135 can also be arranged so that it discharges a certain quantity into the low-pressure region in dependence on the current andlor the voltage present.

Usually, an electrical fuel pump with a direct current motor (DC motor) or an electrically commutating direct current motor (EC motor) is used as the preliminary conveying pump 110. For higher conveyed quantities, such as for commercial motor vehicles, several preliminary conveying pumps connected in parallel can be used. In this case, EC motors are preferred because of their higher service life and the higher availability.

Alternatively andlor additionally, further setting members can be used for the regulation of the pressure P in the high-pressure region. These are, for example, an electrical preliminary conveying pump adjustable in respect of conveyed quantity, or a controllable high-pressure pump. In addition to the pressure-regulating valve 135, a pressure-] i miting valve can be provided to free, at a preset pressure, the connection between the highpressure region and the low-pressure region.

In the following, changes in quantity or in the quantity throughput of the individual fuel quantities are considered. These changes in quantity are denoted by 6 and describe this quantity. In that case, the quantity is that which flows within a certain time span.

The conveyed quantity & is conveyed by the high-pressure pump 125 into the rail 130. The regulated quantity 6DRV is discharged by way of the press ure-regulating valve 135 into the low-pressure region. The pressure build-up quantity 6R is available for the pressure build-up. The admetered quantity 61 gets to the injectors 131 by way of the rail 130. The quantity 61 is composed of an injected quantity QK of fuel, a leakage quantity and a control quantity of the injector. The leakage quantity and the control quantity are returned to the low-pressure region. The injected quantity is injected into the combustion chambers of the engine.

For the quantitative change 6R of the pressure build-up quantity, there applies:

6R = 6P - 61- 6DRY This magnitude corresponds to the change in quantity in the storage device 130. Since the magnitude 6DRV is always greater than or equal to zero, there applies:

6R: QP - 61.

The pressure build-up in the rail 130 takes place through compression of the quantity OR. The speed of change of the pressure dPIdt is proportional to the change in quantity 6R. The greater the value of bP - (51, the higher the pressure gradient that is attainable. A significant time constant of the regulating path, which consists of the rail and pressureregulating valve, is the magnitude 6R or the difference P - 61.

The regulating parameters of the pressure regulator are preset as function of 6P and 61. For the quantity 6P, which is conveyed by the high- pressure pump 125, there applies the equation to a first approximation:

6P - K1 - N.

6 K1 is a constant and N is the rotational speed of the engine. For the quantity 61, there applies the equation:

QI = K2 OK N.

The quantity QK corresponds to the quantity of fuel injected per stroke into the engine. The magnitude K2 is a constant. For the magnitude 6P 61, there thus applies the equation:

6P - 61 = K1 - N - K2 - OK - N.

In Figs. 2a, 2b and 2c, the target value PS, the actual value P and the drive control signal A for action on the setting member for pressure regulation are entered as a function of time t for different rotational speeds of the engine. The target value PS is shown by a dotted line, the actual value P by a solid line and the control signal A by a dashed line. The target value for the pressure rises in a step to a higher value at the instant M.

The conditions for a mid-range rotational speed are illustrated in Fig. 2a. After the target value step at the instant M, the actual value rises rapidly and approaches the new target value asymptotically. The setting magnitude similarly passes continuously over to its new value. This behaviour is, as a rule, desired of the regulating path.

The conditions for a large quantitative change QIR are illustrated in Fig. 2b. This is applicable, for example, to a high rotational speed, since a large quantity of fuel is then conveyed. This means that the actual value rises very rapidly and has the consequence of only a slow rise in the setting magnitude, since the regulating deviation becomes very small after a very short time. As a result, the actual value fails again before reaching the actual target value and subsequently rises. The slow rise of the setting magnitude has the consequence that the actual value reaches the target value only at a later instant, as for a mid-range rotational speed. This behaviour is not desired.

The conditions for a small quantitative change 6R are illustrated in Figure 2c. This applies, for example, in the case of a low rotational speed, since the high-pressure pump conveys only very little fuel. This means that the actual value rises only very slowly. This has the consequence that the setting magnitude A rises very rapidly, as a result of which the actual value rises more steeply and significantly above the target value. When the 7 actual value exceeds the target value, the magnitude A falls again and approaches the new value asymptotically. A strong overshoot of the pressure in the rail 130 results. This behaviour, too, is undesired.

A similar dependence of the injected quantity of fuel also applies. The behaviour according to Fig. 2a results for medium injected quantities QK of fuel, the behaviour according to Fig. 2b for small injected quantities and the behaviour illustrated in Fig. 2c for large injected quantities.

For low rotational speeds and small quantities of injected fuel, an average quantity 6R of fuel is available for the pressure build-up. The same applies for high rotational speeds and large quantities of injected fuel. The resulting behaviour is similar to that illustrated in Fig. 2a.

For high rotational speeds and small quantities of injected fuel, much fuel is available for the pressure build-up. The value 6R is high and a very rapid rise of the actual value results. The resulting behaviour corresponds with the behaviour in Fig. 2b.

For low rotational speeds and large quantities of injected fuel, very little fuel is available for the pressure build-up. The value 6R is low and a very slow rise of the actual value results. The behaviour illustrated in Fig. 2c results.

If large regulating deviations occur, the press u re-setting member is disposed at an abutment and saturation phenomena arise. This means that in the case of a large regulating deviation, in particular when a strong pressure build-up is desired, the pressureregulating valve is disposed in its completely open state. No change in the regulating quantity 6DIRv results even if the setting magnitude rises further.

The following conditions arise in the case of pressure decay.

For low rotational speeds and small quantities of injected fuel, an average quantity 6R of fuel is available for the pressure decay. The same applies for high rotational speeds and large quantities of injected fuel.

8 For high rotational speeds and small quantities of injected fuel, very little fuel is available for the pressure decay. The value dR is low and a very slow decay of the actual value results.

For low rotational speeds and large quantities of injected fuel, very much fuel is available for the pressure decay. The value 6R is high and a rapid decay of the actual value results.

Accordingly, different regulating parameters, in particular a different regulating amplification, are therefore preset for different operating parameters, in particular rotational speed, injected quantity of fuel and sign of the regulating deviation.

In dependence on the regulating deviation, i.e. in dependence on whether a pressure build-up or a pressure decay is desired, different data sets are filed.

If a large quantity is available for the pressure change, i.e. the value 6R is high, then high values are preset for the proportional amplification andlor the integration constant. In the case of pressure build-up, this is the case for, in particular, high rotational speed andlor small quantity QK of injected fuel.

In the case of a low value for 6R, low values for the proportional amplification andlor the integration constant are preset. In the case of pressure build-up, this is the case for, in particular, a low rotational speed andlor large quantity of injected fuel.

in order to avoid unstable states and to adapt the regulator to the large signal behaviour and the small signal behaviour in the regulating path, different sets of parameters are used for large and small regulating deviation.

One form of the pressure regulating means is illustrated in detail in Fig. 3. A regulator is denoted by 300 and acts on the pressure-regulating valve 135 by the control signal A. However, the regulator can act on other or further setting members. These can be, for example, a regulable high-pressure pump, a controllable preliminary conveying pump andlor other components which influence the conveyed quantity andlor the pressure. Further, other regulating structures can be selected, for example a regulating structure with two regulators which act on different setting members.

9 The output signal of an interlinking point 310 is fed to the regulator 300. The output signal P of the pressure sensor 140 is present with positive sign at a first input of the interlinking point 310 and a target value PS of a target value presetting device 320 is present at a second input.

Different regulating parameters KF, which determine the transmission behaviour of the regulator 300, are filed in dependence on different operating characteristic magnitudes in a characteristic values field 330. The field 330 is acted on by the output signals of an interlinking point 340 and the interlinking point 310. The output signal of a first proportional member 350, at the input of which the output signal of the rotational speed sensor 165 is present, is applied with positive sign to a first input of the interlinking point 340. The output signal of the rotational speed sensor 165 is also applied to an interlinking point 360, the output signal of which is applied with negative sign to a second input of the interlinking point 340.

The output signal of a second proportional member 370, which is acted on by an output signal of a quantity-presetting device 380, is present at a second input of the interlinking point 360. The quantity-presetting device 380 provides a signal which corresponds to the quantity QK of fuel to be injected per stroke into the engine. In this case, the signal is preferably present in the control device and used for the control of the engine and the control of the quantity of fuel to be injected. For this purpose, for example, the quantity injected per stroke and cylinder or another injection quantity signal, for example the drive control duration of the injectors, is used.

The target value presetting device 320 is also a part of the control and presets the target value PS in dependence on different operating characteristic magnitudes.

The first proportional member 350 multiplies the rotational speed N by a first amplification factor KII. The second proportional member multiplies the quantity OK of fuel to be injected by a second amplification factor K2. This amplified fuel quantity signal is multiplied by the rotational speed N in the interlinking point 360. At the output of the interlinking point 340, the magnitude 6P - 61 is present, which results according to the formula:

6P-QI=M N-K2OKK The regulating parameters for the pressure regulator 300 are filed in dependence on this magnitude in the field 330. It is particularly advantageous when, in addition, the regulating parameters are filed in dependence on the sign of the regulating deviation and the magnitude of the regulating deviation.

Preferably, the proportional amplification P and the integration constant 1 for the regulator are filed in dependence on the magnitude 6R = 6P - 61 for large positive regulating deviations and large negative regulating deviations as well as for medium regulating deviations in the field 330.

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Claims

1. A method of controlling an internal combustion engine, comprising the steps of conveying fuel by conveying means from a low-pressure region of a fuel supply installation of the engine to storage means for storing fuel to be supplied to the engine, detecting fuel pressure in the storage means, setting the pressure in the storage means by regulating means in dependence on the detected pressure value and a target pressure value, and setting the transmission behaviour of the regulating means in dependence on at least one operating parameter of the engine or a vehicle fitted with the engine.

2. A method as claimed in claim 1, wherein the step of setting the transmission behaviour comprises setting parameters for the transmission behaviour of the regulating means in dependence on a fuel pressure buildup quantity available for pressure build-up in the storage means.

3. A method as claimed in claim 1 or claim 2, wherein the step of setting the transmission behaviour comprises setting parameters for the transmission behaviour of the regulating means in dependence on at least one of engine speed and a magnitude indicative of fuel quantity fed into the engine.

4. A method as claimed in any one of the preceding claims, wherein the step of setting the transmission behaviour comprises setting parameters for the transmission behaviour of the regulating means in dependence on the sign of the difference between the detected value and the target value.

5. A method as claimed in any one of the preceding claims, wherein the step of setting the transmission behaviour comprises setting parameters for the transmission behaviour of the regulating means in dependence on the amplitude of the difference between the detected value and the target value.

6. A method as claimed in claim 2, wherein in the case of high values of the fuel pressure build-up quantity the parameters are set so that at least one of a proportional amplification and an integration constant of the regulating means has a high value.

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7. A method as claimed in claim 2 or claim 6, wherein in the case of low values of the fuel pressure build-up quantity the parameters are set so that at least one of a proportional amplification and an integration constant of the regulating means has low value.

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

9. 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 to be supplied to the engine, detecting means for detecting fuel pressure in the storage means, means for setting the pressure in the storage means by regulating means in dependence on the detected pressure value and a target pressure value, and means for setting the transmission behaviour of the regulating means in dependence on at least one operating parameter of the engine or a vehicle fitted with the engine.

10. Control means as claimed in claim 9, wherein the storage means is a common fuel rail of a fuel injection system.

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

CLAIMS 1. A method of controlling an internal combustion engine, comprising the steps of conveying fuel by conveying means from a low-pressure region of a fuel supply installation of the engine to storage means for storing fuel to be supplied for combustion in the engine, detecting fuel pressure in the storage means, setting the pressure in the storage means by regulating means in dependence on the detected pressure value and a target pressure value, and setting the transmission behaviour of the regulating means in dependence on at least one operating parameter of the engine or a vehicle fitted with the engine.

-if+ '.

9. 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 to be supplied for combustion in the engine, detecting means for detecting fuel pressure in the storage means, means for setting the pressure in the storage means by regulating means in dependence on the detected pressure value and a target pressure value, and means for setting the transmission behaviour of the regulating means in dependence on at least one operating parameter of the engine or a vehicle fitted with the engine.