GB2314944A

GB2314944A - Controlling fuel injection in an internal combustion engine

Info

Publication number: GB2314944A
Application number: GB9713693A
Authority: GB
Inventors: Christoph Burckhardt
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1996-07-02
Filing date: 1997-06-27
Publication date: 1998-01-14
Anticipated expiration: 2017-06-27
Also published as: FR2750734A1; IT1293066B1; GB2314944B; ITRM970388A1; DE19626536A1; FR2750734B1; DE19626536C2; GB9713693D0; ITRM970388A0

Abstract

Instabilities such as "bucking" in an ic engine are controlled by controlling fuel injection quantity according to accelerator pedal travel and the rate of change of engine speed. Signal U FP from pedal 1 and engine speed signal n are used in conjunction with families of driving and pressure characteristics 8, 9 to derive a desired torque signal M 1 . This signal is converted by a model of vehicle characteristics 10 into an expected rate of change of engine speed and the difference between that and the rate of change of engine speed calculated from n by differentiator 12 is fed into a parameter table of family characteristics 13 along with the torque signal M 1 to provide an injection quantity correction signal #m e . This correction quantity is weighted by an average value of engine speed provided by band-pass filter 15 to produce a fuel injection quantity correction signal for controlling fuel injection into the engine Further adjustments to the signals, according to vehicle transmission ratios, can also be made.

Description

2314944 Method for controlling the injection quantity of fuel fed to an

internal combustion engine The invention relates to a method for controlling the injection quantity of fuel fed to an internal combustion engine, and to a device for carrying out this method.

DE 37 21 300 Al describes a device which acts on an adjusting device of a fuel injection pump. In this arrangement, an element for adjusting the fuel delivery quantity, which element can be adjusted by means of a fuelquantity and control/regulating device as a function of operating parameters of the internal combustion engine, can additionally be adjusted by means of an actuating member which, for its part, is controlled by an anti-bucking signal which is formed as a function of the occurrence of a rapid engine speed change or relative movements of the internal combustion engine on the vehicle, referred to as bucking, and counteracts the bucking by means of fuel deliveryquantity elements. An adjusting lever, which is coupled to the element for adjusting the fuel delivery quantity, can be pivoted between two stops, which define a basic setting. In a control unit, to which at least the speed of the internal combustion engine is fed, so-called anti-bucking signals are generated by means of an algorithm and fed to a stepping motor. This stepping motor rotates by a defined number of steps and, in this way, adjusts the stops for the adjusting lever which define the range of adjustments.

The known arrangement is suitable only for mechanical injection systems, the adjusting lever being acted upon, on the one hand, by a spring that engages on the lever and by a centrifugal engine-speed sensor, on the other. The control unit cannot exert a direct influence on the position of the adjusting lever but serves merely to change the position of the stops, i.e. to effect a change in the range of adjustment. Because of the inertia of the masses which are acting and which have to be moved, the known arrangement is not suitable for modern injection 2 systems with switching valves where in some cases the switching speed is in a range of < 1 millisecond.

The present invention seeks to provide a method for controlling the injection quantity of the fuel fed to the cylinders of an internal combustion engine, by means of which movements of the accelerator pedal can be processed as rapidly as possible to give an injection-quantity correction and a corresponding control signal is fed to a device which effects injection of the fuel. It is furthermore an object of the invention to specify a device for carrying out the method.

According to one aspect of the present invention there is provided a method for controlling the injection quantity of fuel fed to an internal combustion engine, with the following method steps:

a) a pedal-value transmitter signal is produced as a function of the change in position of an accelerator pedal, b) the pedal-value transmitter signal is fed to a control unit, to which at least the current speed of the internal combustion engine is input as a further input variable, c) a rate of change of the engine speed is determined from the value of the current speed by differentiation, d) the value of an injection-quantity correction is calculated in the control unit as a function of the change in the pedal-value transmitter signal and the rate of change of the engine speed, the value of the injection-quantity correction being negatively amplified in a region adjacent to the full load and positively amplified in a region adjacent to no load, e) the injection-quantity correction is multiplied by an engine speed- weighting factor to give a weighted injection-quantity correction, f) the weighted injection-quantity correction is fed to a convertor which, as a function of the weighted injection-quantity correction, produces control 3 signals, which are fed to a device which effects injection of the fuel.

According to a second aspect of the invention there is provided a device for controlling the injection quantity of fuel fed to an internal combustion engine, with a control unit, a pedal-value transmitter, which is connected to the control unit and feeds a pedal-value signal to the latter as a function of the actuation of an accelerator pedal, a speed detection device for the current engine speed, which is likewise connected to the control unit, and with means for the formation of a rate of change in the engine speed, and means for calculating an injectionquantity correction taking into account a family of quantity characteristics, stored in the control unit, of a device, arranged on the output side of these means, for weighting the value of the injection- quantity correction, and a converter, which, on the input side, receives the weighted injection-quantity correction and, on the output side, is connected to a device which effects injection of the fuel.

The essential advantages of the invention are to be seen in the fact that evaluation of the engine speed and pedal-value signal takes place extremely rapidly and account is simultaneously taken of whether the speed is in a range adjacent to full load or in a range adjacent to no load. By means of this measure and by including a speed-weighting factor, bucking oscillations can be reliably prevented.

It is expedient to include in the determination of the value of the injection-quantity correction the respective speed of the vehicle transmission which is currently being used. The rate of change of the speed should therefore be produced by means of a band-pass filter dependent on the respective speeds of a vehicle transmission. It is also advantageous to store vehicle-typespecific data, a so-called vehicle model, in the control unit or to supply the latter with these data. In this way, the calculation of an engine speed-change value takes place as a function of vehicle-typical parameters, so that, for 4 example, the inertia, which is significant for acceleration or deceleration processes, is included in the control process.

A value for the desired torque is calculated in a family of driving characteristics stored in the control unit, taking into account the pedal-value transmitter signal and the current engine speed. From this value, it is possible, taking into account further parameters, to form a load ratio of the torques, namely desired quantity/maximum quantity (MWunsch:Mmax), the maximum quantity being dependent, inter alia, on the A value. The respective maximum torque can thus be determined in a family of characteristics in the control unit as a function of certain parameters, in order, for example, to achieve smoke limitation, so that, at a certain operating point, only a certain quantity of fuel is released, irrespective of whether a higher demand for fuel is present by virtue of the respective position of the accelerator pedal. Th e invention is explained in greater detail below with reference to the drawing, in which:

Fig. 1 shows a schematic representation of a device for injectionquantity control as a function of the accelerator pedal, Fig. 2 shows an arrangement for producing an injection-quantity correction signal and Fig. 3 shows an arrangement for producing an engine-speed change value specific to the vehicle.

Fig. 1 shows schematically a device for injectionquantity control as a function of the accelerator pedal. A control unit 5 serves to produce a signal for injectionquantity control or a corresponding change value as a function of a plurality of parameters input into the control unit. of particular significance here, of course, is the position of an accelerator pedal 1, which is mounted pivotably on a chassis 2. This accelerator-pedal position is fed to the control unit 5 as a voltage UFPI the change in the position of the accelerator pedal I resulting, of course, in a change in the voltage UFP The control unit 5 is furthermore supplied with a current engine speed n determined by an engine-speed detection device 26.

The boost pressure PLI the coolant temperature T. and the boosttemperature TL 1 f or example, can serve as further input variables for the control unit 5. The output signal calculated in the control unit 5 on the basis of the input parameters corresponds to the change in the injection quantity, indicated by m el which is required on the basis of the change in the accelerator pedal. This signal is fed to a convertor 6, the output signal of which serves as current I for the purpose of driving an injector 7. The injector 7 can, for example, be part of a common-rail injection system.

Fig. 2 shows that the accelerator pedal 1, which is mounted pivotably on the chassis, acts by means of a coupling device 3 on a pedal-value transmitter 4, which, in the exemplary embodiment, is embodied as a variable resistor. A Hall generator or an inductive transmitter can also be used instead of the resistor. By means of this pedal-value transmitter 4, the voltage U is varied as a function of the pedal position or of the change in the accelerator pedal 1 and fed as a voltage UFP to the control unit 5 shown in Fig. 1. According to the representation in Fig. 2, this control unit 5 first of all comprises a family of driving characteristics 8 with a family of parameters stored in it. In addition to the voltage UFP of the pedalvalue transmitter 4, the control device is also supplied with the instantaneous engine speed n.

According to the exemplary embodiment in Fig. 2, further calculation in the control unit should take place on the basis of the desired torque indicated by the actuation of the accelerator pedal. For this reason, the value of the desired torque Msoll is fed from the family of driving characteristics 8 to a family of pressure characteristics 9 arranged on the output side of the latter. The boost pressure PL is entered into the family of pressure characteristics 9 as a further parameter, so that, 6 ultimately, on the basis of the torque characteristics stored in the family. of pressure characteristics, a correspondingly limited quantity of fuel is injected by injector 7 in Fig. I as a function of the level of the respective boost pressure. In this way, the family of pressure characteristics 9 acts as a smoke-limiting device. The signal M, at the output of the family of pressure characteristics 9 corresponds to the quotient of the desired torque Mwunsch to the maximum torque Mmax, the latter being determined in accordance with the I value of the family of pressure characteristics 9.

In the control unit 5 in Figure I there is, in accordance with the representation in Fig. 2, a so-called vehicle model 10, in which the vehicle-specific values for calculation adequate for the vehicle type are stored. In this way, an acceleration corresponding to an expected enginespeed change value n is calculated from the torque M, and the speed n of the internal combustion engine by way of the vehicle model 10. The expected engine-speed change value n calculated in the vehicle model 10 is fed to a summing element 11, to which the engine-speed change n formed by means of a DT, element is also applied. The difference between the expected engine-speed change value n and the engine-speed change n is fed to a family of quantity characteristics 13, to which the torque M, is input as a further variable.

The family of parameters in the family of quantity characteristics 13 is set up in such a way that a value for the injection-quantity correction Ame is calculated as a function of the torque value Mi determined by means of the change in the accelerator pedal, of the expected enginespeed change value n and of the engine-speed change n. In order to counteract control problems which could arise in the vicinity of full load or of no- load (when the accelerator pedal 1 is released), the signal for the injection-quantity correction Ame emerging from the family of quantity characteristics 13 is fed to a multiplying 7 element 14, which is also supplied with a value for the average engine speed n produced by way of a band-pass filter 15. There thus takes place in the multiplying element 14 a weighting of the rate of change of the engine speed against the load ratio and the engine speed.

Fig. 3 shows an arrangement for producing a vehicle-specific engine-speed change value. The torque M, and the current engine speed n are required as input signals for this purpose. The torque M 1 is f ed to an injectionquantity correction unit 25, which essentially comprises the f amily of quantity characteristics 13 and the multiplying element 14 of the arrangement shown in Fig. 2. The value of the torque M, is furthermore applied to a summing element 16. The current engine speed n is f irst of all fed via a band-pass filter 21 to a DT, element 22. The band-pass filter 21 is designed in accordance with the transmission ratios of the speeds of the transmission. The output signal of the DT, element 22 is the engine-speed change n, which is fed to a PT1 element 20. The engine-speed change n is furthermore fed to a summing element 18, to which the signal of the expected engine-speed change value n is also applied.

In the PT, element 20, a signal is formed taking into account the respective speed of the transmission in which drive is currently taking place, and is f ed to a summing element 19. The expected engine-speed change value n is also applied to the summing element 19, this value being subtracted f rom the output value f ormed in the PT, element 20. The result formed in the summing element 19 is converted in an integrator 24 to a torque value, which corresponds to the quotient of AM:Mmax' In the summing element 16, this torque value expressed by the quotient is subtracted from the desired torque M 1 also applied to the summing element 16, and the result is fed to a PT, element 17. In this PT, element 17, the expected engine-speed change value n is formed from the torque value, this change value n, as already mentioned, being applied to the summing 8 element 18. A difference An corresponding to the subtraction n - n is therefore formed in the summing element 18.

The speed change value formed in this way is fed to the injectionquantity correction device 25 and processed in a family of quantity characteristics, taking into account the torque value M, applied to the said device, to give a value for the injection-quantity correction Ame, The average engine speed n is formed from the current engine speed n in a PT, element 23, and this average engine speed is fed to the injectionquantity correction means 25. In this injection-quantity correction device 25, the rate of change of the engine speed is weighted, i.e. the value for the injection-quantity correction Ame is multiplied by the engine speed weighting factor, resulting ultimately in a weighted injection-quantity correction me 9

Claims

Claims

A method for controlling the injection quantity of fuel fed to an internal combustion engine, with the following method steps:

a) a pedal-value transmitter signal is produced as a function of the change in position of an accelerator pedal, b) the pedal-value transmitter signal is fed to a control unit, to which at least the current speed of the internal combustion engine is input as a further input variable, c) a rate of change of the engine speed is determined f rom the value of the current speed by differentiation, d) the value of an injection-quantity correction is calculated in the control unit as a function of the change in the pedal-value transmitter signal and the rate of change of the engine speed, the value of the injection-quantity correction being negatively amplified in a region adjacent to the full load and positively amplified in a region adjacent to no load, e) the injection-quantity correction is multiplied by an engine speed- weighting factor to give a weighted injection-quantity correction, f) the weighted injection-quantity correction is fed to a convertor which, as a function of the weighted injection-quantity correction, produces control signals, which are fed to a device which effects injection of the fuel.
2. A method according to Claim 1, wherein the rate of change of the engine speed is produced by means of a bandpass filter, which is dependent on the respective gears of a vehicle transmission, and a DT, element.
3. A method according to Claim 1 or 2, wherein vehicle-type-specific data are stored in the control unit or can be fed to the latter, and the calculation of an expected speed-change value takes place as a function of the vehicle model.
4. A method according to Claim 3, wherein the expected speed-change value produced in the vehicle model is reduced by the value of the rate of change of the speed.
5. A method according to any one of the preceding claims, wherein a value for the desired torque is calculated in a family of driving characteristics, taking into account the pedal-value transmitter signal and the current engine speed.
6. A method according to Claim 5, wherein a load ratio between the desired quantity and the maximum quantity is formed from the vale of the desired torque, taking into account further parameters.
7. A device for controlling the injection quantity of fuel fed to an internal combustion engine, with a control unit, a pedal-value transmitter, which is connected to the control unit and feeds a pedal-value signal to the latter as a function of the actuation of an accelerator pedal, a speed detection device for the current engine speed, which is likewise connected to the control unit, and with means for the formation of a rate of change in the engine speed, and means for calculating an injection-quantity correction taking into account a family of quantity characteristics, stored in the control unit, of a device, arranged on the output side of these means, for weighting the value of the injection-quantity correction, and a converter, which, on the input side, receives the weighted injection-quantity correction and, on the output side, is connected to a device which effects injection of the fuel.
8. A device according to Claim 7, wherein the control 11 unit comprises a vehicle model which is drawn up in accordance with vehicle-specific data and in which, in particular, the transmission ratio of the speeds of the transmission is taken into account.
9. A device according to Claim 7 or 8, wherein the means for producing the rate of change of the engine speed comprise a band-pass filter and a differentiating transfer element with a delay.
10. A device according to any one of Claims 7 to 9, wherein the control unit comprises a family of driving characteristics and a family of pressure characteristics.
11. A method for controlling the injection quantity of fuel fed to an internal combustion engine, substantially as described herein with reference to, and as illustrated in, the accompanying drawings.
12. A device for controlling the injection quantity of fuel fed to an internal combustion engine, substantially as described herein with reference to, and as illustrated in, the accompanying drawings.