GB2255374A

GB2255374A - Determination of i.c.engine fuel injection timing

Info

Publication number: GB2255374A
Application number: GB9209160A
Authority: GB
Inventors: Martin Lutat; Georg Sobczyk
Original assignee: Kloeckner Humboldt Deutz AG
Current assignee: Kloeckner Humboldt Deutz AG
Priority date: 1991-04-29
Filing date: 1992-04-28
Publication date: 1992-11-04
Also published as: GB9209160D0; DE4113958C2; DE4113958A1

Description

22 _) 5_-) -4 A fuel injection device D E S C R I P T 1 0 N The invention

relates to a method of determining the injection time of a fuel injection device for an internal combustion engine according to the preamble of claim 1.

DE-OS 34 01 751 discloses a device which calculates the speed signals of an internal combustion engine. The speed signals are calculated on the basis of pulses delivered by a speed pick-up and pulses generated in the control unit. The engine is controlled by a control unit which actuates a final control element of the fuel injection device. If the engine speed alters between detection of the speed and actuation of the final control element, the alteration, unfortunately, is not taken into account as regards the amount of fuel injected. This may be the case, for exampl if the position of the accelerator pedal, and consequently e, z the speed, changes rapidly. The known device is also incapable of optimum control of fuel injection, since, an exact calculation of the time for actuating the final control element is impossible.

lhe aim of the invention is to disclose a method for exactly determining (calculating) a time, more particularly the injection time of a fuel injection device-for an internal combustion engine, in dependence on at least the engine speed, more particularly the change in speed.

To this end according to the invention, the calculation of the time is repeated until the [injection ?] time begins. The time to be calculated is preferably the injection time of a fuel injection device. The advantage of this, as compared with the prior art, is that the injection time is repeatedly calculated from the actual speed and at least one other operating parameter of the engine, until the time, allowance being made for actual values such as the speed or operating parameters of the engine. The injection time can therefore be exactly determined (calculated) from these actual values.

According to another feature of the invention, calculation is made in dependence on at least one time parameter of the fuel injection device and with allowance for the duration of calculation. The time required by the fuel injection device can e.g. be the operating time of a solenoid valve, since fuel is not injected into the engine combustion chamber simultaneously with actuation of the valve. In order to determine the injection time accurately, it is necessary to take account of other time parameters of the fuel injection device, since these may delay the fuel injection. Allowance must also be made for the duration required for calculating the injection time. This duration is influenced e.g. by the computer, the signal acquisition and processing, and the method of calculation.

According to another feature of the invention, the speed is 0 calculated from speed signals delivered by a speed pick-up which detects the motion of an engine shaft. A known speed pick-up detects the motion of a shaft, e.g. the engine camshaft or crankshaft, by scanning markings on the shaft or without contact, e.g. by scanning marking pick-ups on the shaft. The markings after suitable signal processing, preferably yield a rectangular signal sequence representing the engine speed. The speed is calculated on the basis of two successive speed signals, the speed (or the angular frequency of the shaft) being obtained by detecting the duration between two successive speed signals and detecting the angle swept over during this duration. To calculate the speed, the detected angle is related to the detected duration and, starting from this calculation of the speed, a time interval between a speed signal and the injection time is calculated. To this end, advantageously use is made of the second of the two successive speed signals, and the exact time interval between the second speed signal and the injection time is calculated therefrom. This calculation is made with particular allowance for the time required by the fuel injection device, the duration of calculation and the length of time between the two successive speed signals.

According to another feature of the invention, the time interval is calculated with allowance for a change in the engine speed, more particularly a maximum change. This has the advantage that the injection time can be accurately calculated even if the engine speed changes between the detected speed signal and the injection time. To this end, advantageously a speed signal or two successive speed signals are chosen such that the time interval between the speed signal, or the second of the two successive speed signals, and the calculated injection time is at a minimum. This has the advantage that, starting from the actual speed signals and operating parameters of the engine, the corresponding injection time can be exactly calculated even if a parameter alters.

According to another feature of the invention, at least a part of the time interval between a speed signal and the calculated time in the dynamically critical region, more particularly at high speeds, is taken from a characteristic diagram. The advantage of this is that if the speed signals follow one another very rapidly, the comparatively slow calculation (longer duration of calculation) of the time interval is omitted and a stored value for the time interval corresponding to the detected parameters can be taken from the characteristic diagram. If on the other hand there is sufficient time to calculate the time interval in the dynamically non-critical region, particularly at low speeds, the interval is calculated exactly.

According to another feature of the invention, when the time interval falls below a preset limiting value, the successive speed signals for calculating it, more particularly the second of two successive speed signals, is used for the final calculation of the injection time and for triggering a control signal for the fuel injection device. If the calculated time interval falls below a preset limiting value, this means that the two successive speed signals cannot be taken into account in calculating the injection time. To this end, if the speed falls below the preset limiting value, the previously detected succession of speed signals has to be used in calculating the injection time. Accordingly a control signal for the injection device is triggered, e.g. by actuating a solenoid valve. Note that the method according to the invention is applicable both to diesel and to spark- ignition engines.

The method according to the invention and a fuel injection device suitable for working the method are shown in simplified form, in the diagrams and explained in detail in the following description. In the drawings:

Fig. 1 shows a fuel injection device which can be operated by the method according to the invention; Fig. 2 shows a simplified method of calculating the injection time, and Fig. 3 shows a sequence of speed signals and the associated times.

Fig. 1 shows an example of a fuel injection device which can be operated by the method according to the invention. Note that the method according to the invention is also applicable to other devices. An engine (not shown), more particularly a diesel engine, is associated with a control device 8. The control device 8 substantially comprises a computer 8.17 an actuating unit 8.2, associated with at least one quantity-determining component of the fuel injection device, and a store 8.3, more particularly a characteristic diagram store, connected by a data line to the computer 8.1. On the input side, the control device 8 is connected to sensors 9, more particularly a speed sensor 9.1 and a temperature sensor 9.2, which detect the engine speed and temperature respectively. The speed sensor 9.1, which is of known construction, supplies the control device 8, more particularly the computer 8.1, with a signal (or signal sequence) representing the engine speed and e.g. in the form of a sequence of rectangular pulse signals as illustrated in Fig. 3. The control device 8 is associated with other sensors 9.m, which detect other engine operating parameters such as the oil pressure, charging-air pressure, coolant temperature or battery voltage. The subscript m denotes the number of available sensors and is greater than 2. The control device 8 is associated with another sensor 10 which detects an external power requirement (e.g. an accelerator-pedal sensor). On the output side, the control device 8 is associated with fuel-metering components 11 of the fuel injection device. These components, depending on the number n of engine cylinders, can be solenoid valves 11.1 to ll.n, where m is greater than or equal to unity. The solenoid valves 11.1 to 11.n are suitably actuated by the actuating unit 8.2 of the control device 8. The injection time is calculated and the solenoid valves 11.1 to 11.n are actuated by the method according to the invention, as shown in simplified form in Fig. 2 hereinafter.

Fig. 2 illustrates a basic simplified calculation of the injection time. In a first step 1, speed signals of the engine are detected by the speed sensor 9.1. The second step 2 is to detect operating parameters of the engine, using sensors 9.2 to 9.m and sensor 10. The quantities detected in steps 1 and 2 are used in a step 3 to calculate the injection time resulting from these detected quantities. The next step 4 is to calculate the time interval between detection of a speed signal and the calculated injection time. In an enquiry 5, the calculated time interval is compared with a preset limiting value. If the result is not below this value, e.g. if the injection time has not yet been reached, a jump back is made from enquiry 5 to the beginning of step 1. so that the previously -described calculation process begins again and the injection time is repeatedly calculated. If the value in enquiry 5 falls below the limiting value, the fuel-metering components are actuated at a point 6. To this end3 the computer 8.1 uses the detected speed signals and the detected operating parameters of the engine to calculate the injection time and delivers a signal to the actuating unit 8.2, which actuates the solenoid valves 11.1 to 11.n. Alternatively a single solenoid valve can be actuated. In this manner, each solenoid valve is associated with a separately calculated injection time. The sequence can then begin again.

Fig. 3 shows a speed signal sequence and the times required for calculating the injection time. The speed sensor 9.1 shown in Fig. 1 delivers a sequence of speed signals corresponding to the engine speed. In Fig. 3 the speed signals are denoted by 12a to 12h and represent an arbitrary portion of the delivered sequence of speed signals. The interval between individual signals 12 can vary with the engine speed. For clarity and to simplify the explanation, the interval between individual speed signals 12 is shown as constant in Fig. 3. Also, the speed signals 12 can be detected either continuously or only at certain intervals. One such interval can be characterised e.g. by a beginning (e. g. a special marking on an engine shaft representing the top dead centre position of a selected cylinder), the beginning being denoted 1A and shown in Fig. 3, and an end denoted by E The method according to the invention will also be illustrated by the following time parameters and other time parameters. The time parameter TM is a time (measuring time), between two successive speed signals 12, e.g. 12a and 12b. During this time, the shaft of the engine or of the speed pick-up sweeps over an angle WM The angle % is divided by the measuring time TM to calculate the speed N or the corresponding angular frequency of the engine. This calculated speed N and other operating parameters of the engine are used to calculate the injection time TE, A time interval TZ from the second speed signal 12b of the two successive speed signals 12a and 12b is calculated up to the injection time TE During this time interval, the shaft of the engine or of the speed pick-up covers an angle WZ. The time interval Tz includes various other time parameters. The measuring time TM has to be taken into account, and there is also a calculation duration TR and a time TT required by the fuel injection device. The calculation duration TR is the time required by the computer 8.1 to calculate the injection time TE The time TT required by the fuel injection device can e. g. be the C operating time 1 of the solenoid valves 11.1 to 11.n. The time TT is either continuously re-measured or is stored e.g. in the store 8.3. When the measuring time TM, the calculation duration TR and the time TT required by the fuel injection device are taken into account, there only remains a time TV during which other speed signals (e.g. 12c to 12e) can occur. Note that the interval between subsequent speed signals is not necessarily constant but can vary. This is particularly the case if high power is suddenly required from the engine via the accelerator-pedal sensor 10. Advantageously therefore the remaining time TV is calculated with allowance for a change D in the speed N. To this end, for example, the time interval Tz is first reduced by the measuring time TM, the calculation duration TR and the time TT required by the fuel injection device. The time interval TZ which takes account of the change D in speed N is calculated as follows: the root of the addition of the quotient of twice the angle WZ and the change D and the squared quotient of the speed N and the change D are reduced by the quotient of the speed N and the change D. Thi s calculation of the time interval TZ is essential to the invention and is a function of the angle WZ and the speed N. The change D can be the maximum change, e.g. when the engine is accelerated from idling to the maximum speed or viceversa. Alternatively, use can be made of the change from the actually detected speed to the idling speed or to the maximum speed. The time interval Tz can thus be used to calculate the remaining time TV with allowance for the change D in speed N. The time interval TZ in the dynamically non-critical region, more particularly at low speeds, can be calculated by the computer 8.1 exactly since sufficient time for calculation is available in this case. On the other hand in the dynamically critical region, particularly at high speeds, values for the time interval TZ can be taken from a characteristic diagram store (e.g. store 8.3) since the time interval TZ is a function of the angle WZ and the speed N and an exact calculation would take up too much time. If the calculation of the remaining time TV7 with allowance for the aforementioned quantities, shows that the value of the remaining time TV is above a preset limiting value, the next speed interval (e.g. 12c and 12d) can be used for calculating the injection time TE If the calculated value of the remaining time TV is below the preset limiting value, the computer 8.1 generates an injection signal 13 which represents the injection time TE and is used to actuate the solenoid valve or valves 11. 1 to 11.n via the actuating unit 8.2.

-13 A fuel injection device

Claims

C L A I M

S A method of determining a time, more particularly the injection time of a fuel injection device for an internal combustion engine, the time being calculated from the speed and at least one other operating parameter of the engine, characterised in that the calculation of the time is repeated until the [injection ?] time begins.
2. A method according to claim 1, characterised in that the calculation is made in dependence on at least one time parameter of the fuel injection device.
3. A method according to claim 1 or 2, characterised in that the calculation is made with allowance for the duration of calculation.
4. A method according to any of the preceding claims, characterised in that the speed is calculated from speed signals delivered by a speed pickup which detects the motion of an engine shaft.
5. A method according to any of the preceding claims, characterised in that the speed calculation is based on two successive speed signals, the speed being obtained from the 0 length of time between two successive speed signals divided by the angle swept over by the speed pick-up during this duration, and this calculation is used to calculate a time interval between a speed signal and the [injection ?] time.
6. A method according to any of the preceding claims, characterised in that the time interval between the second of two successive speed signals and the time is calculated with allowance for the time required by the fuel injection device, the duration of calculation and the time between the two successive speed signals.
7. A method according to any of the preceding claims, characterised in that the time interval is calculated with allowance for a change, more particularly a maximum change, in the engine speed.
8. A method according to any of the preceding claims, characterised in that the time interval between the second of two successive speed signals and the time is at a minimum.
9. A method according to any of the preceding claims, characterised in that at least a part of the time interval between a speed signal and the calculated time in the dynamically critical region, more particularly at high speeds, is taken from a characteristic diagram.
10. A method according to any of the preceding claims, characterised in that at least a part of.the time interval between a speed signal and the calculated time in the dynamically non-critical region, more particularly at low speeds, is calculated exactly.
11. A method according to any of the preceding claims, characterised in that when the time interval is below a preset limiting value, the successive speed signals resulting in the calculation, more particularly the second of two successive speed signals, is used to calculate the time and to trigger a control signal.