GB2073444A

GB2073444A - Device for regulating fuel injection quantities in diesel engines

Info

Publication number: GB2073444A
Application number: GB8104316A
Authority: GB
Original assignee: KARL MARX STADT AUTOMOBILBAU
Current assignee: KARL MARX STADT AUTOMOBILBAU
Priority date: 1980-02-15
Filing date: 1981-02-12
Publication date: 1981-10-14
Also published as: FR2476212A1; DE3043326A1; GB2073444B; DD154268A3

Abstract

A device for regulating fuel injection quantities provides an engine temperature dependent regulation, which is especially suited to the requirements of a diesel engine during its starting phase. The device provides, in the region below idle, optimum regulation of injection with respect to injection duration and position relative to piston top dead centre in dependence on engine temperature and engine speed, i.e. as engine speed reduces so the start of injection is advanced. On approach of the normal or operating temperature of the engine and the idling speed, a constant injection end is again provided. For realising the engine temperature and speed dependent regulation, an engine temperature dependent voltage (U1) from an engine temperature transmitter (26) is applied, in place of a voltage Up) which is product of engine speed and set load voltages, to an input (E3) of a comparison device (40) to determine the start of a pulse (IE) controlling injection duration. Limitation of the pulse length to a maximum injection duration, and thus of the injection quantity, is provided by a limiting device (45) insofar as a reference voltage (Ub) applied to the comparison device (40) does not itself terminate the pulse before its length exceeds this maximum duration. <IMAGE>

Description

SPECIFICATION Device for regulating fuel injection quantities The present invention relates to a device for regulating fuel injection quantities to be provided by an electronic fuel injection installation of an internal combustion engine, especially a diesel engine.

In DD-P 120 508 there is described an electronic fuel injection installation which comprises a multiplies for multiplying together a voltage dependent on engine speed and a voltage dependent on engine load setting to give a product voltage , and initiating and terminating a pulse, which determines injection duration, when a voltage derived from the engine crankshaft and decreasing in the rotational direction through an injection range as a function of crankshaft angle is equal to, respectively, the product voltage and a reference voltage. An injection installation of this category is also described in DD-P 126 669. No account is taken in description of these installations of the aspect of injection regulation for engine starting.

In DE-OS 2728 414 there is described an electronically controlled injection installation for an internal combustion engine with applied ignition, the installation including a starting device. This starting device lengthens the period of excitation of electromagnetic injection valves as a function of the engine coolant temperature. The lengthened excitation is reduced as a function of time or speed. The quantity of start enrichment is preferably constant in a lower temperature range and is reduced with rising temperature.

It is also known from DE-OS 2743991 to provide a special starting circuit in an electronically controlled injection installation for, preferably, internal combustion engines with applied ignition. By means of the starting circuit, which is made operative by the starting operation or other parameters typical for the start, a large change in the fuel flow rate as a function of temperature results due to a correspondingly high increase in the duration of the injection pulse. If the starting conditions are absent, the starting circuit becomes inoperative and control is in accordance with a normal operating state. The temperature-dependence on the injection quantity is highly limited in accordance with its actual influence on the operation of the engine.

For the change between the starting and normal operating states, a special change-over switch is provided, which alternatingly switches on or off the then effective circuit arrangement determining injection duration.

The above-described starting devices do not, inter alia, fulfil the requirements in a diesel engine in respect of variation of the injection timing relative to piston top dead centre. The realization of starting devices in other types of electronic injection installations is also described.

There is accordingly a need for a device, which enables regulation of fuel injection quantities in an engine starting range in such a mannerthatinjection can be controlled in respect of duration and timing relative to piston top dead centre in the engine speed range below idling speed, whereby, by contrast to the normal control behaviour of an injection installation, a temperature-dependently determined start, and a temperature and speed dependently determined end, of injection can be realised.

According to the present invention there is provided a device for regulating fuel injection quantities to be provided by an electronic fuel injection installation of an engine, the device comprising a multiplier for multiplying together a voltage dependent on engine speed and a voltage dependent on selected engine loading so as to provide a product voltage, an engine temperature sensor for providing a voltage indicative of engine temperature, pulse length determining means for determining the length of pulses for controlling injection duration, the determining means being adapted to initiate such a pulse when a voltage at an input thereof is equal to a voltage which in the course of each engine crankshaft rotation changes as a continuous function in dependence on crankshaft angle over a predetermined angular range of such rotation and to terminate the pulse when the changing voltage is equal to a reference voltage, switching means for selectively connecting the multiplier and sensor to the deter- mining means to apply the product voltage or temperature voltage to said input, engine speed detecting means so controlling the switching means as to cause the determining means to be connected at said input thereof to the multiplier in the engine speed range above engine idling speed and to the sensor in the engine speed range below the idling speed, and limiting means to limit the length of such pulses to a length representing a predetermined maximum injection duration.

With a device embodying the invention, at engine speeds below the idling range the commencement of injection is entirely temperature-dependent, so that the lower the temperature of the engine the earlier injection occurs before piston top dead centre. In addition, as engine speed increases the end of injection approaches piston top dead centre, i.e. is situated by a lesser amount before top dead centre. This advantageous control may be achieved by, for example, a respective voltage level associated with each temperature level of the engine, this voltage triggering the commencement of injection, and by the limiting means acting to limit the maximum duration of injection pulses in a timeconstant manner.

The limiting means preferably comprises a timing element connected to the output of the determining means, and an AND-element connected at one input thereof to the output of the determining means and at another input thereof to the output of the timing element, injection pulses being derived from the output of the AND-element and the time constant of the timing element being equal to the maximum admissible injection duration or quantity for the engine.

The engine speed detecting means preferably comprises a disc mounted on the crankshaft or a camshaft of the engine and provided with a plurality of pulse marks so arranged that, starting from a constant starting position, a number of such marks is present in a range determined by a measuring period at lowest engine idling speed. Associated with the disc is a pick-up, a measuring period generator triggered by a signal indicating the start ing position, and an AND-element connected at one input thereof to the generator and at another input thereof to the pick-up. The output of the AND .element is connected to the input of a resettable binary counter, with which there is associated a decoder circuit which, when the counter position is at the programmed number, emits a signal which is applied to a control input of the switching means.

Preferably, the counter is resettable by a resetting pulse obtained from the output of the measured period generator, the rear flank of the measured period pulse serving asthetrigger.

Advantageously, an interrupted switch may be provided between the switching means and the output of the multiplier, the interrupter switch being adapted to open when pressure and/or temperature conditions dangerous to engine operation are present. By means of this interrupter switch, the engine is effectively protected at too high temperature or too low lubricant pressure. By the disconnection of the multiplier from the determining means, the engine can then be operated only below the idling range and receives only a temperature-dependent voltage, which permits continued running but does not permit load operation of the engine. Advantageously, the temperature voltage transmitter emits a voltage which corresponds to the injection time at lowest engine idling speed for the injection quantity necessarv at the lowest temperature.

Preferably, the temperature voltage transmitter can provide an output voltage as a function of a plurality of engine temperatures. By this means, specific values of different thermal conditions of the engine can be taken into account.

An embodiment of the present invention will now be more particularly described with reference to the accompanying drawings, in which: Figure 1 is an overall circuit diagram of a device embodying the invention for controlling the fuel injection quantities, Figure 2 is a circuit diagram of a speed detector of the device, Figures 3a-c are diagrams showing injection range voltages (Uss) and temperatu re-dependent voltages (U) plotted over an injection range of 40'to provide injection pulses having a duration limited to 4 ms, the diagrams representing engine speeds (nk) of 500 rpm (Figure3a), 300 rpm (Figure 3b), and 100 rpm (Figure 3c) and also showing the resulting injection pulses IE of various durations and positions in the injection range, Figure 4 is a diagram showing the dependence of injection pulse duration (tE) on engine temperature and speed belowthe idling range, and Figure 5is a diagram showing pulses provided by the device after the lowest idling speed (nLK) has been reached, together with a sequence of nonequidistant pulse marks (121) and associated measuring period (tm) used in the device for calculating change-overto engine temperature dependent determination ofthe injection pulse duration.

Referring now to the drawings, there is shown in Figure 1 the circuit diagram of a device for controlling the fuel injection quantities to be provided by an electronic fuel injection installation, the device including means to take account of engine starting requirements. The device comprises a pick-up and pulse shaper 10 associated with a rotatable disc 110 with a sawtooth 11, the pick-up 10 being adapted to generate a voltage Uss over an injection range ss as the tooth 11 passes by the pick-up. The voltage Up begins with a maximum voltage value Ussa and decreases linearly over the injection range P to a final voltage value Ussa of zero.The voltage UP always has a reference value of 100 between its initial voltage value Ussa and final voltage value Ussa.

The sawtooth 11 of the disc 110 extends over the injection range p, and the injection range is so designed that, at the maximum crankshaft rotational speed nkmaX and maximum injection quantity VEmax, the injection period tE can end before or after piston top dead centre.

A pulse shaper 12 forms from the voltage UP a square-wave pulse which extends overthe injection range and is termed injection range pulse IP.

Atransmitter 25 generates an increasing voltage Uawith increasing accelerator pedal deflection. By means of this transmitter 25 the load setting for the engine is adjustable. The voltage Ua rises from a reference value 0, at which the accelerator pedal is not actuated, to a reference value 10, at which reference value the highest load for the engine is set.

A disc 210 is mounted on the engine crankshaft or a camshaft and is provided with a plurality of pulse marks 21. Associated with the disc 210 is a pick-up and pulse shaper 20 which, in correspondence with the pulse marks 21, generates square-wave pulses 121 of constant width, the width of the squarewave pulse being smaller than the closest pulse sequence at highest engine speed. The pulse marks 21 are arranged on the disc 210 in non-equidistant succession and correspond in their distribution to an injection quantity limiting characteristic curve VE max ofthe engine.

A voltage transformer 22 converts pulses 121 entering in a constant measuring period tm into an analogous angular speed voltage UOk corresponding to the detected number cm of pulses 121. Each pulse 121 entering the voltage transformer 22 results in a higher voltage output and this builds up in staircase fashion to reach, at the end of the measuring period tm, a specific value which represents the angular speed voltage U(ok. At the crankshaft speed nk = 0, its reference value is also 0.

The voltage transformer 22 can be set to 0 by way of a setting pulse applied to a cancelling input R thereof after each transforming operation, the front flank P of the injection range pulse IP acting as this zero setting pulse. The output 22A of the transformer is connected to an input 50E of a memory 50.

A measuring period generator 23 generates a pulse 1m representing constant measuring time tm which must be smaller than the time for one revolution of the crankshaft at maximum nominal speed. The generator 23 is triggered through an input 23E thereof by the rear flank Isse of the injection range pulse IP.

A gate 24 allows the pulses 121 to issue at its output 24A as long as the pulse Im is applied to its input 24E2.

The memory 50, which an an analogue value memory, retains the voltage Uk at its input 50E when the measuring time pulse 1m is not present at its input 50H. When the measuring time pulse Im is applied to its input 50H, storage is interrupted, since during this period new storage is carried out.

A multiplier 30 multiplies the values of the voltage Ua and U(ssk, which are present at inputs 30E1 and 30E2 of the multiplier, to provide a product voltage Up at its output 30A, the product voltage, in normal operating conditions, being applied to an input 40E3 of a comparator device 40. The multiplier 30 thus realises the basic formula s = v.t. In a given time t, in the present case the requisite injection pulse duration tE as set by the accelerator pedal, the injection pulse angle XE is obtained in accordance with the following formula: 0 = V tE In the comparator device 40, the product voltage Up formed by the multiplier 30 is compared with the voltage UP and plotted against the latter.The multiplication of the reference values of the voltages Ua and U must lead to a true statement when compared with the value of the voltage UP through the associated angle KE. On this basis the comparator device 40 forms, in all operating ranges except the range below the idling speed range, the injection pulse 1E The inputs 40E1, 40E2 and 40E3 of the comparator device 40 are fed with, respectively, a reference voltage Ub, the voltage UP and the product voltage Up. When the voltage UP and product voltage Up are equal, the injection pulse IE is triggered and is provided at the output 40A. When the voltage UP and reference voltage Ub are equal, the injection pulse IE is terminated.

The reference voltage Ub is generated by a reference voltage generator 60. In the present application, the reference voltage will considered to be constant at 0, as it is unimportant in engine starting conditions.

For meeting the starting requirements of an injected diesel engine, a change-over switch 41 is provided between the multiplier 30 and the comparator device 40 and serves to connect, below the lowest idling rotational speed n,K, a temperature voltage transmitter 26 to the input 40E3 of the comparator device 40 so as to feed temperaturedependent voltages U1 or U1'; U1"; U1"' to the input 40E3. Starting conditions are present when the engine speed is below an idling speed range bounded by a lowest and a highest idling speed. The switch 41 is controlled by an engine speed detector 28.

Connected to the output 40A of the comparator device 40 is a limiter device 45, which limits the pulses emitted by the comparator device 40 when a maximum injection pulse duration tE max is exceeded.

The limiting device 45 comprises a timing element 42, the time constant of which is equal to the maximum admissible injection pulse duration tE max of the engine and the input 42E of which is connected to the output 40A of the comparator device 40. The timing element 42 is connected at its output 42A to one input 43E2 of an AND-element 43, the other input 43E1 of which is connected directly with the output 40A of the comparator device 40. The injection pulses IE are issued at the output 43A of the AND-element 43.

In addition to the switch 41, an interrupter switch 27 is connected between the multiplier 30 and the comparator device 40. The interrupter switch 27 is opened at a lubricating oil pressure or engine temperature that endangers the engine.

Referring now in detail to the interconnection of the above-described components of the device and also to the circuit of Figure 2, the voltage UP generated by the pick-up and pulse shaper 10 is delivered from its output 1 0A to the input 40E2 of the comparator device 40 and to the input 12E of the pulse shaper 12, which provides the injection range pulse IP at its output 12A. The injection range pulse IP is fed to the input 23E of the measuring time generator 23 and to the cancelling input 22R of the angular speed voltage transformer 22. The output 23A of the measuring time generator 23 is connected with the input 24E2 of the gate 24 and with the control input 50H of the memory 50.

The output of the pick-up and pulse shaper 20 for providing the pulse 121 in correspondence with the pulse marks 21 is connected with the input 24E1 of the gate 24. The output 24A of the gate 24 is connected to the input 22E of the transformer 22.

The output 22A of the transformer 22 is connected to the input 50E of the memory 50. The output 50A of the memory 50 is connected to the input 30E2 of the multiplier 30. The input 30E1 of the multiplier 30 is connected to the output 25A of the accelerator pedal setting voltage transmitter 25 and the output 30A of the multiplier 30 is connected to the interrupter switch 27 which, as already explained, opens at temperature and lubrication pressure levels that endanger the engine. The two inputs 41 eel and 41 E2 of the switch 41 are connected to, respectively, the temperature voltage transmitter 26 and the interrupter switch 27, and the output 41A of the switch 41 is connected to the input 40E3 of the comparator device 40.The switch 41 is governed by the engine speed detector 28 in such a manner that, below a minimum idling speed nLK, it connects the temperature voltage transmitter 26 to the input 40E3 of the comparator device 40, while above this idling speed, and provided the interrupter switch 27 is closed, it connects the output 30A of the multiplier 30 to the input 40E3.

The reference voltage generator 60 is connected at its output 60A to the input 40E1, and the pulse shaper 10 at its output 1 OA to the input 40E2, of the comparator device 40. The output 40A of the comparator device is connected to the limiting device 45, which operates to ensure that an injection pulse IE of greater duration than the period tE max cannot appear at its output.

In Figure 2, there is shown a circuit for the engine speed detector 28. The pulses 121 picked up during the measuring period tm are fed to one input 281 El of an AND-element 281 and a pulse is applied to another input 281 E2 of the AND-element when a binary counter 29 of the detector 28 has not yet reached the predetermined number n during and after the measuring time tm. The input 281 El of the AND-element 281 is connected to the output 24A of the gate 24.

The binary counter 29 comprises counting stages 291,292,293 and 294 and is connected at an input 291 E thereof to the output 281A of the AND-element 281. The counter 29 can be reset to zero by the forward flank of the measuring time pulse Im applied to a resetting input 29R of the counter.

The final number n for recognition of the minimum idling speed nLK is detected by means of an AND-element 282 connected to the outputs 293A and 294A of the counting stages 293 and 294.

The AND-element 282 controls the switch 41 when the final number n has been reached by the counter 29 in the measuring period tm and simultaneously blocks the AND-element 281 against further pulses 121.

In the above-described state, the switch 41 connects the multiplier 30 with the input 40E3 of the comparator device 40. The pulse diagram for the afore-mentioned circuit of the detector 28 is shown in FigureS.

In general, the basic method of operation of a device of this kind - apart from operation in connection with engine starting - is described in DD-P 120 508 and the aspects of the limiting of the injection quantity over the entire operating range and downward-regulating range ofthe highest nominal engine speed are explained in DD-P 126669 and 132992.

The operation of the device for regulating fuel injection below the engine idling speed range is described in the following.

A characterising feature of the regulation below the idling speed range is that.there is applied to the input 40E3 of the comparator device 40 not an engine speed dependent voltage, but a voltage U1, dependent solely on engine temperature. The effect of this is, as shown in Figures 3a to 3c which are plotted in time-proportional representation, that one specific commencement of injection, independent of crankshaft speed, is associated with each temperature-dependentvoltage U1, U1, etc. This is brought about in that, when the voltage UP is equal to the temperature-dependent voltage U1, the injection pulse IE istriggered at each engine speed in the same angular position.The angular position of the end of the injection pulse is different for different engine speeds and temperatures, due to the constant maximum injection pulse duration tE max It will be appreciated that, with increasing engine speed and rising temperature, the end of injection becomes progressively later with an injection pulse duration of tE max and thus moves nearer to piston dead centre, until the injection pulse duration tE is limited by the reference voltage Ub and then possesses a shorter duration than t5 max.

These conditions can be seen from Figure 4, in which the effects of temperature and engine speed on the magnitude of the injection pulse duration tE are plotted.

The above-described behaviour of the device in regulating the fuel injection quantity for starting conditions results from the influencing of the entire system in the low engine speed and temperature range from the limiter device 45 and from the dependence of the commencement of injection on the engine temperature dependent voltage U1.

With increasing approach of the engine temperature to normal conditions, the voltage U1 becomes smaller, so that the end of injection is determined even at a fairly low engine speed by the reference voltage Ub, as will be appreciated from a comparison, of the voltages U1" and lui"in Figure 3b.

In Figures 3a to 3there are shown pulses 1ui' and lui' arising in the device for the temperaturedependent voltages U1 and U1". The references 40A, 42A and 43A have the following meanings: 40A = pulse at the output 40A of the comparator device 40, 42A = pulse at the output 42A of the timing element 42, and 43A = pulse at the output 43A of the AND-element 43 (also the injection pulse IE).

A particularly advantageous aspect of the device hereinbefore described is the arrangement of the limiter device 45 at the output of the comparator device 40. All errors in the determination of the injection duration which give rise to longer durations than the maximum injection duration tE max, or technical defects which have the same result, are corrected by the limiter device 45, which ensures that in all operating conditions the injection pulses will have a maximum duration tE

Claims

CLAIMS:

1. A device for regulating fuel injection quantities to be provided by an electronic fuel injection installation of an engine, the device comprising a multiplier for multiplying together a voltage dependent on engine speed and a voltage dependent on selected engine loading so as to provide a product voltage, an engine temperature sensor for providing a voltage indicative of engine temperature, pulse length determining means for determining the length of pulses for controlling injection duration, the determining means being adapted to initiate such a pulse when a voltage at an input thereof is equal to a voltage which in the course of each engine crankshaft rotation changes as a continuous function in dependence on crankshaft angle over a predetermined angular range of such rotation and to terminate the" pulse when the changing voltage is equal to a reference voltage, switching means for selectively connecting the multiplier and sensor to the determining means to apply the product voltage or temperature voltage to said input, engine speed detecting means so controlling the switching means as to cause the determining means to be connected at said input thereof to the multiplier in the engine speed range above engine idling speed and to the sensor in the engine speed range below the idling speed, and limiting means to limit the length of such pulses to a length representing a predetermined maximum injection duration.

2. A device as claimed in claim 1, the limiting means comprising timing means connected to an output of the determining means, the time constant of the timing means being equal to said maximum injection duration, and an AND-element so connected at one input thereof to the output of the determining means and at another input thereof to an output of the timing means as to provide at its output pulses for controlling injection duration.

3. A device as claimed in either claim 1 or claim 2, the engine speed detecting means comprising a rotatable carrier element drivable by a rotary shaft of the engine and provided with a plurality of angularly spaced marks so arranged that starting from a fixed angular reference point a given number of such marks is present in a range determined by a measuring period at the lowest engine idling speed, pick-up means responsive to the marks to generate pulses in correspondence therewith, signal generating means responsive to a signal indicative of said reference point to generate a signal representing the measuring period, an AND-gate connected at one input thereof to the pick-up means and at another input thereof to the generating means, a resettable binary counter connected at its input to the output of the AND-gate, and decoding means adapted to provide a control signal to trigger switching of the switching means on counting by the counter of said given number within the measuring period.

4. A device as claimed in claim 3, wherein the binary counter is connected to the signal generating means to be resettable by the rear edge of each such measuring period signal.

5. A device as claimed in any one of the preceding claims, comprising an interrupter switch responsive to at least one of an operating level and a lubricant pressure level of the engine to interrupt connection of the multiplier to the determining means when the or either level passes a predetermined safety threshold.

6. A device as claimed in any one of the preceding claims, wherein the transmitter is adapted to provide a minimum voltage which corresponds to the injection duration at the lowest engine idling speed for the injection quantity necessary at the lowest engine temperature.

7. A device as claimed in any one of the preceding claims, wherein the transmitter is adapted to selectively provide a plurality of different levels of voltage respectively associated with a corresponding plurality of different levels of temperature.

8. A device for regulating fuel injection quantities to be provided by an electronic fuel injection installation of an engine, the device being substantially as hereinbefore described with reference to the accompanying drawings.