EP0089482A1 - Method of controlling the fuel supply in a combustion engine with self-ignition - Google Patents

Abstract

An electronic control device for a diesel fuel metering system is proposed, in which, at the start of the starting process, a constant amount of fuel is first specified, which then rises in steps or ramps. Above a certain speed or starting quantity there is a speed-dependent quantity reduction to e.g. 90% of the full load quantity takes place. The starting quantity control or regulation ends when e.g. 800 revolutions per minute. In addition to a possible implementation of the control device of analog circuit technology shown in the block diagram, a flowchart for a computer control is also specified. It is essential that the control device according to the invention can dispense with the processing of a temperature signal and thus the use of a temperature sensor.

Description

The invention relates to an electronic control device for a fuel metering system of an internal combustion engine with auto-ignition according to the preamble of the main claim. From DE-OS 28 03 750.5 an electronic diesel controller with air and fuel quantity pilot control is known. Its start control processes a start and speed signal, as well as the signal from a temperature sensor. Although this known electronic diesel regulator is generally able to provide satisfactory results, problems can arise when starting with a warm engine. If, for example, the tank was run empty on a warm machine and thus the injection lines are partly empty, then after filling up the tank only a small temperature-dependent starting quantity is released at start-up, which may not be sufficient for a safe start. One of the objects of the invention is now to show ways in which such special cases can also be safely managed. Finally, the aim is to avoid processing a temperature signal for reasons of savings.

Advantages of the invention

With the electronic control device for a fuel metering system with the features of the main claim, a temperature signal can be dispensed with, which means a saving of a temperature sensor. In addition, pump tolerances in series production are compensated for the starting quantity. And finally, the start-up time is shortened considerably with empty injection lines and a warm engine.

Further advantages of the invention and expedient configurations result in connection with the subclaims from the following description of exemplary embodiments.

drawing

Embodiments of the invention are shown in the drawing and are described in more detail below ben and explained. FIG. 1 shows an extremely rough block diagram of an electronically controllable fuel metering system of an internal combustion engine with auto-ignition, FIG. 2 shows a diagram of the fuel quantity during the start over time. FIG. 3 shows control characteristics of the starting quantity versus the speed, FIG. 4 shows a block diagram of the electronic control device according to the invention for a diesel fuel metering system, and FIG. 5 shows a flow chart to illustrate the invention in the case of a problem being solved by means of a computer.

Description of the embodiments

The exemplary embodiments relate to electronic control devices for fuel metering systems in internal combustion engines with auto-ignition.

In Figure 1, sensors for the accelerator pedal position, the speed and a start switch with 10, 11 and 12 are designated. Their output lines are led to a signal processing unit 13, at the output of which a fuel quantity target signal is provided. It controls an electromagnetic signal box 14 for setting the injection quantity, e.g. a diesel distributor pump.

Figure 2 shows the starting amount plotted against time. After actuation of the starter and the presence of a minimum speed, a certain amount of fuel QSTO is released for a period of time T. It is this for example the full load quantity, 80% of the full load quantity etc. After the time period T there is an increase in the fuel quantity. A solid line shows a ramp function, which can be time and / or speed dependent. Lung-shaped increases as well as an increase in a steady but non-linear manner are shown in dashed lines.

The starting quantity shown in FIG. 2 remains effective up to a speed threshold. The injection quantity of accelerator pedal, speed and other influencing variables is then determined. However, the accelerator pedal has no influence on the injection quantity during the starting process. However, a solution is also conceivable in which the accelerator pedal can only exert an influence during the starting process if the amount of fuel specified by the accelerator pedal is greater than the starting amount.

A speed-dependent reduction in the starting quantity is used to avoid excessive bursts of smoke during starting. It becomes effective by selecting a minimum value above a certain speed. An example of the speed limitation is shown in FIG. By reducing the amount of fuel over the engine speed, there are no impermissibly high smoke bursts. The start time is also shortened if larger amounts of fuel are injected at low engine speeds.

It is now essential that the two diagrams shown in FIGS. 2 and 3 are superimposed on one another, which in the case of analog circuit technology, e.g. can be reached by means of an electronic control device as shown in FIG. 4. Figure 4 shows a block diagram of an embodiment of the electronic control device according to the invention. A start signal switch 12 is coupled via a switch 20 to a timing element 21 and a basic quantity signal generator stage 22. The output of the timing element 21 is followed by a function generator 23 for providing a time-dependent additional quantity signal QKST1. The outputs of both signal generator stages 22 and 23 lead to a summation point 24, which is followed by a series connection of minimum value selection stage 25, maximum value selection stage 26 and ultimately the electromagnetic signal box 14. The output signal of the speed sensor 11 goes to the control input of the switch 20 and also to a function generator 28 which outputs the speed-dependent quantity signal QKSTn on the output side and supplies it to the minimum value stage 25 as its second input signal. Finally, the maximum value stage 26 also receives a control signal from a function generator 30 which controls the setpoint value of the injection quantity during normal operation.

• Erreicht nach Betätigen des Startschalters die Brennkraftmaschine eine Minimaldrehzahl, dann bestimmt zunächst die Grundmengensignalerzeugerstufe 22 den Einspritzmengenwert. Ihm überlagert sich nach Ablauf der Zeitdauer T von Figur 2 ein Zusatzsignal vom Funktionsgenerator 23, in Figur 2 rein zeitabhängig dargestellt, so daß das Ausgangssignal des Summationspunktes 24 den Signalverlauf nach Figur 2 aufweist. Da gleichzeitig bei sich drehender Brennkraftmaschine der Funktionsgenerator 28 für die drehzahlabhängige Steuerung der Kraftstoffzumessung zur Wirkung kommt, bestimmt letztlich die Minimalwertauswahlstufe 25, welches der beiden Signale von Figur 2 oder 3 als Kraftstoffmengensteuerwert QKST weitergeleitet wird. In der nachfolgenden Maximalwertauswahlstufe 26 wiederum wird entschieden, ob die Startsteuerung dominiert oder jedoch das Signal vom Funktionsgenerator 30 für den allgemeinen Fahrbetrieb.

The mode of operation of the circuit arrangement described in FIG. 4 is now as follows:

• If the internal combustion engine reaches a minimum speed after actuation of the start switch, then the basic quantity signal generator stage 22 first determines the injection quantity value. It overlaps after the Time T of Figure 2 an additional signal from the function generator 23, shown in Figure 2 purely time-dependent, so that the output signal of the summation point 24 has the waveform of Figure 2. Since the function generator 28 for the speed-dependent control of the fuel metering comes into effect at the same time when the internal combustion engine is rotating, the minimum value selection stage 25 ultimately determines which of the two signals of FIG. 2 or 3 is passed on as the fuel quantity control value QKST. In the subsequent maximum value selection stage 26, in turn, a decision is made as to whether the start control dominates or the signal from the function generator 30 for general driving operation.

A toggle switch 26 'is drawn as a separate element in FIG. 4 and, depending on the desired embodiment, can replace the maximum value selection stage 26. The changeover switch 26 'is controlled by means of a speed-dependent signal, the transition from start control to normal control then being purely speed-dependent.

FIG. 5 shows a flow chart for the computer-controlled simulation of the above-mentioned functional profiles.

The start program begins at block 40 according to this flow chart shown in FIG. 5. A query follows for a speed value of 20 revolutions per minute (41). As long as this speed value has not yet been reached, a flag A = 1 and a flag B = 0 are set (42). The flag follows A to the value 1 (43). As long as the flag is not set to 1, no fuel is metered in according to block 44 and the query starts again. If flag A has the value 1, the value of flag B is queried. In the start case, ie at speeds below 20 revolutions per minute, flag B has the value = 0, so that in this start case flag B query 45 a no signal occurs. This is followed by a further speed query 46, the limit value of which is 60 revolutions per minute. As long as this speed has not yet been reached, block 44 also comes into effect after no fuel metering occurs. However, once the 60 revolutions per minute threshold has been reached, flag B is set to 1 (47) and a time count 48 to 0. At the same time, the fuel metering is activated with an initial value QKST = QSTO (49). This corresponds to the quantity jump in FIG. 2. Following this quantity determination 49, the speed dependence of the fuel metering is calculated in a special program step 50 and a starting quantity with the value QKST is defined in block 49 in the following program step 51. A query 52 then decides whether the starting quantity value is larger or smaller than the current speed-dependent quantity value QKSTn. As long as it has not yet reached this value, there is a return to the program. However, if the starting quantity has reached the speed-dependent value, then the speed dependency dominates and the respective starting quantity is assigned this value.

Since flag B = 1 was set in block 47, comes with a new program run at the query unit 45 the second - the yes output - to bear. A speed query follows for the value 800 revolutions per minute in the unit 55. As long as this value has not yet been reached, a time count begins and continues in block 56 and finally a time query for the time period T, 57 Representation of Figure 2, the basic starting quantity QSTO (block 49). In the other case, an integration process with a certain increase takes place with each program run (58). Above a speed of 800 revolutions per minute (interrogation unit 55) the flag A = 0 is set (60), the starting quantity is also set to zero (61) and the normal program for the fuel metering during normal driving is switched on (62). 63 finally marks the end of the overall program.

In detail, the flow chart shows the following program flow. For safety reasons, a starting process is only defined as such above a speed of 20 revolutions per minute. Fuel is only measured above a speed of 60 revolutions per minute. This is followed by a time period T with constant fuel metering and then a fuel metering with increasing function, the increase depending on the type of increase, see block 58. This increase now lasts until the speed-dependent quantity characteristic QKSTn according to FIG. 3 is reached. If it has been reached, the speed-dependent cut-off dominates, so that the metered fuel quantity is no longer continuously increased, but is reduced according to the characteristic curve in FIG. 3. Above one At a speed of 800 revolutions per minute, the starting process is considered finished and the normal program begins.

In the flowchart according to FIG. 5, the output values of blocks 49, 50 and 58 in particular can be variable in order to be able to variably set basic fuel quantity values, speed-dependent fuel quantity values and growth rates. Of course, the re-starting point of the program run can also be selected differently than is shown in FIG. 5.

Claims (4)

1. Electronic control device for a fuel metering system of an internal combustion engine with auto-ignition with sensors for operating parameters and function transmitters for a setpoint value of the fuel quantity depending on operating parameters, characterized in that a time and / or speed-dependent starting quantity is specified during the start in a certain speed range and above one determined speed value or a fuel quantity value, the target fuel quantity can be reduced at least depending on the speed. (Figure 2 and Figure 3) 2. Control device according to claim 1, characterized in that the time-dependent function has a constant value at the beginning and then ramps up non-linearly, stepwise or continuously. 3. Control device according to claim 1, characterized in that in the speed-dependent start area (Figure 3) the target fuel quantity with stei gender speed decreases. 4. Control device according to at least one of claims 1 to 3, characterized in that above a speed of preferably 60 revolutions per minute the fuel supply starts and above a speed of 800 revolutions per minute the fuel metering is determined detached from the start quantity signal generation.

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