GB2268600A

GB2268600A - Controlled driving of an electromagnetic load

Info

Publication number: GB2268600A
Application number: GB9314270A
Authority: GB
Inventors: Burkhard Veldten
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1992-07-10
Filing date: 1993-07-09
Publication date: 1994-01-12
Anticipated expiration: 2013-07-09
Also published as: FR2693508B1; IT1264664B1; ITMI931447A0; GB9314270D0; FR2693508A1; JPH0688545A; GB2268600B; ITMI931447A1; DE4222650A1

Abstract

A method of and drive means for controlled driving of an electromagnetic load (120), in particular an electromagnetic valve of a fuel injection system in an internal combustion engine, entails presetting the switching times of the valve, for the determination of the start and/or the end of injection, in dependence on an engine operating parameter, especially engine speed. The drive means comprises a first switch (110) and a second switch (165) respectively in series and in parallel with the valve (120) and respectively associated with a rapid-quenching diode (150) and a freewheel diode (160). The second switch (165) is so selectively driven by an electronic control unit (100) in dependence on engine speed range that current decay through the valve on switch off by the first switch (110) is influenced by the diodes in a manner varying the valve switching time according to the speed range, whereby a compromise can be achieved between desired short switching times and desired low noise generation. <IMAGE>

Description

2268600 CONTROLLED DRIVING OF AN ELECTROMAGNETIC LOAD The present

invention relates to a method of and drive means for controlled driving of an electromagnetic load, in particular an electromagnetic valve in a fuel injection system of an internal combustion engine.

A method and drive means for the control of an electromagnetic load is known from SAE paper 85 05 42, which describes control equipment for a fuel pump in which an electronic control unit controls, by way of a power output stage, an electromagnetically actuated valve associated with the pump. This control unit determines the desired. instants for the start and the end of conveying of the fuel pump in dependence on the operational state of an internal combustion engine supplied by the pump. The control unit computes the controlled driving instants for the power output stage from those desired instants so that the electromagnetic valve assumes a setting whereby the fuel pump either conveys fuel or terminates the conveying.

In that case, the driving pulse is issued a certain time before the desired instant at which the valve shall be actuated to initiate or terminate fuel conveying. This delay is based on the switching times of the valves. The switch-on time signifies the delay between the driving pulse and the closing of the valve. The switch-off time signifies the delay between the pulse and the opening of the valve.

A. device for the control of an electromagnetic load, in particular for an electromagnetic valve of an injection system for an internal combustion engine, is known from DE-OS 40 18 320. In this equipment, the valve is briefly driven for the shaping of the course of injection, in such a manner that the injection is interrupted or the pressure build-up is delayed. In this controlled driving for the shaping of the course of injection, the otherwise short switching times of the valve are prolonged. A variation of the switching times for the determination of the start and end of injection is not provided in this equipment.

In the prior art equipment, there is undue generation of noise, particularly,at low engine speeds.

There is thus a need to reduce noise output in the controlled operation of electromagnetic loads such as electromagnetic valves in fuel injection systems.

According to a first aspect of the present invention there is provided a method for the controlled driving of an electromagnetic load, in particular an electromagnetic valve of a fuel injection system of an internal combustion engine, wherein switching times of the load are presettable in dependence on operating parameter magnitudes in the case of the controlled driving for determination of the beginning and/or the end of injection.

For preference, the switching times are presettable in dependence on the rotational speed. In particular, short switching times can be presettable for high rotational speeds and long switching times for low rotational speeds.

According to a second aspect of the invention there is provided drive means for the controlled driving of an electromagnetic load, in particular an electromagnetic valve of a fuel injection system of an internal combustion engine, comprising means for presetting the 5 switching times of the load in dependence orr operating parameter magnitudes in the case of the controlled driving for determination of the beginning and/or the end of injection.

Preferably, the drive means comprises control means to drive first switching means which releases the current flow through the electromagnetic load and second switching means which activates a freewheel circuit. For preference, the switching times are settable by means of the second switching means. This can be closed at low engine speeds and opened at high engine speeds. Moreover, the second switching means. can be initially closed at medium engine speeds and opened after a preset time.

The noise output may be able to be reduced by such a method and drive means.

Methods exemplifying and drive- means embodying the present invention will now be more particularly described with reference to the accompanying drawings, in which Fig. 1 is a block circuit diagram of drive means embodying the invention; Figs. 2a, b and c are diagrams showing strokes of and current flows through a valve driven by such drive means; and Figs. 3a, b and c are flow charts illustrating steps in methods exemplifying the invention.

Referring now to the drawings there is shown in Fig. 1 drive means associated with a fuel injection system of an internal combustion engine and comprising an electronic control unit 100 connected with a first switch 110. The switch 110 is connected by one terminal with ground and by the other terminal to battery voltage UBat by way of an electromagnetic load 120, which in the following is referred to as an electromagnetic valve, and a resistor 130. The electronic control unit 100 is also connected with difference sensors 105, which comprise at least one rotational speed sensor.

A rapid-quenching diode 150 connects the output line of the unit 100, which drives the switch 110, with the junction between the switch and the electromagnetic valve 120. This junction is also connected with the battery voltage UBat by way of a freewheel diode and a second switch 165. The second switch 165 is termed a freewheel switch in the following. The freewheel switch 165 is also driven by the electronic control unit 100.

The switches 110 and 165 are preferably field effect transistors.

Other realisations are also possible. The resistor 130 serves as measuring equipment for detection of the current flowing through the valve 120.

In the case of inductive loads such as electromagnetic valve, a freewheel diode 160 is usually provided, and connected in parallel with the inductive load. The rapid-quenching diode 150, connected between the switching input of the switch 110 and the inductive load, has the effect that the current decays very rapidly when switching off takes place. This has the consequence that the switching time of the valve becomes very small,' which is important particularly at high engine rotational speeds, as otherwise inaccuraciesin the fuel injection may arise. These short switch-off times are achieved by inter alia rapid quenching of the valve current, during which a defined back-voltage is induced by the inductance of the valve coil.

In the case of short switching times, increased noise output occurs at low engine speeds. This can be reduced ov: eliminated by causing the switching times of the valve to be longer for low engine speeds. To achieve this, the freewheel switch 165 is switched through by the control unit 100 at low engine speeds. In this case, no back voltage can build up. The current is reduced by the resistive losses in the quenching circuit, whereby the current decay time increases by a multiple in comparison with the rapid quenching.

Since the drive means has rapid quenching provided by the rapid quenching diode 150 and also comprises a freewheel circuit formed by the freewheel switch 165 and the freewheel diode 160, improved noise behaviour with high accuracy of the fuel injection at the same time can be achieved through activation of the freewheel circuit at low engine speeds and activation of the rapid quenching at high engine speeds. At medium engine speeds, the freewheel quenching is preferably activated initially and then terminated after a defined time through opening of the freewheel switch 165, after which the influence of the rapid quenching predominates. The time during which the freewheel quenching is activated can be increasingly smaller at higher speeds.. Above a preset speed, the freewheel circuit is no longer activated and merely the rapid quenching takes place.

- 6 These different possibilities are illustrated in Figs. 2a, b and c. In Fig. 2a, the current I and the stroke H of a needle of the val ve, is shown for low engine speeds. At the instant T1, the switch 110 is so driven that it separates the valve 120 from the supply voltage.

The freewheel switch 165 is closed. The current I flowing through the valve 120 decays to zero according to an exponential function. At the instant T2, the current has fallen to the value of zero and the valve has passed over into its other state. The time interval between the instants T1 and T2 is relatively long.

In Fig. 2b, the current and the stroke of the valve needle for medium speeds is shown. At the instant T1, the switch 110 is so driven that it separates the valve from the supply voltage. The freewheel switch 165 is closed. The current flowing through the valve 120 falls to zero accordingtoan exponential function. At the instant T2, the freewheel switch 165 is opened. From this instant onward, the influence of the rapid-quenching diode 150 predominates. This means that the current I falls very rapidly to zero. After some time, the valve needle gains its new setting at the instant T3. The time interval between the instants T1 and T3 is shorter than in the case of Fig. 2a.

In Fig. 2c, the current and the stroke of the valve for high speeds is entered. At the instatit T1, the switch 110 is so driven that it separates the valve from the supply voltage. The freewheel switch 165 is open. In this case, the influence of the rapid - quenching diode 150 predominates, which means that the current I falls very rapidly to zero. After some time, the valve needle reaches its new setting at the instant T4. The time interval between the instants T1 and T4 is still shorter than for Fig. 2b.

- 7 Figs. 3a, b and c are respective flow diagrams for each of different examples of the method for driving the electromagnetic valve 120. A simple realisation is illustrated in Fig. 3a. In a first step 300, the switch 110 is driven in such a manner that it opens.

Thereby, the controlled driving of the valve. is terminated. The engine rotational speed N is detected in a step 305. In an interrogation step 310, a check takes place as to whether the actual speed N is greater than a threshold speed NS. If this is the case, the freewheel switch 165 is so driven in a step 315 that it opens.

This has the consequence that the freewheel circuit is not active. In this case, merely a rapid quenching takes place at high speeds, which has the consequence of a very small switching time of the valve.

If it is recognised in the interrogation step 310 that the speed is lower than the threshold NS, the freewheel switch 165 is so controlled driven in a step 320 that it closes. In this case, the freewheel circuit comes into effect and the switching time of the valve is correspondingly prolonged. The noise output caused by the short switching times of the valve at low speeds can be appreciably reduced by this measure.

Since only two different switching times are selectable in this example, no optimum operating behaviour results in, in particular, the range of the speed threshold NS. This disadvantage can be eliminated by the example according to Fig. 3b. In a step 300, the switch 110 is controlled driven in such a manner that it opens. Thereby, the controlled driving of the valve is terminated. The engine rotational speed N is detected in a step 305. Subsequently in a step 330, the optimum switching time TF is either read out from a characteristic values field in dependence on at least the instantaneous engine speed or is computed starting from at least the instantaneous speed by means of a function F. For the determination of the optimum switching time TF, other operating parameter magnitudes, such as engine load or temperature values, can be taken into consideration.

In a step 335, the freewheel switch 165 is so driven that it closes. It is the.n checked in an interrogation 340 whether the optimum switching time TF has elapsed. If this is not yet so, the freewheel switch 165 continues to remain open. When the time has elapsed, the freewheel switch 165 is driven in a step 345 so that it closes. This means that the rapid quenching becomes active from this instant onward and the current returns to zero at once.

A further example is illustrated in Fig. 3c. In this case, a ccmbination of the examples according to Figs. 3a and 3b is concerned.

After the first switch 110 has been driven for opening in a step 300, the detection of the engine rotational speed, N takes place in a step 305. It is checked in an interrogation step 350 whether -the speed N is lower than a first rotational speed threshold NS1. If this is the case, the freewheel switch 165 is closed in a step 352. If, however, the speed N is greater than the first threshold NS1, it is checked in a second interrogation step 355 whether the speed N is higher than a second rotational speed threshold NS2. In this case, the freewheel switch 165 is opened in a step 363. If the speed N lies between the two thresholds, then the optimum switching time TF is determined by a factor F starting from at least the instantaneous speed N in a step 365 in correspondence with Fig 3b and the freewheel switch 165 is closed in a step 370. It is then checked in aninterrogation step 375 whether the switching time TF has elapsed. After elapsing of the switching time TF, the freewheel switch 165 is opened again in the step 363.

The drive control speed for an electromagnetic valve controlling a diesel injection pump can be chosen in dependence on engine speed by a method exemplifying the invention. In particular, a long switching time for the valve can be set at low engine speeds and a short switching time at high engine speeds in order to achieve a lower noise output.

11 - 10

Claims

1. A method of controlled driving of an electromagnetic valve determining at least one of the start and end of fuel injection in an internal combustion engine, the method comprising the step of presetting the switching times of the valve in dependence on at least 5 one operating parameter of the engine.

2. A method as claimed in claim 1, wherein the parameter is engine speed.

3. A method as claimed in claim 2, wherein the switching times are preset to be shorter in the case of a higher engine speed range and longer in the case of a lower engine speed range.

4. A method as claimed in claim 1 and substantially as hereinbefore described with reference to any one of Figs. 3a, 3b and 3c of the accompanying drawings.

5. Drive means for controlled driving of an electromagnetic valve determining at least one of the start and end of fuel injection in an internal combustion engine, the drive means comprising means for presetting the switching times of the valve in dependence on at least operating parameter of the engine.

6. Drive means as claimed in claim 5, comprising first switching means to control current flow through the electromagnetic valve, second switching means to control a freewheel circuit associated with the valve and control means to drive the first switching means and the 5 second switching means.

7. Drive means as claimed in claim 6, wherein the switching times are settable by the second switching means.

8. Drive means as claimed in claim 6 or claim 7, the control means being arranged to cause the second switching means to be closed in the case of a lower engine speed range and to be opened in the case of a higher speed range.

9. Drive means as claimed in any one of claims 6 to 8, the control means being arranged to cause the second switching means to be initially closed in the case of a medium engine speed range and then to be opened after elapsing of a predetermined period of time.

10. Drive means substantially as hereinbefore described with reference to Figs. 1, 2a, 2b and 2c,of the accompanying drawings.

11. An internal combustion engine equipped with a fuel injection system comprising an electromagnetic valve determining at least one of start and end of injection and drive means as claimed in any one of claims 5 to 10 for the valve. 1