ELECTRONIC ENGINE CONTROL FOR A MOTOR VEHICLE

Abstract: An electronic engine control (EEC) equipped with a fuel cut-off safety device in the form of a relay (12) controlling the winding of the fuel pump (16), comprising a single conductor (FCOM) connecting the fuel pump power supply line with the EEC in order to test and/or monitor the voltage applied across the terminals of the fuel pump, at least when the engine is started up.

Description: This invention relates to an electronic engine control (EEC) for a motor vehicle and more especially to an EEC equipped with a fuel cut off safety device, according to the first part of claim 1 or 6. A safety device for an EEC for a motor vehicle engine is known from U.K. Patent No. 2040503 (OLS 2839467). In this known device, the position of the fuel throttle and of the accelerator pedal, and possibly also the condition of an automatic speed controller (ASC) are checked by means of switches connected in the power supply line to a relay which controls energisation of the winding of an electric fuel pump. U.K. Patent Specification No. 1133540 discloses an EEC for a motor vehicle having a safety device wherein the engine speed is monitored and the fuel pump relay is de-energised to stop the fuel pump if the engine speed drops below a predetermined but possibly adjustable value. However, this function is blocked during starting, and the fuel pump relay is temporarily energised via a switching device. After a predetermined delay, typically about two seconds, the EEC speed-dependent controller (safety device) takes over the energisation of the fuel pump relay. However, when reliance is to be placed on such a safety device when travelling, possibly at high speed, it would be advantageous to be able to check the operational condition of an EEC safety device as aforesaid, prior to making a journey. UK-Patent application No. 21 44 180 discloses a method for monitoring a fuel injection system of an internal combustion engine. If the first engine overrun operation following starting occurs, a safety device which suck empty a suction chamber of an injection pump in the injection system in the event of a fault is briefly switched on and the reaction of the engine fuel system is evaluated. If the fuel system does not react in a predetermined manner, then a fault is present and the engine is switched off or switched over to emergency operation. The testing and monitoring of a safety device for cutting off the power supply to an electric fuel pump is not disclosed in this patent application. It is an object of this invention to enable a fuel cut off safety device in an electronic engine control to be tested and/or monitored. This object is achieved with the features according to claims 1 or 6. The invention applies more especially to an EEC of the general kind described in the above-mentioned U.K. Patent Specification No. 1133540. In this case, the voltage at the terminals of the fuel pump is measured when the engine is started, i.e. during the approximate two second delay period which occurs on switching on the ignition before the speed-dependent controller takes over, and if the correct voltage is not detected at the EEC, the speed-dependent controller is prevented from taking over. The correct test voltage to be detected at the EEC will normally be ground voltage. If ground voltage is not detected, this is indicative of a short circuit, broken electrical contact, jammed or welded relay contact or the like at the fuel pump winding/control relay combination, whereby the vehicle is unsafe to drive. It may be possible, alternatively, to arrange for the EEC to activate an alarm device for indicating the fault, whilst still maintaining the on-condition of the fuel pump, so that the vehicle can be driven to the nearest garage. In this way, continuous monitoring of the fuel pump voltage may be made possible, to assist in isolation of the source of a fault in the EEC safety device which may develop during travel. The invention as described can be made possible with minimal expense simply by the addition of a single conductor connecting to the fuel pump power supply circuit, and modification of the injection system is not required. A practical example of electronic engine control (EEC) with checkable safety device in accordance with the invention is shown in the accompanying drawings, in which: Figure 1 shows the arrangement as a simplified circuit diagram; and Figure 2 is a voltage timing diagram. Referring to the drawings, there is shown a circuit block 10 which represents an EEC equipped with a fuel cut-out safety circuit, for example in accordance with the device described in U.K. Specification No. 1133450. In an EEC, the throttle is controlled by the accelerator pedal through an electrical transmission which includes position sensors and a servo-motor, as well known in the art. The known EEC circuit comprises switches the states of which are dependent on the positions of the throttle and the accelerator pedal. These switches are connected in the power supply circuit to the fuel pump relay and, if not in the correct states relative to one another, cause de-energisation of the fuel pump relay, with consequential stopping of the supply of fuel by the fuel pump, which leads to slowing down and eventual stopping of the engine. In addition, the known EEC circuit includes a safety device which switches off the fuel pump if the r.p.m. of the engine drop below a given value. This safety unit is temporarily blocked on ignition, giving a delay of approximately two seconds at which ground voltage should be present at the terminals of the fuel pump winding. In accordance with the invention, if this ground voltage is not detected at the EEC on ignition, the EEC, including in particular the aforesaid safety device, is prevented from taking over and energising the fuel pump winding at normal engine speeds, so that the vehicle cannot be driven. In the drawing, the fuel pump relay which serves for fuel cut off is referenced 12, and the line FCO indicates the power line through which energisation and de-energisation of the relay is controlled. The fuel pump relay 12 has a movable contact 14 in the power supply line to the fuel pump 16. In the absence of an error in the throttle/pedal relationship, the relay 12 is constantly energised during running of the engine, provided also that the engine speed does not fall below a predetermined value. However, in the event of error in the throttle/pedal relationship or a failure in the safety device, the fuel pump relay 12 is de-energised via the FCO line. Before commencing a journey, it would be advantageous to be able to test the EEC safety circuit, and in accordance with the invention this is made possible by monitoring the voltage across the fuel pump terminals. In the drawing, the line FCOM indicates the conductor via which the voltage across the fuel pump terminals is fed back to the EEC. When the ignition switch is first turned to the power-on condition, the EEC then immediately carries out a test on the fuel pump 16 and checks the reaction of the relay 12. For this purpose, the EEC causes a voltage to be temporarily applied on the FCO line which should cause a switching off of the pump 16. The reaction of the relay 12 is detected by the EEC by means of a check on the reaction voltage on the FCOM line. If the reaction voltage does not occur on the FCOM-line in a predetermined time period after applying the voltage to switch off the fuel pump (16) via the FCO-line, the EEC recognises a fault condititon of the safety means (12) and the engine is prevented from starting. Figure 2 shows in the upper diagram the voltage charge applied on the FCO line by the EEC, whilst the lower diagram shows the reaction voltage detected on the FCOM line when the relay is responding correctly and no fault condition exists.

Claims: Method for controlling and monitoring an internal combustion engine of a motor vehicle by an electronic engine control system (10, EEC), equipped with safety means (14) for cutting off the power supply to an electric fuel pump (16), when supplied with an on-signal characterized by the first step of detecting the voltage at the terminals of the fuel pump (16), the second step of a plausibility check of that voltage against the on-signal of a safety means (14), and the third step of preventing operation of the engine, if the said plausibility check failed or of activating an alarm device for indicating the fault, whilst still maintaining the on-condition of the fuel pump, if the said plausibility check failed. Method according to claim 1, characterized in that the plausibility check is correct, when the detected voltage at the terminals of a fuel pump (16) occurs in a predetermined time period after supplying the on-signal. Method according to claim 1, characterized in that the safety means (14) cut off the power supply of the fuel pump (16) in the event of a fault. Method according to claim 1, characterized in that the on-signal is generated during the start of the engine before commencing a journey. Method according to the claims 1 and 4, characterized in that the on-signal is generated for a time period, which is not longer than about 2 seconds. Electronic engine control system (10, EEC), for controlling and monitoring an internal combustion engine of a motor vehicle, for carrying out the method according to claim 1, equipped with safety means (14) for cutting off the power supply to an electric fuel pump (16), when supplied with an on-signal, characterized by first means for detecting the voltage at the terminals of the fuel pump (16), second means for providing a plausibility check of the said voltage against the on-signal of the safety means (14), third means for preventing the operation of the engine if the said plausibility check failed, or for activating an alarm device for indicating the fault, whilst still maintaining the on-condition of a fuel pump (16), if the said plausibility check failed. Electronic engine control system according to claim 6, comprising the addition of a single conductor connecting the fuel pump power supply line with the electronic engine control system. Electronic engine control system according to claim 6 or claim 7, wherein the electronic engine control system has a speed-dependent safety device which is blocked during ignition and the fuel pump voltage is detected on an ignition.

Inventors: BARTKE, RALF MICHAEL, DIPL.-ING
Applicants: ROBERT BOSCH GMBH
Application year: 1989
Main classification: F02D41
IPC codes: F02D45, F02D11, F02D35, F02D41, F02M37, F02D3