Engine throttle control system

Abstract: An engine throttle control apparatus for controlling the position of an engine throttle is provided with an accelerator pedal. A force sensor (55) measures the restoring force provided by return springs (53, 54) acting to return an accelerator pedal (50) to a rest position. The restoring force is compared with a threshold or with a signal dependent on the accelerator pedal position to determine the integrity of the springs (53, 54).

Description: The present invention relates to an engine throttle control apparatus, for instance for use in controlling an internal combustion engine for driving a vehicle. Throttle control systems for controlling petrol and diesel engines for vehicles include the so-called "drive by wire" system in which there is no mechanical linkage between a driver actuated accelerator pedal or cruise control command switch and a mixture controlling system, such as one or more carburettors or a fuel injection system. Systems of this type also lend themselves readily to automatic traction control functions for preventing wheel spin during heavy acceleration and/or in conditions of poor ground adhesion. However, special requirements are placed on the performance and safety of such systems, which must function reliably and in accordance with various design parameters at all times. In such systems, the angular position of the throttle is normally derived from measurement of the accelerator pedal position. It is possible to provide two return springs acting on the accelerator pedal so as to urge it towards the idle position. The accelerator pedal is actuated by the foot of a driver against these spring forces, and it is possible that a driver would not notice if one spring were to weaken or break or become disconnected. The failure might only become apparent when the other spring failed, again leading to loss of control of the engine throttle. It is further possible that a failure may occur giving rise to the accelerator pedal position detector sending a signal to a control unit representing a pedal depression in excess of that demanded by the driver, but less than a maximum legitimate pedal depression. EP-A-0 230 722 relates to a failsafe engine controller comprising an accelerator pedal, a spring, a linear potentiometer, a force sensor and a control circuit. According to the present invention, there is provided an engine throttle control apparatus comprising a mounting,an accelerator pedal movable relative to said mounting, at least one accelerator pedal return spring, a sensor responsive to the stress in the at least one return spring and mounted between the or each return spring and either said pedal or said mounting, and detection means for detecting when the stress sensed by the sensor is less than an expected stress value. It is thus possible to provide early detection of possibly hidden faults so as to allow remedial action to be taken before a catastrophic failure occurs. The detection means may provide an indication to a vehicle driver, for instance by controlling illumination of a warning light. Additionally, or alternatively, the detection means may be arranged to cause the engine to operate in a predetermined condition, for instance by closing the throttle so as to shut down the engine or return it to an idling condition. The detection means may alternatively or additionally shut down the engine by removing a source of ignition or fuel supply or by blocking an exhaust path. The expected stress value may be a constant value or may be a function of the position and/or velocity of the pedal. It is thus possible to detect a weakened or broken return spring which might not otherwise be detected by a driver, so as to allow a repair to be made before complete failure of the accelerator pedal return springing. It is also possible to detect errors in a pedal position transducer which would otherwise cause acceleration demand to exceed the required demand e.g. if the transducer were to supply a signal representing a pedal depression greater than that imposed by a driver but less than the maximum legitimate pedal depression. The sensor is preferably mounted between the or each return spring and an anchorage to which the pedal is attached, but may be mounted between the or each return spring and the pedal. In an embodiment where, under normal operation, the stress and pedal position are related by a predictable monotonic function of pedal position, the signal from a pedal position transducer may be supplied to a characteristic function generator having a transfer function representing the function and providing the expected stress value. In another such embodiment, the signal from the sensor may be supplied to a characteristic function generator having a transfer function representing the function, preferably including hysteresis. The output of the function generator may then be compared with the pedal position by the detection means. If the output of the function generator is smaller than the pedal position but larger than the expected stress value, the function generator output may be used for controlling throttle position instead of the pedal position signal. The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic block diagram of a "drive-by-wire" engine control system; Figure 2 is a diagram of an accelerator pedal arrangement constituting an embodiment of the present invention; Figures 3 to 5 are block schematic diagrams of circuits for use with the arrangement of Figure 2. The system shown in Figure 1 comprises a control unit 1 which receives from an accelerator pedal position transducer 2 a required throttle position or demand signal. The control unit 1 has an output for driving a brushless DC motor 3 which directly actuates a butterfly or throttle 4 of an internal combustion engine carburettor or fuel injection system. The throttle 4 is provided with a return spring 5 which urges the throttle towards a closed position or an idle position. The throttle is connected to a position sensor 6 which supplies a signal  representing the actual position of the throttle 4, this signal being supplied to a feedback input 7 of the control unit 1. The throttle position signal  is also supplied to the input of a function generator 8 which produces an output signal, as a function of throttle position and speed of angular movement, which represents the minimum expected power level of power supplied to the motor 3. The output of the function generator 8 is supplied to a subtracter 9, which forms the difference between this signal and the power actually supplied by the control unit 1 to the motor 3. The output of the subtracter 9 is supplied to an engine shut down circuit 11 which sends signals to ignition and fuelling control circuits for returning the engine to idle operation. The circuit 11 also controls a switch contact 12 for disconnecting the control unit 1 from the motor 3. The system thus monitors the power supplied to the motor 3, which power is related to the return force exerted by the return spring 5. The power supplied to the motor 3 is determined mainly by the torque which the motor has to produce in order to overcome the action of the return spring 5 in driving the throttle 4 to the demanded position. The minimum power required for any particular position and angular speed of the throttle 4 is calculated in the function generator 8 and, if the motor power is less than the minimum expected power, action is taken. Thus, if the return spring 5 weakens, breaks, or becomes detached, the reduced return torque is associated with a reduction in power supplied to the motor 3. This condition is detected and appropriate action taken. In the embodiment shown, the various engine control systems cause the engine to be shut down or returned to idle operation. Alternatively or additionally, a warning indication may be given to a driver of a vehicle in which the engine is installed. Thus, if the engine is not disabled, it is possible for the driver to return the vehicle to his home or to a garage for suitable remedial action. A further possible action is to restrict the maximum opening of the throttle 4 so as to limit engine power and hence maximum speed of the vehicle until a repair is made. Figure 2 shows an accelerator pedal arrangement, in which an accelerator pedal 50 is pivotally mounted to a mounting 51 fixed to the vehicle. The pedal 50 is connected to a position sensor 52 (corresponding to 2 in Figure 1) whose output provides a signal α representing the position of the pedal. A pair of return springs 53 and 54 are each connected at one end to the pedal 50 and at the other end to a force sensor 55 mounted on the mounting 51. The force sensor 55 supplies a signal representing the total of the stresses in the springs 53 and 54. Figure 3 shows the force sensor 55 connected to an input of a comparator or subtracter 56 whose other input is connected to an expected force circuit 57. The output of the comparator 56 is connected to an engine shut down circuit 58 corresponding to 11 in Figure 1 for shutting down the engine or taking any other appropriate action. The force sensor 55 monitors the total stress in the springs 53 and 54 and this is compared in the comparator 56 with the expected force from the circuit 57. If the sensed force differs from the expected force and, in particular, is less than the expected force, then the engine is shut down or returned to some other predetermined operating state. Such a difference is indicative of weakening, a breakage, or disconnection of one or both of the springs 53 and 54. For instance, if one spring fails, appropriate action is taken even though the failure may not be detected by a driver. The expected force circuit 57 may provide an expected force signal of constant value. However, Figure 4 shows an expected force circuit 57a which produces an expected force signal as a function of the position and rate of change of position of the accelerator pedal 50, the circuit being connected to the output of the position sensor 52. Such an arrangement provides more accurate detection of failure or imminent failure in cases where, under normal operation, the stress in the springs 53 and 54 is a predictable and monotonic function of accelerator position and/or speed of movement. The characteristic function of the function generator 57a represents the response of a normal set of return springs. Figure 5 shows a further refinement, in which the output of the force sensor 55 is supplied to a characteristic function generator 59 having a hysteresis function. The output of the generator 59 and the signal α are supplied to a select low circuit, which selects the lower of the two signals and supplies this as a throttle command signal to a control unit 61, which receives a feedback throttle position signal  and controls a motor for actuating the throttle. The control unit 61 corresponds to 1 in Figure 1. The function generator 59 has a characteristic function which converts the force signal from the sensor 55 into a signal representing the position of the accelerator pedal 50 and this is compared with the position sensor signal α in a comparator 62. The difference between these signals is supplied by the comparator 62 to a further comparator 63 which compares the difference with a maximum expected error signal supplied by a circuit 64 and causes the engine shut down circuit 58 to shut down the engine as described hereinbefore if the difference exceeds the maximum expected error signal. The force sensor 55 is shown as being located between the mounting 51 and the springs 53 and 54 in order to respond to the actuating force imposed by a driver. However, it could also be located between the springs 53 and 54 and the accelerator pedal 50. It is thus possible to detect a weakened or broken accelerator pedal return spring.

Claims: An engine throttle control system for controlling a motor for actuating an engine throttle, comprising a mounting (51), an accelerator pedal (50) movable relative to said mounting (51), at least one accelerator return spring (53, 54) acting between said pedal (50) and said mounting (51), and, a sensor (55) responsive to stress in the at least one return spring (53, 54), the system being characterised in that said sensor (55) is positioned between the at least one return spring (53, 54) and either said pedal (50) or said mounting (51) and detecting means (56, 57) is arranged to detect when the stress sensed by the sensor (55) is less than an expected stress value. A system as claimed in Claim 1, characterised in that the detecting means is arranged to compare the stress sensed by the sensor (55) with a fixed expected stress value. A system as claimed in Claim 1, including an accelerator pedal position transducer, characterised in that the detecting means includes means (57a) for generating the expected stress value as a function of an output signal and/or a rate of change of the output signal of the accelerator pedal position transducer (52). A system as claimed in any one of the preceding claims, characterised by a function generator (59) connected between the sensor (55) and the detecting means. A system as claimed in Claim 4, characterised in that the function of the function generator (59) includes hysteresis. A system as claimed in any one of the preceding claims, characterised by means (181) responsive to the detecting means for providing a fault indication. A system as claimed in any one of the preceding claims, characterised by means (11, 30, 58, 182, 202, 205) responsive to the detecting means for inhibiting engine operation. A system as claimed in any one of Claims 1 to 6, characterised by means (11, 30, 58, 182, 202, 205) responsive to the detecting means for limiting engine operation to a predetermined fault mode. An engine characterised by including a system as claimed in any one of the preceding claims. A vehicle characterised by including an engine as claimed in Claim 9.

Inventors: FOX PETER MARTIN, IRONSIDE JOHN MICHAEL, MCQUEEN ALISTAIR MALCOLM, PRICE DAVID RICHARD, FOX, PETER MARTIN, IRONSIDE, JOHN MICHAEL, MCQUEEN, ALISTAIR MALCOLM, PRICE, DAVID RICHARD
Applicants: LUCAS IND PLC, LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1990
Main classification: F02D11
IPC codes: F02D11, F02B3