POWER SUPPLY CONTROL DEVICE FOR AN ELECTRONIC CONTROL SYSTEM

Abstract: Devices on an automobile, such as a gear transmission, a clutch, etc. are controlled by an electronic control system (8) comprising a microcomputer. A power supply (1) for the electronic control system is connected to a self-holding means (4) for continuing to supply electric power to the electronic control system even if a key switch (2) is turned off in error, which would result in a power cutoff. If the power is cut off, either inadvertently or intentionally, the electronic control system detects such a power cutoff, and continues to perform a predetermined task. Upon completion of the task, the electronic control system turns off the self-holding means to cut off the electric power supplied to the electronic control system.

Description: This invention relates to a power supply control device for use with an electronic control system, and more particularly to a power supply control device having a self-holding circuit, for use with an automotive electronic control system. Various automobiles, ranging from passenger cars to large-size trucks, are recently controlled by electronic control systems comprising microcomputers. One representative example of such an electronic control system is disclosed in US-A-4 601 369. In the disclosed system, the depth to which an accelerator pedal is depressed and the automobile speed are detected at all times, and a gear transmission position is determined from the detected pedal depth and speed for changing transmission gears. In synchronism with the changing of the transmission gears, a clutch is also controlled by the control system as if human intervention were involved. In the conventional electronic control system for such an automotive control, when a key switch is turned on, a voltage is applied by a battery to a constant-voltage circuit in the electronic control system, and a voltage is applied by the constant-voltage circuit to energise the electronic control system in readiness for operation. When the key switch is turned off, the voltage applied to the constant-voltage circuit is cut off to make the electronic control system inoperative. Therefore, if the key switch is turned off in error, or a fuse connected between the battery and the key switch melts, then the following problems will arise: (1) An electronically-controlled gear transmission, an electronically-controlled clutch, and other devices that are controlled by the electronic control system will be brought entirely out of control. (2) Where a power steering system is of the speed-responsive type, operation of the power steering system to control the load on the steered wheels will be interrupted, making the steering wheel feel unduly heavy or light. These drawbacks are so serious that they may lead to major automobile accidents. JP-A-59/171744 discloses a system in which the power supply in an automobile is cut-off only in the case where a key switch is switched off and a brake switch is on. However, inadvertent operation of the brake will nevertheless cause shutdown of the electronic control. It is an object of the present invention to provide a device, for example on an automobile controlled by an electronic control system, for preventing electric power supplied to the electronic control system from being cut off inadvertently. According to the present invention there is provided an automobile having an engine, a clutch and a power supply control device for supplying electric power to an electronic control system, such as a computer for controlling devices on the automobile, the device comprising main supply means for supplying electric power from a power supply on the automobile to at least the electronic control system; and, a self-holding circuit separate from the main supply means for supplying electric power to the electronic control system when the electric power supplied by the main supply means to the electronic control system is cut off; characterised by power cutoff means for cutting off the electric power supplied by the self-holding circuit to the electronic control system when the engine has stopped and the clutch is connected after the electric power supplied by the main supply means to the electronic control system has been cut off. Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram partly in block form, of an embodiment of the present invention; Fig. 2 is a schematic diagram showing one form of means for turning off a self-holding circuit; Fig. 2A is a circuit diagram, partly in block form, of an electronic control system used in Fig. 2; Figs. 3(a) and 3(b) are flowcharts of operation of the embodiment illustrated in Fig. 1; Figs. 4(a) and 4(b) are flowcharts of operation of the embodiment shown in Fig. 2; Fig. 5 is a circuit diagram of an equivalent circuit, in the form of a logic circuit, of the embodiment shown in Fig. 1; Fig. 6 is a circuit diagram of an equivalent circuit, in the form of a logic circuit, of the embodiment shown in Fig. 2; Fig. 7 is a circuit diagram, partly in block form, of a modification of the embodiment of Fig. 1; Fig. 8 is a schematic diagram of a modification of the embodiment of Fig. 1; and Fig. 9 is a circuit diagram, partly in block form, of a modification of the embodiment of Fig. 2. Fig. 1 shows an embodiment of the present invention. A battery 1 for use on an automobile comprises an ordinary lead storage battery having an output voltage of 12, 24 or 48 volts. A power supply switch 2, preferably in the form of a key switch, is turned on when it is in an "accessory" position and in a "power-on" or "start" position. The power supply switch 2 will hereinafter be referred to as a "key switch". The battery l and the key switch 2 are coupled to fuses 3-l, 3-2, and the fuse 3-2 is coupled to a power supply relay 4 for self-holding a power supply circuit. An electronic control system 6 includes a constant-voltage regulated power supply 5 for converting the output voltage of l2, 24, or 48 volts from the battery l to a voltage of 5.5 volts, for example, which is required to drive an electronic control system (described later). The electronic control system 6 also includes a driver transistor 7 for energizing the power supply relay 4, a microcomputer 8 comprising a read-only memory 8a, a central processing unit (CPU) 8b, an input/output buffer 8c, and an input/output interface 8d, and diodes l0, ll, l2 for preventing currents from flowing back therethrough. The circuit arrangement shown in Fig. l has a self-holding means for continuously supplying electric power to the electronic control system 6 when the key switch 2 is opened, and a means for turning off the self-holding means to stop operation of the power supply of the electronic control system 6 when the electronic control system 6 has completed a predetermined sequence of operation after detecting when the electric power supplied to the automobile was cut off inadvertently or intentionally. The self-holding circuit will be described below. When the key switch 2 is closed, the voltage of the battery l is applied via the key switch 2 and the diode l0 to the constant-voltage regulated power supply 5 to energize the electronic control system 6. At the same time, the voltage is impressed via the diode ll on the base of the transistor 7 to energize the transistor 7, thus energizing the relay 4 to close its contacts, whereupon the voltage from the battery l is also applied through the relay 4 to the constant-voltage regulated power supply 5. This condition is assumed when the automobile is at rest and about to run, or is running. The microcomputer 8 is supplied with signals from various sensors through the input/output interface 8d and the input/output buffer 8c. The CPU 8b executes various programs stored in the ROM 8a to supply various control signals to different devices on the automobile through the input/output buffer 8c and the input/output interface 8d. The input/output buffer 8c issues a signal for turning on the driver transistor 7. This signal is applied via the diode l2 to the base of the driver transistor 7 to render the latter conductive. A current now flows through the coil of the relay 4 to close the contacts thereof, so that the voltage from the battery l is held and applied to the constant-voltage regulated power supply 5. In the event that the key switch 2 is turned off in error or the fuse 3-l melts, the current supplied to the power supply 5 via the diode l0 and the current supplied to the base of the driver transistor 7 through the diode ll are cut off. However, since the transistor 7 remains energized via the input/output buffer 8c and the diode l2 to keep the relay 4 actuated, the voltage from the battery l is continuously applied to the electronic control system 6. The electronic control system 6 is therefore prevented from being de-energized even when the key switch 2 is turned off erroneously or the fuse 3-l melts. Fig. 2 shows another embodiment of the present invention, and Fig. 2A illustrates the internal arrangement of an electronic control system shown in Fig. 2. The means for turning off the self-holding means to cut off the electric power supplied to the electronic control system will be described in detail with reference to Figs. 2 and 2A. In Fig. 2, a clutch mechanism 2l for selectively transmitting engine power comprises a flywheel 22, a driven plate 23, a pressure plate 24, a clutch lever 25, a release bearing 26, a release lever 27, and a return spring 28 which normally urges the clutch mechanism connected when there is no fluid pressure supplied to a clutch actuator 29 from a clutch disconnecting valve 30. Designated at 3l is a clutch connecting valve 3l, an accumulator 32, a fluid pressure source 33 comprising a pump, 34 a working fluid tank, and 35 a stroke sensor for detecting the operation stroke of the clutch actuator 29. A detected signal from the stroke sensor 35 is applied to the electronic control system 6. The clutch disconnecting valve 30 and the clutch connecting valve 3l are opened and closed under the control of the electroinc control system 6 for disconnecting and connecting the clutch mechanism 2l. A rotation signal issued by an engine rotation sensor 20 and indicative of the rotation of the engine is delivered to the electronic control system 6. Operation of the embodiment shown in Figs. 2 and 2A is as follows: When the key switch 2 is closed, the electronic control system 6 is continously supplied with electric power by the self-holding circuit. In the event that the automobile is stopped and the key switch 2 is turned off by the automobile driver, the electronic control system 6 first reads in a rotation signal from the engine rotation sensor 20. Upon confirming that the engine rotation is stopped, the electronic control system 6 sends a command to the clutch connecting valve 3l to reduce the fluid pressure in the clutch actuator 29, allowing the clutch mechanism 2l to be engaged under the resiliency of the return spring 28. Then, the electronic control system 6 reads in a signal from the stroke sensor 35. After confirming that the clutch actuator 29 is in a clutch-connecting position, the current supplied via the diode l2 to the driver transistor 7 (Fig. 2A) is cut off to de-energize the relay 4, thus cutting off the current supplied from the battery l to the electronic control system 6. Therefore, after the key switch 2 has been turned off by the driver, the self-holding means which has kept the electronic control system 6 energized is turned off to cut off the electric power supplied to the electronic control system 6. The self-holding means and the means for turning off the self-holding means are effective in preventing the clutch mechanism from being connected in the absence of the electric power even if the key switch 2 is turned off before the engine is stopped, so that the automobile is prevented from moving unexpectedly. The means for turning off the self-holding means has been described above with reference to Figs. 2 and 2A in which the clutch mechanism is connected after confirming that the engine has been stopped. However, where the automobile is to be parked on a slope with transmission gears in mesh, the means for turning off the self-holding means may be actuated by applying a gear position signal from the gear transmission to the electronic control system after confirming that the clutch mechanism is disconnected after the engine has been stopped, the gear transmission is then shifted into a first (low) gear position or a reverse gear position, and thereafter the clutch mechanism is connected. Figs. 3(a) and 3(b) show operation sequences for the embodiment of Fig. l. Fig. 3(a) shows an operation sequence to be executed after the key switch is turned on. When the key switch 2 is turned on, the electric power from the battery l is supplied through the diode l0 to the constant-voltage regulated power supply 5 in a step l, and the CPU 8b starts operating in a step 2. Then, a command is delivered via the input-output buffer 8c and the diode l2 to the driver transistor 7 to energize the relay 4 for thereby self-holding the electric power supplied to the electronic control system 6 in a step 3. The step 3 is followed by normal control. Fig. 3(b) illustrates an operation sequence to be executed when the key switch is turned off erroneously or the fuse is caused to melt. When the key switch 2 is turned off erroneously or the fuse melts in a step 4, normal control is carried out in a step 5. If the automobile is brought into a safe condition, such as when the clutch mechanism is connected after the engine has stopped, as indicated by an external input applied to the input/output interface 8d, then control goes from the step 4 to a step 6 in which the driver transistor 7 is rendered non-conductive through the input/output buffer 8c and the diode l2 to de-energize the coil of the relay 4, thereby turning off the self-holding means in a step 6. The electric power supplied to the electronic control system 6 is cut off in a step 7. Figs. 4(a) and 4(b) illustrate operation sequences for the embodiment of Figs. 2 and 2A. Fig. 4(a) shows an operation sequence to be executed after the key switch is turned on. When the key switch 2 is turned on, the coil of the relay 4 is energized by the electronic control system 6 to connect the contacts of the relay 4 in a step ll. The electric power supplied to the electronic control system 6 is held in a step l2 to allow the electronic control system 6 to effect normal control. Fig. 4(b) illustrates an operation sequence to be carried out when the key switch is turned off. The electronic control system 6 reads in the signal from the engine rotation sensor 20 in a step l3. After confirming that the engine is stopped, the electronic control system 6 issues a command to enable the clutch actuator 29 to connect the clutch mechanism 2l in a step l4. Then, the electronic control system 6 reads in the signal from the stroke sensor 35 to determine the condition of the clutch mechanism 2l in a step l5. If the clutch mechanism 2l is fully connected, then control proceeds to a step l6 in which the relay 4 is de-energized to cut off the electric power supplied to the electronic control system 6 through the self-holding means, whereupon the operation sequence is completed. Fig. 5 is illustrative of an equivalent circuit of the embodiment of Fig. l, the circuit being in the form of a logic circuit. The circuit includes an AND gate l3 representative of the relay 4, and an OR gate l4 indicative of the diodes ll, l2 and the driver transistor 7. When a input of a high level (H) is applied to a control circuit 8′ after the key switch 2 has been turned on, the electric power from the battery l is continously applied, and when an input of a low level (L) is applied to the control circuit 8′ after the key switch 2 has been turned on, the electric power from the battery l is cut off. Fig. 6 shows an equivalent circuit, in the form of a logic circuit, of the embodiment illustrated in Fig. 2. The circuit includes an AND gate l3 representative of the relay 4, and an OR gate l4 indicative of the diodes ll, l2 and the driver transistor 7, as with the equivalent circuit of Fig. 5. H and L inputs applied to the control circuit 8′ indicate whether the self-holding means is to remain turned on or be turned off. According to a modification, shown in Fig. 7, of the embodiment of Fig. l, the relay 4 is replaced with a transistor 7a for controlling a large current. Parts in Fig. 7 which are identical to those of Fig. l are denoted by identical reference characters and will not be described in detail. As shown in Fig. 7, the cathodes of the diodes ll, l2 for preventing a current from flowing back are connected to the base of the transistor 7a, with its collector coupled to the fuse 3-2 and the emitter to the constant-voltage regulated power supply 5. When a signal is applied via the diode ll or l2 to the base of the transistor 7a, the transistor 7a is rendered conductive to supply tne electric power from the battery l to the constant-voltage regulated power supply 5. The same self-holding ability as described above with reference to Fig. l is therefore provided by the circuit arrangement of Fig. l. Fig. 8 shows a modification of the embodiment of Fig. l, employed for controlling a gear transmission. Denoted at l8 is a gear transmission control unit, l9 an automobile speed sensor mounted on a gear transmission, and 20 an engine rotation sensor. The electronic control system 6 applies a command for controlling gear positions to the gear transmission control unit l8, and is supplied with detected signals from the respective automobile speed sensor l9 and the engine rotation sensor 20. When the key switch 2 is operated in error or the fuse is caused to melt while the automobile is running, the electronic control system 6 holds the electric power supplied through the self-holding means, and also reads in the signals from the engine rotation sensor l9 and the automobile speed sensor 20. Until these signals indicate that the engine and the automobile are stopped, the electronic control system 6 continuously delivers an appropriate signal to the gear transmission control unit l8 to control the running of the automobile, while preventing undesired accidents from occurring due to an unexpected cutoff of the electric power during travel of the automobile. Fig. 9 shows a modification of the embodiment of Fig. 2, employed for clutch control. In Fig. 9, a frequency-to-voltage converter l6 serves to convert the frequency of a pulse signal from the engine rotation sensor 20 to a voltage. A clutch control circuit l7 controls the clutch actuator 29 (Fig. 2) and also controls the driver transistor 7 in response to a signal from the stroke sensor 35. The frequency-to-voltage converter l6 receives the signal from the engine rotation sensor 20 and converts the frequency thereof to a voltage proportional thereto. Therefore, while the engine is in rotation, the frequency-to-voltage converter l6 produces an output voltage corresponding to the rotation of the engine to render the driver transistor 7 conductive for thereby keeping the electric power supplied to the electronic control system 6. When the engine is stopped and a signal indicative of the full clutch connection is supplied from the stroke sensor 35, the relay 4 is de-energized by the frequency-to-voltage converter l6 and the clutch control circuit l7 via the driver transistor 7. Accordingly, the electric power supplied to the electronic control system 6 is cut off.

Claims: An automobile having an engine, a clutch and a power supply control device for supplying electric power to an electronic control system (6), such as a computer (8) for controlling devices on the automobile, the device comprising main supply means (2) for supplying electric power from a power supply (1) on the automobile to at least the electronic control system (6); a self-holding circuit (4) separate from the main supply means (2) for supplying electric power to the electronic control system (6) when the electric power supplied by the main supply means (2) to the electronic control system (6) is cut off; and power cutoff means (7) for cutting off the electric power supplied by the self-holding circuit (4) to the electronic control system (6) after the electric power supplied by the main supply means (2) to the electronic control system (6) has been cut off, characterised in that the self holding circuit (4) is turned off when the engine has stopped and the clutch is connected. An automobile according to claim 1, wherein the main supply means includes a key switch (2) of the automobile for supplying electric power to the electronic control system (6). An automobile according to claim 1 or claim 2, wherein the self-holding circuit (4) includes a relay (4) for making and breaking the self-holding circuit. An automobile according to claim 1 or claim 2, wherein the self-holding circuit (4) includes an electronic switching element (7a) for making and breaking the self-holding circuit. An automobile device according to any preceding claim, wherein the self-holding circuit (4) is responsive to a signal from the electronic control system (6) for self-holding the electric power supplied to the electronic control system (6) at the same time that the power supply (1) is turned on. An automobile according to any preceding claim, further comprising an engine rotation sensor (20) for detecting the rotation of the engine on the automobile and an automobile speed sensor (19) for detecting the speed of the automobile; and in that the self-holding circuit (4) is turned off when desired gear transmission control has been effected and signals from the engine rotation sensor (20) and the automobile speed sensor (19) are no longer supplied.

Inventors: TAMAI, HIDEFUMI
Applicants: ISUZU MOTORS LIMITED
Application year: 1986
Main classification: B60K20
IPC codes: B60R16, F16D48, F16H61, B60K23