System and method for automatically controlling vehicle speed to desired cruise speed using microcomputer

Abstract: A system and method for automatically controlling a vehicle speed to a desired cruise speed are disclosed in which whether a microcomputer of a control unit is enabled to perform a cruise speed control is determined on the basis of a plurality of determining factors and a power supply of a throttle actuator for actuating an engine throttle valve so as to adjust an opening angle of the throttle valve is enabled only when all of the determining factors satisfy a condition of enabling the cruise speed control via the actuator and is disabled when at least one of the determining factors does not satisfy the condition.

Description: The present invention relates to a system and a method for automatically inhibiting cruise speed control in case that it is realized that at least one of a plurality of determining factors is not fulfilled which determine whether cruise speed control can be execcuted safely. Such a system is known from US-A-4 337 511, showing the subject-matters of the first part of claim 1. US-A-4,539,642 describes a system and a method in which a microprocessor provides the cruise speed control by outputting control signals to an actuator means in accordance with commands as they are received from a command switch means, and in accordance with the current vehicle speed as it is measured by speed sensor means. For fail safe operation, the system comprises a coincidence gate and a bistable device physically separated from the microcomputer, which device stores a signal indicating whether the cruise speed control should be activated or deactivated. The microprocessor runs test routines with the bistable device. When the microprocessor or the bistable device do not operate correctly, this indicates that a condition to enable the cruise control run is not satisfied. In this case, the cruise control run is automatically disabled. It is the object of the present invention to provide a cruise speed control fail safe system with very high fail safe reliability. It is another object of the present Invention to provide a very reliable cruise speed control fail safe method. The cruise speed control fail safe system according to the present invention is defined in claim 1. The cruise speed control fail safe method according to the present invention comprises the steps as defined in claim 2. The advantage of the inventive system and the inventive method is that, when cruise speed control shall be inhibited, this is done by inhibiting the power supply to actuator means which controls the vehicle speed. In the prior art system and method itwas possible that cruise speed control was inhibited, but anyhow the actuator means had influence on the vehicle speed due to a failure in the actuator means. Preferably the actuator means are connected with a power source only then when at least one signal Indicates that cruise speed control really should be executed. Such signals are e.g. the commapd as issued from command switch means, control'command signals as issued from the microprocessor to control the actuator means, and/or a cruise signal issued by said microcomputer do indicate that cruise speed control should be executed. Preferably, a plurality of signals is checked commonly and only then, when the level of all checked signals is reasonable for cruise speed control, the actuator means is connected with a power supply means. The invention will be explained in more detail in the following by a preferred embodiment by reference to a drawing. Fig. 1 is a schematic circuit wiring diagram of a system for automatically controlling a vehicle speed to a desired cruise speed according to the present invention. The automatic cruise speed controlling system shown in Fig. 1 includes an operation unit 1 having a group of command switches, each switch issuing a command on a cruise speed control and installed on a part of a vehicle body easy to access from the vehicle driver, and a microcomputer 3 which outputs control command signals to a throttle actuator 5 to control opening and dosing of control valves constituting the actuator 5 so that the opening angle of an engine throttle valve is adjusted in accordance with the contents of the command issued from the operation unit 1. Thus, the vehicle speed is controlled. In detail, the operation unit 1 Includes a set/cruise switch S1, an acceleration switch S2, and a resume switch S3. One end of each switch S1 to S3 is connected to a battery (DC voltage supply) 7 via an ignition switch S4. The ignition switch S4 is turned on when a vehicular ignition device is operated. The other end of each command switch S1 to S3 is connected to the microcomputer 3 and to a energizing coil 11 of a power supply relay 9, for controlling the power supply to the actuator 5, via a corresponding diode D1 to D3. The microcomputer 3 generally includes an I/O port, CPU, RAM, ROM, and common bus. Next, functions of the set/cruise switch S1, acceleration switch S2, and resume switch S3 will be described. The set/cruise switch S1 is a switch for setting a cruise run state of the vehicle. When the set/cruise switch S1 is depressed and released (turned on and thereafter turned off) with the vehicle speed falling in a cruise run allowable range from, e.g., 50 Km/h to, e.g., 100 Km/h, the vehicle speed at the time of the release of the set/cruise speed is set as cruise speed. The cruise control is carried out at the set cruise speed. It is noted that when the set/cruise switch is continued to be depressed, the vehicle speed is decreased due to occurrence of an engine braking according to a duration of time during which the switch S1 is depressed. The acceleration switch S2 is a switch for operatively increasing the vehicle speed at a constant acceleration. When the vehicle cruises under the cruise speed control at a speed above the lower limit value of the cruise speed control allowable range and the acceleration switch S3 is depressed, the vehicle is accelerated and after the vehicle speed reaches another vehicle speed at which the vehicle is desired to cruise, the acceleration switch S3 is released. The cruise speed run at that new cruise speed is carried out. The resume switch S3 is a switch for returning to the original cruise speed before the vehicle speed reduction caused by a temporary decrease of the vehicle speed, e.g., by an application of the brake or shift range change of a vehicular transmission. When the resume switch S3 is operated after the vehicle speed is decreased due to the braking or the operation of the set/cruise switch S1, the cruise speed is returned to the cruise speed before the reduction of the vehicle speed and the cruise run is restarted at that speed. The power supply relay 9 includes contacts 13 whose one end is connected to a battery 7 via a brake switch S6 and clutch switch S7. The brake switch S6 is turned off (open) when the brake pedal is depressed and the clutch switch S7 is turned off (open) when the clutch pedal is depressed. The other end of the contacts 13 is connected to a safety valve (release valve) 5a, acceleration valve (supply valve) 5b, and an deceleration valve (air valve) 5c of the actuator 5. The actuator 5 receives the power supply from the battery 7 via the switches S4 to S7 and the power supply relay 9. Hence, with the brake system or clutch system operated under the cruise control operation, the brake switch S6 or clutch switch S7 is open so that the power supply to the actuator 5 is halted to release the cruise speed control and the power supply relay 9 is in an off hold state. When a main switch S5 is turned on, any one of the commands on the cruise speed control from the command switch group 1 is received by the microcomputer 3. The cruise speed control operation is started and the microcomputer 3 issues a cruise signal indicating the vehicle is in the cruise run state to the base of a transistor Q1. The collector of the transistor Q1 is connected to the battery 7 via the ignition switch S4, the main switch 5, and a cruise lamp 15 illuminating when the vehicle is in the cruise run state. The emitter is connected to ground. When the cruise signal is at high level, the transistor Q1 conducts to illuminate the cruise lamp 15. In addition, the cruise signal outputted from the microcomputer 3 is supplied to one input terminal of a NAND gate 19 via an inverter 17. The microcomputer 3 supplies a receipt signal indicating that one of the commands on the cruise speed control was received from the operation unit 1 to a set input terminal of an R-S flip-flop circuit (RS F/F) 21. The reset input terminal of the RS F/F 21 is connected to respective switches S1 to S3 of the operation unit 1 via corresponding diodes D1 to D3. The set input terminal of the RS F/F 21 is connected to the microcomputer 3 and the output terminal of the RS F/F 21 is connected to an input terminal of the AND gate 22. That is to say, the RS F/F 21 is reset when at least one command switch of the group of the command switches S1 to S3 is operated and the command at the high level state is supplied to the microcomputer 3. When the receipt signal is turned to the high level upon receipt of the command, a high level recognition signal, indicating that the command is supplied to the microcomputer 3 and received thereby, is supplied to the RS F/F 21 and set so that the output terminal of the RS F/F 21 is turned to the high level. The microcomputer 3 supplies the control command signals to respective bases of NPN type transistors Q2, Q3, and Q4 to control energization of the actuator 5, i.e., the safety valve 5a, acceleration valve 5b, and deceleration valve 5c. It is noted that the safety valve 5a is normally open, accelerator valve 5b is normally closed, and the deceleration valve 5c is normally open. The transistor Q2 is connected between the safety valve 5a and ground. When the control command signal supplied to the base is turned to the high level state, a current path for a current to flow through the safety valve 5a is closed to close the safety valve 5a. The transistors Q3 and Q4 receive the control signals from the microcomputer 3 to control opening or closing of the corresponding acceleration and deceleration valves 5b and 5c upon receipt of the corresponding control command signals from the microcomputer 3. In addition, the control command signals for controlling the energization and deenergization of the actuator 5 are supplied to an input terminal of a NOR gate 23. An output terminal of the NOR gate 23 is connected to another input terminal of the NAND gate 19. When low-level control command signals are supplied to the transistors Q2 to Q4 from the microcomputer 3 the valves 5a to 5c of the actuator 5 are all in the deenergized states so that the opening angle of the throttle valve is decreased and the output terminal of the NOR gate 23 is in the high level state. A watchdog timer 25 for detecting the operation state of the microcomputer 3 is connected to the microcomputer 3. The watchdog timer 25 serves to detect whether the microcomputer 3 executes a program normally. The watchdog timer is a timer set by the program to prevent the microcomputer 3 from looping endlessly or becoming idle because of program errors or equipment faults. The watchdog timer 25 receives a pulse signal from the microcomputer 3 during the execution of the program, determines whether a period of the pulse signal falls in a predetermined range, and outputs a determination signal to the microcomputer 3 and an AND gate 22. That is to say, in a case when the pulse signal has the predetermined period, the output signal of the watchdog timer 25 is kept at the high level. When the watchdog timer 25 outputs the low-level reset signal, due to the pulse signal being out of the predetermined period, to the reset terminal RES of the microcomputer 3 the microcomputer 3 is reset. The microcomputer 3 is then maintained in the optimum operation state. The microcomputer 3 is connected to a vehicle speed sensor 27 for measuring the current vehicle speed in accordance with a speed indicative pulse signal derived from the vehicle speed sensor 27. A vehicle speed determining circuit 29 is connected to the vehicle speed sensor 27 for determining whether the current vehicle speed falls in the above-described cruise speed control allowable range. If the current vehicle speed is within the cruise speed control allowable range, the high-level determination signal is supplied to the AND gate 22. On the other hand, if the current vehicle speed detected by the vehicle speed sensor 27 is out of the cruise speed control allowable range, the low-level determination signal is supplied to the AND gate 22. The NAND gate 19 forms the negative logic product of the outputs of both inverter 17 and NOR gate 23 and supplies the result of the negative AND to an input terminal of a NAND gate 31. The other input terminal of the NAND gate 31 is connected to an input terminal of an inverter 33 and the output terminal of the inverter 33 is connected to a connecting point between the relay 9 and the actuator 5. The output terminal of the NAND gate 31 is connected to an input terminal of the AND gate 22. That is to say, when the output signal level is in the high level state with the power supply relay 9 in the non-conducting state, the open command to the actuator 5 is outputted from the microcomputer 3 and the output signal of the NOR gate 23 is in the high level state. At this time, when the cruise signal is in the low level state, the output signal of the inverter 17 is in the high level state. The output signal of the NAND gate 19 is then turned to the low level state and therefore the output signal of the NAND gate 31 is turned to the high level state. Hence, in a case where the microcomputer 3 is enabled to operate, the control command signals supplied to all transistors Q2 to Q4 are first all in the low-level states. Then, since the above-described states occur immediately before the transfer from the cruise release state to the cruise state, the cruise signal is turned to the low level. The output terminal of the NAND gate 31 is in the high level state. On the other hand, with the power supply relay 9 in the conducting state and the output signal of the inverter 33 in the low level state, the cruise signal is in the high level state and the control command signal of the transistors Q2 to Q4 is turned to the high level state. If the microcomputer 3 is not in the operable state, the output signal of the NAND gate 31 is turned to the low level state. The AND gate 22 forms the logic AND of the above-described signals. Its output terminal is connected to the base of a NPN type transistor Q5 connected between the other end of the coil 11 constituting the power supply relay 9 and ground for controlling the power supply to the coil 11. Hence, the power supply to the coil 11 of the power supply relay 9 is controlled by turning the transistor Q5 conductive through the output signal of the AND gate 22. That is to say, the AND gate 22 receives determination factors to determine whether the control valves 5a to 5c of the actuator 5 receives the power supply, namely, the output signals of R/S flip-flop circuit 21, watchdog timer 2S, vehicle speed determining circuit 29, and NAND gate 31. Then, only when all of these output signals indicate the enable of the cruise speed run, the AND gate 22 turns the transistor Q5 conductive so that an energization current flows through the coil 11 of the power supply relay 9 to hold the power supply relay 9 in the on state so that the power supply to the actuator 5 is enabled. Next, an operation of the preferred embodiment shown in Fig. 1 will be described. The microcomputer 3 receives one of the command signals from the operation unit 1 and executes the cruise speed control. Now, it is assumed that during the cruise speed control run, the brake switch S6 or clutch switch S7 is opened due to the operation of the brake pedal or clutch pedal so that the power supply to the actuator 5 is halted and the power supply relay 9 is in the off hold state. The cruise control is released. Then, when the brake switch S6 or clutch switch S7 is closed due to releasing the brake pedal or clutch pedal, the vehicle speed falls in the cruise speed control allowable range, the determination signal from the vehicle speed determining circuit 29 is in the high level state, and, the microcomputer 3 operating normally, the AND gate 22 outputs the high level signal. That is to say, the condition of the high level output of the AND gate 22 is such that the cruise signal is in the low level state, the output signal of the inverter 17 is in the high level state, the reset signal of the watchdog timer 25 is in the high level state, the control signals to conduct the transistors Q2 to Q4 are all in the low level states, all control valves 5 are deenergized, the output signal of the NOR gate 23 is in the high level state, the command from at least one of the command switches S1 to S3 is supplied to the microcomputer 3, the microcomputer 3 outputs the high-level receipt signal to the RS F/F 21 in response to the command, and the recognition signal derived from the RS F/F 21 is therefor in the high level. Thus, the transistor Q5 becomes conductive, the energization current flows through the coil 11 of the power supply relay 9 via the operated command switch S1 to S3 from the power supply (battery 7) so that the power supply relay 9 is held in an on state. Thus, the power supply to the control valves 5 is carried out to execute the cruise speed control. The relationship between the opening angle of the throttle valve, the current vehicle speed V and set cruise speed V s , and the control valves 5a to 5c is described below. (1) V s > V --- In this case, the contents of the control command signals derived from the microcomputer indicate all "1" so that the safety valve 5a is closed, the air pressure (compressed air) valve 5b is open, and the air valve 5c is closed, and a diaphragm is displaced so as to open the throttle valve, and consequently the vehicle speed V is increased. (2) V s = V --- In this case, the content of the control command signals indicate that only the acceleration valve 5b is closed, safety valve 5a and air valve 5c are open so that the opening angle of the throttle valve remains at a constant angle. (3) V s < V -- In this case, the contents of the control command signals derived from the microcomputer 3 indicate that the safety valve 5a is closed, the air pressure supply valve is closed, and the air valve 5c is open so that the opening angle of the throttle valve is closed to decrease the vehicle speed V. (4) The brake switch S₆ or clutch switch S₇ is open --- In this case, the contents of the control command signals are all "0" so that all valves 5a to 5c are deenergized, the opening angle of the throttle valve is decreased, and the cruise speed control described above is released. When the plurality of determination factors, i.e., the outputs of the RS F/F 21, NOR gate 23, watchdog timer 25, the vehicle speed determining circuit 29, and inverter 17 are in the low level states, the output signal of the AND gate 22 is turned to the low level to render the transistor Q5 in the non-conducting state. Thus, the energization current to the coil 11 is not supplied and the power supply relay 9 remains in the off hold state. In addition, since at this time the power supply to the control valves 5 (5a to 5c) is halted, the normal run using an accelerator pedal can be carried out. Since, in the system and method for automatically controlling a vehicle speed to a desired cruise speed according to the present invention, when at least one of the plurality of determining factors to determine whether the microcomputer 3 can execute the cruise speed control does not satisfy a condition to enable the cruise control run, the power supply to the actuator is inhibited, a more safe and stable run of the vehicle can be achieved with the system. The present invention is also applicable to an automatic transmission mounted vehicle and, in this case, a cut relay and inhibitor switch are used in place of the brake switch and clutch switch.

Claims: A cruise speed control fail safe system comprising: speed sensor means (27) for measuring a current vehicle speed; a operation unit (1) comprising at least one command switch (S1) for operatively outputting command signals on a cruise speed control; a throttle actuator (5) for controlling the vehicle speed in response to a control command signals thereto, in the case of activated cruise speed control; a microcomputer (3) for outputting the control command signals to control said throttle actuator (5) in accordance with the contents of the command issued from said operation unit (1) and the vehicle speed signal from said speed sensor means (27) so that the vehicle speed is maintained at a desired cruise speed determined by the command switch operation; first inhibiting means including switches (S6, S7) for halting the power supply to said actuator (5) when the brake system or clutch system is operated under cruise control operation; and a vehicle speed determining circuit (29) connected to the speed sensor means (27) for determining whether the current vehicle speed falls in within a predetermined cruise speed control allowable range and generating a control signal; second inhibiting means (22, Q5) activated by said control signal for inhibiting an activation of said actuator (5) when the vehicle speed is out of the predetermined cruise speed control allowable range; characterized in that the system includes means (17, 23, 19, 33, 31, 22; 21, 22; 25, 22) for activating said second inhibiting means (22, Q5) for interrupting the power supply to said actuator (5) so as to inhibit cruise speed control when either/both of the following conditions is/are detected: that the vehicle speed is out of said predetermined cruise speed control allowable range, and/or that the microcomputer (3) is not executing a program normally. A cruise speed control fail safe method comprising the steps of measuring a current vehicle speed; issuing commands on a cruise speed control; in the case of actuated cruise speed control outputting control command signals to control the vehicle speed by a throttle actuator in accordance with the contents of the issued commands and the measured current vehicle speed; halting by first inhibiting means the power supply to said actuator when the brake system or clutch system is operated under cruise control operation; determining whether the vehicle speed is out of a predetermined cruise speed control allowable range and inhibiting an activation of said actuator by second inhibiting means to interrupt the cruise speed control when said vehicle speed is out of the predetermined cruise speed control allowable range, characterized in that the power supply to said actuator is interrupted by said second inhibiting means when either/both of the following conditions is/are detected: that the vehicle speed is out of said predetermined cruise speed control allowable range and/or the microcomputer (3) is not executing a program normally. A method according to claim 2, characterized in that as one condition to enable the cruise control run, it is checked whether one of said commands is issued. A method according to claim 2 or claim 3, characterized in that as one condition to enable the cruise control run it is checked whether the vehicle speed is within a cruise speed control allowed range. The method according to one of the claims 2-4, characterized in that as one condition to enable the cruise control run it is checked whether the watchdog timer means proves correct operation of the microprocessor which is provided for outputting said control command signals. A method according to one of the claims 2-5, characterized in that as one condition to enable the cruise control run it is checked whether a control command signal is of high level while a cruise signal, which is issued by said microcomputer when cruise speed control is activated, is also of high level.

Inventors: HIROSHI INOUE, HIROYUKI NOMURA, ISAO YAMAMOTO, KAZUYUKI MORI, KINICHIRO NAKANO, KIYOSHI YOSHIDA, KOICHI SUZUKI, YOSHIYUKO ETOH, HIROSHI, INOUE, HIROYUKI, NOMURA, ISAO, YAMAMOTO, KAZUYUKI, MORI, KINICHIRO, NAKANO, KIYOSHI, YOSHIDA, KOICHI, SUZUKI, YOSHIYUKO, ETOH
Applicants: NISSAN MOTOR, NISSAN MOTOR CO., LTD.
Application year: 1988
Main classification: B60K31
IPC codes: B60K31, F02D29, B60W30