A system and method for automatically controlling a vehicle speed to a desired cruise speed with a release function

Abstract: A system and method for automatically controlling a vehicle speed to a desired cruise speed are disclosed in which in addition to a control unit (30) and a throttle actuator (31) through which an opening angle of an engine throttle valve is adjusted so that the vehicle speed detected by a vehicle speed sensor (20) coincides with a target cruise speed set by a vehicle driver through a set switch (17,18), a vehicle speed determining circuit (40) is provided for determining whether the vehicle speed detected by the ve­ hicle speed sensor (20) exceeds a lowest control unit and throttle actuator (31) becomes effective. When the vehicle speed is below the lowest speed limit, the power supply (43) to the throttle actuator (31) is interrupted so that the cruise control by means of the throttle actuator is can­ celled.

Description: The present invention relates to a system and method for automatically controlling a vehicle speed to a desired cruise speed according to the preambles of claims 1 and 10, respectively. Recently, vehicle speed automatically controlling systems have been installed in vehicles by means of which the vehicles automatically run at desired cruising speeds (so called ASCD (Automatic Speed Control) Devices). In such vehicles, operators (drivers) accelerate the vehicles to reach speeds at which the drivers desire the vehicles to cruise. When the vehicles become run at the desired speeds, the drivers recognize that the vehicles run at the desired cruising speeds through speedometers and the drivers set the vehicle speeds through set buttons. At this time, the systems adjust opening angles of throttle valves or carburetors so that the actual vehicle speeds coincide with the set vehicle speeds. In EP-A-0171287, a system and method of the type mentioned at the beginning are disclosed. Another vehicle speed automatically controlling system as described above is exemplified by JP-A-59-58134, published on April 3, 1984. When such vehicle speed automatically controlling systems are installed in the vehicles, it is convenient for the driver since no depression on an accelerator pedal is needed to cruise the vehicle during run on a freeway. Furthermore, the automatic speed controlling function described above is released when the driver actuates a clutch pedal or brake pedal. In addition, when the accelerator pedal is depressed, the vehicle speed can exceed the set cruising speed . When the accelerator pedal depression is halted, the vehicle can again run at the set cruise speed after the speed reduction caused by an engine brake. A microcomputer is installed which controls a throttle valve actuator according to a vehicle speed difference between the actual vehicle speed and set vehicle speed in the above-described vehicle speed controlling system. An opening angle of a throttle valve is adjusted through the actuation of the throttle actuator. In the system of EP-A-0171287, the microcomputer is adapted to cancel the automatic speed control process if the actual vehicle speed does not fall in a predetermined speed range (for example between 48 and 136 km/h) in which the speed control works adequately. In the system of JP-A-59-58134 the microcomputer is adapted to inhibit a power supply to the throttle actuator if the actual vehicle speed is inappropriate for the cruising speed (for example 45 km/h or below) since it is uncontrollable speed. However, the controlling means constituted by the microcomputer described above often erroneously detects the vehicle speed being unsuitable for adequate speed control as a controllable vehicle speed so that inappropriate automatic vehicle speed control is performed. It is therefore an object of the present invention to provide a system and method for automatically controlling a vehicle speed to a desired cruising speed of the above type in which the function of the automatic speed controlling can positively be released if the vehicle speed does not fall in a predetermined speed range in which the automatic vehicle speed control is performed adequately. This object is achieved by a system according to claim 1 and by a method according to claim 10. Further advantageous features follow from the sub-claims. In the following, preferred embodiments of the present invention are described with reference to the accompanying drawings. Figs. 1 (A) and 1 (B) are integrally a schematic circuit wiring diagram of a system for automatically controlling a vehicle speed to a desired cruising speed in a preferred embodiment according to the present invention. Figs. 2 and 3 are signal waveform charts of a vehicle speed determining circuit shown in Fig. 1 (B). Fig. 4 is a schematic circuit block diagram of an electric field detecting apparatus. Fig. 5 is a schematic connection diagram of another preferred embodiment according to the present invention. Reference will hereinafter be made to the drawings in order to facilitate understanding of the present invention. Fig. 1 is an electrical circuit of a system for automatically controlling a vehicle speed to a desired cruise speed according to the present invention. In Fig. 1, a DC power supply (battery) denoted by 1 is connected between a horn 7 and ground. A switch 2 called an ignition switch is connected between a positive pole of the battery 1 and a fuse 3. A horn relay 5 connected to a horn switch 6 is connected between the positive pole of the battery 1 and horn 7. When the horn switch 6 is turned on, the horn 7 is sounded. Numeral 8 denotes a cruising main switch which can be placed on an ON position or on an OFF position. Numeral 9 denotes a cruise relay connected in series with the ignition switch 2 via the fuse 3. The main switch 8 is a self-holding switch which is self-held by means of the cruising relay 9 and is installed on a part of an instrument panel (not shown ). Numeral 10 denotes a main lamp which illuminates when the main switch 8 is turned on. A normally closed clutch switch 11 is connected to the self-holding relay 9 and is open when a clutch of a vehicular transmission is depressed and a normally closed brake switch 12 is connected to the clutch switch 11 and is open when a brake pedal is depressed. These clutch and brake switches are connected to an input terminal T 1 of a control unit 30. It is noted that a cut relay and inhibitor switch are connected in series in place of the brake and clutch switches 11 and 12 in the case of an equipment of an automatic transmission on the vehicle. Furthermore, a stop lamp 16 which illuminates when a stop lamp switch 15 is turned on upon a depression of the brake pedal. A set/cruise switch 17 which is turned on when the vehicle speed is set as the cruising speed and the set vehicle speed is reduced during the cruising run is connected to an input terminal T 2 of the control unit 30. Numeral 19 denotes a cancel switch which is turned on when the driver has an intention to release forcibly the cruising mode therethrough. It is noted that these switches are installed on a part of a steering wheel. One contact of each switch 17, 18, and 19 is connected to either of the input terminals T 2 and T 3 of the control unit 30. Numeral 20 denotes a vehicle speed sensor outputting the vehicle speed signal and which is connected to the control unit 30. The control unit 30 includes a microcomputer which receives on and off signals from the various switches, discriminates various conditions on the basis of such on and off signals, and controls an actuator 31 enclosed with a dot line, for actuating a throttle valve provided in the vehicular engine. The actuator 31 is of a positive pressure type adjusting an opening angle of the throttle valve using a compressed air, comprising a release valve 31a for discharging the compressed air from a compressed air tank to the atmosphere, an air valve 31b for opening the compressed air to the atmosphere, and an air supply valve 31c for supplying the compressed air. A throttle wire connected to a diaphragm actuated by these valves causes control for the opening angle of the throttle valve. A tank for reserving the compressed air is installed as a drive source of the actuator 31. A pressure switch 31d is installed in the tank which is turned on when the compressed air pressure exceeds a constant value. When the pressure switch 31d is turned on, a motor relay 31e is energized so that its normally closed contact is open so as to interrupt the power supply to a motor 31f. Thus, the operation of the compressor is halted, thus halting the increase in the compressed air tank. In this way, the air pressure in the compressed air is held constant. A vehicle speed determining circuit 40 is connected to the vehicle speed sensor 20. The vehicle speed determining circuit 40 is installed independently of the control unit 30. An output signal of the vehicle speed determining circuit 40 is supplied to an AND circuit 41. A transistor 42 with its bias circuit (not shown) is connected to an output end of the AND circuit 41. A relay having a normally open contact 43 is connected between an input terminal T 5 of the control unit 30 and actuator 31. The relay 43 supplies the power to the actuator 31 when the transistor 42 is conducted and a magnet portion thereof is energized. The detailed construction of the vehicle speed determining circuit 40 will be described below. A base of a transistor T r is connected with a resistor R 1 and a capacitor C 1 for eliminating noise and the output end of the vehicle speed sensor 20 to receive an analog quantity indicating the vehicle speed information. A collector of the transistor T r is connected to a constant voltage (e.g., dc 5 volts) supply circuit (not shown) provided in the control unit 30 via a resistor R 2 . A pulse signal A 1 having a rectangular shape and a period corresponding to the vehicle speed is supplied to a monostable multivibrator 40a. The pulse signal A 1 is generated in response to an intermittent signal derived from the vehicle speed sensor 20 by means of the transistor T r . The monostable multivibrator 40a is connected to an inverting input terminal of a comparator 40b via a resistor R 3 and a capacitor C 2 . The multivibrator 40a produces a rectangular pulse signal A 2 having a pulsewidth of T as shown in Figs. 2 and 3 in accordance with the input signal A 1 at each rising edge of the input signal A 1 . The pulse signal A 2 is smoothed by means of the resistor R 3 and the capacitor C 2 so that an average voltage signal A 3 of the pulse train signal A 2 is supplied to the inverting input terminal of the comparator 40b. In a case when the vehicle speed V is below a predetermined speed V TH (for example, 45 Km/h), a value V L of the voltage signal A 3 will be described with reference to Fig. 2. The value V L is expressed as follows. V L = 5 x T x f L , , wherein f L denotes an inverted number of the pulse period of the pulse signal A 1 ,i.e., the frequency of the pulse signal A 1 when the vehicle speed V is below the predetermined vehicle speed V TH . Similarly, when the vehicle speed V is above the predetermined vehicle speed V TH , the value V H of the voltage signal A 3 is expressed below. V H = 5 x T x f H , wherein f H denotes the inverted number of the pulse signal period, i.e., the frequency of the pulse signal A 1 when the vehicle speed V is above the predetermined speed V TH . Since the frequency of the pulse signal A 1 becomes large as the vehicle speed increases, the value of the voltage signal A 3 becomes increased. As the vehicle speed increases, the value of the voltage signal A 3 is also increased. It is noted that the value of the predetermined speed V TH is set with the speed below which the cruising speed is not appropriate to be taken into consideration. In addition, a non-inverting input terminal of the comparator receives a reference voltage signal V o . The value of the reference voltage signal V o is set as follows. V L < V o < V H In the above inequalities, V L denotes the value of the voltage signal A 3 when the vehicle cruises at a low speed and V H denotes the other value of the voltage signal A 3 when the vehicle cruises at a high speed. Therefore, when the value of the voltage signal A 3 is below the reference voltage signal V o , the comparator 40b outputs a high level signal A 4 . When the value of the voltage signal exceeds the reference voltage signal V o , the comparator 40b outputs a low level signal A 4 The output signal of the comparator 40b is supplied to an inverter 40c and the one input terminal of the AND circuit 41. Hence, the low level signal is supplied to the AND circuit 41 when the vehicle speed is low and the high level signal is supplied to the AND circuit 41 when the vehicle speed is high. An output signal of an electric field intensity determining circuit 44 shown in Fig. 4 is supplied to the other input terminal of the AND circuit 41. Although a protective circuit is provided adjacent to the control unit 30 against a strong electric field intensity, the control unit 30 may often errorneously operate if the control unit is exposed to a strong electric field exceeding a dielectric strength of the protective circuit. Therefore, an electric field intensity measuring circuit 47 measures an induced voltage of a loop coil 46 wound around a harness 45 extended about a connector part of the control unit as shown in Fig. 4. The measured voltage value is checked to determine whether it is above a predetermined voltage value by means of an electric field intensity determining circuit 44. If the measured voltage value is above the predetermined value (strong electric field), the L level signal is supplied to the AND circuit 41. If the measured voltage value is below the predetermined volt value, the H level signal is supplied to the AND circuit 41. Consequently, if both output signals of the vehicle speed determining circuit 40 and electric field intensity determining circuit 44 are at the H level, the AND circuit 41 outputs the H level signal so that the transistor 42 is conducted and the relay 43 is turned on to supply the power to the actuator 31. Next, the operation of the preferred embodiment shown in Figs. 1 to 4 will be described below. First, when the main switch 8 is turned on with the ignition switch 2 turned on, the cruising relay 9 is energized and is held in the ON position so that the main lamp 10 is illuminated. Then the input terminals T 1 and T 4 of the control unit receive the power supply voltage from the battery 1. The operation of the preferred embodiment in a case when the vehicle runs at a low speed, i.e., the vehicle speed V is below the predetermined speed V TH will be described below. During such a low speed as described above, the power supply is not supplied to the output terminal T 5 due to an issue of an instruction from the microcomputer of the control unit 30. Consequently, the actuator 31 is not operated. That is to say, although not shown in the drawings, the input terminal T 1 of the control unit 30 is connected to the output terminal T 5 via a normally open contact of a relay, a coil thereof receiving the power supply by means of a switching transistor conducted upon receipt of an ON signal from the microcomputer. However, when the actual vehicle speed calculated on the basis of the signal derived from the vehicle speed sensor 20 is below V TH , the microcomputer does not output to the above-described switching transistor so that the input terminal T 1 is not connected to the output terminal T 5 . However, even if the control unit 30 errorneously detects the vehicle speed so that the input terminal T 1 is connected to the output terminal T 5 , the power supply to the actuator 31 cannot be carried out since the relay 43 remains off. In details, When the vehicle speed determining circuit 40 calculates the vehicle speed V on the basis of the vehicle speed indicative signal from the vehicle speed sensor 20 in terms of an analog quantity and determines that the calculated vehicle speed is below the predetermined vehicle speed V TH , the L level signal is outputted to the AND circuit 41, thus the output signal of the AND circuit 41 indicating the L level. Thus, the transistor 42 is not conducting so that the relay 43 remains off. Next, when the vehicle speed V is above the predetermined vehicle speed V TH , the microcomputer issues the instruction so that the input terminal T 1 is connected to the output terminal T 5 . The vehicle speed determining circuit 40, at the same time, outputs the H level signal to the AND circuit 41. If the electric field intensity is below the predetermined value, the electric field intensity determining circuit 44 outputs the H level signal. Thus, the AND circuit 41 outputs the H level signal so that the transistor 42 is conducting so that the relay 43 is turned on to supply the power to the actuator 31. It is noted that when the electric field intensity determining circuit 44 determines the electric field intensity and outputs the L level signal, the power supply to the actuator 31 is interrupted. After the relay 43 is turned on and the vehicle speed reaches a desired vehicle speed, the driver can freely depress the set/cruise switch 17. When the set/cruise switch 17 is depressed, the control unit 30 stores the set vehicle speed and compares the actual vehicle speed signal outputted from the vehicle speed sensor with the set vehicle speed. Then, the control unit 30 controls according to, e.g., the difference therebetween the open and close of the release valve 31a, the air valve 31b, and supply valve 31c. That is to say, when the vehicle speed is above the set vehicle speed, the control unit 30 closes the release valve 31a, opens the air valve 31b, and closes the supply valve 31c, thus the throttle valve being directed toward the close position. When the vehicle speed is below the set vehicle speed, the control unit 30 closes the release valve 31a, the air valve 31b, and opens the supply valve 31c, thus the throttle valve being directed toward the open position. In this way, the opening angle of the throttle valve being adjusted so that the engine revolution is controlled so that the vehicle speed settles the set vehicle speed. During the cruise control described above, the driver depresses the clutch pedal or brake pedal. At this time, the clutch switch 11 or brake switch 12 is open so that the supply of the power to the input terminal T 1 of the control unit 30 is interrupted so that the actuator 31 receives no power supply. Thus, the cruise control is also interrupted. The same interruption of the cruise control is carried out by the turn off of the cruise main switch 8. On the other hand, a cancel switch 19 is provided which is turned on so that the input terminals T 2 and T 3 receive simultaneously the power supply voltage, thus stopping the vehicle speed control operation. During the cruise control, if the driver continues to depress the accelerator switch 18 to increase the set vehicle speed and the vehicle speed reaches the new desired vehicle speed, the driver releases the switch 18. At this time, the vehicle speed is set to the new desired vehicle speed. If the driver continuous to depress the set/cruise switch 17 to decrease set vehicle speed during the cruise control, the vehicle speed is decreased due to the engine braking. When the vehicle speed reaches the new desired vehicle speed, the driver releases the set/cruise switch 17 so that the vehicle speed is settled to the new set vehicle speed. Although in the above-described preferred embodiment the analog vehicle speed determining circuit 40 is used as the vehicle speed determining means, such a switch as shown in Fig. 5 may be utilized. In details, the switch including a movable contact 52 having a constant length and which is extended on a part of a peripheral edge of an insulating disc plate 51 rotating with a pointer 50 of a speedometer and a fixed contact 53 fixed on a speedometer side surface is connected between the output terminal T 5 of the control unit 30 and the actuator 31. When the vehicle stops or the vehicle speed is below the predetermined vehicle speed, the movable contact 52 is not contacted with the fixed contact 53 so that no power supply is received by the actuator 31. However, when the vehicle speed increases, the insulating disc plate 51 rotates in a clockwise direction as viewed from Fig. 5. When the vehicle speed exceeds the predetermined value (for example, 45 Km/h), the movable contact 52 is contacted with the fixed contact 53 so that the actuator 31 receives the power supply. In this way, when the vehicle speed is below the predetermined value, the contacts 52, 53 do not contact with each other so that the power supply to the actuator 31 is interrupted. As described hereinabove, since in the automatic vehicle speed controlling system and method according to the present invention the vehicle speed determining means is provided in addition to the controlling means for the actuator, the vehicle speed determining means causes the interruption of the power supply to the actuator upon the determination that the vehicle speed is below the predetermined vehicle speed (lower limit speed). Consequently, when the vehicle speed is below the predetermined speed, the cruising control operation can more positively be interrupted without failure. It will fully be appreciated by those skilled in the art that the foregoing description is made in terms of the preferred embodiments and various changes and modifications may be made without departing from the scope of the present invention which is to be defined by the appended claims.

Claims: A system for automatically controlling a vehicle speed to a desired cruise speed, comprising: (a) a vehicle speed sensor (20) for detecting the vehicle speed and outputting a signal indicative thereof; (b) a switch (17,18,19) for setting a current vehicle speed as the desired cruise speed; and (c) a control unit (30) including a microcomputer and adapted to compare the detected speed with both the desired cruise speed and a predetermined vehicle speed range in which the control unit (30) works adequately, and (c1) upon determining the detected speed being within the predetermined range, to actuate an engine driving force adjusting mechanism (31) installed in a vehicular engine so that the vehicle speed is maintained at the desired cruise speed, and (c2) upon determining the detected speed falling outside the predetermined range, to instruct first interrupt means to interrupt power supply to the actuating mechanism (31) for withholding the automatic speed control, characterized in that (d) a vehicle speed determining unit (40;51,52,53) is installed independently from the control unit (30) and is adapted to independently determine whether the detected vehicle speed falls in the predetermined speed range, and (c) a second interrupt means (41,42,43;51,52,53) is connected to the vehicle speed determining unit (40;51,52,53) for interrupting : power supply of said engine driving force adjusting mechanism (31) independently from the first interrupt means if the vehicle speed determining unit (40;51,52,53) determines that the detected vehicle speed does not fall in said predetermined speed range. A system according to claim 1, characterized in that an electric field determining unit (44,46,47) is adapted to determine whether an electric field in the environment of the control unit (30) falls in a predetermined field range in which the control unit (30) works adequately, and is connected to the interrupt means (41,42,43) which is adapted to interrupt the power supply of the engine driving force adjusting mechanism (31) if the determined electric field does not fall in said predetermined field range. A system according to claim 1 or 2, characterized in that said predetermined speed range is defined by those vehicle speed values being greater than a predetermined speed value (V TH ). A system according to any of the preceding claims, characterized in that said engine driving force adjusting mechanism comprises a throttle actuator (31) linked to an engine throttle valve and having electromagnetic valves (31a,31b,31c) through which air pressure applied to a diaphragm is adjusted to control an opening angle of the throttle valve independently of an accelerator. A system according to claim 4, characterized in that said interrupt means (41,42,43;51,52,53) is adapted to interrupt a power supply to said electromagnetic valves (31a,31b,31c). A system according to claim 3, characterized in that said vehicle speed determining unit (40) comprises a monostable multivibrator circuit (40a) which receives said signal of the vehicle speed sensor (20), and which outputs a pulse signal (A 2 ) with a predetermined pulsewidth and a frequency (f L ,f H ) corresponding to the vehicle speed; a smoother (R 3 ,C 2 ) for smoothing said pulse signal (A 2 ); a comparator (40b) for comparing the smoothed signal (A 3 ) from the smoother (R 3 ,C 2 ) with a reference signal (V O ), the reference signal (V O ) being set to a voltage corresponding to said predetermined speed value (V TH ), and for outputting a high level signal (A 4 ) when said smoothed signal (A 3 ) is smaller than the reference signal (V O ); and an inverter (40c) connected to the comparator (40b). A system according to claim 6, characterized in that said interrupt means comprises an AND circuit (41) connected to the inverter (40c) and a relay circuit (43) which turns on to connect the power supply to the throttle actuator (31) upon receipt of a high level signal from said AND circuit (41). A system according to claims 2 and 7, characterized in that said electric field determining unit comprises a coil (46) wound around the control unit (30); an electric field intensity measuring circuit (47) for measuring an electric field intensity in the environment of the control unit (30) using said coil (46); and an electric field intensity determining circuit (44) for determining whether the electric field intensity exceeds a predetermined value and for outputting a low level signal to said AND circuit (41) when the electric field intensity exceeds said predetermined value. A system according to any of claims 1 to 5, characterized in that said vehicle speed determining unit comprises a switch including a movable contact (52) having a constant length defining said speed range and extended on a part of a peripheral edge of an insulating disc plate (51) rotating with a pointer (50) of a speedometer, and including a fixed contact (53) extended on a side surface of the speedometer, the switch being connected to an output terminal (T 5 ) of the control unit (30) and to said engine driving force adjusting mechanism (31), the switch being turned on to supply the power to the engine driving force adjusting mechanism (31) with the movable contact (52) contacted with the fixed contact (53) when the vehicle speed indicated by the speedometer falls in said speed range. A method for automatically controlling a vehicle speed to a desired cruise speed, comprising the steps of: (a) detecting the vehicle speed and outputting a signal indicative thereof, said signal being supplied to a control unit (30) including a microcomputer; (b) setting a current vehicle speed as the desired cruise speed; (c) comparing, in said control unit, the desired cruise speed with the vehicle speed and actuating an engine driving force adjusting mechanism (31) so that the vehicle speed is maintained at the desired cruise speed; (d) determining, in said control unit, whether said detected vehicle speed falls in a predetermined speed range in which the operation of step (c) is performed adequately; and (e) cancelling said operation of step (c) and instructing first interrupt means to interrupt power supply to the engine driving force adjusting mechanism if the detected vehicle speed does not fall in said predetermined speed range, characterized in that a second step of determining whether said detected vehicle speed falls in said predetermined speed range is performed independently of the operation of step (d), and in that said cancellation of step (c) is performed by interrupting power supply of said engine driving force adjusting mechanism (31), independently from said first interrupt means if it has been found in said second determining step that the speed is not within said predetermined range.

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