FAIL-SAFE SYSTEM IN A POWER REGULATION CIRCUIT FOR AN AUTOMOTIVE ELECTRONIC CIRCUIT

Abstract: A fail-safe system in a power regulation circuit for an automotive electronic circuit such as electronic anti-skid brake control system, which fail-safe system can perform the fail-safe operation even when the power regulation circuit (10) is damaged and thereby the supply voltage from the power regulation circuit (10) varies significantly. The fail-safe system in a power regulation circuit includes a monitor power supply circuit (12) independently of the power regulation circuit. The monitor power supply circuit (12) is adapted to produce a reference signal (E₇) to be compared with the output of the power regulation circuit in a fail-safe circuit. The fail-safe circuit (13) produces an error signal when the output signal value drops below a given threshold defined by the reference signal value to activate an alarm signal generator (20,Tr1,18) and disconnect an actuator controlled by the control system in order to prevent the actuator from malfunctioning due to errors in the control system.

Description: Field of Technology The present invention relates generally to a fail-safe system in a power regulation circuit for an automotive electronic circuit, such as an anti-skid electronic brake control system, for fail-safe control of the electrical voltage to be applied to the electronic circuit. Prior Art US-A-3 874 743 discloses a fail-safe system comprising a power regulation circuit and a monitor power supply circuit both being to be connected directly to the power source of a vehicle. The power regulation circuit provides a regulated output voltage and the monitor power supply circuit provides a reference voltage, both voltages being compared by said comparing means. The comparing means provides a disabling signal to an automotive electric circuit as soon as the regulated output voltage differs from the reference voltage. US-A-4 246 566 discloses a fail-safe system for an automotive electronic circuit which system checks different voltages. As soon as the checked voltage does not keep a predetermined level or as soon as a checked voltage leaves a predetermined range of voltages, a fail-safe signal is provided. Summary of the Invention It is an object of the present invention to provide a very reliable fail-safe system in a power regulation circuit for an automotive electronic circuit. In the inventive system a first voltage dividing means provides a divided regulated voltage and a second voltage dividing means provides during orderly operation of the fail-safe system an upper divided reference voltage being higher than said divided regulated voltage and a lower divided reference voltage being lower that said divided regulated voltage. The comparing means comprises a first comparing circuit and a second comparing circuit both providing disabling signals as soon as said divided regulated voltage is not within the range between said upper and said lower divided reference voltages, however, said first comparing circuit being supplied with said reference voltage as the supply voltage and said second comparing circuit being supplied with said regulated output voltage as the supply voltage. This means that two comparing circuits making the same comparison are provided whereby, however, the circuits are provided with different supply voltages so that there is a high probability that at least all with one comparing circuit will work orderly. Brief Description of the Drawings The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings, which, however, should no be taken as limitative to the invention but for elucidation and explanation only. In the drawings: Fig. 1 is a schematic block diagram of a fail-safe system in a power regulation circuit of an electronic anti-skid brake control system; and Fig. 2 is a circuit diagram of a fail-safe system of the invention. Referring now to the drawings, particularly to Fig. 1, there is illuminated a fail-safe system in a power regulation circuit. The power regulation circuit 10 is connected to an electronic anti-skid control system 24 to supply a given constant voltage of electrical power to the latter. The anti-skid control system 24 is connected to wheel r.p.m. sensors 22a, 22b and 22c to receive sensor signals respectively representative of driving and driven wheel speeds. Based on the sensor signals, the anti-skid control system 24 activates and deactivates electromagnetic actuators 26a, 26b and 26c through transistors Tr₂, Tr₃ and Tr₄. The electromagnetic actuators 26a, 26b and 26c control application and release of wheel cylinders in a hydraulic brake system for preventing vehicle wheels from skidding. The electromagnetic actuators 26a, 26b and 26c are connected to a power source, i.e. a vehicle battery via a relay switch 20a. The power regulation circuit 10 is also connected to a fail-safe circuit 13. To the fail-safe circuit 13 is also connected a monitor power supply circuit 12 which is, in turn, connected to the vehicle battery acting as a power source V B . The fail-safe circuit 13 includes a pair of comparators 14 and 16. The positive input terminal (+) of the comparator 14 is connected to the power regulation circuit 10 via dividing resistor R₁ and to ground via dividing resistor R₂. Likewise, the negative input terminal (-) of the comparator 16 is connected to the power regulation circuit 10 and ground via the dividing resistors R₁ and R₂ respectively. The positive input terminal (+) of the comparator 14 and the negative input terminal (-) of the comparator 16 thus receive the divided voltage V a . Here, assuming the resistance values of the dividing resistors R₁ and R₂ are respectively r₁ and r₂, and the output voltage of the power regulation circuit 10 is E₀, the imput voltage V a to the comparator 14 and 16 from the power regulation can be calculated by the following equation: V a = r₂ r₁ + r₂ × E o On the other hand, the negative input terminal (-) of the comparator 14 is connected to the monitor power supply circuit 13 via dividing resistor R₃, and to ground via dividing resistors, R₄ and R₅. The positive input terminal (+) of comparator 16 is also connected to the monitor power supply circuit 12 via the dividing resistors R₃ and R₄ and to ground via dividing resistor R₅. The input voltages V b and V c respectively applied to the comparators 14 and 16 can be respectively expressed by the following equations: V b = r₄ + r₅ r₃ + r₄ + r₅ × E₁ V c = r₅ r₃ + r₄ + r₅ × E₁ where r₃ is resistance value of resistor R₃ r₄ is resistance value of resistor R₄ r₅ is resistance value of the resistor R₅ E₁ is output voltage of the monitor power supply circuit. Here, as seen from Fig. 1, the comparators 14 and 16 are energized with voltage E₁ from the monitor power supply circuit 12. Therefore, the comparator 14 is adapted to produce a HIGH level comparator signal when the signal voltage V a is larger than that of V b . On the other hand, the comparator 16 is adapted to produce a HIGH level comparator signal when the signal voltage V a is smaller than that of V c . The output terminals of the comparators 14 and 16 are respectively connected to a base electrode of a transistor Tr via respective diodes D₁ and D₂ and a common resistor R₆. The collector electrode of the transistor Tr₁ is connected to a fault indicator lamp 18 and, in turn, to a relay coil 20 which serves as a collector load. The anti-skid brake control system is constructed in per se known circuit construction as disclosed in US-A-3,744,851, for example. Other anti-skid control systems have been disclosed in British Patent Prepublications GB-A-2,061,435, GB-A-2,062,786 and GB-A-2,066,894. The disclosures in the above-referred publications are hereby incorporated by reference. As is well known, the electronic anti-skid control system generally controls application and release of brake pressure in the wheel cylinder in order to control tread/road friction to near the maximum value. The anti-skid control signal to be fed to the electromagnetic actuators 25a, 26b and 26c to control actuation of the fluid pressure in the wheel cylinder of the hydraulic brake system. As will be appreciated, the anti-skid control system can comprise a digital circuit including CMOS and/or TTL elements, or an analog circuit including an operational amplifier, comparators and so forth. Either of the digital and analog circuits would be influenced by variations in the power regulation circuit output voltage. In the case of a TTL-based anti-skid brake control system, the allowable voltage variation of the power regulation circuit 10 is within the range 5.25V - α<E₀<5.25V + α, where α is the allowable voltage variation of the TTL circuit elements. When the power regulation circuit 10 is damaged or malfunctions to produce a higher output voltage than normal, the input voltage V a to the comparators 14 and 16 becomes greater than normal corresponding to the increase of the output voltage of the power regulation circuit. Thus, the input voltage V a becomes higher then the input voltage V b . The comparator 14 thus produces a HIGH level comparator signal. The HIGH level comparator signal of the comparator 14 is fed to the transistor Tr₁ via the diode D₁ and the resistor R₆. The transistor Tr₁ is turned off in response to the HIGH level comparator signal from the comparator 14 to produce a bias voltage at the collector electrode thereof. The bias voltage of the transistor Tr₁ is fed to the indicator lamp 18 to turn the latter on. At the same time, the relay coil is energized by the bias voltage of the transistor Tr₁ to open the relay switch 20a. As a result, the electromagnetic actuators 26a, 26b and 26c are disconnected from the power source, i.e., from the vehicle battery, to be rendered inactive. Alternatively, if damage or malfunction of the power regulation circuit 10 causes a significant drop in the output voltage, the input voltage V a to the positive input terminal of the comparator 14 and the negative input terminal of the comparator 16 becomes lower then normal. This causes the comparator 16 to produce a HIGH level comparator signal to be fed to the transistor Tr₁ via the diode D₂ and the resistor R₆. As in the foregoing case, the transistor Tr₁ is cut-off by the HIGH level comparator signal of the comparator 16 to turn on the indicator lamp 18 and energize the relay coil. As will be appreciated, as long as the power regulation circuit 10 is in the normal state and produces a voltage within the predetermined allowable voltage variation range, the comparator signals of the comparator 14 and 16 are maintained at LOW level to keep the transistor Tr₁ ON. In this case, the indicator lamp 18 is maintained OFF and the relay coil 20 is deenergized to allow power supply to the electromagnetic actuators 26a, 26b and 26c to make the anti-skid control system active. It should be noted that, in order to prevent the fail-safe circuit 13 from malfunctioning due to sudden significantly HIGH voltages, the comparator 14 and 16 must be designed to withstand even substantially HIGH voltages, i.e., voltages exceeding 12V. This will ensure the operation of the fail-safe system of the shown embodiment. Referring to Fig.2, there is illustrated a fail-safe circuit of the invention This fail-safe circuit 113 comprises two pairs of comparators 114, 116 and 130 and 132. The power regulation circuit 10 and ground are connected to positive input terminals (+) of the comparators 114 and 130 and to negative input terminals (-) of the comparator 116 and 132, via dividing resistor R₁₁ and R₁₂ respectively. The monitor power supply circuit 12 and ground are connected to the negative input terminal (-) of the comparator 14 and the positive input terminal (+) of the comparator 16 via the dividing resistors R₁₃, R₁₄ and R₁₅. As set forth, the positive input terminal of the comparator 14 and the negative input terminal of the comparator 16 receive divided voltage V a . The negative input terminal of the comparator 14 receives the divided voltage V b and the positive input terminal of the comparator 16 receives the divided voltage V c . Thus, the comparators 114 and 116 act similarly to the foregoing system on the transistor Tr₁₁ via the diodes D₁₁ and D₁₂ and the common resistor R₁₆ when the input voltage V a from the power regulation circuit 10 is out of a given range defined by the input voltage from the monitor power supply circuit 12 and resistors R₁₃, R₁₄ and R₁₅. The indicator 118 is turned on and the relay coil 120 is energized when the transistor is cut-off. The comparators 114 and 116 receive power from the monitor power supply circuit 12 for operation and, in turn, the comparators 130 and 132 receive power from the power regulation circuit 10. The comparators 130 and 132 are adapted to monitor the monitor power supply circuit 12 for malfunctions. As with the comparators 114 and 116, the positive input terminal of the comparator 130 and the negative input terminal of the comparator 132 receive divided voltage V a . The negative input terminal of the comparator receives the input voltage V b from the monitor power supply circuit 12 via the dividing resistors R₁₃, R₁₄ and R₅. Similarly, the divided voltage V c from the dividing resistors R₁₃, R₁₄ and R₁₅ is applied to the positive input terminal of the comparator 132. The comparator 130 thus compares the input voltages V a and V b and produces a HIGH level comparator signal when the input voltage V a is larger than V b . On the other hand, the comparator 132 is adapted to produce a HIGH level comparator signal when the input voltage V a is less than V c . The comparators 130 and 132 are connected to the base electrode of the transistor Tr₁₁₀ via respective diodes D₁₃ and D₁₄ and a common resistor R₁₇. The transistor Tr₁₁₀ is responsive to application of a HIGH level comparator signal via the resistor R₁₇ to turn OFF. When the transistor Tr₁₁₀ is applied to the indicator lamp 118 and the relay coil 120. Thus, the indicator lamp 118 is turned ON and the relay coil 120 is energized. Therefore, in the shown embodiment, the fail-safe circuit 113 monitors not only the output voltage of the power regulation circuit 10 but also the output voltage of the monitor power supply circuit 12.

Claims: A fail-safe system in a power regulation circuit for an automotive electronic circuit comprising a power regulation circuit (10) to be connected to a power source (V B ) and adapted to provide a regulated output voltage (E₀) to said automotive electronic circuit (24), first voltage dividing means (R11, R12) connected to the output of the power regulation circuit (10) for providing a divided regulated voltage (V a ), a monitor power supply circuit (12) to be connected to said power source (V B ) and adapted to produce a reference voltage (E₁), and comparing means (114, 116, 130, 132) for comparing said divided regulated voltage (V a ) with said reference voltage (E₁) and for providing a disabling signal to said automotive electric circuit (24) as soon as said divided regulated voltage (V a ) is not in agreement with the comparison condition, characterized in that second voltage dividing means (R13, R14, R15) are connected to the output of the monitor power supply circuit ( 12) for providing during orderly operation of the fail-safe system an upper divided reference voltage (V b ) being higher than said divided regulated voltage (V a ) and a lower divided reference voltage (V c ) being lower than said divided regulated voltage (V a ), and in that said comparing means comprises a first comparing circuit (114, 116) and a second comparing circuit (130, 132) both providing disabling signals as soon as said divided regulated voltage (V a ) is not within the range between said upper and said lower divided voltages (V b , V c ), however, said first comparing circuit being supplied with said reference voltage (E₁) as the supply voltage and said second comparing circuit being supplied with said regulated output voltage (E₀) as the supply voltage.

Inventors: MATSUDA, TOSHIRO
Applicants: NISSAN MOTOR CO., LTD.
Application year: 1982
Main classification: B60T17
IPC codes: H02H3, H02H7, B60R16, B60T8