Vehicle control system

A vehicle control system is provided for a vehicle that is steered by steer-by-wire, the system including a battery mounted in the vehicle, a steer-by-wire steering system that turns wheels by an electric motor that is operated by electric power supplied from the battery, a steering controller for controlling the operation of the steer-by-wire steering system, and an engine controller for controlling, by electric power supplied from the battery, the operation of an engine for making the vehicle travel. A booster circuit boosts the voltage applied to the steering controller so that, when the voltage of the battery decreases, the voltage applied to the engine controller falls below its minimum operating voltage before the voltage applied to the steering controller falls below its minimum operating voltage. With this arrangement, it is possible to provide fail-safe operation when there is a decrease in the voltage of the battery which supplies electricity to the steering controller.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2003-193299, filed Jul. 14, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle control system that includes a battery mounted in a vehicle, an electrically operated device that is operated by electric power supplied from the battery and drives a critical system of the vehicle, electrically operated device control means for controlling the operation of the electrically operated device, and engine control means for controlling, by electric power supplied from the battery, the operation of an engine for making the vehicle travel.

2. Description of the Related Art

Japanese Patent Application Laid-open No. 11-5550 and Japanese Patent No. 3364673 disclose steer-by-wire (SBW) steering systems in which mechanical connection between a steering wheel and a steering gearbox is absent, and steering control means controls the drive of an electric motor provided in the steering gearbox based on an electrical signal generated by operation of the steering wheel, thereby turning left and right wheels.

However, because mechanical connection between the steering wheel and the steering gearbox is absent in the steer-by-wire steering system and the wheels are turned by driving the steering gearbox by the driving force of the electric motor which employs a battery as a power source, if the voltage of the battery that supplies electricity to the steering control means decreases, appropriate turning of the wheels may become impossible.

SUMMARY OF THE INVENTION

The present invention has been achieved under the above-mentioned circumstances, and it is an object thereof to provide fail-safe operation when there is a decrease in the voltage of a battery that supplies electricity to an electrically operated device that drives a critical system of the vehicle.

In order to accomplish this object, in accordance with a first aspect of the present invention, there is proposed a vehicle control system comprising: a battery mounted in a vehicle; an electrically operated device that is operated by electric power supplied from the battery and drives a critical system of the vehicle; electrically operated device control means for controlling the operation of the electrically operated device; and engine control means for controlling, by electric power supplied from the battery, the operation of an engine for making the vehicle travel, wherein the vehicle control system further comprises a booster circuit that boosts the voltage applied to the electrically operated device control means so that, when the voltage of the battery decreases, the voltage applied to the engine control means falls below a minimum operating voltage of the engine control means before the voltage applied to the electrically operated device control means falls below a minimum operating voltage of the electrically operated device control means.

With this arrangement, when the voltage of the battery that supplies electric power to the electrically operated device control means and the engine control means decreases, the voltage applied to the electrically operated device control means is boosted by the booster circuit so that the voltage applied to the engine control means falls below its minimum operating voltage before the voltage applied to the electrically operated device control means falls below its minimum operating voltage. Therefore, it is possible to ensure the safety of the vehicle by stopping the engine before the electrically operated device control means becomes inoperable due to the decrease in voltage. Furthermore, such a voltage decrease is often caused by malfunction of a power generation system, but because the engine is stopped, electric power that would have been consumed by the engine control means can be distributed to the electrically operated device control means, so that the function of the critical system of the vehicle can be maintained for as long as possible.

Furthermore, in accordance with a second aspect of the present invention, there is proposed a vehicle control system comprising: a battery mounted in a vehicle; an electrically operated device that is operated by electric power supplied from the battery and drives a critical system of the vehicle; electrically operated device control means for controlling the operation of the electrically operated device; and engine control means for controlling, by electric power supplied from the battery, the operation of an engine for making the vehicle travel, wherein the vehicle control system further comprises minimum operating voltage increasing means that makes a minimum operating voltage of the engine control means higher than a minimum operating voltage of the electrically operated device control means after the engine control means has started.

With this arrangement, the minimum operating voltage increasing means makes the minimum operating voltage of the engine control means higher than the minimum operating voltage of the electrically operated device control means after the engine control means has started. Therefore, during a process in which the battery voltage decreases, the voltage first falls below the minimum operating voltage of the engine control means to stop the engine, that is, it is possible to ensure the safety of the vehicle by stopping the engine before the battery voltage further decreases and the electrically operated device control means becomes inoperable due to the voltage decrease. Moreover, because the engine is stopped, the electric power that would have been consumed by the engine control means can be distributed to the electrically operated device control means, so that the function of the critical system of the vehicle can be maintained for as long as possible.

Moreover, in accordance with a third aspect of the present invention, there is proposed a vehicle control system comprising: a battery mounted in a vehicle; an electrically operated device that is operated by electric power supplied from the battery and drives a critical system of the vehicle; electrically operated device control means for controlling the operation of the electrically operated device; and engine control means for controlling, by electric power supplied from the battery, the operation of an engine for making the vehicle travel, wherein the vehicle control system further comprises battery voltage monitoring means for monitoring the voltage of the battery, and the battery voltage monitoring means stops the supply of electricity to the engine control means when the voltage of the battery decreases, e.g., below a predetermined threshold level.

With this arrangement, when the voltage of the battery that supplies electric power to the electrically operated device control means and the engine control means decreases, the battery voltage monitoring means stops the supply of electricity to the engine control means. Therefore, it is possible to ensure the safety of the vehicle by stopping the engine before the electrically operated device control means becomes inoperable due to the decrease in voltage. Moreover, because the engine is stopped, the electric power that would have been consumed by the engine control means can be distributed to the electrically operated device control means, and the function of the critical system of the vehicle can be maintained for as long as possible.

A steer-by-wire steering system11of embodiments disclosed herein corresponds to the critical system of the present invention, an electric motor12of the embodiments corresponds to the electrically operated device of the present invention, and steering control means Us of the embodiments corresponds to the electrically operated device control means of the present invention.

The above-mentioned object, other objects, characteristics, and advantages of the present invention will become apparent from an explanation of preferred embodiments that will be described in detail below with reference to the attached drawings.

DESCRIPTION OF THE PRESENT EMBODIMENTS

The first embodiment of the present invention is explained below with reference toFIG. 1.

Steering control means Us employs a vehicle-mounted 12V battery10as a power source and controls the operation of an electric motor12of a steer-by-wire steering system11so as to turn wheels W. A normally open relay14is disposed between the battery10and an H bridge circuit13for pulse width modulation (PWM) control of the electric motor12. The steering control means Us, which controls the H bridge circuit13and the relay14, includes a booster circuit15for boosting the voltage of the battery10by a predetermined value (2V in the embodiment), a regulator17that regulates the voltage boosted by the booster circuit15at a predetermined voltage (e.g., 5V to 3.3V), a microcomputer18that is operated by electric power supplied from the regulator17, a drive interface19that is connected to the microcomputer18and controls the operation of the H bridge circuit13, and a drive interface20that is connected to the microcomputer18and controls the operation of the relay14. An ignition switch21is disposed between the battery10and the steering control means Us. When the ignition switch21is turned ON, operation of the steering control means Us is started. The minimum operating voltage of the steering control means Us is set at 6V in the embodiment.

Engine control means Ue, to which electricity is supplied from the battery10by turning the ignition switch21ON, includes a regulator22that regulates the battery voltage at a predetermined voltage (e.g., 5V), a microcomputer23that is operated by electric power supplied from the regulator22, and a drive interface24that is connected to the microcomputer23and controls the operation of an electronic fuel injection valve of the engine E. The minimum operating voltage of the engine control means Ue is set at 6V in the embodiment.

The operation of the first embodiment having the above-mentioned arrangement is now explained.

When the ignition switch21is turned ON, the battery10is connected to the steering control means Us, and the microcomputer18operates. When the microcomputer18outputs an ON command signal to the relay14via the drive interface20, the relay coil14ais energized so as to turn the relay14ON, and the H bridge circuit13is connected to the battery10. The microcomputer18carries out PWM control of the electric motor12of the steer-by-wire steering system11via the drive interface19based on a vehicle speed V and a steering torque T that is input to the steering wheel by the driver, and as a result a turning angle of the wheels W corresponding to the operation of the steering wheel can be obtained.

When the ignition switch21is turned ON, the engine control means Ue is connected to the battery10, and a voltage of 5V obtained by regulating the battery voltage by the regulator22is applied to the microcomputer23. The microcomputer23controls the amount of fuel injected by the electronic fuel injection valve of the engine E via the drive interface24based on, for example, the degree of throttle opening θTH.

Since the battery10normally has a voltage of about 12V, the steering control means Us and the engine control means Ue, whose minimum operating voltages are both 6V, can be operated without problem, but there are circumstances due to, for example, a malfunction of an AC generator, etc., in which the voltage of the battery10gradually decreases from 12V. When the voltage of the battery10decreases to 6V which is the minimum operating voltage, if the steering control means Us stops functioning prior to the engine control means Ue, there is a possibility that the steering function of the wheels W might not be sufficiently exhibited while the vehicle travels by means of the engine E.

However, in the present embodiment, because the booster circuit15provided in the steering control means Us increases the battery voltage by 2V, a voltage of 6V, which is the minimum operating voltage, can be applied to the regulator17until the battery voltage decreases to 4V, that is, even when the engine control means Ue stops functioning due to the decrease in voltage, the function of the steering control means Us can be maintained for a while. In particular, because the engine control means Ue stops functioning, the load of the battery10is reduced by the amount of electric power that would have been consumed by the engine control means Ue, and the function of the steering control means Us can be maintained for a longer period of time.

In this way, when the battery voltage decreases, the function of the engine control means Ue is stopped prior to the function of the steering control means Us being stopped, and supply of fuel to the engine E is thus cut off before the function of steering the wheels W by the steering control means Us is inhibited, thereby forcing the vehicle to stop and ensuring the safety of the vehicle.

A second embodiment of the present invention is now explained with reference toFIG. 2. In the second embodiment, elements corresponding to those of the first embodiment are denoted by the same reference numerals and symbols as in the first embodiment, and their explanation is omitted.

Steering control means Us of the second embodiment includes, instead of the booster circuit15, a drive interface31connected to a microcomputer18. In the second embodiment, minimum operating voltage increasing means34including a normally closed relay32and a zener diode33connected in parallel to the relay32, is connected between a battery10and engine control means Ue, and a relay control switch35is connected between the drive interface31and a relay coil32a.The breakdown voltage of the zener diode33is set at 2V in the embodiment. The relay control switch35is turned ON and OFF by a signal from battery voltage monitoring means36for monitoring the voltage of the battery10.

When the battery voltage monitored by the battery voltage monitoring means36is normal, the relay control switch35is OFF, and thus the normally closed relay32of the minimum operating voltage increasing means34of the engine control means Ue is ON, so that the battery voltage is applied to the regulator22of the engine control means Ue as it is. The operation of the second embodiment in this state is the same as that of the first embodiment described above.

If, for example, the voltage of the battery10gradually decreases from 12V to close to 8V due to a malfunction of an AC generator, etc., the relay control switch35is turned ON by a signal from the battery voltage monitoring means36, and the relay32of the minimum operating voltage increasing means34of the engine control means Ue is turned OFF. As a result, the battery10and the regulator22are connected to each other via the zener diode33, and a voltage that is lower than the battery voltage by 2V which is the breakdown voltage of the zener diode33, is applied to the regulator22. Hence, when the battery voltage decreases to 8V, the voltage applied to the regulator22decreases to 6V which is the minimum operating voltage of the engine control means Ue, supply of fuel to the engine E is forcibly cut off, and the vehicle stops.

During this process, because a battery voltage of 8V, which is higher than 6V that is the minimum operating voltage of the steering control means Us, is applied to the steering control means Us, even when the engine control means Ue stops functioning due to the voltage decreasing, the function of the steering control means Us can be maintained for a while. In particular, because the engine control means Ue stops functioning, the load of the battery10is reduced by the amount of electric power that would have been consumed by the engine control means Ue, so that the function of the steering control means Us can be maintained for a long period of time.

A third embodiment of the present invention is now explained with reference toFIG. 3. In the third embodiment, elements corresponding to those of the second embodiment are denoted by the same reference numerals and symbols as in the second embodiment, and their explanation is omitted.

The third embodiment, which is a modification of the second embodiment, includes a normally closed relay37instead of the minimum operating voltage increasing means34of the second embodiment, and this relay37is turned OFF by a signal from battery voltage monitoring means36.

When the battery voltage monitored by the battery voltage monitoring means36decreases and approaches 6V which is the minimum operating voltage of steering control means Us and engine control means Ue, the relay37is turned OFF by a signal from the battery voltage monitoring means36, and supply of electricity to the engine control means Ue is cut off. As a result, the operation of the engine control means Ue is stopped prior to the operation of the steering control means Us being stopped, and it is possible to cut off the supply of fuel to the engine E so as to stop the vehicle while the function of the steering control means Us is maintained.

Hence, in accordance with this third embodiment, the same effects as in the first and second embodiments can be achieved.

Although embodiments of the present invention are explained above, the present invention can be modified in a variety of ways without departing from the spirit and scope thereof.

For example, in the embodiments, the minimum operating voltage of the steering control means Us coincides with the minimum operating voltage of the engine control means Ue, but it is not necessary for them to be identical to each other.

Furthermore, in the embodiments, the engine control means Ue controls the fuel injection to the engine E, but it may instead, for example, control ignition of the engine E. That is, the invention is not limited to the control means of the disclosed embodiments, but may use other control means as long as the engine E can be stopped.

It is also possible to obtain the same effects as in the present invention if the minimum operating voltage of the steering control means Us is reduced by employing low voltage components for the regulator17and the microcomputer18of the steering control means Us, by making the relay14of the steering control means Us a semiconductor relay, or by providing an internal power source in the steering control means Us.

Moreover, in the embodiments, explanation is given to the arrangement where the engine E is stopped by hardware, but the present invention is applicable to an arrangement where the engine E is stopped by software employing CAN communication, etc., which has become common practice in automobiles in recent years.

Furthermore, the critical system in the present invention is not limited to the steer-by-wire steering system11of the embodiments, and can be applied to any other system that is critical for vehicle safety, such as a brake-by-wire system in which a brake is operated by an electric motor.