Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
1999-11-08
2001-02-13
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S071000, 36, 36, C303S011000, C303S113400, C303S115200, C303S122000
Reexamination Certificate
active
06188947
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to vehicle antilock brake systems and in particular to a closed loop method for controlling the speed of a pump motor in an antilock brake system.
An Anti-lock Brake System (ABS) is often included as standard equipment on new vehicles. When actuated, the ABS is operative to modulate the pressure applied to some or all of the vehicle wheel brakes. A typical ABS includes a plurality of solenoid valves mounted within a control valve body and connected to the vehicle hydraulic brake system. The valve body also includes an accumulator for the temporary storage of brake fluid during an anti-lock braking cycle.
A separate hydraulic source, such as a motor driven pump, is usually included in the ABS for reapplying hydraulic pressure to the controlled wheels during an ABS braking cycle. Alternately, the pump can return brake fluid from the accumulator to the vehicle master brake cylinder during an ABS braking cycle. The pump is typically included within the control valve body with the pump motor mounted upon the exterior of the control valve body. The pump motor is usually a direct current motor which operates from the vehicle power supply. Typically, the motor runs continuously during an ABS braking cycle.
An ABS further includes an electronic control module which has a microprocessor. The microprocessor is electrically connected to the pump motor, a plurality of solenoid coils associated with the solenoid valves, and wheel speed sensors for monitoring the speed and deceleration of the controlled wheels. The assembled valve body, motor and control module form a compact unit which is often referred to as an ABS control valve.
During vehicle operation, the microprocessor in the ABS control module continuously receives speed signals from the wheel speed sensors. The microprocessor monitors the speed signals for potential wheel lock-up conditions. When the vehicle brakes are applied and the microprocessor senses an impending wheel lock-up condition, the microprocessor is operative to initiate an ABS braking cycle. During the ABS braking cycle, the microprocessor actuates the pump motor and selectively operates the solenoid valves in the control valve to cyclically relieve and reapply hydraulic pressure to the controlled wheel brakes. The hydraulic pressure applied to the controlled wheel brakes is adjusted by the operation of the solenoid valves to limit wheel slippage to a safe level while continuing to produce adequate brake torque to decelerate the vehicle as desired by the vehicle operator.
The microprocessor includes a memory portion which stores an ABS control algorithm. The ABS control algorithm comprises a set of instructions for the microprocessor which control the operation of the ABS. Typically, the instructions include a set of operational checks which are run during vehicle start up to assure that the ABS is functional. The control algorithm also includes subroutines for monitoring the vehicle operation to detect a potential lock-up of the controlled wheel brakes and for the actual operation of the ABS during an anti-lock braking cycle.
SUMMARY OF THE INVENTION
This invention relates to a closed loop method for controlling the speed of a pump motor in an antilock brake system.
An ABS is typically equipped with a Direct Current (DC) pump motor. DC motors run at a speed which is proportional to the magnitude of the applied voltage. While the voltage level in a vehicle may fluctuate, it will usually remain within a rather narrow range. Accordingly, the DC pump motor operates at a generally constant speed. During operation of the ABS, the pump motor is actuated and generates some noise during operation. Usually, the pump motor noise is masked by other vehicle sounds. However, when the vehicle operates upon a low mu road surface, the ABS can be operative to modify the ABS response to a potential brake lock-up to compensate for the low mu surface. When such a situation occurs, the demand upon the pump is reduced; however, because the pump motor operates at a generally constant speed, the sound of the pump motor may seem loud to the vehicle operator. Similarly, during the final portion of a stopping cycle, the ABS demand upon the pump is again reduced but the pump speed remains generally constant. As the vehicle slows to a stop, the pump motor sound will become more apparent and may be objectionable to the vehicle operator. Thus, it would be desirable to reduce the pump motor noise by controlling the pump motor speed.
The present invention contemplates a system for controlling at least one vehicle wheel brake that includes a pump that supplies pressurized brake fluid to the controlled wheel brake. A motor is connected to the pump for driving the pump and a control valve is connected between the pump and the controlled wheel brake. The control valve is operable to control the flow of pressurized brake fluid from the pump to the controlled wheel brake. The system also includes a sensor for measuring the speed of the pump motor and a controller electrically connected to the pump motor speed sensor and the pump motor. The controller is operative to provide power to the pump motor and to control the pump motor speed as a function of the sensed pump motor speed.
The invention further contemplates that the controller is operable after the pump motor has operated for a predetermined time period to sense the pump motor speed. The controller is further operative to de-energize the pump motor and measure a motor back emf, the controller being operative to convert the measured motor back emf into a sensed pump motor speed. The controller is also operable to determine the difference between the sensed pump motor speed and a predetermined pump motor speed threshold. When the sensed pump motor speed is greater than the pump motor speed threshold the controller maintains the pump motor in the de-energized state. However, when the sensed pump motor speed is less than the pump motor speed threshold the controller energizes the pump motor for a period of time which is a function of the difference between the sensed pump motor speed and the pump motor speed threshold.
When the controller energizes the pump motor, the controller generates a pulse width modulated voltage which is applied to the pump motor. The pulse modulated voltage has a variable duty cycle and a variable frequency which are functions of the difference between the sensed pump motor speed and the pump motor speed threshold.
The controller continues to sense the pump motor speed and to determine the difference between the sensed pump motor speed and the pump motor speed threshold. Additionally, it is contemplated that the predetermined pump motor speed threshold is one of a plurality of predetermined pump motor speed thresholds, with the controller being operative to select one of the plurality of predetermined pump motor speed thresholds for determination of the speed difference. In the preferred embodiment, the selection of a predetermined pump motor speed threshold is determined as a function of duration of a braking cycle.
The invention also contemplates a process for controlling the speed of a pump motor and associated pump for supplying pressurized brake fluid to at least one vehicle wheel brake. The pump motor is connected to a controller, which is operative to supply power to the pump motor. The controller also is connected to a speed sensor for monitoring the pump motor speed. The pump motor is operated for a predetermined time period after which the actual pump motor speed is sensed. The sensed pump motor speed is compared to a predetermined pump motor speed threshold. If the sensed pump motor speed is greater than the pump motor speed threshold the pump motor is de-energized.
The process further contemplates continuing to sense the actual pump motor speed and continuing to compare the sensed pump motor speed to the pump motor speed threshold. If the sensed pump motor speed is less than the pump motor speed threshold, the pump motor is energized by applying a pulse
Cuchlinski Jr. William A.
Kelsey-Hayes Company
MacMillan Sobanski & Todd LLC
To Tuan
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