Modulator noise reduction via motor control

The invention provides a method for controlling a vehicle with a braking system including a modulator pump. A first fluid line can communicate brake fluid from the master cylinder to a brake caliper. An isolation valve including a pressure bypass can be disposed along the fluid line between the master cylinder and the brake caliper. A second fluid line can extend from a first position along the first fluid line between the master cylinder and the isolation valve to a second position along the first fluid line between the isolation valve and the brake caliper. A modulating pump is disposed along the second fluid line to pump fluid to the brake caliper during a controlled brake event. The modulator pump is engaged to pump fluid to the brake caliper until the pressure in the first fluid line reached slightly below the predetermined pressure to prevent the isolation valve from opening in response to excessive pressure.

TECHNICAL FIELD

The invention relates to a braking system for a vehicle and, more specifically, the invention provides a method for controlling a brake pump to reduce noise, especially during driver braking.

BACKGROUND OF THE INVENTION

A braking system of a vehicle can include a control unit for exercising control over the braking system of the vehicle under certain conditions. For example, during movement of the vehicle the control unit can receive signals from various sensors and, based on a control program stored in memory, control the operation of various parts of the braking system including pumps and valves. Specifically, the controller can receive signals from sensors, wherein the signals correspond to existing driving conditions. The controller can receive the signals and quantify the existing driving conditions. These quantified conditions are compared to predetermined values by a processor of the control unit and command signals are emitted in response to these comparisons. Reasons for taking control of the braking system generally relate to enhancing or optimizing vehicle dynamics.

The braking system can include a modulator or modulating pump to apply fluid pressure to a controlled wheel. When the modulator is used to apply pressure to the controlled wheel, prime and isolation valves are energized and the pump motor is turned on. Excess fluid that is pulled from the master cylinder must be relieved in some manner. This normally occurs through the isolation valve when pumping forces overcome the force of the isolation valve and fluid returns to the master cylinder. The forced opening of the isolation valve may cause noise, especially when the master cylinder is generating pressure on the opposite side of the isolation valve, as during driver braking.

SUMMARY OF THE INVENTION

The present invention provides a method for increasing brake pressure including the step of pumping fluid to a brake caliper with a pump and discontinuing the pumping before the fluid pressure causes a bypass valve to open. The braking system can include a first line extending between a master cylinder and a brake caliper. A bypass or bypass-isolation valve can be positioned along the first fluid line between the master cylinder and the brake caliper. The bypass-isolation valve can be in a closed position and forced to an open position in response to a predetermined level of fluid pressure in the fluid line. A second fluid line can extend from the first fluid line to move fluid to the caliper around the bypass-isolation valve. A pump can be disposed along the second fluid line to pump fluid to the brake caliper.

Noise is generated when the bypass-isolation valve is forced to the open position by pump pressure. This noise is especially noticeable when master cylinder pressure is present. The present invention provides for stopping the pump substantially immediately prior to the forced opening of the bypass-isolation valve and reduces the likelihood that the valve will open. Noise generated by the braking system is reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now toFIG. 1, a braking system10according to the exemplary embodiment of the invention includes a master cylinder12in fluid communication with a plurality of brake calipers14a,14b,14cand14d. The system10can define a four channel diagonal split having a first fluid circuit16abetween the master cylinder12and the calipers14aand14band a second fluid circuit16bbetween the master cylinder12and the brake calipers14cand14d. The structure of the fluid circuits16a,16bcan be substantially similar and the components disposed along the first fluid circuit16acan be substantially similar to the components disposed along the second fluid circuit16b.

A first fluid line18places the master cylinder12and the brake caliper14bin fluid communication with one another. A first valve20is disposed along the first fluid line18between the master cylinder12and the brake caliper14b. The first valve20includes a pressure bypass valve such that the valve20is forced from a closed position to an open position in response to a predetermined fluid pressure in the first fluid line18. In the exemplary embodiment of the invention shown inFIG. 1, the valve20is a solenoid bypass isolation valve set in the open position when de-energized. The valve20moves to the closed position when energized. When the valve20is in the closed position, an excessive fluid pressure difference across the valve20, high pressure in the first fluid line18as compared to the pressure at point24, can induce movement of the valve20to the open position. By way of example only, the isolation valve20can open when the pressure difference is greater than 500 psi.

A second fluid line22extends from a first position24along the first fluid line18between the valve20and the master cylinder12to a second position26along the first fluid line18between the valve20and the brake caliper14b. A fluid pump28is disposed along the second fluid line22and powered by a motor29. The pump28can pump brake fluid to the brake calipers14a,14bfrom the master cylinder12by pulling fluid through the valve30and pushing fluid out to position26, feeding the calipers14aand14b. The pump28is disengaged substantially immediately prior to the fluid pressure in the first fluid line18reaching a predetermined pressure, the predetermined pressure being the pressure at which the valve20opens in response to the pressure in the first fluid line18.

In the exemplary embodiment of the invention, a prime valve30is disposed along a second fluid line22between the pump28and the first position24. The prime valve30is a solenoid valve set in the closed position when de-energized. The valve30moves to the open position when energized. The pump28can draw fluid from the master cylinder12through the open prime valve30during a controlled brake event.

The system10also includes a release valve and an apply valve positioned between the master cylinder12and each of the calipers14a,14b,14cand14d. The release and apply valves can enhance the controlled movement of fluid to the calipers. An apply valve32is disposed along the first fluid line18between the second position26and the caliper14b. An apply valve33is disposed along the first fluid line18between the second position26and the caliper14a. In the exemplary embodiment of the invention, the valves32,33are solenoid bypass isolation valves set in the open position when de-energized. Valve33is shown in the closed position to enhance the clarity of the steps of the inventive method, set forth more fully below, but is normally open when de-energized. The valves32,33move to the closed position when energized. When the valves32,33are in the closed position, excessive fluid pressure in the first fluid line18can induce movement of the valve32or the valve33or valve20to the open position. But in the case when the valves32and33are both closed, fluid is not required at the caliper14band the pump28is not engaged.

A third fluid line34extends from a third position36along the first fluid line18between the valve32and the brake caliper14bto a first position38along the second fluid line22between the pump28and the valve30. A release valve40is disposed along the third fluid line34. The valve40is a solenoid valve set in the closed position when de-energized. The valve40moves to the open position when energized. An accumulator42is disposed along the third fluid line34between the valve40and the first position38.

A pressure sensor44is disposed along the first fluid line18between the valve20and the master cylinder12. A controller46can communicate with the sensor44and control the valves20,30,32,40and the pump28. To enhance the clarity ofFIG. 1, lines of communication between the controller and the sensor44, the pump28, and the valves20,30,32and40are not shown, although said lines of communication exist.

The process for executing a controlled brake event at the right front wheel according to the exemplary embodiment of the invention is shown in the simplified flow diagram ofFIG. 2. This exemplary event focuses on applying to one caliper in which case the opposite caliper of the same fluid path will be prevented from receiving fluid by energizing the apply valve associated with that caliper, caliper14ain this case. The process starts at step48. At step50, the controller46closes the valves20,33. The valve33is shown inFIG. 1as closed to support the description of the inventive method; however, the valve33is normally open when in a de-energized position. The controller46opens the valve30at step52. At step54, the motor29is supplied electrical power for a predetermined period of time. This predetermined time is based on the known characteristics of the pump28and motor29combination. In response to the supply of electrical power to the motor29, the pump28will move and fluid will be pumped to the caliper14b. Fluid is pumped to the caliper14bto increase the fluid pressure at the caliper14bto a desired pressure or based upon fluid requirements of that wheel as determined by the controller46. The predetermined period of time that power is supplied to the motor29can be a minimum amount of time required to insure that the motor29spins and begins the movement of fluid. For example, the pump motor29can be engaged for thirty milliseconds.

At step55, the power supplied to the motor29is stopped. As a result of momentum, the motor29will continue to spin and the pump28will continue to pump fluid in response to movement of the motor29. The motor will continue to spin until the momentum, generated during the period of time when power is supplied to the motor29, is exhausted.

At step58, the controller46determines whether fluid is requested at the caliper14bbased on the control algorithms stored in the memory of the controller. Fluid can be requested at the caliper14bif the fluid pressure at the caliper14bis lower than desired. Fluid is requested in order to increase braking force applied by the caliper14bat the wheel.

If fluid is not requested at the caliper14b, the process ends at step72. If fluid is requested at the caliper14bbased on the control algorithms, the process continues to step60. Step60determines if the motor29is still spinning. In other words, step60determines if the momentum of the motor29has been exhausted. A sensor56can be associated with the motor29to determine motor speed; in the exemplary embodiment, the voltage across the motor29is sensed to perform this function but other sensing strategies are possible. The voltage across the motor29corresponds to the spinning of the motor29. For example, if the sensor56detects zero voltage across the motor29, the motor29is not spinning. Likewise, if the sensor56detects voltage across the motor29, the motor29is spinning.

The controller46can communicate with the sensor56and control the pump motor29in response to signals received from the sensor56. For example, if the sensor56senses zero voltage across the motor29at step60, the controller46can return to step54and power can be supplied to spin the motor29for a predetermined period. If the motor29is spinning, even though the motor29was turned off at step55, the pump28will be pumping fluid and the process returns to step58. In this way, the pump motor29is continuously pulsed to provide fluid to one of the calipers14a,14bas needed without forcing the isolation valve20open. In cases when pressure is to be maintained or released at the caliper14b, the pump motor29is not engaged.

The minimum amount of time for engaging the pump motor29, or the predetermined period, can be adjusted during the controlled brake event. For example, the predetermined time period during a first completion of step54can be greater than, less than, or equal to the predetermined period during a subsequent completion of step54. Vehicle operating conditions can change during a controlled braking maneuver and the present invention can accommodate changes in operating conditions.

Alternatively, the controller46will control the pump28in response to the fluid pressure sensed by the sensor44and a control program stored in the memory of the controller46. For example, the pump28can be controlled in response to a vehicle stability enhancement program, a traction control system, an anti-lock braking system, and/or a panic brake assist program. The pump28can be pulsed in an on-off fashion or continuously engaged as determined by the master cylinder pressure, pump-motor voltage, and fluid demands as determined by the control algorithm. In the preferred embodiment of the invention, the pump motor29is pulsed on and off to prevent the isolation valve from being forced open by pressure in line18. The on-off pulses are based on pump voltage response and pressure build requirements as indicated by the controller46.