Abstract:
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.

Description:
TECHNICAL FIELD  
       [0001]     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  
       [0002]     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.  
         [0003]     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  
       [0004]     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.  
         [0005]     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.  
         [0006]     Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The description herein makes reference to the accompanying drawings, wherein like reference numerals refer to like parts throughout the several views and wherein:  
         [0008]      FIG. 1  is a schematic illustration of a braking system according to the exemplary embodiment of the invention; and  
         [0009]      FIG. 2  is a simplified flow diagram illustrating the steps performed by the exemplary embodiment of the invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]     Referring now to  FIG. 1 , a braking system  10  according to the exemplary embodiment of the invention includes a master cylinder  12  in fluid communication with a plurality of brake calipers  14   a ,  14   b ,  14   c  and  14   d . The system  10  can define a four channel diagonal split having a first fluid circuit  16   a between the master cylinder  12  and the calipers  14   a  and  14   b  and a second fluid circuit  16   b  between the master cylinder  12  and the brake calipers  14   c  and  14   d . The structure of the fluid circuits  16   a ,  16   b  can be substantially similar and the components disposed along the first fluid circuit  16   a  can be substantially similar to the components disposed along the second fluid circuit  16   b.    
         [0011]     A first fluid line  18  places the master cylinder  12  and the brake caliper  14   b  in fluid communication with one another. A first valve  20  is disposed along the first fluid line  18  between the master cylinder  12  and the brake caliper  14   b . The first valve  20  includes a pressure bypass valve such that the valve  20  is forced from a closed position to an open position in response to a predetermined fluid pressure in the first fluid line  18 . In the exemplary embodiment of the invention shown in  FIG. 1 , the valve  20  is a solenoid bypass isolation valve set in the open position when de-energized. The valve  20  moves to the closed position when energized. When the valve  20  is in the closed position, an excessive fluid pressure difference across the valve  20 , high pressure in the first fluid line  18  as compared to the pressure at point  24 , can induce movement of the valve  20  to the open position. By way of example only, the isolation valve  20  can open when the pressure difference is greater than 500 psi.  
         [0012]     A second fluid line  22  extends from a first position  24  along the first fluid line  18  between the valve  20  and the master cylinder  12  to a second position  26  along the first fluid line  18  between the valve  20  and the brake caliper  14   b . A fluid pump  28  is disposed along the second fluid line  22  and powered by a motor  29 . The pump  28  can pump brake fluid to the brake calipers  14   a ,  14   b  from the master cylinder  12  by pulling fluid through the valve  30  and pushing fluid out to position  26 , feeding the calipers  14   a  and  14   b . The pump  28  is disengaged substantially immediately prior to the fluid pressure in the first fluid line  18  reaching a predetermined pressure, the predetermined pressure being the pressure at which the valve  20  opens in response to the pressure in the first fluid line  18 .  
         [0013]     In the exemplary embodiment of the invention, a prime valve  30  is disposed along a second fluid line  22  between the pump  28  and the first position  24 . The prime valve  30  is a solenoid valve set in the closed position when de-energized. The valve  30  moves to the open position when energized. The pump  28  can draw fluid from the master cylinder  12  through the open prime valve  30  during a controlled brake event.  
         [0014]     The system  10  also includes a release valve and an apply valve positioned between the master cylinder  12  and each of the calipers  14   a ,  14   b ,  14   c  and  14   d . The release and apply valves can enhance the controlled movement of fluid to the calipers. An apply valve  32  is disposed along the first fluid line  18  between the second position  26  and the caliper  14   b . An apply valve  33  is disposed along the first fluid line  18  between the second position  26  and the caliper  14   a . In the exemplary embodiment of the invention, the valves  32 ,  33  are solenoid bypass isolation valves set in the open position when de-energized. Valve  33  is 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 valves  32 ,  33  move to the closed position when energized. When the valves  32 ,  33  are in the closed position, excessive fluid pressure in the first fluid line  18  can induce movement of the valve  32  or the valve  33  or valve  20  to the open position. But in the case when the valves  32  and  33  are both closed, fluid is not required at the caliper  14   b  and the pump  28  is not engaged.  
         [0015]     A third fluid line  34  extends from a third position  36  along the first fluid line  18  between the valve  32  and the brake caliper  14   b  to a first position  38  along the second fluid line  22  between the pump  28  and the valve  30 . A release valve  40  is disposed along the third fluid line  34 . The valve  40  is a solenoid valve set in the closed position when de-energized. The valve  40  moves to the open position when energized. An accumulator  42  is disposed along the third fluid line  34  between the valve  40  and the first position  38 .  
         [0016]     A pressure sensor  44  is disposed along the first fluid line  18  between the valve  20  and the master cylinder  12 . A controller  46  can communicate with the sensor  44  and control the valves  20 ,  30 ,  32 ,  40  and the pump  28 . To enhance the clarity of  FIG. 1 , lines of communication between the controller and the sensor  44 , the pump  28 , and the valves  20 ,  30 ,  32  and  40  are not shown, although said lines of communication exist.  
         [0017]     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 of  FIG. 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, caliper  14   a  in this case. The process starts at step  48 . At step  50 , the controller  46  closes the valves  20 ,  33 . The valve  33  is shown in  FIG. 1  as closed to support the description of the inventive method; however, the valve  33  is normally open when in a de-energized position. The controller  46  opens the valve  30  at step  52 . At step  54 , the motor  29  is supplied electrical power for a predetermined period of time. This predetermined time is based on the known characteristics of the pump  28  and motor  29  combination. In response to the supply of electrical power to the motor  29 , the pump  28  will move and fluid will be pumped to the caliper  14   b . Fluid is pumped to the caliper  14   b  to increase the fluid pressure at the caliper  14   b  to a desired pressure or based upon fluid requirements of that wheel as determined by the controller  46 . The predetermined period of time that power is supplied to the motor  29  can be a minimum amount of time required to insure that the motor  29  spins and begins the movement of fluid. For example, the pump motor  29  can be engaged for thirty milliseconds.  
         [0018]     At step  55 , the power supplied to the motor  29  is stopped. As a result of momentum, the motor  29  will continue to spin and the pump  28  will continue to pump fluid in response to movement of the motor  29 . The motor will continue to spin until the momentum, generated during the period of time when power is supplied to the motor  29 , is exhausted.  
         [0019]     At step  58 , the controller  46  determines whether fluid is requested at the caliper  14   b  based on the control algorithms stored in the memory of the controller. Fluid can be requested at the caliper  14   b  if the fluid pressure at the caliper  14   b  is lower than desired. Fluid is requested in order to increase braking force applied by the caliper  14   b  at the wheel.  
         [0020]     If fluid is not requested at the caliper  14   b , the process ends at step  72 . If fluid is requested at the caliper  14   b  based on the control algorithms, the process continues to step  60 . Step  60  determines if the motor  29  is still spinning. In other words, step  60  determines if the momentum of the motor  29  has been exhausted. A sensor  56  can be associated with the motor  29  to determine motor speed; in the exemplary embodiment, the voltage across the motor  29  is sensed to perform this function but other sensing strategies are possible. The voltage across the motor  29  corresponds to the spinning of the motor  29 . For example, if the sensor  56  detects zero voltage across the motor  29 , the motor  29  is not spinning. Likewise, if the sensor  56  detects voltage across the motor  29 , the motor  29  is spinning.  
         [0021]     The controller  46  can communicate with the sensor  56  and control the pump motor  29  in response to signals received from the sensor  56 . For example, if the sensor  56  senses zero voltage across the motor  29  at step  60 , the controller  46  can return to step  54  and power can be supplied to spin the motor  29  for a predetermined period. If the motor  29  is spinning, even though the motor  29  was turned off at step  55 , the pump  28  will be pumping fluid and the process returns to step  58 . In this way, the pump motor  29  is continuously pulsed to provide fluid to one of the calipers  14   a ,  14   b  as needed without forcing the isolation valve  20  open. In cases when pressure is to be maintained or released at the caliper  14   b , the pump motor  29  is not engaged.  
         [0022]     The minimum amount of time for engaging the pump motor  29 , or the predetermined period, can be adjusted during the controlled brake event. For example, the predetermined time period during a first completion of step  54  can be greater than, less than, or equal to the predetermined period during a subsequent completion of step  54 . Vehicle operating conditions can change during a controlled braking maneuver and the present invention can accommodate changes in operating conditions.  
         [0023]     Alternatively, the controller  46  will control the pump  28  in response to the fluid pressure sensed by the sensor  44  and a control program stored in the memory of the controller  46 . For example, the pump  28  can 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 pump  28  can 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 motor  29  is pulsed on and off to prevent the isolation valve from being forced open by pressure in line  18 . The on-off pulses are based on pump voltage response and pressure build requirements as indicated by the controller  46 .  
         [0024]     While the invention has been described as referenced to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the invention, but that the invention will include all embodiments falling within the scope of the claims.