Abstract:
A pressure locking master cylinder including a fluid reservoir for storing a hydraulic fluid, a housing, a piston slidably received within the housing and defining a working chamber and a blocking chamber, wherein the blocking chamber is in fluid communication with the reservoir, and a valve positioned between the blocking chamber and the reservoir, the valve being adapted to selectively trap the hydraulic fluid within the blocking chamber to lock the piston in a position with respect to the housing.

Description:
[0001]     This application claims priority from U.S. Provisional Patent App. No. 60/552,874 filed on Mar. 12, 2004, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     The present application relates to vehicle braking systems and, more particularly, vehicle braking systems that utilize a hydraulic master cylinder.  
         [0003]     It is common for vehicles such as automobiles to be operated on unlevel terrain. When a vehicle equipped with a manual transmission begins to move on an uphill grade, the driver must release the vehicle&#39;s brake pedal while at the same time releasing the clutch pedal and pressing on the accelerator pedal. If the hill is particularly steep, the vehicle may roll backward if the brake pedal is released before the clutch is engaged. This can cause the vehicle to collide with objects and/or a loss of control. Even properly executed, this process of “slipping the clutch” contributes to driver fatigue and wearing of the vehicle&#39;s clutch and brake.  
         [0004]     Likewise, vehicles utilizing automatic engine-stopping technology also encounter difficulties when operating on unlevel terrain. These “idle-stop” vehicles are adapted to turn off the engine when the vehicle is stopped (such as at a traffic light) to conserve fuel and reduce emissions. The engine automatically restarts when the driver presses on the accelerator. To enable restarting, the transmission is automatically disengaged while the engine is off, and is automatically re-engaged only after the engine is running again. While the transmission is disengaged, the vehicle is free to roll forward or backward. Since there is an inherent lag between the time the engine is started and the time the transmission is re-engaged, there is a need for a means to keep an idle-stop vehicle from rolling when started from a stopped position on unlevel terrain.  
         [0005]     It is desirable to provide an automatic braking system for use with idle-stop vehicles and vehicles having a manual transmission. Various braking systems that utilize a hydraulic master cylinder are preferably adapted for use in an automatic braking system due to the prevalence of hydraulic brakes. Examples in the art include Delphi TCS6, DBC7, Smartboost and Eboost systems. However, available hydraulic braking systems all suffer from one or more drawbacks, such as noise, limited brake holding time, limited brake pressure at altitude, and limited brake pressure with the engine off. These drawbacks limit their use as automatic brakes.  
         [0006]     Accordingly, there is a need for a low-noise automatic brake holding system that is capable of holding the brake for a sufficient period of time, operating at higher elevations and providing sufficient brake pressure with the engine off. There is a particular need for an automatic brake holding system having a hill-holding capability that is able to automatically keep the brakes applied after a stop, such that the driver need not keep his or her foot on the brake, and then gradually releases the brakes when the accelerator is engaged, enabling a smooth start and preventing the vehicle from unintentionally rolling when operated on unlevel terrain.  
       SUMMARY  
       [0007]     One aspect of the pressure locking master cylinder includes a fluid reservoir for storing a hydraulic fluid, a housing, a piston slidably received within the housing and defining a working chamber and a blocking chamber, wherein the blocking chamber is in fluid communication with the reservoir, and a valve positioned between the blocking chamber and the reservoir, the valve being adapted to selectively trap the hydraulic fluid within the blocking chamber to lock the piston in a position with respect to the housing.  
         [0008]     A second aspect of the pressure locking master cylinder includes a fluid reservoir for storing a hydraulic fluid, a housing, a first piston slidably received within the housing, the first piston defining a first working chamber and a blocking chamber, wherein the blocking chamber is in fluid communication with the reservoir, a second piston slidably received within the housing, the second piston defining the first working chamber and a second working chamber, and a normally open solenoid valve positioned between the blocking chamber and the reservoir, wherein the solenoid valve is adapted to selectively prevent a flow of hydraulic fluid from the blocking chamber to the reservoir.  
         [0009]     Another aspect of the pressure locking master cylinder includes a method for locking a brake including the steps of providing a master cylinder having a piston slidably received therein, the piston defining a working chamber and a blocking chamber, filling the working chamber and the blocking chamber with a hydraulic fluid, advancing the piston into the working chamber to actuate the brake, thereby decreasing a volume of the working chamber while increasing a volume of the blocking chamber, trapping the hydraulic fluid within the blocking chamber to prevent the piston from retracting into the blocking chamber, thereby locking the brake, and selectively releasing the hydraulic fluid from the blocking chamber to release the brake.  
         [0010]     Other aspects of the pressure locking master cylinder will be apparent from the following description, the accompanying drawings and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a top plan view of one aspect of the pressure locking master cylinder assembly;  
         [0012]      FIG. 2  is a side elevational view, in section, of the master cylinder of  FIG. 1 ;  
         [0013]      FIG. 3  is a first portion of a flow diagram of a control algorithm for the pressure locking master cylinder assembly of  FIG. 1 ;  
         [0014]      FIG. 4  is a second portion of the flow diagram of  FIG. 3 ; and  
         [0015]      FIG. 5  is a third portion of the flow diagram of  FIG. 3 . 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  illustrates a top plan view of a pressure locking master cylinder assembly  10 . Pressure locking master cylinder assembly  10  includes three major components: a master cylinder  12 , a valve  14  (e.g., a normally open solenoid valve) and a bridge  16 . Master cylinder  12  acts as an interface between a mechanical brake actuator input, such as a brake pedal (not shown) and a hydraulic braking system (not shown). Solenoid  14  controls the flow of hydraulic fluid in master cylinder  12 , as will be described more fully below. Bridge  16  serves as a mounting fixture for connecting master cylinder  10  to the vehicle (not shown). A control unit or device  17 , such as a microprocessor or a programmable logic device (“PLD”), may be used to control actuation of proportional solenoid valve  14 . The control device  17  may utilize a predetermined set of instructions, such as a computer program or algorithm  100  (see  FIGS. 3-5 ). According to one aspect of the pressure locking master cylinder, master cylinder  12  and bridge  16  may be combined into one machined component.  
         [0017]      FIG. 2  illustrates a side elevational, cross-sectional view of master cylinder  12 . In one aspect, as shown in  FIG. 2 , master cylinder  12  may be a bypass hole type master cylinder. Master cylinder  12  may include a master cylinder housing  11 , a primary working chamber  18  and a secondary working chamber  20 . Primary working chamber  18  may include a return spring  19 , a primary piston  26 , a check valve  28  and a blocking chamber  30 . Primary working chamber  18  may be connected to hydraulic fluid reservoir  37  by primary reservoir port  56 . Secondary working chamber  20  may include a return spring  22  and a secondary piston  24 . Secondary working chamber  20  may be connected to hydraulic fluid reservoir  37  by secondary reservoir port  58 .  
         [0018]     During normal braking operation, a mechanical force is applied to the primary piston  26  generally at location  32  by the output rod from a vacuum booster (not shown) when a driver depresses an associated brake pedal (not shown). Primary piston  26  moves upwardly (i.e., advances) such that a primary lip seal  34  moves past a by-pass opening  36  and decouples primary working chamber  18  from hydraulic fluid reservoir  37 . Additional movement of piston  26  compresses hydraulic fluid in primary working chamber  18  (i.e., reduces the volume of working chamber  18 ) and provides hydraulic pressure that is transferred to the vehicle&#39;s primary wheel braking circuit (not shown). Secondary piston  24  and secondary working chamber  20  function in a likewise manner to provide braking pressure to the vehicle&#39;s secondary braking circuit.  
         [0019]     As primary piston  26  advances, the volume of blocking chamber  30  expands, thereby drawing hydraulic fluid from the reservoir  37  through a primary reservoir port  56 . Reservoir  37  is divided into two chambers by divider  55 , each dedicated to one of primary working chamber  18  and secondary working chamber  20 .  
         [0020]     In one aspect of the pressure locking master cylinder, fluid may be drawn from the reservoir  37  to the blocking chamber  30  by either of two routes. In a first route (i.e., the piston route), fluid can be drawn through a compensation opening  38 , a compensation chamber  40 , and check valve  28  to blocking chamber  30 .  
         [0021]     In a second route (i.e., solenoid route), (see  FIG. 1 ) as long as solenoid valve  14  is open, fluid may be drawn through a first passageway  42 , solenoid valve  14 , a second passageway  44 , a third passageway  46 , and a fourth passageway  48  to blocking chamber  30 . A plug  50  closes off passageway  42 . A bleeder screw port  52  closes off third passageway  46  and facilitates service bleeding of blocking chamber  30  when maintenance is performed on the vehicle&#39;s braking system. It should be understood that other configurations and routes are within the scope of the present application.  
         [0022]     Referring again to  FIG. 2 , as vacuum booster force in the vehicle braking system (not shown) is released when the driver releases the brake pedal (not shown), primary piston  26  is slidably pushed to a resting position by return spring  19  and compresses fluid in blocking chamber  30 . The fluid in blocking chamber  30  returns to primary reservoir port  56  through solenoid valve  14  via the second route (see  FIG. 1 ). Check valve  28  (i.e., a one-way valve) blocks flow back to reservoir port  56  by means of the first route.  
         [0023]     With continued reference to  FIGS. 1 and 2 , when an automatic braking function, such as hill-holding, electrically actuated parking brake apply assist, and idle-stop braking is engaged, as the driver applies pressure to the brake pedal (not shown), the vacuum booster for the vehicle braking system (not shown) applies force to master cylinder  12  in the same manner as that of a normal application of brakes, discussed above. When commanded by a control algorithm  100  (discussed below), solenoid valve  14  is actuated and blocks fluid flow from blocking chamber  30  and reservoir port  56  (i.e., the second route is cut off), thereby trapping fluid in chamber  30 . As force is released from primary piston  26 , the pressure increases in blocking chamber  30 . The pressure retains primary piston  26  in the brakes-applied position. Then, when commanded by the control unit  17  and algorithm  100 , solenoid  14  releases the pressure in blocking chamber  30  in a predetermined manner, such as a gradual release, and thus piston  26  returns to its resting position and the braking pressure on the vehicle wheels (not shown) is released.  
         [0024]     In alternative aspects of the pressure locking master cylinder, check valve  28  may be located in parallel to solenoid valve  14  instead of in primary piston  26 . Solenoid valve  14  may then be located between fluid passageways  42 ,  46 . Further, primary piston  26  may be made of two portions  26 ,  26   a  (see  FIG. 2 ) so that check valve  28  can be pressed into the primary piston. Still further, a wall divider  54  may separate hydraulic fluid in blocking chamber  30  from communicating with the vacuum booster of the vehicle&#39;s braking system vacuum chamber (not shown).  
         [0025]      FIGS. 3-5  provide an exemplary control algorithm  100  for use with the pressure locking master cylinder. Algorithm  100  begins with vehicle status checks, checking at block  102  whether the vehicle is moving faster than a threshold speed, such as about ten miles per hour. If the vehicle is moving faster than the threshold speed, a check of the vehicle&#39;s electrical system voltage level is made at block  104 . If the voltage level is above a minimum threshold voltage, such as about 12 VDC, the vehicle&#39;s transmission is checked at block  106  to see if the vehicle is in one of a set of predetermined modes such as “neutral,” “drive,” “1,” “2” and “3” gear selections. If the transmission is in a predetermined mode, an auto-stop braking control function is enabled at block  108 .  
         [0026]     The enabled auto-stop braking function monitors vehicle speed at block  110  to determine when the vehicle is stopped. If the vehicle is not stopped, algorithm  100  continues to monitor vehicle speed at block  110  until the vehicle is stopped. When the vehicle is stopped at block  110 , the pressure of the brakes is checked at block  112  to determine whether the brake pressure is above a predetermined threshold, such as about 100 PSI, indicating that the brakes are being applied by the driver. If the brakes are not being applied, algorithm  100  jumps to a prior set of steps beginning at block  110 . If the brakes are being applied at block  112 , a time delay, such as about one second, is inserted as at block  114 .  
         [0027]     Algorithm  100  moves to block  116 , as indicated by B in  FIGS. 3 and 4 , and the road speed is again checked to see if the vehicle is stopped. If the road speed is greater than a threshold value, such as about 1 mile per hour, algorithm  100  jumps to a set of prior steps, beginning at block  110 , as indicated by A in  FIGS. 3 and 4 . If the road speed is less than the threshold value, another check is made of the vehicle&#39;s brake pressure at block  118 . If the brake pressure is less than a threshold value, such as about 100 PSI, at block  118 , algorithm  100  jumps to a set of prior steps, beginning at block  110 , as indicated by A in  FIGS. 3 and 4 .  
         [0028]     If the brake pressure is above the threshold value of block  118 , the vehicle&#39;s electrical system voltage is again checked at block  120 . If the voltage is below a threshold value, such as about 12 VDC, algorithm  100  jumps to the beginning, as indicated by C in  FIGS. 3 and 4 . If the voltage is above the threshold value, a check of the vehicle transmission is made at block  122 . If the transmission is not in one of a predetermined set of operating modes, algorithm  100  jumps to the beginning, as indicated by C in  FIGS. 3 and 4 .  
         [0029]     If the transmission is in one of a predetermined set of operating modes at block  122 , such as “neutral,” “drive,” “1,” “2” and “3,” solenoid valve  14  of master cylinder assembly  10  (see  FIG. 1 ) is pulse width modulated (“PWM”) at block  124  by a control (not shown) such that the valve is fully open for a period of time, such as about 100 milliseconds. Then, at block  126 , the valve is PWM controlled in proportion to a predetermined braking value, such as brake caliper position or displacement, or brake pressure. The vehicle&#39;s engine may be stopped at block  128  to conserve fuel and reduce emissions.  
         [0030]     At block  130  (see  FIG. 5 ) the transmission is again checked to ensure that it is in one of a predetermined set of operating modes. If the transmission is not in a predetermined mode, such as “neutral,” “drive,”“1,” “2” and “3,” algorithm  100  jumps to the beginning, as indicated by C in  FIGS. 3 and 5 . If the transmission is in a predetermined mode, a check of the vehicle&#39;s brake pressure is made at block  132  to see if the pressure is below a predetermined threshold point, indicating that the brake pressure has fallen below a level sufficient to apply the brakes. If the brake pressure is above the threshold point of block  132 , algorithm  100  jumps back to a prior set of steps, beginning with block  130 . If the brake pressure of block  132  is below the threshold point, the vehicle&#39;s transmission is disengaged at block  134  and the engine is started at block  136 . The vehicle&#39;s throttle is then monitored at block  138  until the throttle reaches a predetermined threshold position or “move point” indicating that the driver is pressing on the vehicle&#39;s accelerator pedal.  
         [0031]     If the throttle has exceeded the move point threshold value at block  138 , the transmission is re-engaged at block  140 . At block  142  solenoid valve  14  (see  FIG. 1 ) is PWM controlled to about 0%, closing the valve and allowing the pressure in primary working chamber  18  to decrease. Primary piston  26  is returned to its resting position by return spring  19 , releasing the vehicle&#39;s brakes. In one embodiment of the pressure locking master cylinder, the braking pressure may be released over a fixed period of time to gradually and smoothly release the brakes. In another embodiment of the pressure locking master cylinder, the rate of change of the PWM may be ramped at approximately the throttle apply rate. Thus, if the driver depresses the accelerator sharply, commanding rapid vehicle acceleration, the brake pressure is released more quickly in order to prevent brake drag, which would detract from the vehicle&#39;s acceleration and contribute to brake wear.  
         [0032]     A delay, such as about 15 seconds, is inserted at block  144 . Algorithm  100  then returns to the beginning, as indicated by C in  FIGS. 3 and 5 .  
         [0033]     Although the pressure locking master cylinder is shown and described with respect to certain embodiments, it is obvious that modifications will occur to those skilled in the art upon reading and understanding the specification. The pressure locking master cylinder includes all such modifications and is limited only by the scope of the claims.