Abstract:
A method and apparatus for safely braking a vehicle using a brake system under control of a controller. The system includes a parallel system of an electronic brake system for applying the brake and a mechanical brake system for controlling the brake. The mechanical system includes at least one restrictor connected to at least one parking brake. The restrictor reduces the flow of brake fluid from the parking brake so that the parking brake is gradually applied to one or more wheels.

Description:
RELATED APPLICATION  
       [0001]     This application is claiming the benefit, under 35 U.S.C. § 119(e), of the provisional application filed on Jul. 7, 2003, under 35 U.S.C. § 111(b), which was granted Ser. No. 60/485,199, and is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a system for safely braking when using brake-by-wire systems.  
       BACKGROUND OF THE INVENTION  
       [0003]     Brake-by-wire systems are well known for service brakes, however, back-up systems are required to provide braking if electrical or mechanical power cannot be supplied to the brake-by-wire system. Some back-up systems require a complex electronic controller that must be programmed for various contingencies and provided with back-up power. Often, this programming is difficult, time-consuming and expensive. Other back-up mechanical or electromechanical systems do not provide the reliability and/or inexpensive construction required for modern vehicles.  
         [0004]     Further, the prior art back-up mechanical or electromechanical systems fail to gradually, but effectively, apply the brakes during a power failure. Instead, the systems often apply the brakes of the vehicle rapidly. A rapid application of the brakes could cause the vehicle to lose control and/or lose some portion of the load it is carrying.  
         [0005]     Known back-up systems include, by way of example only, that shown in U.S. Pat. No. 5,704,693, which provides for a hydraulic and electric powered parking brake system. A hydraulic and an electric signal are provided simultaneously and independently to a parking actuator assembly. The assembly has an electric motor pump communicating with a reservoir and an outlet line which includes a check valve. The outlet line connects the assembly with mechanical brake apply means. In this case, the means are standard spring-apply, hydraulic-release actuators. When the operator engages the system, an electrical signal is sent to a solenoid to open, thus venting the stored hydraulic pressure into a chamber and allowing the springs of the braking means to move the brakes into the wheels. Redundantly, the operator&#39;s action causes a cam member to displace a plunger against a caged spring mechanism which displaces a piston. The displacement of the piston opens a control valve, thereby venting the fluid pressure which causes the springs to overcome the pressure and the parking brake to engage the wheels. Thus, the piston and the solenoid can be operated independently or simultaneously to effect the release of hydraulic pressure from the brakes.  
         [0006]     U.S. Pat. No. 6,354,672 teaches a first hydraulic pressure source which includes a first pump used to pressurize hydraulic fluid. The &#39;672 patent also teaches a second hydraulic pressure source to pressurize the hydraulic fluid. A brake-cylinder-pressure control device operates to control the fluid pressurized by the first pressure source when the brake cylinder of the system is connected to the first hydraulic pressure source.  
         [0007]     The &#39;672 patent also teaches an emergency communication device used when the brake-cylinder-pressure control device and the first pump device fail to normally function. The emergency device holds the brake cylinder in communication with the second hydraulic pressure source. A separate energy storage portion, having at least one accumulator, is included to operate a booster and a pressure-increasing device in case the above described system fails. The accumulator is said to have a large enough capacity to operate the booster a relatively large number of times, allowing the operator to direct the vehicle to a suitable place to repair the device.  
         [0008]     U.S. Pat. No. 5,302,008 provides for a brake-by-wire system with an auxiliary mechanical brake system capable of immediately actuating if the brake-by-wire system fails. The patent teaches a brake pedal and a brake pedal status sensor connected to the pedal. An electric controller receives a signal from the sensor and controls a brake actuating means. The actuating means generates a brake fluid pressure based upon the signal from the sensor. The controller signals a solenoid valve which transmits the brake fluid pressure to the brakes. If the brake actuating means cannot communicate with the brakes, a separate brake fluid pressure, generated upon the actuation the brake pedal connected to a master cylinder, is provided to the brakes.  
         [0009]     In light of the state of the art discussed above, it would be advantageous for a brake-by-wire system to safely and gradually apply at least one parking brake to stop or slow a vehicle without requiring complex hardware or software for the controller.  
       SUMMARY OF THE INVENTION  
       [0010]     The invention relates to an apparatus for and a method of using a vehicle braking system. The invention comprises at least one spring apply, hydraulic release parking brake and at least one parking brake valve connected to the parking brake through at least one fluid line. A restrictor is in fluid communication with the parking valve and the brake. Under certain conditions, brake fluid is allowed to flow from the parking brake and through the valve and restrictor. The restrictor restricts the flow of brake fluid from the parking brake so that the brake is gradually applied. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which:  
         [0012]      FIG. 1  is a schematic view of an embodiment of the present invention; and  
         [0013]      FIG. 2  is a schematic view of a component of the invention depicted in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts of the present invention. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise.  
         [0015]     A vehicle braking system  10  of the present invention is schematically depicted in  FIG. 1 . An electronic vehicle controller  12  is provided having at least one input connector  14  and at least one output connector  16 . Preferably, the controller  12  has a plurality of input connectors  14  and a plurality of output connectors  16 . The input connectors  14  receive electronic and/or fluid pressure signals from, among other components, at least one sensor  18  connected to a vehicle accelerator pedal  20 . The sensor  18  determines a deflection  22  of the pedal  20  caused by a force  24  on the pedal  20  and provides a signal  26  to the controller  12  regarding the deflection  22 .  
         [0016]     The controller  12  also has an input connector  14  for an electronic and/or fluid pressure signal from a sensor  28  connected to a vehicle brake pedal  30 . The sensor  28  senses a deflection of the pedal  30  into a first deflection zone  32  caused by a force  34  on the pedal  30  and provides a signal  36  to the controller  12  regarding the deflection.  
         [0017]     The controller  12  uses the signal  36  from the vehicle brake pedal sensor  28  and the signal  26  from the accelerator sensor  18  to generate at least one signal  38  to at least one service brake valve  40 . Typically, the signal  38  leaves the controller  12  through one of the output connectors  16 . By way of example only, the controller  12  can also provide one or more signals to other braking devices and/or the engine (not shown). The signal(s) can be communicated to the service brake valve  40  and/or anywhere else electronically and/or through fluid pressure means.  
         [0018]     The service brake valve  40  is in fluid communication with a supply reservoir  42  of brake fluid  44 . A pump  46  draws the brake fluid from the supply reservoir  42  and pressurizes it within a brake line  48 . A brake fluid pressure regulator  50  is located within the brake line  48  for electronically and/or mechanically regulating the brake fluid pressure as needed.  
         [0019]     A first accumulator  52  is in fluid communication with the brake line  48  to receive and store brake fluid under pressure. A one-way valve  54 , upstream from the first accumulator  52 , prevents brake fluid from returning to the fluid supply  42  and maintains fluid pressure downstream of the valve  54  when the engine is off. The first accumulator  52  maintains a sufficient volume and pressure of brake fluid to allow at least one and preferably two or three service brake applications before it is exhausted.  
         [0020]     The first accumulator  52  is in fluid communication with at least a service brake line  56  and also to a parking brake line  58 . The service brake line  56  is in fluid communication with the service brake valve  40 . The parking brake line  58  is in fluid communication with at least one parking brake valve  60 .  
         [0021]     The service brake valve  40  is in fluid communication with at least one service brake  62 . The service brake  62  may be a drum or a disc type brake as known to those skilled in the art. According to the preferred embodiment, the service brake  62  is a spring-apply, hydraulic release brake, as known to those skilled in the art.  
         [0022]     In addition to the above-described connection between the brake pedal  30  and the service brake valve  40 , the brake pedal  30  is also mechanically connected to the service brake valve  40 . The brake pedal  30  engages the service brake valve  40  when the pedal  30  is located in a second deflection zone  64 . The second deflection zone  64  is located beyond the first pedal deflection zone  32 .  
         [0023]     A second accumulator  66  is in fluid communication with the parking brake valve  60 . The second accumulator  66  stores a quantity of pressurized brake fluid  44 . The quantity of pressurized brake fluid is small in comparison to the pressurized brake fluid stored in the first accumulator  52 . A parking brake  68  is located in fluid communication with the second accumulator  66 . Preferably, the parking brake  68  is a spring-apply, hydraulic-release brake, as known to those skilled in the art.  
         [0024]     At least one restrictor  70  is in fluid communication with the parking brake valve  60  through at least one fluid line  72 .  FIG. 1  depicts only one restrictor  70 , however, it can be appreciated that any number of restrictors can be located anywhere in line  72  in communication with the parking brake  68 . The fluid line  72  also connects the restrictor  70  to a sump  74 .  
         [0025]     As shown in  FIG. 2 , the restrictor  70  is preferably a restriction  71  in the fluid line  72 . The restriction  71  can be a necked down portion of the fluid line  72  or it can be a separate component that is connected to the fluid line  72 . If the restriction  71  is a separate component, the fluid line  72  may be connected to the restriction  71  by mechanical means, friction means, adhesive means and/or welding means. Regardless of the type of restrictor used, the restrictor  70  provides a smaller cross-sectional area  75 , for the brake fluid to flow through as compared to the cross-sectional area  75 A of line  72 . The decrease in cross-sectional area the brake fluid can flow through results in less brake fluid moving through the line  72  for any particular unit of time.  
         [0026]     Those skilled in the art will appreciate that the restrictor  70  can be located anywhere in line  72 . Those skilled in the art will also appreciate that the restrictor  70  can restrict fluid line  72  in a manner other than the symmetrical manner depicted in  FIG. 2 . By way of example only, the restrictor  70  can be any non-symmetrical restriction for a fluid line having any shape including, but not limited to, round or elliptical. It can also be appreciated that the size and the length of the restriction  71  can be varied to increase or decrease the quantity of brake fluid passing therethrough for any particular unit of time.  
         [0027]     A preferred method of using the present invention will now be described. When electrical or mechanical power is supplied to the brake fluid pump  46 , it delivers pressurized brake fluid to the service brake valve  40  and the parking brake valve  60 . The brake fluid flows through the parking brake valve  60  and into the parking brake  68 . The pressurized brake fluid urges one or more friction means (not shown) associated with the parking brake  68  from engagement with one or more friction means associated with the wheel (not shown), thereby allowing the wheel to rotate as known by those skilled in the art. The pressurized brake fluid also flows into the accumulator  66 .  
         [0028]     A vehicle operator may manually or automatically engage the parking brake valve  60  to engage the parking brake  68  under normal operating conditions. For example, the vehicle operator may engage switch  76  with force  78  on valve  60 . The parking brake valve  60  disconnects the parking brake  68  from the parking brake line  58  and connects the parking brake  68  to fluid line  72 . Pressurized brake fluid flows from the parking brake  68 , through the parking brake valve  60 , through line  72  and through restrictor  70 . The restrictor  70  restricts the flow of the pressurized brake fluid from the parking brake  68 . By restricting the flow of the pressurized brake fluid from the parking brake  68 , the one or more friction means within the parking brake  68 , previously held off the wheel friction means by the pressurized fluid, are allowed to gradually frictionally engage one another. The gradual frictional engagement of the parking brake friction means with the wheel friction means gradually slows the rotation of the wheel.  
         [0029]     Engagement of the service brake  62  will now be described. Locating the brake pedal  30  into the first deflection zone  32  results in the brake pedal sensor  28  measuring the deflection and providing the controller  12  with a deflection signal  36 . The controller  12  processes the deflection signal  36 , along with any signal  26  from the accelerator sensor  18 . An electronic and/or fluid pressure signal  38 , proportional to at least the deflection signal  36 , is sent to the service brake valve  40 . The service brake valve  40  engages the spring-apply, hydraulic-release service brake  62  to slow or stop the vehicle based upon the signal  38 , as known to those skilled in the art.  
         [0030]     If a brake system failure occurs, wherein the controller  12 , the pump  46  and/or the engine fails, the brake pedal  30  may be deflected beyond the first deflection zone  32  into a second deflection zone  64 . During any brake system failure, the controller  12  need only be programmed to end its control of the brake system  10  upon sensing the failure. This eliminates the requirement for a controller needing complex hardware or software to control braking during a system failure.  
         [0031]     In the second deflection zone  64 , the brake pedal  30  mechanically engages the service brake valve  40 . The degree to which the brake pedal  30  is located within the second deflection zone  64  is proportional to the amount of braking desired to slow or stop the vehicle.  
         [0032]     Deflecting the brake pedal  30  into the second deflection zone  64  opens the service brake valve  42  so that it is in at least fluid communication with the brake fluid stored in the first accumulator  52 . The brake fluid can pass through the service brake valve  40  and flow into one or more of the service brakes  62  to apply them in a controlled and predictable manner.  
         [0033]     Before or after the first accumulator  52  is emptied, the brake fluid pressure in line  58 , which is connected to parking brake  68 , decreases below the pressure of the brake fluid stored within the second accumulator  66 . The pressurized brake fluid within the second accumulator  66 , as well as in the parking brake  68 , flows from the second accumulator  66  according to well-known fluid pressure equalization theories. The brake fluid is communicated from the parking brake  68  and the accumulator  66 , through the parking brake valve  60 , through the restrictor  70  and into the sump  74 .  
         [0034]     The restrictor  70  restricts the flow of brake fluid from the parking brake  68  so that the one or more friction means within the parking brake  68 , previously held off the wheel friction means by the pressurized brake fluid, are allowed to gradually frictionally engage one another, as describe above. The parking brake  68  is gradually engaged in a controlled and predicable manner. Preferably, the vehicle is decelerated at a safe rate to avoid tipping and/or loss of load.  
         [0035]     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.