Abstract:
A parking brake system for a vehicle with wheel brakes, the system, normally applied, including a main housing having interconnected cavities and bores; a hydraulic pump in one housing cavity, an electric motor for driving the pump and producing pressurized fluid, an internally preloaded actuator having an axially movable output member, mounted in another housing cavity and hydraulically connected with the one cavity, a Hall-Effect sensor with a built-in relay for controlling the motor mounted in a housing bore, a normally-open control valve connected with the another cavity, a piston in another cavity mechanically interconnected with the actuator/output member.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/689,865, filed Jun. 13, 2005, the disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a hydraulic parking brake system for use on vehicles with wheel brakes. The parking brake system is normally applied and is disengaged via hydraulic pressure acting on a piston in opposition to a preloaded actuator.  
       BACKGROUND OF THE INVENTION  
       [0003]     Parking brake systems are well known in the art and are most commonly used on wheeled vehicles in a manually operated manner wherein the operator, generally via hand or foot operation, activates a cable or linkage that in turn physically applies a stationary brake member into engagement with a brake component that normally rotates with or relative to a vehicle wheel, thus arresting the latter.  
         [0004]     Fail-safe parking brake systems include mechanisms that normally bias these mechanisms to the applied position and it is necessary to specifically override these mechanisms in order to be able to move the vehicles. Such mechanisms are often cumbersome, bulky, expensive and difficult to install, particularly in retrofit types of installations.  
       SUMMARY OF THE INVENTION  
       [0005]     Accordingly, in order to overcome the deficiencies of the prior art devices, the present invention provides a Hydraulic Integral Parking Brake System Package (HIPBSP) for vehicles, such as fork-lift trucks that can easily be installed as integrated units in any desired position. This construction which requires no external wiring minimizes installation space requirements and cost. Also provided is an emergency manual disengagement option.  
         [0006]     Specifically, the present invention in one embodiment relates to a parking brake system for a vehicle which includes wheel brakes with the parking brake system being normally applied under the control of a preloaded actuator, the parking brake system comprises: a main housing having a plurality of interconnected cavities and bores as well as an integral a source of hydraulic fluid; a hydraulic pump secured in and submerged within a first cavity of the main housing; an electric motor, connected with a source of applicable electric power, attached to the main housing, at the first cavity, and operatively interconnected with the hydraulic pump for providing pressurized hydraulic fluid; the preloaded actuator including a movable output member, secured to a second cavity of the main housing and being hydraulically interconnected with the hydraulic pump; the main housing further including, in a bore portion thereof, a Hall-Effect sensor with a built-in relay for controlling the electric motor; a normally open control valve operatively connected with the second cavity and a reservoir; a first piston, located in the second cavity, mechanically interconnected with the preloaded actuator and its output member, and hydraulically interconnected with the hydraulic pump; during a release of the parking brake system the first piston being axially displaced via hydraulic pressure and moving against the preload of the actuator; the Hall-Effect sensor detecting the presence of the first piston at the top of its stroke controlling the delivery of electric power to the electric motor.  
         [0007]     One version of the parking brake system further includes an emergency release mechanism. In the event of the absence of electrical power, the release mechanism including a release member retained in an aperture in the main housing with an inner end of the release member abutting a bottom surface of the first piston; and an outer end of the release member extending axially outwardly from the aperture and being provided with a tool-application portion for permitting manual rotation of the release member to axially displace the first piston in opposition to the preload of the actuator, thereby releasing the parking brake system.  
         [0008]     In another version of the parking brake system, the preloaded actuator takes the form of a strut assembly having an internal compression spring preloaded to a predetermined value. In a variation thereof, the strut assembly output member axially extends from both ends thereof, with an output member outer end being provided with adjustment and jam nuts as well as an attachment member for operative mechanical interconnection with the wheel brakes. In another variation thereof, an inner end of the output member includes a stepped portion that terminates within the first piston.  
         [0009]     In a further version of the parking brake system, the axial movement of the first piston, and consequently of the actuator output member, is sufficient, depending upon the direction of movement thereof, to one of apply and release the parking brake system.  
         [0010]     A differing version of the parking brake system further includes, within the main housing and within the pluralities of bores, a relief valve and a check valve, both located downstream of the hydraulic pump.  
         [0011]     In still another version of the parking brake system, the location of the Hall-Effect sensor with its built-in relay, within the main housing is axially spaced from an at-rest position of the first piston at a distance substantially corresponding with a predetermined length of axial movement of the first annular piston.  
         [0012]     An additional version of the parking brake system further includes a steel ring interposed between an inner end surface of the second cavity and the first piston.  
         [0013]     In yet another version of the parking brake system the specific vehicle to which the system is applied is a fork-lift truck.  
         [0014]     In a yet differing version, the preloaded actuator includes: a spring cylinder having a fully open lower end, a constricted upper end and an intermediate cavity; the movable output member extending from both ends thereof; the lower end being closed by a stepped annular cap; a second piston located within the cavity; and a compression spring, located within the cavity between an inner surface of the second piston and an inner surface of the spring cylinder constricted upper end. In one variation thereof, the compression spring is preloaded to a predetermined value, depending upon the specific application of the parking brake system. In another variation thereof, the first and second pistons are of differing diameters. In this variation, the main housing second cavity is stepped and includes a smaller diameter inner bore, for housing the first piston, and a larger diameter outer bore, for housing the second piston. A yet differing variation thereof, further including a bushing located intermediate the first and second pistons.  
         [0015]     In still another version, the normally-open control valve is a rotary solenoid operated valve. In another version, the built-in relay of the Hall-Effect sensor includes bladed terminals. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a perspective view of the parking brake system of the present invention.  
         [0017]      FIG. 2  is an elevational view of one side of the parking brake system of this invention.  
         [0018]      FIG. 3  is an enlarged sectional view, taken along line  3 - 3  of  FIG. 2 .  
         [0019]      FIG. 4  is an elevational view of the side of the parking brake system opposite to that of Fig.  
         [0020]      FIG. 5  is an elevational view of one end of the parking brake system of this invention.  
         [0021]      FIG. 6  is an enlarged sectional view taken along line  6 - 6  of  FIG. 3 .  
         [0022]      FIG. 7  is a hydraulic schematic of the parking brake system of this invention.  
         [0023]      FIG. 8  is an electrical schematic of the parking brake system of this invention.  
         [0024]      FIG. 9  is a top plan view, with parts broken away and partly in section, of a generic industrial vehicle, such as a fork lift truck, incorporating the parking brake system of this invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Illustrated in the perspective view of  FIG. 1  is a complete hydraulically operated parking brake system  20  which is utilized, for example, in at least one particular application, as a parking brake system  22  of a forklift  24  ( FIG. 9 ) In  FIG. 9 , any desired, brake assembly  26 , interposed between motor-driven transmissions  28 ,  30  acts on driven, opposed, front wheels  32 ,  34  in a manner known in the art. It is an objective of this invention to provide a complete integral hydraulic parking brake system, such as that shown by reference number  20  that can be easily installed to function as a parking brake system  22 .  
         [0026]     Returning briefly to the  FIG. 1 , as well as turning to  FIGS. 2, 4  and  5 , illustrated therein is parking brake system  20  which includes a main housing or block  36 . Attached to the main housing  36  is an actuator or application cylinder, such as spring-loaded cylinder  40 , with an application member  42 , a preferably 12 volt D.C. rotatable electric motor  44  with an electrical lead-in  45 , a Hall-Effect sensor or sensor module  46  with a built-in relay  48  and a manual release member, such as a threaded rod  50 . Thus, the parking brake system  20  is an integrated package. As best seen in  FIG. 6 , secured and submerged within a main housing first cavity  54 , is a hydraulic gear pump  52 .  FIG. 6  also shows the placement of a normally open solenoid controlled or operated valve  58  mounted within a stepped bore  60  that is operatively connected with first cavity  54 . A relief valve  64  and a check valve  62  are located downstream of hydraulic pump  52  in bores  63  and  65 , respectively. Normally-open control valve  58  is used to release the hydraulic pressure within as well as activate the parking brake system  20  in a manner to be described in more detail hereinafter.  
         [0027]     As best seen in  FIGS. 4, 5  and  6 , electric motor  44 , is bolted to main housing  36  via a plurality of retaining bolts  66  and is operatively interconnected with and drives hydraulic pump  52  via a coupling member  68  ( FIG. 6 ). While 12 volt DC use is currently preferred, voltage ranges from about 12 to 42 are readily envisioned, depending upon application. Main housing  36  is also provided with a second, stepped, housing cavity  70  having a smaller diameter inner bore portion  72  and a larger diameter outer bore portion  74 . The bottom surface  73  of inner bore portion  72  is operatively interconnected with stepped bore  65  and check valve  62  via a connecting passage or bore  76 , with stepped bore  65  also being operatively interconnected with the output portion of hydraulic pump  52  via a connecting bore or passage  78 .  
         [0028]     Located within second cavity inner bore portion  72 , at a bottom surface  73  thereof, are an inner steel ring  82  and an abutting, stepped, inner annular piston  86 , the latter cradling a peripheral seal member  84  therebetween. Adjoining an upper surface  87  of piston  86  is a bushing  88  of a length sufficient to enter second cavity outer bore portion  74 . Fixedly secured in cavity  74  is the lower end  94  of application cylinder  40  which, for example, may take the form of a commercial strut assembly. Strut assembly  40  utilizes a preloaded compression spring  90  confined within a spring cylinder  92  having a fully open lower end  94  and a constricted upper end  96  with application member or rod  42  extending from both ends thereof as best illustrated in  FIG. 3 .  
         [0029]     As best seen in  FIG. 6 , strut assembly lower end  94  is closed by a stepped annular cap  100  with bushing  88  extending therethrough and into the lower end of strut cavity  98  and abutting the lower surface  104  of an annular strut piston  102  which is provided with a peripheral lathe cut ring  108  for sealing purposes. Strut piston  102  is retained within strut cavity  98  via a steel retaining ring  110  located within a groove in the inner surface of spring cylinder  92 . Also located within strut cavity  98  is compression spring  90  that is preloaded to a predetermined amount, depending upon the specific application. In one operative example, the preload of compression spring  90  is 900 pounds, with spring  90  being confined between strut piston upper surface  106  and an inner surface  112  of spring cylinder constricted upper end  96 .  
         [0030]     As shown in  FIGS. 2, 3  and  4 , the stepped outer end  116  of application rod  94  extends through strut assembly upper end  96  and is provided with an adjustment nut  118 , a jam nut  120  and an attachment member  122  for a cable and/or rod, etc. (neither shown) extending to and operatively connected with brake assembly  26 . A lower end  117  of application rod  42  extends from strut assembly  40  through bushing  88  and includes a stepped end portion  119  ( FIG. 3 ) terminating in annular inner piston  86  and inner steel ring  82 . Also illustrated in  FIG. 3  is that manual release member  50  is retained in a stepped aperture  124  in main housing or block  36 , in a threaded relationship therewith, via an apertured hex plug  126 , with an inner end  130  of release member  50  abutting a bottom surface  83  of steel ring  82  in cavity portion  72 . An outer end  132  of release member  50  is preferably provided with a hexagonal external shape for tool-application purposes which will be explained later.  
         [0031]     Prior to describing the operation of the parking brake system  20 , attention is first directed to the hydraulic schematic  134  of  FIG. 7  and the electrical schematic  136  of  FIG. 8 . Schematic  134  illustrates that electric motor  44  and hydraulic gear pump  52  operate, in unison and in one direction, for pumping hydraulic fluid into strut cylinder  40 , with relief valve  64  limiting the amount of fluid pressure in order to avoid damaging the other hydraulic components. In-line check valve  62  serves to eliminate hydraulic fluid leakage through pump  52 . Normally open solenoid-operated valve  58  controls the flow of hydraulic fluid by switching valve  58  open or closed, this function being initiated by the operator. Hall-Effect sensor  46  ( FIG. 3 ) and its integral relay  48  turn off electric motor  44  when stepped inner piston  86  ( FIG. 3 ) has reached the top end of its stroke. Plugs  114 ,  115  ( FIG. 2 ), serve to temporarily close off associated respective ports connected with integral reservoir in main housing cavity  54 .  
         [0032]     Electrical schematic  136 , illustrated in  FIG. 8 , shows that the operator must activate panel switch  138  in order to initiate the operation of parking brake system  20 . If so desired, the operation of parking brake system  20  may also be initiated, for example by being wired to a transmission control circuit which will activate system  20  when the transmission is shifted into a “Park” position, or, in another alternative, operation could be initiated by being wired to a load cell in the operator&#39;s seat cushion so as to activate system  20  whenever the operator leaves his seat. As indicated in schematic  136 , the electrical connection from the vehicle to parking brake system  20  can easily be attached via the Hall-Effect sensor/relay bladed terminal  47  shown in  FIGS. 1 and 4 . Furthermore, it should be evident that different combinations of switching parking brake system  20  on and off can be accomplished very easily.  
         [0033]     Turning now to the description of the actual operation parking brake system  20 , it must be initially clear that the vehicle is in “park” mode and that system  20  has already been engaged. Thus, once the system  20  has been engaged, the operator applies electric power, via a switch, so as to disengage the system  20  from its “parked” position as follows:  
         [0034]     The operator activates panel switch  138  ( FIG. 8 ), causing motor/pump combination  44 / 52  to start operation so as to build up hydraulic pressure in strut assembly  40 , thereby extending strut piston  102  (acting via inner piston  86  and bushing  88 ) against the opposing force of preloaded spring  90  in cylinder or strut assembly  40 . Electric power to motor/pump combination  44 / 52  is automatically shut off when Hall-Effect sensor  46  ( FIG. 3 ) detects the presence of inner piston  86  at the top of its stroke. Relay  48  is then deactivated and shuts off the delivery of electric power to electric motor  44 . The hydraulic pressure, built-up within strut assembly  40 , keeps strut piston  102  in place against the opposing force of compression spring  90 . At this time, parking brake system  20  is no longer applied and the vehicle can now be moved, if so desired. The operator sets or applies the system  20  by activating panel switch  138 , thereby causing normally-open solenoid-controlled valve  58  to release the hydraulic pressure within strut assembly  40 , thereby causing spring  40  to apply force to vehicle brake(s)  26  in the manner already described.  
         [0035]     It should be understood, at this time that electric power is used to release the system  20 , once applied; otherwise vehicle  24  cannot be moved. In case of a power failure, such as the unavailability of battery power, an emergency manual release of the system  20  can be achieved by manually turning threaded release rod  50 , at hex end  132 , thereby axially displacing steel ring  82  which, in turn, further compresses spring  90  and axially displaces application rod  42 .  
         [0036]     The parking brake system  20  can be secured to the frame of a vehicle ( FIG. 9 ), such as a fork-lift truck  24 , so that its brake cable or rod (neither shown per se) can be easily attached. System  20 , or system  22  in the specific case of a lift truck, can be mounted in vertical, horizontal or intermediate positions, depending on the best scenario for linking same to the fork-lift truck&#39;s brake cable/rod. The force of spring-loaded cylinder  40  in systems  20  and  22  “parks” vehicle  24  by pulling the brake cable/rod. Systems  20 / 22  counteract the preload of mechanical spring  90  by generating the hydraulic force that is necessary to disengage spring  90  from its “parked” position. Looking at it in another way, the parking brake is normally applied, via spring  90 , unless overridden by the hydraulic force generated by motor/pump combination  44 / 52  and can thus be denominated as a “fail-safe” system. An emergency parking brake release can be accomplished by manual rotation of release member  50  in the manner previously described, and can be used in case of electrical power failure in vehicle  24  if the latter must be moved before electrical power can be restored. The strategic placement of Hall-Effect sensor  46 , as previously described, uses the magnetic field principles thereof to detect when lower piston  86  reaches the top of its stroke. As already noted, Hall-Effect sensor  46  utilizes a built-in relay  48  for providing the electrical connection with electric motor  44 .  
         [0037]     The unique design and structural attributes of the present invention include the completely integrated system that can be utilized in a turn-key manner and installed as a completely self-contained unit. Second, Hall-Effect sensor  46  with a built-in relay  48  and a solenoid operated control valve  58 , are assembled into one main housing or block  36  with the other components of the system  20 . Hall-Effect sensor  46  has relay  48  built into its module for simplicity, ease of installation and cost efficiency. By introducing the sensor/relay module  46 / 48 , no external wiring is required; the space requirement therefore is reduced to a minimum and it allows easy wiring with reference to the lift truck power source and the panel switch. Thirdly, systems  20 ,  22 , are complete, unitary packages that are ready for installation and can be mounted, at any desired spatial attitude in a vehicle frame for achieving an easy conversion, among other things, from an existing manual system to a fully hydraulic system while allowing the end user to determine an optimal location fit for the joining same to the existing brake cable/rod. Finally, the previously-discussed emergency release option, via release rod  50 , in case of a vehicle electrical power failure, permits release of systems  20  and  22 , if so desired.  
         [0038]     It is deemed that one of ordinary skill in the art will readily recognize that the several embodiments of the present invention fill remaining needs in this art and will be able to affect various changes, substitutions of equivalents and various other aspects of the invention as described herein. Thus, it is intended that the protection granted hereon be limited only by the scope of the appended claims and their equivalents.