RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/739,810 filed Nov. 23, 2005, which is hereby incorporated by reference. 


   FIELD OF THE INVENTION 
   The present invention relates generally to brake systems. More particularly, the invention relates to parking brake systems for mowers. 
   BACKGROUND OF THE INVENTION 
   Hydrostatic transmissions have many uses, including the propelling of vehicles, such as mowing machines, and offer a stepless control of the machine&#39;s speed. A typical hydrostatic transmission system includes a variable displacement main hydraulic pump connected in a closed hydraulic circuit with a fixed displacement hydraulic motor. The closed hydraulic circuit includes a first conduit connecting the main pump outlet with the motor inlet and a second conduit connecting the motor outlet with a pump inlet. Either of these conduits may be the high pressure line depending upon the direction of pump displacement from neutral. For most applications, the pump is driven by a prime mover, such as an internal combustion engine or an electrical motor, at a certain speed in a certain direction. Changing the displacement of the main pump will change its output flow rate, which controls the speed of the motor. Pump outflow can be reversed, thus reversing the direction of the motor. In a vehicle, the motor is typically connected through suitable gearing to the vehicle&#39;s wheels or tracks. 
   In some vehicles, such as zero-turn-radius mowers, separate hydraulic pumps and motors are used to independently drive separate wheels of an axle. By independently driving the wheels in opposite directions, for example, the vehicle can be made to turn with zero radius. Zero-turn-radius mowers are increasingly popular as the size and costs of such mowers decrease. 
   Movement of some zero-turn-radius mowers is controlled by a pair of steering arms connected to each hydraulic pump. By moving the steering arms, an operator can control the pump flow displacement and direction of each pump and, thus, the speed and direction of rotation of each rear wheel. Accordingly, the operator can both steer the mower and control the speed of the mower by manipulating the steering control arms. 
   Mowers often are equipped with parking brakes that can be activated by an operator to secure the wheels against rotation when the vehicle is parked. Such parking brakes are typically normally disengaged, and are engaged upon activation by the operator. Thus, if the operator forgets to activate the parking brake, the mower could potentially roll if on uneven ground. 
   SUMMARY OF THE INVENTION 
   The present invention provides a normally engaged parking brake system for a mower that automatically disengages a parking brake when a steering arm is moved from a park position. Accordingly, the operator does not need to act to set or release the parking brake during normal operation. The system utilizes a hydraulic actuator that releases the parking brake when pressurized fluid is supplied thereto from a hydraulic pump of the mower. A manual pump, which can be configured to be operated by moving a steering arm of the mower, is provided for supplying pressurized fluid to the hydraulic actuator to release the brake in the event the hydraulic pump is not operating. 
   Accordingly, a parking brake system for a mower having a hydrostatic transmission comprises a normally engaged parking brake connectable to a wheel of the vehicle for braking rotation thereof, and a hydraulic parking brake actuator connectable to a hydraulic pump driven by a motor of the vehicle and configured to disengage the parking brake when high pressure fluid is supplied thereto. A valve is operable to cause high pressure fluid to flow to or from the actuator, and a sensor is configured for sensing a position of a steering lever of the mower corresponding to a park position. The sensor is connected to the valve and controls the valve so as to cause high pressure fluid to flow to the actuator to disengage the parking brake when the sensor senses the steering lever is not in the park position. A manual pump, which may be a plunger pump, is connectable to the steering lever of the vehicle and configured to supply pressurized fluid to the hydraulic actuator. The manual pump and the sensor can be provided in a common housing mountable to the frame as a unit. 
   More particularly, the sensor includes a switch having a first position and a second position. The switch is configured to move between the first position and the second position in response to movement of the steering lever from the park position. The parking brake member can be a drum brake, a disk brake, or a cam brake. 
   According to another aspect of the invention, a mower comprises a frame, a wheel mounted to the frame for supporting the mower for movement over a surface, a steering control lever for controlling rotation of the wheel, the lever movable between a plurality of positions including a park position. A normally engaged parking brake member is configured to brake the wheel and an actuator is configured to disengage the parking brake member when pressurized fluid is supplied thereto. A valve is operable to cause high pressure fluid to flow to or from the actuator, and a sensor senses when the steering control lever is in a park position. The sensor is connected to the valve and controls the valve so as to cause high pressure fluid to flow to the actuator to disengage the parking brake when the sensor senses the steering lever is not in the park position. 
   More particularly, the steering control lever is movable between a forward position, a reverse position and a park position, and movement of the steering control lever is constrained by a T-shape opening through which the steering lever extends. The T-shape opening has a leg portion, and the steering lever is configured such that is in the park position when the steering lever is in a portion of the leg portion of the T-shape opening. A manual pump connectable to the steering lever of the vehicle can be configured to supply pressurized fluid to the hydraulic actuator. The manual pump can be configured to be operated by the steering control lever when the steering control lever is moved within the T-shape opening, for example between park and neutral positions. 
   The sensor can be a switch having a first position and a second position, and the sensor can be configured such that the first position or second position is associated with the steering control lever being in the park position. The actuator can be a hydraulic actuator coupled to a hydraulic circuit of the mower and configured to disengage the parking brake member when pressurized fluid is supplied thereto. 
   Further features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exemplary zero-turn-radius mower employing a parking brake system in accordance with the invention. 
       FIG. 2  is a schematic diagram of an exemplary hydraulic circuit in accordance with the invention. 
       FIG. 3  is a top view of a T-shape slot through which a control arm of the mower of  FIG. 1  extends. 
       FIG. 4  is a front view of one of the control arms of the mower of  FIG. 1 . 
       FIG. 5  is a schematic view of an exemplary normally engaged parking brake assembly. 
       FIG. 6  is a schematic view of the parking brake assembly of  FIG. 5  including a manual release mechanism. 
   


   DETAILED DESCRIPTION 
   Referring now to the drawings in detail, and initially to  FIG. 1 , an exemplary zero-turn-radius mower  10  is illustrated. The mower  10  includes a frame  12 , a mower deck  14  supported by the frame  12  for mowing grass, an operator seat  15 , and steering control levers  16  for operating the mower  10 . A rear mounted engine is mounted to the frame  12  behind the seat  15  and provides power to first and second hydrostatic transmissions (motor and hydrostatic transmissions not shown in  FIG. 1 ) also mounted to the frame  12 . The first and second hydrostatic transmission are each coupled to respective rear wheels  18  which are the drive wheels in the illustrated embodiment. The steering levers  16  are configured to rotate a trunnion or other control member on a respective hydrostatic transmission for controlling pump output and direction. Thus, the hydrostatic transmissions can be controlled by an operator to independently drive respective rear wheels  18  to propel the mower and provide zero-turn-radius functionality. The design of the illustrated mower  10  is merely exemplary in nature, and it will be appreciated that other mower designs and vehicle types can be used in accordance with the invention. 
   Turning to  FIG. 2 , an exemplary hydraulic circuit  30  for actuating a parking brake in accordance with the invention is illustrated. The illustrated hydraulic circuit  30  is a charge circuit that also provides makeup flow to a closed loop of a hydrostatic transmission. It will be appreciated that the exemplary hydraulic circuit  30  could be an auxiliary hydraulic circuit, for example, or any other suitable circuit. It will be appreciated that a separate circuit  30  can be and usually would be provided for each drive wheel of the vehicle. 
   The circuit  30  includes a pump  32  and a pump discharge line  34  connected to a brake actuator  36  for supplying pressurized fluid thereto. The brake actuator  36  is configured to disengage a normally engaged parking brake assembly  37  when high pressure fluid is supplied thereto. 
   A high pressure relief valve  38  and a bypass valve  40  are connected in parallel between the discharge line  34  and a makeup flow supply line  42 . The makeup flow supply line  42  supplies makeup flow to a closed loop of a hydrostatic transmission (not shown). A low pressure relief valve  44  permits flow from the makeup flow supply line  42  to a sump  46 . 
   It will be appreciated that the bypass valve  40  between the discharge line  34  and the makeup flow supply line  42  can be selectively actuated to bypass flow around the high pressure relief valve  38  from the discharge line  34  to the makeup flow supply line  42 . Accordingly, when the bypass valve  40  is closed, the maximum pressure in the discharge line  34  is generally controlled by the high pressure relief valve  38 . When the bypass valve  40  is open, the maximum pressure in the discharge line is generally controlled by the low pressure relief valve  44 . It will be appreciated that although there will be some pressure in the discharge line  34  when the bypass valve  40  is open, the pressure is generally not sufficient to overcome the bias of the parking brake assembly  37 . Accordingly, when the bypass valve  40  is open the parking brake assembly  37  will be engaged. 
   As will be described in more detail below, the bypass valve  40  is configured to be controlled in response to a signal received from a sensor that senses a position of a steering control lever, such as one of the steering control levers  16  in  FIG. 1 . When the bypass valve is closed, high pressure fluid is supplied to the brake actuator  36  and the parking brake assembly  37  is disengaged. When the bypass valve  40  is open, high pressure fluid is not supplied to the brake actuator  36  and the parking brake assembly  37  is engaged. 
   Turning to  FIGS. 3 and 4 , the steering control lever  16  and sensor  70  arrangement will be described.  FIG. 3  illustrates a T-shape opening  50  through which the steering control lever  16  extends. The T-shape opening in  FIG. 3  is for the right side steering control lever  16  and constrains movement of the steering lever  16  passing therethrough. The T-shape opening  50  has a leg (or stem) portion  60 , a forward portion  62  extending forwardly from one end of the stem portion  60  and a rearward portion  64  extending rearwardly from the same end of the leg portion  60 . The T-shape opening  50  can be formed in a frame member of the mower  10 , or a body member, for example. 
   Four positions of the steering lever  16  are illustrated: a full speed forward position  52 , a full speed reverse position  54 , a neutral position  56 , and a park position  58 . Neutral position  56  corresponds to a neutral position of the associated hydrostatic transmission whereat no power is transmitted to the wheel connected to the hydrostatic transmission. Park position  58  also corresponds to the neutral position of the hydrostatic transmission, except that steering lever  16  has been shifted outward into the leg portion  60  of the T-shape opening  50 . In the park position  58 , forward and reverse movement of the steering control lever  16  is restricted. It will be appreciated that openings of other shapes can be used. For example, a straight slot could be used. 
   In  FIG. 4 , a sensor  70  is provided for sensing a position of the steering control lever  16 . In the illustrated example, the sensor  70  is configured to sense when the steering control lever  16  is either in the neutral position  56  or the park position  58  (steering lever  16  shown in phantom in the park position in  FIG. 4 ). In this regard, the sensor  70  can be a plunger-type electrical switch as illustrated that is in an “on” state (e.g., closed circuit) when a plunger  71  is depressed (e.g., when the steering control lever is in the park position  38 ), and in an “off” state when the plunger  71  is not depressed (e.g., when the steering control lever is not in the park position  38 ). The plunger  71  is biased against the steering lever  16  to maintain contact therewith. Other types of sensors can be used, such as linear variable displacement transducers (LVDTs), for example. 
   The sensor  70  sends a signal to the bypass valve  40  depending on the position of the steering control lever  16 . For example, when the steering control lever  16  is in the park position  58 , the sensor  70  signals the bypass valve  40  to open, thereby relieving pressure from the discharge line  34  and engaging the parking brake assembly  37 . When the steering control lever  16  is not in the park position  58 , the sensor  70  signals the bypass valve  40  to close, thereby supplying high pressure fluid to the discharge line  34  and disengaging the parking brake  37 . 
   It will be appreciated that the bypass valve  40  can be configured to respond to both the presence of a signal received from the sensor  70  and the absence of a signal received from the sensor  70 . Alternatively, the bypass valve  40  can be biased open (or closed) and configured to close (or open) in response to receiving a signal from the sensor  70 . A manual override can be provided for manually opening and/or closing the bypass valve  40 . 
   It will be appreciated that the bypass valve  40  can be configured in a variety ways. For example, the bypass valve  40  can be biased open (brake engaged), and configured to close (brake disengaged) in the presence of an electrical signal from the sensor  70 . Alternatively, the bypass valve  40  can be biased closed (brake disengaged) and configured to open (brake engaged) in response to an electrical signal from the sensor  70 . Thus, it will be appreciated that in some applications the parking brake assembly will be engaged when the pump  32  is not operating and/or in the absence of a signal from the sensor  70 . 
   To disengage the parking brake  37  when pump  32  is not operating (e.g., for towing a disabled mower), a manual pump  72  is provided for supplying pressurized fluid to the actuator  36 . The manual pump  72  pumps fluid from the sump  46 , or other suitable source to the pump discharge line  34 . The manual pump  72  can be a simple plunger pump with check valves  73  for maintaining one way flow through the pump  72 . 
   The manual pump  72  can be provided adjacent to a steering control lever  16  of the mower  10  and can be connectable thereto so that movement of the steering control lever  16  results in movement of the manual pump  72  and pressurization of the discharge line  34 . For example, the manual pump  72  can be releasably connectable to a lower end of the steering control member  16  above the pivot point of the steering control member  16  such that movement of the steering control member  16  between the park position  38  and the neutral position  36  results in pumping of fluid to discharge line  34 . As mentioned, the bypass valve  40  can be provided with a manual override for closing the bypass valve (if necessary) to allow high pressure to be supplied to the actuator  36 . 
   With reference to  FIG. 4 , it will be appreciated that the manual plunger pump  72  and sensor  70  can be provided in a common unit wherein the plunger  71  of the sensor, for example, is also a plunger of the manual pump  72 . The combined plunger  71  can be provided with a hook or other means for releasable connection to the steering member  16  for reciprocating movement therewith. 
   Turning to  FIG. 5 , the parking brake assembly  37  will be described. The parking brake assembly  37  includes a drum  80  fixable to a wheel for rotation therewith, brake shoes  82  mounted to a pivot  84  for engagement with the drum  80 , and springs  86  for biasing the brake shoes  82  into engagement with the drum  80 . Connected to the parking brake assembly  37  is a double piston assembly  88  (actuator) connected via push rods  90  to brake shoes  82  for disengaging the brake shoes  82  from the brake drum  80  when pressurized fluid is supplied thereto via discharge line  34 , as described above. 
   As mentioned, the parking brake assembly  37  is normally engaged and, accordingly, disengaging the parking brake  37  when pump  32  is not operating for the purposes of towing may be necessary. The manual pump  72  described above is one way in which the parking brake assembly  37  can be disengaged. Alternatively, a manual brake release can be provided. 
   Turning to  FIG. 6 , the parking brake  37  of  FIG. 5  is illustrated with manual parking brake release mechanisms  92  attached to the brake shoes  82 . The release mechanisms  92  are configured to disengage the shoes  82  from the drum  80  when pulled. Accordingly, handles and/or cam mechanisms (not shown) can be provided on the distal ends of the release mechanisms  92  for assisting in pulling. Alternatively, the release mechanisms  92  can be releasably connected to a steering control arm  16  such that movement of the steering control arm  16  results in disengaging the brake shoes  82  from the drum  80 . In this regard, it will be appreciated that a mechanical advantage can be achieved by connecting the release mechanisms  92  to a lower portion of a steering control arm  16 . 
   It will be appreciated that a wide variety of types of brakes can be used. Further, it will be appreciated that the hydraulic circuit  30  can be part of a hydrostatic transmission, or can be a separate auxiliary circuit of a vehicle. 
   Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
A normally engaged parking brake system for a mower that automatically disengages a parking brake when a steering arm is moved from a park position. Accordingly, the operator does not need to act to set or release the parking brake during normal operation. The system utilizes a hydraulic actuator that releases the parking brake when pressurized fluid is supplied thereto from a hydraulic pump of the mower. A manual pump, which can be configured to be operated by moving a steering arm of the mower, is provided for supplying pressurized fluid to the hydraulic actuator to release to brake in the event the hydraulic pump is not operating.