Abstract:
A self propelled power machine is provided with a drive system and a traction lock mechanism. The drive system includes a speed range selector and associated mechanism that can operate the power machine in high and low speed ranges. The traction lock mechanism, when applied stops the drive system from moving the wheels of the power machine. A controller insures the drive system is in the low speed range prior to engaging the traction lock mechanism. The controller determines whether the drive system is operating in a low speed range or a high speed range. If the drive system is in the high speed range, the controller places the drive system in the low speed range and the controller then applies the traction lock after a short time delay to provide some dynamic slowing of the drive. If the system is already in the low speed range, the drive system remains there and the controller applies the traction lock.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present disclosure relates to self propelled power machinery. More particularly, the present disclosure relates to an apparatus for controlling speed range and braking in a power machine.  
         [0002]     Power machines, such as skid steer or wheel loaders, can usually be found in many different construction sites. Loaders typically include a movable lift arm that can support a wide variety of interchangeable work tools such as a bucket or an auger. Most power machines also include a drive system that includes wheels or tracks for propelling the power machine.  
         [0003]     The drive system is typically powered with an engine that operates a pair of hydraulic pumps that are each connected to hydraulic traction motors that, in turn, power movement of the wheels. Many power machines are equipped with speed range mechanisms that are capable of operating the power machine in one of a number of speed ranges, such as in high and low speed ranges. An operator can select the low speed range when traversing difficult terrain or operating a sensitive tool. The operator can also select a different speed range, such as a high speed range, when simply driving down a road.  
         [0004]     It is desirable that under certain circumstances the power machine be positively stopped. Many power machines are equipped with a traction lock mechanism that stops the drive system from moving the wheels. The traction lock mechanism can be operated by the user, automatically, or both. One example of such a system is described in U.S. Pat. No. 5,551,523, which is incorporated by reference. There is a continuing need, however, to develop efficient and durable traction lock mechanism systems in power machines, including power machines having multiple speed ranges.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention relates to a power machine having a multiple speed drive system and traction lock mechanism. The drive system includes a speed range mechanism that can operate the power machine in at least high and low speed ranges. The traction lock mechanism is operable to stop the drive system from moving the wheels or tracks of the power machine when a brake is applied. A controller receives a signal when the brake is applied and places the drive system in the low speed range prior to engaging the traction lock mechanism.  
         [0006]     For example, the controller determines whether the drive system is operating in a low speed range or a high speed range. If the drive system is in the high speed range, the controller places the system in the low speed range and the controller then applies the traction lock. If the system is already in the low speed range, the drive system remains there and the controller applies the traction lock.  
         [0007]     In one aspect, the disclosure describes a power machine having a drive system with a speed range mechanism including a speed range selector. The speed range mechanism selectively operates the power machine in high and low speed ranges (and possibly other ranges as well). The power machine also includes a traction lock mechanism adapted to stop the drive system from moving the power machine. The power machine also includes a brake control circuit receiving a brake input (indicating a desire to activate the traction lock mechanism) from at least one source, such as from a traction lock switch in the cab of the power machine. The brake control circuit provides a controller with a brake output signal in response to the brake input. The controller is adapted to provide a controller output to the traction lock mechanism and to the speed range selector mechanism in response to the brake output. The controller output is provided when the power machine is operating in a speed range that is not the low speed range, such as the high speed range, and includes selecting the low speed range and preferably after a short time delay activating the traction lock mechanism.  
         [0008]     In still another aspect, the disclosure includes a process for use with a power machine having a drive system with selectable high and low speed ranges and a traction lock mechanism. The process includes receiving a brake input signal. In response to the brake input signal, a determination is made as to whether the power machine is in a low speed range. If the power machine is in the low speed range, the traction lock mechanism is applied. If the power machine is not in the low speed range, such as in the high speed range, the low speed range is selected and the traction lock is selected. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a side elevation view of a typical power machine incorporating features of the present disclosure;  
         [0010]      FIG. 2  is a schematic block diagram of a control circuit of the power machine of  FIG. 1 ;  
         [0011]      FIG. 3  is a schematic diagram of an example of a traction lock system for use in the power machine of  FIG. 1  and operated by the control circuit of  FIG. 2 ; and  
         [0012]      FIG. 4  is a flow diagram illustrative of a process applied by the control circuit of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]      FIG. 1  shows a side elevation view of a skid steer loader  10 , which is one example of a power machine. The skid steer loader  10  includes a frame  12  supported by wheels  14 . The frame  12  also supports a cab  16  that defines an operator compartment that substantially encloses a seat  19 . An operator sits on the seat  19  to control the skid steer loader  10 . A seat bar  21  is coupled to a portion of the cab  16 . When the operator occupies seat  19 , the operator then pivots seat bar  21  from the raised position, shown in phantom, to the lowered position shown in  FIG. 1 .  
         [0014]     A lift arm  17  is coupled to frame  12  at pivot points  20 , one of which is shown in the figure, the other of which is disposed on the opposite side of the skid steer loader  10 . A pair of hydraulic cylinders  22 , again only one of which is shown, is pivotally coupled to the frame  12  at pivot points  24  and to lift arm  17  at pivot points  26 . The lift arm  17  is also coupled to a working tool that, in the illustration, is a bucket  28 . The lift arm  17  is pivotally coupled to the bucket  28  at pivot points  30 . Another hydraulic cylinder  32  is pivotally coupled to the lift arm  17  at pivot point  34  and to bucket  28  at pivot point  36 . While only one cylinder  32  is shown, it is to be understood that any desired number of cylinders could be used to work bucket  28  or any other suitable tool.  
         [0015]     The operator in the cab  16  can manipulate the lift arm  17  and bucket  28  by selectively actuating hydraulic cylinders  22  and  32 . By actuating cylinders  22  and causing them to increase in length, the operator moves lift arm  17 , and consequently bucket  28 , generally vertically upward in the direction indicated by arrow  38 . The bucket  28  moves generally vertically downward to the position shown in the figure when the operator actuates cylinder  22  and causes it to decrease in length.  
         [0016]     The operator can also manipulate bucket  28  by actuating cylinder  32 . The bucket  28  tilts forward about pivot points  30  when the operator causes the cylinder  32  to increase in length. Conversely, the bucket  28  tilts rearward about pivot points  30  when the operator causes cylinder  32  to decrease in length. The tilting is generally along an arcuate path indicated by arrow  40 .  
         [0017]     The loader  10  includes an engine (not shown) used to power systems including the lift arm and a drive system in a manner well known in the art. The drive system includes a pair of hydraulic pumps, such as a left pump and a right pump, coupled to the engine. The left pump is coupled to a left hydraulic drive motor that is used to drive the wheels  14  on the left side of the loader  10 . The right pump is coupled to a right hydraulic drive motor that is used to drive the wheels  14  on the right side of the loader  10 .  
         [0018]     The drive system receives a number of operator inputs to control the skid steer loader  10 . Hand control levers located inside of the cab are one example of drive systems controls. The operator moves the hand control levers to control the speed and direction of the loader  10 . The hand control levers often also include a neutral position that causes the loader  10  to stop. Another device included in the drive system and used to stop the loader is a traction lock system, or brake, that can override the hand control levers. The traction lock system is discussed below in greater detail with reference to  FIG. 3 . Still another feature of the drive system is a multiple speed range selector. The multiple speed range selector includes at least a high speed range and a low speed range. If the low speed range is selected, the loader can be operated between a first initial speed (which is often “stop”) and a low maximum speed. If the high speed range is selected, the loader can be operated between a second initial speed (often “stop”) and a high maximum speed, where the high maximum speed is greater than the low maximum speed. The drive system is also connected to a control circuit used to control operation of the loader  10 .  
         [0019]      FIG. 2  illustrates a control circuit used in controlling the operation of a power machine, such as the skid steer loader  10 . The control circuit includes a speed range selector switch  44  and brake switch input circuit  46  each providing an input signal to a controller  48 , such as a logic controller. The controller  48  processes the inputs and can provide a useable output to a speed-selector valve  50 , which in turn controls drive motor units  52 , which forms part of the speed range mechanism  53 ; and to a brake control  54 , which forms part of a traction lock mechanism  56 . The drive motor units are pump and motor assemblies where the amount of the pump portion controls the motor speed.  
         [0020]     The speed-selector switch  44  receives an input from the operator and provides an output to the controller  48  to place the power machine  10  in one of a plurality of speed modes, or speed ranges. For example, a power machine can be equipped with two speed ranges, i.e., a low speed range and a high speed range. In one example, the drive controls in the low speed range allow for finer positioning of the skid steer loader than in the high speed range. The operator can select the low-speed range for operating a sensitive tool or maneuvering difficult terrain, for example. The high speed range provides for more responsive drive controls, and an operator can select the high speed range for driving down a road, for example. The power machine can include additional operator-selectable speed ranges.  
         [0021]     The brake switch input circuit  46  provides a signal to the controller  48  to stop the wheels  14  of the loader  10 . A number of operator controlled, automatic, or otherwise, brake inputs can be provided to the brake switch  46  to indicate a desire to stop the loader  10 . For example, the switch  46  can be connected to a seat bar sensor that indicates whether the seat bar  21  is in a lowered position and the operator occupies the seat  19 . If the seat bar sensor indicates the seat bar  21  is in a raised position and the loader  10  is operational, the controller  48  may seek to stop operation of the loader  10 . Other inputs to the brake switch input circuit  46  can include other operator-selected mechanisms, such as a cab mounted traction lock switch, used to indicate a desire to stop operation of loader  10  and activate the traction lock mechanism  56 .  
         [0022]     Based on a brake input received from the brake switch input circuit  46 , the control  48  circuit provides an output to activate the traction lock mechanism  56 . One example of a traction lock mechanism  56  is shown in  FIG. 3 . The traction lock mechanism  56  of the example includes a disc  59  having a number of lugs  61  mounted to a portion of the drive mechanism  66 , such as an axle  63  ( FIG. 3 ), or other drive train component, used to drive the wheels  14  of the loader  10 . A wedge  65  is manipulated with a solenoid  64  including slug or plunger  67  that is coupled to two coils  69 ,  71 . The solenoid  64  can correspond with the brake control  54 , for example, described above. In one example, the coils  69 ,  71  are disposed one inside the other around plunger  67 . When the wedge  65  is allowed to drop onto the disc  59 , in the direction of arrow  73 , the wedge becomes engaged by lug  61  and locks up the axle  63 , precluding rotation of the axle  63  and thus precluding rotation of the wheels  14  and movement of the loader  10 . When the wedge  65  is lifted from the path of the lugs  61  on the disc  59 , the axle  63  is unlocked and the loader  10  is permitted to move.  
         [0023]     Two coils  69 ,  71  of solenoid  64  include a first coil  69  (or pull coil) that is a relatively high current coil, which can be used to pull the wedge  65  up and away from the path of the lugs  61 . When the wedge is clear of the lugs  61 , the first coil  69  is de-energized and the second coil  71  (or hold coil) is energized to hold the wedge  65  out of the path of the lugs  61 . The hold coil  71  in the example is a relatively lower current coil than the pull coil  69 . Thus, the controller  48  provides an output to de-energize the hold coil  71  and allow the wedge to drop into the path of the lugs  61  thereby locking the drive mechanism  66 , or to energize the pull coil to pull the wedge  65  out of engagement with the drive mechanism  66  and allowing the loader  10  to move.  
         [0024]     Referring again to  FIG. 2 , the controller  48  also provides a useable output to the speed selector valve  50  that is coupled to the drive motors  52 . The speed selector valve in the example is a two speed valve, or high/low valve. The valve is used to control hydraulic fluid in the drive motor units  52 . When the operator selects a high speed mode, the valve  50  is set to a high speed setting that causes the drive motors to operate in a high range. When the operator selects the low speed mode, the valve  50  sets the drive to the drive motors  52  such that the speed range is lower. The maximum speed of the loader  10  is greater in the high speed mode than in the low speed mode.  
         [0025]      FIG. 4  shows an exemplary process applied in the controller  48  to operate the brake control  54  of the traction lock mechanism  56 . During operation, the controller  48  is on standby to receive the input from the brake switch  46 , as indicated in block  75 . When the brake switch provides an input to the controller  48 , the controller  48  determines whether the loader is operating in the high speed range as indicated at block  77 . If the loader  10  is operating in the low speed range, the controller  48  activates the brake control  54  at block  83 . In one variation, the controller  48  only provides a signal to the brake control  54  and not to the selector valve  50 . If the loader  10  is operating in the high speed range, the controller  48  provides a signal to the selector valve  50  to place the drive motors  52  in the low speed range as shown at block  79 . A short time delay is provided as indicated at block  81 . The time delay in the example is a fraction of a second, and then the controller  48  applies the traction to the lock mechanism.  
         [0026]     Several variations of the process of  FIG. 4  are contemplated and a few are noted here. For example, one variation includes removing the determination of whether the loader is operating in the high speed range at block or stop  77 . In this variation, the controller  48  can always provides a signal to the selector valve  50  to place the drive motors  52  in the low speed range,  79 . If the drive motors  52  are already in the low speed range, the selector valve  50  does nothing, but the process still “selects the low speed range.” The process of Figure shows step  77  performed after step  75 , or in series.  
         [0027]     In another variation block of steps  75  and  77  are performed at or about the same time, or in parallel. In still another variation, the controller  48  can provide two signals, one signal to the speed range mechanism  53  to select the low speed range and a second signal, through a time delay, to the traction lock mechanism  56 . Still other variations are contemplated and intended to be within the scope of the invention.  
         [0028]     The present invention thus slows the vehicle through operation of the speed range selector before the traction lock mechanism is engaged. The time delay is very short, after the lower speed is selected, before the traction lock is engaged. The traction lock is a positive lock to hold the drive from moving the power machine.  
         [0029]     Although the present invention has now been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.