Abstract:
A three transmission position shift control includes a forward position, a neutral position and a reverse position, and a switch or button operable for engaging a park brake or park lock when in the neutral position. The control can include a shift lever shiftable or between the forward, neutral and reverse positions. The park switch or button which can be a momentary switch on the lever or a hand grip of the lever is operable for controlling a solenoid that activates the park brake or park lock. Park is deactivated or released by shifting into forward or reverse.

Description:
TECHNICAL FIELD 
   This invention relates generally to a transmission shift control for vehicles, particularly work machines such as tractors and the like, and more particularly, to a transmission shift control movable or shiftable between forward, rearward and neutral positions or modes, and which includes a switch or button operable for actuating or engaging a park brake or park lock when the control is in the neutral position or mode, the control being automatically operable for deactuating or releasing the park brake or lock when moved or shifted from the neutral position or mode to the forward or reverse positions or modes. 
   BACKGROUND ART 
   Controls for the park brake or park lock on tractors having power-shuttle transmissions are typically one of two known types. The first type has a park position on a shift lever that also controls forward, neutral, and reverse operation of the transmission. The second type uses a separate mechanical park brake lever, which allows use of a three position shuttle lever. A possible shortcoming of the first type is a greater space requirement for accommodating shifting between four positions, which can result in occasional inadvertent shifting into park. A possible shortcoming of the second type is that because the shuttle lever and brake lever are separate, the shuttle lever can be operated while the park brake is inadvertently engaged. 
   Thus, what is sought is a transmission shift control operable for selecting forward, reverse, neutral and park modes, without requiring a separate park position so as to provide relative compactness, yet which reduces or eliminates the possibility of inadvertent shifting into park, and operating the transmission in the forward and reverse modes while the park brake or lock is inadvertently actuated or applied. 
   SUMMARY OF THE INVENTION 
   According to the present invention, a three position or mode shift control including a forward position or mode, a neutral position or mode, and a reverse position or mode, and a switch or button operable for engaging a park brake or park lock, is disclosed. The control preferably includes a shift lever shiftable or between the forward, neutral and reverse positions or modes, and a park switch or button is preferably a momentary switch on the lever or a hand grip of the lever operable for controlling a solenoid that actuates the park brake or park lock. Also preferably, the park switch or button is clearly visible. Park is actuated by operating the switch or button while the shift control is in the neutral position or mode. Park is deactuated or released by shifting into the forward or reverse position or mode. 
   An advantage of the present invention is a compact shuttle shift pattern with only three positions and no additional movement of the shift control to select park. As another advantage, shuttle shifting can be performed with less possibility of accidentally moving the control to the park position. As still another advantage, no separate lever is required to engage or actuate the park brake or lock. Additionally, park is automatically deactuated or released when the shift control is shifted into the forward or reverse positions. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified schematic representation of a transmission shift control including a switch for actuating or engaging a park brake or park lock when in a neutral position according to the invention; 
       FIG. 2  is a simplified, high level flow diagram showing steps of one method of operation of the shift control according to the invention; 
       FIG. 3  is a simplified block diagram showing elements of circuitry of one shift control according to the invention; 
       FIG. 4  is a simplified block diagram of circuitry of another shift control according to the invention; and 
       FIG. 5  is a perspective view of a shifter grip for the shift control of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, in  FIG. 1  a transmission shift control  10  constructed and operable according to the present invention for selecting forward, reverse, neutral and park, is shown. Control  10  includes a shift lever assembly  12  locatable adjacent to the operator position such as in the operator cab adjacent to the operator seat, or at another convenient location on a vehicle, which can be a work machine such as a tractor (not shown). Shift lever assembly  12  will be suitably connected to a transmission control (not shown) of the vehicle in a well known manner, and includes a shifter lever  14  selectably movable relative to a controller  16  between a neutral position shown aligned along a line  18 , and forward and reverse positions aligned along lines  20  and  22 , respectively, for shifting the transmission of the vehicle between neutral, forward, and reverse operating modes in the well known manner. When lever  14  is in the neutral position it is desirable to have the capability to actuate or engage a park or parking brake or lock, without having to move an additional, separate element such as a lever or pedal, and to automatically deactuate or disengage or release the brake or lock when lever  14  is moved from the neutral position to either of the forward or reverse positions. The park brake or lock will be controlled by a park brake/lock solenoid  24  which will receive power from a power source  26  of the vehicle, through controller  16 . Preferably, the park brake or lock will be actuated or engaged when solenoid  24  does not receive power from power source  26 , and disengaged when solenoid  24  is energized by the power source. The park brake or lock is manually actuable or engageable by depressing or otherwise changing the state of a park switch  28  located at a predetermined position on lever  14 . Lever  14  is movable from the neutral position by depressing a neutral latch  30 , also on lever  14 . Controller  16  is connected to power source  26 , solenoid  24 , and the transmission control by suitable conductive paths, such as wires of a wiring harness of the vehicle or the like, in the well known manner. 
   Referring also to  FIG. 2 , which shows a diagram  32  including steps of a preferred method of operation of control  10 , beginning at start block  34 , it is determined if shifter lever  14  is in the neutral position, as denoted at decision block  36 . If not, the manual control of the parking brake or lock through switch  28  is disabled, that is, switch  28  cannot be used to actuate the brake or lock, as denoted at block  38 . If shifter  14  is in the neutral position, the parking brake or lock is enabled, as denoted at block  40 . That is, switch  28  can be used. It is now determined if there is a change of state of switch  28 , as denoted at decision block  42 . If not, the state of brake remains the same. If the state of switch  28  changes, it is determined if the brake is actuated, as denoted at block  44 . If the brake is not presently actuated, it is actuated, as denoted at block  46 . If at block  44  the brake is presently actuated, the brake is deactuated or released, as denoted at block  48 . This illustrates the capability to actuate and deactuate or release the brake with shifter  14  in the neutral position using switch  28 . The brake is also automatically deactuated or released when shifter  14  is moved from the neutral position to either of the forward or reverse positions. 
   Referring also to  FIG. 3 , a preferred embodiment of controller  16  for shift control. 10  is illustrated. Controller  16  includes a forward switch  48 , a reverse switch  50 , and a neutral switch  52 , all being single pole, single throw switches having first contacts connected commonly to a power source and second contacts individually connected to an electronic control unit (ECU) transmission control  54  that can be of conventional construction and operation. Park switch  28  is shown as a normally closed momentary contact switch having a contact connected to the second contact of neutral switch  52  through a diode  58  and an opposite contact connected to one side of a coil of a relay  56 . Relay  56  has a first contact connected to the power source and a second contact connected to the second contact of neutral switch  52  through diode  58 . Solenoid  24  is connected commonly with park switch  28  and relay  56  through diode  58  to the second contact of neutral switch  52 . As noted, controller  16  is shown in neutral with normally closed park switch  28  pressed which opens the switch to effect a change of its state. 
   In operation, at start up in neutral, neutral switch  52  is open and park switch  28  is in its normally closed state, such that no power is present at solenoid  24  and, as a result, the park brake or lock is actuated. Then, when the shifter is shifted into either forward or reverse, neutral switch  52  closes, supplying power to solenoid  24  to automatically deactuate or release the brake. At the same time, because park switch  28  is normally closed, power through neutral switch  52  will flow through park switch  28  to the coil of relay  56  to close or latch it so as to connect solenoid  24  to power therethrough. Then, the shifter can be shifted through forward, reverse and neutral with the park brake or lock deactuated or released. To actuate park, when in neutral, park switch  28  can be pressed to change its state to open. This de-energizes relay  56  causing it to open. Because neutral switch  52  is open, power is removed from solenoid  24  and the brake is actuated. Then, when the shifter is moved to one of the other positions, power is supplied through neutral switch  52  to the solenoid and through the park switch to the relay to latch it and deactuate or release the brake. 
   Turning also to  FIG. 4 , a simpler version of controller  16  is shown for use with an ECU transmission control  60  having an electronic actuator and circuitry for controlling solenoid  24  via a high side driver (HSD). Controller  16  includes forward switch  48 , reverse switch  50 , and neutral switch  52  connected essentially as before to an ECU transmission control  60 . Park switch  28  connects directly to the power source and to the ECU  60 , and is operable for actuating solenoid  24  in a desired manner, such as described in reference to  FIG. 2  above. 
   In  FIG. 5 , a shifter grip  64  for lever  14  is shown, including park switch  28  at a predetermined location recessed into the side of grip  64  and upshift and downshift switches  66  and  68  thereabove. Neutral latch  30  is shown in essentially the same position as in FIG.  1 . Here, it should be noted that the grip configuration shown in  FIG. 5  is but one option and that many alternative configurations are contemplated. For example, switch  28  can alternatively be located in the upper region of grip  64  or elsewhere, as desired. 
   It will be understood that changes in the details, materials, steps, and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown.