Abstract:
A vehicle steering mode selection control system includes an operator controlled push-to-turn switch steering mode select device, and a control circuit operatively connected to the mode select device, to steering mode actuators, to steering mode indicators and to wheel alignment indicators. The control circuit includes a timer which is actuated for a certain time period in response to pushing of the push-to-turn switch. A lamp control module is connected to the timer and permits illumination of the wheel alignment indicator lamps only during this time period. A relay is connected between the push-to-turn switch and the timer to prevent the lamp control module from responding during the time period to further pushing of the steering mode select device.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a mode selection control, and more particularly, to a vehicle steering mode selection control. 
     Various types of vehicles, including telescopic handler vehicles, or “telehandlers”, have four wheel drive, four wheel Ackermann type steering and multiple steering modes. These steering modes can include a 4-wheel steering mode for tight situations (wherein the front wheels steer opposite to the rear wheels), a 2-wheel steering mode for road travel (wherein only the front wheels are steered), and a 4-wheel crab steer mode (wherein the front and rear wheels turn in the same direction) so that the vehicle moves in a different direction, but its orientation does not change. 
     Various apparatus and means for switching between these different steering modes are known. For example, it is known to use a solenoid operated three position valve to control fluid communication from a steering valve to the front and/or rear axle steering actuators. It is also known to use electrical switches to control the operation of the three position valve, and with such a system the operator may choose to look at the position of the wheels and switch between steering modes when the wheels are judged to be in a straight orientation. Some known production vehicles include a steering position sensor and illuminate a lamp on the operator console to provide the operator with information as to whether or not the wheels are straight. It is know to use sensors on both axles and two lamps, one for each axle. 
     It is also known to use various types of switches or control devices to switch between modes, the most common being a rocker or rotary switch. It is also known to use a separate switch to disable the indicator lamps when not in the process of switching between steering modes. Also known are automated systems which permit pre-selection of the desired steering mode, but wherein the steering mode is not actually changed until the wheels are steered to the center. With such automated systems, the operator is not provided with an indication of the position of the wheels. 
     There are certain problems associated with these known designs. For example, the steering mode can be accidentally or inadvertently changed by incidental contact with the switch. This could result in an undesired movement of the vehicle. Also, in the systems with the indicator lamps, the lamps are illuminated each time the wheels are steered through the straight ahead position. This illumination of the lamps is potentially distracting to the operator and does not provide any advantages during normal machine operation. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide a vehicle steering mode selection control which prevents accidental or inadvertent changing of the steering mode. 
     A further object of the invention is to provide such a vehicle steering mode selection control which prevents unnecessary illumination of indicator lights. 
     These and other objects are achieved by the present invention, wherein a vehicle steering mode selection control includes a dual motion (push to turn) rotary switch which cooperates with a timer circuit, a lamp control unit, wheel alignment sensors, wheel alignment lamps, and a “system on” lamp. To change modes, the operator pushes the switch so that it can be turned to select a different steering mode. Pushing the switch starts the timer, activates the wheel alignment sensors, activates or energizes the lamp control unit for a limited time period and illuminates the “system on” lamp, indicating that the wheel alignment sensors and the lamp control unit are ready for use by the operator. When the wheels are steered to the centered or straight ahead position, the wheel alignment sensors and the lamp control unit cooperate to illuminate the corresponding wheel alignment lamps so that the operator can rotate the switch to change steering modes knowing that the wheels associated with the illuminated lamp are aligned straight. The timer provides a limited, pre-determined length of time for making the steering mode change with the assistance of the wheel alignment lamps. When the timer times out, all the wheel alignment lamps are kept off, but the operator can still change steering modes without the assistance of the wheel alignment lamps. If the operator chooses to push the switch and then immediately turn it to change the steering mode (without checking the status of the lamps), the system will immediately respond and change the steering mode as commanded. If timer times out before the switch is turned, the sensors and lamp control unit are de-activated, but the operator can still change steering modes without the assistance of the wheel alignment lamps. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view of a portion of an operator&#39;s control panel showing a steering mode select switch and indicator displays according to the present invention; 
     FIG. 2 is an electrical schematic diagram of the steering mode and indicator light control circuit of FIG. 1; 
     FIG. 3 is an electrical schematic diagram of the steer indicator module of FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a portion of a vehicle control panel  10  for a vehicle (not shown) having wheels (not shown) and a steering system (not shown) which is capable of steering the vehicle in a plurality of steering modes. Panel  10  includes a steering mode select switch  12 . Switch  12  is preferably a dual motion switch, such as a commercially available push-to-turn switch. The portion of panel  10  includes a crab steer symbol  14 , a 2 wheel steer symbol  16  and a 4 wheel steer symbol  18 . Panel  10  also includes a wheel or axle alignment symbol  20  with openings behind which are mounted indicator lamps or LEDs, including a pair of front wheel alignment lamps  22 , a pair of rear wheel alignment lamps  24  and an alignment “system on” lamp  26  (preferably green). The switch  12  has a knob  28  with an alignment mark  30  which will point to one of the symbols  14 - 18  as it is rotated to actuate the corresponding steering mode. The switch  12  and the lamps  22 - 26  are connected to a control circuit  32 , which is connected to wheel alignment sensors  33  and to steering mode control solenoids  34 . The crab steer symbol  14  is preferably illuminated by a lamp or LED  15 . 
     Referring now to FIG. 2, the switch  12  includes a first set of contacts  36  connected to a crab steer solenoid  38 , a second, unused set of contacts, a third set of contacts  40  connected to a 4 wheel steer solenoid  42 , and a fourth set of contacts  44  connected to a terminal  46  of an axle lamp relay  48 . The switch element  50  of switch  12  is connected to +12 volts via fuse  52 . The first set of contacts  36  are also connected to steer indicator module  54 . 
     Relay  48  also includes a terminal  56  connected to a terminal B 1  of module timer unit  58 . Timer unit  58  includes a terminal A 1  connected to +12 volts via fuse  62 , a terminal C 1  connected to steer indicator or lamp control module  54  and to a front axle or wheel alignment sensor  70  and a rear axle or wheel alignment sensor  72 , and a terminal B 2  connected to ground. Timer  58  operates to connect terminal A 1  to C 1  for 90 seconds (thus applying +12 volts to the lamp control module  54  and to the sensors  70  and  72 ) when +12 volts is applied to terminal B 1 . Relay  48  also includes a terminal  68  connected to timer terminal C 1 . Sensors  70  and  72  are also connected to ground and to the lamp control module  54 . Sensors  70  and  72  are preferably steering cylinder (not shown) position sensors, such as commercially available magnetic sensors which generate a signal when the steering cylinder, or wheels (not shown) is centered, which are commercially available from Ognibene SPA, or the equivalent. The lamp control module  54  is connected to lamps  15  and  22 - 26 , and to +12 volts via headlight switch  74 . 
     Referring to FIG. 3, the lamp control module  54  includes an array of driving transistors connected as shown between, on one hand, sensors  70  and  72 , +12 volts, crab steer solenoid  38 , a +12 volt dimmer control (not shown) and ground, and on the other hand, front wheel alignment lamps  22 , rear wheel alignment lamps  24 , system “ON” lamp  26  and crab steer lamp  15 . 
     The above described system actuates the steering mode selected by the switch  12 , and additionally controls the lamps  15  and  22 - 26 . Before switch  12  can be turned, it must first be pushed in, and this acts as a reminder to the operator in case the operator desires to coordinate the steering mode change with alignment of the wheels (not shown). Pushing the switch  12  causes the timer  58  to energize the lamp control module  54  for a time period, such as 90 seconds, and turns on lamp  26 , which indicates to the operator that the lamp control module  54  is “on” and that the indicator lamps  22 - 24  can be used in connection with changing the steering mode. When the front or rear wheels (not shown) are centered, a signal from the corresponding wheel alignment sensor  70  and/or  72  causes the illumination of the corresponding front/rear wheel alignment lamp  22  and/or  24  on the panel  10 . These lamps serve as a convenient guide signaling to the operator when it is desirable to change modes. When the timer  58  times out after 90 seconds, the lamps  22 - 26  are extinguished. However, the system will change steering modes in response to rotation of knob  28  after the timer  58  times out. 
     Preferably, the steering mode switch  12  is a commercially available three position, push-to-turn, rotary switch with momentary contacts  44  activated by the “push” function. The switch  12  cannot be turned without the closing of the momentary contacts  44 . When switch  12  is in a first position with mark  30  pointing to crab steer symbol  14 , the control circuit  32  applies current to the crab steer solenoid  38 , which places the vehicle (not shown) in a crab steering mode. When switch  12  is in a second position with mark  30  pointing to 2 wheel steer symbol  16 , the switch output is 0V and the control circuit  32  de-energizes solenoids  38  and  42 , which places the vehicle (not shown) in a 2 wheel steering mode. When switch  12  is in a third position with mark  30  pointing to 4 wheel steer symbol  18 , the control circuit  32  applies current to the 4 wheel steer solenoid  42 , which places the vehicle (not shown) in a 4 wheel steering mode. 
     More specifically, when the steering mode switch  12  is pushed it activates an “alignment mode”. This engages the momentary contacts  44  and voltage is applied through relay  48  to the timer  58 , which energizes and starts the timer  58 . The timer  58  will remain energized for the certain time period, and during this time period the output of timer  58  will be +12 volts, and +12 volts will be applied to the steering indicator module  54 . The energizing of the timer  58  also energizes relay  48 , which causes relay  48  to open and thereby preventing the system from responding to further “pushes” of switch  12 . The timer  58  also energizes and activates front wheel alignment sensor  70  and rear wheel alignment sensor  72 . Lamp  26  is turned on to indicate that the lamp control module  54  is energized and activated. When the front or rear wheels are centered, the output of corresponding sensor  70 , 72  goes “low” and module  54  turns on the corresponding lamps  22 , 24  on the display panel  10 . A conventional dimmer control (not shown) may be used to dim the lamps  22 - 26  during the night. 
     If timer  58  times out (the certain time period expires) before knob  28  is turned, the module  54  is de-activated and the lamps  22 - 26  will not turn on, even when the front or rear wheels are centered. 
     While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.