Abstract:
A steering system for a vehicle that uses primary and secondary steering actuation devices in combination with primary and secondary valve elements to provide fluid flow within a valve body. The primary and secondary valve elements are both electrically actuated by a control unit such that if the primary steering actuation device or valve element fails the secondary steering actuation device and valve element can supply pilot oil to the system.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a steering device for a vehicle. More specifically, this invention relates to a steer by wire valve system. 
         [0002]    Steering systems for hydraulically driven vehicles involve complex systems that use valve elements to control the operation of a spool valve. These systems however do not provide electric control of the movement of the spool valve, nor are they integrated into a single valve package. 
         [0003]    Steering by wire driving systems eliminate the mechanical link between the steering wheel and wheels by providing two separate closed control system loops. The first loop controls the actuation associated with the steering wheel while the second loop controls the actuation associated with the wheels. By combining the two with a control unit improved vehicle handling is achieved. Despite these advantages often times the steering actuators and valves used in the steer by wire system become worn and malfunction causing the entire system to be replaced. 
         [0004]    Therefore, it is a principal object of the present invention to provide an improved steer by wire steering system, with electrically redundant actuation. 
         [0005]    Another object of the present invention is to provide an improved steer by wire steering system in a single package. 
         [0006]    Yet another object of the present invention is to provide a durable, long lasting steering system for a vehicle. 
         [0007]    These and other objects, features or advantages of the present invention will become apparent from the specification and claims. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The steering system for a vehicle. The steering system has a primary actuator that is fluidly connected to a primary valve element that is fluidly connected with a steer by wire valve body. Within the valve body is a proportional control spool valve that controls steering operations. Additionally the valve body empties or drains into a tank. The system also adds a secondary valve element that is fluidly connected to the valve body by a secondary valve element. Thus, when the primary valve element is in a first position and the secondary valve element is also in a first position, the primary valve directs pilot oil from the primary actuator to the proportional control spool valve while the secondary actuator directs fluid to the tank. When the primary actuator malfunctions a control unit is able to actuate the primary and secondary valve elements into second positions wherein the primary actuator directs fluid to the tank while the secondary actuator directs pilot oil to the proportional spool valve to continue operation of the steering system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic diagram of a steering system; and 
           [0010]      FIG. 2  is a schematic diagram of a steering system. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0011]      FIG. 1  shows a steering system  10  that is a steer by wire system used as a hydraulic steering system for a wheel loader or the like. The system contains a valve body  12  with an inlet  14  that has a pilot pressure port  16 , a load sense port  18 , a high system load sense pressure port  20 , and a pressure port  22 . In a preferred embodiment the valve body is a wire valve body. The inlet ports  16 ,  18 ,  20  and  22  allow fluid to flow within the system to a plurality of valve elements  24  within the valve body  12  to an outlet  26  that contains a low pressure tank port  28  and a tank port  30 . Additionally, within the valve body  12  is a proportional control spool valve  32 . 
         [0012]    Fluidly connected to the valve body  12  is a primary steering actuator  34  that fluidly connects with the valve body  12  via first and second primary fluid lines  36  and  38  that flow through primary valve element  40  to the valve body  12 . The primary valve element  40  is within a primary cartridge manifold  42  and in a preferred embodiment is a solenoid cartridge control valve. 
         [0013]    The primary valve element  40  in a first position provides a direct fluid flow path for directing pilot oil from the primary steering actuator  34  to the proportional control spool valve  32  to actuate this valve. Meanwhile, when the primary valve element  40  is actuated the valve creates a fluid flow path that directs pilot oil from the primary steering actuator  34  to drain out of the low pressure tank  28 . 
         [0014]    On the opposite side of the valve body  12  a secondary steering actuator  44  provides first and second secondary fluid lines  46 ,  48  that flow into a secondary valve element  50  within a secondary cartridge manifold  52 . In a preferred embodiment the secondary valve element  50  is a solenoid cartridge control valve. The secondary valve element  50  operates such that when in a first position a fluid flow path directs pilot oil from the secondary steering actuator  44  to drain from the low pressure tank. Whereas when actuated in a second position the control valve  50  provides a fluid flow path that directs pilot oil from the second steering actuator  44  to the proportional control spool valve  32  to actuate the valve. 
         [0015]    In a preferred embodiment the primary and secondary valve elements  40  and  50  are electrically controlled by a control unit  54 . The control unit  54  monitors the functioning of the primary actuator  34  and valve element  40  such that when a failure in either is detected the control unit  54  simultaneously actuates the primary and secondary valve elements  40  and  50  from their first positions to their second positions. 
         [0016]    Thus, in operation when the primary valve element  40  and secondary valve element  50  are in a first position, pilot oil flows from the primary steering actuator to the proportional control spool valve  32  to operate the system  10  while the secondary steering actuator  44  drains pilot oil to the low pressure tank  28  or tank  30 . When a malfunction is detected within the primary valve element  40  the controller or control unit  54  sends a signal to actuate the primary valve element  40  from a first primary position wherein the pilot oil flows to the proportional control valve  32  from the primary actuator  34  to a second primary position wherein the pilot oil flows from the primary actuator  34  to the tank  28 . 
         [0017]    Simultaneously, the control unit  54  actuates the secondary valve element  50  from a first secondary position wherein pilot oil flows from secondary actuator  44  to the tank  28  to a second secondary position wherein the pilot oil flows from the secondary actuator  44  to the proportional control spool valve  32 . Thus, the proportional control spool valve  32  remains operational despite malfunction of the primary valve element  40  or the primary steering actuator  34 . Additionally this arrangement allows a controller to electrically control the operation of the spool valve  32  by positioning the primary and secondary valve elements  40  and  50 . 
         [0018]    Therefore, the valve or steering system  10  contains an integral secondary electronic valve actuator to allow proportional control of the spool in the event the primary electronic valve actuator fails. The secondary actuator can provide equal performance and functionality of the primary actuator. This design, by having a single package, also allows mobility for usage on the smaller product line of proportional hydraulic valve. Thus, at the very least, all of the stated objectives have been met. 
         [0019]    It will be appreciated by those skilled in the art that other various modifications could be made to the device without the parting from the spirit in scope of this invention. All such modifications and changes fall within the scope of the claims and are intended to be covered thereby.