Patent Publication Number: US-11396323-B2

Title: Electro-hydraulic steering control system

Description:
RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 15/477,705, filed Apr. 3, 2017, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present invention generally relates to a steering control system for a vehicle, and more particularly to a steering control system for a work vehicle configured to reduce the likelihood of a system failure resulting in an undesirable steering action. 
     BACKGROUND 
     Agricultural equipment, such as a tractor or a self-propelled combine-harvester, includes an electro-hydraulic steering control system to adjust the position of one or more of a vehicle&#39;s wheels to adjust a moving direction of the vehicle. Steering control systems include electro-hydraulic valves which respond to a steering control signal generated by a steering device, such as a steering wheel or joystick, or a steering control signal provided by a global positioning system (GPS) signal. Steering control systems often include one or more sensors configured to sense a position of the steering device or a position of the wheels with respect to a frame of the vehicle. In these types of systems, a failure of an electro-hydraulic valve or an incorrect steering signal to an electro-hydraulic valve by the controller software can initiate an unwanted or undesirable steering action. Such a steering action is identified by one or more of the system sensors and interpreted by a system controller. Once the undesirable steering action is identified by the system controller, a corrective signal is generated by the system controller to prevent unintended steering resulting from the failure. The identification and response to the failure takes a certain amount of time, which is often too long to prevent an undesirable result. What is needed therefore is a steering control system, which is configured such that steering action cannot be initiated by an electro-hydraulic valve or electronic command only, but must also require steering initiation action by the vehicle&#39;s driver. 
     SUMMARY 
     An electronically controlled electro-hydraulic steering system is disclosed to overcome electro-hydraulic or electrical failures of a steering control system that initiate an undesired steering action. 
     In one embodiment of the disclosure, there is provided a steering system for a work vehicle having a steerable wheel. The steering system includes a steering input device, configured to provide a steering input to move the steerable wheel, and a pilot system operatively connected to the steering input device. The pilot system includes a pilot line operatively connected to the steering input device. A piloted system includes a direction control valve, operatively connected to the pilot line, and has a piloted control valve output. A steering cylinder is operatively connected to the steerable wheel and to the piloted control valve output, wherein the steering cylinder is configured to move the steerable wheel in response to the piloted control valve output. 
     In another embodiment, there is provided a steering system for a work vehicle having a steerable wheel. The steering system includes a steering input device configured to provide a first steering input configured to move the steerable wheel in a first direction and a second steering input configured to move the steerable wheel in a second direction. A pilot system is operatively connected to the steering input device. The pilot system includes a first pilot line operatively connected to the first steering input, a second pilot line operatively connected to the second steering input, a first metering pilot valve operatively connected between the first pilot line and the second pilot line, and a second metering pilot valve operatively connected between the first pilot line and the second pilot line. A piloted system is operatively connected to the pilot system. The piloted system includes a first pressure control valve operatively connected to the first pilot line and having a first pressure control valve output, a second pressure control valve operatively connected to the second pilot line and having a second pressure control valve output, and a direction control valve operatively connected to the first pressure control valve output and to the second pressure control valve output. The direction control valve includes a first direction control valve output and a second direction control valve output. A steering cylinder is operatively connected to the steerable wheel and to the first direction control valve output and to the second direction control valve output, wherein the first direction control valve output moves the steerable wheel in a first direction and the second direction control valve output moves the steerable wheel in a second direction. 
     In still another embodiment, there is provided a work vehicle including steerable wheel, a steering input device configured to provide a steering input to move the steerable wheel, and a steering system, operatively connected to the steerable wheel and the steering input device. The steering system includes a pilot system operatively connected to the steering input device. The pilot system includes a pilot line operatively connected to the steering input device. A piloted system includes a direction control valve, operatively connected to the pilot line, and has a piloted control valve output. A steering cylinder is operatively connected to the steerable wheel and to the piloted control valve output, wherein the steering cylinder is configured to move the steerable wheel in response to the piloted control valve output. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned aspects of the present invention and the manner of obtaining them will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention, taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a side elevational view of a work vehicle, and more specifically, of an agricultural vehicle such as a tractor. 
         FIG. 2  is a simplified schematic diagram of an electro-hydraulic control system for a work vehicle having steerable wheels. 
         FIG. 3  is one embodiment of an electro-hydraulic steering control system. 
         FIG. 4  is another embodiment of an electro-hydraulic steering control system. 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the novel invention, reference will now be made to the embodiments described herein and illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the novel invention is thereby intended, such alterations and further modifications in the illustrated devices and methods, and such further applications of the principles of the novel invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the novel invention relates. 
       FIG. 1  is a side elevational view of an agricultural vehicle, and more particularly a tractor  10 , including a frame  12  supported on a pair of front wheels  14  and a set of rear wheels  16 . An operator cab  18  is mounted on the frame  12  and contains various controls for the vehicle  10  so as to be within the reach of a seated or standing operator. In one aspect, these controls may include a steering wheel  20 . An engine  22  is mounted on the frame  12  beneath a housing  24  and supplies power for driven components of the tractor  10 . The engine  22 , for example, is configured to drive a transmission (not shown), which is coupled to drive the front wheels  14  at various selected speeds and either in forward or reverse modes. In other embodiments, the rear set of wheels is driven to move the tractor, or all of the wheels are driven in an all-wheel drive mode to move the tractor  10 . 
     While the described embodiments are discussed with reference to a tractor, in addition to addition to agricultural vehicles, other work vehicles are contemplated including construction vehicles, forestry vehicles, lawn maintenance vehicles, as well as on-road vehicles such as those used to plow snow, spread salt, or vehicles with towing capability. 
     The cab  18  defines an operator workstation  26 , which is supported by the frame  12 . The cabin  18  also encloses a seat  28  for seating the operator. The operator workstation  26 , in different embodiments, includes one or more of an operator user interface, steering wheel, a joystick, an accelerator pedal, and a power take-off (PTO) control device for turning on or off the PTO. Pedals for a brake and a clutch are also located in the cabin  18 , but are not shown. 
     The user interface includes a plurality of operator selectable buttons configured to enable the operator to control the operation and function of the tractor  10 . The user interface, in one embodiment, includes a user interface screen having a plurality of user selectable buttons to select from a plurality of commands or menus, each of which are selectable through a touch screen having a display. In another embodiment, the user interface includes a plurality of mechanical push buttons as well as a touch screen. In another embodiment, the user interface includes a display screen and only mechanical push buttons. A communication antenna  30  is supported by the cabin  18  and provides for the transmission and reception of signals transmitted through the air. In one embodiment, the communication antenna  30  is a GPS antenna configured to receive and to send global positioning data to and from a GPS satellite as is known by those skilled in the art. 
       FIG. 2  is a simplified schematic diagram of the vehicle  10  and a steering control system embodying the invention. In the illustrated embodiment, the front wheels  14  are steerable by the steering wheel  20  which is located in the cab  18 . A wheel angle position sensor  32  senses the angular position of the wheels  14  with respect to the frame  12  and includes an output line  33  coupled to an electronic control unit  34 , or controller. A steering wheel angle sensor and steering input device  26  operatively connected to the steering wheel and connected via signal lines to the controller  34  and hydraulic valve assembly  46 . A wheel speed sensor  36  includes an output line  38 , which is coupled to the controller  34 , and which provides a wheel speed signal. In other embodiments, wheel speed is alternatively provided by a sensor connected to the rear wheels. Vehicle speed could also be alternatively provided by processing GPS signals. In one embodiment, the wheel speed sensor  36  is used to provide a speed of the vehicle  10 . The antenna  30  is operatively connected to a communication circuit  40 , which is operatively coupled to the controller  34 . A GPS unit  42  provides a vehicle position signal to the controller  34 . 
     The communication circuit  40  is configured to transmit signals generated by the controller  34 , which in some applications have been generated in response to information submitted by an operator through the user interface located at the operator workstation  26 . A memory  44  is operatively coupled to the controller  34  and is configured to store information. In different embodiments, the memory  44  is an internal memory located within the controller  34  or is in externally located memory. 
     The controller  34  is configured to execute software instruction stored in the memory  44 . The software includes one or more specific applications, components, programs, objects, modules or sequence of instructions typically referred to as “program code”. The program code includes one or more instructions located in memory and other storage devices which execute control algorithms to adjust the position of the wheels  14  in response to, for instance, the sensed position of the wheels provided by the sensor  32 , commands by the operator via the steering wheel or GPS signals. 
     In some embodiments, the communication circuit  40  is used for internal communication among devices or circuits located in the vehicle. In still other embodiments, the communication circuit  40  provides for unidirectional or bidirectional communication to and from the antenna  30  as well as to and from the GPS unit  42 . 
     The controller  34 , in different embodiments, includes a computer, computer system, or programmable device, e.g., multi-user or single-user computers. In other embodiments, the controller  34  includes one or more processors (e.g. microprocessors), and the associated internal memory including random access memory (RAM) devices comprising the memory storage of the controller  34 , as well as any supplemental levels of memory, e.g., cache memories, non-volatile or backup memories (e.g. programmable or flash memories), read-only memories, etc. In addition, the memory can include a memory storage physically located elsewhere from the processing devices and can include any cache memory in a processing device, as well as any storage capacity used as a virtual memory, e.g., as stored on a mass storage device or another computer coupled to controller  34  through the communication circuit  40 . The mass storage device can include a cache or other dataspace which can include databases. 
     The steering control system further includes a valve assembly  46  including one or more hydraulic circuits, including various hydraulic valves, for instance electrically controlled valves, and various hydraulic and electrical lines. The valve assembly  46  receives a charge pressure and an operating pressure from various pumps including a pump  48  and a pump  50 . In certain embodiments, the pump  48  is configured as a lower pressure charge pump and the pump  50  is configured as a higher pressure steering pump. 
     Control signals, for instance, hydraulic and electrical signals, are received by the valve assembly  46  from one or more controllers, here identified as the controller  34 , over a signal line  52 . Control signals are also received by the valve assembly  46  from the combined steering wheel angle sensor/metering pump  26  through a signal line  53 . The signal line  52 , while illustrated as a single line, in different embodiments, includes one or more signal lines to transmit electrical signals to and from the hydraulic and electrical valves of the valve assembly  46 . 
       FIG. 3  illustrates one embodiment of an electro-hydraulic steering control system  60  including the steering wheel  20  which is coupled to a drive shaft  62  operatively connected to an input metering device  64 , such as a gear, vane, piston or any other type of positive displacement pump. The metering device  64  includes a first port  66  and a second port  68 , each of which directs pressurized fluid flow in response to movement of the drive shaft  62  about a longitudinal rotational axis. A steering command angle sensor  70  is operatively connected to one of the steering wheel  20 , the drive shaft  62 , and the metering device  64 , and is configured to provide a steering command angle signal to indicate a position of the steering wheel  20  and ultimately to provide an indication of a desired angle of one or all of the steered wheels. The steering command angle sensor  70  is operatively connected to the controller  34  to provide the steering angle command signal. 
     Port  66  is operatively connected to metering pilot flow bypass restrictor valves  72  and  82  which are controlled by the controller  34  through control lines  74  and  84 . Port  66  also delivers pressurized fluid flow to pressurize a pilot line  76 , which is operatively connected to a first pilot operated pressure control valve  80 . In the same fashion, port  68  is operatively connected to metering pilot flow bypass restrictor valves  72  and  82  which are controlled by the controller  34  through control lines  74  and  84 . Port  68  also delivers pressurized fluid flow to pressurize a pilot line  86  which is operatively connected to a second pilot operated pressure control valve  88 . 
     Valves  72  and  82 , in different embodiments, are either normally open or normally closed when the system is not operational. In one specific embodiment, one of the valves  72  and  82  is a normally open valve and the other is normally closed valve so that in the event of a general electrical or hydraulic failure, steering response is neither least responsive nor most aggressive. In the illustrated embodiment, valve  72  is normally closed and valve  82  is normally open. Each of the valves  72  and  82  are continuously variable valves in which the amount of flow through the valve is adjusted by the controller  34  through control lines  74  and  84 . 
     Pilot line  76  and pilot line  86  are operatively connected to a low pressure source  81  including a sump  83 . A valve  85  is coupled between lines  76  and  86  to assure that the pilot system remains full of fluid. The external pressure source could be a separate pump, flow from another unrelated system on the vehicle, or from a pressure reducing valve connected to a main source of steering flow, such as a pump  110 . 
     The metering device  64  directs fluid flow and consequently adjusts the pressure of the fluid in both the pilot line  76  and pilot line  86 . The amount of pressure of the fluid in one of the fluid lines is a direct result of steering direction determined by the metering device  64 . 
     A check valve  87  and a relief valve  89  assure that pressure in the pilot system does not exceed predetermined allowable limits. The relief valve  89  is operatively connected to the sump  83 . When the input metering device  64  is embodied as a positive displacement pump, a rotation of the steering wheel in a first direction, for instance a clockwise direction as illustrated, enables the port  68  to provide a positive flow of fluid into the pilot line  86 . At the same time, a negative flow of fluid into the port  66  occurs. Counterclockwise rotation of the steering wheel, as illustrated, provides a positive flow of fluid into the pilot line  76  and a negative flow of fluid into the port  68 . 
     The fluid pressure in each of the pilot lines  76  and  86  is adjusted by each of the valves  72  and  82  in response to control signals generated by the controller  34  and transmitted through control lines  74  and  84 . By controlling the amount of pressure in each of the pilot lines  76  and  86 , the pressure signal to each of the first pilot operated pressure control valve  80  and the second pilot operated pressure control valve  88  is provided. 
     Since the valve  72  and valve  82  have an orifice size controlled by the controller  34  and provide the appropriate amount of pressure in pilot lines  76  and  86 , these valves are considered to be part of a pilot system. The pilot system also includes the fixed orifices or restrictors  92  and  96 , external low pressure source  81 , metering pump  64  and the other described valves which establish fluid pressure in pilot lines  76  and  86 . In other embodiments, the pilot system includes fewer number of or a larger number of devices. The pilot system output lines, pilot lines  76  and  86  are connected to valves  80  and  88  which control a flow and directional control valve which ultimately controls the direction of the wheels. Valves  80  and  88  are considered to be a piloted system. 
     The flow produced by the metering pump  64  at port  68  along pilot line  86  moves not only to a pilot area  90  of valve  88 , but some flow attempts to move to the port  66  of the metering pump  64 , through a restrictors  92  and  96  and valves  72  and  82  instead of pressurizing the pilot area  90  of valve  88 . This bypass flow creates pressure on pilot area  90  of pressure control valve  88 . Valve  88  then provides an output pressure generally proportional to the pressure applied to its pilot area  90 . Valve  88  includes an output pilot area  91 . 
     Likewise, the flow produced by the metering pump  64  at port  66  along pilot line  76 , moves not only to a pilot area  94  of valve  80 , but some flow attempts to move to the port  68  of the metering pump  64 , through a restrictors  96  and  92  and valves  82  and  72 , instead of pressurizing the pilot area  94  of valve  88 . This bypass flow creates pressure on pilot area  94  of pressure control valve  80 . Valve  80  then provides an output pressure generally proportional to the pressure applied to the pilot area  94 . Valve  80  includes an output pilot area  93 . 
     Each of the valves  80  and  88  generates an output pressure at pressure outputs  98  and  100  respectively. Pressure output  98  is operatively connected to a pilot operated flow and direction control valve  102  at a first pilot area  104 . In one embodiment, the control valve  102  is a three position, pilot pressure controlled spool valve. The pressure output  100  is operatively connected to the control valve  102  at a second pilot area  106 . Fluid pressure provided at either one of the first or second pilot areas  104  and  106  causes the spool of the valve  102  to move from a center position to cause oil to flow to a steering cylinder  108  which moves the wheels  14  in a direction dictated by the steering device  20 . A valve sensor  109  is configured to determine the position of the spool of the valve  102  and to provide the determined position as a signal to the controller  34 . The position of the steering cylinder  108  is identified by a cylinder position sensor  111 . The identified position of the cylinder  108  is provided to the controller  34 . Alternatively, a steered wheel angle position sensor could be used instead of the steering cylinder position sensor. Both the sensor  111  and the steered wheel angle position sensor  32  are considered as steering output feedback sensors. 
     By specifying a difference in the input pilot area  90  and an output pilot area  91  of valve  88 , and likewise for output pilot area  93  of valve  102 , a pilot pressure is provided to valve  102  which is higher than the output pressure provided by the metering pump  64 . In this way steering hand wheel torques can be reduced. 
     In the illustrated embodiment, valves  80  and  88  are pilot operated pressure reducing/relieving valves. In another embodiment by connecting a flow source directly to the pilot areas of valve  102 , valves  80  and  88  are configured as pilot operated pressure relief valves. 
     A hydraulic pump  110  is operatively connected to the valve  102 , which when activated by one of the first and second pilot areas  104  and  106 , supplies fluid under pressure to move the steering cylinder  108 . The hydraulic pump  110  is also operatively connected to pressure control valves  80  and  88 . A sump  112  includes a source of fluid for use by the pump  110 . Each of the valves  80 ,  88 , and  102  includes fluid outputs which deliver excess fluid to the sump  112  when not required to adjust the position the steering cylinder  108 . The pump  110  is generally considered to be a high pressure source of fluid. 
     The output pressure from valve  88  is applied to the pilot area  106  of valve  102  causing it to move from its center position which in turn causes oil to flow to cylinder  108  and hence turn the steerable wheels. It is usually desired to have a position responsive steering system whereby the position of cylinder  108  (and the steered wheels) is generally proportional to the rotational position of the steering wheel from a center point. In one embodiment, the position responsive steering is accomplished by controlling or preventing bypass of the pilot flow through orifices  92  and  96  through control of valves  82  and  72 . Valves  82  and  72  are controlled by the controller  34 . 
     In one embodiment, the controller  34  monitors signals from sensors  70 ,  109 , and  111  when all are utilized. In one possible control algorithm, input sensor  70 , valve sensor  109 , and cylinder position sensor  111  are monitored and valves  82  and  72  are controlled such that valve  102  produces flow to cylinder  108  to provide position responsive steering. In this control scheme, there is an inner control loop using sensor  109  and sensor  70  and an outer control loop between sensor  111  and sensor  70 . The inner control loop is used by the controller  34  to monitor the rate of turning of the steering device  20  via sensor  70  and to monitor the position of valve  102  via sensor  109 , and in response to these sensor outputs, control valves  72  and  82  are adjusted such that given the output/input characteristics of valve  102 , a flow is produced that approximately provides position responsive steering. The outer control loop is used by the controller to monitor the position of steering device  20  via sensor  70  and the steered wheel position or angle via sensor  111  to make additional adjustments to the control of valves  72  and  82  to improve the accuracy of the position responsive steering. 
     In one embodiment, when steering cylinder  108  reaches an end of travel or is prevented from moving further due to overload, valves  82  and  72  are closed to give tactile feedback to the operator that steering has either reached its limit or stalled. 
     In another embodiment, the control algorithm is designed to include variable steering ratio, either as a function of vehicle speed, turn angle or some other parameter. For example, under medium speed driving conditions of approximately 16 kilometers per hour (kph) as determined by signals from a wheel speed or GPS sensor the control algorithm might be written so that three (3) complete turns of the steering wheel  20  results in turning the steerable wheels from full left to full right. Whereas, at lower and higher speeds the control algorithm could be written so that the internally coded parameters result in a full left to right turn with only one and one half (1.5) turns or five (5) turns respectively of the steering wheel  20 . In like manner it would be possible to change the control parameters as a function of steered wheel angle to effect steering ratio rather than vehicle speed. In like manner it would be possible to change the control parameters from some external input provided by the attached or towed implement or from a setting input by the driver to result in more or less responsive steering. The means to accomplish this are well known by those schooled in the art of control software development. 
     In still other embodiments, the steering system includes one or more fluid temperature sensors to identify fluid temperature(s) which may be utilized to improve performance. 
       FIG. 4  illustrates another embodiment of an electro-hydraulic steering control system  120  having an external steering control using an electronic guidance system, such as one using GPS or row following signals. In this embodiment, the steering control system of  FIG. 3  is configured to include additional pilot valves to provide an integrated cost effective external control. The devices which are common to both of the embodiments of  FIGS. 3 and 4  are identified with the same element numbers and different or additional devices are newly identified. 
     As illustrated in  FIG. 4 , the steering system  120  includes the capability of external steering control such as guidance systems based on GPS (Global Positioning System) signals. In this embodiment, the steering system is be configured to include additional pilot valves to provide an integrated cost effective external control. 
     One means of providing integrated external control capability shown in  FIG. 4  includes the addition of external control valves  122 ,  124 ,  126 , and  128 . A relief valve  130  and pressure reducing valve  132  are provided to enable pump  81  to keep the main steering system pilot circuit full of fluid and to also provide a pressure and flow source for the external control. Alternatively, the pressure and flow source for external control may be provided by supplying the pressure and flow through a pressure reducing valve connected to the high pressure pump  110 . The GPS unit  42  is operatively connected to the controller  34  as illustrated in  FIG. 2 . 
     Each of the external electronic control valves  122 ,  124 ,  126  and  128  includes control lines operatively connected to a controller  136 , which in this embodiment is configured with a different or additional set of control instructions than the controller  34  of  FIG. 3 . The control valves  126  and  128 , in this embodiment, provide redundancy against unintended external control in the event of failure of valves  122  and  124 . In other embodiments, valves  126  and  128  are not included. In the illustrated embodiment, valves  122  and  124  are represented as direction/flow control type valves. In other embodiments, the valves  122  and  124  are pressure reducing/relieving valves. 
     A switch  135  is operatively connected to the controller  136 . Operation of the switch in concert with the controller  34  results in a first state indicating that the vehicle is to be operated in a manual mode and a second state indicating that the vehicle is to be operated in an external control mode, i.e. the GPS mode. In one embodiment, the switch  135  is located at the operator workstation  26  for use by the operator. The operator moves the switch from one state to the other state to signal to the controller  136  that the vehicle is in one of the manual control mode or the external control mode. In addition, movement of the steering wheel as indicated by the sensor  70  will cause the controller  136  to change control mode from external to manual mode. 
     Since the steering control system  120  includes the use of the external control to adjust the cylinder  108 , a pilot operated flow and direction control valve  134  includes a first pilot area  137  operatively connected to the pilot line  98  and a second pilot area  138  operatively connected to the pilot line  100 . The pilot areas  137  and  138  provide the same function as pilot areas  104  and  106  of  FIG. 3 . The valve  134  includes two additional pilot areas, pilot areas  140  and  142 , in this embodiment. Pilot area  142  is operatively connected to valve  126  and pilot area  142  is operatively connected to valve  128 . A valve position sensor  143  identifies the position of the valve  134 . 
     In another embodiment, the valve  134  does not include the pilot areas  140  and  142 . Instead the valves  80  and  88  each include an additional pilot area (not illustrated) which connects to one of the outputs of the valves  126  and  128 . In this case, valves  122  and  124  are configured as pressure reducing relieving valves. 
     For a normal steering using an input at the steering device  20 , each of the valves  122 ,  124 ,  126 , and  128  are in a non-energized position which drains any control pilot pressure provided by the pump  81  to the drain  83 . Steering is accomplished as described with respect to  FIG. 3 . 
     During an external control mode of the embodiment of  FIG. 4  which includes the extra pilot areas  140  and  142  of valve  134 , valves  122 ,  126 ,  124  and  128  are controlled by the controller  136 . In the alternative configuration with the extra pilot areas on valves  80  and  88 , one or both of valves  72  and  86  are held in the open position. 
     To execute an externally controlled turn in one direction, valve  126  is energized to connect the output of valve  122  to one external control pilot area  142  of valve  134 , or to valve  88  if that configuration is used. Valve  122  is then energized, sending oil to move valve  134  directly, or via an increase in output pressure from valve  88 , such that flow is directed to cylinder  108 . Electronic control of valve  122  is accomplished through closing a control loop around desired turn angle and sensor  111  and possibly valve position sensor  143  in a similar manner as described for the embodiment of  FIG. 3 . A turning of the wheels in the opposite direction is accomplished similarly by energizing valves  128  and  124 . 
     In additional embodiments, an additional external steering valve, such as steering valve  134 , is provided to operatively connect in parallel with the illustrated vehicle steering system. 
     While exemplary embodiments incorporating the principles of the present disclosure have been described hereinabove, the present disclosure is not limited to the described embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this disclosure pertains and which fall within the limits of the appended claims.