Patent Publication Number: US-2007114092-A1

Title: Hydraulic brake and steering system

Description:
TECHNICAL FIELD  
      The present disclosure relates to a hydraulic system and, more particularly, to a hydraulic brake and steering system.  
     BACKGROUND  
      Vehicles such as, for example, automobiles, trucks, work machines, and other types of vehicles, often include one or more traction devices to affect movement of the vehicle relative to the ground or other surface. These traction devices are driven by a vehicle power device and are often controlled with multiple hydraulic systems to affect steering or braking of the traction devices. Vehicles often include three separate hydraulic systems, one hydraulic system configured to affect braking and two hydraulic systems, a primary and a secondary system, configured to affect steering. The secondary hydraulic system is typically a redundant, back-up system and is configured to affect steering upon malfunction or failure of the primary hydraulic system. Each of these hydraulic systems often includes an electro-hydraulic valve arrangement fluidly connected between a pump and one or more actuators to control a flow rate and direction of pressurized fluid to and from chambers of the one or more actuators. As such, the valve arrangement affects braking or steering, such as, for example, by moving an actuator to affect the engagement of mechanical brakes relative to a moving part of the traction devices or by moving an actuator to affect the angle of one or more traction devices relative to a vehicle frame. Although vehicles having three separate hydraulic systems may establish adequate control of the traction devices, multiple hydraulic systems may increase the complexity of the vehicle.  
      U.S. Pat. No. 6,935,445 (“the &#39;445 patent”) issued to Johnson discloses a back-up steering system for track laying vehicles when a primary steering system is not properly functioning. The &#39;445 patent discloses a hydraulic system having a plurality of valves connected between a pump and left and right service brakes. Simultaneous actuation of the services brakes acts to slow an associated vehicle and independent actuation of the service brakes acts to steer the associated vehicle. Specifically, the &#39;445 patent discloses an electrically controlled main valve which selectively directs fluid toward a mode control valve to hydraulically bias movement thereof. Upon actuation of the main valve, the mode control valve responsively communicates fluid from the pump to the service brakes for simultaneous actuation thereof. The &#39;445 patent also discloses a pair of back-up solenoid valves which selectively and independently communicate fluid from the pump to one of the service brakes via the mode control valve. As such, the &#39;445 patent provides dual control of the right and left service brakes in either a normal braking mode, e.g., actuation of the main valve, or a back-up mode, e.g., actuation of one or both of the back-up valves.  
      Although the &#39;445 patent may provide a back-up steering system to control a track laying vehicle when a primary steering system is not properly function, the disclosed system may not be capable of increasing the maneuverability of the associated vehicle during proper functioning of the primary steering system. Additionally, the &#39;445 patent may disconnect the normal braking system when providing back-up steering to the associated vehicle. Furthermore, the &#39;445 patent may require a complex valve arrangement and control method to achieve back-up steering control of the associated vehicle.  
      The present disclosure is directed to overcoming one or more of the problems set forth above.  
     SUMMARY OF THE INVENTION  
      In one aspect, the present disclosure is directed to a hydraulic system. The hydraulic system includes a source of pressurized fluid and a plurality of fluid actuators configured to vary an amount of resistive torque applied to an associated traction device. The hydraulic system also includes a plurality of valves, each configured to selectively communicate pressurized fluid to one of the plurality of fluid actuators. The hydraulic system further includes a controller configured to control the plurality of valves as a function of at least a steering command.  
      In another aspect, the present disclosure is directed to a method of operating a hydraulic system. The method includes pressurizing a fluid and directing pressurized fluid to a plurality of valves, each one of the plurality of valves operatively associated with one of a plurality of actuators. The method also includes selectively directing pressurized fluid through each of the plurality of valves toward the plurality of actuators as a function of a first signal. The method further includes selectively directing pressurized fluid through a subgroup of the plurality of valves as a function of a second signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exemplary diagrammatic illustration of a vehicle in accordance with the present disclosure; and  
       FIG. 2  is an exemplary schematic illustration of a hydraulic system of the vehicle of  FIG. 1 . 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  illustrates an exemplary vehicle  10 . Vehicle  10  may embody an automobile, a truck, a work machine, and/or any mobile vehicle. For clarification purposes only, vehicle  10  is illustrated as a dump truck, however, it is noted that the disclosure herein is applicable to any mobile vehicle. Specifically, vehicle  10  may include a frame  12 , an operator interface  14 , and a plurality of traction devices  18 .  
      Frame  12  may include any structural unit that supports movement of vehicle  10 . Frame  12  may be, for example, a stationary base frame connecting a power source to traction devices  18 , e.g., a chassis, a movable frame member connecting one or more implements to a power source, e.g., a linkage system, and/or any other type of frame known in the art.  
      Operator interface  14  may be configured to receive inputs from an operator indicative of a desired operation, such as, for example, movement of frame  12 , traction devices  18 , and/or any other suitable operation of vehicle  10 . Specifically, operator interface  14  may include one or more operator interface devices  16  that may include proportional-type controllers, such as, for example, pedals and/or steering wheels, configured to position and/or orient components of vehicle  10 . It is contemplated that additional and/or different operator interface devices  16  may be included within operator interface  14  such as, for example, multi-axis joysticks, knobs, push-pull devices, switches, and/or other operator interface devices known in the art.  
      Traction devices  18  may include wheels, tracks, and/or other mechanisms configured to support and/or affect the yaw of vehicle  10  with respect to a surface such as, for example, the ground. Each of traction devices  18  may or may not be steerable and may include any number of mechanisms at one or more locations relative to frame  12 , e.g., one of traction devices  18  may include two adjacent wheels cooperatively coupled to one another. For example, vehicle  10  may include a first, second, third, and fourth traction device  18   a ,  18   b ,  18   c ,  18   d , two of which, first and third traction devices  18   a ,  18   c , are illustrated in  FIG. 1 . For clarification purposes only, first, second, third, and fourth traction devices  18   a ,  18   b ,  18   c ,  18   d , may be considered as a front left, front right, rear left, and rear right traction device, respectively, as conventionally referenced with respect to a mobile vehicle. It is contemplated that traction devices  18  may be configured by any conventional arrangement such as, for example, enabling steering of each of traction devices  18  or enabling steering of only first and second traction devices  18   a ,  18   b . It is also contemplated that traction devices  18  may be operatively connected together, to frame  12 , and/or to a power source of vehicle  10  in any conventional manner including, for example, a drive train, differential gear transfers, shock absorbing mechanisms and/or other suitable mechanisms. It is further contemplated that each of traction devices  18  may include one or more individual mechanisms arranged adjacent to one another, such as, for example, providing each of third and fourth traction devices  18   c ,  18   d  with two wheels each as is conventionally known in the art.  
      As illustrated in  FIG. 2 , traction devices  18  may each be operably connected to a hydraulic system  20 . Specifically, hydraulic system  20  may include one or more hydraulic actuators  22  each configured to affect the engagement of a mechanical brake and thus the amount of resistive torque applied to a respective one of traction devices  18 . The mechanical brake system may include any conventional brake system configured to apply a resistive torque to one of traction devices  18  as a function of an extension and/or retraction of a hydraulic actuator. For example, the mechanical brake system may include a disc brake apparatus wherein calipers thereof may frictionally engage a brake disc as a function of the extension and/or retraction of an associated hydraulic actuator. As such, for clarification purposes, a further description of the mechanical brake system is omitted. It is contemplated that the speed of movement of one of traction devices  18  may be a function of the amount of resistive torque applied thereto.  
      Hydraulic actuators  22  may each be respectively associated with one of traction devices  18 . For example a first, second, third, and fourth actuator  22   a ,  22   b ,  22   c ,  22   d  may be respectively associated with first, second, third, and fourth traction devices  18   a ,  18   b ,  18   c ,  18   d . Further description of hydraulic actuators  22  is made below with reference to first actuator  22   a  for clarification purposes only, and it is noted that the description thereof is applicable to second, third, and fourth actuators  22   b ,  22   c ,  22   d.    
      First hydraulic actuator  22   a  may include a tube  23  defining a cylinder and a piston  24  separating the cylinder into a first chamber  25  configured to contain pressurized fluid and a second chamber  26  configured to contain a spring  27 . Piston  24  may be movable in a first direction in response to fluid pressure supplied to first chamber  25  and may be movable in a second direction, opposite the first direction, in response to spring  27  within second chamber  26 . Specifically, pressurized fluid within first chamber  25  may bias piston  24  in the first direction to increase the frictional engagement of a mechanical brake operably connected with first traction device  18   a . Conversely, spring  27  within second chamber  26  may bias piston  24  in the second direction to decrease the frictional engagement of the mechanical brake operably connected to first traction device  18   a . As such, the amount of engagement of the mechanical brake, and thus the amount of resistive torque applied to first traction device  18   a , may be a function of the amount of pressurized fluid supplied to first chamber  25 . It is contemplated that hydraulic actuators  22  may alternatively be spring biased toward a extended position and hydraulically biased toward a retracted position.  
      Hydraulic system  20  may also include a source  30  of pressurized fluid, a low pressure source  32 , and one or more valves  34  to affect the extension and/or retraction of hydraulic actuators  22 . It is contemplated that hydraulic system  20  may include a plurality of fluid passages fluidly communicating one or more components with one another as is conventional in the art. It is also contemplated that hydraulic system  20  may include additional and/or different components such as, for example, temperature sensors, position sensors, relief valves, accumulators, pressure regulators, and/or other components known in the art. It is further contemplated that hydraulic system  20  may also be configured to affect engagement of stationary, e.g., parking, brakes, on one or more of traction devices  18 .  
      Source  30  may be configured to produce a flow of pressurized fluid and may include a variable displacement pump, a fixed displacement pump, and/or other sources of pressurized fluid known in the art. Source  30  may be drivably connected to a power source by, for example, a countershaft, a belt, an electrical circuit, or in any other suitable manner. Source  30  may be disposed upstream of low pressure source  32  and may supply pressurized fluid to valves  34 . It is contemplated that source  30  may alternatively include a plurality of pumps configured as stage pumps as is conventional in the art.  
      Low pressure source  32  may include, for example, a reservoir or a tank, configured to hold a supply of fluid. The fluid may include, for example, a dedicated hydraulic oil, an engine lubrication oil, a transmission lubrication oil, or any other fluid known in the art. One or more hydraulic systems within vehicle  10  may draw fluid from and return fluid to low pressure source  32 . It is contemplated that hydraulic system  20  may be connected to multiple separate low pressure sources.  
      Valves  34  may include first, second, third, and fourth valves  34   a ,  34   b ,  34   c ,  34   d , each respectively associated with first, second, third, and fourth hydraulic actuators  22   a ,  22   b ,  22   c ,  22   d . Valves  34  may each be configured to regulate a flow of pressurized fluid to one of hydraulic actuators  22 . Specifically, valves  34  may each include a proportional valve element that may be spring biased and solenoid actuated to move the valve element toward any of a plurality of positions. Further description of valves  34  is made with reference to first valve  34   a  for clarification purposes only, and it is noted that the description thereof is applicable to second, third, and fourth valves  34   b ,  34   c ,  34   d.    
      For example, the valve element of first valve  34   a  may be movable from a first position in which a flow of pressurized fluid may be substantially blocked from flowing toward first hydraulic actuator  22   a . The valve element may also be movable from the first position toward either a second position, in which a maximum flow of pressurized fluid may be allowed to flow from source  30  toward first hydraulic actuator  22   a , or a third position, in which a maximum flow of pressurized fluid may be allowed to flow from first hydraulic actuator  22   a  toward low pressure source  32 . It is contemplated that first valve  34   a  may alternately be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. It is also contemplated that first valve  34  may include a plurality of independent metering valves, a fixed flow area valve, and/or any other valve arrangement known in the art. It is noted that the amount of frictional engagement of the mechanical brake and thus the amount of resistive torque applied to first traction device  18   a  may be a function of the amount of actuation of the valve element of first valve  34   a  and, correspondingly, the amount of flow area through which pressurized fluid is allowed to flow.  
      As also illustrated in  FIG. 2 , hydraulic system  20  may be controlled by a control system  100 . Specifically, control system  100  may be configured to receive operator inputs via operator interface devices  16  and operate one or more components of hydraulic system  20  in response thereto. Specifically, control system  100  may include a controller  104  and a sensor  106  and may be configured to control movement of valves  34 . It is contemplated that control system  100  may include additional components such as, for example, signal communication lines, amplifiers, filters, power devices, and/or other components known in the art.  
      Controller  104  may include one or more microprocessors configured to control the operation of hydraulic system  20 . Controller  104  may include a memory, a data storage device, a communications hub, and/or other components known in the art. Specifically, controller  104  may be configured to receive inputs from operator interface devices  16  and sensor  106 . Controller  104  may also be configured to perform one or more algorithms and/or access one or more relational databases, such as, for example, maps, equations, and/or look-up tables. Controller  104  may issue commands to valves  34  as a function of the received inputs, the performed algorithms, and/or the accessed databases. For example, controller  104  may issue a signal, e.g., a current or a voltage, to affect movement of the valve elements of valves  34  to selectively control a flow rate, a pressure, and/or a direction of pressurized fluid relative to hydraulic actuators  22 . It is contemplated that controller  104  may also receive and/or issue commands to additional components of hydraulic system  20 , such as, for example, source  30 . It is also contemplated that controller  104  may be configured as a separate controller or be integrated within a general vehicle control system capable of controlling various additional functions of vehicle  10 . It is further contemplated that controller  104  may include a plurality of controllers, each configured to control one or more components of hydraulic system  20 .  
      Sensor  106  may include any conventional sensor and may be configured to sense one or more parameters indicative of an operational condition of a separate steering system  200 . Sensor  106  may include, for example, a pressure sensor configured to sense a pressure of a pressurized fluid within steering system  200 . As such, sensor  106  may communicate a signal to controller  104  which may be compared with an acceptable value or range of values to determine if steering system  200  is malfunctioning, e.g., not properly functioning. It is contemplated that sensor  106  may alternatively be any type of sensor such as, a position sensor, a temperature sensor, a power sensor, a flow sensor, a voltage sensor, a current sensor, and/or any other sensor known in the art. It is also contemplated that control system  100  may include any number of sensors configured to sense one or more parameters of steering system  200 .  
      Steering system  200  may include any conventional system configured to affect the orientation of one or more of traction devices  18  relative to frame  12  to thereby affect and/or control the yaw of vehicle  10  relative to a surface. For example, steering system  200  may include a hydraulic system, an electrical system, and/or a mechanical system. As such, for clarification purposes, a further description of steering system  200  is omitted. It is also contemplated that steering system  200  may be considered to be malfunctioning based on any rationale, such as, for example, insufficient actuation pressure within a hydraulic system, insufficient voltage within an electrical system, less than the desired actuation and/or control of one or more components with the steering system, and/or any other desired criteria. It is further contemplated that steering system  
      change the orientation of traction devices  18  by changing the angle of traction devices  18  with respect to frame  12  in any suitable orientation.  
     INDUSTRIAL APPLICABILITY  
      The disclosed hydraulic system may be applicable to any vehicle having braking and steering manipulation and/or control of traction devices. The disclosed system may be configured to provide back-up steering capability upon malfunction of a primary steering system and/or augment a functioning primary steering system. The operation of hydraulic system  20  is explained below.  
      Referring to  FIG. 2 , source  30  may receive pressurized fluid from low pressure source  32  and supply pressurized fluid to upstream sides of valves  34 . Valves  34  may selectively control the flow rate, pressure, and/or direction of pressurized fluid in response to the relative position of a respective valve element thereof. For example, valves  34  may each be movable from the first position, substantially blocking pressurized fluid from flowing toward a respective one of hydraulic actuators  22 , toward either the second or third positions. Movement of the valve element of one of valves  34  toward the second position may allow pressurized fluid to flow from source  30  toward a first chamber  25  of an associated one of hydraulic actuators  22  to establish a force capable of compressing spring  27 . Movement of the valve element of one of valves  34  toward the third position may allow pressurized fluid to flow from a first chamber  25  of an associated one of hydraulic actuators  22  toward low pressure source  32  to establish a force capable of releasing spring  27 . As a result, selective movement of the valve elements of valves  34  may affect selective movement of hydraulic actuators  22  which may, in turn, affect the amount of resistive torque applied to each of traction devices  18 .  
      Hydraulic actuators  22  may be movable in response to operator inputs communicated via operator interface devices  16 . For example, a drive torque may be supplied to traction devices  18  via a vehicle drive train to propel vehicle  10  relative to a surface as is conventional in the art. An operator may desire to slow vehicle  10  and, accordingly, may actuate one of operator interface devices  16 , e.g., an operator may depress a pedal of vehicle  10 . Additionally, an operator may desire to change the direction of vehicle  10  relative to a surface and, accordingly, may actuate another one of operator interface devices  16 , e.g., an operator may actuate a steering wheel of vehicle  10 . Actuation of one or more of operator interface devices  16  may communicate signals, corresponding to the relative positions thereof, to controller  104 . Controller  104  may, in response to one or more received signals, control one or more of valves  34  to allow pressurized fluid to flow from source  30  toward respective hydraulic actuators  22  and/or to allow pressurized fluid to flow from respective hydraulic actuators toward low pressure source  32 .  
      In response to an operator input to slow vehicle  10 , controller  104  may control movement of each of valves  34  toward the second positions thereof. For example, controller  104  may control the valve element of first hydraulic valve  34   a  toward the second position to thereby fluidly communicate pressurized fluid supplied from source  30  toward first chamber  25  of hydraulic actuator  22   a . The pressurized fluid supplied to first chamber  25  may act against the bias of spring  27  to affect movement of piston  24  and, as a result, increase the resistive torque applied to traction device  18   a . Controller  104  may similarly control second, third, and fourth valves  34   b ,  34   c ,  34   d , and as a result, vehicle  10  may be slowed as a function of the amount of actuation of one of operator interface devices  16 . It is contemplated that controller  104  may be configured to selectively increase the restrictive torque on third and fourth traction devices  18   c ,  18   d  a predetermined length of time before increasing the restrictive torque on first and second traction devices  18   a ,  18   b  as is conventional in the art, so as to reduce a resulting moment about first and second traction devices  18   a ,  18   b . That is, controller  104  may be configured to increase the resistive torque on the rear traction devices of vehicle  10  before increasing the resistive torque on the front traction devices to reduce a resultant moment which may tend to pivot vehicle  10  about the front traction devices, potentially reducing the traction of third and fourth traction devices  18   c ,  18   d  with respect to a surface.  
      In response to an operator input to change the direction of vehicle  10 , e.g., to affect a change in yaw of vehicle  10 , controller  104  may selectively control movement of one or more of valves  34  toward the second positions thereof. For example, controller  104  may compare a signal received from sensor  106  with a predetermined value to evaluate the operation state of steering system  200 . Controller  104  may determine that steering system  200  is malfunctioning if the signal received from sensor  106  is less than the predetermined value. For example, considering that sensor  106  may include a pressure sensor, controller  104  may determine that steering system  200  is malfunctioning when a received signal is indicative of substantially no or insufficiently low pressure within, for example, a hydraulic steering system  200 . Accordingly, controller  104  may be configured to selectively control hydraulic system  20  to achieve the desired steering of vehicle  10 . It is contemplated that controller  104  may substantially simultaneously control first and third valves  34   a ,  34   c  to substantially simultaneously increase the resistive torque applied to first and third traction devices  18   a ,  18   c . It is also contemplated that controller may similarly control second and fourth valves  34   b ,  34   d  and second and fourth traction devices  18   b ,  18   d.    
      Controller  104  may selectively control hydraulic system  20 , and in particular valves  34 , to affect steering of vehicle  10  when a steering command is received and it is determined that steering system  200  is malfunctioning. For example, in response to a command to turn vehicle  10  toward the left direction, controller  104  may increase the resistive torque applied to first and third (e.g., left front and rear) traction devices  18   a ,  18   c . Controller  104  may control the respective valve elements of first and third valves  34   a ,  34   c  toward the second positions to allow pressurized fluid to flow toward first and third actuators  22   a ,  22   c . As such, first and third traction devices  18   a ,  18   c  may be slowed relative to second and fourth (e.g., right front and rear) traction devices  18   b ,  18   d  resulting in vehicle  10  turning toward the left direction. Similarly, controller  104  may increase the resistive torque applied to second and fourth (e.g., right front and rear) traction devices  18   b ,  18   d  to affect vehicle  10  turning toward the right direction. Specifically, as is known in the art, the traction devices of a vehicle that are on an inner turning radius (e.g., first and third traction devices  18   a ,  18   c  when vehicle  10  is turning left), operate at a slower speed than the traction devices that are on the outer turning radius. As such, by selectively slowing first and third  18   a ,  18   c  or second and fourth  18   b ,  18   d  traction devices, controller  104  may affect turning of vehicle  10  when steering system  200  may be malfunctioning.  
      Controller  104  may also selectively control hydraulic system  20 , and in particular valves  34 , to augment steering of vehicle  10  when a steering command is received and it is determined that steering system  200  is not malfunctioning. For example, in response to a command to turn vehicle  10  in a left direction at a particular turning radius, controller  104  may increase the resistive torque applied to first and third (e.g. left front and rear) traction devices  18   a ,  18   c . As such, controller  104  may enable vehicle  10  to establish a turning radius smaller than that which could be established by steering system  200  only controlling the orientation of traction devices  18 . It is contemplated that controller  104  may include one or more algorithms and/or receive one or more inputs to indicate that an operator desired turning radius may not be achievable by steering system  200  alone. Specifically, controller may determine that a steering command input from one of operator interface devices  16  is greater than a predetermined limit value, e.g., an operator actuated one of operator interface devices  16  to establish a turning radius of vehicle  10  that steering system  200  alone may not establish without being augmented by hydraulic system  20 .  
      In response to an operator input to change the speed and direction of vehicle  10 , e.g., an operator desires slowing and steering of vehicle  10  when steering system  200  is malfunctioning, controller  104  may selectively control movement of one or more of valves  34  as a function of the input to change the speed of vehicle  10  before selectively controlling valves  34  as a function of the input to change the direction of vehicle  10 . Specifically, controller  104  may be configured to control valves  34  to suitably affect a desired resistive torque applied to traction devices  18  to establish a desired amount of slowing of vehicle  10  prior to establishing a desired amount of turning of vehicle  10 . For example, controller  104  may increase the resistive torque applied to each of traction devices  18  to slow vehicle  10  as described above before additionally increasing a resistive torque applied to first and third traction devices  18   a ,  18   c  to establish a turning radius for vehicle  10 . As such, controller  104  may be configured to establish operator inputs to slow vehicle  10  as higher priority inputs than operator inputs to change the direction of vehicle  10 . It is contemplated that controller  104  may be configured to perform one or more algorithms to establish a desired amount of slowing of vehicle  10  before establishing a desired amount of turning of vehicle  10 . It is also contemplated that controller  104  may prioritize operator inputs to slow and turn vehicle  10  by establishing a single command, e.g., a command configured as a function of an operator input to slow and an operator input to turn, or establishing multiple commands, e.g., two commands each separately configured as a function of an operator input to slow or to turn, for each of valves  34  to control the movement thereof in response to an operator input to change the speed and direction of vehicle  10 .  
      Because hydraulic system  20  and, in particular, controller  104 , may selectively control the movement of hydraulic actuators  22  and thus may independently control the corresponding amount of resistive torque applied to traction devices  18 , hydraulic system  20  may provide a back-up steering system to vehicle  10 . As such, a separate, back-up steering system may not be necessary and the complexity of vehicle  10  may be reduced. Also, because hydraulic system  20  and, in particular controller  104 , may be configured to affect the turning of vehicle  10  independent of steering system  200 , hydraulic system  20  may augment the steering capability vehicle  10 . As such, the turning radius of vehicle  10  may be reduced which may increase the maneuverability of vehicle  10 . Additionally, because hydraulic system  20  may include control system  100  configured to control valves  34  in response to both operator desired braking and steering commands, steering of turning of vehicle  10  may be accomplished through selective control of a hydraulic braking system without additional components. As such, a simple valve arrangement and controller may be achieved.  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed hydraulic system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents