Patent Publication Number: US-6655709-B2

Title: Steer-by-wire steering apparatus with actuatable mechanism

Description:
TECHNICAL FIELD 
     The present invention relates to a steering apparatus for turning the steerable wheels of a vehicle in response to rotation of a vehicle steering wheel. 
     BACKGROUND OF THE INVENTION 
     Power steering gears are common in modern vehicles. Typically, one or more rigid shafts connect a vehicle steering wheel to an input shaft of the power steering gear. The rigid shafts must be routed from the vehicle steering wheel to the input shaft of the power steering gear. Routing the rigid shafts between the steering wheel and the steering gear is often difficult, as other vehicle components must not interfere with the shafts. 
     Some known vehicle steering systems have eliminated the rigid shafts. Such systems are commonly referred to as “steer-by-wire” systems. In steer-by-wire systems, there is no mechanical connection between the steering wheel and the steering gear. Instead, an assembly associated with the steering wheel sends an electronic signal to an assembly associated with the steering gear. The electronic signal actuates the steering gear. Since steer-by-wire systems have no mechanical connection, routing of the rigid shafts between the steering wheel and the steering gear is avoided. However, with no mechanical connection, steering control of the vehicle is lost if the steer-by-wire system fails. 
     SUMMARY OF THE INVENTION 
     The present invention is a steering apparatus for turning steerable wheels of a vehicle in response to rotation of a vehicle steering wheel. The apparatus comprises a first assembly, a second assembly, and a mechanism. The first assembly is operatively coupled to the steering wheel. The first assembly includes components for monitoring applied torque and angular rotation of the steering wheel and for transmitting a first signal indicative of the applied torque and angular rotation of the steering wheel. The second assembly includes a steering gear for, when actuated, turning the steerable wheels of the vehicle and components for receiving the first signal and actuating the steering gear in response to the first signal. The mechanism has first and second modes of operation. The mechanism, when in the first mode of operation, provides a mechanical connection between the steering wheel and the steering gear for enabling manual actuation of the steering gear. When the mechanism is in the second mode of operation, the steering wheel and the steering gear lack a mechanical connection for enabling manual actuation of the steering gear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic illustration of a vehicle steering apparatus constructed in accordance with the present invention in a condition providing a mechanical connection between a steering wheel and a steering gear; 
     FIG. 2 is a schematic illustration of a vehicle steering apparatus constructed in accordance with the present invention in a condition without a mechanical connection between the steering wheel and the steering gear; 
     FIG. 3 is a schematic elevation view, partially in section, through the steering gear of the vehicle steering apparatus of FIG. 1; 
     FIG. 4 is a cross-sectional view taken approximately along line  4 — 4  of FIG. 3; 
     FIG. 5 is a cross-sectional view taken approximately along line  5 — 5  of FIG. 1; 
     FIG. 6 is a schematic illustration of a portion of a clutch of the vehicle steering apparatus of FIG. 1 shown in a first condition of engagement; and 
     FIG. 7 is a schematic illustration of a portion of a clutch of the vehicle steering apparatus of FIG. 1 shown in a second condition of engagement. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 schematically illustrates a vehicle steering apparatus  10  constructed in accordance with the present invention. The vehicle steering apparatus  10  includes a vehicle steering wheel  12 . The steering wheel  12  is of known construction and is manually rotatable by a vehicle operator. 
     A shaft  14  is fixed to the center or hub of the steering wheel  12 . Angular rotation of the steering wheel  12  results in an equivalent angular rotation of the shaft  14 . The shaft  14  extends from the steering wheel  12  through a first assembly  16 . 
     The first assembly  16  is operatively coupled to the vehicle steering wheel  12  via the shaft  14 . The first assembly  16  includes a torque/position sensor  18 , a first electric motor  20 , and a first electronic control unit  22 . The first assembly  16  is integrated into a single unit through which the shaft  14  passes. 
     The torque/position sensor  18  of the first assembly  16 , shown schematically in FIG. 1, is operable to sense operator applied torque and angular rotation of the steering wheel  12 . The torque/position sensor  18  also generates signals indicative of the applied torque and angular rotation of the steering wheel  12 . The torque/position sensor  18  may be any known sensor or group of sensors for sensing applied torque and angular rotation of the steering wheel  12  and for generating signals indicative of the sensed parameters. In one embodiment, the torque/position sensor  18  is an optical sensor of known construction. 
     The first electric motor  20  is connected to the shaft  14 . Preferably, a gear assembly  24  connects an output of the first electric motor  20  to the shaft  14 . The first electric motor  20  is actuatable to provide resistance to rotation of the steering wheel  12  and thus, is commonly referred to as a “steering feel motor.” 
     The first electronic control unit  22  is operatively coupled to the torque/position sensor  18  and to the first electric motor  20 . The first electronic control unit  22  receives the signals indicative of the applied torque and angular rotation of the steering wheel  12  from the torque/position sensor  18 . In response to the signals from the torque/position sensor  18 , the first electronic control unit  22  generates and transmits a first signal corresponding to the sensed torque and angular rotation of the steering wheel  12  sensed by the torque/position sensor  18 . 
     The second assembly  26  includes a second electronic control unit  28 , a second electric motor  30 , a torque/position sensor  32 , and a hydraulic power steering gear  34  for turning the steerable wheels (not shown) of the vehicle (not shown). Alternatively, an electric power steering gear may be used. If an electric power steering gear is used, the second electric motor  30  is eliminated and the electric motor of the electric power steering gear is controlled by the second electronic control unit  28  to turn the steerable wheels of the vehicle. The components of the second assembly  26  are integrated into a single unit. 
     The second electronic control unit  28  receives the first signal from the first electronic control unit  22 . The second electronic control unit  28  is further operatively coupled to the second electric motor  30 . The second electronic control unit  28  controls the operation of the second electric motor  30  in response to the first signal. 
     The second electric motor  30  has an output shaft that is connected with an input shaft  40  of the power steering gear  34 . A gear assembly  36  may be used to connect the output shaft of the second electric motor  30  to the input shaft  40  of the power steering gear  34 . The second electric motor  30 , upon receiving a signal from the second electronic control unit  28 , is operable to actuate the power steering gear  34 . 
     The power steering gear  34  is an integral hydraulic power steering gear  34 . Other steering gears are contemplated by this invention, such as rack and pinion steering gears and electric power steering gears. The integral hydraulic powered steering gear  34  is illustrated in FIG.  3 . 
     The power steering gear  34  includes a housing  42  and a drive mechanism  44 . The drive mechanism  44  is moved in response to rotation of the input shaft  40  of the power steering gear  34 . Motion of the drive mechanism  44  results in a turning of the steerable wheels of the vehicle. 
     The drive mechanism  44  includes a sector gear  46  having a plurality of teeth  48 . The sector gear  46  is fixed on an output shaft  50  that extends outwardly through an opening in the housing  42  of the power steering gear  34 . The output shaft  50  is typically connected to a pitman arm (not shown) that is connected to the steering linkage (not shown) of the vehicle. Thus, as the sector gear  46  rotates, the output shaft  50  is rotated to operate the steering linkage. As a result, the steerable wheels of the vehicle are turned. 
     The power steering gear  34  further includes a hydraulic motor  52  for moving the drive mechanism  44 . The hydraulic motor  52  is located within the housing  42  of the power steering gear  34 . The housing  42  of the power steering gear  34  has an inner cylindrical surface  54  defining a chamber  56 . A piston  58  is located within the chamber  56  and divides the chamber  56  into opposite chamber portions  60  and  62 . One chamber portion  60  is located on a first side of the piston  58  and the other chamber portion  62  is located on a second side of the piston  58 . The piston  58  creates a seal between the respective chamber portions  60  and  62  and is capable of axial movement within the chamber  56 . 
     A series of rack teeth  64  is formed on the periphery of the piston  58 . The rack teeth  64  act as an output for the hydraulic motor  52  and mesh with the teeth  48  formed on the sector gear  46  of the drive mechanism  44 . When the piston  58  moves axially, the rack teeth  64  of the piston  58  interact with the teeth  48  of the sector gear  46  to rotate the sector gear  46 . 
     A pump (not shown) supplies hydraulic fluid from a reservoir (not shown) to the hydraulic motor  52 . Typically, the engine (not shown) of the vehicle drives the pump. However, the pump could be driven otherwise, such as by a dedicated electric motor. The pump forces hydraulic fluid into an inlet (not shown) of the housing  42 . The inlet directs the flow of the fluid to a directional control valve  66 . 
     The directional control valve  66  directs the fluid to an appropriate chamber portion  60  or  62  of the hydraulic motor  52 . The flow of hydraulic fluid toward one of the chamber portions  60  or  62  increases the pressure within that chamber portion  60  or  62 . When the pressure of one chamber portion  60  or  62  increases relative to the pressure of the other chamber portion  60  or  62 , the piston  58  moves axially until the pressure within each chamber portion  60  or  62  again equalizes. As the piston  58  moves axially, the volume of one chamber portion  60  or  62  increases and the volume of the other chamber portion  60  or  62  decreases. The decreasing chamber portion  60  or  62  is vented to allow a portion of the fluid contained in the decreasing chamber portion  60  or  62  to escape. The escaping fluid exits the housing  42  via a return (not shown) and is directed into the reservoir. 
     An embodiment of the directional control valve  66  is shown in FIG.  4 . The directional control valve  66  contains a valve core part  68  and a valve sleeve part  70 . A portion of the valve core part  68  is contained within and is rotatable relative to the valve sleeve part  70 . 
     The valve sleeve part  70  includes three radially directed passages  72  that extend from an outer circumference of the valve sleeve part  70  to an inner circumference of the valve sleeve part. Each of these radial passages  72  is supplied with hydraulic fluid that enters the housing  42  through the inlet. Two axially extending grooves  74  and  76  are associated with each radial passage  72 . The axially extending grooves  74  and  76  are located on the inner circumference of the valve sleeve part  70 . As shown in FIG. 4, one groove  76  is located clockwise from each radial passage  72  and one groove  74  is located counter-clockwise from each radial passage. The grooves  74  and  76  are equidistant from a respective radial passage  72 . Each groove  74  leads to a passage  78  extending radially outwardly through the valve sleeve part  70 . Each groove  76  leads to a passage  80  extending radially outwardly through the valve sleeve part  70 . Each groove  74  and  76  and associated passage  78  and  80  is associated with a particular chamber portion  60  and  62  of the hydraulic motor  52 . For example, with reference to FIG. 4, each groove  76  and associated passage  80  located immediately clockwise of a radial passage  72  will supply hydraulic fluid to chamber portion  62 ; whereas, each groove  74  and associated passage  78  located immediately counter-clockwise from a radial passage  72  will supply hydraulic fluid to chamber portion  60 . 
     Six grooves  82  are located around the outer circumference of the valve core part  68 . The valve core part  68  also includes six protrusions  84  or lands. A protrusion  84  separates adjacent grooves  82  on the outer circumference of the valve core part  68 . Side walls of the protrusion  84  form side walls of the grooves  82 . 
     When the valve core part  68  is located relative to the valve sleeve part  70  such that each protrusion  84  of the valve core part  68  is centered relative to a respective groove  74  or  76  of the valve sleeve part  70 , the directional control valve  66  is in a neutral position. FIG. 4 illustrates the directional control valve  66  in the neutral position. In the neutral position, the pressure within each chamber portion  60  and  62  of the hydraulic motor  52  is the same so that the piston  58  is stationary. When the valve core part  68  is rotated relative to the valve sleeve part  70 , access to one of the two associated grooves  74  or  76  of the valve sleeve part  70  is restricted by a protrusion  84  of the valve core part  68 , while access to the other of the two associated grooves  74  or  76  is increased. This allows a greater amount of the hydraulic fluid to flow toward the open groove  74  or  76 , resulting in an increase in pressure of the respective chamber portion  60  or  62  associated with that groove  74  or  76 . As a result of the increased pressure within the respective chamber portion  60  or  62 , the piston  58  of the hydraulic motor  52  is moved. For example, if the valve core part  68  is rotated clockwise as viewed in FIG. 4, the groove  74  of the valve sleeve part  70  located on the counter-clockwise side of the radial passage  72  becomes blocked and the groove  76  located on the clockwise side of the radial passage  72  becomes open. Thus, a greater amount of the hydraulic fluid is directed toward the open groove  76 . Pressure in the chamber portion  62  of the hydraulic motor  52  associated with the open groove  76  is increased relative to the pressure in chamber portion  60 . As a result, the piston  58  is moved in an axial direction and rotates the sector gear  46 , causing the steerable wheels of the vehicle to be turned in the appropriate direction. 
     The piston  58  of the hydraulic motor  52  contains a bore  86  that is open toward the directional control valve  66 . The valve sleeve part  70  and a follow-up member  88  form an integral one-piece unit that is supported for rotation relative to the piston  58  by a plurality of balls  90 . The outer periphery of the follow-up member  88  is threaded. The plurality of balls  90  interconnects the threaded outer periphery of the follow-up member  88  with an internal thread  92  formed in the bore  86  of the piston  58 . As a result of the interconnecting plurality of balls  90 , axial movement of the piston  58  causes the follow-up member  88  and the valve sleeve part  70  to rotate. The rotation of the follow-up member  88  and the valve sleeve part  70  returns the directional control valve  66  to the neutral position. 
     The valve core part  68  of the directional control valve  66  is fixedly connected to an input shaft  40  (FIG.  3 ). A first end  96  of a torsion bar  94  is fixed relative to the input shaft  40  and the valve core part  68 . A second end  98  of the torsion bar  94  is fixed relative to the valve sleeve part  70  and the follow-up member  88 . At least a portion of the torsion bar  94  extends through an axially extending bore  100  in the valve core part  68 , as shown in FIGS. 3-5. 
     When the resistance to turning of the steerable wheels of the vehicle is below a predetermined level, rotation of the input shaft  40  of the power steering gear  34  is transferred through the torsion bar  94  and causes rotation of the follow-up member  88 . As a result, the directional control valve  66  remains in the neutral position. Rotation of the follow-up member  88  causes movement of the piston  58  and results in turning of the steerable wheels. 
     When resistance to turning the steerable wheels of the vehicle is at or above the predetermined level, rotation of the follow-up member  88  is resisted. As a result, rotation of the input shaft  40  of the power steering gear  34  rotates the first end  96  of the torsion bar  94  relative to the second end  98  of the torsion bar. The rotation of the first end  96  of the torsion bar  94  relative to the second end  98  of the torsion bar applies torsion across the torsion bar  94  and causes the valve core part  68  to rotate relative to the valve sleeve part  70 . 
     As discussed above, when the valve core part  68  rotates relative to the valve sleeve part  70 , hydraulic fluid is directed toward one of the chamber portions  60  and  62 . As a result, the piston  58  moves within the chamber  56 . Movement of the piston  58  results in turning of the steerable wheels of the vehicle, as well as, rotation of the follow-up member  88 . As discussed above, rotation of the follow-up member  88  rotates the valve sleeve part  70  until the directional control valve  66  is again in the neutral position. When the directional control valve  66  is in the neutral position, the torsion across the torsion bar  94  is removed and the first end  96  of the torsion bar  94  is no longer rotated relative to the second end  98  of the torsion bar. 
     As shown in FIG. 5, the valve sleeve part  70  also includes first and second lugs  102  that are disposed in diametrically opposed cut-outs  104  in the valve core part  68 . Upon rotation of the valve core part  68  of between 2° and 8° relative to the valve sleeve part  70 , the lugs  102  of the valve sleeve part  70  engage the cut-outs  104  in the valve core part  68  to cause the valve sleeve part  70  to be rotated along with the valve core part  68 . Such rotation of the valve sleeve part  70  causes the piston  58  to move within the chamber  56  and, hence, allows for the steerable wheels of the vehicle to be turned by the turning of the input shaft  40  of the power steering gear  34 . Thus, even if a loss in hydraulic fluid pressure has occurred, turning the input shaft  40  of the power steering gear  34  enables the turning of the steerable wheels of the vehicle. 
     As shown schematically in FIGS. 1 and 2, the second assembly  26  also includes at least one position sensor  32  for sensing rotation of the output shaft  50  of the drive mechanism  44  of the power steering gear  34 . The position sensor  32  is preferably a non-contacting position sensor. Upon sensing the rotation of the output shaft  50 , the position sensor  32  generates a signal indicative of the rotation of the output shaft  50 . 
     The second electronic control unit  28  receives the position signal from the position sensor  32 . The second electronic control unit  28  is operable to generate and transmit a second signal corresponding to the position of the output shaft  50  of the drive mechanism  44  of the power steering gear  34  that the position sensor  32  sensed. 
     In the illustrated embodiment, the first electronic control unit  22  is electrically connected to the second electronic control unit  28  by a communication wire  106 . The communication wire  106  transfers the first signal generated by the first electronic control unit  22  to the second electronic control unit  28  and also transfers the second signal generated by the second electronic control unit  28  to the first electronic control unit  22 . In one embodiment, the communication wire  106  is a fiber optic cable and the first and second signals are optical signals. Alternatively, other forms of communication between the first electronic control unit  22  and the second electronic control unit  28  are contemplated by the present invention. For example, wireless communication or hard wiring between the first and second electronic control units  22  and  28  may be used. 
     The first electronic control unit  22  receives the second signal. In response to the second signal, the first electronic control unit  22  controls the first electric motor  20  to control the steering resistance applied to the steering wheel  12 . The first electronic control unit  22  may run a known algorithm that uses the second signal and vehicle speed as parameters to determine the amount of resistance to apply to the steering wheel  12 . The first electric motor  20 , through the gear assembly  24 , applies a force to the shaft  14  to resist rotation of the steering wheel  12 . 
     The steering apparatus  10  also includes a mechanism  108 . The mechanism  108  includes a clutch  110  and a flexible cable  112 , as is illustrated in FIGS. 1 and 2. The mechanism  108  includes two modes of operation. In the first mode of operation, illustrated in FIG. 1, the mechanism  108  mechanically connects the steering wheel  12  to the input shaft  40  of the power steering gear  34 . In the second mode of operation, illustrated in FIG. 2, the mechanism  108  does not mechanically connect the steering wheel  12  to the input shaft  40  of the power steering gear  34  and a mechanical connection between the steering wheel  12  and the steering gear  34  is lacking. 
     The clutch  110  of the mechanism  108  is a known device for engaging and disengaging members. The clutch  110  illustrated schematically in FIGS. 1 and 2 includes first and second members  114  and  116 , respectively. The first member  114  includes an upper surface  118  and a lower surface  120 . The upper surface  118  of the first member  114  is fixed relative to the shaft  14  opposite the steering wheel  12 . A lower surface  120  of the first member  114  includes a plurality of teeth  122 . 
     The second member  116  also includes an upper surface  124  and a lower surface  126 . The upper surface  124  of the second member  116  includes a plurality of teeth  128  for meshingly engaging teeth  122  of the first member  114 . The lower surface  126  of the second member  116  is fixed to the flexible cable  112 . 
     The second member  116  of the clutch  110  is supported relative to and is biased toward the first member  114 . A device (not shown) that forms a part of the clutch  110  is coupled to the second member  116  for moving the second member  116  out of engagement with the first member  114 . The device may be an electric solenoid, a pneumatic cylinder, or any other known device for moving the second member  116  out of engagement with the first member  114 . The clutch  110  is normally closed, meaning that when the device for moving the second member  116  out of engagement is not actuated, the first member  114  is in meshing engagement with the second member  116 . 
     The clutch  110  is coupled to a power source (not shown). Preferably, the power source is the vehicle battery or air supply. When the clutch  110  receives electric, pneumatic, or other energy from the power source, the device for disengaging the second member  116  from the first member  114  is actuated and, the second member  116  is moved out of meshing engagement with the first member  114 . 
     When the clutch  110  is engaged, rotation of the steering wheel  12  results in rotation of the second member  116 . When the clutch  110  is disengaged, the second member  116  is not rotated by rotation of the steering wheel  12 . 
     FIG. 6 schematically illustrates a portion of the clutch  110  with the first member  114  in engagement with the second member  116 . When the clutch  110  is engaged, angled portions of the teeth  122  of the first member are received in angled portions of the second member  116  and angled portions of the teeth  128  of the second member are received in angled portions of the first member, as shown in FIG. 6 during rotation in the direction R. This engagement of the first and second members  114  and  116  is sufficient to actuate the steering gear  34  of the second assembly  26 . This condition of the clutch  110  may occur, for example, when a portion of the first assembly  16  is not operating properly but the second assembly  26  is operating properly. 
     However, if the second assembly  26  fails to operate properly, excessive torque levels may be required for turning the steerable wheels. As a result, the torque levels that must be transferred through the clutch  110  increase. The increased torque levels result in the first and second members  114  and  116  of the clutch  110  rotating relative to one another so that portions of the teeth  122  and  128  that extend perpendicular to the direction of rotation R contact one another, as shown in FIG.  7 . The relative rotation results in a feel of looseness or play in the steering wheel  12 . The looseness gives the operator a physical indication that maintenance or repairs to the apparatus  10  may be necessary. 
     The flexible cable  112  of the mechanism  108  includes a first end portion  130  and a second end portion  132 . The first end portion  130  of the flexible cable  112  is fixed to the second member  116  of the clutch  110  and is rotatable with rotation of the second member  116 . The second end portion  132  of the flexible cable  112  is fixed to the input shaft  40  of the steering gear  34 . 
     The flexible cable  112  is preferably a braided steel cable. Although radially flexible, the flexible cable  112  has a high torsional rigidity. The flexibility allows the flexible cable  112  to be easily routed between the first assembly  16  and the second assembly  26  by allowing the flexible cable  112  to be routed around and through vehicle components that would interfere with a rigid connection. The flexible cable  112  also allows the steering gear  34  to be mounted on a portion of the vehicle that is movable relative to the steering wheel  12 . The high torsional rigidity of the flexible cable  112  causes the second end portion  132  of the flexible cable  112  to rotate when the first end portion  130  of the flexible cable  112  is rotated. 
     During normal operation of the steering apparatus  10 , power is supplied to the clutch  110 . As a result, the second member  116  of the clutch  110  is disengaged from the first member  114  of the clutch and the mechanism  108  is in the second mode of operation, as is illustrated in FIG.  2 . When the mechanism  108  is in the second mode of operation, the steering apparatus  10  is steered-by-wire and there is no mechanical connection between the steering wheel  12  and the steering gear  34 . It is noted that when the clutch  110  is disengaged, rotation of the input shaft  40  of the power steering gear  34  will rotate the second member  116  of the clutch  110 . However, since the clutch  110  is disengaged, rotation of the second member  116  will not cause rotation of the steering wheel  12 . 
     In the event of a failure that causes the steer-by-wire operation of the steering apparatus  10  to automatically shutdown or in the event of a purposeful disengagement of the steer-by-wire operation, the second member  116  of the clutch  110  moves into meshing engagement with first member  114  of the clutch. Thus, the mechanism  108  is in the first mode of operation and a mechanical connection is created between the steering wheel  12  and the steering gear  34 , as is illustrated in FIG.  1 . When the mechanism  108  is in the first mode of operation, rotation of the steering wheel  12  is transferred through the clutch  110  and the flexible cable  112  to the input shaft  40  of the steering gear  34  to enable manual actuation of the power steering gear  34 . The mechanical connection also enables manual turning of the steerable wheels of the vehicle if the lugs  102  of the valve sleeve part  70  contact the valve core part  68 . 
     Alternatively, the clutch  110  may be operatively coupled to the first electronic control unit  22 . The first electronic control unit  22  may control the mode of operation of the mechanism  108  in response to the second signal from the second electronic control unit  28 . For example, if in response to the second signal, the first electronic control unit  22  determines that the steering gear  34  is not being properly actuated in response to the first signal, the first electronic control unit may shutdown steer-by-wire operation and engage the first and second members  114  and  116  of the clutch  110  to enable manual actuation of the steering gear  34 . 
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, when operating with the clutch  110  engaged as a result of a hydraulic failure in steering gear  34 , the electric motors  20  and  30  may combine their efforts to achieve a redundant power assist. Alternatively, either motor  30  or motor  20  may operate to provide a power assist. 
     Also, electric motor  20  may be operated such that its resistance torque increases dramatically as the steering gear  34  nears its mechanical end of travel. This increased resistance will signal the operator to stop turning the steering wheel  12  before fluid is shut off to valve  66 , thus maintaining cooling fluid flow in the steering gear  34 . Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.