Patent Publication Number: US-2023150570-A1

Title: Steering apparatus

Description:
FIELD OF THE INVENTION 
     The present invention relates to a steering apparatus for turning steerable wheels of a vehicle in response to rotation of a vehicle steering wheel. 
     BACKGROUND OF THE INVENTION 
     Power steering assemblies are common in modern vehicles. Typically, one or more rigid shafts connect a vehicle steering wheel to a steering rack of the power steering assembly. The rigid shafts must be routed from the vehicle steering wheel to the steering rack. Routing the rigid shafts between the steering wheel and the steering rack 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 rack of the power steering assembly. Instead, an assembly associated with the steering wheel sends an electronic signal to the power steering assembly. The electronic signal actuates the power steering assembly. Since steer-by-wire systems have no mechanical connection, routing of the rigid shafts between the steering wheel and a steering rack is avoided. 
     Some known steer-by-wire systems include steering feel motors that utilize torque control to produce a desired steering feel for the vehicle operator. The torque control methodology is intuitive in that the motor will produce a resistance torque feel for the vehicle operator. A low resistant torque (e.g., less than 5 Nm) is typically sufficient for normal driving operations. Though, occasionally, a high resistance torque (e.g., 15 Nm or higher) may be desirable for parking and/or emergency maneuvers. Therefore, with torque control, a relatively high-power output (e.g., 15-20 Nm) motor is typically provided to produce a desired steering feel for both low-resistant and high-resistant torque events. Because the high-power output motor only provides resistance to the rotation of the steering wheel, the motor does not do positive work and, thus, the energy provided for actuating the motor is converted to heat, noise, vibration, and/or hardness in the steer-by-wire system. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the invention, alone or in combination with any other aspect, a steer-by-wire steering apparatus is provided for turning steerable wheels of a vehicle. The steering apparatus comprises a steering wheel rotatable about a steering axis by a vehicle operator to effect turning of the steerable vehicle wheels. A first sensor is for determining a steering torque applied to the steering wheel by the vehicle operator. A power steering system is configured to turn the steerable vehicle wheels in accordance with the determined steering torque. The power steering system has a second sensor for sensing a position of a portion of the power steering system. A motor is operably connected to the steering wheel and controllable to apply a force to the steering wheel. The motor is controlled in accordance with the sensed position. 
     According to another aspect, alone or in combination with any other aspect, in a fail state, the motor can be prevented from applying the force to the steering wheel, the first sensor can sense the steering torque applied by the vehicle operator to the steering wheel, and the power steering system can turn the steerable vehicle wheels in accordance with the sensed steering torque. 
     According to another aspect, alone or in combination with any other aspect, a method can be provided for operating a steering apparatus of a vehicle. The method can comprise determining a steering torque applied to a steering wheel by a vehicle operator through the use of a first sensor. Steerable vehicle wheels can be turned with a power steering system in accordance with the determined steering torque. A position of a portion of the power steering system can be sensed by the second sensor. The motor can be controlled in accordance with the sensed position. 
     According to another aspect, alone or in combination with any other aspect, a steering apparatus can be provided for turning steerable wheels of a vehicle. The steering apparatus can comprise a steering wheel rotatable about a steering axis by a vehicle operator to effect turning of the steerable vehicle wheels. A rotatable member can be operably connected to the steering wheel and rotatable about a first axis. A first motor can be operably connected to the rotatable member and configured to rotate the rotatable member about the first axis. A first sensor is for determining a steering torque applied to the steering wheel by the vehicle operator. A power steering system can be provided for turning the steerable vehicle wheels. The power steering system can have a second motor operably connected to a steering rack and configured to linearly move the steering rack along a rack axis. An output of the second motor can be controlled in accordance with the determined steering torque. The power steering system can have a second sensor for sensing a linear position of the steering rack. The first motor can be controlled to rotate the rotatable member to a rotational position that directly corresponds to the sensed linear position of the steering rack. 
     According to another aspect, alone or in combination with any other aspect, a method can be provided for operating a steering apparatus. The method can comprise determining a steering torque applied to a steering wheel by a vehicle operator through the use of a first sensor. An output of the second motor can be controlled in accordance with the determined steering torque. A linear position of the steering rack can be sensed with the second sensor. The first motor can be controlled to rotate the rotatable member to a rotational position that directly corresponds to the sensed linear position of the steering rack. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the invention will become apparent to one skilled in the art to which the invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, in which: 
         FIG.  1    is a schematic illustration of a steering apparatus for a motor vehicle; and 
         FIG.  2    is a schematic illustration of a portion of an example power steering system of the steering apparatus of  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG.  1    schematically illustrates a steering apparatus  10  for a motor vehicle. The steering apparatus  10  illustrated in  FIG.  1    is a steer-by-wire steering apparatus. However, the teachings of the present disclosure may be adapted for use in non-steer-by-wire steering apparatus. The steering apparatus  10  includes a steering wheel  12 . The steering wheel  12  is of known construction and is manually rotatable by a vehicle operator about a steering axis  14 . 
     A first bar end  16  of a torsion bar  18  is fixed to a center or hub  20  of the steering wheel  12 . The first bar end  16  may be directly fixed to the hub  20 , or may be indirectly fixed to the hub by one or more intervening components. A second bar end  22  is operably connected to a first electric motor  24 . Preferably, a first gear assembly  26  operably connects the first electric motor  24  to the second bar end  22 . 
     The first gear assembly  26  includes a first gear  28  (e.g., a worm screw) that is fixed for rotation with a drive shaft  30  of the first electric motor  24 . The first gear  28  may be formed separately from the drive shaft  30  and subsequently attached, or may be formed integrally with the drive shaft. The drive shaft  30  extends along a drive shaft axis  32 . The first gear  28  rotates with the drive shaft  20  about the drive shaft axis  32 . 
     The first gear assembly  26  also includes a second gear  34  (e.g., a worm wheel) that is fixed for rotation with a gear shaft  35  that extends along a gear shaft axis  37 . The gear shaft  35  is fixed for rotation with the second bar end  22  and, thus, the second bar end is fixed for rotation with the second gear  34  through the gear shaft. At least one of the second gear  34 , the gear shaft  35  and the second bar end  22  may be formed separately from the other of the second gear, the gear shaft and the second bar end and subsequently attached. Alternatively, at least one of the second gear  34 , the gear shaft  35  and the second bar end  22  may be formed integrally from the other of the second gear, the gear shaft and the second bar end. The torsion bar  18  extends along a bar axis  36 . As shown in  FIG.  1   , the gear shaft axis  37 , the bar axis  36  and the steering axis  14  are coaxial. The second bar end  22  thus rotates with the second gear  34  about the bar axis  36 . However, at least one of the gear shaft axis  37 , the bar axis  36  and the steering axis  14  may be at any other desired orientation relative to at least one other of the gear shaft axis, the bar axis and the steering axis. For example, at least one of the gear shaft axis  37 , the bar axis  36  and the steering axis  14  may be parallel to, perpendicular to, at an acute angle relative to, or at an obtuse angle relative to at least one other of the gear shaft axis, the bar axis and the steering axis. Therefore, the steering apparatus  10  may be configured such that the second gear  34  is rotatable about the gear shaft axis  37 , the torsion bar  18  is rotatable about the bar axis  36 , and the gear shaft axis and bar axis are not coaxial. 
     Although the second bar end  22  is shown and described as being fixed to the second gear  34  through the gear shaft  35 , the first gear assembly  26  can be configured such that the gear shaft is omitted and the second bar end is fixed directly to the second gear. In such case, the second gear  34  may be formed separately from the second bar end  22  and subsequently attached, or may be formed integrally with the second bar end. 
     As shown in  FIG.  1   , the second gear  34  may meshingly engage the first gear  28 . Alternatively, the first and second gears  28 ,  34  may be indirectly connected to one another by one or more intermediate components/gears. The first and second gears  28 ,  34  are shown as being a worm screw and a worm wheel, respectively. As such, the drive shaft axis  32  about which the first gear  28  rotates may be transverse (e.g., perpendicular) to the axis  36 ,  37  about which the second gear  34  rotates. 
     A steering torque applied by the vehicle operator to the steering wheel  12  urges the second gear  34  to rotate about the bar axis  36 . The first gear assembly  26 , however, is may be a non-reversible drive in that the first gear assembly may be driven by the first electric motor  24  only, and not by the steering torque applied to the steering wheel  12 . Therefore, the second gear  34  is prevented from being rotated by the applied steering torque. Because the second gear  34  is fixed for rotation with the second bar end  22  through the gear shaft  35 , the second gear prevents at least the second bar end from being rotated about the bar axis  36  by the steering wheel  12 , which correspondingly provides a predetermined rotational resistance to the steering wheel. 
     However, by including the torsion bar  18 , the steering apparatus  10  is configured so that the vehicle operator can rotate the steering wheel  12  about the steering axis  14  relative to the second gear  34 . For example, the vehicle operator may be able to rotate the steering wheel  12  about 3-6° relative to the second gear  34 . Therefore, the first bar end  16  may thus twist relative to the second bar end  22  in response to a predetermined applied steering torque, thereby permitting relative rotation between the steering wheel  12  and the second gear  34 . 
     The first electric motor  24  may be controlled to control the resistance to the rotation of the steering wheel  12  and thus, is commonly referred to as a “steering feel motor.” In particular, actuation of the first electric motor  24  causes the drive shaft  30  to rotate the first gear  28  about the drive shaft axis  32 . The second gear  34  is rotated about the bar axis  36  by the first gear  28 . Through the gear shaft  35 , the rotating second gear  34  applies torque (i.e., a rotational force) to the second bar end  22  (and correspondingly, the entirety of the torsion bar  18 ) to provide steering feel. The torque applied by the second gear  34  may be in the same direction that the vehicle operator rotates the steering wheel  12  about the steering axis  14  and, thus, may make it easier for the vehicle operator to turn the steering wheel. In doing so, the first electric motor  24  reduces the amount of steering torque required by the vehicle operator to turn the steering wheel  12  about the steering axis  14  to a desired position. 
     The second gear  34  and second bar end  22  may thus be rotated by the first electric motor  24  in the same direction as the steering wheel  12  and first bar end  16  about the steering axis  14 . However, the steering wheel  12  and first bar end  16  may be rotated ahead of the second bar end  22  and second gear  34  based on the amount of steering torque that the vehicle operator applies to the steering wheel. 
     The first electric motor  24  may be of any known type suitable for use in the steering apparatus  10 . For example, the first electric motor  24  may be a variable reluctance motor, a permanent magnet alternating current motor or a brushless direct current motor. 
     A first electronic control unit (“ECU”)  38  is operably connected to the first electric motor  24 . The first ECU  38  actuates and controls the first electric motor  24  to control the steering resistance (i.e., the resistance to the rotation of the steering wheel  12 ) provided to the steering wheel. The first ECU  24  is preferably a microcomputer. Alternatively, the first ECU  24  may be formed from discrete circuitry, an application-specific-integrated-circuit (“ASIC”), or any other type of control circuitry. 
     The steering apparatus  10  may include at least one torque/position sensor  40  that is operatively connected to the steering wheel  12  (or a component that is fixed for rotation with the steering wheel, such as, for example, the first bar end  16  or the hub  20 ) and the second gear  34  (or a component that is fixed for rotation with the second gear, such as, for example, the gear shaft  35 ). The torque/position sensor  40  is operable to sense the rotational position (i.e., rotational angle) of the second gear  34 , and a relative rotational position (i.e., rotational angle) between the steering wheel  12  and the second gear. The torque/position sensor  40  may be any known sensor or group of sensors for sensing the rotational position of the second gear  34  and the relative rotational position between the steering wheel  12  and the second gear  34 , and for generating signals indicative of the sensed parameters. The torque/position sensor  40  may include, for example, an optical, a magnetic and/or a mechanical sensor of known construction. 
     The torque/position sensor  40  may be configured to internally determine a steering torque applied to the steering wheel  12  by the vehicle operator as a function of a spring constant of the torsion bar  18  and the relative angle between the steering wheel  12  and second gear  34 . In such case, the signals generated by the torque/position sensor  40  would include the vehicle operator applied steering torque. 
     A second ECU  42  is operatively coupled to the torque/position sensor  40  and to the first ECU  38 . The second ECU  42  receives the signals indicative of the rotational position of the second gear  34  from the torque/position sensor  40  and the relative rotational position between the steering wheel  12  and the second gear  34 . The second ECU  42  may also receive the signals from the torque/position sensor  40  indicative of the vehicle operator applied steering torque when determined by the torque/position sensor  40 . Alternatively, the second ECU  42  may receive signals indicative of the relative angle between the steering wheel  12  and second gear  34  and internally determine the applied steering torque as a function of those received signals and the spring constant of the torsion bar  18 . In response to the signals from the torque/position sensor  40 , the second ECU  42  generates and transmits a first signal corresponding to the sensed vehicle operator applied steering torque. The second ECU  42  may also be operatively connected to and communicate with a vehicle CAN bus  44 . The second ECU  42  may request and/or receive certain vehicle operating characteristics, such as vehicle speed, from the vehicle CAN bus  44 . The second ECU  42  is preferably a microcomputer. Alternatively, the second ECU  42  may be formed from discrete circuitry, an application-specific-integrated-circuit (“ASIC”), or any other type of control circuitry. 
     The steering apparatus  10  also includes a power steering system  46  configured to turn steerable vehicle wheels  48 . In the example configuration of  FIGS.  1 - 2   , the power steering system  46  is an electric power steering system. However, the steering apparatus  10  can be configured to include other types of power steering systems besides electric (e.g., hydraulic). 
     The power steering system  46  includes a third ECU  50 . The third ECU  50  receives the first signal from the second ECU  42 . The third ECU  50  is further operatively coupled to a second electric motor  52 . The third ECU  50  controls the operation of the second electric motor  52  in accordance with the first signal. For example, the third ECU  50  may run an algorithm that uses the vehicle operator applied steering torque from the first signal a parameter for controlling the operation of the second electric motor  52 . The third ECU  50  is preferably a microcomputer. Alternatively, the third ECU  50  may be formed from discrete circuitry, an application-specific-integrated-circuit (“ASIC”), or any other type of control circuitry. Although the power steering system  46  is shown and described as having a single electric motor  52  controlled by a single ECU  50 , the power steering system may have any number of electric motors and ECUs for turning the steerable vehicle wheels  48 . 
     The second electric motor  52  may be of any known type suitable for use in the steering apparatus  10 . For example, the second electric motor  52  may be a variable reluctance motor, a permanent magnet alternating current motor or a brushless direct current motor. 
     The second electric motor  52  effects turning of the steerable vehicle wheels  48  through a second gear assembly  54 .  FIG.  2    schematically depicts an example second gear assembly  54  that is operably connected to the second electric motor  52 . The second gear assembly  54  of  FIG.  2    includes a worm screw  56  that is fixed for rotation with a drive shaft  58  of the second electric motor  52 . The worm screw  56  may be formed separately from the drive shaft  58  and subsequently attached, or may be formed integrally with the drive shaft. The drive shaft  58  extends along a drive shaft axis  60 . The worm screw  56  rotates with the drive shaft  58  about the drive shaft axis  60 . 
     A worm wheel  62  meshingly engages and is rotatable by the worm screw  56 . The worm wheel  62  is fixed for rotation with a first pinion end  64  of a pinion  66 . The worm wheel  62  may be formed separately from the first pinion end  64  and subsequently attached, or may be formed integrally with the first pinion end. The pinion  66  extends along a pinion axis  68 . The first pinion end  64  rotates with the worm wheel  62  about the pinion axis  68 . 
     A second pinion end  70  has a gear portion  72  that is meshingly engaged to a gear portion  74  of a steering rack  76 . Rotation of the pinion  66  about the pinion axis  68  causes the steering rack  76  to move linearly along a rack axis  77  relative to the vehicle. As shown in  FIG.  1   , each end of the steering rack  76  is connected to an associated steerable wheel by a tie rod  78 . Therefore, the linear movement of the steering rack  76  acts on the steerable vehicle wheels  48  through the tie rods  78  to turn the steerable vehicle wheels. The steering rack  76  may be supported by a housing  80  and may linearly move relative to the housing. At least one of the components of the second gear assembly  54  may be supported in the housing  80 . 
     The second electric motor  52  thus effects the turning of the steerable vehicle wheels  48  in accordance with to the first signal through the second gear assembly  54 . The number and type of components in the second gear assembly  54  described and shown in the present disclosure is merely just one example gear assembly used to operably connect the second electric motor  52  to the steering rack  76 . The second gear assembly  54  may include any number and type of components necessary for operably connecting the second electric motor  52  to the steering rack  76 . 
     As shown in  FIGS.  1 - 2   , the power steering system  46  may include at least one position sensor  82  for sensing a linear position of the steering rack  76  along the rack axis  77 . The position sensor  82  may be any known sensor or group of sensors for sensing a linear position of the steering rack  76  along the rack axis  77  and for generating signals indicative of the sensed linear position of the steering rack. The position sensor  82  may include, for example, an optical, a magnetic and/or a mechanical sensor of known construction. As shown in  FIG.  1   , the position sensor  82  is operatively connected to the second ECU  42 . The second ECU  42  receives the signals indicative of the linear position of the steering rack  76  from the position sensor  82 . 
     In the illustrated embodiment, the torque/position sensor  40  is electrically connected to the third ECU  50  by the second ECU  42 . The second ECU  42  generates and transfers the first signal to the third ECU  50 . The third ECU  50  controls a torque output of the second electric motor  52  in accordance with the vehicle operator applied steering torque provided in the first signal. For example, the third ECU  50  may control the amount of torque outputted by the second electric motor  52  and the direction of the outputted torque. The second electric motor  52  thus is torque controlled (i.e., controlled as a function of the vehicle operator applied steering torque). 
     The second ECU  42  receives the signals indicative of the linear position of the steering rack  76  from the position sensor  82 . Using the linear position of the steering rack  76 , the second ECU  42  determines a rotational position of the second gear  34  that directly corresponds to the linear position steering rack  76 . The determination may be made by running algorithms that transform the received linear position of the steering rack  76  into a corresponding rotational position of the second gear  34 . Alternatively, the determination may be made by accessing stored reference data that includes predetermined linear positions of the steering rack  76  and predetermined rotational positions of the second gear  34  that directly correlate to the predetermined linear positions of the steering rack. 
     The second ECU  42  then compares a current rotational position of the second gear  34  (i.e., the rotational position of the second gear  34  that was sensed by the torque/position sensor  40  and received by the second ECU) with the determined rotational position of the second gear  34  that directly corresponds to the linear position steering rack  76 . The second ECU  42  generates and transmits a second signal corresponding to the difference between the current rotational position of the second gear  34  and the determined rotational position of the second gear  34  that directly corresponds to the linear position steering rack  76 . The second signal is transmitted to the first ECU  38 . 
     The first ECU  38  receives the second signal. In response to the second signal, the first ECU  38  controls the first electric motor  24  to rotate the second gear  34  as a function of the difference between the second gear&#39;s current position and the determined rotational position of the second gear that directly corresponds to the linear position steering rack  76  so that the second gear may be rotated to the rotational position that directly corresponds to the linear position steering rack. Therefore, the first electric motor  24  is position control (i.e., controlled as a function of the linear position of the steering rack  76 ). 
     The sensors  40 ,  82 , the first electric motor  24  and the first and second ECUs  38 ,  42  may thus function as a closed loop position control for the second gear  34  in that the position sensor measures the linear position of the steering rack  76 , the second ECU receives a signal from the position sensor, the second ECU transmits the second signal to the first ECU, the first ECU controls the first electric motor to rotate the second gear from a first rotational position measured by the torque/position sensor to the rotational position that directly corresponds to the linear position steering rack. The first electric motor  24  may be controlled to rotate the second gear  34  until the torque/position sensor  40  senses that the second gear is in the rotational position that directly corresponds to the linear position steering rack  76 . 
     The second gear  34  rotating to the rotational position that directly corresponds to the linear position steering rack  76  applies torque to the second bar end  22  (and correspondingly, to the steering wheel  12  through the torsion bar  18 ). The second gear  34  may be rotated in the same direction that the vehicle operator rotates the steering wheel  12  about the steering axis  14  and, thus, may reduce the amount of steering torque required by the vehicle operator to turn the steering wheel about the steering axis to a desired position. The first electric motor  24 , by rotating the second gear to the position that directly corresponds to the linear position of the steering rack  76 , may thus reduce the amount of steering resistance provided to the steering wheel  12 . 
     How much the first electric motor  24  reduces the amount of steering resistance may be a function of the speed at which the second gear  34  is rotated by the first electric motor. The first ECU  38  may be configured to determine and control the operating speed of the first electric motor  34 . Alternatively, the second ECU  42  may be configured to determine the operating speed of the first electric motor  34  and transmit that operating speed to the first ECU  38  for controlling the first electric motor. The determined operating speed of the first electric motor  34  may be a function of the rotational distance that the second gear  34  needs to rotate in order to assume the rotational position that directly corresponds to the linear position of the steering rack  76 , the speed at which the second electric motor  52  drives the steering rack  76 , the amount of vehicle operator applied steering torque, the type of driving maneuver being performed by the vehicle operator (e.g., parking, turning, and/or slight veering), and/or other vehicle characteristics, such as the vehicle speed. 
     In case of a failure of the first gear assembly  26 , the first electric motor  24  and/or the first ECU  38 , the first electric motor may not be functional to rotate the second gear  34  to a rotational position that corresponds to the linear position of the steering rack  76 . In this case, the vehicle operator applied steering torque is still determined and sent to the power steering system  46  for controlling the steerable vehicle wheels  48  accordingly. Operation of the power steering system  46 , the steering apparatus  10  and/or the vehicle may be adjusted in response to the failure. 
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, the first electric motor  24  may be controlled by the first ECU  38  to apply a resistance torque to the torsion bar  18  that opposes the vehicle operator applied steering torque. 
     Although the power steering system is described and shown as having a rack-and-pinion drive, the power steering system may include any other type of drive, such as, for example, a belt drive and/or a drive that utilizes a ball-nut assembly. 
     Algorithms, determinations, and/or computing processes for controlling the first electric motor  24  may be performed in either the first ECU  38  and/or the second ECU  42 . Algorithms, determinations, and/or computing processes for controlling the second steering electric motor  52  may be performed in either the third ECU  50  and/or the second ECU  42 . 
     The steering apparatus  10  may be configured with only the first and third ECUs  38 ,  50 , and without the second ECU  42 . The first and third ECUs  38 ,  50  would thus perform all of their respective algorithms, determinations, computing processes, control functions and directly communicate with one another. In this case, the first ECU  38  may be operatively connected to the torque/position sensor  40 , generate the first signal, and transmit the first signal. Similarly, the third ECU  50  may be operatively connected to the position sensor  82 . The third ECU  50  may generate a signal indicative of the linear position of the steering rack  76 , and transmit that signal to the first ECU  38 . The first ECU  38 , after receiving the signal from the third ECU  50 , may then perform all processes necessary for controlling the first electric motor  34 . 
     The functions of the ECUs  38 ,  42 ,  50  can be divided between the ECUs as described above, or can be distributed among the ECUs in a different manner. The three ECUs  38 ,  42 ,  50  can be located at any physical location in the vehicle. The three ECUs  38 ,  42 ,  50  can be combined into two or one ECU located at any physical location in the vehicle. 
     Also, although a torsion bar  18  has been provided to permit the steering wheel  12  to rotate relative to the second gear, the steering apparatus  10  may utilize structures other than the torsion bar  18  to permit such relative movement. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.