STEERING COLUMN ARRANGEMENT FOR A VEHICLE

Abstract

A steering column assembly for a vehicle comprises an elongated steering column (14) mounted to rotate about its longitudinal axis (16) and configured to mount a steering wheel (18) at one end, a gear (24) connected to the steering column at a location spaced from the steering wheel mounting location and configured to rotate with the steering column, a motor (44) comprising a rotatable output shaft, a first worm gear (30) directly connected and rotatable with the output shaft (34) of the motor and meshing with the gear (24), a damper (60) comprising a rotatable shaft (36), a second worm gear (32) directly connected and rotatable with the shaft (32) of the damper and meshing with the gear (24), and control means configured to operate the motor.

Description

The present invention relates to steering column assemblies for vehicles and, more particularly, to such assemblies for use with a steer-by-wire hand wheel actuator.The invention also relates to vehicles comprising a steer-by-wire hand wheel actuator according to the invention.In steer-by-wire arrangements, a hand wheel (steering wheel) is connected to one end of a rotatably mounted shaft whose angular displacement is measured to produce a signal used to control the orientation of the steerable wheels of the vehicle. The arrangement is also usually provided with an electric motor connected to the shaft for providing a controlled level of torque in the opposite direction to the torque applied by the driver for providing a sense of road feel to the driver.In such arrangements, an electric motor typically drives a worm under the control of an ECU (electronic control unit) that engages a worm wheel that rotates with the shaft to which the steering wheel is connected. It is desirable to take measures to ensure that the worm always engages the worm wheel to reduce gear chatter, which may occur when the torque and direction of the motor are reversed.According to a first aspect of the present invention, a steering column assembly for a vehicle comprises:an elongated steering column mounted for rotation about its longitudinal axis and configured for mounting a steering wheel at an end;a gear connected to the steering column at a location spaced from the steering wheel attachment location and configured for rotation with the steering column;a motor comprising a rotatable output shaft; a first worm directly connected and rotatable with the output shaft of the motor and engaged with the gear;a damper comprising a rotatable shaft;a second worm directly connected to the shaft of the damper and rotatable and engaged with the gear; andcontrol means configured to operate the motor.The motor is operated to generate a feedback torque to the steering column and the steering wheel to provide a road feel sensation to the driver, and the damper amplifies the motor feedback torque. Moreover, in the event of an engine failure, the damper provides passive feedback torque to the driver. By coupling the damper via a second worm that engages the gear connected to the steering column, a compact package is provided that is easier to install in vehicles.The damper preferably includes a fluid chamber configured to receive a damping fluid and a body located in the fluid chamber, the body configured to move with the rotatable shaft of the damper.The use of such a viscous damper generates a driver feedback torque that increases with the steering speed.The body located in the fluid chamber may comprise a plurality of projections and / or depressions.The body located in the fluid chamber may be spaced from the wall of the fluid chamber.The body located in the fluid chamber may include a portion having a greater width.The body located in the fluid chamber may be part of the rotatable shaft of the damper or may be attached to the rotatable shaft of the damper.The rotatable shaft of the damper can furthermore be longitudinally displaceable in the direction of its axis of rotation.By providing axial movement and damping of the damper rotatable shaft, the noise resulting from backlash between the second worm and the steering column mounted gear is reduced, particularly when the steering column is reversed in direction of rotation.The rotatable shaft of the damper may be mounted to allow pivoting or deflection thereof.This integrates any lateral movement of the damper shaft as a result of its longitudinal displacement.Preferably, the steering column assembly includes bearing means configured to allow pivoting or deflection of the rotatable damper shaft.The steering column assembly may further comprise biasing means configured to urge the second worm into contact with the gear connected to the steering column.This reduces the clearance between the second worm and the steering column mounted gear and helps reduce rattle noise that may occur particularly during torque reversal events.Preferably, the steering column assembly includes bearing means for rotatably mounting the rotatable shaft of the damper with which the biasing means engages.The biasing means may be engaged with an outer ring of the bearing means.Preferably, the biasing means comprises a spring, for example a leaf spring.The steering column assembly may further include a spring acting on the rotatable output shaft of the motor configured to apply torque to the motor shaft and / or a spring acting on the rotatable shaft of the damper configured to apply torque to the damper shaft.The return spring may be arranged to provide a return torque over the entire angular range of the steering column. The net torque provided by the spring may act in a direction to return the steering column to the straight-ahead position. In addition, the torque provided by the spring increases with increasing rotation of the steering column away from the straight-ahead position.The spring acting on the rotatable output shaft of the motor and / or the spring acting on the rotatable shaft of the damper preferably comprise a helical spring.The steering column assembly may further comprise motor position sensor means for sensing the rotational position of the motor output shaft, the sensor means comprising a target member rotatable with the motor shaft and a sensor for detecting the target member.This assists in calculating an appropriate feedback torque to be generated by the motor.The steering column assembly may further comprise position sensor means for sensing the rotational position of the damper shaft, the sensor means comprising a target member rotatable with the damper shaft and a sensor for detecting the target member.By measuring the angular displacement and / or velocity of the damper shaft, the prediction of the torque level produced by the damper and, consequently, the torque level to be produced by the engine is improved.The steering column assembly may comprise a member configured to rotate with the rotatable damper shaft and with respect to which the damper shaft is slidable along its axis of rotation and to which the target member is attached.Such an arrangement integrates movement of the damper shaft in an axial direction and ensures that there is a constant distance between the target member and the sensor means.For example, the steering column assembly may comprise a cup-shaped member fixed to one end of the rotatable damper shaft and to which the motor position sensor means is fixed.The first worm may be part of the motor output shaft and / or the second worm may be part of the rotatable damper shaft.The first and second worms may be engaged at diametrically opposite locations with the gear connected to the steering column.The steering column assembly preferably includes a housing in which the first and second worms and the gear connected to the steering column are located.The present invention also includes a vehicle including a steering column according to the present invention.Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 is a schematic illustration of a known steer-by-wire steering system; FIG. 2 is a perspective view, partially cut away, of a first embodiment of a steering column assembly according to the present invention; FIG. 3 is a vertical cross-section through the steering column arrangement of FIG. 2 as seen in the direction of the arrows III-III of FIG. 2, the section A being shown enlarged; FIG. 4 is a side view of the steering column assembly of FIG. 2 ; FIG. 5 is a schematic illustration of the torque control of the steering column assembly of FIG. 2 ; FIG. 6 is a perspective view, partially cut away, of a second embodiment of the steering column assembly according to the present invention; FIG. 7 is a vertical cross-section through the steering column arrangement of FIG. 6, looking in the direction of the arrows VII-VII of FIG. 6, wherein the section B is shown enlarged; FIG. 8 is a vertical cross-section through a portion of a third embodiment of a steering column assembly according to the present invention, which is a modification of the steering column assembly of FIG. 6; FIG. 9 is a perspective view, partially cut away, of a fourth embodiment of a steering column assembly according to the present invention, showing section C enlarged; FIG. 10 shows a vertical cross section through the steering column arrangement of FIG. 9 as seen in the direction of the arrows X-X of FIG. 9 ; and FIG. 11 is a cross-sectional view of a fifth embodiment of a steering column assembly according to the present invention, which is a modification that can be used with any of the previous embodiments.FIG. 1 illustrates a known steer-by-wire system S for a vehicle that includes a steering assembly 10 according to the present invention. The steer-by-wire system S includes a hand wheel actuator in the form of a steering wheel A to allow a driver of the vehicle to provide a steering input command. The steering wheel A is connected to one end of an elongated steering shaft B.A steering input introduced by the steering wheel A is measured by a steering sensor that is part of the steering column assembly, as shown schematically at C in FIG. 1. A signal representative of the steering input (i.e., the rotation of the steering wheel A and steering shaft B) is sent from the sensor C to an electronic control unit (ECU) D, which in turn controls a steering axle actuator E. The steering axle actuator E applies the steering input to the steering axle F and thus steer the steerable wheels G as a function of the rotational position of the steering wheel A.The electronic control unit D is also configured to supply current to a torque feedback motor H that is connected to the shaft B and that applies torque in the opposite direction to the torque applied to the steering wheel A to provide a "sense of road feel" to the driver.A damper J schematically illustrated in FIG. 1 is connected to the steering shaft B and provides a feedback torque to the steering wheel A when a steering input is input. Although the damper J is fixed at an intermediate position along the steering shaft B, i.e., between the ends of the steering shaft B so that the steering shaft B passes through the damper J as shown in FIG. 1, it is not necessary to do so.A first embodiment of the steer-by-wire steering column assembly 10 according to the present invention is illustrated in Figures 2 through 4. The assembly 10 includes a straight elongated steer-by-wire steering column 14 (only the lower end of which is shown) rotatably mounted about its longitudinal axis 16. A steering wheel 18, which is schematically shown in FIG. 1 and with which the steering column 14 can be rotated by a driver, is secured to the upper end of the steering column 14. In the drawings, the steering column 14 is shown as a single shaft, but in practice is likely to be formed from a series of components. For example, the steering column may be formed from some telescopic parts and may include a torque sensor (e.g., a torsion bar assembly) between the steering wheel 18 and the steering column 14.The opposite lower end of the steering column 14 is received in a housing 20 in which it is rotatably mounted. As best seen in FIG. 3, a spur gear (pinion gear) 24 is fixedly secured to the lower end of the steering column 14 in the housing 20 and is thereby restricted from rotation with the steering column 14 and the steering wheel 18.Two identical screws 30, 32 are rotatably mounted in the housing 20 and mesh with the spur gear (pinion gear) 24 at diametrically opposite positions on opposite sides of the gear. Each of the screws 30, 32 is formed on the surface of a respective shaft 34, 36, the two shafts being oriented parallel to each other and perpendicular to the axis of rotation 16 of the steering column 14. The shafts 34, 36 are rotatably mounted in the housing by lower and upper bearings 38, 40 located, in use, just beyond the lower and upper ends of the screws 30, 32.As best seen in FIG. 3, the first shaft 34 forms the output shaft of an electric motor 44 and is directly driven by the motor. A target magnet 48 of the motion position sensor (MPS) is fixedly secured to the lower end of a mounting collar 50 fixedly secured to the lower end of the shaft 34 below the motor 44, and thereby rotates with the shaft 34. An electronic control unit (ECU) (not shown in the drawings) is also fixed to the circuit board 54. The MPS target magnet 48 and the MPS sensor 52 are known, and various types of magnets and sensors may be used depending on the circumstances.With continued reference to FIG. 3, a viscous damper, generally indicated at 60, is mounted to the other shaft 36 at a location below the lower bearing 38. The viscous damper includes a generally cylindrical block 62 rotatably mounted in a complementarily shaped cylindrical recess 63 in the housing 20. The cavity 63 includes a damping fluid (e.g., silicone fluid) retained by lower and upper annular seals 64, 65 that contact the lower and upper portions of the cylindrical block 62, respectively. The central portion of the cylindrical block 62 is provided with four identical, equally spaced, annular grooves 66 defining three identical, annular webs 68, the peripheries of which abut but are slightly spaced from the wall of the recess 63.The torque applied by the viscous damper is a function of the distance between the periphery of the cylindrical block 62 and the wall of the recess 63, the number and dimensions of the grooves 66 and annular lands 68, and the viscosity of the damping fluid, as will be discussed in more detail below.A target magnet 70 of the motion position sensor (MPS) is fixedly secured to the lower end of a mounting collar 72 fixed to the lower end of the damper shaft 36 below the viscous damper 60, and thereby rotates with the shaft 36. The MPS target magnet 70 and the MPS sensor 74 are known, and various types of magnets and sensors may be used depending on the circumstances.The motor 44 provides a feedback torque to the steering column 16 (and thus to the steering wheel 18) as a function of the driver request. The viscous damper 60 also resists rotation of the steering wheel and applies feedback torque to the driver, which is a function of the rotational speed of the steering wheel. The viscous damper 60 also helps maintain the worm 30 connected to the output of the motor 44 in contact with the spur gear 24, and also helps reduce gear chatter, which may occur as the torque and direction of the motor are reversed. Moreover, the viscous damper 60 also ensures that a certain degree of feedback torque is always generated even when the engine 44 is not operating.The above-described embodiment can be controlled according to the method schematically illustrated in FIG. 5. In the following description, "step" is abbreviated as "S".At S 100, a desired driver feedback torque is calculated using information from the angular displacement and angular velocity of the hand wheel actuator (e.g., steering wheel 18) in a known manner. The calculation may involve other inputs such as estimated front axle actuator rack force, inputs from vehicle motion sensors (e.g., yaw rate, lateral acceleration, and vehicle speed), and the like. At S 102, the damper torque is estimated according to the damper angular velocity calculated from the position of the damper determined by the MPS target magnet 70 and the MPS sensor 74, for example, by determining the change in the angular position over a period of time. Alternatively, at S 102, the damper angular velocity may be estimated by measuring another system component, such as the movement and / or position of the motor 44 and / or the steering column 14, and deriving the damper angular velocity.The damper torque estimated at S 102 is then subtracted from the total torque request calculated at S 100, and the remainder is the torque required by the engine 44. Optionally, at S 104, a friction compensation torque component may be estimated using known methods from the torque required by the engine 44 and a signal representative of the speed of the engine 44. The estimated friction compensation torque component is added to the previously calculated torque required by the engine 44, and at S 106, the active request is scaled based on the gear ratio to determine a torque request for the engine 44.Optionally, a sensor may be installed in the input shaft 14 / 16 to measure the net torque felt by a driver. In this case, control may be used to control the active parts of the system to achieve the desired driver feedback torque.A second embodiment of the invention is illustrated in Figures 6 to 8. Many of the features of the second embodiment are closely similar to those of the first embodiment, and corresponding features are identified with the same reference numerals, plus 200.The assembly 210 includes a straight elongated steer-by-wire steering column 214 (only the lower end of which is shown) that is rotatably mounted about its longitudinal axis 216. A steering wheel 218, which is schematically shown in FIG. 1 and with which the steering column 214 can be rotated by a driver, is secured to the upper end of the steering column 214. In the drawings, the steering column 214 is shown as a single shaft, but in practice is likely to be formed from a series of components. For example, the steering column may be formed from some telescopic parts and may include a torque sensor (e.g., a torsion bar assembly) between the steering wheel 18 and the opposite end of the steering column 214.The opposite lower end of the steering column 214 is received in a housing 220 in which it is rotatably mounted. As best seen in FIG. 7, a spur gear (pinion gear) 224 is fixedly secured to the lower end of the steering column 214 in the housing 220 and is thereby restricted from rotation with the steering column 214 and the steering wheel 218.Two identical screws 230, 232 are mounted in the housing 220 and mesh with the spur gear (pinion gear) 224 at diametrically opposite positions on opposite sides of the gear. Each of the screws 230, 232 is formed on the surface of a respective shaft 234, 236, the two shafts being oriented parallel to each other and perpendicular to the axis of rotation 216 of the steering column 214. The shaft 234 is rotatably mounted in the housing by lower and upper bearings 238, 240 which are located, in use, just beyond the lower and upper ends of the worm 230. The shaft 236 is rotatably mounted in the housing by a lower bearing 239 located at the lower end of the shaft 236 and an upper bearing 240 located directly beyond the upper end of the worm 230 in use.As best seen in FIG. 7, the first shaft 234 forms the output shaft of an electric motor 244 and is directly driven by the motor. A target magnet 248 of the motion position sensor (MPS) is fixedly secured to the lower end of a mounting collar 250 fixed to the lower end of the shaft 234 below the motor 244, thereby rotating with the shaft 234. The rotation of the MPS target magnet 240 is detected by an MPS sensor 252 fixed to the upper surface of an MPS sensor circuit board 254 fixed in the housing 220. An electronic control unit (ECU) (not shown in the drawings) is also fixed to the circuit board 254. The MPS target magnet 248 and the MPS sensor 252 are known, and various types of magnets and sensors may be used depending on the circumstances.With continued reference to FIGS. 7 and 8, a viscous damper, generally indicated at 260, is mounted to the other shaft 236 at a location below the worm 232. The viscous damper includes a generally cylindrical block 262 rotatably mounted in a complementarily shaped cylindrical recess 263 in the housing 220. The cavity 263 contains a damping fluid (e.g., silicone fluid) retained by lower and upper annular seals 264, 265 that contact the lower and upper portions of the cylindrical block 262, respectively. The central portion of the cylindrical block 262 is provided with five identical, equally spaced, annular grooves 266 defining four identical, annular webs 268 whose peripheries abut but are slightly spaced from the wall of the recess 263.A target magnet 270 of the motion position sensor (MPS) is fixedly attached to the lower end of a mounting collar 272. The lower end of the damper shaft 236 is slidably mounted in the mounting collar 272 to permit its displacement along its axis of rotation, but is rotatably positioned relative to the mounting collar 272 by a spring key 273. The damper shaft 236 thereby rotates with the mounting collar 272, but is axially movable relative thereto. The rotation of the MPS target magnet 270 is detected by an MPS sensor 274 attached to the upper surface of an MPS sensor circuit board 276. The MPS target magnet 270 and the MPS sensor 274 are known, and various types of magnets and sensors may be used depending on the circumstances.As with the first embodiment, the viscous damper 260 resists rotation of the steering wheel and applies feedback torque to the driver, which is a function of the rotational speed of the steering wheel. Moreover, in this embodiment, the damper shaft 236 is also longitudinally movable coaxial with its axis of rotation, such that the damper 260 provides damping in both the rotational and axial directions.The upper end of the damper shaft 236 is slidably mounted in the upper bearing 240. As previously mentioned, the lower end of the damper shaft 236 is slidably mounted within but non-rotatably fixed with respect to the mounting collar 272. Thus, the damper shaft 236 is also slidable along its rotational axis, but by mounting the lower end of the damper shaft 236 in the mounting collar 272, a constant distance is maintained between the MPS target magnet 270 and the MPS sensor 274 regardless of the axial position of the damper shaft 236.It is also noted that lower and upper annular compliant beams 280, 282 are secured to the damper shaft 236. The lower compliant support 280 is secured between the lower end of the cylindrical block 262 of the viscous damper 260 and the upper end of the mounting collar 272, and the upper compliant support 282 is secured between a radially extending annular shoulder 284 located immediately above the upper end of the damper scroll 232 and the inside of the upper bearing 240. The lower and upper compliant beams 280, 282 are identical and known and each comprise identical upper and lower cup shaped disks 286 disposed with their concave sides facing each other and an elastically deformable annular plug 288 (e.g., of silicone rubber) disposed between and separating the concave sides of the two disks 286.The torque applied by the viscous damper 260 is a function of the distance between the periphery of the cylindrical block 262 and the wall of the recess 264, the number and dimensions of the grooves 266 and annular lands 268, and the viscosity of the damping fluid, as in the first embodiment.Moreover, in this embodiment, the damper shaft 236 is also longitudinally slidable along its rotational axis, thereby providing longitudinal damping and assisting in reducing noise that may occur from impacts between the spur gear 224 and the worm 232 as the direction of travel of the spur gear changes. The lower and upper compliant beams 280, 282 provide a soft impact of the damper shaft 236 at the outer end points of its longitudinal displacement.A third embodiment of the present invention, which is a modification of the second embodiment, is shown in Fig. 8. The third embodiment is much similar to the second embodiment and corresponding features are identified with the same reference numerals, plus 100. The modification is present in the damper body 262 of the second embodiment, and thus only this portion 362 of the third embodiment is illustrated.As shown in FIG. 8, a viscous damper 360 includes a generally cylindrical block 362 rotatably mounted in a complementarily shaped cylindrical recess 364 in a housing 320. The cavity 363 includes a damping fluid (e.g., silicone fluid) retained by lower and upper annular seals 364, 365 that contact the lower and upper portions 362 a, 362 bof the cylindrical block 362, respectively. The central portion 362 cof the cylindrical block 362 is also cylindrical, but has a larger diameter, and is spaced from the lower and upper portions 362 a, 362 bby circumferential grooves 366 a, 366 b. The diameter of the central portion 362 cis slightly smaller than the inner diameter of the recess 363, and the central portion 362 cis thus slightly spaced apart from the inner wall of the recess 363.As in the second embodiment, the damper 360 is slidable in both the rotational and longitudinal directions along its rotational axis. The larger central portion 362 cof the cylindrical block 362 generates a piston action in the depression 364 when the worm shaft 336 moves axially, i.e. by fluid transfer between the fluid cavities 367 a, 367 bon both sides of the central portion 362 c.The construction and operation of the third embodiment are otherwise identical to those of the second embodiment.A fourth embodiment of the present invention is illustrated in Figs. 9 and 10. Many of the features of the fourth embodiment are closely similar to those of the first embodiment, and corresponding features are identified with the same reference numerals, plus 400.The assembly 410 includes a straight elongated steer-by-wire steering column 414 (only the lower end of which is shown) that is rotatably mounted about its longitudinal axis 416. A steering wheel 418, schematically shown in FIG. 1, for rotating the steering column 414 by a driver is secured to the upper end of the steering column 414. In the drawings, the steering column 414 is shown as a single shaft, but in practice is likely to be formed from a number of components. For example, the steering column may be formed from some telescopic parts and may include a torque sensor (e.g., a torsion bar assembly) between the steering wheel 418 and the opposite end of the steering column 414.The opposite lower end of the steering column 414 is received in a housing 420 in which it is rotatably mounted. As best seen in FIG. 3, a spur gear (pinion gear) 424 is fixedly secured to the lower end of the steering column 414 within the housing 420 and is thereby constrained to rotation with the steering column 414 and the steering wheel 418.As best seen in Figure 10, two identical screws 430, 432 are mounted in the housing 420 and mesh with the spur gear (pinion gear) 424 at diametrically opposite positions on opposite sides of the gear. Each of the screws 430, 432 is formed on the surface of a respective shaft 434, 436, the two shafts being oriented parallel to each other and perpendicular to the axis of rotation 416 of the steering column 414. The shafts 434, 436 are rotatably mounted in the housing by lower and upper bearings 438a, 440a; 438b, 440b. The lower and upper bearings 438 b, 440 bof the motor shaft 434 are located directly beyond the lower and upper ends of the worm 430 of the motor. The upper bearing 440 bof the damper shaft 436 is located directly beyond the upper end of the damper scroll 432, and the lower bearing 438 bis positioned toward the lower end of the damper shaft 436, unlike the position of the lower bearing of the first embodiment. In this embodiment, a cover plate 451 is also secured to the housing 420 over the upper end of the damper shaft 436.As shown in FIGS. 9 and 10, a leaf spring 490 is fixed to the outside of the housing 420. The leaf spring includes a longer generally straight portion 491 (but which may be curved in use as will be explained) having a larger head 492 at one end by which it is secured to the outer surface of the housing 420 by a screw 493. A second shorter generally straight portion 494 extends substantially perpendicular to the longer portion 491 and the two portions are joined at a curved junction 495. The shorter portion 494 of the leaf spring 490 passes through a recess 496 in the housing 420 and has its free end abutting the outer ring 498 of the upper bearing 440b of the damper shaft 436.In use, the leaf spring 490 is fixed to the housing 420 such that the longer portion 491 is bent, whereby a radial force is applied from the free end of the shorter portion 494 to the outer ring 498 of the upper bearing 440 bof the damper shaft 463 to keep the worm 432 in contact with the teeth of the spur gear 424.As best seen in FIG. 10, the first shaft 434 forms the output shaft of an electric motor 444 and is directly driven by the motor. A target magnet 448 of the motion position sensor (MPS) is fixedly secured to the lower end of a mounting collar 450 fixed to the lower end of the shaft 434 below the motor 444, thereby rotating with the shaft 434. The rotation of the MPS target magnet 440 is detected by an MPS sensor 452 mounted on the upper surface of an MPS sensor circuit board 454 mounted in the housing 420. An electronic control unit (ECU) (not shown in the drawings) is also fixed to the circuit board 454. The MPS target magnet 448 and the MPS sensor 452 are known, and various types of magnets and sensors may be used depending on circumstances.With continued reference to Figure 10, a viscous damper, generally indicated at 460, is mounted on the other shaft 436 at a location between the lower bearing 438b and the lowermost end of the damper scroll 432. The viscous damper 460 includes a generally cylindrical block 462 rotatably mounted in a complementarily shaped cylindrical recess 463 in the housing 420. The cylindrical block 462 of this embodiment is considerably longer than the corresponding cylindrical block 62 of the first embodiment, and its lower end extends to and is fixed in the lower bearing 438 b. The central portion of the cylindrical block 462 is provided with five identical, equally spaced, annular grooves 466 defining four identical, annular webs 468 whose peripheries abut but are slightly spaced from the wall of the recess 463. The cavity 463 includes a damping fluid (e.g., silicone fluid) retained by lower and upper annular seals 464, 465 that contact the portions of the cylindrical block 462 immediately below and above the annular ridges 468. The seals are chosen to integrate the movement of the shaft 436 as it is deflected to maintain contact with the spur gear 424.The torque applied by the viscous damper is a function of the distance between the periphery of the cylindrical block 462 and the wall of the recess 463, the number and dimensions of the grooves 466 and annular lands 468, and the viscosity of the damping fluid, as in the previous embodiments. In this embodiment, the damper is designed to be relatively insensitive to changes in the distance between the block 462 and the walls 463 that may occur upon deflection of the shaft 436.A motion position sensor (MPS) target magnet 470 is fixedly secured to the lower end of a mounting collar 472 fixed to the lower end of the damper shaft 436 below the viscous damper 460, and thereby rotates with the shaft 436. The rotation of the MPS target magnet 470 is detected by an MPS sensor 474 attached to the upper surface of an MPS sensor circuit board 476. The MPS target magnet 470 and the MPS sensor 474 are known, and various types of magnets and sensors may be used depending on the circumstances.The motor 444 provides a feedback torque to the steering column 416 (and thus to the steering wheel 418) as a function of the driver request. The viscous damper 460 also resists rotation of the steering wheel and applies feedback torque to the driver, which is a function of the rotational speed of the steering wheel. The viscous damper 460 also helps maintain the worm 430, connected to the output of the motor 444, in contact with the spur gear 424 and also helps reduce gear chatter, which may occur as the torque and direction of the motor are reversed. Moreover, the viscous damper 460 also ensures that a certain degree of feedback torque is always generated even when the engine 444 is not operating.Although the use of a spring 490 to bias the damper worm shaft is shown with respect to a particular embodiment, this is equally true for all previous embodiments.FIG. 11 is a cross-section of a fifth embodiment of the present invention, which is a modification that can be used with any of the previous embodiments. The modification will be described with reference to the first embodiment, but is equally applicable to all embodiments.The modification of FIG. 11 includes adding a return spring that acts on the motor shaft 34, on the damper scroll shaft 36, or on both the motor shaft 34 and the damper scroll shaft 36. FIG. 11 shows the input shaft 14 meshing with the spur gear (pinion gear) 24. Spur gear 24 in turn meshes with worm 30 on worm shaft 34 and with worm damper 32 on shaft 36.In this embodiment, a coil spring type coil spring 502 is fixed to the upper end of the motor shaft 34, the inner end of the spring 502 is attached to the motor screw shaft 34, and the outer end of the spring 502 is attached to the housing 20. Similarly, a second identical coil spring 504 is attached to the upper end of the damper shaft 36, with the inner end of the spring 502 attached to the damper shaft 36 and the outer end of the spring 504 attached to the housing 20. The coil springs allow a large angle of rotation in a small package.In this particular embodiment, the two springs 502, 504 are arranged to partially oppose each other. The springs 502, 504 may be biased in opposite directions to keep them biased in the same direction throughout their full operating range. This biasing action compensates for the backlash between the respective screws 30, 32 and the spur gear (pinion) 24.In an alternative configuration, only a single spring 504 is used along with the power worm shaft 34. In this case, the return spring is arranged to provide a restoring torque over the entire angular range of the hand wheel 18. The net torque provided by the spring acts in a direction to return the hand wheel to the straight angle. Moreover, the torque provided by the spring increases as the hand wheel rotates away from the straight angle.In all of the above embodiments, the damper provides rotational damping for amplifying engine feedback torque. Moreover, in the event of an engine failure, the damper provides passive feedback torque to the driver.Coupling the damper via a second worm shaft provides a compact package, thereby facilitating assembly in vehicles.In those embodiments in which axial movement and damping of the worm shaft are possible, noises resulting from play in the worm gear are reduced, in particular if the direction of the hand wheel is reversed.Coupling the damper via a second worm shaft and controlling backlash in the worm gear with a sprung worm system as indicated above for the fifth embodiment allows damper to be integrated into a compact package while controlling gear noise.By providing a return spring on both the motor shaft and the damper shaft with a bias, the worm / wheel compensation compensates, which may be sufficient to omit additional mechanisms.The invention is not limited to the details of the above embodiments.

Claims

A steering column assembly for a vehicle, comprising: an elongate steering column mounted for rotation about its longitudinal axis and configured to mount a steering wheel at one end; a gear connected to the steering column at a location spaced from the steering wheel mounting location and configured for rotation with the steering column; a motor comprising a rotatable output shaft; a first worm directly connected to the output shaft of the motor and rotatable and engaged with the gear; a damper comprising a rotatable shaft; a second worm directly connected to the shaft of the damper and rotatable and engaged with the gear; and control means configured to operate the motor.The steering column assembly of claim 1, wherein the damper comprises a fluid chamber configured to receive a damping fluid and a body located in the fluid chamber, the body configured to move with the rotatable shaft of the damper.The steering column assembly of claim 2, wherein the body located in the fluid chamber comprises a plurality of protrusions and / or depressions.A steering column assembly according to claim 2 or claim 3, wherein the body located in the fluid chamber is spaced from the wall of the fluid chamber.The steering column assembly of any of claims 2 to 4, wherein the body located in the fluid chamber comprises a portion having a greater width.A steering column assembly according to any one of claims 2 to 5, wherein the body located in the fluid chamber is part of the rotatable shaft of the damper.The steering column assembly of any of claims 2 to 5, wherein the body located in the fluid chamber is attached to the rotatable shaft of the damper.A steering column assembly according to any preceding claim, wherein the rotatable shaft of the damper is longitudinally slidable in the direction of its axis of rotation.The steering column assembly of claim 8, wherein the damper rotatable shaft is mounted to allow pivoting or deflection thereof.A steering column assembly according to claim 9, comprising bearing means configured to allow pivoting or deflection of the rotatable damper shaft.A steering column assembly according to any preceding claim, comprising biasing means configured to urge the second worm into contact with the gear connected to the steering column.A steering column assembly according to claim 9, comprising bearing means for rotatably mounting the rotatable shaft of the damper with which the biasing means is engaged.A steering column assembly according to claim 10, wherein the biasing means engages an outer ring of the bearing means.A steering column assembly according to any one of claims 11 to 13, wherein the biasing means comprises a spring.The steering column assembly of claim 14, wherein the spring comprises a leaf spring.The steering column assembly of any preceding claim, comprising a spring acting on the rotatable output shaft of the motor configured to apply torque to the motor shaft and / or a spring acting on the rotatable shaft of the damper configured to apply torque to the damper shaft.The steering column assembly of claim 16, wherein the spring acting on the motor's rotatable output shaft and / or the spring acting on the damper's rotatable shaft comprise a coil spring.A steering column assembly according to any preceding claim, comprising motor position sensor means for sensing the rotational position of the motor output shaft, the sensor means comprising a target member rotatable with the motor shaft and a sensor for detecting the target member.A steering column assembly according to any preceding claim, comprising motor position sensor means for sensing the rotational position of the damper shaft, the sensor means comprising a target member rotatable with the damper shaft and a sensor for detecting the target member.A steering column assembly according to claim 19 comprising a member configured to rotate with the rotatable damper shaft and with respect to which the damper shaft is slidable along its axis of rotation and to which the target member is attached.A steering column assembly according to claim 20, comprising a cup-shaped member fixed to one end of the rotatable damper shaft and to which the motor position sensor means is fixed.The steering column assembly of any preceding claim, wherein the first worm is part of the motor output shaft and / or wherein the second worm is part of the rotatable damper shaft.The steering column assembly of any preceding claim, wherein the first and second worms engage the gear connected to the steering column at diametrically opposite locations.A steering column assembly according to any preceding claim, comprising a housing in which the first and second augers and the gear connected to the steering column are located.A vehicle comprising a steering column assembly according to any preceding claim.

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