Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
  • B62D—MOTOR VEHICLES; TRAILERS
  • B62D5/00—Power-assisted or power-driven steering
  • B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
  • B62D5/0409—Electric motor acting on the steering column
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16H—GEARING
  • F16H55/00—Elements with teeth or friction surfaces for conveying motion; Worms, pulleys or sheaves for gearing mechanisms
  • F16H55/02—Toothed members; Worms
  • F16H55/22—Toothed members; Worms for transmissions with crossing shafts, especially worms, worm-gears
  • F16H55/24—Special devices for taking up backlash
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16H—GEARING
  • F16H57/00—General details of gearing
  • F16H57/02—Gearboxes; Mounting gearing therein
  • F16H57/021—Shaft support structures, e.g. partition walls, bearing eyes, casing walls or covers with bearings
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16H—GEARING
  • F16H57/00—General details of gearing
  • F16H57/02—Gearboxes; Mounting gearing therein
  • F16H57/021—Shaft support structures, e.g. partition walls, bearing eyes, casing walls or covers with bearings
  • F16H2057/0213—Support of worm gear shafts
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16H—GEARING
  • F16H57/00—General details of gearing
  • F16H57/02—Gearboxes; Mounting gearing therein
  • F16H57/021—Shaft support structures, e.g. partition walls, bearing eyes, casing walls or covers with bearings
  • F16H57/022—Adjustment of gear shafts or bearings
  • F16H2057/0222—Lateral adjustment
  • F16H2057/0224—Lateral adjustment using eccentric bushes

Definitions

• This invention relates to improvements in gear assemblies and in particular to gear assemblies for use in electric power assisted steering systems of the kind which incorporate a worm and wheel gear assembly for transferring torque from an electric motor to a steering shaft or output shaft operatively connected thereto.
• a power steering system for a vehicle comprising an electric motor having a stator and a rotor, an input shaft operatively connected to the rotor and adapted to rotate therewith, an output shaft associated with a steering shaft, and a gearbox adapted to transfer torque from the input shaft to the output shaft in response to a measure of the torque in the output shaft as produced by a torque sensor.
• the motor is typically operated to apply an increasing torque to the output shaft as the measured torque increases, thus applying assistance which helps reduce the effort needed to steer the vehicle.
• the input shaft carries a worm gear
• the output shaft carries a wheel gear.
• the teeth of the worm and wheel intermesh to transfer the torque.
• This system is simple and robust whilst providing relatively high gearing with a low component count.
• a problem in such gearboxes with noise and vibration due to incorrect meshing between the worm and wheel. This may arise due to manufacturing tolerances, thermal changes in dimensions or distortion due to torsional loads and wear during service.
• the invention provides a gearbox for use in an electric power assisted steering system comprising: a housing; an input shaft located at least partially within the housing which carries a worm gear and includes means for coupling to a motor rotor at one end; an output shaft located at least partially within the housing which carries a wheel gear; a first bearing assembly which supports the input shaft at a side of the worm distal from the end of the shaft which connects to the motor rotor and second bearing assembly which supports the input shaft at the other side of the worm; and an adjustable bearing support means which is secured to the housing in such a manner that it can be rotated about an axis of rotation, the first bearing assembly being mounted on the support means in a position that is eccentric to the axis of rotation such that upon rotation of the support means the first bearing assembly in displaced either towards or away from the wheel gear.
• the support means may comprise a sleeve that is located within a recess and which is free to rotate about its axis within the recess, and in which the sleeve supports the first bearing assembly at a position offset from the axis of rotation of the sleeve.
• it may comprise a support that is fixed to a face of the housing.
• the recess may comprise a cylindrical hole that passes through the sleeve and which receives the bearing.
• the sleeve may have a cylindrical outside form and may be received in a complimentary cylindrical opening in the housing. This would in theory allow the sleeve to rotate through a complete 360 degree angle. Other forms of sleeve are possible, provided that their shape and that of the opening in which it is received permits it to rotate relative to the housing.
• the sleeve may be provided with at least one set of teeth spaced at least partially around its axis of rotation, for example around an outer circumferential face of the sleeve, and the assembly may further include an adjuster screw or bolt which passes through an opening that is fixed relative to the housing, the adjuster screw or bolt having a thread which engages with the set of teeth such that rotation of the screw causes the sleeve to rotate relative to the housing.
• the axis of rotation of the bolt may be orthogonal to the axis of rotation of the sleeve.
• the adjuster bolt may have a bolt head at one end and may be secured in its hole by a lock nut at the other end. This should be sufficiently tight to remove unwanted free play yet allowing the bolt to be rotated when required.
• the screw and the set of teeth act in the manner of a worm and wheel to cause the wheel (in this case the sleeve) to rotate.
• the sleeve may have a flange at its free end which is provided with at least one slot that receives a bolt that passes through the slot into a threaded opening in the housing.
• the flange may be outwardly extending, and the slot may be arcuate, the length of the slot being substantially equal to the maximum angle of rotation of the sleeve required in use for adjustment.
• the slot will need to be longer than that by the width of the bolt used, i.e. the required angle plus bolt thickness.
• Two slots may be provided, with a locking bolt received in each one. They may be diametrically offset around the flange.
• the adjuster screw or bolt may be retained in the housing by means of a torque nut or other secured type of nut.
• a washer may be provided, which may be situated between the torque nut and the housing, has a tab which intrudes into its central hole and which engages with a groove in the adjuster screw or bolt forcing the washer to rotate with the adjuster screw or bolt.
• the first bearing assembly may comprise a fixed race secured to the sleeve and a moving race secured to the input shaft, the two races being separated by one or more bearings which may be of the ball or needle type. They may be secured through an intermediate element.
• the races may each be substantially annular.
• the input shaft may be provided with means for connection to the rotor of a motor, and an opening may be provided in the housing to permit connection between motor and input shaft to be effected.
• the input shaft preferably protrudes through the opening, which also serves to locate the second bearing means. Therefore, in a preferred arrangement the first bearing means is provided at the side of the worm farthest from the motor.
• a flexible coupling may be provided between the input shaft and any motor rotor attached to it.
• the second bearing means may be adapted to permit a degree of tilt of the input shaft within the bearing relative to the housing.
• This tilting bearing is preferably the one closest to the motor to minimise misalignment between motor rotor and input shaft for a given amount of tilt.
• the bearing may allow an angle of tilt of up 0.5 degrees or higher, say up to 1.0 degrees or thereabouts.
• Each of the first bearing means and the second bearing means may comprise two bearing elements rotatably coupled by one or more bearings preferably such as ball bearings.
• the elements may define bearing races which define the path of the bearings.
• the input shaft may connect directly to the rotor of a motor, or indirectly through a coupling.
• the invention provides an electric power assisted steering system comprising a gearbox assembly according to the first aspect of the invention, an electric motor fixed to the housing and to the input shaft of the gearbox assembly, a steering shaft which is operatively coupled to the output shaft of the gearbox, a torque sensor which is adapted to measure the torque in the output shaft, a controller which is adapted to produce a motor control signal according to at least the measured torque, and a motor drive circuit which is adapted to apply a drive signal to the motor in response to the control signal.
• Figure 1 is a side view in cross section of a gearbox assembly in accordance with a first aspect of the invention
• Figure 2 is an exploded view of the component parts of the assembly
• Figure 3 is a view in cross section taken along the line A-A in Figure 1;
• Figure 4 is an alternative view in cross section taken along the line F-F as indicated in Figure 3.
• FIG. 1 An embodiment of a gearbox assembly in accordance with the first aspect of the invention is shown in Figure 1.
• a housing 1 supports an input shaft 15 which carries a worm gear 3.
• the housing 1 also provides support for an output shaft which carries a wheel gear 2. Both shafts are supported in bearings which are mounted recesses in the housing. Only the two bearings 4 and 5 that support the input shaft can be seen in Figure 1.
• the input shaft takes torque from an electric motor (not shown) coupled to the housing.
• a coupling 14 on the end of the input shaft enables secure connection to a rotor of a motor to be made.
• the worm transfers the torque from the motor through the wheel 2 to the output shaft. This torque is then passed from the output shaft to a part of a steering shaft assembly so as to assist a driver in steering a vehicle.
• the end of the input shaft 15 nearest the motor is supported in a bearing assembly 5, whilst the end furthest from the input shaft is supported by a further bearing assembly 4. Supporting the shaft at both ends in this way provides good control over the position of the shaft and prevents the shaft from bending under loads passed back to the worm from the wheel gear.
• the distance between the worm 3 and the wheel 2 can be manually adjusted by rotating an eccentric sleeve 7 or collar fitted to the housing and which supports the bearing 4 furthest from the motor.
• An adjusting bolt 6 engages a track of teeth 7a around the sleeve such that the sleeve 7 can be rotated by turning the screw.
• the bearing 5 nearest the motor is designed such that it permits a small degree of angular movement of the input shaft without introducing excess friction.
• the sleeve 7 and the adjuster bolt 6 are best seen in Figure 2 of the accompanying drawings.
• the sleeve 7 comprises a tubular body having a central bore which is offset from the axial centre of the tube. Thus, as the tube rotates the centre of the bore will move in a circular path.
• the body is provided at one end with an outwardly extending flange 7b.
• This has two bolt receiving slots 7c which, when aligned with corresponding holes in the housing permit the flange to be locked in position by two bolts.
• the slots 7c are elongate and arcuate, extending circumferentially around the axis of the tube. This allows the tube to be rotated through an angle equal to the angular length of the slots when the bolts are loosened.
• the tubular body of the sleeve fits within a complimentary cylindrical recess within the housing. The fit is loose enough to permit the collar to rotate but without allowing any unwanted free play.
• a portion with a reduced diameter which locates an annular bearing assembly.
• This bearing assembly comprises an outer race that may be press fitted into the sleeve and an inner race which in use is fixed to the end of the input shaft. Ball or needle bearings mounted in a bearing cage separate the two races. As the bearing assembly is concentric with the hole in the tube, it is eccentric to the outer form of the tube.
• the portion with a reduced diameter may be slightly bigger in diameter than the bearing and there may be an annular groove cut into it containing a compliant ring 8 which grips the outer race of the bearing thus preventing it from rotating while allowing a small amount of radial displacement relative to the sleeve.
• the tubular body of the collar is provided with a set of teeth 7a which extend around at least a part of the circumference of the body.
• a hole 13 is bored in the housing body at a normal to the cylindrical opening and offset from its axis such that the hole intersects the wall of the cylindrical opening at a point along its length that corresponds with the set of teeth. The dimensions 13 of this hole are such that the teeth can be seen when looking down the hole as extending a small way into the hole.
• This hole 13 receives a threaded bolt 6 which has a thread pitch that allows it to mesh with the teeth on the collar in the manner of a worm and wheel.
• the bolt 6 extends through the hole 13 and out of the housing, and receives a torque nut 11 on its free end over a washer 10.
• the torque nut 11 allows the tightness of the bolt to be adjusted to remove free play whilst permitting it to be rotated using a suitable tool.
• Washer 10 has a tab which intrudes into its central hole and which engages with a groove in the threaded bolt.
• the washer which is situated between the torque nut and the housing, rotates with the threaded bolt while the bolt is being rotated for the purposes of adjusting the engagement of the worm with the wheel gear. This ensures that the setting of the torque nut is not disturbed by frictional contact with the housing.

Landscapes

• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Transportation (AREA)
• Power Steering Mechanism (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=36775583

Family Applications (1)

Country Status (3)

Cited By (1)

Families Citing this family (8)

Family Cites Families (3)

• 2006
  • 2006-06-14 GB GB0611718A patent/GB0611718D0/en not_active Ceased
• 2007
  • 2007-06-13 EP EP07733210A patent/EP2032413A1/de not_active Withdrawn
  • 2007-06-13 WO PCT/GB2007/002204 patent/WO2007144618A1/en active Application Filing

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events