GB2475549A

GB2475549A - A vehicle steering lock and power steering unit

Info

Publication number: GB2475549A
Application number: GB0920501A
Authority: GB
Inventors: Jeff Jones
Original assignee: Nissan Motor Manufacturing UK Ltd; Nissan Technical Centre Europe Ltd
Current assignee: Nissan Motor Manufacturing UK Ltd; Nissan Technical Centre Europe Ltd
Priority date: 2009-11-24
Filing date: 2009-11-24
Publication date: 2011-05-25
Also published as: GB0920501D0

Abstract

A steering lock apparatus 100 for a vehicle steering system having a steering shaft, the apparatus comprising: a power steering unit having at least one rotational member coupled to the shaft; and locking means for locking rotation of the rotational member to thereby lock rotation of the shaft. The power steering unit may include a worm gear 126 and the rotational member may comprise a cooperating worm wheel 123. The locking means may comprise a locking pin 111, wherein the worm wheel comprises a plurality of locking points 140 for cooperation with the locking pin and, wherein the locking pin is arranged to selectively lock rotation of the worm wheel. The worm wheel may be supported on the shaft by a friction clutch configured to permit the shaft to rotate relative to the worm wheel only if a torque applied to the shaft exceeds a pre-determined limit. A method of selectively locking a steering shaft is also disclosed, where the method includes monitoring the position of the worm wheel relative to the locking pin, and the worm wheel is adjusted to align the closest available locking point with the locking pin.

Description

IMPROVEMENTS IN VEHICLE STEERING LOCKS

Field of the invention.

The invention is concerned with improvements in vehicle steering locks and particularly, but not exclusively to steering locks for electrically assisted power steering systems. Aspects of the invention relate to an apparatus, to a system, to a method and to a vehicle.

Background of the invention.

Modern vehicles intended for use on public roads such as passenger cars are frequently fitted with power assisted steering. There are a variety of technologies used in modern vehicle steering systems today to assist the driver while operating the vehicle.

Most vehicle steering systems comprise a steering wheel, with which the driver applies a steering force to the steering system, a steering column or shaft, a steering gear formed by a steering rack and corresponding pinion gear, steering arms and at least one road wheel. The steering wheel is mounted to one end of the steering shaft. The steering shaft is arranged to transmit input torque from the steering wheel to the pinion gear. The pinion gear engages with the steering rack to translate rotational movement of the steering wheel and shaft to a linear motion of the steering rack. The steering rack is connected to the at least one road wheel by the steering arm. The linear movement of the steering rack applies a force on the steering arm which causes the road wheel to pivot about a substantially vertical axis known as the steering axis.

In some cases, power steering systems utilise a pressurised hydraulic system to assist the driver in turning the steered road wheels. Hydraulic pressure is provided by a pump. The pump may be driven by an electric motor or directly from the vehicle engine. A double-acting hydraulic cylinder applies a force to the steering rack. The force applied by the hydraulic cylinder is proportional to the input from the steering wheel. The steering rack is displaced in a generally lateral direction by the combined forces applied by the pinion gear and the hydraulic cylinder. The movement of the steering rack applies a torque via the steering arms to the steering axis of the steered road wheels. When the driver turns the steering wheel, the flow of hydraulic fluid to the cylinder is controlled by valves operated by the steering wheel; the more torque the driver applies to the steering wheel and steering shaft to which the steering wheel is attached, the more hydraulic fluid the valves allow through to the cylinder. In this way, the driver can safely and predictably steer the vehicle in the known way.

Another technology used to provide power assistance to the vehicle steering system is known as electric power steering, often abbreviated to EPS or EPAS.

EPAS uses an electric motor to reduce the effort required at the steering wheel by the driver. A sensor is arranged to detect the torque applied to the steering shaft by the steering wheel, and a control module determines the appropriate torque required from the electric motor. The electric motor may be coupled directly to the steering gear or the steering column.

EPAS systems allow varying amounts of assistance to be supplied by the electric motor depending on driving conditions. Such systems improve vehicle fuel economy as they reduce parasitic loads on the engine. Parasitic loads are reduced because the electric motor in an EPAS system only provides assistance when required, whereas the pump in a hydraulic system is running constantly when the vehicle is in use.

The improvement in fuel economy provided by EPAS systems over hydraulic power steering systems has resulted in a shift away from hydraulically assisted steering systems especially in smaller cars.

One challenge the EPAS system does pose however is the packaging of the electric motor. The diameter of the motor is relatively large compared to the diameter of the steering shaft due to the torque required to provide sufficient assistance to the driver. If the motor is to be mounted on the steering shaft or column it tends to be located between the steering wheel and the pinion gear. In this location, the motor may occupy the space previously used to package a steering lock assembly. The steering lock assembly typically clamps around the steering shaft and selectively locks and unlocks the steering shaft to prevent the vehicle from being driven without the owner's consent.

In known column mounted EPAS systems, the motor applies torque to the shaft via a worm gear and worm wheel arrangement. In this example, the shaft of the motor is directly connected to the worm gear and both the motor and the worm gear are mounted parallel to the steering shaft and the worm wheel is connected to the steering shaft. The worm wheel has a diameter greater than the steering shaft and so requires more packaging space around the steering shaft than a hydraulically assisted steering system.

The strength of the steering lock is dictated by legislation and insurance organisations both intent on reducing incidences of vehicle theft. In Europe, vehicles fitted with a steering lock must withstand a torque of 300 Nm applied to the steering wheel without component failure as dictated by Directive 95/56/EC.

Some vehicle manufacturers employ friction clutches in the steering lock mechanism to manage these extreme conditions. There is provision for such friction clutches in the legislation which states that the clutch must withstand 100 Nm applied to the steering wheel without slip and must prevent damage to the system at 300 Nm, effectively uncoupling the steering wheel from the locked shaft.

In this case, the critical components of the steering system must remain intact and once the steering lock is unlocked the steering wheel must be re-coupled to the steering shaft. In the UK, the motor vehicle insurance test institute, Thatcham demand that the steering lock must withstand 400 Nm applied at the steering wheel in order for a vehicle to receive favourable insurance ratings. With such high loads, the use of a steering lock clutch by vehicle manufacturers is common.

It is against this background that the present invention has been conceived. It is an aim of the present invention to address the issue of packaging an EPAS system using a steering shaft mounted motor improving robustness and reducing parts complexity and cost. Aspects and embodiments of the invention may provide a steering lock apparatus for a vehicle steering system arranged to withstand the severe loading required by vehicle insurers arranged to occupy a smaller packaging volume, and a method of operating the same. Other embodiments of the invention may provide a means for selectively immobilising the worm wheel of a vehicle steering system without applying load to the teeth around the perimeter of the worm wheel. This approach greatly improves the performance of the steering lock apparatus whilst reducing parts complexity, mass and cost. Other aims and advantages of the invention will become apparent from the following

description, claims and drawings.

Summary of the invention.

According to an aspect of the present invention there is provided a steering lock apparatus for a vehicle steering system having: a worm gear; a worm wheel for cooperating with the worm gear; and a locking pin, wherein the worm wheel comprises a plurality of locking points for cooperation with the locking pin and, wherein the locking pin is arranged to selectively lock rotation of the worm wheel.

Advantageously, positioning the locking points around the worm wheel permits the locking pin of the steering lock apparatus to be positioned close to the worm wheel, keeping packaging volume to a minimum. Additionally, locking the worm wheel directly with the locking pin minimises the loading of the locking pin by the steering system when the pin is in cooperation with a locking point. Minimising loading of steering components minimises fatigue and improves the reliability and performance of the steering lock apparatus.

In addition, the present invention provides the advantage that a conventional steering lock, independently mounted just below the steering wheel, may no longer be necessary depending on the vehicle application. This increases the available area for the driver's knees and greatly increases interior styling freedom.

In an example, the worm wheel comprises a hub portion arranged for cooperating with a steering shaft.

Advantageously, mounting the worm wheel directly to the steering shaft permits overall packaging volume of the steering lock apparatus to be kept to a minimum while optimising the use of materials used within the vehicle steering system.

In an example, the longitudinal axis of the locking pin is substantially parallel with the axis of rotation of the steering shaft.

Advantageously, positioning the locking pin adjacent to the steering shaft and aligned substantially parallel therewith allows for efficient packaging of the steering lock apparatus. Additionally, arranging the locking pin in this way provides additional protection against tampering as the pin is surrounded on at least two sides by the shaft and the worm gear.

In an example, the locking pin is arranged to move between a locked position, where the pin is engaged with a locking point, and an unlocked position where the pin is not engaged in a locking point.

In an example, the locking pin is moved between the locked and the unlocked position by an actuator.

In an example, the locking pin actuator moves the locking pin in dependence on a locking actuation controller.

Preferably, the locking pin is moved between a locked and an unlocked position by the locking actuator which may be mechanically, pneumatically, hydraulically, magnetically or electrically actuated. Additionally, the locking actuator may be biased by a biasing means towards either the locked or the unlocked position as may be appropriate for the particular steering system.

In an example the actuator comprises a solenoid.

In an example, the actuator comprises a worm gear driven by a locking motor.

In an example, the locking pin comprises a series of gear teeth in at least one surface, said gear teeth configured for engaging the actuator worm gear.

Advantageously, use of direct actuation of the locking pin improves the cycle time of the steering lock apparatus whilst making it far less susceptible to tampering by a car thief. Additionally, the use of a locking pin incorporating gear teeth arranged to engage with a locking actuator worm gear or other suitable gear, minimises the number of joints or linkages required to actuate the pin and thus improves functional reliability parts complexity.

In an example, the locking points are arranged in a generally circular locus and regularly spaced apart around that circular locus.

In one example, the locking points are formed by indentations formed in at least one surface of the worm wheel.

In another example, the locking points are formed by through holes perforating the worm wheel.

Advantageously, the provision of multiple locking points into which the locking pin may be received, greatly reduces the likelihood that the pin has not engaged a locking point when the user operates the steering lock. The use of indentations or perforations, arranged around a substantially circular path on or through a face of the worm wheel, provides a plurality of locations for which the pin may positively locate and reliably lock the worm wheel. Additionally, this also provides the benefit of greatly improving the perceived quality for the user of the steering lock system as the pin is more likely to find a locking point quickly without necessitating the user rotating the steering wheel back and forth to find a locking point.

In an example, the worm wheel is supported on a shaft by a friction clutch configured to permit the shaft to rotate relative to the worm wheel only if a torque applied to the steering shaft exceeds a pre-determined limit.

In an example, the locking pin and locking point are arranged to withstand the pre-determined torque required to cause the friction clutch to permit relative movement between the shaft and the worm wheel.

Advantageously, the provision of a friction clutch between the worm wheel and the steering shaft serves to protect the worm wheel and worm gear if excessive force is applied to the steering system, improving reliability and the robustness of the steering system. Preferably, the friction clutch is provided by a tolerance ring located between the steering shaft and the worm wheel. In this way, a single friction clutch may be employed to exceed the requirements of the legislation intended to prevent vehicle theft and also function to safeguard the worm wheel, worm gear and motor against damage caused by excessive forces applied to the steering system.

In an example, a steering lock apparatus for a vehicle steering system comprises: a worm gear; a worm wheel, mounted on a steering shaft; and a locking pin, wherein the worm wheel comprises: an inside diameter, defined by the diameter of the steering shaft; an outside diameter, defined by a plurality of teeth for engagement with the worm gear; and a plurality of locking points arranged in a generally circular locus between the inner and the outer diameter, wherein the locking pin is arranged to selectively cooperate with at least one locking point to prevent rotation of the steering shaft relative thereto.

In an example, the locking points are formed by indentations formed in or through at least one surface of the worm wheel and located on a radius about the axis of rotation thereof so as to form a substantially circular locus of locking points arranged between the steering shaft and a root circle radius prescribed by the root of each tooth around the perimeter of the worm gear.

Advantageously, the locking points may be moved as close as possible to the root circle, maxim ising their effective radius from the axis of rotation and thus maximising the mechanical advantage afforded to the locking pin over the steering shaft.

In another aspect, there is provided a steering shaft or column comprising a steering lock apparatus according to any preceding paragraph.

In still another aspect, there is provided a vehicle comprising a steering lock apparatus according to any preceding paragraph.

In further aspect, there is provided a method of selectively locking a steering shaft of a vehicle steering system, the method comprising: monitoring the selection mode of a lock actuator control; monitoring the position of a worm wheel relative to a locking pin; and monitoring a wheel rotation sensor output from at least one vehicle road wheel, wherein upon determining the selection mode of the lock actuator control corresponds to a lock command and, determining from the rotation sensor of the or each road wheel that the vehicle is stationary, the orientation of the worm wheel is adjusted to align a locking point located on the worm wheel with the locking pin to facilitate the engagement of the locking pin with the locking point and, wherein the locking point selected for engagement with the locking pin is the closest available to the locking pin when the lock command was determined.

In an example of the method according to the preceding paragraph, upon determining the selection mode of the lock actuator control corresponds to an unlock command, and determining from the rotation sensor of the or each road wheel that the vehicle is stationary, the orientation of the worm wheel is adjusted to align a locking point located on the worm wheel with the locking pin to facilitate disengagement of the locking pin from the locking point.

The method provides the advantage that the steering lock system automatically aligns the locking point with the locking pin of the steering lock apparatus, reducing side-loading on the pin and static loading on the worm wheel and steering shaft.

This greatly improves reliability and performance whilst minimising wear on the component parts of the steering system.

According to a still further aspect of the present invention for which protection is sought there is provided a combined power assisted steering unit and steering lock for a vehicle steering system.

According to a still further aspect of the present invention for which protection is sought there is provided a power assisted steering apparatus for a vehicle steering system, the apparatus comprising locking means for locking rotation thereof so as to hinder or prevent rotation of the steering system.

According to a still further aspect of the present invention for which protection is sought there is provided a steering lock apparatus for a vehicle steering system, the apparatus comprising locking means for engaging with a rotational part of a power assisted steering apparatus of the vehicle steering system thereby to hinder or prevent rotation thereof.

In an embodiment, the locking means may comprise a pin or a gear for engagement with the power assisted steering apparatus.

It will also be appreciated by one skilled in the art, that the apparatus of the present invention may be suitable for use in other vehicle-based applications.

Within the scope of this application it is envisaged that the various aspects, embodiments, examples, features and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings may be taken independently or in any combination thereof. In particular, features described in connection with one embodiment are applicable to the other embodiment, except where there is an incompatibility of features.

Brief Descrirjtion of the Drawincis The present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a schematic view of a known vehicle steering system comprising a column mounted EPAS system; Figure 2 shows a schematic view of a known vehicle steering lock; Figure 3 shows a schematic view of a known EPAS vehicle steering system in detail; Figure 4 shows a detailed perspective view of a vehicle steering lock apparatus according to an embodiment of the present invention; and Figure 5 shows a detailed plan view of the worm wheel and worm gear of the vehicle steering lock apparatus according to an embodiment of the present invention.

While the examples given for suitable applications for the present invention relate to steering systems for road vehicles, it will be appreciated by one skilled in the art that there are potentially other uses for the present invention with vehicles not intended for use on public roads.

Figure 1 shows a system view of a known vehicle steering system 10. In the example shown, the vehicle steering system 10 is assisted electrically, known as electric power assisted steering or EPAS. The steering system 10 comprises a steering wheel 2, a steering column or shaft 3, a motor assembly 5, a steering lock 6 a steering rack 7, a pair of steering arms 8 and a pair of steered road wheels 9 (only one is shown for clarity) which are typically the front wheels of a vehicle.

To change the direction of travel of the vehicle using the known steering system 10, the driver turns the steering wheel 2 in the desired direction. The steering wheel 2 is connected to the shaft 3 which is arranged to transmit the torque applied to the steering wheel 2 to the steering rack 7. The steering rack 7 translates the rotational movement of the shaft 3 into a linear movement. A steering arm 8 couples this linear movement to each steered road wheel 9. The force applied to the steering arm 8 by the steering rack 7 causes the road wheel 9 to rotate about a steering axis. Both ends of the steering rack 7 are arranged to move simultaneously in response to movement of the steering wheel thereby turning both road wheels 9 simultaneously and causing the vehicle to change direction as desired.

The motor assembly 5 is provided to assist the driver and reduce the effort required to turn the steering wheel 2 during driving. When the driver applies a steering input torque to the steering wheel 2 a sensor 24a (shown in Figure 3) determines the direction and magnitude of the input applied by the driver. In response to the output of that sensor 24, a controller 24 (also shown in Figure 3) supplies the motor assembly 5 with an appropriate electrical current, activating the motor assembly 5 and providing the desired assistance to the driver. An example of a motor assembly 5 for a known EPAS steering system 10 is shown in greater detail in Figure 3.

To prevent or at least mitigate the risk of theft of the vehicle, the driver may selectively lock the steering shaft 3 using the steering lock or steering lock assembly 6. In this example, the steering lock assembly 6 is mounted on a bracket around the shaft 3. The bracket is rigidly connected to the vehicle. The steering lock 6 is arranged to selectively engage with a feature (not shown for clarity) on the shaft 3. When the steering lock 6 is in the locked position, rotation of the steering shaft relative to the vehicle is prevented or greatly restricted, as the steering lock assembly 6 effectively couples the shaft 3 to the bracket 15.

Figure 2 shows an exploded view of a known steering lock assembly 6 in more detail. As described above, the steering lock assembly 6 comprises a steering lock body 12 supporting a locking pawl 11 arranged to engage a pawl receiver 13 mounted to the steering shaft 3 via a tolerance ring 14. The steering lock body 12 is formed in two halves, a steering lock body upper 1 2U (not shown for clarity) and a steering lock body lower 12L, arranged to clamp around the steering shaft.

The tolerance ring 14 is made from a band of spring steel at least partly surrounded by a series of perforations or serrations 14s formed around the band, arranged to tightly grip the steering shaft 3.The tolerance ring 14 is substantially circular in cross section with a diameter less than or equal to the steering shaft 3.

The perimeter of the tolerance ring 14 is not continuous but rather has a narrow slot or gap 1 4g cut through the band parallel with the axis of rotation of the steering shaft 3. The gap 14g is arranged to facilitate the installation of the tolerance ring 14 to the shaft 3. The axis of rotation of the steering shaft 3 is indicated by a chain dash line in Figure 2.

The tolerance ring 14 is press fit over the shaft 3 and the pawl receiver 13 is press fit over the tolerance ring 14. The pawl receiver 13 and tolerance ring 14 may only be rotated around the shaft if a pre-determined slip torque is exceeded. Typically, slip torque is tuned to be greater than 100 Nm so as to greatly minimise the possibility of a thief being able to drive the vehicle with the steering lock engaged.

The steering lock body lower 12L is arranged to permit the pawl 11 to be selectively moved from a locked position to an unlocked position. In the locked position, the pawl 11 protrudes from the steering lock body lower 1 2L towards the axis of rotation of the shaft 3. By moving towards the steering shaft 3, the pawl 11 engages with cooperating features arranged around the perimeter of the pawl receiver 13. An inner surface 1 3t of the pawl receiver 1 3 is arranged to fit tightly over the serrations 14s of the tolerance ring 14 to resist relative movement of the pawl receiver 13 relative to the shaft 3 when the pawl 11 is in the locked position.

The friction between the pawl receiver 13, the tolerance ring 14 and the shaft 3 is tuned to provide a sufficiently high slip torque, providing an effective locking means for the steering system.

Securing the pawl receiver 13 to the shaft 3 by means of a tolerance ring 14 effectively provides a friction clutch arrangement. This mitigates the risk of damage to steering components if a thief were to apply a large manual force to the steering wheel. Thus, even using a lever through the steering wheel in an attempt to break the steering lock, will be prevented by the action of the friction clutch and so the thief is prevented from driving the vehicle away when the steering lock is engaged.

In the unlocked position, the pawl 11 is retracted away from the axis of rotation of the shaft 3, disengaging with the pawl receiver 13 and permitting free rotation of the shaft 3 relative to the steering lock body 12.

Figure 3 shows a motor assembly 5 for a known EPAS steering system. The motor assembly 5 comprises a motor 20, a motor controller or ECU 22, a torque sensor 24a, a sensor controller 24, a worm gear 26 and a worm wheel 23. Torque applied to the steering wheel by the driver is detected by the torque sensor 24a whose output is monitored by the sensor controller 24. The sensor controller 24 is electrically connected to the motor controller 22. In some known steering systems, the sensor controller 24 and the motor controller 22 are integrated into the same unit. The motor controller 22 is connected to an electrical power supply, typically the vehicle battery (not shown). The motor controller 22 is arranged to calculate the amount of mechanical assistance required from the electric motor 20 to aid the driver steer the vehicle and supply the motor 20 with the appropriate current via a supply harness 21.

The motor 20 does not produce sufficient torque to drive the steering shaft 3 directly so the output from the motor 20 is geared down via a worm gear assembly comprising the worm gear 26, mounted directly onto the end of the motor 20, engaging with the worm wheel 23 mounted directly on the steering shaft 3. The worm gear 26 engages with a plurality of gear teeth 25 (partly shown for clarity) arranged around the perimeter of the worm wheel 23. The gear teeth 25 are formed from a plastics material such as nylon or the like, chosen for its low friction properties. A low friction material is desirable to minimise friction in use losses between the worm wheel 23 and worm gear 26. The centre of the worm wheel 23, also known as the hub 23h is formed from a suitable metal such as steel or an aluminium alloy for strength, and the gear teeth 25 are either over-moulded over the hub or bonded on using a suitable adhesive.

It will be appreciated from Figures 1 to 3 that the typical steering system 10 uses a separate motor assembly 5 and steering lock assembly 6 both mounted on or adjacent to the steering shaft 3. The separate mounting of the separate motor assembly 5 and the steering lock assembly 6 on the steering shaft requires relatively high assembly time and costs and presents several undesirable packaging restraints on the vehicle designer.

The present invention has been conceived to improve upon the separate mounting of the motor assembly 5 and steering lock assembly 6 on the steering shaft 3. A steering lock apparatus 100 of the present invention is shown in Figure 4. It will be noted that like-features have been given similar reference numerals for clarity.

Figures 4 and 5 show a steering lock apparatus 100 of the present invention. The steering lock apparatus 100 comprises a worm gear 126; a worm wheel shown generally at 123, arranged for cooperation with the worm gear 126; and a pawl or locking pin 111. Provided in a surface of the worm gear 126 are a plurality of locking points 140 for cooperation with the locking pin 111. The locking pin 111 is arranged to selectively engage with the locking points 140 so as to prevent rotation of the worm wheel 123 relative to the locking pin 111 when the locking pin 111 is engaged with a locking point 140. It will be appreciated that the worm gear 126, worm wheel 123 and the locking pin may be covered by a protective housing arranged to prevent the ingress of dirt and to resist tampering by unauthorised personnel or car thief.

The worm wheel 123 comprises an inside diameter 103 and an outside diameter 125od, the latter being defined by a plurality of teeth 125t arranged for engagement with the worm gear 126. At the base of each gear tooth 1 25t is a root, the roots collectively proscribing a root circle radius 125r (shown in Figure 5), whose centre is the centre of rotation of the worm wheel 123. The inside diameter 103 is configured for mounting the worm wheel 123 onto a steering shaft such that rotation of the worm wheel results in a rotation of the steering shaft. On the other hand, engagement of the locking pin 111 in a locking point 140 effectively locks the steering shaft, preventing rotation. The steering shaft is not shown in Figure 4 or 5 for clarity. The locking points 140 take the form of indentations in a surface of the worm wheel 123 between the inside diameter and the root circle radius 125r proscribed by the gear teeth 1 25t. Alternatively, the locking points may be formed by through-holes allowing the locking pin 111 to pass through the worm wheel 123 when in the locked position. In this way, the locking pin 111 may engage with a locating feature formed in the protective housing of the steering lock apparatus such that when the pin 111 is in the locked position it is supported at each end, increasing the load capacity of the steering lock apparatus.

It will also be appreciated that whilst the example of the present invention shown in Figure 4 shows the locking pin 111 aligned substantially parallel with the axis of rotation of the steering shaft, the angle of the pin 111 relative to the worm wheel 123 may be adjusted as required, to overcome any packaging constraints around the worm wheel 123.

The worm wheel 123 further comprises a hub portion 123h arranged between the inside diameter 103 and the outside diameter 125od. The locking points 140 are arranged so as to form a generally circular locus between the inside diameter 103 and the root circle radius 125r.

Figure 4 shows the hub 123h surrounded by a gear tooth ring 125 formed from a low friction plastics material such as nylon. The hub 1 23h itself is formed from a suitable metal such as steel or aluminium alloy which may be machined from billet, cast or sintered as desired. The outside diameter of the hub 1 23h provides the gear tooth ring 125 with sufficient surface area to reliably secure the ring 125 to the hub 123h using adhesive or over-moulding without risk of the ring 125 slipping on the hub 123h in use. To increase the surface area between the gear tooth ring 125 and the hub 123h, the hub 123h is provided with a shoulder 130 of locally increased material thickness. In the example shown, the locking points 140 are arranged evenly around the shoulder 130 beneath the gear tooth ring 125.

In use, the locking pin 111 may be selectively moved between a locked or engaged position, wherein the pin 111 engages with a locking point 140, and an unlocked or retracted position, wherein the pin 111 is not in contact with the worm wheel 123.

In the locked position, the engagement of the pin 111 with one of the locking points couples the steering shaft (not shown) to the vehicle via the worm wheel 123, thus effectively locking the vehicle steering and preventing unauthorised use of the vehicle. In the unlocked or retracted position, the locking pin 111 is no-longer in contact with the worm wheel 1 23 and so the steering shaft may rotate, so that the vehicle steering may be operated as normal.

It may be seen in Figure 4 that the locking pin is located adjacent to the worm wheel and is aligned so as to be substantially perpendicular to the worm wheel and substantially parallel with the axis of rotation of the steering shaft. In the example shown in the Figures, the locking pin 111 is orientated in such a way as to minimise packaging volume, located between the steering shaft and the worm wheel. However, the orientation of the locking pin 111 may be adjusted to suit the packaging constraints of a particular steering system application. In addition the pin 111 is shown in Figure 4 as a square section elongate member but it will be appreciated that the pin may be provided with features to facilitate the engagement and disengagement with the locking points 140. For example, the end of the pin arranged for engagement with the locking points 140 may be tapered to facilitate engagement and reduce wear. Additionally, the locking pin 111 may be provided with features arranged for cooperation or integration with a locking actuator (not shown for clarity). In an embodiment (not shown), the locking pin 111 is integrated into a solenoid, forming a locking pin feature at one end of the solenoid armature. In this embodiment, energising the solenoid causes the pin to move from a locked position to an unlocked position, withdrawing the pin 111 from a locking point 140.

In an alternative embodiment (not shown), the locking pin 111 is an elongate member provided with an engagement tip at one end and a gear rack formed along at least one surface at the other end. The engagement tip is arranged to cooperate with a locking point 140 in use. The locking pin 111 is supported in a guide arranged to guide the locking pin 111 and align it with the locking points 140. The guide permits reciprocal movement of the locking pin 111 relative to the worm wheel 123. The gear rack is configured to cooperate with an actuator which is provided with a suitable gear to engage the gear rack feature on the locking pin.

The actuator is arranged to move the locking pin 111 in the guide between a locked and an unlocked position.

In an alternative embodiment (not shown), the worm wheel 123 is secured to the steering shaft by a tolerance ring. The interaction between the steering shaft, tolerance ring and the worm wheel forms a friction clutch arrangement, providing the benefits of improved durability and performance as previously described. In this way, excessive loading of the steering system, for example during an attempted theft of the vehicle, will not result in damage to the worm wheel 123 or worm gear 126 and the steering system will remain intact but inoperative until the locking pin 111 is moved to the unlocked position.

In a preferred embodiment of the steering lock apparatus, the locking pin actuator is controlled by a lock controller (not shown). The lock controller is in communication with the EPAS motor assembly via the EPAS motor controller into which the lock controller may be integrated. The lock controller operates the actuator in response to an appropriate input from authorised user. This input may take the form of mechanical or electronic key that is unique to the vehicle or user and serves to identify an authorised user in the usual manner.

The lock controller is arranged to monitor a variety of vehicle parameters such as orientation of the steering wheel and whether the vehicle is in motion or not. The lock controller is provided with suitable means, such as a processor (not shown), to align a locking point on the worm wheel with the locking pin in response to a user input corresponding to a lock or unlock command. The lock controller aligns the locking point with the locking pin by controlling the EPAS motor to rotate the worm wheel to the desired position.

When the lock controller, receives a lock command, the processor is arranged to determine the position of the worm wheel relative to the locking pin and, by monitoring the output from a wheel rotation sensor mounted on at least one vehicle road wheel to determine that the vehicle is stationary, adjust the orientation of the worm wheel until a locking point is aligned with the locking pin. In this way, the engagement of the locking pin with the locking point is facilitated and wear of the locking pin and the locking point is minimised.

Preferably, the processor is arranged to align the locking point closest to the locking pin when the command is received, minimising the necessary displacement of the steering shaft by the motor.

Upon receipt of an unlock command, the lock controller will determine that the vehicle is stationary from the output of the or each road wheel rotation sensor and then adjust the orientation of the worm wheel to align the engaged locking point with the locking pin. This to facilitates disengagement of the locking pin from the locking point and greatly reduces the effort required to extract the locking pin from a locking point, reducing power consumption and wear. In this way, any twisting loads applied to the steering system by the resilient sidewalls of the road tyres when the vehicle is stationary, will be compensated for and not cause the locking pin to bind in the locking point.

Other advantages will be apparent to one skilled in the art and the present examples and embodiments are to be considered illustrative and not restrictive.

The invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.

Claims

CLAIMS1. An apparatus for a vehicle steering system having a steering shaft, the apparatus comprising: a power steering unit having at least one rotational member coupled to the steering shaft; and locking means for locking rotation of the at least one rotational member thereby to lock rotation of the steering shaft relative to the vehicle.
2. An apparatus as claimed in claim 1, wherein the power steering unit comprises: a worm wheel coupled to the steering shaft; and a worm gear arranged to cooperate with the worm wheel; wherein the locking means is arranged to lock rotation of the worm wheel thereby to lock rotation of the steering shaft relative to the vehicle.
3. An apparatus as claimed in claim 2, wherein the locking means comprises: a locking pin; and a plurality of locking points disposed on the worm wheel; wherein the locking pin is arranged selectively to engage with one of the plurality of locking points thereby to lock rotation of the worm wheel.
4. An apparatus as claimed in claim 3, wherein the longitudinal axis of the locking pin is substantially parallel with the axis of rotation of the steering shaft.
5. An apparatus according to claim 3 or claim 4, wherein the locking pin is arranged to move between an unlocked position wherein the pin is not engaged in a locking point, and a locked position wherein the pin is engaged with a locking point.
6. An apparatus according to claim 5, comprising actuator means for moving the pin between the locked and the unlocked position.
7. An apparatus according to claim 6, comprising control means for controlling the actuator means.
8. A steering lock apparatus according to claim 6 or claim 7, wherein the actuator means comprises a solenoid.
9. An apparatus according to claim 6 or claim 7, wherein the actuator comprises a worm gear driven by a locking motor.
10. An apparatus according to claim 9, wherein the locking pin comprises a series of gear teeth in at least one surface, said gear teeth configured for engaging the actuator worm gear.
11. An apparatus according to claim 3 or any claim dependent on claim 3, wherein the locking points are regularly spaced in a generally circular locus around the worm wheel.
12. An apparatus according to claim 3 or any claim dependent on claim 3, wherein the locking points are formed by indentations formed in at least one surface of the worm wheel.
13. An apparatus according to claim 3 or any claim dependent on claim 3, wherein the locking points are formed by through holes perforating the worm wheel.
14. An apparatus as claimed in claim 3 or any claim dependent on claim 3, wherein the worm wheel is supported on the steering shaft by a friction clutch configured to permit the steering shaft to rotate relative to the worm wheel only if a torque applied to the steering shaft exceeds a pre-determined limit.
15. An apparatus according to claim 14, wherein the locking pin and locking point cooperatively engage so as to withstand the pre-determined torque threshold required to cause the friction clutch to permit relative movement between the steering shaft and the worm wheel.
16. A steering shaft or column comprising an apparatus according to any preceding claim.
17. A vehicle comprising an apparatus, or a steering shaft or column according to any preceding claim.
18. A method of selectively locking a steering shaft of a vehicle steering system, the method comprising: monitoring the selection mode of a lock actuator control; monitoring the position of a worm wheel relative to a locking pin; and monitoring a wheel rotation sensor output from at least one vehicle road wheel, wherein upon determining the selection mode of the lock actuator control corresponds to a lock command and, determining from the rotation sensor of the or each road wheel that the vehicle is stationary, the orientation of the worm wheel is adjusted to align a locking point located on the worm wheel with the locking pin to facilitate the engagement of the locking pin with the locking point and, wherein the locking point selected for engagement with the locking pin is the closest available to the locking pin when the lock command was determined.
19. A method of selectively locking a steering shaft of a vehicle steering system according to claim 17, wherein upon determining the selection mode of the lock actuator control corresponds to an unlock command and determining from the rotation sensor of the or each road wheel that the vehicle is stationary, the orientation of the worm wheel is adjusted to align a locking point located on the worm wheel with the locking pin to facilitate disengagement of the locking pin from the locking point.
20. An apparatus constructed and arranged substantially as described herein with reference to Figures 4 and 5.