Abstract:
A lock assembly for use in automotive and industrial transmission systems comprises: an actuator ( 2 ) having an impeller ( 6 ) movable between two rest positions by energizing the actuator, wherein the impeller is retained in each of the two rest positions by passive magnetic forces generated by the actuator; a locking arrangement ( 10, 22; 42, 52; 62, 64; 70, 74; 80, 96 ) switchable between a first configuration in which rotation of a shaft is unimpeded by the locking arrangement and a second configuration in which rotation of said shaft is blocked by the locking arrangement; and a linkage ( 14, 16; 44, 46, 61, 88 ) between the impeller and the locking arrangement, wherein the assembly is arranged such that in one of the impeller rest positions, the locking arrangement is in its first configuration and said shaft is freely rotatable, and in the other of the impeller rest positions, the locking arrangement is urged towards and into its second configuration.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a lock assembly for use in automotive transmission systems, and also in industrial and other off-highway transmission systems. More particularly, it relates to a lock assembly suitable for selectively locking the rotational position of a shaft or other rotating component. 
     BACKGROUND OF THE INVENTION 
     Lock mechanisms, such as the park lock of a vehicle, are often manually operated. However, this means that they may be subject to abusive treatment by an operator. For example, if engagement is attempted at high vehicle speeds, the loads through the lock components and their mountings can be excessive. Also, manually-operated locks tend to require detailed dynamic analysis, testing and development to ensure that the components are sufficiently durable. 
     Electrically-operated park locks can significantly reduce the requirement for detailed analysis and testing of their components, as their abusive operation can be prevented by their electrical control system. They must though be configured in such a way that the park lock is engaged and the associated shaft locked when power to the vehicle is disconnected. In the case of a system actuated by a solenoid, it must therefore be configured so that the lock is engaged when the solenoid is de-energised. This means that electrical power is required at all times during normal vehicle operation in order to keep the park lock disengaged. Constant operation of the electrical system of the lock is a constant drain on the vehicle power source and can also compromise the durability of the brake owing to the associated heat generation. 
     An electrically-operated system may also be powered by a motor. This may avoid the need for constant power for the lock to remain disengaged during vehicle use. However, the size of the motor may cause packaging issues and additional cost may be involved in adapting a motor to the vehicle&#39;s mechanical system. 
     SUMMARY OF THE INVENTION 
     The present invention provides a lock assembly for selectively locking the rotational position of a rotatably mounted object such as a shaft, comprising:
         an actuator having an impeller movable between two rest positions by energising the actuator, wherein the impeller is retained in each of the two rest positions by passive magnetic forces generated by the actuator;   a locking arrangement switchable between a first configuration in which rotation of said shaft is unimpeded by the locking arrangement and a second configuration in which continuous rotation of said shaft is blocked by the locking arrangement; and   a linkage between the impeller and the locking arrangement, wherein the assembly is arranged such that in one of the impeller rest positions, the locking arrangement is in its first configuration and said shaft is freely rotatable, and in the other of the impeller positions, the locking arrangement is urged towards and becomes locked in its second configuration.       

     As the actuator impeller is held in position by passive magnetic forces generated by the actuator, continuous or extended application of electrical current to the actuator is not required. This considerably reduces the energy consumption of the device and avoids other electrical issues associated with a constantly powered electrical device. 
     As the lock assembly is electrically powered, it is possible to operate it in conjunction with a control system that prevents engagement in hazardous situations or conditions that will cause damage to components. This reduces the need for extensive analysis and testing of its mechanical components relative to a manually-operated lock. 
     Furthermore, shift cable insulation issues that may arise with manually-operated park brake installations are avoided. Avoiding the need for a shift cable also removes the associated noise and vibration transmission issues, and reduces the cost and weight of the park lock assembly. 
     A lock assembly according to the present invention may be small, lightweight and have a low part count relative to a motor-driven manually-operated system. 
     The linkage of the assembly may be arranged such that when the impeller moves into its other rest position, the linkage resiliently urges the locking arrangement towards its second configuration. A portion of the linkage may be resiliently urged against the locking arrangement to urge it towards its second configuration. This resilient urging force may be provided by a resiliently compressible component or a resiliently extensible component, with the force being exerted due to compression or extension of the component, respectively. For example it may be a spring such as a coil spring. 
     The linkage may be arranged such that the locking arrangement is urged towards its second configuration when the impeller is in its other rest position. This compliance is beneficial for an actuator which maintains this impeller position with passive magnetic forces. This is because, even if the locking arrangement does not move initially into its second configuration, the impeller is able to move fully into its rest position where it is firmly held without requiring additional electrical energy input. The linkage accommodates the fact that the locking arrangement is out of its second configuration, and the arrangement continues to be urged towards that configuration without additional power input. 
     The linkage may be arranged such that when the locking arrangement is in its second configuration, blocking further rotation of the shaft, the linkage prevents the locking arrangement from moving out of its second configuration. In this way, as well as transferring motion of the impeller to the locking arrangement, the linkage also effects locking of the locking arrangement in its second configuration. 
     In a preferred embodiment, one of the linkage and the locking arrangement defines a cam surface and the other defines a cam follower which are resiliently urged together when the impeller moves into its other rest position. 
     The cam surface and cam follower may be arranged such that after the locking arrangement has been urged into it second configuration, it is prevented from moving out of its second configuration by the interaction between the cam surface and the cam follower. 
     The locking arrangement may comprise a pawl for engagement with a toothed circumferential surface which rotates with the shaft. A surface which rotates with the shaft (in this and other embodiments) may be provided by a wheel or other member mounted on the shaft, or in the form of a surface defined by the shaft itself for example. 
     In preferred embodiments, the impeller is switchable between the two rest positions by application of a single input pulse to the actuator. Thus, a minimal amount of electrical energy is required to achieve engagement or disengagement of the lock. The actuator is preferably a bistable actuator switchable between two stable rest positions. 
     The actuator may include an energy storage arrangement for mechanically storing potential energy as the impeller moves into its other rest position, and releasing this stored energy to the impeller as it moves away from its other position. Preferably, such an energy storage arrangement is only associated with the other rest position of the impeller. 
     The invention further provides a lock system including a lock assembly as described herein and a control arrangement for controlling operation of the lock assembly in response to input signals initiated by a user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described by way of example and with reference to the accompanying schematic drawings, wherein: 
         FIG. 1  is a cross-sectional side view of a first lock assembly embodying the invention in its disengaged position; 
         FIGS. 2 and 3  are views similar to that of  FIG. 1 , but with the park lock in its engaged and locked positions, respectively; 
         FIGS. 4 and 5  are enlarged cross-sectional side views of the actuator shown in  FIGS. 1 to 3  in its disengaged and engaged configurations, respectively; 
         FIG. 6  shows a cross-sectional side view of one side of a second lock assembly embodying the invention, along with an end view and a view of the opposite side; 
         FIG. 7  is an enlarged version of the cross-sectional side view shown in  FIG. 6 ; 
         FIG. 8  shows a cross-sectional side view of one side of a third lock assembly embodying the invention, along with an end view and a view of the opposite side; 
         FIG. 9  is an enlarged version of the cross-sectional side view shown in  FIG. 8 ; 
         FIGS. 10 and 11  show a plan view and a cross-sectional side view, respectively, of a different linkage configuration; 
         FIG. 12  shows a side view of one side of a fourth lock assembly embodying the invention, along with an end view and a cross-sectional view of the opposite side; 
         FIG. 13  is a cross-sectional side view of a fifth lock assembly embodying the invention; 
         FIG. 14  shows a cross-sectional side view, an end view and a side view of the opposite side of an actuator for an assembly embodying the invention which includes integrated power and control electronics; 
         FIG. 15  is a diagram illustrating the inputs and outputs to the integrated controller shown in  FIG. 14 ; 
         FIGS. 16 and 17  are a cross-sectional side view and an enlarged partial cross-sectional side view respectively of an actuator for use in embodiments of the invention; and 
         FIG. 18  is a circuit diagram of an electronic driver suitable for operating a bistable actuator in a lock assembly embodying the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the embodiments of the invention shown in the drawings, a bistable linear actuator (for example as described in the present applicant&#39;s United Kingdom Patent Publication Nos. 2342504 and 2380065, International Patent Publication No. WO 2010/067110, and U.S. Pat. No. 6,598,621, the contents of which are incorporated herein by reference) is combined with a compliant linkage, and a locking arrangement to create a device which can selectively lock a rotatable shaft or other rotatably mounted object. 
     When the actuator is in one rest position, the shaft is free to rotate, and in its other rest position, the shaft becomes locked against further rotation. When used in an automotive or off-highway transmission, the device may be employed to lock one of the shafts directly connected to wheels. For example, it may be deployed as a park lock of the type required with automotive transmissions by legislation in order to provide a positive method of stopping the vehicle from rolling when the power source to the lock is disconnected. The lock assembly may also be used as a shaft lock in industrial machinery that uses rotating components. 
     A first embodiment is depicted in  FIGS. 1 to 3 . As shown in  FIG. 1 , a bistable actuator  2  is mounted on a transmission casing  4 . The impeller or actuation rod  6  of the actuator is coupled to a linkage  8 . The linkage is in engagement with a locking arrangement in the form of a pawl  10 . 
     Linkage  8  includes a cam  12  slidably mounted on a linear support  14 . Cam  12  is coupled to a cam spring  16 . Cam spring  16  acts to push the cam along support  14  in a direction away from the actuator  2 . Cam  12  is in contact with a pin or roller  18  and the distal end of pawl  10 . Pawl  10  is pivotably mounted on a pivot  20  supported on the transmission casing. Pawl  10  is resiliently biased against the cam  12  by a biasing arrangement not shown in  FIG. 1 . 
     In the cross-sectional side view of  FIG. 1 , it can be seen that cam  12  defines a tapered surface having two opposite sides with their spacing decreasing with distance from the actuator. This tapered surface joins to a portion of the cam having substantially parallel sides in cross-sectional side view which is closer to the actuator. The cam also has another portion located further from the actuator than the tapered portion which again has substantially parallel sides in cross-sectional side view as can be seen in  FIG. 1 . This narrower, parallel sided portion is located between pawl  10  and pin  18  in the disengaged position shown in  FIG. 1 . In this configuration, pawl  10  is disengaged from a toothed wheel  22  mounted on a shaft  24  in a fixed position relative to the shaft. 
     In  FIG. 1 , the actuator is shown in one of its two stable rest positions, in which the impeller is retracted away from pawl  10 . In this configuration, the pawl is disengaged from the toothed wheel. 
     As shown in  FIG. 2 , when the actuator is energised by application of a suitable input pulse, the impeller  6  is switched from one stable rest position to the other which is closer to pawl  10 . This causes the linkage to push cam  12  through the gap between pawl  10  and pin  18 . This causes the pawl and pin to run over their respective tapered surfaces on the cam  12 , causing the cam to push the pawl downwardly into full engagement with a space between adjacent teeth on the toothed wheel  22 . The pawl thereby prevents the shaft from rotating, locking it in position. The actuator is held in this position by passive magnetic forces and maintains the cam in its locking position via spring  16 . 
     If the actuator moves to the engaged position and the pawl is prevented from engaging with a gap between adjacent teeth on the toothed wheel because it contacts the upper surface of one of the teeth, the actuator remains in its engaged position as shown in  FIG. 3 . The cam spring urges the cam in the direction of engagement. Then, any subsequent rotation of the transmission shaft will cause the biased cam to force the pawl into engagement with the very next tooth space on the wheel so that the shaft becomes locked. The toothed wheel and pawl are configured such that the pawl defines a wheel engagement portion that is complementary to each tooth space on the wheel. 
     The configurations of the actuator in each rest position corresponding to when the brake assembly is in its disengaged and engaged arrangements are shown in  FIGS. 4 and 5 , respectively. The actuator includes a coil spring  30  which engages the armature  32  of the actuator as it moves into the configuration shown in  FIG. 5 . This stores mechanical potential energy in the spring which is then subsequently employed to accelerate the armature away from that position when the actuator is switched into its other configuration. 
     Preferably, a greater amount of energy is stored during movement of the assembly into the lock-engaged configuration, relative to that stored when the assembly moves into the disengaged configuration. Thus in the embodiment illustrated, a coil spring is only provided on one side of the actuator. In other implementations, energy storage arrangements with different or substantially equal properties may be provided on respective sides of the actuator. 
     In embodiments where a greater amount of energy is stored in the lock-engaged position of the actuator (relative to its lock-disengaged position), the actuation coil  34  adjacent to the lock-engaged position preferably has a greater number of turns than the other actuation coil  36 , as shown in  FIG. 4 . This provides greater force to shift the armature and therefore ensure the transition of the locking arrangement to its disengaged configuration. 
     More energy is preferably stored when the assembly moves to engage the lock, as the extra energy is then employed to provide the greater force needed to disengage the cam from between pin  18  and pawl  20 . 
     Whilst the embodiment illustrated in  FIGS. 1 to 3  involves cam motion in a direction tangential to the circumferential surface of the shaft, it will be appreciated that other configurations may be adopted. For example, the cam motion could alternatively be in a direction parallel to the axis of the shaft. 
       FIGS. 6 and 7  relate to a second assembly embodying the present invention. In this implementation, the locking arrangement is in the form of a “dog clutch”  40 . In this implementation, the impeller  6  of actuator  2  is coupled to a sliding sleeve  42  of the clutch via a resilient coupling, in the form of an external spring  44  in combination with a shift fork  46 . 
     Sliding sleeve  42  carries a plurality of axially extending dog teeth on each of its transverse faces. Facing these teeth are similar teeth  50  on an opposing face of an engagement ring  52 . 
     When the locking arrangement is in its disengaged position, the dog teeth  48  of the sliding sleeve are not in contact with the engagement ring dog teeth  50 . The sliding sleeve and the engagement ring are free to rotate independently of each other. 
     When the impeller moves into its lock engagement position, external spring  44  is compressed so as to exert an axially directed force on the shift fork  46 . This in turn pushes the sliding sleeve towards the engagement ring. When the dog teeth of the sliding sleeve align with gaps between the dog teeth of the engagement ring, they are urged together by the shift fork so that relative rotation is only permitted through a small angle. Where the teeth on the sliding sleeve initially sit on top of the teeth of the engagement ring, energy to shift the sliding sleeve into its locking position is stored by the external spring until the sliding sleeve can move into engagement with the engagement ring. Thus, once the impeller has moved into its lock engagement position, no further electrical energy is needed to complete transfer of the locking arrangement into its locked configuration. In this configuration, continued rotation of the shaft coupled to the engagement ring will be blocked by the lock assembly. 
     A third embodiment similar to that of  FIGS. 6 and 7  is shown in  FIGS. 8 and 9 . In this case, the locking arrangement is in the form of a synchroniser  60 . Sliding sleeve  62  and engagement ring  64  have respective continuous sets of complementary teeth  66  and  68  respectively. It operates in a similar manner to the embodiment of  FIGS. 6 and 7 . 
     In the embodiments of  FIGS. 6 to 9 , one end of the spring  44  is coupled to and moves with the actuation rod  6  of the actuator. The other end bears against the shift fork  46  when the actuator is moved into its engaged or locking position. Fork  46  in turn acts on the sliding sleeve  62 . 
     Variations on the linkage between the actuator and the locking arrangement shown in  FIGS. 8 and 9  are illustrated in  FIGS. 10 and 11 . 
     In  FIGS. 10 and 11 , the actuation rod  6  is connected to an elongate rail  61  which is slidingly received by an end stop  63 . A shift fork  46  is slidably mounted on the rail. Spring  44  is engaged at one end by a flange  65  provided on the rail  61 . When actuator  2  is shifted into its engaged or locking position, the rail is shifted away from the actuator, causing the spring to be urged against shift fork  46 . 
     Another lock assembly configuration embodying the present invention is shown in  FIG. 12 . In this implementation, a round-headed pin  70  is mounted (in a fixed manner or slidable axially) on one end of the impeller  6 . A circular arrangement of holes  72  or recesses of a diameter complementary to that of the pin is defined in the face of an engagement disc  74 . 
     When the lock assembly is in its disengaged configuration, the pin and the engagement disc are spaced apart. The engagement disc is free to rotate. 
     When the actuator impeller is moved into its engagement position, an external spring  76  is urged against pin  70 . The head of the pin is then biased against the opposing face of the engagement disc  74  until a hole on the disc rotates into alignment with the pin. The pin is then pushed into the hole via the external spring  76  to restrict further the rotation of the disc. 
     A fifth embodiment of the present locking arrangement is depicted in  FIG. 13 . The impeller  6  of actuator  2  is coupled to a locking arrangement in the form of a band brake  80 . The band brake is in the form of a strip of material defining an incomplete circle in side view. One end  82  of the band is coupled to a fixed location, for example provided by a surrounding housing, providing a “ground reaction”  84 . The other end  86  of the band is coupled to the impeller  6 . This coupling takes the form of a linkage  88  mounted (in a fixed manner or slidable axially) on one end of the impeller and pivotally mounted about a pivot  90  connected to end  86  of the band brake. An external spring  92  is provided between an end face of the actuator housing and an opposed surface  94  defined by linkage  88 . 
     Band brake  80  is provided in concentric alignment with and around an inner rotor  96 . When the locking arrangement is in its disengaged configuration, the inner rotor is free to rotate. 
     When the actuator impeller shifts to its lock engagement position, linkage  88  exerts a tangential force on pivot  90 , causing the radius of the band brake  80  to reduce such that it clamps against the outer circumferential surface of inner rotor  96 . This serves to slow and then prevent further rotation of the inner rotor. 
       FIG. 14  illustrates a preferred actuator configuration in which an integrated power electronics and actuator controller module  100  is provided at one end of the actuator housing, with impeller  6  extending through its centre. 
     Electrical inputs and outputs to and from the controller module are illustrated schematically in  FIG. 15 . Power is fed to the module along a pair of lines  102 . Control signals are fed to and from the module via lines  104  and  106 , respectively, which are coupled to an external controller (not shown). 
     The module governs the operation of the actuator  2  by sending current pulses to each of the pair of coils  34 ,  36  in the actuator along pairs of lines  108  and  110 , respectively. 
     The control signals may be in analogue, digital or CAN format for example. They may emanate, for example from a vehicle transmission or central vehicle controller for example. 
     The module  100  may be configured to detect the disposition of the impeller within the actuator and feed this information to the external controller. This position sensing may be achieved for example by monitoring the inductance of the actuator coils, using a Hall sensor. The position of the impeller and armature of the actuator relative to the coils changes the measurable inductance in each coil. Detection of these changes facilitates derivation of the position of the impeller. 
     The coils of the actuator may be wired together in different embodiments in series, in parallel, or individually. 
     In the actuator configuration shown in  FIG. 16 , a sensing or search coil  120  is provided in association with actuation coil  34  and similarly a sensing or search coil  122  is provided in association with actuation coil  36 . Each search coil is provided coaxially with, and circumferentially around, the respective actuation coil. Region “A” of  FIG. 16  is enlarged in  FIG. 17 . 
     The amount of flux linking each search coil will be different depending on which stable rest position the armature of the actuator is in. Accordingly, the current induced in each coil is responsive to the armature position, enabling the armature position to be sensed by the external controller. 
     Electrical energy storage means may be provided in combination with the actuator, for example in the form of capacitors, to provide a local power source. 
     Depending on the requirements of a particular application, the lock assembly may be configured to revert to a particular configuration upon detection of predetermined external conditions. These conditions may for example be a power supply or other device failure, or detection of a predetermined vehicle speed or location for example. The position reverted to may be the locked configuration or the open configuration depending on the associated conditions. Where a local energy source is provided for the actuator, this switching to a selected position may be driven by the local power source so that it is not dependent on external power sources. 
     Provision of a dedicated energy source for the actuator may reduce the size of the control cabling leading to the actuator. The source may be embodied by a capacitor connected across each coil of the actuator. Voltage multiplier circuits may be incorporated to increase the speed of response. 
     A driver circuit suitable for operating a bistable actuator in a lock assembly embodying the invention is shown in  FIG. 18 . An actuator  2  having actuation coils  34  and  36  is shown schematically in the centre of the Figure. 
     Power is supplied in this example from a 12V DC supply via resistor  128 . A capacitor  130  provides local power storage, together with voltage regulator circuit  138 . Control lines from an external controller are coupled to a local controller in the form of a microprocessor  132 . This in turn feeds control currents along lines  140 ,  142  to the coils via respective H-bridge circuits  134  and  136 .