The present invention relates to actuators, particularly though not exclusively for automotive use, and is concerned with that type of actuator which comprises a motor which is connected to rotate a flywheel which carries the input of a centrifugal clutch, the output of which is connected to the output of the actuator.

An actuator of this type is disclosed in WO 2006/095126. This actuator comprises an electric motor connected to rotate a flywheel, which carries the input of a centrifugal clutch. This input comprises an elongate slider which is constrained to be able to move only linearly in a diametral direction. It has a relatively massive enlargement at one end and carries a coupling formation. The slider is movable between a disengaged position, in which the coupling formation is free to rotate with respect to the output of the centrifugal clutch, and an engaged position. The slider is biased by a spring into the disengaged position. When the flywheel is rotated, centrifugal force acting on the slider urges it towards the engaged position and when a predetermined speed of the flywheel is reached, the centrifugal force acting on the slider is sufficient to overcome the force of the spring and the slider moves into the engaged position in which the coupling formation on it engages with a coupling formation on a shaft and the shaft then rotates with the slider and thus with the flywheel. The shaft is connected to a worm gear which is in mesh with teeth on the exterior of a worm wheel. The worm wheel, which effectively constitutes the output of the actuator, thus begins to rotate also, though at a considerably slower speed due to the fact that the worm gear and worm wheel act as step-down gearing. The known actuator is extremely efficient and effective and is relatively small for the function which it has to perform. Thus the known actuator is intended primarily for automotive applications, e.g. for operating electric windows or an electric door latch. As a matter of practice, the force or torque needed to cause the window or latch components to start moving is considerably greater than that required to maintain the movement, once it has started. This is due to the inertia of the system and "stiction", that is to say the fact that the coefficient of static friction between the relatively movable components is greater than the coefficient of dynamic friction. The space available for actuators in an automotive environment is extremely limited and it is therefore desirable that such actuators are as small as possible so as to save space, weight and cost. However, the size of an actuator is related to the maximum torque which it is to produce and conventional actuators had to be constructed to produce the relatively high torque needed to start the relatively movable components of the window, latch or the like moving and were thus relatively large. The incorporation of the centrifugal clutch and a flywheel on the input side of that clutch in WO 2006/095216 means that when the electric motor is actuated, it is not initially connected to the output of the actuator. The energy of the motor is thus used initially to accelerate the flywheel and thus also the input side of the centrifugal clutch up to a relatively high speed. When a predetermined speed is reached, the centrifugal clutch engages and the motor is then connected to the output. However, when engagement occurs, the spinning flywheel is suddenly connected to the stationary output and the significant momentum of the flywheel means that there is initially a very high torque applied to the output. This "torque spike" or "kick start" means that the relatively movable component to which the actuator is connected starts to move rapidly and although the applied torque then drops rapidly, the reduced torque is nevertheless sufficient to maintain movement of the component in question. What this means is that the actuator of the prior document need not be sized to produce the high torque needed to start movement of the movable component but can be sized to produce the lower torque needed to maintain this movement. This means that the actuator of the prior document may be smaller than conventional actuators.

However, the actuator of the prior document has a relatively high part count and is thus still relatively large and heavy. This is due, at least in part, to the presence of two relatively large and massive components, namely the flywheel and the worm gear. Furthermore, when the actuator of the prior document is in use and is connected to e.g. the latch member of an electrically operated latch, it cannot be driven in the reverse direction by the application of a force to the latch member because the low mechanical efficiency of the gearset constituted by the worm gear and worm wheel means that it can only be driven by rotation of the input and not by rotation of the output, i.e. that it can not be back driven. The result of this is that if there should be a power failure or some other operational defect part way through the closing of an electrical latch by such an actuator, it is not possible to complete the closure process by the application of manual pressure to the associated latched member, such as a door, boot lid, tailgate or the like and the latch is instead locked in a partially latched position. This is an unacceptable failure mode for any automotive latch.

It is therefore the object of the present invention to provide an actuator of the type referred to above which has a reduced part count and is thus smaller and lighter. It is a further object to provide such an actuator which may be driven in the reverse direction manually so that in the event of a power failure during closing of an electrical door latch, the closing operation may be completed by the application of manual force to the mechanical components of the latch via the door or tailgate.

According to the present invention, an actuator of the type referred to above is characterised in that the output of the centrifugal clutch constitutes the output of the actuator. This is of course in contrast to the actuator in the prior document in which the output of the centrifugal clutch is connected to the output of the actuator via a meshing worm wheel and worm gear. This change means that when the motor is not operating, the input and the output of the centrifugal clutch are not connected together and the output is thus freely movable. What this means in practice is that if a power failure should occur during a closure process, the application of a manual force to the components of the latch via the associated door or tailgate is readily possible and is not prevented by the components of the actuator and results merely in backward rotation or movement of the output of the actuator.

The motor may be of any known type but is preferably an electric motor.

In the preferred embodiment, the motor is connected to a worm gear in mesh with a worm wheel and the worm wheel constitutes the flywheel. What this means is that the separate flywheel in the construction of the prior document is omitted and the wormwheel acts as the flywheel. The centrifugal clutch in the actuator in accordance with the present invention is therefore carried by the wormwheel, which constitutes a flywheel, and not by a separate flywheel. Although this change might appear superficially to be relatively minor, its effect is of great significance. The invention is based on the recognition that the actuator in the prior document includes not only a flywheel but also a further component, namely the gearwheel, which is inherently suited to act as a flywheel and thus that the separate flywheel is not in fact necessary. This results in a saving in the part count and, more importantly, a saving in both weight and size of the actuator.

The centrifugal clutch could potentially be of a number of different types but it is preferred that it is of the type disclosed in the prior document and thus that the input of the centrifugal clutch includes a slider which carries a first coupling formation and is carried by the gearwheel by a structure which constrains it to be movable relative to the gearwheel only linearly in a diametral direction, the slider being movable under the action of centrifugal force from a disengaged position to an engaged position in which the first coupling formation is in engagement with a second coupling formation carried by the output, whereby the input and output are rotationally connected and thus rotate together. It is preferred that biasing means are provided which bias the slider towards the disengaged position.

Thus, in use, the slider is normally situated in the disengaged position and the centrifugal clutch is disengaged. If the electric motor is activated, it will rotate the wormwheel and as the speed of the wormwheel increases, the centrifugal force acting on the slider will increase also. When the speed of the wormwheel reaches a predetermined threshold value, the centrifugal force acting on the slider will be greater than the biasing force exerted on it by the biasing means, e.g. a spring, and the slider will then be caused to move by the centrifugal force into the engaged position. In this position, a first coupling formation or dog on the slider will be in engagement with a second coupling formation or dog connected to an output gear or shaft which will then rotate with the wormwheel. As the centrifugal clutch moves into engagement, the kinetic energy of the rapidly rotating wormwheel will deliver a "kick start" to the output and thus also to whatever component the output is connected to and the actuator is dimensioned such that the torque applied to the output is sufficient to move whatever component it is that the output is connected to. This peak torque will decrease rapidly from its initially high value to a lower value which is nevertheless sufficient to maintain the movement of the component in question. If there should be a power failure or some other problem should arise during operation of the actuator, rotation of the output will cease and the centrifugal clutch will then automatically disengage as a result of movement of the slider back to the disengaged position under the action of the return spring. The component to which the output is connected may then be moved by the application of manual pressure and this movement will not be prevented by the centrifugal clutch or by the connection between the electric motor and the wormwheel due to the fact that the input and output of the centrifugal clutch are no longer connected to rotate together.

Whilst the centrifugal clutch may include only a single slider, the centre of gravity of such a slider would inherently be eccentric for at least part of the time and this would be likely to result in imbalance of the gearwheel and thus vibration or juddering of the gearwheel. It is therefore preferred that the centrifugal clutch includes two sliders, both of which are constrained to be movable relative to the gearwheel only linearly in a diametral direction, the sliders being movable in opposite directions under the action of centrifugal force, the biasing means acting on the two sliders to bias them in opposite directions. The provision of two sliders, which are preferably identical and which move at all times in opposite directions, means that static balance of the centrifugal clutch and thus of the gearwheel may be maintained at all times, thereby eliminating the risk of vibration.

It is preferred that there is only a single biasing means which acts on the two sliders to bias them in opposite directions. This biasing means may comprise a coil spring located concentrically with the flywheel, that is to say extending around the rotary shaft of the flywheel.

In order to maximise the effect of centrifugal force on the or each slider, it is preferred that the or each slider has a massive enlargement at one end, which will in practice be the outermost end, that is to say the end which is closest to the external periphery of the gearwheel.

It is convenient if each slider includes an elongate plate portion, at one end of which there is the massive enlargement, the two plate portions being slidably superimposed on one another and the massive enlargements being at opposite ends of the two plate portions, the two plate portions affording respective openings through which a shaft extends, the shaft carrying a gearwheel which constitutes the output of the actuator. Whilst it would be possible for both sliders to carry a first coupling formation, which is movable into engagement with a corresponding coupling formation on the output in the engaged position of the sliders, this is not necessary and whilst it is desirable for both sliders to carry a coupling formation, so as to ensure that they are truly symmetrical about the axis of rotation of the gearwheel in order to maintain the balance of the gearwheel, it is simpler if only one of the two coupling formations is engageable with a corresponding coupling formation on the output. The identity of the two sliders also reduces manufacturing costs.

It is preferred that the or each slider constitutes a plastic moulding and that the or each massive enlargement defines a recess accommodating a metallic weight. Plastic material is inherently both lighter and cheaper than metal and the provision of a weight which is metallic and thus relatively heavy within each massive enlargement will result in the centre of gravity of the or each slider being within or at least close to the massive enlargement, that is to say situated a relatively large distance from the centre of rotation of the gearwheel and this will maximise the centrifugal force acting on the or each slider when the gearwheel rotates.

Further features and details of the invention will be apparent from the following description of one specific embodiment which is given by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a plan view of an actuator in accordance with the invention;

Figure 2 is an exploded perspective view of the actuator of Figure 1;

Figure 3 is an exploded perspective view of the centrifugal clutch;

Figure 4 is a longitudinal sectional view of the centrifugal clutch;

Figure 5 is an exploded longitudinal sectional view of the centrifugal clutch;

Figures 6 and 7 are plan views of the centrifugal clutch in the disengaged and engaged positions, respectively;

Figures 8 and 9 are underneath views of the centrifugal clutch in the disengaged and engaged positions, respectively; and

Figures 10 and 11 are views of a motorised automotive latch assembly including the actuator in the unlatched and latched positions, respectively.

The actuator illustrated in Figures 1 to 9 is accommodated, in use, in an outer housing, which forms no part of the present invention and only one half of which is shown in Figures 1 and 2 for the sake of clarity. The actuator includes an electric motor 2 connected to an output shaft 4, which is rotationally fixed to a worm gear 6. The worm gear 6 is in mesh with teeth defined on the peripheral edge of a worm gear 8. Formed in the centre of the worm gear 8 is an elongate opening 10, which is traversed by a web 12 in which an axial hole 14 is formed. The upper surface of the web 12 is somewhat below the upper surface of the surrounding portion of the upper surface of the worm wheel 8. Extending along each side of the elongate recess 10 is an upstanding flange 16, the inner surfaces of which define a respective longitudinally extending groove 18. Also formed in each inner side surface of each flange 16 is a number of recesses which communicate both with the upper surface of the flange and with the groove 18. Defined between these recesses are projections 21, the purpose of which will be described below. Accommodated in the recess in the upper surface of the worm wheel 8 defined by the opening 10 and the web 12 are two sliders 22, which constitute identical one-piece plastic mouldings. Each slider 22 includes an elongate generally rectangular plate-shaped portion 24 in which an oval hole 26 is formed. At one end of each plate-shaped portion 24 there is an integral, upstanding enlarged portion 28, formed in which is a blind hole or recess, which accommodates a heavy metallic bobweight 30. Formed at the other end of each of the plate-shaped portions 24 is an upstanding projection or dog 32. Projecting laterally from each longitudinal side edge of each plate-shaped portion 24 is a flange 34 which is received in a respective groove 18 in an associated upstanding flange 16. Formed in the outer edge of each flange 34 is a number of recesses 23 which correspond to the projections 21 and can accommodate those projections. The provision of the projections 21 and recesses 23 permits the sliders to be inserted between the two flanges 16 from above and thus to locate the flanges 34 within the grooves 18. The two sliders are received in the recess in the worm wheel 8 with a reverse orientation such that the two massive projections extend in opposite axial directions. The two plate-shaped portions 24 are in sliding engagement with one another. In use, a shaft (not shown) extends through the hole 14 in the web 12 and through the two oval holes 26 in the sliders 22. Extending around the upper portion of this shaft, as seen in Figure 3, is a plastic sleeve 36. Extending around the sleeve 36 is a helical spring 38 with two projecting arms 40. The spring 38 is accommodated within a cavity constituted by two cooperating recesses 42, which are formed in the upper surface of one of the plate-shaped portions 24 and in the lower surface of the other plate-shaped portion 24. The two arms 40 act on the end surface of one of the recesses 42 and the opposite end surface of the other recess 42 and thus urge the two sliders inwardly relative to one another. The shaft which passes through the elongate openings 26 and the sleeve 36 also rotatably carries an output gear 44, which carries two opposed radially projecting coupling formations or dogs 46.

When the worm wheel 8 is stationary, the two sliders 22 are urged inwardly, that is to say towards one another, by the biasing force of the spring 38. The centre of gravity of each slider 22 is located a significant distance away from the rotary axis of the worm wheel 8 due to the presence of the enlarged portion 28 and the heavy metal weight 30 accommodated within it. This means that when the worm wheel 8 starts to rotate, an outwardly directed centrifugal force acts on each slider. This outward force is initially smaller than the restoring force exerted by the spring 40 but as the speed of the worm wheel 8 increases, a speed is reached at which the centrifugal force exceeds the spring restoring force and the two sliders 22 then move outwardly in opposite directions until the outer surfaces of the two enlarged portions 22 engage the opposed end surfaces of the opening 10 in the worm wheel 8, whereafter further outward movement is prevented. Due to the retention of the lateral flanges 34 in the grooves 18, the two sliders are constrained to move only linearly in a diametral direction. Due to the fact that the two sliders are identical and that their movement is always equal and opposite, whereby their centres of gravity are always equally spaced from the axis of rotation of the worm wheel 8 and on opposite sides of it, the worm wheel and sliders are always in perfect balance and the worm wheel can therefore rotate at high speeds without vibration occurring. When the two sliders move outwardly, the downwardly directed dog 32 on the lowermost slider 22 moves progressively towards the dogs 46 connected to the output gear 44 until the dogs 32 and 46 move into engagement with one another. The positions of the two sliders when in the disengaged position is shown from above and below in Figures 6 and 8 and is shown in the engaged position from above and below in Figures 7 and 9. As the dogs 46 and 32 move into engagement, the output gear 44 is suddenly accelerated to rotate at the same speed as the worm gear 8. The substantial size and mass of the worm gear 8 and the sliders 22 carried by it means that the worm wheel 8 functions as a flywheel and has a substantial momentum. A very substantial torque is therefore initially exerted on the output gear 44 and whatever component it is connected to and the actuator and electric motor are sized and controlled such that the torque applied on engagement of the dogs 32 and 46 is sufficient to start the movement of whatever component the output gear 44 is connected to. The torque applied to the output gear 44 will rapidly drop to a level below the initial high or "kick start" level but only to a level sufficient to maintain the movement of the component to which the output gear 44 is connected.

Figures 1 and 2 show that the output gear 44 is in mesh with a quadrant gear 50 but the component to which the output of the actuator is connected will of course vary depending on the particular application of the actuator. One specific application will now be described briefly with reference to Figures 10 and 11, which show a motorised automotive door latch. This door latch includes a claw 52, which defines a recess 53 in which a door striker (not shown) is received, when the latch is closed. The claw 52 is mounted to pivot about a shaft 54, which carries a spring 56 which biases the claw to rotate anticlockwise, as seen in Figures 10 and 11, out of the latched position seen in Figures 10 and 11 so that the striker can move downwardly, as seen in Figures 10 and 11, to permit the door to be opened. In the latched position shown in Figure 11, anticlockwise rotation of the claw 52 is prevented by a pawl 58. The pawl 58 is an elongate member, which is mounted to rotate at a point adjacent one end about a shaft 60. The shaft 60 carries a spring 62 which urges the pawl into the fully latched position shown in Figure 11 in which a portion of the pawl engages a portion of the claw and thus prevents rotation of the claw and thus opening of the latch. If, however, it is desired to open the latch, the motor 2 of the actuator is operated and once the worm wheel 8 has reached a predetermined threshold speed and the centrifugal clutch constituted by the sliders 22 and gear 44 has engaged, the quadrant gear 52 is caused to rotate in the clockwise direction, as seen in Figures 10 and 11 , into the position shown in Figure 10. The segment gear 50 carries an arm 64 and as the segment gear rotates in the clockwise direction, this arm 64 comes into contact with the free end of the pawl 58 remote from the shaft 60 and rotates it in the anticlockwise direction into the position shown in Figure 10. This rotation of the pawl moves the engaging portions of the pawl 58 and claw 52 out of contact with one another so that the claw is now free to rotate. Downward force exerted on the claw 52 by the striker, typically by the rubber seals around the door in question and the claw return spring, will result in rotation of the claw in the anticlockwise direction, which leaves the way clear for the striker to move downwards, as seen in Figures 10 and 11, thereby permitting opening of the door or tailgate or the like.

When the door is closed again, the door is moved to a position in which the claw 52 approaches the position shown in Figures 10 and 11, with the striker within the recess 53. The motor 2 is then operated in the reverse direction and the segment gear 50 and thus also the arm 64 are thus caused to rotate in the anticlockwise direction. As it does so, the arm 64 engages a portion of the claw remote from the shaft 54 and causes it to rotate in the clockwise direction. As it does so, it traps and retains the striker and thus moves the door into the fully closed position against the resilience of the rubber seals and the claw return spring and then holds it in that position.

If there should be a power failure during this closure process, the closure process may be completed manually by the application of pressure to the door in question. This pressure will result in further clockwise movement of the claw 52 and by virtue of its engagement with the arm 64 this will result in rotation also of the segment gear 50. The segment gear 50 is in mesh with the gear 44 of the actuator and rotation of the gear 44 can readily occur because it is not rotationally connected to the gearwheel. Accordingly, the actuator does not impede manual closing of the door associated with the latch.