Motor Arrangement

The present invention relates to a motor arrangement, and in particular a motor arrangement suitable for changing the state of a latch assembly, in particular releasing or locking/unlocking a latch assembly, in particular a latch assembly for use with car doors and car boots.

Latch assemblies are known to releasably secure car doors in a closed position. Operation of an inside door handle or an outside door handle will release the latch allowing the door to open. Subsequent closure of the door will automatically relatch the latch.

In order to ensure that rain does not enter the vehicle, the doors are provided with weather seals around their peripheral edge which close against an aperture in the vehicle body in which the door sits. In addition to providing protection from rain, the weather seals also reduce the wind noise. The ongoing requirement for improved vehicle occupant comfort requires minimising of wind noise which in turn requires the weather seals to be clamped tighter by the door. The door clamps the seals by virtue of the door latch and accordingly there is a tendency for the seal load exerted on the latch to be increased in order to meet the increased occupancy comfort levels required. Because the seal forced on the latch is increased, then the forces required to release the latch are correspondingly increased.

UK patent application GB0330264 shows a latch mechanism in which a primary pawl is operable to hold a rotating claw in a closed position. The primary pawl is mounted on a toggle link and the toggle link is held in position (when the latch is closed) either directly or indirectly by a secondary pawl. The motor arrangement of the present invention, when applied to a latch assembly, can be utilised to move the secondary pawl.

Latch assemblies are also known to include motors which can be actuated to lock and unlock the latch. Other known latch assemblies include motors which can put the latch into a child safety on condition i.e. a condition where operation of an inside door handle does not open a latch. The motor can also be used to put the latch into a child safety off condition, i.e. a condition whereby operation of the inside door handle does open the latch.

Thus, according to the present invention there is provided a latch arrangement as defined in the accompanying independent claims.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figures 1, IA, IB, ID and ID' shows a view taken from the backplate side of a latch showing certain components of a latch arrangement including a motor arrangement according to the present invention, in a closed position, Figure 1C show a view taken from the retention plate side of the latch showing certain components of the latch arrangement of Figure 1 in a closed position,

Figure 2A, 2A', 2A", 2B, 2B', 2B", 2C, 1C and 2C" show certain components of figure 1 whilst the latch is being opened,

Figure 3 shows certain components of the latch of figure 1 in an open position, Figure 4 shows certain components of the latch of figure 1 during closing,

Figure 5 and 5' show the motor arrangement of figure 1 according to the present invention,

Figures 5 A to 5D shows the motor arrangement of figure 5 in various positions,

Figures 6 to 8 show a further embodiment of a motor arrangement according to the present invention, Figures 9 and 10 show a further embodiment of a motor arrangement according to the present invention, and

Figure 11 shows the torque output from the motor arrangement according to the present invention.

With reference to the figures 1 to 5 there is shown a latch assembly 10, the major components of which are a latch chassis 12, a latch bolt in the form of a rotating claw 14, a compression pawl 16, an eccentric arrangement in the form of a crank shaft assembly 18 and a release actuator assembly 20.

Latch assembly 10 is mounted on a door 8 (only shown in figure 1).

The major components of the latch chassis 12 are a retention plate 22 and a back plate 24. Retention plate 22 is generally planar (but having an up turned edge 22A). The generally

planar portion includes a mouth 26 for receiving a striker (not shown). The retention plate 22 includes three threaded holes 27 which in use are used to secure the latch assembly to the door. Projecting from the retention plate is a claw pivot pin 28, and stop pins 29 and 30. Stop pin 29 is fixed relative to the chassis and includes a cylindrical outer surface 29 A, the purpose of which will be described below.

Backplate 24 includes holes 3 IA, 3 IB and 31C for receiving ends of claw pivot pin 28, stop pin 29 and stop pin 30 respectively. During assembly the ends of pins 28, 29 and 30 are peened over in order to secure the backplate 24 relative to the retention plate 22.

Rotating claw 14 is pivotally mounted on claw pivot pin 28 and includes a mouth 32 for receiving the striker, a first safety abutment 33 and a closed abutment 34. A spring abutment 35 is engaged by spring 36 to bias the rotating claw towards its open position.

The rotating claw is generally planar and includes a reset pin 37 which projects out of general plane of the rotating claw.

The pawl 16 includes a pawl tooth 40, a first arm 41 having an abutment surface 42, a second arm 43, a third arm 44 having an abutment surface 45. Pawl 16 also has a pivot hole 46 of internal diameter D. Pawl 16 is biased in a clockwise direction when viewing figure 1C about axis Y (see below) by spring 47 engaging second arm 43. Stop pin 30 acts to limit rotation of the pawl in an anticlockwise direction when viewing figure 3 by engaging third arm 44.

The major components of crank shaft assembly 18 are a crank shaft 50, a reset lever 51 and release lever 653.

Crank shaft 50 includes a crank pin 54 in the form of disc having a crank pin axis Y. A square shaft 55 projects from one side of crank pin 54 and a cylindrical pin 56 projects from the other side of crank pin 54. Square shaft 55 and cylindrical pin 56 together define crank shaft axis A. Cylindrical pin 56 is rotatably mounted in a hole (not shown) of retention plate 22. The retention plate thereby provides a bearing for pin 56.

The diameter of crank pin 54 is a running fit in pawl pivot hole 46, i.e. the diameter of crank pin 54 is slightly less than D. The radius of crank pin 54 is R. The crank pin axis Y therefore defines a pawl axis about which the pawl can rotate (see below). The thickness of crank pin 54 is substantially the same as the thickness of pawl 16.

Reset lever 51 includes an arm 60 and a boss 61 secured to arm 60. Boss 61 has a cylindrical outer surface 62 and has a central hole of square cross section. Accordingly, when the boss 61 is assembled onto square shaft 55, as shown in figure 3, then arm 60 becomes rotationally fast with crank shaft 50. Cylindrical outer surface 62 of boss 61 is mounted in a hole in the backplate, which thereby provides a bearing surface for outer surface 62. It will be appreciated that cylindrical outer surface 62 and the outer surface of cylindrical pin 56 are concentric and together define the crank shaft axis A.

Arm 60 includes an edge 6OA (also known as a reset abutment) which interacts with reset pin 37 as will be described further below.

A release arrangement 652 consist of three major components, namely release lever 653, link 654 and lever 655. The lever 653 includes a square hole 664. Square hole 664 is mounted on square shaft 55. Thus, lever 653 is rotationally fast with the crank shaft.

Lever 655 is pivotally mounted on pivot pin 680, which in turn is secured to the latch chassis 12. Lever 655 includes a release abutment 65.

Link 654 is pivotally mounted to lever 653 and is also pivotally mounted to lever 655.

A bolt and washer (not shown) is screwed into threaded hole 57 of square shaft 55 to secure the crank shaft, reset lever and lever 653 together. Accordingly, it will be appreciated that the crank shaft, reset lever and lever 653 are all rotationally fast relative to each other.

When assembled, the crank pin 54 and the reset lever 51 are positioned between the retention plate and backplate with the cylindrical outer surface 62 of boss 61 being rotationally mounted in a hole (not shown) of the backplate 24. It will be appreciated that

the lever 653 lies on an opposite side of backplate 24 to the reset lever 51 and crank pin 54 (best seen in figure 2A).

The latch assembly 10 includes a release actuator 20 in the form of motor arrangement 100.

Motor arrangement 100 includes a brushless DC motor 110, an output member 112 (also known as a movable abutment) and motor stops 114 and 116.

Motor 110 includes a stator 118 and a rotor 120.

The stator includes an electromagnetic coil 122 having a coil axis A. The coil 122 is mounted on a ferromagnetic core 124 which extends through a bore in the coil. End 124A of core 124 is connected to a first stator arm 126. A second end 124B of the core 124 is connected to a second stator arm 128. It can be seen that the first and second stator arms extend generally perpendicularly to coil axis A. Furthermore, the first and second stator arms extend in the same direction (i.e. towards the rotor) from the core 124. The first and second stator arms are made from a ferromagnetic material, An end 126A of the first stator arm 126 remote from the core 124 defines a first stator magnetic pole 130 which partially surrounds the rotor and in this case is generally arcuate. A first end 128 A of the second stator arm 128 remote from the core 124 defines a second stator magnetic pole 132 which also partially surrounds the rotor, and in this case is generally arcuate.

The portion of the first stator arm and second stator arm proximate the core is generally flat. In this case each stator arm is made from a rectangular blank of sheet metal which is then subsequently formed to provide the arcuate stator magnetic poles 130 and 132. When the electromagnetic coil 122 is supplied with a DC current (as will be further described below) then either the first stator magnetic pole 130 becomes a north pole in which case the second stator magnetic pole 132 will become a south pole or the first stator magnetic pole 130 will be a south pole in which case the second stator magnetic pole 132 will be a north pole. Clearly the polarity of the stator poles can be selected, depending upon the polarity of the connection of the coil terminals to the DC power source.

The rotor 120 consists of a ring magnet 140, which in this case is a permanent magnet. Accordingly, the ring magnet has a north pole N and a south pole S. Arrow MA shows the magnetic axis of the ring magnet, (i.e. an arrow passing through the south pole and north pole of the magnet). The ring magnet 140 is mounted on a core 142 which preferably is a ferromagnetic core. The rotor core (and hence the ring magnet) are rotatably mounted about rotor axis B. In this case an axis C of the ring magnet is coincident with the rotor axis B though in further embodiments this need not be the case. In particular manufacturing tolerances may result in the ring magnet being offset slightly from the rotor axis but this is not significant in terms of the operation of the motor arrangement. As can be seen from figure 5, the north rotor magnetic pole is situated on one side of the rotor axis and the south rotor magnetic pole is situated on another side, in this case the opposite side of the rotor axis.

Projecting generally upwardly (when viewing figure 2) from the rotor core 142 i.e. projecting in a direction generally parallel with the rotor axis B is a first peg 144 and a second peg 146, the purpose of which will be described further below. First peg 144 has a portion 144 A proximate to the rotor and a portion 144B remote from the rotor. Similarly, second peg 146 has a portion 146 A proximate to the rotor and a portion 146B remote from the rotor.

As mentioned above, the rotor is rotatable about rotor axis B and this is enabled by virtue of a rotor axle 148 upon which is mounted the rotor core 142. The rotor axle 148 has a first end 148A which is rotatably mounted in a hole 150 of plate 51 and is secured in a fixed position relative to the latch chassis. An opposite end of the rotor axle is similarly located in a further hole. In summary, the ring magnet 140, rotor core 142 and rotor axle 148 all rotate together, as will be further described below.

The rotor axle 148 also includes a cylindrical surface 152 which acts as a bearing surface for the output member 112.

The output member 112 includes a central circular hole 160 which is mounted on the cylindrical portion 152. The output member 112 further includes a first arm 164 and a second arm 162. The first arm 164 includes an abutment 164A engageable by portion

144 A of first peg 144 and the second arm 162 includes an abutment 162 A engageable by portion 146 A of second peg 146 as will be described further below. The second arm 162 acts as a secondary pawl for the release arrangement 652.

It will be seen that second arm 162 is presented opposite to release abutment 65 when the latch is in the closed position as shown in figure IB. In summary to release the latch, the output member 112 is pivoted out of the path of release abutment 65 (as shown in figure 2B), thereby allowing lever 65 to pivot to the position shown in figure 2B.

Figure 5 shows the motor arrangement in isolation, i.e. prior to assembly into the latch 10. It is shown in one rest position with the north rotor magnetic pole N being directly opposite the first pole 130 and the south rotor magnetic pole S being directly opposite the second pole 132. Note that in this rest position the electromagnetic coil is not energised and hence the first pole 130 and second pole 132 are neutral i.e. they are neither a north pole or south pole. Nevertheless, because the first pole 130 and second pole 132 are made from a magnetic material in this case a ferromagnetic material, if the rotor is close to the figure 5 position then the rotor will rotate to the figure 5 position such that the north pole N is directly opposite the first pole 130 and the south pole S is directly opposite the second pole. Figure 5 A is a plan view of the motor arrangement shown in figure 5. The rotor position shown in figures 5 and 5A are identical.

The position shown in figure 5A is a "stable equilibrium" position. Thus, if the rotor was rotated slightly from the figure 5A position and then released, it would return to the figure 5A position.

Figure 5B shows an alternative "stable equilibrium" position wherein the north rotor magnetic pole N is adjacent the second stator magnetic pole 132 and the south rotor magnetic pole S is adjacent the first stator magnetic pole 130. It will be appreciated that the rotor position shown in figure 5 A and 5B are 180 degrees apart. The rotor position in figure 5B is also a stable equilibrium position because if the rotor was rotated slightly from this position and released it would return to this position.

Figures 5C and 5D also show the rotor in an equilibrium position, however, in both cases this is an unstable equilibrium position. Thus, if the rotor is positioned in the figure 5C position and rotated slightly (say 10 degrees) in a clockwise direction and then released, it would move to the stable equilibrium position shown in figure 5A. Conversely, if, starting at the figure 5C position the rotor was rotated slightly (say 10 degrees) in an anticlockwise direction and release it would then move to the stable equilibrium position shown in figure 5B.

Similar if the rotor is positioned as shown in figure 5D and rotated slightly in a clockwise direction it will move to the figure 5B position when released and if rotated slightly in an anticlockwise direction it will move to the figure 5A position when released.

It should be emphasised that the motor arrangement shown in figures 5, 5A, 5B, 5C and 5D are all in isolation, i.e. prior to assembly into the latch 10. When assembled into the latch 10, stops (as will be described below) prevent the rotor from achieving the figure 5 A position or the figure 5B position or the figure 5D position. Furthermore, when assembled into the latch the rotor only ever moves through the figure 5C position and is never stationary in this position.

The torque output from the rotor is not constant. Figure 11 shows test results and an averaged line of torque output against rotor angle. Zero degrees represents the position shown in figure 5B and 90 degrees represents the position shown in figure 5C. It can be seen that applying a current to the coil when the rotor is in the figure 5B position produces zero torque. However, the torque output reaches a maximum value when the magnetic axis MA of the rotor is aligned with line TMAX as shown in Figure 5C. In other words, when the motor is being powered the maximum torque occurs when the rotor is in its unstable equilibrium position as defined when the rotor is unpowered. Note that the line is not linear, rather as the rotor angle approaches the 90 degree position the curve flattens out. This means that 90% of the maximum torque is still achieved at a 70 degree rotor angle and 80% of the maximum torque is still achieved at a 60 degree rotor angle.

When the motor 110 is assembled into the latch assembly, the remote portions 144B and 146B of the first and second pegs 144 and 146, in conjunction with the motor stops 114

and 116 ensure that the rotor never achieves the positions shown in figure 5, 5A, 5B or 5D. Thus, figure 2C shows the limit of clockwise rotation of the rotor since remote portion 144B of first peg 144 is in engagement with motor stop 114. Figure ID shows the limit of anticlockwise rotation of the rotor since the remote portion 146B of second peg 146 is in engagement with motor stop 116 (motor stop 116 is not shown in figure 1 D).

It can be seen from figure 2C" that the angle Xl subtended at axis B between motor stops 114 and 116 is approximately 190 degrees. The angle X2 subtended between the remote portion 114B of first peg 144 and the remote portion 146B of second peg 146 that engage motor stops 114 and 116 is approximately 120 degrees. Therefore the total angle through which the rotor can move is approximately 70 degrees.

As mentioned above, prior to the motor 110 being assembled into the latch the rotor has two stable equilibrium positions, i.e. it has one stable equilibrium position as shown in figure 5/5 A and a second stable equilibrium position as shown in figure 5B. In this case these are the only two stable positions and hence the rotor is bistable, but in further embodiments this need not be the case. These two stable equilibrium positions are 180 degrees apart. When the motor is assembled into the latch, the rotor still has two distinct stable equilibrium positions, one as shown in figure 2C and the other as shown in figure ID. However, these stable equilibrium positions are approximately 70 degrees apart since, as mentioned above, the rotor is restricted to turning through only 70 degrees.

Consideration of figure 2C" shows that the rotor position (see magnetic axis MA) is approximately 30 degrees rotated clockwise from the maximum torque position TMAX (i.e. the position shown in figure 5C), i.e. the angle Yl between TMAX and MA is 30 degrees. In the absence of any current passing through the electromagnetic coil, the magnetic forces act on the rotor when in the figure 2C position and create a torque on the rotor turning it in a clockwise direction. This torque is reacted by remote portion 144B of pin 144 engaging motor stop 114. Similarly, when the rotor is in the figure IB/ ID position, the magnetic axis MA is angled 40 degrees (angle Y2 = 40 degrees) anticlockwise from the maximum torque position TMAX. Hence there is a torque acting on the rotor in an anticlockwise direction and this torque is reacted by remote portion 146B of pin 146 engaging motor stop 116.

Figure IB shows second peg 146 in engagement with second abutment 162 A, and the first peg 144 being spaced from first abutment 164A. Figure 2A" shows the rotor having being rotated clockwise through angle Zl (in this case approximately 35 degrees). In figure 2A" the second peg 146 is spaced from the second abutment 162 and the first peg 144 is in contact with the first abutment 164A. Thus, it is apparent that the rotor can rotate relative to the output member 112 to a limited extent as defined by the position of the abutments on the output member and by the position of the abutments on the rotor. In this case, the output member can rotate approximately 35 degrees relative to the rotor.

Consideration of figures 1 to ID show the latch assembly 10 and associated door 8 in a closed condition. The claw is in a closed position, retaining the striker (not shown). The pawl is in an engaged position whereby pawl tooth 40 is engaged with the closed abutment 34, thereby holding the claw in its closed position. The weather seals of the door are in a compressed state and the striker therefore generates a seal force FS on the mouth 32 of claw 14, which tends to rotate the claw in a clockwise direction when viewing figure 1 (an anticlockwise direction when viewing figure 1C).

Force FS in turn generates a force FP onto the pawl tooth 40 and hence onto the pawl 16. Force FP in turn is reacted by the crank pin 54 of the crank shaft. The force FP reacted by the crank pin is arranged so as to produce a clockwise (when viewing figure 1) torque (or turning moment) on the crank shaft about the crank shaft axis A (an anticlockwise torque when viewing figure 1C). However, the crank shaft assembly 18 is prevented from rotating clockwise when viewing figure 1 (anticlockwise when viewing figure 1C) by virtue of the engagement between release abutment 65 of release lever 52 and first arm 162 (see figure IB).

As shown in figure ID, the magnetic forces on the rotor create a torque in anticlockwise direction (since no current is flowing through the coil). As mentioned above, this torque is reacted by motor stop 116, but in particular the proximate portion 146B of second peg 146 has engaged and moved second arm 162 to the position shown in figure ID i.e. to a position where it faces release abutment 65 and therefore holds the release arrangement 652 in place.

In order to release the latch, electric current is supplied to coil 122 which creates a magnetic force which causes the first pole 130 to become a south magnetic pole and causes the second pole 132 to become a north magnetic pole. This causes a clockwise torque on the rotor since north pole N is repelled from second pole 132 and attracted to first pole 130 and south pole S is repelled from first pole 130 and attracted to second pole 132.

Figures 2A, 2B and 2C show the sequence of events that occur during opening of the latch. Note that the rotor moves continuously from the figure ID position to the figure 2B position i.e. at no point between the figure ID position and figure 2B position does the rotor stop moving.

Thus, as shown in figure 2A" the rotor has rotated approximately 35 degrees clockwise (angle Zl = 35 degrees) such that the proximate portion 144A of first peg 144 has engaged but not yet moved first arm 164. It can be seen that second arm 162 is still in engagement with release abutment 65.

The rotor continues to rotate in a clockwise direction a further approximately 35 degrees to the position shown in figure 2B. It can be seen that the second arm 164 has been engaged and moved by the proximate portion 144A of first peg 144. As shown in figure 2B, the output member 112 has rotated approximately 35 degrees in a clockwise direction when compared with figure 2A. This results in the second arm 162 disengaging from the release abutment 65.

Thus, figure 2B shows the moment at which the second arm 162 has disengaged from the release abutment 65 but prior to the release arrangement 652 beginning to move. Once the first arm 162 has disengaged from the release abutment 65 the lever 655 is free to rotate clockwise to the position shown in figure 2C. Note that the release arrangement 652 moves to the position shown in figure 2C as a result of the force FP that was reacted by the crank pin 54.

Once the components reach the figure 2C position, a sensor (not shown) senses that the lever 655 is in the figure 2C position and indicates this to a logic controller (not shown)

which in turn reverses the polarity of the electromagnetic coil. This then creates a north magnetic pole at the first pole 130 and a south magnetic pole at the second pole 132. This causes the rotator to rotate in an anticlockwise direction such that the proximate portion 146 A second peg 146 engages and then moves the output member 112 in an anticlockwise direction returning both the rotor and the output member to near the figure ID position. The output member 112 and rotor are prevented from returning fully to the figure ID position because the tip 112A engages the arcuate edge 655A of lever 655. When in this position the output member 112 is approximately 20 degrees away from the figure ID position. Nevertheless, because when the rotor and output member from the figure IB position the magnetic axis MA is angled at 40 degrees relative to the maximum torque position, when the tip 112 is engaged with the arcuate edge 655 A the magnetic axis of the rotor is still 20 degrees anticlockwise from the maximum torque position. As such, even in this position when the power to the coil is cut, there is still a torque acting on the rotor in an anticlockwise direction.

Whilst the rotor and output member are near the figure ID position, the lever 655 is still in the figure 2C position. Lever 655 is returned to the figure ID position as follows:-

Considering figure 1 C, the crank shaft rotation upon opening is anticlockwise about axis A, i.e. anticlockwise relative to the latch chassis 12. It will be appreciated that crank shaft axis A is defined by cylindrical pin 56 being rotatably mounted in the retention plate (as mentioned above) and boss 61 being rotatably mounted in the backplate (as mentioned above). Accordingly, crank shaft axis A is fixed relative to the latch chassis 12.

As mentioned above, when viewing figure 1C, force FP generates an anticlockwise torque upon the crank shaft 50 about the crank shaft axis A. Once the crank shaft is freed to rotate (i.e. once arm 162 has disengaged from release abutment 65) then the crank shaft will move in an anticlockwise direction since crank pin axis Y is constrained to move about an arc centred on crank shaft axis A. It will be appreciated that since the pawl pivot hole 46 is a close running fit on crank pin 54, then the pawl axis Z (i.e. the centre of pawl pivot hole 46) is coincident with the crank pin axis Y. Accordingly, the pawl axis Z is similarly constrained to move about an arc centred on crank shaft axis A.

As the crank shaft 50 starts to rotate in an anticlockwise direction from the position shown in figure 1C, it will be appreciated that the claw 14 starts to open. It will also be appreciated that it is the action of the claw pushing on the pawl that causes the pawl to move i.e. it is the claw that drives the pawl to the disengaged position by virtue of the weather seal load acting on the claw. As the pawl moves, the angular position of the pawl is controlled by engagement between abutment surface 42 of arm 41 and stop pin 29, more particularly contact point B defined between abutment surface 42 and part of the cylindrical outer surface 29A (which is also known as a chassis control surface).

Note that generally speaking the movement of the pawl can be approximated to rotation about point B (i.e. rotation about the contact point between abutment surface 42 and cylindrical outer surface 29A). However, the movement is not truly rotational since a part of the pawl (namely the pawl axis Z) is constrained to move about axis A rather than about point B. Thus, the movement of the pawl at contact point B relative to stop pin 29 is a combination of rotational movement and transitional (sliding) movement. Indeed contact point B is not stationary and will move a relatively small distance around the cylindrical outer surface 29A, and will also move a relatively small distance along abutment surface 42. Thus, contact point B is the position where (at the relevant time during opening of the latch) abutment surface 42 contacts the cylindrical outer surface 29A.

It will be appreciated that, starting from the figure 1C position, once arm 162 has disengaged from release abutment 65, the closed abutment 34 of the claw pushes the pawl (via the pawl tooth) to a position whereby the closed abutment 34 can pass under the pawl tooth 40 when viewing figure 1C. Continued anticlockwise rotation of claw 14 (when viewing figure 1C) will cause the first safety abutment 33 to approach the pawl tooth 40. As this occurs, pawl tooth 40 will momentarily engage the first safety abutment 33, since pawl 16 is biased in a clockwise direction when viewing figure 1C by spring 47. However, the geometry of the system is such that immediately after momentary engagement between first safety abutment 33 and pawl tooth 40, the first safety abutment pushes the pawl (via pawl tooth 40) to a position whereby the first safety abutment 33 continues to rotate in an anticlockwise direction when viewing figure 1C under the pawl tooth 40.

Once the pawl tooth 40 has thus disengaged from first safety abutment 34 of the claw, the claw is then free to rotate to the fully open position as shown in figure 3. However, in doing so the reset pin 37 engages and then moves edge 6OA of reset lever 60. This in turn rotates the crank shaft back to the position shown in figure 1, thereby resetting the crank pin axis Y to the figure 1 position, and also returning the release arrangement 652 to the figure ID position. In particular, as the lever 655 returns to the figure ID position the torque acting on the rotor in an anticlockwise direction will cause the output member 112 to move the remaining 20 degrees to the figure ID position, and this is in the absence of any power to the coil.

Once the latch and associated door has been opened, then closing of the door will automatically relatch the latch. Note however that no rotation of the crank shaft occurs during closing of the door. Accordingly, the crank pin axis does not rotate and as such the crank pin itself acts as a simple pivot having a fixed axis. Figure 4 shows the latch assembly 10 during the closing process and it can be seen that the pawl is free to rotate about pawl axis Z to provide conventional closing dynamics for the first safety and fully latched positions.

As mentioned above, a sensor is included to determine when the lever 655 reaches the figure 2C position and upon this determination the coil is reversed polarised to rotate the rotor in an anticlockwise direction. Alternatively, the sensor could be arranged to determine when the lever 655 has been returned to the figure ID position and upon this determination the coil can be reverse, polarised to rotate the rotor in an anticlockwise direction.

In an alternative embodiment, it is possible to power the coil for a pre-determined short period of time also the pre-determined time would be sufficient to ensure that the lever 655 reaches the figure 2C position. After the pre-determined time the coil would be reversed polarised to rotate the rotor in an anticlockwise direction. Under these circumstances the above mentioned sensor is not required.

In an alternative embodiment, a spring can be used to rotate the rotor in an anticlockwise direction once the lever 655 has reached the figure 2C position. Under these circumstances the above mentioned sensor is not required.

In a yet further embodiment, the rotor, first peg 144, second peg 146, motor stops 114 and 116 and output member 112 and lever 655 can be configured so that less than 90 degrees of rotation of the rotor is required for example only 30 degrees of rotation is required. Under these circumstances the rotor will naturally return to the figure ID position without the need to reverse polarise the coil and without the need of a return spring. Thus, as shown in figure ID the north pole N of the rotor is approximately 45 degrees clockwise from the position where it aligns directly with the second pole 132 by configuring the system so that the latch is released by only 30 degrees of clockwise rotation of the rotor from the figure ID position it will be appreciated that the north pole N at most is 75 degrees clockwise from direct alignment with the second pole 132. Because the rotor then only ever moves between the 45 degree and 75 degree angles (and thus never reaches the figure 5C position), then at all times when the coil is not energised, the magnetic forces acting on the rotor will always tend to rotate it in an anticlockwise direction. Thus, it is only ever necessary to power the coil in one direction since the north pole N never gets past the 90 degree "dead centre" position shown in figure 5C.

In the embodiments shown in figures 1 to 4, the motor arrangement 110 is used to release a latch. In further embodiments, motor arrangements according to the present invention can be used to perform other functions on a latch. In particular, it can be used to change the security status of a latch. It is known for latches to have a locked security status and an unlocked security status and it is known for motors to change the latch status between locked and unlocked. The present invention can be used to change a latch status between locked and unlocked.

It is also known for latches to include a child safety on security status and a child safety off security status. The present invention can be used to change the security status of a latch between the child safety on and child safety off status. It is also known for latches to have a superlocked security status and a non superlocked security status and the present

invention can be used to change a latch between a superlocked security status and a non superlocked security status.

Figures 6 to 8 show a further embodiment of a motor arrangement 210 in which components which fulfil substantially the same function as those of motor arrangement 110 are labelled 100 greater. The motor arrangement is mounted on a plate 308. In this case a gear 310 is rotatably fast with the rotor and is engaged by a gear sector 312 which is pivoted at pivot 314. Stops 316 and 318 limit clockwise and anticlockwise rotation respectively of the gear sector and hence limit anticlockwise and clockwise rotation of the rotor. In this case the rotor is limited in its anticlockwise direction such that the north pole is aligned at angle θ\ (approximately 45 degrees) and the rotor is limited in its clockwise rotation such that the north pole is limited to angle θ2 (approximately 135 degrees). It would be appreciated that the rotor therefore can move through approximately 90 degrees. Figure 6 shows output member 320 in a first position and figure 8 shows output member 320 in a second position.

It will be appreciated that the rotor positions shown at figures 6 and 8 are both stable rotor positions. Furthermore, because the rotor 240 includes a permanent magnet, then, in the absence of an electric current flowing through coil 222, in the position shown at figure 6 the magnetic forces provide an anticlockwise turning moment on the rotor which is resisted by stop 316. Similarly, in a position shown at figure 8 the magnetic forces acting on the rotor create a clockwise moment which is resisted by stop 318. Thus the motor arrangement will naturally hold itself in the figure 6 position or the figure 8 position as appropriate. This is particularly beneficial because in prior art locking systems and "over centre" spring is typically required to hold the locking system in either the locked or unlocked condition. Such a spring is not required when the motor arrangement 210 shown in figures 6 to 8 is used. The motor arrangement 410 (as described below) operates similarly, and also does not require an over centre spring.

Output member 320 can be used to lock and unlock a latch. Alternatively output member 320 can be used to change between the child safety on and child safety off status of a latch. Alternatively output member 320 can be used to change between a superlocked condition of a latch and a non superlocked condition of a latch.

Figures 9 and 10 show a motor arrangement 410 in which components that fulfil substantially the same function as those shown in motor arrangement 210 are labelled 200 greater. It can be seen that motor arrangement 410 is more compact than motor arrangement 210 because the gear sector 512 lies on the same side of the rotor as the coil

422.

As mentioned above the rotor is limited to rotating through an angle of 70 degrees. However, in further embodiments the rotational of the rotor could be limited to less than 180 degrees. However, preferably the rotational movement of the rotor is less than 100 degrees, more preferably less than 90 degrees. This is because these are angles at which useful torque can be provided (see figure 11).

As mentioned above, the output member can rotate relative to the rotor by 35 degrees. In a further embodiment different angles of rotation are possible but in particular the output member may be rotatable relative to the rotor by more than 20 degrees, preferably more than 30 degrees, and preferably more than 40 degrees.

As mentioned above, the embodiment described has a total rotor movement of 70 degrees. The output member can rotate relative to the rotor by 35 degrees. This means that the output member rotates relative to the latch chassis by 35 degrees in total. In further embodiments the output member could rotate relative to the latch chassis by other angles but preferably the output member rotates relative to the latch chassis by less than the angle through which the rotor rotates relative to the latch chassis.

As mentioned above, figure IB shows that the magnetic axis MA is positioned 40 degrees anticlockwise relative to the maximum output position TMAX when the latch is in a closed position. When the coil is powered to open the latch, initially only the rotor starts to rotate. By the time the rotor has reaches the position shown in figure 2A" it has an amount of rotational inertia that assists in overcoming the static friction between the tip 112A of the output member 112 and the associated notch in the lever 655. Furthermore, when the rotor is in the figure 2A" position, it is nearly at its maximum torque output position (angle Y3 is only 5 degrees). Consideration of figure 11 shows that in spite of the magnetic axis not

quite being aligned with TMAX, nevertheless the rotor is producing 99% of its maximum output. By arranging "lost motion" between the rotor and the output member, i.e. by allowing the rotor to rotate further than the output member, this allows low starting loads on the rotor (i.e. the rotor has only got to rotate itself when starting).

This lost motion also allows the rotor to achieve some rotational intertia before it is required to rotate the output member. The lost motion also allows the rotor to be at or near its maximum torque position before it is required to rotate the output member. The lost motion also allows the stable equilibrium positions to be positioned at relatively large angles from TMAX (in this case 40 degrees from TMAX (see figure IB) and 30 degrees from TMAX (see figure 2C")). The further the stable equilibrium positions are from TMAX then the higher than torque on the rotor forcing it into engagement with stops 114 and 116 (for the avoidance of doubt this is when no power is applied to the coil).

By ensuring that the angle of the stable equilibrium position from TMAX (for example 40 degrees (see figure IB)) is approximately equal to the lost motion between the rotor and the output member (35 degrees (see figure 2 A")) means that the lost motion will be taken up at approximately the position when the magnetic axis of the rotor is at TMAX (5 degrees (as shown in figure 2A" (Y3)). In other words, it is advantageous for the angle between the magnetic axis with the rotor in the stable equilibrium position and TMAX (40 degrees as shown in figure IB) to be less than 20 degrees different from the amount of rotation between the output member and the rotor, preferably this angle is less than 10 degrees different, and more preferably (as in the embodiment shown in figure 2A") is 5 degrees, and more preferably less than 5 degrees different.

The motor 110 is used to release the tip of the output member 112 from the lever 655. In further embodiments, the motor could be used in other mechanism to hold an abutment of the mechanism in the first position and then release that abutment to allow it to move to the second position.