In a motor vehicle, as e. g. a car, many functions have to be controlled from the driver's position. Tradi- tionally these controls were transmitted to the position where the actual operation is to be carried out by mainly mechanical means, like rods and wire, or partly also by hydraulic means. There is a clear tendency in the automo- tive industry to replace such mechanical or hydraulic transmission means by electrical wiring, called"drive by wire".

If the signal to operate the brakes are transmit- ted from the driver's position to the brakes by electric wire, this is called"brake by wire"."Clutch by wire"if the signal to operate the clutch is transmitted from the driver's position to the clutch by electric wire and "steer by wire"if the signal to operate the steering of the vehicle wheels is transmitted from the driver's posi- tion to the wheels by electric wire.

In e. g. the case of"steer by wire", the driver has a steering wheel or a slide or any other means to con- trol the angle of the vehicle wheels with. Traditionally this steering wheel, for example, is connected by means of a system of rods and joints to a steering house, where the rotational movement of the rod is transformed to a linear movement of a rod, to which the steering arms are con- nected, that actually change the angle of the vehicle wheels, and thus the direction in which the vehicle moves.

In the case of"steer by wire", the status of the control means is transformed into an electric signal, which in turn is fed"by wire"to an actuator. This actuator then in turn actuates the steering of the vehicle wheels. Ad- vantages of the"by wire"systems are e. g. saving of weight and freedom of design to position the various sys-

tems and hence also space saving, which in itself can lead to again saving of weight.

For these and other"by wire"systems, but also for non-by wire systems, e. g. the actuator for a power steering device in a steering system with a mechanical link to the steering wheel, there is a need for actuators that have simple and compact design and still demonstrate a large stiffness. Also is it desirable for such actuators to function without producing much noise. Preferably such actuators are relatively simple and hence economical to manufacture on a large production scale.

It is an aim of this invention to provide an ac- tuator for automotive applications that combines a compact design with a large stiffness.

It is another aim of this invention to provide an actuator for automotive applications that is rather silent in operation.

It is still another aim of this invention to pro- vide an actuator for automotive applications that is rela- tively simple and hence economical to manufacture on a large production scale.

To this end the invention provides an actuator for automotive applications according to one or more of the appended claims. Other advantages of the invention will become apparent from the description below.

In a first aspect of the invention the actuator comprises an actuator rod that is arranged to make a lin- ear movement, and is characterised in that the actuator comprises a transformer to transform a rotating movement into the linear movement, and that the transformer is driving the actuator rod and can in use be connected to a rotationally driven shaft of a motor. Such an actuator uses rotational movement as input, and the simplest way to obtain movement on a reasonable scale out of an electrical signal is rotational movement.

Gears provide a stiff and compact mechanical ar- rangement and hence stiffness and compactness is enhanced when the transformer of the actuator has a stationary

frame, that comprises radially inwards pointing teeth, and a gear wheel co-operating with these teeth, this gear wheel being moveable along these teeth and being coupled to the actuator rod. Such an arrangement is also known to be made in a way that very little sound is emitted from the arrangement.

When the teeth and the gearwheel have a transmis- sion ratio, such that at least one predefined point of the gearwheel makes a linear movement during the movement of the gearwheel, then the actuator rod can directly be cou- pled to that point, achieving the desired linear movement in a very simple and compact way.

In an actuator where the gearwheel and the teeth each form a pitch circle and the gearwheel and the teeth are dimensioned such that the pitch circle of the gear wheel has a diameter that equals half the diameter of the pitch circle of the teeth, and that the at least one pre- defined point is positioned on a line that goes through the pitch circle of the gear wheel and is perpendicular to the plane of this pitch circle of the gearwheel, the ac- tuator can substantially be formed with standard compo- nents and using standard methods, and can thus be manufac- tured in a cost effective way.

A compact arrangement in the form of a unit can be reached with an actuator wherein the said motor is at- tached to the said frame and the said rotationally driven shaft is coupled to the gearwheel.

A simple and strong actuator is obtained when the shaft is perpendicular to the pitch circle of the teeth in the stationary frame and the centre of the shaft goes through a centre point of this pitch circle and that the shaft is coupled to the centre of the gearwheel.

A very stiff arrangement is obtained, when the gearwheel is arranged with a recess, such that the gear- wheel remains essentially symmetrical to a plane parallel to the pitch circle of the gearwheel, in which recess a first coupling for connecting the gearwheel to the actua- tor rod is accommodated, such that the actuator rod is

movably positioned in the recess. In this arrangement the bending moments that may occur in the plane of the gear- wheel are strongly reduced.

A somewhat less costly arrangement, but still with high stiffness can be obtained when instead of a relatively wide gearwheel with a recess, a second gear- wheel is provided, co-operating with the teeth, parallel to the first gearwheel on the opposite side of the actua- tor rod, and wherein the first coupling couples both gear- wheels to the actuator rod. In this arrangement the stiff- ness can be increased when a second coupling couples both gearwheels to each other.

The bending moments that may occur in the plane of the gearwheels can be further reduced when the gear- wheel on the non driven side in the centre point is cou- pled with a third coupling, this third coupling being sup- ported in the stationary frame, this support being aligned with the rotationally driven shaft.

When this third coupling is supported in the sta- tionary frame by means of a shaft, it is possible to at- tach auxiliary systems to this shaft.

It is also possible to provide the actuator rod with teeth for co-operation with a gearwheel. This also provides a possibility to attach an auxiliary system that co-operates with the teeth of the actuator rod.

In cases where e. g. a substantially linear rela- tion between angular displacement of the rotating movement and linear displacement of the linear movement takes place, the actuator can be provided with a first control, including appropriate sensors, that limits the linear movement to an area of movement around a central point.

Also in specific applications it can be desirable to control the speed of either the linear movement and/or the rotational movement. Since the mechanical design of the actuator defines a relation between the rotational movement and the linear movement, it is sufficient to con- trol either the linear movement or the rotational move- ment. Since the actuator according to the invention usu-

ally has the rotational movement as input, it is most natural, but not required, to control the rotational move- ment or the rotational speed, also a control that includes the appropriate sensors.

It should be noted that although the actuator ac- cording to the invention has been described so far with the rotational movement as the driving movement, and hence the input, the actuator of the invention is not limited to an input on the rotational movement. The actuator of the invention can with well chosen starting conditions equally be used as actuator where the linear movement is the driv- ing movement, and hence the input.

The actuator according to the invention will now be further explained using preferred embodiments that will be described with reference to drawings, where: Fig. 1 is a view in perspective of a first em- bodiment of an actuator according to the invention, Fig. 2 is an elevation view of the actuator of fig. 1.

Fig. 3 is a partially exploded view in perspec- tive of another embodiment of an actuator according to the invention, and Fig. 4 is a view in perspective of a mechanical back-up in yet another embodiment of the actuator accord- ing to the invention.

In all figures the actuator is generally indi- cated with numeral 1 and an actuator rod is indicated with numeral 2. The actuator 1 comprises a transformer to transform a rotating movement into the linear movement and the transformer is driving the actuator rod 2 and can in use be connected to a rotationally driven shaft 14 of a motor 4. Motor 4 can be equipped with or without a gear reduction. Part of the rotationally driven shaft 14 is shown in fig. 3. In fig. 1 bore 3 is shown through which the shaft 14 is extending. Also the axis of rotation of the shaft 14 is indicated in fig. 1 with a dotted line.

The transformer of the actuator 1 has a stationary frame 5, that comprises radially inwards pointing teeth 6, and a

gear wheel 7 co-operating with these teeth, this gear wheel 7 being moveable along these teeth 6 and being cou- pled to the actuator rod 2.

The gearwheel 7 and the teeth 6 each form a pitch circle with centre points B and A (see fig. 2) respec- tively.

The teeth 6 and the gearwheel 7 have a transmis- sion ratio, such that at least one predefined point of the gearwheel 7 makes a linear movement during said movement of the gearwheel. In the embodiment of the invention that is shown in fig. 1 and 2 the gearwheel 7 and the teeth 6 are dimensioned such that the pitch circle of the gear- wheel 7 has a diameter that equals half the diameter of the pitch circle of the teeth 6. The at least one prede- fined point is positioned on the pitch circle of the gear- wheel 7.

In fig. 2 the centre point of a first coupling 8 is indicated with C. The axis of the first coupling 8 goes through C and also through the at least one predefined point of the gearwheel 7 that makes a linear motion and is perpendicular to the pitch circle of gearwheel 7. Thus the first coupling 8 makes a linear motion and drives actuator rod 2 into making a linear motion.

As can be seen from fig. 1, motor 4 is attached to frame 5. The axis of rotation of rotationally driven shaft 14 is shown with a dotted line. The shaft is coupled to the gearwheel by second coupling 9. Second coupling 9 has a bore 3 in which the shaft 14 is received.

In this first embodiment of the invention, the shaft 14 is perpendicular to the pitch circle of the teeth 6 in the stationary frame 5. The centre of the shaft 14 goes through the centre point A of this pitch circle. The shaft 14 is coupled to the centre B of the gearwheel by means of crank 9.

The actuator in this first embodiment of the in- vention converts rotating movement into linear movement.

Depending on the application and the performance required, it can be used with full rotation or with only part of the

turn. In another, a second embodiment of the invention, which is shown in fig. 3, gearwheel 7 is arranged with a recess, such that gearwheel 7 remains essentially symmet- rical to a plane parallel to the pitch circle of gearwheel 7, in which recess first coupling 8 is accommodated, such that actuator rod 2 is movably positioned in the recess.

Gearwheel 7, and also teeth 6 do have a sufficiently large width, so that it can comprise, between the side faces, a recess of dimensions so first coupling 8 can be accommo- dated in this recess. This means that actuator rod 2 moves in the mid plane of gearwheel 7. In this second embodiment it is not possible to make a full turn since the section of gearwheel 7 that covers the full width of gearwheel 7 will reach actuator rod 2. It is thus limited to cases where rotational movement is restricted to part of a turn, but this embodiment provides a very stiff actuator, since bending moments in the plane of the gearwheel are greatly reduced in this arrangement.

A cheaper, third embodiment that only partly sac- rifices some of the additional stiffness of the previous embodiment will now be described. The actuator 1 comprises a second gearwheel 7, co-operating with teeth 6, parallel to the first gearwheel 7 on the opposite side of actuator rod 2, and wherein first coupling 8 couples both gear- wheels 7 to actuator rod 2. Although some of the rigidity that is provided by the wide gearwheel 7 of the second em- bodiment is given up here, this embodiment still has in- creased stiffness compared to the first embodiment de- scribed, but the cost are reduced in comparison with the second embodiment.

In yet another, a fourth embodiment an increase in the stiffness can be obtained compared to the third em- bodiment with the two gearwheels, described above. In this case second coupling 9 couples both gearwheels 7.

In a fifth embodiment, gearwheel 7 is on the non driven side in centre point B coupled with a third cou- pling 10, third coupling 10 being supported in frame 5, this support being aligned with the rotationally driven

shaft 14, as can be seen from fig. 3. This additional sup- port increases again the stiffness and is applicable to all previous embodiments.

The actuator according to the invention can be used in a steering system, e. g. a steer by wire system. In such a case the steering rods can be coupled to the actua- tor rod, at basically any place that is found suitable. In such an application, there may be the requirement that the vehicle is equipped with, or can be connected to a me- chanical back-up. That is, when there is a power failure, or when there is no power available, as can happen in a repair shop during repairs or in the factory during assem- bly, it should still be possible to steer the vehicle. For that reason the vehicle can be equipped with or can be connected to a mechanical back-up. An schematic example of such a mechanical back-up is given in fig. 4 and is there generally indicated with numeral 13. When the mechanical back-up is present in the vehicle, also during normal op- eration, such a back-up is connected by means of a elec- tromagnetic coupling, that engages in case of power loss.

Such a mechanical back-up 13 can e. g. be connected to the shaft 14, at an end opposite to coupling 9, or, in the case of the fifth embodiment described above, where cou- pling 10 is supported in frame 5 by means of shaft 11, such a mechanical back-up 13 can also be connected to this shaft 11. In all cases it is possible to provide the ac- tuator rod with teeth 12, to which a mechanical back-up can be connected by means of a gearwheel, as is shown in fig. 4.

Although the actuator 1 has been described here as e. g. used in a steer by wire application, it is also suitable to use the actuator in a traditional steering as- sembly. In that case the rotating movement is not provided by the motor 4, but by a manually driven shaft. In that case the positions that are mentioned above to connect the mechanical back-up can be used to connect a motor for as- sisting the steering action, i. e. power steering.

Another example where the actuator can be ap-

plied is in a compressor, such as used e. g. in the cooling section of a climate control unit in cars. The rotating input can be supplied by one or more electro motors and the actuator is then driving a piston. A duplex unit can actuate two pistons, moving in synchronisation, 180° out of phase, or otherwise.

If for a particular application it is desirable to have a substantially linear relation between the angu- lar displacement/velocity and the linear displace- ment/velocity, the movement (stroke) can be restricted to an area of movement around a central point. The closer the movement is restricted to that point, the more linear the relation is. Depending on the requirements to this linear- ity, it is possible with the actuator in this embodiment of the invention to adjust the restriction of the stroke accordingly. To set, adjust and keep such a limit, the ac- tuator can be provided with appropriate control mechanisms that as such are known to a person skilled in the art and hence are not further described here.

It is noted that the same actuator can be used to convert linear movement into rotating movement. The only restriction for this is that the proper starting position has to be chosen. In such an embodiment the actuator ac- cording to the invention can be used to perform the func- tion of a crankshaft in an internal combustion engine.

It should also be noted that the actuator accord- ing to the invention can be designed and equipped with all necessary accessories that are required or advantageous to the application. E. g. the actuator can be equipped with various types of sensors and control systems, with sealing and shielding mechanisms to protect the actuator when used in harmful environments. The actuator can be oil or grease lubricated. Parts can be made of any suitable construction material, including steel as well as injection mouldable material, depending on the requirements.

When the actuator is used e. g. as an actuator in a steer by wire system in a car, the actuator is well pre- pared to be equipped with a mechanical back-up, connected by electro-magnetic coupling, and activated e. g. in case of loss of electric power.