TECHNICAL FIELD

The invention relates to a device for active steering of a vehicle with a power steering arrangement, comprising a valve body arranged to be switched in opposite directions by a steering wheel movement for distribution of a pressurised fluid to a fluid-driven actuator in the power steering

arrangement. The invention also relates to a power steering arrangement provided with such a device.

BACKGROUND

It is presently desired to control power steering arrangements for motor vehicles by using signals which are independent of the driver's own steering wheel movements, e.g. by means of assistance systems such as Lane Assist or Park Assist. Known systems of this kind may comprise an electric motor which at some point in the steering column acts upon, for example, an input to a differential gear which has a second input acted upon by the driver's own steering wheel movements. However, such a solution takes up a relatively large amount of the already limited space around the steering column. It is therefore desirable to be able to save space by utilising the servo system already in place.

SUMMARY OF THE INVENTION

One object of the invention is therefore to provide a device of the kind indicated in the introduction which takes up little space and which can utilise the existing components of the power steering arrangement.

RECCV, /TRANSLATION

(Rule 12,4) According to a version of the invention, the valve body is divided into a pair of parts which are movable in mutually opposite directions, and positioning means operate between the parts in order to switch the valve body independently of the steering wheel movement. This division of the valve body allows the same valve to be used both for external control signals and for the driver's manual control signals. The external control signals can then be superimposed on the driver's control signals, e.g. in order to correct or assist the driver by use of sensors which detect the direction of the carriageway.

Although they may also, depending on the type of power steering, be movable, for example, axially, the parts in one embodiment of the invention are supported for rotation about a common axis, e.g. a steering column axis.

Said positioning means may then operate in a tangential clearance between the parts. They then utilise an insignificant extra space in the power steering arrangement.

The positioning means may also comprise a pair of elements each operating between opposite surfaces of the parts. A pair of opposite elements of this kind allows the parts to be switched in both directions and be returned to an inactive central position.

The positioning means may, for example, be piezoelectric elements. Two such opposite elements may also be arranged to return the parts

automatically to the central position by their inherent elasticity.

The positioning means may also comprise a pressurisable fluid which may be part of the same hydraulic system as that used in the power steering arrangement.

The positioning means may further comprise electromagnetic elements, e.g. a number of electromagnets. Other features and advantages of the invention may be indicated by the claims and description of embodiment examples set out below.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a schematic side view of a power steering arrangement according to the state of the art which may be provided with a device according to the invention;

Fig. 2 is a schematic perspective view with separated portions of part of the power steering arrangement in Fig. 1 ;

Fig. 3 shows, on a larger scale, a broken-off part 3 in Fig. 2 with partly separated portions and provided with a piezoelectric device according to the invention;

Fig. 4 shows two cross-sectional views in different positions through an axially overlapping portion of a divided valve body according to Figs. 2 and 3;

Fig. 5 shows two views corresponding to Fig. 4 with a hydraulic device according to the invention; and

Fig. 6 shows views corresponding to Figs. 4 and 5 of a pair of different electromagnetic devices according to the invention.

Parts with similar functions have mutually similar references throughout.

DETAILED DESCRIPTION OF EMBODIMENTS

The example in Fig. 1 shows a power steering arrangement of a known type, with the general designation 10. The power steering arrangement 10 has a steering housing 12 which forms a section of a steering column and which can be rotated in both directions by a vehicle steering wheel 14.

When there is no servo function, the steering wheel 14 can operate a ball screw 16, which is in threaded engagement with a ball nut bushing 18 which is supported in a rotationally fixed position. The bushing 18 is itself in gear engagement with a lever 42 which is articulatedly connected to a push-pull rod 44 of a steering mechanism 40 for a pair of vehicle wheels 46.

In normal situations when the power steering arrangement 10 is in operation, the steering wheel 14 operates a valve body 22 (Fig. 2) in a valve housing 24 of a hydraulic valve 20 depicted schematically in Fig. 1. The valve 20 is of an open-centre type not shown in greater detail. When the valve body 22 is switched in the valve 20 by a steering movement from the steering wheel 14, hydraulic fluid from a pump 28 is fed into one or other end of an actuator in the form of a hydraulic cylinder 30 through respective pipes 32 and 34. The ball nut bushing 18, which is sealed against the walls of the cylinder 30, can then serve as a hydraulic piston which boosts the turning force exerted by the driver on the steering wheel 14 in order to steer the vehicle wheels 46.

Also operating between the steering wheel 14, the valve body 22 and the ball screw 16 / valve housing 24 is a torsion rod 26 (Fig. 2) which returns the valve body 22 to its central open position with reference to the valve housing 24 when no turning force is exerted on the steering wheel 14.

As can be seen in Fig. 3, the valve body 22 is provided with a device 70 according to the invention to make it possible to superimpose on the abovementioned steering movement from the steering wheel 14 to the valve body 22 an external control signal to the power steering arrangement. The external control signal may be delivered to a vehicle computer 80 from an undepicted sensor, e.g. a sensor which monitors a carriageway marking, and be passed on by the vehicle computer 80 to the valve body 22 via a signal converter 84 and signal connections 82, 86. The valve body 22 is divided for this purpose into two parts 50 and 60 which are supported for rotation, viz. a part 50 which provides the valve function and a part 60 which may be firmly connected to the steering wheel 14. The parts 50, 60 are telescopically accommodated in one another by an insert connection and are mutually movable in a tangential clearance, which in the example shown is achieved by the insert connection being rotatable to a limited extent by an axial ridge 52 which is accommodated with play in an axial groove 62. As may in particular be seen in Figs. 4 and 5, the

tangentially opposite radial surfaces 54, 64 on either side of the ridge 52 may then serve as stop surfaces for positioning means 72 accommodated between the surfaces 54, 64. The positioning means 72 may be arranged such that when they are inactive they hold the part 52 in a tangentially central position relative to the part 62, and that when they are active they rotate the part 52 in one direction or the other. The positioning means 72 need not necessarily be situated alongside one another, as the ridge 52 may have any desired extent in the circumferential direction.

In the embodiment according to Figs. 3 and 4, the positioning means are piezoelectric elements 72 which can be selectively charged and expanded by the signal converter 84 (Fig. 3). Such elements may be appropriate where only small positioning movements are needed to switch the part 50 relative to the part 60. To achieve larger positioning movements, they may of course be situated nearer to the common axis of rotation. When one element 72 expands upon charging, the other element 72 may be arranged to be compressed by its inherent elasticity. The elastic return of the elements to their original extent in angular directions, when neither of them is activated, can also be utilised to automatically return the part 50 to the inactive central position shown in Fig. 4A.

In the embodiment according to Fig. 5, the positioning means 72 comprise a pressurisable fluid, e.g. hydraulic fluid, which can be distributed to the spaces between the surfaces 54, 64 via a valve 84 (Fig. 5A) or directly by a double-acting, motor-driven pump 84 (Fig. 5B), in order to switch the part 50. The return to the central position may in this case be achieved, in a manner not shown, by use of return springs in the valve body 22 or in the pump 84, or by angle sensors which deliver signals to the valve/pump 84 via the vehicle computer 80.

Fig. 6A shows schematically the possibility of using magnetic positioning means such as a pair of attracting electromagnets 72 in the spaces on either side of the ridge 52. Further magnets or return springs may be used, in a manner not shown, for the return of the part 50 to the central position shown.

As implied in Fig. 6B, it is also at least conceivable to configure the axially overlapping portions 72A and 72B of the parts 50, 60 as rotor and stator respectively, with an intermediate air gap, of an electric motor, as also a stepping motor or a tachometer-controlled electric motor, in order to achieve desired angular movements between the parts 50 and 60.

The description set out above is primarily intended to facilitate understanding and no unnecessary limitations of the invention are to be inferred therefrom. The modifications which will be obvious to a specialist perusing the description may be implemented without deviating from the concept of the present invention or the scope of the following claims.