Title:

System for absorbing collision energy for a steering column with motorised depth adjustment

TECHNICAL FIELD OF THE INVENTION

The invention generally relates to the technical field of steering columns and systems for absorbing collision energy which are fitted to steering columns.

The invention relates more specifically to a system for absorbing collision energy for a steering column with depth adjustment in which an internal tube slides in an external tube, preferably in a motorised manner.

The invention is used in the construction of a steering column having motorised adjustment of the depth position of the steering wheel of a vehicle, such as a motor vehicle, and vehicles provided with such a steering column.

In the following description, the term “longitudinal direction” and “transverse direction” are intended to be understood to mean axes which are parallel with or perpendicular to the main axis of the steering column, which is also called the steering axis below. This applies similarly to the front and rear or the upper portion and lower portion which are orientated in the normal travel direction of a vehicle, respectively.

PRIOR ART

Steering columns for a motor vehicle involving a device for absorbing collision energy are known and are the subject of safety standards, in particular in the field of automotive construction. In the event of the vehicle being involved in an acci- dent, more particularly in the case of a front-end collision, the device for absorbing collision energy attenuates the impact of the driver against the steering wheel by axial movement of the steering wheel and a movable portion of the steering column towards the instrument panel under the effect of the impact of the thorax of the driver against the steering wheel. During a front-end collision, different safety systems of the vehicle, such as the airbag and the safety belt, absorb a portion of the energy generated by the vehicle occupants being projected forwards, more particularly the driver. The rest of the collision energy is transmitted to the steering column as a result of the impact of the thorax of the driver against the steering wheel. This residual collision energy is absorbed by the steering column as a result of the plastic deformation of mechanical components, such as wire-like straps or planar straps which are integrated in the steering column. The plastic deformation of these straps causes the steering column to become compressed over a path which is typically from 80 mm to 100 mm. In some countries, the vehicles provided with airbags may be driven without any obligation to fasten the safety belt. Thus, in order to minimise the risk of injury to the driver, the device for absorbing collision energy must be able to absorb a large portion of the kinetic energy of the body of the driver who is projected forwards under the effect of the violent deceleration during the collision. The upper portion of the body of the driver strikes the steering wheel or the airbag integrated in the steering wheel after its deployment.

In the document US 6290258 Bl, a steering column which is adjustable in terms of depth for a motor vehicle is described, wherein a motorised blocking system for the steering column allows the position thereof to be locked once the adjustment has been carried out manually by the driver. This blocking system is also used to dissipate the collision energy by the friction effort brought about on the steering column by a clamping bolt which belongs to the blocking device. A first aperture, through which the clamping bolt extends, defines an adjustment path of the steering column. The depth adjustment path is typically between 40 mm and 60 mm. This first aperture is extended by a second aperture which defines a path for absorbing collision energy. In the event of a collision, the clamping bolt moves from the first aperture to the second aperture by overcoming, with plastic deformation, a boundary which separates the two apertures. After the driver has entered the vehicle, sensors measure the weight, the posture and the position of the driver. In response to the signals provided by these sensors, an electric motor which carries the clamping bolt is controlled in order to increase or decrease the clamping effort of the clamping bolt on the steering column. This device allows adjustment of the collision energy level which can be absorbed by the steering column in accordance with the driver and his/her position. During a collision, an effort peak is observed when the boundary between the two apertures is overcome by the clamping bolt.

Nowadays, vehicles can be used in autonomous driving mode, in which the driver no longer acts on the steering wheel in order to steer it. Since the steering wheel becomes useless in autonomous driving mode, it can be completely retracted in order to release more space for the driver. While the adjustment path of a steering column is typically between 40 mm and 60 mm, the retraction path of a steering column is between 100 mm and 300 mm, which is substantially greater than the usual length of the paths for absorbing collision energy as defined by the safety standards in force.

There is a constant need to reduce the risks of injury to the driver and therefore to increase the safety of the passengers of a motor vehicle. An excessively high level of the mechanical effort in the steering column which absorbs the collision energy and a peak of this effort when the steering column reaches the end of travel and when a plastic deformation occurs in the steering column during the compression thereof increase the risks of injury. Consequently, it is necessary to find a solution which allows a reduction in the mechanical effort which absorbs the collision energy and to prevent a peak of effort.

STATEMENT OF INVENTION

The object of the invention is to completely or partially solve the problems of the prior art set out above by proposing in particular a system for absorbing collision energy which is capable of precisely estimating the collision energy to be absorbed and of distributing the effort which acts counter to the compression of the steering column using a substantial portion of the compression path of the steering column, in particular the retraction path. To this end, there is proposed, according to a first aspect of the invention, a system for absorbing collision energy for a steering column with motorised adjustment at least in terms of depth by sliding an internal tube in an external tube along an adjustment axis. The device for absorbing collision energy comprises a blocking device for the internal tube in the external tube itself comprising an actuator, a clamping mechanism which is driven by the actuator and which is capable of applying a pressure force to the internal tube, bringing about an axial friction force which acts counter to the sliding of the internal tube in the external tube, and a control unit which is capable of controlling the actuator in order to modulate the pressure force applied to the internal tube in a travel mode in accordance with parameters which represent a morphology and a position of a driver. In order to control the actuator, the control unit uses parameters which represent dynamic conditions of a vehicle in travel mode before a collision.

Advantageously, the parameters which represent dynamic conditions of the vehicle comprise a speed of the vehicle and/or an estimate of an angle of impact of the collision and/or the pressure force applied to the internal tube is generated by a clamping torque which is supplied to the clamping mechanism by the actuator and which is modulated by the control unit continuously or in steps until before the collision.

Advantageously, the collision energy is absorbed by the axial friction force between the external tube and the internal tube over at least a substantial portion of the entire length of a continuous sliding path of the internal tube in the external tube.

Advantageously, the clamping mechanism of the internal tube comprises at least one pressure element which acts on the internal tube and a drive mechanism of the irreversible type which connects the actuator to the at least one pressure element and which is capable of clamping or unclamping the at least one pressure element on the internal tube.

Preferably, the drive mechanism comprises a rocker bar which has at least one ramp-shaped profile which can cause the at least one pressure element to slide relative to the external tube along a clamping axis which is transverse relative to the adjustment axis.

Alternatively, the at least one pressure element is a pressure screw and the drive mechanism comprises a rocker bar which can screw or unscrew the at least one pressure screw along a clamping axis which is transverse relative to the adjustment axis.

Alternatively, the drive mechanism comprises a clamping screw which is rotated by the actuator and which is able to cooperate with at least one clamping runner in order to slide it along a clamping axis which is orthogonal and non-secant with respect to the adjustment axis in order to increase or decrease the pressure force on the internal tube.

Alternatively, the drive mechanism comprises a clamping screw which is rotated by the actuator about a clamping axis which is orthogonal and non-secant with respect to the adjustment axis in order to move opposite edges of a slot formed in a covering of the external tube towards or away from each other parallel with the adjustment axis.

According to a second aspect of the invention, there is proposed a steering column with motorised adjustment at least in terms of depth, comprising an external tube, an internal tube which is received in a sliding manner in the external tube, and a depth adjustment device of the steering column comprising a motor element which drives an irreversible drive mechanism of the internal tube in the external tube along an adjustment axis which corresponds to the longitudinal axis of the external tube. The steering column further comprises a system for absorbing collision energy as briefly described above.

Advantageously, the control unit is capable of controlling the actuator of the system for absorbing collision energy in order to reduce or eliminate the pressure force applied to the internal tube in a depth adjustment mode of the steering column or a retraction mode of the steering wheel. Preferably, the irreversible drive mechanism of the internal tube comprises a mechanical breakable element which can release the sliding of the internal tube in the external tube during a collision and/or the steering column further comprises a system for absorbing collision energy by plastic deformation of the strap type.

There is proposed according to a third aspect of the invention a vehicle which is provided with a steering column as briefly described above.

There is proposed according to a fourth aspect of the invention a method for absorbing collision energy of a vehicle by an axial friction force which acts counter to the sliding of an internal tube in an external tube of a steering column with motorised adjustment at least in terms of depth, the axial friction force being brought about by a pressure force which is applied against the internal tube by a blocking device for the internal tube in the external tube, comprising an actuator which is controlled by a control unit. In this method, basic parameters which represent a morphology, a position of a driver and a position of the steering column are acquired by the control unit during a basic phase and, when the vehicle exceeds a threshold speed, the control unit changes into the driving phase. During the driving phase, driving parameters which represent dynamic conditions of the vehicle in travel mode are acquired by the control unit, the control unit establishes the axial driving friction effort necessary to absorb the collision energy in accordance with the basic parameters and driving parameters and the control unit controls the actuator so that it supplies a clamping torque which can generate the axial driving friction effort.

Advantageously, parameters which represent characteristics of a vehicle and the steering column are pre-recorded in the control unit and/or during the collision, the control unit changes to the collision phase and the clamping torque defined by the control unit in the pre-collision phase is maintained.

Preferably, when a collision warning is activated, the control unit changes to the pre-collision phase, during which pre-collision parameters which represent dynamic conditions of the vehicle in travel mode just before a collision are acquired by the control unit, the control unit refines the calculation of the axial driving friction effort necessary to absorb the collision energy taking into consideration the pre-collision parameters and the control unit controls the actuator so that it corrects the clamping torque which is supplied by the actuator before the collision.

Advantageously, the control unit establishes the axial friction effort necessary to absorb the collision energy in accordance with the total available length of the continuous sliding path of the internal tube in the external tube.

Preferably, when the driver adjusts the steering column in terms of depth, the control unit changes into the adjustment phase, during which the control unit controls the actuator so that it supplies an adjustment clamping torque which can generate an axial friction effort which is either zero or less than the axial driving friction effort and which can allow sliding with a reduced resistance of the internal tube in the external tube. When the adjustment of the steering column is carried out, the control unit changes to the basic phase or driving phase in accordance with the speed of the vehicle.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the invention are set out by the following description of non-limiting embodiments of the different aspects of the invention.

The description makes reference to the appended Figures which are also given by way of non-limiting embodiments of the invention:

[Figure 1] Figure 1 illustrates a vehicle with a steering column, [Figure 2] Figure 2 is a perspective view of a steering column, [Figure 3] Figure 3 illustrates a block diagram in order to establish the effort which absorbs the collision energy and the clamping torque,

[Figure 4] Figure 4 is a cross section of a first embodiment of a steering column, [Figure 5] Figure 5 is a partial longitudinal section of a second embodiment of a steering column,

[Figure 6] Figure 6 is a cross section of a third embodiment of a steering column, [Figure 7] Figure 7 is a partial cross section of a fourth embodiment of a steering column. DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 shows a motor vehicle 1 which is provided with a steering column 2 according to one of the embodiments described below. The steering column 2 serves mainly to allow a driver to steer the vehicle 1 in a travel state by acting on a steering wheel 3. As illustrated in Figure 2, the steering column 1 is provided with different devices and mechanisms which allow additional functions which are expected in modern steering columns to be performed. These additional functions usually comprise the adjustment of the position of the steering wheel 3 relative to an instrument panel (not illustrated) by a depth adjustment device 4. After the driver has taken a seat in the vehicle 1, he/she actuates the depth adjustment device 4 in order to adapt the position of a steering wheel 3 to his/her morphology-

The steering column 2 is mechanically connected to the vehicle 1 by a cap 5 which is fixed to a structural portion (not illustrated) of the vehicle 1. The steering wheel 3 is mechanically connected to the steering column 2 by a steering wheel end piece 6 which is located at an upper end of the steering column 2. This steering wheel end piece is the extension of a steering shaft 7 which is guided in terms of rotation in an internal tube 8 in order to transmit the rotational movements imparted by the driver to the steering wheel 3 about a steering axis X. The steering column 2 is connected by its opposite end to the steering wheel end piece 6 to an interface such as a cardan transmission 9 which acts as a bevel gear in order to drive a steering rack 10. The internal tube 8 is received inside an external tube 11 so as to be able to slide axially in the external tube 11. The internal and external tubes 8 and 11 are arranged coaxially relative to the steering axis X. Thus, an adjustment of the steering wheel 3 in terms of depth is obtained particularly by sliding the internal tube 8 in the external tube 11 along an adjustment axis aligned with the steering axis X.

The adjustment of the steering wheel 3 in terms of depth can be carried out manually by the driver acting axially on the steering wheel 3. Nevertheless, nowadays, it is common for the adjustment of the steering wheel 3 in terms of depth to be carried out in a motorised manner as a result of the depth adjustment device 4 which actuates the translational movement of the internal tube 8. The depth ad- justment device 4 is driven by a first motor element, such as a first electric motor 12 as in this case, or any other type of actuator, such as an electric thrustor. The depth adjustment device 4 comprises a kinematic chain which converts the rotational movement of the first electric motor 12 into translational movement of the internal tube 8. The kinematic chain of the depth adjustment device 4 may be of the screw/nut type, as illustrated in Figure 2, or of the type involving a rack, toothed wheel and endless screw (not illustrated). Thus, the driver can actuate the first electric motor 12 in order to adjust the position of the steering wheel 3 between a stretched position, in which the external tube 8 is in its most retracted position relative to a normal movement direction of the vehicle V, and a compressed position, in which the steering wheel 3 is in the most advanced position relative to the normal movement direction of the vehicle V in a driving condition. This adjustment, which is known as comfort adjustment, allows adaptation of the position of the steering wheel 3 in accordance with the morphology of the driver and the driving context. The path of the comfort adjustment is typically between 40 mm and 60 mm. The kinematic chain of the depth adjustment device 4 is generally of the irreversible type so that the axial position of the steering column 2 is locked when the first electric motor 12 is no longer actuated.

The motor vehicles may have an autonomous driving mode in which the vehicle 1 is automatically directed without the driver acting on the steering wheel 3. In autonomous driving mode, the steering wheel 3 can thus be completely retracted in order to increase the space available in front of the driver. The steering wheel 3 can thus be retracted when the vehicle 1 is parked. In order to move into the retracted condition, the depth adjustment device 4 can be used to completely retract the steering wheel out of the zone in which it is located in a manual driving condition. To this end, the retraction path of the internal tube 3 in the external tube 4 must be substantially greater than the path generally used for the comfort adjustment. Typically, the retraction path of the steering wheel 3 is between 100 mm and 300 mm.

The vehicle 1 also comprises safety devices which allow the risks of injury to the driver to be limited in the event of an accident, such as a front-end collision. The safety standards nowadays impose the presence of a safety belt (not illustrated) which the driver must fasten under travel conditions of the vehicle 1 and one or more airbag(s) (not illustrated), including in particular an airbag installed in a hub 13 of the steering wheel 3 in order to protect the driver. These safety devices serve to absorb the energy transmitted by the body of the driver during the violent deceleration of the vehicle following the collision. Thus, the steering column 2 must be able to become compressed in the event of a front-end impact in order to absorb the residual collision energy, that is to say, the energy not absorbed by the safety belt and the airbag when the body of the driver which is projected towards the front of the vehicle strikes the steering wheel 3.

This residual collision energy is absorbed by an axial friction effort which acts counter to the sliding of the internal tube 8 in the external tube 11. The axial friction effort originates from a pressure force which is applied to the internal tube 8 transversely relative to the steering axis X by a clamping mechanism 14 which belongs to a blocking device 15 which is mechanically fixed to the lower portion of the external tube 11. The blocking device 15 further comprises an actuator in the form of a second electric motor 16, as shown in Figure 2. Other types of actuators, such as a solenoid or an electric thrustor, can be used. The clamping mechanism (14) comprises a drive mechanism which is coupled to the second electric motor (16) in order to drive at least one pressure element which applies a pressure force (P) to the internal tube (8). Different embodiments of the clamping mechanism are described below with reference to Figures 4 to 7.

The blocking device 15 is part of a blocking energy absorption system which also comprises a control unit UC which controls the second electric motor 16 in accordance with parameters which represent characteristics of the vehicle and the collision energy absorption system and which are pre-recorded in the control unit UC, and parameters which represent the morphology and the position of the driver and dynamic conditions of the vehicle until just before the collision. These last parameters are transmitted in the form of signals to the control unit UC by sensors which are distributed in the vehicle 1 and in the steering column 2.

The control unit UC mainly serves to estimate as precisely as possible the residual collision energy to be absorbed by the steering column 2 in order to control the second electric motor 16 so that it supplies an appropriate clamping torque under a travel condition of the vehicle 1 to the clamping mechanism 14 in order to bring about a friction effort capable of absorbing the residual collision energy while preventing the occurrence of an effort peak. This is because an effort peak is caused by the arrival at the travel end of the internal tube 8 in the external tube 11 or by the plastic deformation of a mechanical element during the sliding of the internal tube 8. Figure 3 shows a block diagram of the algorithm for controlling the second electric motor 16 by the control unit UC.

According to Figure 3, the control unit UC calculates in real time the setpoint corresponding to the clamping torque which the second electric motor 16 must supply in order to adapt continuously or in steps the friction effort which acts counter to the sliding of the internal tube 8 in the external tube 11. This control setpoint is calculated to be as similar as possible to what is necessary to absorb the collision energy transmitted to the steering wheel by the body of the driver during a front-end impact. To this end, the control unit UC processes information items which are pre-recorded in the control unit and which are received in real time from sensors which are distributed in the vehicle 1 as indicated in Figure 3.

In the upper portion thereof, the block diagram of Figure 3 shows three states of the system for absorbing collision energy from the installation in the steering wheel of the driver in the vehicle 1, corresponding to a basic phase followed by causing the vehicle 1 to move corresponding to a driving phase as far as the occurrence of a possible collision corresponding to a pre-collision phase. This succession of three phases is followed by a collision phase (not illustrated) if the collision really takes place. In this collision phase, the control unit UC no longer controls the second electric motor 16 and the pressure force on the internal tube 8 is maintained by the clamping mechanism 14 which is mechanically irreversible.

The basic phase corresponds to the acquisition of morphological information items of the driver (weight, height of seat, etc.) and his/her environment, such as the position of the driver’s seat, its inclination, the position of the steering wheel in terms of both depth and height which will determine the angle between the steering column and the movement of the body of the driver during the collision and the sliding path length of the internal tube available to continuously absorb the residual collision energy. Furthermore, the control unit will receive an information item which indicates whether the safety belt is fastened or not, which will allow a prediction of the proportion of the total collision energy which will have to be absorbed by the system for absorbing collision energy. These different information items are accessible in the form of basic parameters which originate from the on-board sensors. They are recorded in the control unit UC and are continuously updated. Other information items are processed during the basic phase, involving information items relating to the characteristics of the vehicle, the airbag, the safety belt, the steering column and the clamping mechanism. These information items are pre-recorded in the control unit UC in the form of unchanging basic parameters. Thus, during the basic phase, the control unit UC of the system for absorbing collision energy controls the second electric motor 16 so that it supplies a basic clamping torque to the clamping mechanism 14 so that a pressure force is applied to the internal tube 8 which allows the minimum absorption effort to be ensured on the basis of the (morphological and environmental) data available in this phase.

The driving phase is distinguished by taking into account the movement of the vehicle in order to improve the estimation of the collision energy to be absorbed in the event of a collision. In the driving mode, the steering column 2 is blocked in order to prevent the driver from moving the steering wheel 3 under the effect of a clamping torque which is at least equal to the basic clamping torque. During the driving phase, speed information items of the vehicle 1 are transmitted to the control unit UC in order to establish the level of energy to be absorbed in the event of a front-end collision. This level of energy is permanently re-adjusted continuously or in steps in accordance with the range of speed of the vehicle 1. The driving phase corresponds to a preparation phase which involves pre-positioning the clamping torque and therefore the level of axial friction effort to be as similar as possible to the optimum effort for a potential absorption of collision energy.

The pre-collision phase comprises detecting an imminent collision. The change from the driving phase to the pre-collision phase is triggered by receiving a collision warning. This information item is available from a number of passive safety functions, such as the predictive collision warning. During this brief phase, the system for absorbing collision energy acquires information items specific to the collision which is about to occur, such as the angle of impact, the deceleration of the vehicle and other useful information items. The calculation of the level of en- ergy to be absorbed is thus optimised and a correction is carried out to the clamping torque in order to obtain the level of axial friction force necessary to control the sliding of the internal tube 8 in the external tube 11 during the collision. This phase involves an optimisation of the pressure applied by the clamping mechanism 14 taking into consideration the information items supplied by the different sensors of the vehicle just before the collision.

Finally, during a collision phase (not illustrated), the control unit no longer actuates the second electric motor 16 and the clamping torque optimised during the pre-collision phase is maintained. Furthermore, the system records the context and the pressure levels applied during the collision.

Thus, the dissipation of the residual collision energy is ensured by a variable axial friction force between the internal tube 8 and the external tube 11 of the steering column 2 by means of a clamping mechanism 14 which is actuated by a second electric motor 16 and which ensures the maintenance of the friction effort in the event of the second electric motor 16 not being supplied with electrical power. The second electric motor 16 which is controlled by the control unit UC supplies a clamping torque in accordance with a precise estimation of the energy to be absorbed during a collision in accordance with the morphological knowledge of the driver, his/her driving conditions (safety belt, driver’s seat, position of steering wheel), the characteristics of the vehicle and also the dynamic characteristics of the vehicle under driving conditions and just before the collision.

The system for absorbing collision energy which allows the complete dissipation of the residual collision energy over the entire path of the steering column available so as to prevent an effort peak at the travel end and a high level of axial friction force over a short distance relative to the total path of the steering column 1 available. The total path of the steering column 1 available corresponds to the sliding path of the internal tube 8 in the external tube 11 and comprises the comfort adjustment path and retraction path of the steering wheel 5 without any mechanical element impeding the transition from one portion of the sliding path of the internal tube 8 to another. Different embodiments of the clamping mechanism 14 are described below on the basis of Figures 4 to 7.

Figure 4 shows a detailed view of the clamping mechanism 14 which is illustrated in Figure 2. In this clamping mechanism 14, the second electric motor 16 is coupled to a drive mechanism which comprises a first rocker bar 17 which is driven by a first endless screw 18 which is connected to a rotor axle of the second electric motor 16. The first rocker bar 17 in turn drives a first rack 19. The first rack 19 cooperates with two clamping pinions 20 which each belong to a first pressure mechanism 25 and which are each mechanically connected in terms of rotation to a first clamping screw 21. The first clamping screw 21 cooperates with a tapped hole 22 which is formed through the covering of the external tube 11 in order to convert the rotational movement of the pinion 20 into a translational movement along a clamping axis (Y) which is perpendicular to the adjustment axis (X) of a first pressure element 23 which is capable of applying a pressure force F perpendicularly to the steering axis X to the internal tube 8 by means of a friction runner 24. Thus, the second electric motor 16 supplies a clamping torque to the clamping mechanism 14 which converts it into a pressure force F on the internal tube 8 at each pressure element 23 via the kinematic chain described above. The pressure forces F together bring about an axial friction force which acts counter to the sliding of the internal tube 8 in the external tube 11. This pressure force is modulated by the intensity of the clamping torque supplied by the second motor 16 in accordance with the setpoint signal transmitted by the control unit UC. Furthermore, the magnitude of the axial friction force varies in accordance with the design choices of the clamping mechanism 14, that is to say, the selection of the equipment and the roughness of the friction runner 24, and the number of pressure elements 23. In the embodiment described here, the clamping mechanism 14 comprises two pressure mechanisms 25, but depending on the context there may be one or more than two of them. The pressure mechanism 25 may include a ball type device comprising at least one ball 26 which rolls on a notched track 27 which is formed on the opposite surfaces of the first pressure element 23 and the first clamping screw 21. The design of the kinematic chain of the clamping mechanism from the second motor 16 is mechanically irreversible per se using a wheel/endless screw and/or screw/nut type transmission or another system.

Alternatively to the embodiment of the clamping mechanism 14 described above, the first rocker bar 17 can be replaced by a second rocker bar (not illustrated) which is driven by the second electric motor 16 and which itself directly drives the two pinions 20, which allows the first rack 19 to be dispensed with. Similarly, the notched track 27, on which the ball 26 moves, can be arranged between opposite surfaces of the first rocker bar 17 or the second rocker bar and a cap (not illustrated) which covers at least the clamping mechanism 14.

Figure 5 illustrates an embodiment of the clamping mechanism 14 which is different from the one described above with reference to Figures 2 and 4. Only the differences between the two clamping mechanisms will be described. In the clamping mechanism 14 of Figure 5, the drive mechanism comprises the endless screw 18 which is connected to the second electric motor 16 and which cooperates with a second rack 28. The second rack is extended longitudinally by one or more ramps 29 which each act on the upper end of a second pressure element 30 in order to convert the axial translational movement of the rack 28 into a transverse translational movement of each second pressure element 30 along a clamping axis Y which is perpendicular to the adjustment axis (X). Thus, when the rack slides forwards or backwards under the effect of the clamping torque supplied by the second electric motor 16, the second pressure elements 30 increase or decrease the pressure forces F which they apply to the internal tube 8. Although not illustrated in Figure 5, friction runners can be interposed between each second pressure element 30 and the internal tube 8, as described above. Similarly, there may be one or more than two pressure elements 30 each associated with a ramp 29 in order each to apply a pressure force F to the internal tube 8.

Figure 6 illustrates an embodiment of the clamping mechanism 14 which is different from those described above. In this embodiment of the clamping mechanism 14, the second electric motor 16 rotates a second clamping screw 31 which belongs to the drive mechanism and which extends transversely relative to the lower portion of the external tube 11 along a clamping axis Y which is orthogonal and non-secant with respect to the steering axis X.

A slot 32 is provided parallel with the adjustment axis X through the covering of the external tube 11 and perpendicularly to the clamping axis Y. An axial plane P extends through the slot 32 and the steering axis X. A first threaded end 33 of the second clamping screw 31 cooperates with a tapped element 34 having an external cylindrical shape which extends perpendicularly to the clamping axis Y at one side of the axial plane P. The tapped element 34 is located in a cylindrical housing 35 which is provided in the covering of the external tube 11 at one side of the slot 32. The tapped element 34 thus forms a pivot connection between the second clamping screw 31 and the covering of the external tube 11 at one side of the slot 32.

The second clamping screw 31 is axially stopped by a first bearing (not illustrated) which is mechanically connected to the covering of the external tube 11 and which is located at the other side of the slot 32 relative to the tapped element 34. The first bearing acts as an axial stop for the second clamping screw 31 at least in the direction towards the tapped element 34 or in both directions.

The pressure elements are constituted by a first and a second clamping block 36 and 37 which are located on the internal portion of the external tube 11 at one side and the other of the axial plane P. The first and second clamping blocks 36 and 37 are arranged in housings which are provided in the covering of the external tube 11 at one side and the other of the slot 32. A third and a fourth clamping block 38 and 39 are located on the internal portion of the external tube 11. The third and fourth clamping blocks 38 and 39 project relative to the internal surface of the external tube 11. The third clamping block 38 is diametrically opposite the first clamping block 36 and the fourth clamping block 39 is diametrically opposite the second clamping block 37 so that the internal tube 8 is in contact with the four clamping blocks 36 to 37. Alternatively, instead of the third and fourth clamping blocks 38 and 39, a single additional clamping block can be located on the internal portion of the external tube 11 diametrically opposite the plane P. Instead of being fitted elements, the first and second clamping blocks 36 and 37 can be constructed so as to project from the internal surface of the external tube 11 similarly to the third and fourth clamping blocks 38 and 39.

When the second electric motor 16 is actuated in one direction, it rotates the second clamping screw 31 which is screwed into the tapped element 34, it thus moves together the two opposite edges of the slot 32. The deformation of the external tube 11 in the zone of the slot 32 allows the four clamping blocks 36 to 39 to be pressed against the internal tube 8, which blocks thereby apply pressure forces F to the internal tube 8, which brings about an axial friction force between the two internal and external tubes 8 and 11 which act counter to the sliding of the internal tube 8 in the external tube 11.

When the second electric motor 16 is actuated in the other direction, it rotates the second clamping screw 31 which is unscrewed in the tapped element 34, which serves to reduce the pressure forces F and therefore the axial friction forces between the internal tube 8 and the external tube 11.

The axial deviations of the second clamping screw 31 being relatively small during the screwing and unscrewing thereof, the pivot connection which is formed by the tapped element 34 having a cylindrical shape can be replaced by a hexagonal or square nut which is received in a cavity which has a complementary shape and which is formed in the covering of the external tube 11 in place of the cylindrical housing 35. Alternatively, the second clamping screw 31 can be screwed into a tapped hole which is formed directly in the covering of the external tube 11 in place of the cylindrical housing 35, which reduces the number of components of the device of the clamping mechanism 14 and allows the assembly thereof to be made easier.

Figure 7 illustrates an embodiment of the clamping mechanism 14 which is different from those described above. In this embodiment of the clamping mechanism 14, the second electric motor 16 rotates a third clamping screw 40 which belongs to the drive mechanism which is stopped axially by a second bearing 41 which is mechanically connected to the covering of the external tube 11 at the side of the second electric motor 16. The third clamping screw 40 has a first thread 42 at the end thereof opposite the one cooperating with the second bear- ing 41. The first thread 42 cooperates with a first tapped hole 43 which is formed in a first clamping runner 44. The first clamping runner 44 is mounted in a first groove 45 which is provided in the covering of the external tube 11 at one side of the axial plane P so as to be able to slide along the clamping axis Y perpendicularly to the axial plane P relative to the external tube 11.

A second clamping runner 46 is mounted in a second groove 47 which is provided in the covering of the external tube 11 at the other side of the axial plane P so as to be able to slide along the clamping axis Y transversely to the axial plane P relative to the external tube 11. The third clamping screw 40 has a second thread 48 which cooperates with a second tapped hole 49 which is formed in the second clamping runner 46. The pitch of the second thread 48 is counter to the pitch of the first thread 42 so that, when the third clamping screw 40 rotates, the first and second clamping runners 44 and 46 which constitute the pressure elements slide in opposite directions at one side and the other of the axial plane P.

When the second electric motor 16 is actuated in one direction, it rotates the third clamping screw 40 which, being stopped axially by the second bearing 41, drives the first and second clamping runners 44 and 46 which move towards the axial plane P. The movement together of the clamping runners 44 and 46 applies pressure forces F to the internal tube 11 which is thus clamped between, on the one hand, the first and second clamping runners 44 and 46 and, on the other hand, the third and fourth clamping blocks 38 and 39. The pressure forces F which are thus brought about on the internal tube 8 generate an axial friction force between the internal tube 8 and the external tube 11 which act counter to the sliding of the internal tube 8 in the external tube 11 under driving conditions.

When the second electric motor 16 is actuated in the other direction, it rotates the third clamping screw 40 which, being stopped axially by the second bearing 41, drives the first and second clamping runners 44 and 46 in opposite directions. Thus, they move away from the axial plane P, which releases the pressure forces F which are applied to the internal tube 11. Thus, the axial friction force which is applied between the two internal and external tubes 8 and 11 is reduced. Alternatively, a single clamping block, instead of two, can be located on the internal portion of the external tube 11 diametrically opposite the clamping runners 44 and 46. In this embodiment of the clamping mechanism 14, the slot 32 may be omitted because the clamping of the internal tube 8 is not obtained by deformation of the external tube 11.

The drive mechanism which connects the second electric motor 16 to the second or third clamping screw 31 and 40 is irreversible. It may be, for example, of the wheel and endless screw type. Thus, when the supply of the second electric motor 16 is interrupted, the pressure forces F are maintained on the internal tube 8.

The roughness and the material of the clamping blocks 36 to 39 and/or the clamping runners 44 and 46 is selected in order to increase or decrease the axial friction force brought about by the pressure forces F applied to the internal tube 8.

The second electric motor 16 can drive as many clamping mechanisms 14 as necessary, and they are arranged along the adjustment axis X in order to obtain a total axial friction force which is sufficient to absorb the collision energy.

On the one hand, a play or at least a weak axial friction force is necessary between the internal tube 8 and the external tube 11 in order to allow adjustment of the axial position of the steering wheel in depth adjustment mode or to allow it to be retracted in the retraction mode of the steering wheel 3 without excessive effort and therefore excessive electrical consumption for the first electric motor 12. On the other hand, under driving conditions, the internal tube 8 must be clamped in the external tube 11 in order to ensure a given stiffness of the steering column 2 in order to limit the deflections of the steering wheel 3. The system for absorbing collision energy described above can also be used in order to suppress the operational play and to ensure a minimum stiffness of the connection between the internal and external tubes 8 and 11 under driving conditions or to release the pressure applied between them in the depth adjustment mode or retraction mode of the steering wheel 3. In this configuration, the control unit UC controls the second electric motor 16 in order to reduce or eliminate the pressure forces F which are applied to the internal tube 8 in the depth adjustment mode or retraction mode. Furthermore, in the depth adjustment mode or retraction mode, the control unit UC also allows the activation of the first electric motor 12 which drives the depth adjustment device 4 and the activation of the second electric motor 16 which drives the clamping mechanism 14 to be synchronised.

Under driving conditions, the clamping mechanism 14 is thus in a clamped position. In order to move into a clamped position, the second electric motor 16 is actuated by the control unit UC and the clamping torque developed by the second electric motor 16 generates pressure forces F on the internal tube 8 inside the external tube 11, which increases the axial friction effort applied between the two tubes. Thus, the level of axial friction effort under driving conditions ensures a given stiffness of the steering column 1, which limits the untimely deflections of the steering wheel, and sufficient resistance to the sliding of the two tubes to absorb the collision energy as explained above.

Under depth adjustment or retraction conditions of the steering wheel 3, the clamping mechanism 14 is in an unclamped position. In order to move from the clamped position to the unclamped position, the second electric motor 16 is activated by the control unit UC in order to reduce the pressure forces F which are applied to the internal tube 8 inside the external tube 11, which reduces the axial friction effort which is applied between the two tubes. Thus, the level of axial friction effort which it is necessary to overcome in order to slide the internal tube 8 in the external tube 11 under adjustment or retraction conditions is zero or significantly less than the axial friction effort under driving conditions. Consequently, in order to adjust the axial position of the internal tube 8 relative to the external tube 11, the first electric motor 12 must develop a reduced power, which reduces the energy consumption of the depth adjustment device 4 and the size of the first electric motor 12. Furthermore, the depth adjustment may thus be carried out with improved noise performance levels and at a greater speed without increasing the energy consumption and the power of the first electric motor 12.

The control unit UC controls the second electric motor 16 in order to move the clamping mechanism 14 from the clamped position to the unclamped position before activating the first electric motor 12 in order to adjust the depth of the axial position of the steering wheel 3. Once the depth adjustment or retraction of the steering wheel 3 has been completed, the second electric motor 16 is activated in the opposite direction in order to move the clamping mechanism 14 from the unclamped position to the clamped position after the first electric motor 12 has been stopped.

The depth adjustment device 4 which moves the internal tube 8 in translation in the external tube 11 is of the mechanically irreversible type. In order to allow the internal tube 8 to slide in the external tube 11 in the event of a collision, it is necessary for at least one of the elements which constitute the kinematic chain which connects the first electric motor 12 to the internal tube 8 to be able to act as a mechanical breakable member (not illustrated). In the event of an axial impact on the steering wheel during a collision, the breakage or deformation of this breakable member thus releases the sliding of the internal tube 8.

The system for absorbing collision energy described above can completely replace the systems for absorbing collision energy by plastic deformation of the strap type. It is also possible to combine them in the steering column 2 so that, for example, the system for absorbing collision energy by an axial friction force allows the absorption of the collision energy corresponding to collisions with a low to moderate energy level, and so that the systems for absorbing collision energy by plastic deformation of the strap type (not illustrated) become operational in addition in the event of a collision with greater energy.

As indicated in the preceding description, the different aspects of the invention can be carried out depending on the context in configuration variants which are different from those described above. For example, the steering column 1 may have motorised adjustment or alternatively it may have manual adjustment. It may be fitted to any type of transport vehicle, such as vehicles for ground-based transport, whether for the transport of freight or passengers. Similarly, any type of motorised actuators, such as electric thrustors or solenoids, can be used in place of the clamping motor.