Abstract:
A pedal has a control device ( 2 ) including a mobile pedal ( 6 ), elements for returning ( 20, 22 ) the control device returning the pedal ( 6 ) in its idle position as well as a force-feedback mechanism ( 4 ) to produce a hard spot when the pedal ( 6 ) is depressed. The force-feedback mechanism ( 4 ) includes an electric motor ( 28 ) designed to act on the control device ( 2 ), via one-way linking elements ( 36 ) and gear reduction elements, in the same direction as the return elements ( 20, 22 ). The one-way link prevents any action of the force-feedback mechanism ( 4 ) on the control device ( 3 ) in the direction opposite to the direction of action of the return elements ( 20, 22 ) The one-way link advantageously includes a clearance which enables the electric motor ( 28 ) to rotate in the direction allowing it to act on the control device ( 2 ) without acting immediately on the device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This is the 35 USC 371 National Stage of International Application PCT/EP02/13612 filed on 2 Dec. 2002, which designated the United States of America. 
   FIELD OF THE INVENTION 
   The present invention relates to an immediate thrust return pedal. 
   BACKGROUND OF THE INVENTION 
   A thrust return pedal is used in the field of driving assistance for a motor vehicle and therefore serves as an interface between the vehicle and its driver. 
   This type of pedal is for example used in the field of speed regulation. There are regulators which automatically manage the speed of the vehicle. It therefore suffices to select a cruising speed and an electronic management system ensures that the vehicle is kept at this speed. Speed regulation can also be carried out by creating a hard point during the depression of the accelerator pedal. When the set speed is then reached, the driver feels a hard point in this pedal and he thus knows that the set speed has been reached. 
   The thrust return pedal acts in this case like a luminous or audible alarm which warns the driver. The driver is then free to take note or not to take note of this alarm. This type of information means has the advantage of being perceived only by the driver and not by the other passengers. 
   The document FR 2 685 667 discloses a thrust return pedal. In the disclosed device, a servomotor controlled by an electronic unit acts on the pedal by modifying a return force which depends on the interval between the actual speed and the set limit speed value. The mechanism described is such that when the set speed has been reached the mechanism causes the pedal to gradually harden. The stiffness of the thrust return mechanism varies progressively and it is found that the hard point takes effect slowly. Because of this, the feeling created in the driver&#39;s foot is not very pleasant. 
   The mechanism described in this document acts by only varying the stiffness of the pedal return mechanism. In particular, it does not allow instantaneous control of the thrust to be applied to the pedal nor does it allow rapid vibrations to be produced in the pedal. Moreover, in the event that the thrust return mechanism should malfunction, it may arise that the return force with the maximum stiffness is then applied continuously to the pedal. This does not affect the safety of the vehicle but it is uncomfortable. 
   Finally, the mechanism described has a relatively large overall size such that it cannot be integrated into a pedal module as currently fitted to many motor vehicles. 
   SUMMARY OF THE INVENTION 
   It is thus an aim of the present invention to provide a thrust return pedal in which the thrust applied to the pedal is immediate and well controlled. Advantageously, the occurrence of a hard point will be immediate when the conditions for establishing this hard point have been produced. Preferably, this pedal will additionally make it possible to vary the point of application of the hard point and also the amplitude of this hard point. In one embodiment, it will be advantageous for an alert message, in the form, for example, of a vibration of the pedal, to be able to be transmitted to the driver. 
   To this end it proposes a thrust return pedal comprising a control device having a control member that moves between a raised position of rest and a position of maximum depression, return means of the control device returning the control member to its position of rest, and a thrust return mechanism designed to create a hard point during the depression of the control member. 
   According to the invention, the thrust return mechanism comprises an electric motor intended to act on the control device, by the intermediary of unidirectional connection means and possibly also reduction means, in the same direction as the return means of the control device, the unidirectional connection prohibiting any action of the thrust return mechanism on the control device in the direction opposite to the direction of action of the return means. 
   In this new design, the electric motor does not just carry out an adjustment allowing the stiffness of a control member to be adjusted but also exerts a force transmitted directly, or by the intermediary of a reduction, to this control member. This allows better control of the action applied to this control member. The thrust return pedal according to the invention thus makes it possible to have a hard point present at a predetermined (fixed or variable) position of the travel of the control device and not a hard point which is established when the control device reaches a predetermined position. With a device according to the invention, it is possible for each position of the control member to be assigned a force, which is variable over time, to be applied to this member to keep it in this position according to a predetermined law that can vary over time. The variation of this force to be applied is obtained by managing the value of the current feeding the electric motor. In this way, the amplitude of the hard point may be adapted by the motor which acts on the control device. 
   In a preferred embodiment, the unidirectional connection has a flexibility which makes it possible, according to the relative position of the control device and of the thrust return mechanism, to depress the control member as far as the hard point without transmitting thrust to the thrust return mechanism. Because of this flexibility, the control device and the thrust return mechanism may work independently of one another as long as the connection is free, that is to say where no thrust is transmitted from the thrust return mechanism to the control device (or vice versa). By contrast, when the connection is blocked, the user who depresses the control member does so against the force supplied by the electric motor of the thrust return mechanism or else this mechanism acts to raise the control member. 
   To make it possible to have a hard point whose position is variable during the depression of the control member, the electric motor advantageously allows adjustment of the position of a connection member and the unidirectional connection means are arranged between this connection member and the control device. In this embodiment, the connection member is, for example, a spindle whose angular position is adjusted by the electric motor. 
   Several means of different type may be used to produce the unidirectional connection. A first embodiment of such a connection employs, for example, a free wheel which rotates freely in one direction, without transmission of force, and in engagement in the other direction when a catch has been reached. Several other means may be employed here. In a preferred embodiment, the unidirectional connection is produced by a flexible link. This is, for example, a cable or a strip of flexible material. 
   A cable-type reduction is preferably provided between the electric motor and the connection member. In this way, when the unidirectional connection is engaged, the forces transmitted by a user on the control device are retransmitted to the motor with a lesser torque. Tests also demonstrated that this reduction made it possible to reduce the unwanted variations in the torque of the electric motor which are transmitted to the control member, this being more pleasant for the user. 
   In an embodiment which is well suited to a thrust return pedal according to the invention, the control device comprises a control pedal acting by the intermediary of a connecting rod on a part which pivots about an axis, the return means act on this pivoting part and this pivoting part is connected to the unidirectional connection means. In this case, the unidirectional connection means advantageously consist of a flexible strip of which one end is fixed tangentially to the pivoting part such that the strip winds flat around the pivoting part when the control member has been depressed. In this precise embodiment, when the electric motor then acts on a connection member in the form of a spindle in order to position it angularly this connection member is advantageously mounted parallel with the pivoting part and faces it, the pivoting part pivots by less than 180° about its axis and the flexible strip is advantageously fastened to the pivoting part in a peripheral zone of the pivoting part still situated facing away from the connection member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The details and advantages of the present invention will become more apparent from the following description, given with reference to the appended diagrammatic drawing in which: 
       FIG. 1  is a perspective view of a thrust return pedal according to the invention, 
       FIG. 2  is a side view of the device shown in  FIG. 1 , 
       FIG. 3  is a cross-sectional view along the line III-III of  FIG. 2 , 
       FIG. 4  is a perspective view on a bigger scale of a detail of a cable and pulleys transmission system, 
       FIG. 5  is a response curve of a conventional pedal without thrust return, and 
       FIG. 6  is a response curve of the thrust return pedal shown in  FIGS. 1 to 3 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The thrust return pedal shown in the drawing comprises, on the one hand, an actuating mechanism  2 , hereafter also referred to as a control device, and, on the other hand, a thrust return mechanism  4 . These two mechanisms are connected by a unidirectional connection described below and are both mounted on the same support. 
   The actuating mechanism  2  is a mechanism known to those skilled in the art. Such mechanisms are mounted in series on many motor vehicles. 
   The control device shown in the drawing comprises a control pedal  6  mounted such that it pivots about a spindle  8 . At its end opposite to that of the spindle  8 , the pedal is connected by the intermediary of a ball joint to a connecting rod  10  in order to act on a ring  12  mounted such that it pivots about a fixed spindle  14 . The connection between the connecting rod  10  and the ring  12  is also made by means of a ball joint articulated at the end of an arm  16  integral with the ring  12 . By means of this connection, when the control pedal  6  pivots about the spindle  8 , it induces a rotation of the ring  12  about its fixed spindle  14 . A Hall effect position sensor  18  is mounted on the fixed spindle  14  and measures the position of the ring  12  with respect to that fixed spindle  14 . 
   Two return springs  20  act on the ring  12  in order to bring the latter back to the position of rest, corresponding to the position assumed by the actuating mechanism when no thrust is applied to the control pedal  6 . The return springs  20  act on the ring  12  by the intermediary of cables  22  fixed to the ring  12  at one of their ends, each of the other ends being fixed to a return spring  20 . Each return spring  20  is furthermore attached to a fixed point of the support of the thrust return pedal. In the drawing, the return springs act on the ring  12  and tend to make the latter rotate in the clockwise direction (seen in the same direction as in  FIG. 2 ). 
   The position of rest of the control pedal  6  is defined ( FIG. 2 ) by a hook  24  fixed under the control pedal  6  and cooperating with a fixed stop  26 . As the connections between the ring  12  and the control pedal  6  are ball joints, the forces applied by the cables  22  and the springs  20  to the ring  12  are retransmitted to the control pedal  6  and vice-versa (apart from the slight friction losses of the ball joints). 
   The actuating mechanism such as described above corresponds to a conventional mechanism. The driver of the corresponding motor vehicle acts on the control pedal  6 . In the rest of the description it is considered that this control pedal is an accelerator pedal. Depending on the power that the engine must deliver, the driver depresses the control pedal  6  to a greater or lesser degree. The position sensor  18  makes it possible to know exactly the position of this control pedal  6  and its depression. This information is then supplied to an engine management device and is used for regulating, for example, the angle of opening of a fresh air inlet butterfly valve. 
   The thrust return mechanism  4  comprises an electric motor  28  used for adjusting the position of a pivoting spindle  30 . The latter is parallel with the fixed spindle  14 . Each of these spindles  14 ,  30  carries a pulley,  32  and  34  respectively, the two pulleys facing each other. The pulley  32  mounted on the fixed spindle  14  is integral with the ring  12  whilst the pulley  34  forms only a single part with the pivoting spindle  30 . The two pulleys  32  and  34  are connected to each other by a flexible strip  36  made, for example, from steel (foil) or from a composite material. 
   The strip  36  is fixed to the pulley  32  in such a way that, whatever the direction of rotation of the pulley  34  may be, the strip  36  can act on the ring  12  only in the direction of return of the control pedal  6  towards its position of rest. In the embodiment shown in the drawing, the ring  12  and therefore also the associated pulley  32 , have an angular travel of the order of 60°, that is to say much less than 180°. In this case, there is a zone of the pulley  32  which never faces the pulley  34  and is always facing away from it. The flexible strip  36  therefore becomes fixed on such a zone tangentially to the pulley  32 . When the ring  12  pivots following a depression of the control pedal  6 , the flexible strip  36  winds flatly over a part of the periphery of the pulley  32 , without forming folds. This flexible strip  36  is fixed in a similar way to the pulley  34 . However, as the amplitude of the movement of this pulley  34  can be greater than 180°, the attachment zone of the flexible strip  36  is not necessarily facing away from the pulley  32 . The thrust return pedal management device will ensure that the motor  28  drives the movement of the pulley  34  in such a way that the flexible strip  36  winds around the pulley  34  without forming folds. 
   The motor  28  acts on the pivoting spindle  30  by the intermediary of a reduction unit. For reasons of size, the axis of the motor  28  is not mounted parallel with but perpendicular to the axis of the pivoting spindle  30 . Two stages of reduction are provided between the motor  28  and the pivoting spindle  30 . 
   The electric motor  28  comprises an output shaft  38  integral with a pulley  40  of small diameter. A metal cable connects this pulley  40  to a pulley of large diameter  42 . The latter is mounted such that it pivots on an intermediate spindle  44 , parallel with the pivoting spindle  30  and the fixed spindle  14 . Return pulleys  46  are provided for the cable  48  connecting the pulleys  40  and  42 . 
   The intermediate spindle  44  also carries a pulley  50  of small diameter cooperating, by the intermediary of a cable  52 , with a pulley of large diameter  54 . This latter pulley is integral with the pivoting spindle  30 . 
   Each cable  48 ,  52  corresponds to a reduction stage. Such a stage is shown in  FIG. 4 . It is the stage that makes use of the cable  52 . 
   The pulley  54  consists of two half-pulleys  54   a  and  54   b . These two half-pulleys are of identical diameter and are mounted coaxially on the pivoting spindle  30 . A spring  56  acting torsionally connects the two half-pulleys  54   a  and  54   b.    
   Each end of the cable  52  is provided with a stop ball  58  and each half-pulley  54   a  and  54   b  is equipped with a corresponding recess  60  intended to receive a stop ball  58 . Thus, one end of the cable  52  is fixed to the half-pulley  54   a  by the intermediary of a stop ball  58  and the corresponding recess  60 . The cable then winds over a part of the periphery of that half-pulley  54   a  and is then wound by several turns around the pulley of small diameter  50  and is finally wound around a part of the periphery of the second half-pulley  54   b , the other end of the cable  52  being fixed to this half-pulley  54   b  by the intermediary of the second stop ball  58  and of the corresponding recess  60 . Because of the spring  56  and the degree of freedom of rotation between the two half-pulleys  54   a  and  54   b , the cable  52  is always tensioned. 
   It will be noted on  FIG. 4  that the cable  52  comprises a third stop ball  62 . The latter is placed for example at mid-length on the cable  52 . It takes its place in a corresponding recess  64  formed in the pulley  50 . In this way, no slipping can impede the transmission of the movement of the motor  28  from the pulley  50  to the pulley  54  or, more precisely, the half-pulley  54   a.    
   The transmission between the pulley  40  and the pulley  42  is carried out in the same way. As already mentioned above, in this transmission there are return pulleys  46  which, apart from the change of orientation, do not change the kinematics of the mechanism in any way. Another minor difference is that the cable  48  is not provided with a stop ball at its center. Such a ball and a corresponding recess could of course be provided but they are optional considering the slight forces applied to the cable  48  and therefore the very low risk of slipping of this cable around the pulley  40 . 
   The position of the pivoting spindle  30  is measured by means of a potentiometer  66 . The information provided by this potentiometer  66  makes it possible to know exactly the angular position of the pivoting spindle  30  and therefore of the pulley  34  also. This information, combined with that given by the Hall effect sensor  18 , makes it possible to know the play present in the flexible strip  36 . 
   The functioning of the thrust return pedal described above with reference to  FIGS. 1 to 4  is therefore as follows. 
   This thrust return pedal can firstly function like a conventional pedal. It is assumed here that it is an accelerator pedal. It therefore suffices to position the pivoting spindle  30  in a position such that, whatever the position of the ring  12  and therefore of the pulley  32  may be, the flexible strip  36  is never tensioned. It therefore suffices to provide a flexible strip  36  of sufficient length. This length is calculated according to the distance separating the fixed spindle  14  and the pivoting spindle  30 , the diameters of the pulleys  32  and  34  and also the positions of attachment of the flexible strip  36  on these pulleys. 
   The behavior of the control pedal  6 , not equipped with a thrust return mechanism, is represented diagrammatically in  FIG. 5 . In this figure, the angle of depression A of the pedal which corresponds to the position of the control pedal  6  with respect to its spindle  8 , a position directly proportional to the angle of rotation of the ring  12 , is plotted along the horizontal axis. The force F applied by a driver&#39;s foot on the control pedal  6  is plotted along the vertical axis. In the curve seen in this  FIG. 5  it appears that the force to be applied in order to actuate the control pedal  6  must initially (see reference  80 ) overcome the return force of the springs  20 , intended to return said pedal to its position of rest, and then the law follows a linear form (see reference  82 ). When the control pedal  6  is released, the return to the position of rest also follows a linear law (see reference  84 ). The curve seen in  FIG. 5  shows a hysteresis of the control pedal  6  due, in particular, to the friction produced between the cables  22  and the ring  12 . This behavior is sought in order to increase the comfort and ergonomics of this control pedal  6 . 
   When it is desired that the driver should feel a hard point during the depression of the pedal, the electric motor  28  is operated and the flexible strip  36  is tensioned in such a way that when the control pedal  6  arrives at the position where the hard point must appear, the flexible strip  36  is then tensioned. When the control pedal  6  therefore arrives in the position where the flexible strip  36  is just tensioned, in order to continue to depress the control pedal  6  it is necessary, on the one hand, to continue to overcome the return force of the springs  20  and, on the other hand, to cause the pivoting spindle  30  to pivot against the force applied to this spindle by the motor  28 , which acts by the intermediary of the reduction means described above. 
   A diagrammatic representation of behavior can again be seen in  FIG. 6 . In this figure, the behavior of a conventional pedal without thrust return such as shown in  FIG. 5  has been plotted as a reminder. The new curve reveals the presence of a hard point for an angle of depression α of the control pedal  6 . This hard point is represented on the curve by quasi-vertical portions  86  of the curve. 
   Beyond the hard point, the behavioral law follows a conventional linear form with the presence of hysteresis (see reference  88 ). 
   It is noted that the hard point appears without transition. The stiffness felt by the driver varies suddenly. In fact, in this case the thrust return mechanism works independently of the actuating mechanism. If the instruction given is to form a hard point when the angle of depression of the control pedal  6  is equal to α, the electric motor  28  acts consequently in order to position the pivoting spindle  30  correctly. This adjustment is carried out as soon as the instruction value is known and it is carried out before the control pedal  6  reaches the corresponding position. The thrust return is therefore present when the control pedal  6  reaches the specified position and is not established solely when the control pedal reaches this position. 
   Once the flexible strip  36  is tensioned, by varying the value of the current feeding the electric motor  28 , it is possible to vary the amplitude of the hard point. These different amplitudes are represented diagrammatically in  FIG. 6  by dotted lines (depression of the pedal  6 ) and by dotted and dashed lines (release of the pedal  6 ). It is thus possible to create a hard point that can be overcome easily or a hard point that is difficult to overcome by the driver. This makes it possible to provide the driver with different kinds of information. 
   The thrust return mechanism according to the invention also makes it possible to make the driver feel vibrations in his foot, via the control pedal  6 . In order to do this it suffices to supply the electric motor  28  with current in an alternating manner. An additional means is thus available for providing the driver with information. 
   In an extreme case, it is even possible to imagine that the motor applies to the pivoting spindle  30 , and therefore to the flexible strip  36  and the ring  12 , sufficient force to bring the control pedal  6  back to its position of rest. This can for example be envisaged in cooperation with a safety device, for example detecting the driver falling asleep or other parameters. 
   It is noted that if, for one reason or another, the thrust return mechanism should fail, it would not in any case cause the control pedal  6  to be locked and it always allows the latter to be returned to its position of rest. 
   For the exceptional case in which a large force would be applied to the control pedal  6  whilst the flexible strip  36  is tensioned, in order not to transmit this large force to the electric motor  28  and to protect the latter, a declutching device  68  is provided between the pivoting spindle  30  and the electric motor  28 . This declutching device  68  is for example disposed between the pivoting spindle  30  and the pulley  54 . It is thus guaranteed that no torque greater than a predetermined torque can be transmitted to the electric motor  28 . 
   In the thrust return pedal described above, the electric motor acts directly on the control pedal  6 . Because of the original transmission by cables and pulleys used here, the electric motor supplies minimum force (reduced friction) and can be chosen from a range of small-sized motors whose cost is advantageously relatively low. Another transmission mode, for example by gears, would necessitate a more voluminous and more costly motor. The reduction is of course chosen such that the pressing force of the driver&#39;s foot on the control pedal  6 , even when the driver decides to disregard the warning given by the thrust return mechanism, will not generate excess current in the motor and thus will not risk damaging it. 
   The unidirectional connection, achieved here by the flexible strip  36 , between the thrust return mechanism and the control pedal actuating mechanism, allows the return springs  20  to act freely on the control pedal, independently of the thrust return mechanism. This guarantees, firstly, that only the depression of the control pedal beyond the hard point is mechanically braked, whereas the return to the position of rest is free of any braking, the flexible strip not opposing the working of the return springs. This total decoupling between the thrust return mechanism and the control pedal actuating mechanism allows great flexibility in the (electronic) management of the thrust return pedal according to the invention. 
   The thrust return pedal such as described above can be embodied in the form of a module that is simply screwed and connected at the place allocated for the accelerator pedal in a motor vehicle. This device can be sufficiently compact so as not to obstruct the adjacent brake control pedal. 
   This pedal also has the advantage that one and the same device makes it possible to have very variable behavioral laws: position of the hard point over the whole range of depression of the control pedal, amplitude of the hard point, sending of vibration to the control pedal, etc. 
   The present invention is not limited to the embodiment described above by way of non-limiting example. It also relates to all of the variant embodiments within the capabilities of those skilled in the art covered by the following claims. 
   Thus, the invention has a main application related to the accelerator pedals of motor vehicles. However, other applications can be envisaged: control lever for any type of machine, industrial or domestic, game joystick, etc. 
   The number of reduction stages is two in the example described above. A single stage or, on the contrary, several stages, can also be envisaged. 
   The flexible strip producing a unidirectional connection between the pedal actuating mechanism and the thrust return mechanism could be replaced for example by a free wheel. 
   The tension of the slack length in each reduction stage could be achieved in a different manner than by using, as described above, split pulleys incorporating a tension spring.