Abstract:
An overriding drive for an overriding steering system, wherein a steering angle inputted by the driver can be overridden by another angle by a control according to correcting variables and the transmission ratio can be modified, and which is characterized in that the overriding drive is locked electromechanically in dependence on further correcting variables representative of an operating state of the vehicle.

Description:
TECHNICAL FIELD 
   The present invention relates to a locking device and an overriding drive for an overriding steering system, wherein a steering angle inputted by the driver can be overridden by another angle by means of a control according to correcting variables. 
   BACKGROUND OF THE INVENTION 
   Up-to-date motor vehicles, in particular passenger vehicles, are generally equipped with hydraulic or electrohydraulic servo steering systems, wherein a steering wheel is forcibly coupled mechanically to the steerable vehicle wheels. The power assistance is so configured that actuators, e.g. hydraulic cylinders, are arranged in the mid-area of the steering mechanism. A force generated by means of the actuators assists the actuation of the steering mechanism in response to the rotation of the steering wheel. This arrangement reduces the force the driver has to exert during the steering maneuver. 
   Overriding steering systems are disclosed in DE 101 59 800 A1 and DE 101 59 700 A1, the contents of which are part of the application and on which the application is based. Said overriding steering systems are characterized in that it is possible for an actuator to superimpose another angle, if required, on the steering angle inputted by the driver. The additional angle is defined by a controller and used to enhance the stability and agility of the vehicle. It is also feasible to compensate disturbances and to realize the gradient wheel steering angle by way of the steering wheel angle as a function of the driving speed of the vehicle. Hydraulic or electric actuators are used. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the invention is to provide an overriding drive or a locking device, wherein the driver can apply a steering angle to the wheels of the vehicle when the electronics or the energy supply fails. 
   According to the invention, this object is achieved in that the overriding drive is locked electromechanically in dependence on further correcting variables representative of an operating state of the vehicle. In the overriding drive, a superposition with another angle allows additionally or simultaneously changing the transmission ratio in a favorable way. The overriding drive of the overriding steering system according to the invention in particular enables a safe and comfortable operation. 
   It is advantageous that quantities such as ignition on/off, engine rotational speed and like factors are monitored to detect the operating state, and that the quantities are analyzed for detecting whether the engine is or is not switched off or an energy supply is or is not safeguarded, respectively. The plausibility of the motor&#39;s position and of the sensor signals is monitored to enhance the reliability in operation. 
   In a favorable embodiment, the overriding drive includes a freewheeling mechanism, which is lockable in operative and/or positive engagement. 
   The activation of the locking is preferably switchable and, in an especially preferred fashion, it takes place simultaneously for the operative and positive locking. 
   In another favorable design, the operative locking is provided by at least one first clamping member, preferably by three to nine clamping members, being brought into frictional contact with an inner ring of the freewheeling mechanism by way of a radial actuation, while the positive locking is provided by at least one second clamping member, preferably by three to nine clamping members, being brought into a form-fit contact with the inner ring of the freewheeling mechanism by way of a radial actuation. 
   In addition, it is favorable that a first actuating ring is associated with the freewheeling mechanism for the positive connection and a second actuating ring is associated therewith for the frictional connection, said rings being entrained with the clamping members upon radial actuation thereof so that rotation of the inner ring is prevented by means of a clamping contour at an outer ring of the freewheeling mechanism. Favorably, a defined angle, i.e. twisting angle, is allowed due to the frictional connection before a positive connection develops. 
   The object of the invention is also achieved by way of a locking device that is preferably provided for an overriding drive of the type described hereinabove and characterized by the provision of a freewheeling mechanism, which is operatively and/or positively lockable. 
   The activation of the locking is preferably switchable and, in an especially preferred fashion, it takes place simultaneously for the operative and positive locking. 
   In a favorable design, the operative locking is provided by at least one first clamping member, preferably by three to nine clamping members, being brought into frictional contact with an inner ring of the freewheeling mechanism by way of a radial actuation, while the positive locking is provided by at least one second clamping member, preferably by three to nine clamping members, being brought into a form-fit contact with the inner ring of the freewheeling mechanism by way of a radial actuation. 
   Preferably, the first clamping member is elastically arranged and permits a defined angle, i.e. twisting angle. 
   It is arranged for by the invention that a first actuating ring is associated with the freewheeling mechanism for the operative or frictional connection and a second actuating ring is associated therewith for the positive connection, said rings being entrained with the clamping members upon radial actuation thereof so that rotation of the inner ring is prevented by means of a clamping contour at an outer ring of the freewheeling mechanism. 
   Advantageously, it is provided that locking is effected by an electromechanical transducer that includes a first actuating element for the operative or frictional connection and a second actuating element for the positive connection, said actuating elements acting on the clamping members and being moved by an electromagnetically operable armature in opposition to a spring force for the purpose of locking or unlocking the freewheeling mechanism. This design according to the invention renders it possible to safely fix or lock an element that shall be locked by using very low adjusting and retaining forces and, thus, only low (electrical) energy. The result is that only a small mounting space is required. 
   According to the invention, the freewheeling mechanism has a stepped contour so that the inner ring is initially retained by means of a frictional connection. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, 
       FIG. 1  is a schematic general overview of the overriding steering system of the invention. 
       FIG. 2  is a schematic view of a planetary gear with a freewheeling mechanism and a locking device according to the invention. 
       FIG. 3  is a view of the freewheeling mechanism with locking device. 
       FIG. 4  is a perspective view of the freewheeling mechanism. 
       FIG. 5  is a top view of a section of the freewheeling mechanism with locking device. 
       FIG. 6  is a first section of the freewheeling mechanism with locking device. 
       FIG. 7  is a second section of the freewheeling mechanism with locking device. 
       FIG. 8  is a side view of a section of the freewheeling mechanism. 
       FIG. 9  is a section of the freewheeling mechanism with locking device in the de-energized condition. 
       FIG. 10  is a section of the freewheeling mechanism with locking device in the energized condition. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The overriding steering system shown in  FIG. 1  includes a hand steering wheel  50  that is connected to a steering rod  53  by way of a steering column  51 , into which an overriding drive  6  is inserted, and by way of a steering gear  52 . Displacement of the steering rod  53  permits turning of the wheels  54 ,  55 . Turning of the wheels  54 ,  55  is assisted by means of a hydraulic unit  56  and by a corresponding control of the hydraulic pressure by means of a valve unit  57 . A pump  58  generates the pressure. 
   The function of an overriding drive  6  in the overriding steering system shown in  FIG. 1  involves adjusting an overriding angle  12  irrespective of the driver through a control by means of correcting variables which can be produced e.g. by a driving dynamics system (ESP controller). To this end, a planetary gearing with two sun wheels and three step planet pinions as described in DE 101 59 8000 A1 or DE 101 59 700 A1 is used. The step planet pinions are mounted in a satellite carrier (cage) . However, the invention is expressly not limited to a planetary gearing as overriding drive  6 . Thus, all other pick-off gears known in the art may be used as well. 
   The transmission ratio of the vehicle steering system is composed of the transmission ratio of the steering gear and the overriding drive. Where the objective is to modify the transmission ratio to a defined transmission ratio, it is necessary to additionally drive a component of the overriding drive. Said driving is carried out by way of an electric motor (E-Motor)  8 , whereby the variation of the transmission ratio is possible in a wide range. 
   The motor  8  can be coupled to the gear  6 , thus, to the planet cage in the case of a planetary gearing, by means of a self-locking gear (worm gear or helical gear) or a non self-locking gear (drawing means gearing or toothed gearing) Preferably, however, a drawing means gearing, in particular a belt drive, is used. 
   To realize a fixed transmission ratio in operating states when the motor  8  is switched off, it is absolutely necessary to fix the overriding drive  6 . To this end, the cage is prevented from turning in a planetary gearing. This is possible by means of locking of the gear components to be locked, meaning the cage in a planetary gearing, e.g. in relation to a stationary housing, while a first gear shaft (gear input shaft)  7  is directly connected to a second gear shaft (gear output shaft)  9  by transmission means, especially through the planets of the gear. It is provided in the invention that the cage of the planetary gearing is positively and operatively lockable in dependence on the operating states. 
     FIG. 2  schematically shows the locking device with a freewheeling mechanism and a planetary gearing as an overriding drive in more detail. 
   The locking device  1  includes an electromechanical actuating unit  3  and a positive and operative freewheeling mechanism  2 . The locking device  1  is coupled positively to the gear housing  5  by way of a clutch  13 . Preferably, the locking device  1  is herein used in an electromechanical overriding steering system (ESAS) ( 4 ) for motor vehicles. Other ranges of application with similar safety-relevant requirements are also feasible for the locking device  1 . 
   In the above-mentioned application, the gear housing  5  of the overriding drive  6  is locked by way of the locking device  1  in the non-activated condition or in the case of a fault. Thus, a throughgrip of the two gear shafts  7 ,  9  is effected by way of the planetary gearing  10  with a transmission ratio iG  11  in a range of roughly 1:1.0 to roughly 1:1.2, preferably 1:1.1 or 1:1.2. The overriding steering angle  12  is locked then. 
   The freewheeling mechanism  2  and the adjacent components of the locking device  1  are illustrated in  FIGS. 3 to 8  in more detail. The locking device  1  of the invention is a functionally relevant component. In the de-energized condition of the electromechanical actuating unit  3 , the freewheeling mechanism  2  is locked by way of the one operatively connected freewheeling mechanism  14  and a positively connected freewheeling mechanism  15 . 
   Said freewheeling mechanism  2  generally includes an outer ring  16 , an actuation throughgrip  17 , an immovable bearing  18 , a movable bearing  19 , a clamping member  20  for a frictional connection, a clamping member  21  for a positive connection, an actuating ring  22  for the frictional connection, an actuating ring  23  for the positive connection, a spring element  24 , and an inner ring  25 . 
   When the clamping members  20 ,  21  are actuated radially by means of an actuating force  26  in opposition to the spring force  27  induced by the spring elements  24 , the clamping members  20 ,  21  will get into contact with the rotating or immovable inner ring  25  in frictional and positive connection (see  FIGS. 6 and 7 ). The frictional and positive connection causes entrainment of the two actuating rings  22 ,  23  by way of the spring force  27  and the positive connection  28  and operative connection with the clamping members  20 ,  21 . The result is that the clamping members  20 ,  21  are clamped between the outer ring  16  and the inner ring  25  by means of the clamping contour  29  provided in the outer ring  16 , and block further rotation  30  of the inner ring  25  on both sides. 
   When the actuating force  26  is released again, the acting spring force  27  will produce a restoring torque  31  at the actuating rings  21 ,  22 , and the clamping members  20 ,  21  are reset to their zero position  32  when the rotation  30  is reversed. The resetting torque of the actuating rings  22 ,  23  produced by the spring elements  24  is increased in the zero position  32  due to a special contour  33  of the clamping contour  29 . The embodiment illustrated in  FIGS. 2 to 8  provides a high degree of functionality of the freewheeling mechanism  2  and ensures safe unlocking in the non-actuated condition. The actuating unit  3  of the locking device  1  is shown in detail in  FIGS. 9 and 10 . The purpose of said unit is to ensure safe locking of the freewheeling mechanism  2  by means of a positive and frictional connection. The actuating unit  3  is substantially composed of an electromechanical transducer  34 , an armature  35 , an actuating element  36  for a frictional connection, an actuating element  37  for a positive connection, a compression spring  38 , and an armature spring  39 . 
   In the energized condition (see  FIG. 10 ), the armature  35  is attracted by means of the electromechanical transducer  34  in opposition to an integrated spring element  39  and maintains the two actuating elements  36 ,  37  in their unlocking position  41  by means of an integrated stop  40 . Both freewheeling mechanisms  14 ,  15  adopt their unlocked position. This allows free rotation of the inner ring  25 . The armature  35  is not positively connected to the electromechanical transducer  34  and is attracted and retained alone by way of electromagnetic air slot forces  42 . When the electromechanical transducer is separated from the housing  43  for mechanical reasons, the non-mechanical coupling to the armature  35  will cause the armature to instantaneously lock the freewheeling mechanism  2  by means of the armature spring  39 . 
   When the current at the electromechanical transducer  34  drops, the armature spring  39  integrated at the armature  35  will urge the armature  35  downwards into the locking position  44  (see  FIG. 9 ). The actuating forces  26  acting will activate both freewheeling mechanisms  14 ,  15  to lock the inner ring  25  of the freewheeling mechanism  2 . Due to a stepped diameter  45  of the positive and frictional connection  14 ,  15 , the freewheeling mechanism  2  is so configured that the frictional connection  14  will initially lock the inner ring  25 . When the frictional connection is creeping, the actuating element of the positive connection  37  loaded by the compression spring  38  will push the clamping member  21  and safely lock the positively connected freewheeling mechanism  15 . Safety is optimized in that there is no mechanical coupling between the electromechanical transducer  34  and the armature  35 . 
   Thus, safe locking is ensured in every situation by means of the integration of a positively and operatively connected freewheeling mechanism  14 ,  15  of the invention, effecting a high degree of operational safety of the electromechanical actuating unit  3 , while the positive connection is favorably used to ‘slow down’ the planet cage.