Abstract:
A drive device enabling a movable element to be driven by an actuator via a gear system comprising a motor pinion gear, an intermediate gear and a partial toothed gear. An aim of the invention is to create a particularly compact device which can capture the kinetic energy of the actuator in a particularly reliable manner. The intermediate gear comprises a pinion and a toothed gear. The pinion and toothed gear are connected via a ratchet in such a way that the opinion which is rotationally fixed to the ratchet can be rotated counter to the toothed wheel in a manner similar to that of a locking ratchet wheel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application is a continuation of international application PCT/DE02/02607, filed 17 Jul., 2002, which designated the United States, and claims priority to German priority document 10137026.1, filed 30 Jul., 2001, the both of which are herein incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   The invention relates to a drive device, in which a movable element can be driven by an actuator via a gear unit and in which the gear unit comprises a motor pinion, an intermediate wheel and a toothed ring, and the intermediate wheel comprises a pinion and a gearwheel, the pinion and the gearwheel being connected via a ratchet in such a way that the pinion connected fixedly in terms of rotation to the ratchet can be rotated in relation to the gearwheel in the manner of a locking pawl. 
   To control the quantity of fresh gas of a motor vehicle, throttle valve assemblies are usually used. Throttle valve assemblies comprise a housing with a throttle orifice and a throttle member arranged in the throttle orifice. The throttle member conventionally comprises a throttle valve which is arranged on a throttle valve shaft and which is arranged pivotably in the housing of the throttle valve assembly. The throttle valve assumes a defined position in the throttle orifice for the passage of a defined quantity of fresh gas. For this purpose, the throttle valve shaft can be activated mechanically or electromechanically. 
   In an electromechanical activation of the throttle valve shaft, the throttle valve assembly normally has a position detection means, via which the current position of the throttle valve shaft can be detected. Depending on the in each case current position of the throttle assembly, the current position being indicated by a signal, another signal is then generated either inside or outside the throttle valve assembly, by means of which the throttle valve shaft can be activated via the actuator arranged in the throttle valve assembly. In this case, depending on the position of the throttle valve shaft and consequently of the throttle valve, the throttle orifice is partially closed by the throttle valve, this corresponding to an open position of the throttle valve, or else is also closed completely by the throttle valve, this corresponding to a closing position of the throttle valve. 
   If the actuator adjusts the throttle valve position from open to closed, the actuator current is switched off only after the throttle valve shaft, together with the throttle valve arranged on it, assumes a position in which the throttle valve substantially closes the throttle orifice. However, after the actuator or its current has been switched off, it still rotates a little further on account of the kinetic energy of its rotor. Consequently, the actuator transmits kinetic energy to the gear unit. The gear unit should absorb the kinetic energy without being damaged. If, however, the throttle valve shaft is in a position which corresponds to the closed position of the throttle valve and the throttle valve bears mechanically, in the closing position, against a step in the throttle orifice, the gear unit, on account of the kinetic energy transmitted to it, will attempt to rotate the throttle valve beyond the step in the throttle orifice. Since the abutment is normally harder than the gearwheels of the gear unit, this often results in a fracture of individual gears of the gearwheels of the gear unit, without the throttle valve being pivoted by the throttle valve shaft. This foreseeable gear unit damage considerably shortens the useful life of gear units of this type, as a result of which their use, particularly in throttle valve assemblies, is uneconomical. 
   Such a drive device is known, for example, from EP 0 272 352 A2. Herein, the intermediate gearwheel has a ratchet. The gearwheel has a ring of detent pawls and the pinion has ratchet geometries prestressed in relation to the detent pawls. The pinion is manufactured in one piece with the ratchet geometries. The ratchet consequently prevents excess kinetic energy from being transmitted to the movable element. One disadvantage of the known drive device, however, is that the gear unit has a high weight. The high weight of the drive device decisively contributes, however, to the generation of the excess kinetic energy. 
   It is known from US 6,189,507 B1, in a drive device, to design the toothed ring as a part-toothed ring. This leads to a reduction in weight. This drive device has the disadvantage, however, that the remaining kinetic energy is transmitted directly to the movable element, thus resulting in a short useful life of the drive device. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a drive device of the abovementioned type wherein the gear unit has a particularly low weight and wherein the device may be manufactured in a particularly simple way. 
   These and other objects are achieved, according to the invention, by designing the toothed ring as a part-toothed ring, and in that the gearwheel and the pinion are manufactured from plastic and the ratchet from metal, the ratchet being snapped onto the pinion. 
   As a result of this configuration, the weight of the gear unit is reduced by the toothed ring being designed as a part-toothed ring. Furthermore, the gearwheel and the pinion are manufactured from plastic instead of metal, thus resulting in a further reduction in the weight. The ratchet itself may be manufactured as a thin and stable sheet-metal part and, for assembly, can simply be snapped onto the pinion. 
   Advantageously, the movable element is a throttle valve shaft which is arranged in a throttle valve assembly and on which a throttle valve is arranged pivotably. Throttle valve assemblies with a drive device of this type have a particularly low space requirement and can therefore be used in a particularly versatile way. 
   The advantages achieved by means of the invention are, in particular, that, on the one hand, the drive device has a particularly low space requirement, and that kinetic energy of the actuator can be absorbed reliably with a gear unit of the drive device even when the throttle valve shaft is secured in a fixed position via the throttle valve bearing against an abutment in the throttle orifice. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The present invention is set out with respect to the drawings which depict the following: 
       FIG. 1  depicts a cross section through a throttle valve assembly with a drive device for pivoting a throttle valve arranged on a throttle valve shaft, 
       FIG. 2  depicts a longitudinal section through the throttle orifice of the throttle valve assembly according to  FIG. 1 , 
       FIG. 3  depicts a top view of the drive device of the throttle valve assembly according to  FIG. 1 , 
       FIG. 4  depicts individual parts of the intermediate wheel of the gear unit, and 
       FIG. 5  depicts the intermediate wheel in various views. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Parts corresponding to one another are given the same reference symbols in all the figures. 
   The throttle valve assembly  10  according to  FIG. 1  serves for supplying an air or a fuel/air mixture to a consumer, not illustrated, for example an injection device of a motor vehicle, likewise not illustrated, the fresh gas quantity to be supplied to the consumer being capable of being controlled by means of the throttle valve assembly  10 . For this purpose, the throttle valve assembly  10  has a housing  16  which is manufactured predominantly from metal  18 , in particular aluminum, and has been produced by the injection molding method. Alternatively, however, the housing  16  may also be manufactured completely from plastic. The housing  16  has a throttle orifice  20  via which air or a fuel/air mixture can be supplied to the consumer. 
   To set the volume of fresh gas to be supplied, a throttle valve  23  is arranged on a throttle valve shaft  22 . The throttle valve  23  cannot be seen on account of the sectional illustration, but is illustrated in FIG.  2 . However, the fastening points  24 , at which the throttle valve  23  is fastened on the throttle valve shaft  22 , can be seen. A rotation of the throttle valve shaft  22  about its axis of rotation  26  gives rise at the same time to the pivoting of the throttle valve  23  arranged on the throttle valve shaft  22 , with the result that the active cross section of the throttle orifice  20  is. increased or reduced. By means of an increase or reduction in the active cross section of the throttle orifice  20  by means of the throttle valve  23 , a regulation of the throughput of the air or fuel/air mixture through the throttle orifice  20  of the throttle valve assembly  10  takes place. 
   The throttle valve shaft  22  may be connected to a pulley, not illustrated, which, in turn is connected via a Bowden cable to a setting device for a power requirement. The setting device may in this case be designed as the accelerator pedal of a motor vehicle, so that, by this setting device being actuated by the driver of the motor vehicle, the throttle valve  23  can be brought from a position of minimum opening, in particular a closed position, into a position of maximum opening, in particular an open position, in order to control the power output of the vehicle. 
   In contrast, the throttle valve shaft  22  may either be set by an actuator over a part or total range of adjustment via the accelerator pedal. In so called E-gas or Drive-by-wire systems, the mechanical power control, for example the depression of an accelerator pedal, is converted into an electrical signal. This signal is supplied, in turn, to a control unit which generates an activation signal for the actuator. In these systems, there is no mechanical coupling between the accelerator pedal and the throttle valve during normal operation. 
   In order to adjust the throttle valve shaft  22  and consequently the throttle valve  23 , therefore, the throttle valve assembly  10  has a drive device  30  which is arranged in the housing  16  of the throttle valve assembly  10 . The drive device  30  is shown in section in FIG.  1 . 
   The drive device  30  is arranged in the housing  16  of the throttle valve assembly  10  and comprises an actuator  32  designed as an electric motor. The actuator  32  designed as an electric motor moves the throttle valve shaft  22  via a gear unit  34  designed as a reduction gear unit. The gear unit  34  also belongs to the drive device  30 . The actuator  32  is connected, in a way not illustrated in any more detail, to a current source arranged outside the throttle valve assembly  10  and to a control unit. The control unit transmits to the actuator  32  a signal, by means of which the actuator  32  brings about a defined position of the throttle valve shaft  22  via the gear unit  34  designed as a reduction gear unit. The actual position of the throttle valve shaft  22  can be detected via a position detection means  36  which is designed as a potentiometer and in which the slide of the position detection means  36  designed as a potentiometer is connected to the throttle valve shaft  22  in a way not illustrated in any more detail. 
   To transmit a rotational movement from the actuator  32  designed as an electric motor to the throttle valve shaft  22 , the gear unit  34  designed as a reduction gear unit comprises a motor pinion  38  which is connected fixedly in terms of rotation to the drive shaft, not illustrated in any more detail in the drawing, of the actuator  32  designed as an electric motor. The motor pinion  38  meshes with an intermediate wheel  40  which likewise belongs to the gear unit  34  and which is arranged on an axle  42  rotatably in the housing  16  of the throttle valve assembly  10 . 
   The intermediate wheel  40  comprises a pinion  44  and a gearwheel  46 . The pinion  44  and the gearwheel  46  are manufactured from plastic  48 . The pinion  44  and the gearwheel  46  are connected to one another in the manner of a locking pawl via a ratchet  50 . The ratchet  50  is in this case manufactured in a spring-like manner from metal. The ratchet  50  engages, on the one hand, into undercuts  54  of the pinion  44 , in such a way that the ratchet  50  and the pinion  44  are connected fixedly in terms of rotation to one another. On the other hand, the ratchet  50  engages into a ratchet arrangement  56  which is arranged on the toothed ring  46 . The ratchet arrangement  56  is designed in such a way that, when a defined force threshold is exceeded, the gearwheel  46  rotates in relation to the pinion  44 . In this case, the ratchet  50  in the ratchet arrangement  56  moves one or more units along the ratchet arrangement  56  as a function of the force exerted on the gearwheel. Below a defined force threshold, therefore, the gearwheel  46  and the pinion  44  are connected fixedly in terms of rotation to one another, whereas, above a defined force threshold, the gearwheel  46  can be rotated in relation to the pinion  44 . 
   The pinion  44  meshes with a part-toothed ring  58  which is likewise assigned to the gear unit  34 . The part-toothed ring  58  is arranged on a lever  60  which is connected fixedly in terms of rotation to the throttle valve shaft  22 . The part-toothed ring  58  and the lever  60  are likewise assigned to the gear unit  34 . Furthermore, the throttle valve shaft  22  is connected to a first end of a coil spring  62 , the second end of which is connected fixedly to the housing  16 . 
   The throttle orifice  20  has a contour  64 , as can be seen in detail in FIG.  2 . This contour has the effect that, during an adjustment of the throttle valve  23  by means of the drive device  30  in the direction of the closing position, the throttle valve  23  comes to bear against the contour  64  and cannot be moved beyond this abutment position by the actuator  32 . 
     FIG. 3  shows the drive device  30  of the throttle valve assembly  10  in a top view. The motor pinion  38  connected fixedly in terms of rotation to the drive shaft of the actuator  32  meshes with the gearwheel  46  of the intermediate wheel  40 . The gearwheel  46  is connected to the pinion  44  via the ratchet  50 . This connection is arranged on the side facing away from the observer of FIG.  3  and therefore cannot be seen in FIG.  3 . What can be seen, however, is the pinion  44  which meshes with the part-toothed ring  58 . The part-toothed ring  58  is in this case arranged on the lever  60  connected fixedly to the throttle valve shaft  22 . 
     FIG. 4  shows the individual parts, pinion  44 , toothed ring  46  and ratchet  50 . The pinion  44  of the intermediate wheel  40  has, on one of its sides, a toothed-ring structure  70  and, on its other side, an undercut  54 , into which the ratchet  50  can be locked for a rotationally fixed connection to the pinion  44 . In this case, the pinion  44  is to be arranged in the gearwheel  46  of the intermediate wheel  40  by means of a continuous web  72 . 
   The toothed ring  46  has an outer continuous toothedring structure  74  and an inner ratchet arrangement  56 . The ratchet arrangement  56  comprises a number of regular inclined planes or ratchet arrangements  76  which are lined up with one another in a circle. In three of these planes or ratchet arrangements  76 , the ratchet  50  engages with ratchet geometries  78 , preferably spherical, which are arranged at the ends of the three legs  80  of the ratchet  50 . 
     FIG. 5  shows the intermediate wheel from the front in  FIG. 5   a,  from the side in  FIG. 5   b  and from the rear in  FIG. 5   c . 
   If, then, a force which exceeds a defined force threshold acts on the gearwheel  46 , the spheres or ratchet geometries  78  of the ratchet  50  travel up on the respective inclined planes or ratchet arrangements  76 , in order then to lock into the next adjacent inclined plane or ratchet arrangement  78 . In this case, as a function of the force acting on the gearwheel, the spheres or ratchet geometries  78  of the ratchet  50  move one or more inclined planes or ratchet arrangements  76  further on. 
   When the throttle valve assembly  10  is in operation, the throttle valve  23  arranged on the throttle valve shaft  22  is opened and closed via the drive device  30 . In this case, the actuator  32  is activated by a control device, not illustrated in any more detail in the drawing. If, then, the actuator  32  or the coil spring  62  moves the throttle valve  23  into the closing position via the gear unit  34 , high forces can act on the gear unit  34  in the closing position. The closing position is in this case the position in which the throttle valve  23  substantially closes the throttle orifice  20 . After the closing position of the actuator  32  is reached, however, its drive shaft moves further on account of the kinetic energy which is still present in the electric motor. This residue of kinetic energy is transmitted from the drive shaft of the actuator  32  to the gearwheel  46  of the intermediate wheel  40  via the motor pinion  38 . However, since the throttle valve  32  now bears against the contour  64 , the pinion  44  does not follow the rotational movement of the gearwheel  46 . The forces in this case acting on the gearwheel  46  are such that the gearwheel  46  rotates in relation to the pinion  44  by means of the ratchet  50 . The ratchet arrangement  56  of the gearwheel  46  is in this case arranged in such a way that the rotational movement of the gearwheel  46  in relation to the pinion  44  corresponds to the preferential direction of rotation of the ratchet engagement between the pinion  44  and the gearwheel  46 . Without the ratchet engagement between the pinion  44  and the gearwheel  46 , there would be the risk that, when the closing position was reached by the throttle valve  23 , individual teeth of the gear unit, in particular of the pinion  44 , could fracture, with the result that the throttle valve assembly  10  would, in an extreme situation, become incapable of functioning. 
   The connection of the pinion  44  to the gearwheel  46  via the ratchet  50  reliably ensures that excess kinetic energy of the actuator  32  can be absorbed even when the throttle valve  23  is secured, for example, in a closing position in the throttle orifice  20  of the throttle valve assembly  10 .