Abstract:
A window regulator includes an electric motor having a drive shaft, a window slider, a transmission having an input driven by a drive shaft and an output driving the slider. A geared motor includes a drive shaft, a reduction gear coupled to the drive shaft and having a transmission ratio less than  1 , and a piezoelectric element selectively locking the drive shaft. The window regulator can be used to prevent fraudulent opening of a window and to reduce the jamming force of an object between the window and the window frame.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This applications claims priority to PCT Applications PCTFR02/03483 filed on Oct. 11, 2002, which claims priority to French Patent Application FR 01 13 198 filed on Oct. 12, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     Technical Field 
     The invention relates generally to geared motors for window regulators in vehicles and more particulary to window regulators with a window braking and irreversibility device. 
     Known window regulators have a system for driving a vehicle window up and down. A person may try to open the vehicle window by applying downward pressure to the vehicle window when the window is closed or partially open to illegally gain access to the passenger compartment of the vehicle. 
     One known window regulator, includes an electric motor with a reduction gear and an output shaft having teeth at one end and forming a worm. The worm engages a wheel to form a wheel and worm reduction gear, and the wheel transmits movement to a cable driving drum. A cable wound around the drum drives a slider attached to the vehicle window upwardly and downwardly. In this window regulator, the wheel and worm reduction gear have a transmission efficiency of approximately 40 percent. When pressure is applied to the vehicle window, the motor and the low efficiency transmission prevent rotation of the wheel, and the irreversible driving up and down of the vehicle window by the drum is thus assured. 
     However, this device has disadvantages. Because of the low transmission efficiency, the motor that drives the drum is oversized relative to the drive force actually applied to the drum, and therefore the motor is bulky and costly. 
     German Patent Application DE-A-3110368 discloses a window regulator including a drive component coupled to a drum. The drum drives a window upwardly and downwardly by a cable attached to a window slider. The drum is equipped with a mechanical locking device. A gear placed on an axis of a drive shaft is equipped with axially projecting lugs. The axially projecting lugs lock against a fixed plate arranged in the structure of the window regulator. The window regulator is released when the drive shaft drives the drums and the window regulator is locked when the drum drives the drive shaft. 
     There are several drawbacks to this device. For one, the device is complex and costly, and the drum is bulky. The device also requires an additional braking system to stop the window from rising when an obstruction is detected. 
     Known devices may also include an anti-pinch system that measures the current consumed by the motor and the rotating speed of the motor. The anti-pinch system detects the pinching of an object between the top of the window and the window frame from variations in these parameters. The power supply to the motor is then stopped, and the driving of the window is stopped. 
     The anti-pinch system has disadvantages. The response time between the pinching of an object and the actual stopping of the movement of the window is significant. The window is still being driven during this response time, and a user may possibly be injured. It is also more difficult to obtain approval for vehicles using this type of window regulator. 
     There is therefore a need for a window regulator and a geared motor that provides a solution to one or more of these disadvantages. 
     SUMMARY OF THE INVENTION 
     The present invention provides a window regulator including a geared motor having a drive shaft, a window slider, a transmission having an input driven by the drive shaft and an output driving the slider. A piezoelectric element selectively locks the position of the slider. 
     In one embodiment, the piezoelectric element acts upon the drive shaft. In another embodiment, the piezoelectric element has a friction surface that is able to lock the position of the slider. In a further embodiment, the friction surface has a coefficient of friction on the drive shaft greater than 0.15. In yet another embodiment, the transmission has a reduction gear with a speed reduction ratio between the input and the output of the geared motor of less than 1. 
     The reduction gear can include a worm wheel system, and a worm is provided on the drive shaft. In one embodiment, the piezoelectric element forms a journal of the drive shaft. In another embodiment, the piezoelectric element locks the drive shaft by a split bearing. 
     In a further embodiment, the motor includes a housing with a journal, and the piezoelectric element has an outer surface permanently housed in the journal and an inner surface acting upon the split bearing. In yet another embodiment, the piezoelectric element is piezostrictive. The piezoelectric element can also selectively brake the movement of the slider. 
     The present invention also provides a geared motor including a drive shaft, a reduction gear coupled to the drive shaft with a speed reduction ratio between the input and the output greater than 1, and a piezoelectric element that selectively locks the drive shaft. 
     In one embodiment, the piezoelectric element has a friction surface which is able to lock the drive shaft, and the friction surface preferably has coefficient of friction with the drive shaft greater than 0.15. In another embodiment, the reduction gear has a worm wheel system, and a worm is provided on the drive shaft. In a further embodiment, the piezoelectric element forms a journal of the drive shaft. In yet another embodiment, the piezoelectric element locks the drive shaft by a split bearing. 
     The geared motor can include a housing with a journal, and the piezoelectric element has an outer surface permanently housed in the journal and an inner surface acting upon the split bearing. In one embodiment, the piezoelectric element is piezostrictive. In another embodiment, the piezoelectric element selectively brakes the drive shaft. 
     The present invention also provides a method for operating a window regulator including the steps of locking a position of the slider position by using the piezoelectric element when the motor is switched off and unlocking the position of the slider position when the motor is supplied with power. 
     In one embodiment, the piezoelectric element has two terminals, is piezostrictive, and is not supplied with power during the step of locking the slider. In another embodiment, the method includes the steps of the driving of the slider by the motor, detecting an obstruction, and braking the movement of the slider by the piezoelectric element. In a further embodiment, the method also includes a step of short-circuiting the power supply to the motor after detecting an obstruction. 
     Other characteristics and advantages of the invention are given in the following description of embodiments of the invention, given by way of example and with reference to the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates a window regulator including a geared motor according to the invention; 
         FIG. 2  schematically illustrates a longitudinal cross-section view of the geared motor of the invention; and 
         FIG. 3  schematically illustrates a transverse cross-section view of details of FIG.  2 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention provides a window regulator and a geared motor that drives a window slider. A piezoelectric element locks the position of the slider when the motor is switched off. Thus, the window stays locked in this position if an attempt is made to open the window by an outside force. 
       FIG. 1  shows a schematic view of a window regulator  1  according to an embodiment of the invention. The window regulator  1  includes a slider  2  attached to a window (not shown). The slider  2  is slidable on a guide rail  3 . A cable  4  driven by a drum  5  drives the slider  2 . The drum  5  is coupled to a wheel  61  (shown in  FIG. 2 ) of a geared motor  6  by a damper  73  (shown in FIG.  2 ). The geared motor  6  is fixed to a structural part  7  of the window regulator  1 . 
     As shown in more detail in  FIG. 2 , the geared motor  6  is housed in a housing  67 . The geared motor  6  includes a motor  64  having a rotor  65 , a power supply, and a control device  66  that can be produced as known. The wheel  61  is driven by a worm gear  62  on a drive shaft  63  of the motor  64 . The wheel  61  is the output element of a wheel and a worm reduction gear. The reduction gear ensures the transmission of mechanical power between the drive shaft  63  and the drum  5 . The reduction gear also has a speed reduction ratio between the input and the output of the geared motor  6  greater than one. The input speed of the reduction gear is thus greater than the output speed of the reduction gear. Although a wheel and worm reduction gear is described, it is possible to use any type of reduction gear. The damper  73  connects the drum  5  and the wheel  61  and absorbs the shocks during the transient drive phases of the motor  64 . The drum  5  serves as winding component for the cable  4  that drives the slider  2 . 
     The geared motor  6  includes a piezoelectric element  68  that selectively locks the position of the slider  2 , allowing a small size-locking part with a simple shape to be used. The piezoelement  68  is also easy to produce. The locking of the slider  2  can be selectively controlled using a simple device with the piezoelectric element  68 . The piezoelectric element  68  can lock the position of the slider  2  by braking. If the position of the slider  2  is locked to a force of, for example, 500 N applied to the window, it is locked. The position of the slider  2  is selectively locked to ensure the irreversibility of the window regulator  1 . Therefore the slider  2  cannot be driven by the windows, but the slider  2  can be driven by the motor  64 . The selective locking of the slider  2  will be detailed later. Generally, the slider  2  position is locked when the motor  64  is switched off, and the slider  2  position is unlocked when the motor  64  is supplied with power. The irreversibility is selective, and it is possible to use a reduction gear with high transmission efficiency. A less powerful motor  64 , such as a 20 watt motor, can then be used. 
     In  FIG. 2 , the position of the slider  2  is locked by locking the drive shaft  63  by the piezoelectric element  68 . As further shown  FIG. 3 , the piezoelectric element  68  can be used as a journal of the motor  64 , and the geared motor  6  can thus be kept small. Moreover, the volume of the drum  5  is not increased. The piezoelectric element  68  can be substantially cylindrical. The piezoelectric element  68  can be placed in a recess in the housing  67  or be mounted with a tight fit in a hole in the housing  67 . Preferably, the piezoelectric element  68  is arranged in the housing  67  of the geared motor  6 . Generally, an outer surface of the piezoelectric element  68  can be permanently housed in a hole in the housing  67 . The electrical connections of the piezoelectric element  68  can be located in the same location as the motor  64  power supply electrical connections, and the electrical wiring of the window regulator  1  can therefore be simplified. 
     The piezoelectric element  68  can lock the drive shaft  63  via a shaft rotation guide component. As shown in  FIG. 3 , a split bearing  69  can be used for this. In this embodiment, the split bearing  69  is housed against an inner surface of the piezoelectric element  68 . The split bearing  69  has a substantially longitudinal split  70 , and the diameter of the split bearing  69  can therefore vary. By placing a radial load on the split bearing  69 , the width of the split  70  and the diameter of the split bearing  69  can be reduced, and the brake force applied by the split bearing  69  on the drive shaft  63  is increased. When the piezoelectric element  68  is in a dilated position, i.e. when its inner diameter reaches a minimum size, the inner surface of the piezoelectric element  68  acts upon the split bearing  69  and reduces the width of the split  70 . The rotation of the drive shaft  63  is then locked by the split bearing  69 . 
     The piezoelectric element  68  can be made of quartz or barium titanate. Preferably, the piezoelectric element  68  is made of a piezostrictive material. Thus, the piezoelectric element  68  is in a dilated position or locking position when idle. When the power supply to the piezoelectric element  68  is interrupted, such as due to a dead battery, the piezoelectric element  68  still continues to lock the slider  2  position. In one example, a 10 mm×8 mm×5 mm piezoelectric element  68  can be used with a reduction gear with a speed reduction ratio of 73 to ensure a locking force of 500 N on the slider  2 . An unlocking voltage of 12 V to 60 V between the electrodes releases the drive shaft  63 , in this example. 
     An electrode (not shown) is preferably arranged on both the outer circumference and the inner circumference of the piezoelectric element  68 , ensuring a greater variation of the inner diameter of the piezoelectric element  68 . 
     In one example, the split bearing  69  is made of sintered and lubricated bronze. In one example, the split bearing  69  has an inner diameter of 8 mm, a minimum thickness of 5 mm and a minimum outer diameter of 10 mm to ensure the drive shaft  63  is locked. 
     The piezoelectric element  68  can act directly upon the drive shaft  63 . Preferably, the piezoelectric element  68  has a friction surface with a high coefficient of friction with the drive shaft  63 . A coating with a high coefficient of friction with the drive shaft  63  can also be used. The coating can be applied to the surface of the piezoelectric element  68  contacting the drive shaft  63 . Preferably, the friction surface has a coefficient of friction greater than 0.15. 
     The arrangement of the piezoelectric element  68  upstream of the reduction gear, and in particular on the drive shaft  68 , provides several advantages. The piezoelectric element  68  can have reduced braking power because the reduction gear multiplies the braking torque applied by the piezoelectric element  68  on the slider  2 . 
     The piezoelectric element  68  can also selectively brake the movement of the slider  2 . The arrangement of the piezoelectric element  68  on the drive shaft  63  is also advantageous for carrying out the braking. It is possible to brake the movement of the slider  2  when an obstruction is detected in the window. By using the piezoelectric element  68  for braking, the inertia of the motor  64  can be reduced more quickly, reducing the response time between identifying an obstruction and stopping the slider  2  and the window. Moreover, a piezoelectric element  68  that already exists to ensure irreversible movement of the slider  2  can be used for the selective braking. 
     The piezoelectric element  68  and the motor power supply can share a control. The control can apply different voltages to the terminals of the piezoelectric element  68  depending on the operation to be carried out. Different braking or unlocking voltages can be used depending on detected external conditions, such as the temperature, the power supply status of the motor, or the pinching of an object. 
     The invention also relates to a method for operating the window regulator  1  and the geared motor  6  described above. 
     The position of the slider  2  is locked by the piezoelectric element  68  when the motor  64  is switched off. The piezoelectric element  68  can be kept idle during this step, such as when a piezostrictive piezoelectric element  68  is used. The position of the slider  2  is unlocked by exciting the piezostrictive piezoelectric element  68  when the motor  64  is supplied with power. 
     According to a second method for operating the window regulator  1 , the slider  2  is driven by the motor  64 . When an obstruction is detected in the window , a braking instruction is sent to the piezoelectric element  68 . The piezoelectric element  68  then brakes the slider  2 . 
     According to one embodiment, the power supply to the motor  64  is short-circuited after an obstruction is detected. Additional braking is then provided by a motor brake. 
     Of course, this invention is not limited to the examples and embodiments described and shown, but is open to a number of embodiments accessible to a person skilled in the art. Although the locking of the position of the slider  2  on the drive shaft  13  has mainly been described, the locking can occur in any suitable place. For example, a piezoelectric locking element  68  placed on a slider  2  and acting on a guide rail can be installed. A piezoelectric element  68  on the reduction gear wheel acting upon the housing  67  of a geared motor  6  can also be employed. 
     The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.