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:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to geared motors for window regulators in vehicles and more particularly window regulators with a window braking and irreversibility device.  
         [0002]     The known window regulators have means for driving a window up and down. Persons may try to open a vehicle window by applying a downward pressure to the closed or partly opened window, in order to illegally gain access to the passenger compartment of the vehicle.  
         [0003]     A window regulator, sold by the assignee under reference number 101087, comprises an electric motor with a reduction gear; an output shaft of the motor has teeth at one end forming a worm. This worm engages with a wheel to form a wheel and worm reduction gear. The wheel transmits the movement to a cable driving drum. The cable drives a slider attached to the window up and down. In this window regulator, a wheel and worm reduction gear with transmission efficiency of the order of 40 percent is used. When pressure is applied to the window, the motor and the low efficiency transmission lock the rotation of the wheel. The irreversible driving up and down of the window by the drum is thus assured.  
         [0004]     This device has disadvantages. Because of the low transmission efficiency, driving the drum requires the use of a motor that is oversized relative to the drive force actually applied to the drum. The motor is thus bulky and costly.  
         [0005]     German Patent Application DE-A-3110368 discloses a window regulator comprising a drive component coupled to a drum. The drum drives a window up and down by means of a cable attached to a window slider. The drum is equipped with a mechanical locking device. A gear placed on the axis of the drive shaft is equipped with lugs projecting axially. These 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 drum and locked when the drum drives the drive shaft.  
         [0006]     This device is complex and costly. Moreover, the drum is bulky. This device also requires the use of an additional braking system in order to stop the window from rising when an obstruction is detected.  
         [0007]     The device sold by the assignee under reference number 101087 also comprises an anti-pinch system. The system measures the current consumed and the rotating speed of the motor. The 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 interrupted and the driving of the window is thus stopped.  
         [0008]     This anti-pinch device has disadvantages. The response time between the pinching of an object and the actual stopping of the movement of the window is significant. As the window is still being driven during this response time, a user may be injured. It is also more difficult to obtain approval for vehicles using this type of window regulator.  
       SUMMARY OF THE INVENTION  
       [0009]     There is therefore a need for a window regulator and a geared motor that provide a solution to one or more of these disadvantages. The object of the invention is thus a window regulator comprising an electric motor having a drive shaft, a window slider, a transmission having an input driven by the drive shaft and an output driving the slider, with a piezoelectric element selectively locking the position of the slider.  
         [0010]     According to one embodiment, the piezoelectric element acts upon the drive shaft.  
         [0011]     According to another embodiment, the piezoelectric element has a friction surface that is able to lock the position of the slider.  
         [0012]     According to a further embodiment, the friction surface has a coefficient of friction on the shaft greater than 0.15.  
         [0013]     According to 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.  
         [0014]     Provision may also be made for the reduction gear to comprise a worm wheel system, the worm being provided on the drive shaft.  
         [0015]     According to one embodiment, the piezoelectric element forms a journal of the drive shaft.  
         [0016]     According to another embodiment, the piezoelectric element locks the drive shaft by means of a split bearing.  
         [0017]     According to a further embodiment, the motor comprises 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 bearing.  
         [0018]     According to yet another embodiment, the piezoelectric element is piezostrictive.  
         [0019]     Provision may also be made for the piezoelectric element to selectively brake the movement of the slider.  
         [0020]     Another object of the invention is a geared motor comprising 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 selectively locking the drive shaft.  
         [0021]     According to one embodiment, the piezoelectric element has a friction surface which is able to lock the shaft, this surface preferably having a coefficient of friction with the shaft greater than 0.15.  
         [0022]     According to another embodiment, the reduction gear has a worm wheel system, the worm being provided on the drive shaft.  
         [0023]     According to a further embodiment, the piezoelectric element forms a journal of the drive shaft.  
         [0024]     According to yet another embodiment, the piezoelectric element locks the drive shaft by means of a split bearing.  
         [0025]     Provision may also be made for the geared motor to comprise a housing with a journal, the piezoelectric element having an outer surface permanently housed in the journal and an inner surface acting upon the bearing.  
         [0026]     According to one embodiment, the piezoelectric element is piezostrictive.  
         [0027]     According to another embodiment, the piezoelectric element selectively brakes the drive shaft.  
         [0028]     A further object of the invention is a method for operating a window regulator comprising the steps of locking the slider position by means of the piezoelectric element when the motor is switched off and unlocking the slider position when the motor is supplied with power.  
         [0029]     According to one embodiment, the piezoelectric element has two terminals, is piezostrictive and is not supplied with power during the slider locking step.  
         [0030]     According to another embodiment, the method comprises the steps of the driving of the slider by the motor, obstruction detection and braking of the movement of the slider by means of the piezoelectric element.  
         [0031]     According to a further embodiment, the method also comprises a stage of short-circuiting the power supply to the motor after an obstruction has been detected.  
         [0032]     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  
       [0033]      FIG. 1  is if a schematic representation of a window regulator comprising a geared motor according to the invention;  
         [0034]      FIG. 2  is a longitudinal cross-section view of a geared motor according to the invention;  
         [0035]      FIG. 3  is a transverse cross-section view of details in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0036]     The invention provides in particular a window regulator and a geared motor driving a window slider. A piezoelectric element locking the slider locks the position of the slider when the motor is switched off. Thus when an attempt is made to open the window by forcing it from the outside, the window stays locked in its position.  
         [0037]      FIG. 1  shows a schematic view of a window regulator  1  according to an embodiment of the invention. The window regulator  1  comprises a slider  2  attached to a window, not shown. The slider  2  can slide for example on a guide rail  3 . A cable  4  drives the slider  2 . This cable  4  is itself driven by a drum  5 . This drum  5  is coupled to the wheel of a geared motor  6 , for example by means of a damper. The geared motor is for example fixed to a structural part  7  of the window regulator  1 .  
         [0038]     As shown in more detail in  FIG. 2 , the geared motor  6  is housed in a housing  67 . A motor  64  has a rotor  65  and a power supply and control device  66  that can be produced in a way known per se. The wheel  61  is the output element of a wheel and worm reduction gear. The wheel  61  is driven by a worm gear pair  62  made on the output shaft  63  of the motor  64 . 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 greater than 1. 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 was used in the example, it is possible to use any type of appropriate reduction gear. A damper  73  connects the drum  5  and the wheel  61 . The damper in particular absorbs the shocks during the transient drive phases of the motor. The drum  5  serves as winding component for the cable  4  that drives the slider.  
         [0039]     In this embodiment, the geared motor comprises a piezoelectric element that selectively locks the position of the slider. The use of a piezoelectric element for locking the slider permits the use of a small size locking part with a simple shape. An appropriate piezoelement is moreover easy to produce. The locking of the slider can also be selectively controlled using simple means with a piezoelectric element. The piezoelectric element can lock the slider position by braking. Braking that locks the position of the slider to a force of 500 N applied to the window is seen as locking. The slider position is selectively locked in order to ensure the irreversibility of the window regulator. Thus, the driving of the slider by the window is prevented, while the driving of the slider by the motor is permitted. Means allowing for the selective locking of the slider will be detailed later. Generally, the slider position is locked when the motor is switched off and the slider position is unlocked when the motor is supplied with power. As the irreversibility is selective, it is possible to use a reduction gear with high transmission efficiency. A less powerful motor can then be used, for example a 20-Watt motor.  
         [0040]     The slider position is locked in the example in  FIG. 2  by locking the drive shaft by means of the piezoelectric element. As shown in more detail in  FIG. 3 , the piezoelectric element can be used as a journal of the motor. The geared motor can thus be kept small. Moreover, the volume of the drum is not increased. A substantially cylindrical piezoelectric element can be used. The piezoelectric element can be placed in a recess in the housing  67  or be mounted with a tight fit in a hole in the housing  67 . Generally, an outer surface of the piezoelectric element can be permanently housed in a hole in the housing. It is advantageous to arrange the piezoelectric element in the housing  67  of the geared motor  6 . The electrical connections of the piezoelectric element can thus be located in the same place as the motor power supply electrical connections. The electrical wiring of the window regulator  1  can thus be simplified.  
         [0041]     The piezoelectric element  68  can lock the drive shaft  63  by means of a shaft rotation guide component. A split bearing  69  can for example be used for this, as shown in  FIGS. 2 and 3 . In this embodiment, the split bearing  69  is housed against an inner surface of the piezoelectric element  68 . The bearing has a substantially longitudinal split  70 . The diameter of the bearing  69  can thus vary. By placing a radial load on the bearing  69 , the width of the slit  70  and the diameter of the bearing can be reduced. The brake force applied by the bearing  69  on the shaft  63  is thus increased. When the piezoelectric element  68  is in a dilated position, i.e. when its inner diameter has 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 bearing  69 .  
         [0042]     A piezoelectric element  68  made of quartz or barium titanate can be used. A piezostrictive material is preferably used to make the piezoelectric element. Thus, the piezoelectric element is in a dilated position or locking position when idle. When the power supply to the piezoelectric element is interrupted, due to a dead battery for example, the piezoelectric element  68  still continues to lock the slider position. A 10 mm×8 mm×5 mm piezoelectric element 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. An unlocking voltage of 12 to 60 V between the electrodes releases the drive shaft.  
         [0043]     An electrode is preferably arranged on the outer circumference of the piezoelectric element and another electrode on the inner circumference of the piezoelectric element. A greater variation of the inner diameter of the piezoelectric element is thus ensured.  
         [0044]     A split bearing  69  made of sintered and lubricated bronze can be used. A bearing with dimensions of inner diameter  8 , a minimum thickness of 5 mm and a minimum outer diameter of 10 mm is suitable to ensure the locking of the drive shaft  63 .  
         [0045]     Provision can also be made for the piezoelectric element  68  to act directly upon the drive shaft  63 . A piezoelectric element  68  with a friction surface with a high coefficient of friction with the drive shaft will preferably be used. A coating with a high coefficient of friction with the drive shaft can also be used. This coating can for example be applied to the surface of the piezoelectric element coming into contact with the drive shaft. A friction surface with a coefficient of friction greater than 0.15 is preferably used.  
         [0046]     The arrangement of the piezoelectric element  68  upstream of the reduction gear, and on the drive shaft in particular, is advantageous. A piezoelectric element with reduced braking power can be used because the reduction gear multiplies the braking torque applied by the piezoelectric element on the slider.  
         [0047]     The piezoelectric element  68  can also be used to selectively brake the movement of the slider  2 . The arrangement of the piezoelectric element on the drive shaft is also advantageous for carrying out this braking. It is possible to brake the movement of the slider when an obstruction of the window is detected. The braking using the piezoelectric element allows for the inertia of the motor to be reduced more quickly. The response time between the identification of an obstruction and the stopping of the slider and the window can thus be reduced. Moreover, a piezoelectric element that already exists to ensure that the movement of the slider is irreversible is used for this.  
         [0048]     A piezoelectric element control shared with the control of the motor power supply can be used. Provision can be made for the control to apply different voltages to the terminals of the piezoelectric element depending on the operation to be carried out. Different braking or unlocking voltages can be used depending on the external conditions detected, such as the temperature, the power supply status of the motor or the pinching of an object.  
         [0049]     The invention also relates to methods for operating the window regulator and the geared motor described.  
         [0050]     According to a first method of operation, the slider position is locked by means of the piezoelectric element when the motor is switched off. The piezoelectric element can for example be kept idle during this step, for example when a piezostrictive piezoelectric element is used. The position of the slider is unlocked, for example by exciting a piezostrictive piezoelectric element, when the motor is supplied with power.  
         [0051]     According to a second method for operating a window regulator, the steps of driving the slider by the motor are carried out. An obstruction of the window is detected by appropriate means. A braking order is then sent to the piezoelectric element for example when an obstruction is detected. The movement of the slider is then braked by means of the piezoelectric element.  
         [0052]     According to one embodiment, the power supply to the motor is short-circuited after the detection of an obstruction. Additional braking is thus provided by a motor brake.  
         [0053]     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 slider position on a drive shaft has mainly been described, provision can of course be made to carry out this locking in any suitable place. For example, provision can be made to install a piezoelectric locking element placed on a slider and acting on a guide rail. Provision can also be made for a piezoelectric element on the reduction gear wheel acting upon the housing of a geared motor.