Abstract:
The invention relates to a device ( 2 ) for controlling a position sensor ( 13 ) of a steering wheel ( 3 ) of a vehicle. Said device ( 2 ) includes a means ( 9 ) for generating a control signal for the acquisition periods of the position sensor ( 13 ) when the vehicle is stopped, the frequency of said signal increasing upon the detection of a variation in the position of said steering wheel ( 3 ). The invention can be used in the field of automobiles, and the position sensor can be associated with the rotor of the steering assist motor.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device for controlling a position sensor of a motor vehicle fitted with a power-steering motor. 
     The vehicles of today are fitted increasingly frequently with a power-steering motor. Such vehicles comprise a steering system formed by a steering column supporting at its top end a steering wheel capable of being actuated by the driver of the vehicle, a rack on which the bottom end of the steering column acts and a power-steering motor mechanically connected to the rack. An electronic management system of the ECU (electronic control unit) type controls the power-steering motor in order to prevent the steering of the vehicle becoming too light at normal speed or too heavy at virtually zero speed. 
     For the correct operation of the power-steering motor, it is necessary to have an item of information reflecting the angular position of the steering wheel in order to perform the function of automatic return of the steering wheel. This information is usually supplied by a steering-wheel sensor situated on the steering wheel. The presence of a steering-wheel sensor dedicated to this function however causes a considerable extra cost. 
     The angular position of the steering wheel of a vehicle may also be obtained by virtue of a position sensor situated on the power-steering motor. 
     However, the use of this type of sensor poses certain problems. Specifically, the position of the steering wheel must be known at all times (i.e. when stationary and when running). Accordingly, it is necessary to keep the position sensor of the power-steering motor powered up even if the ignition of the vehicle is switched off. Keeping powered up in this way causes a risk of discharging the battery. 
     In this context, the object of the invention is to remedy the aforementioned problems of the prior art by proposing a device capable of determining, when the ignition of the vehicle is switched off, the angular position of the steering wheel, with precision and exactitude, while ensuring minimum electrical consumption and while preventing a risk of discharging the battery of the vehicle. 
     BRIEF SUMMARY OF THE INVENTION 
     For this purpose, the invention proposes a device for controlling a sensor of the position of a steering wheel of a motor vehicle, said device being characterized in that it comprises means for generating a control signal for the acquisition periods of the position sensor when the vehicle is stationary, the frequency of said signal increasing when a change in the position of said steering wheel is detected. 
     In addition to the main features that have just been mentioned in the above paragraph, the device according to the invention may have one or more additional features mentioned below, considered individually or in all the possible technical combinations:
         said means for generating a control signal generate a signal at a standby frequency suitable for detecting a half-turn of a rotor;   said standby frequency is between 500 Hz and 1000 Hz;   said means for generating a control signal generate a signal at an active frequency that is strictly higher than said standby frequency when said position sensor detects a rotary movement of said steering wheel;   said means for generating a control signal generate a signal at a frequency changing proportionally with an acceleration or a deceleration of the rotation speed of said steering wheel;   said means for generating a control signal reduce said active frequency to reach said standby frequency when:
           said position sensor detects a deceleration of the rotation speed of said steering wheel; or   said sensor detects no rotation of said steering wheel over a certain period.   
               

     The invention also relates to a power-steering system for a motor vehicle, characterized in that it comprises at least:
         a steering column supporting at its top end a steering wheel;   a rack on which the bottom end of said steering column acts;   a power-steering motor mechanically connected to said rack;   a torque sensor associated with the steering column making it possible to measure the torque applied by the driver to said steering wheel;
 
said system also comprises a control device as claimed in the invention making it possible to keep said position sensor alert for counting the number of half-turns or turns of a rotor of said motor by means of a reduction ratio operating on said rotor and:
   on said rack; or   on said steering column.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will clearly emerge from the description that is given thereof below, as an indication and in no way limiting, of embodiments making reference to the figures appended hereto in which: 
         FIG. 1  is a simplified schematic representation of a steering system for a motor vehicle and of a control device according to the invention; 
         FIG. 2  illustrates schematically the various control signals of the position sensor generated by the control device according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For reasons of clarity, the same elements have been indicated by similar reference numbers. Likewise, only the elements that are of use for understanding the invention have been shown, without regard to scale and in a schematic manner. 
       FIG. 1  illustrates schematically, in order to make it easier to understand the invention, a steering system  1  for a motor vehicle which comprises:
         a steering column  5  supporting at its top end a steering wheel  3  capable of being rotated by the driver of the motor vehicle;   a rack  6  on which the bottom end of the steering column  5  acts;   a power-steering motor  7  mechanically connected to said rack  6 ;   a torque sensor  4  associated with the steering column  5  making it possible to measure the torque applied by the driver to the steering wheel  3 ;   a position sensor  13 ;   a control device  2  making it possible to keep the position sensor  13  alert.       

     The position sensor  13  is meant to be a sensor making it possible to count the number of half-turns or turns of a rotor  8  of the motor  7  by means of a reduction ratio operating on said rotor and on the rack  6 . This type of sensor is used in power-steering motors of the prior art but without making use of the information that can be derived therefrom. 
     The control device  2  receives, amongst other things, items of information from the torque sensor  4  and from the position sensor  13 . Said items of information reflect respectively the torque applied by the driver to the steering wheel  3  and the position of the rotor  8 . 
     The control device  2  also comprises means  9  for generating a control signal and a regulator  15  for controlling said means  9 . 
     Moreover, the device  2  generates a control signal making it possible to activate the sensor  13 . The sensor  13  comprises a data-storage memory  10  and a data processing module  18 . 
     The data processing module  18  comprises:
         a position detector  16  capable of detecting an angular change of the rotor  8 ;   a comparison module  11  communicating with the memory  10 ;   a computing module  12 .       

     When the vehicle is started by the driver, the sensor is supplied with power continuously by a power supply  14  such as a battery. 
     On the other hand, when the ignition of the vehicle is switched off, the regulator  15  regulates the frequency of the acquisition periods of the position sensor  13  so as not to adversely effect the operation of the power supply  14  of the vehicle by discharging it. 
     Specifically, excessive consumption by the sensor  13  when the ignition is switched off would have the effect of discharging the power supply  14 . In order to protect the life of the power supply, the electrical consumption of the sensor  13  in standby mode is preferably less than or equal to 200 μA. 
     When the ignition of the vehicle is switched off, the regulator  15  powers the memory  10  and the means  9  for generating a control signal. 
     The means  9  for generating a control signal then transmit a control signal at a predetermined frequency, called the standby frequency, to the data processing module  18 . The general electrical consumption of the device is thereby reduced. 
     The memory  10  makes it possible to store the position of the steering wheel that was detected beforehand; in other words, as soon as a change in the position of the steering wheel is detected, the information is transmitted to the memory  10  which stores this information. 
     In parallel, the position detector  16  makes it possible to determine at all times a change in the position of the steering wheel corresponding to at least a half-turn or a turn of the rotor  8 . 
     Because of the reduction ratio that exists between the rack  6  and the rotor  8 , it should be noted that the change in position of said rotor  8  reflects with precision and exactitude the change in the angular position of the steering wheel  3 . 
     According to one method of implementation not shown, the reduction ratio may be situated on the steering column  5 . 
     Therefore, when the driver turns the steering wheel  3 , the detector  16  detects the number of half-turns or turns that the rotor  8  makes. 
     This information is transmitted simultaneously to the comparison module  11 . The latter also receives items of information from the memory  10 . 
     Therefore, the comparison module  11  compares the stored value with the detected value and then transmits these data to the computing module  12 . 
     This computing module  12  computes the angular difference and/or the number of half-turns or turns of the rotor  8  and transmits this information to the memory  10 . This information then becomes a previous data item. 
     Once processed by the sensor  13 , these items of information are transmitted to the control device  2  and more particularly to the regulator  15 . 
     Said device  2  also receives data from the sensor  4  for measuring torque applied by the driver to the steering wheel. 
     Thus, said data, obtained by the torque sensor  4  and the position sensor  13  make it possible respectively to ascertain the torque exerted by the driver on the steering wheel  3  and the angular position of said steering wheel  3 . 
     This being so, when the torque exerted by the driver exceeds a predetermined threshold or is below said threshold, the control device  2  acts on the motor  7  which generates an assistance torque by means of the rotor  8  providing assistance in turning the steered wheels of the vehicle. 
     Moreover, the sensor  13  communicates with the sensor  15  when the computing module  12  detects a change in position of the rotor  8 . 
     This regulator will thus control the means  9  for generating a control signal which will in turn generate a control signal to the data processing module  18 . 
     As an example,  FIG. 2  illustrates two examples of control signals of the module  18  for detecting change in the position of the steering wheel. These signals are pulsed-based signals, one pulse corresponding to one acquisition period during which the module  18  is “wakened” (i.e. carries out a detection). 
     The curve  2   a  is a schematic representation of the acceleration in rotation of the steering wheel  3  caused by the driver of the vehicle.  FIG. 2C  illustrates a first acquisition-period control signal generated by the generation means  9 . This first signal has two frequencies:
         a low frequency A corresponding to the standby frequency;   a high frequency B strictly higher than frequency A, corresponding to an active frequency.       

     In such an application, when no movement of the rotor  8  has been detected by the sensor  13 , the module  18  receives a low-frequency signal A. This standby frequency A is suitable for wakening the sensor  13  so as not to miss a half-turn or turn of the rotor  8  when the rotor  8  changes from immobility to a phase of rotational acceleration. In order to minimize the consumption of the sensor  13  when it has detected no movement for a certain period, the standby frequency A is as low as possible. 
     When a rotary movement of the steering wheel  3  is detected, the means  9  transmit a control signal to the module  18  at an active frequency B strictly higher than the standby frequency A and suitable for not missing half-turns or turns when the speed of rotation of the steering wheel  3  is maximal. 
     This particular feature provides the sensor  13  with a characteristic of optimal consumption. Specifically, when no movement is detected, the consumption of the position sensor  13  is low and preferably less than or equal to 200 μA. Therefore, the power supply  14  is used very little. 
     Then, so as not to “miss” a half-turn of the rotor  8 , the frequency is increased in order to move to an active frequency B making it possible to keep the module  18  alert more frequently. 
     Specifically, a lack of angular precision would be a handicap particularly for the steering-wheel return function provided by the current power-steering devices. 
     A variant, not illustrated, provided by the invention consists in:
         generating a control signal of the data processing module  18  at low frequency when no rotary movement of the rotor  8  is detected by the position detector  16 ; and   generating a continuous control signal when a half-turn or turn of the rotor  8  is detected by the module  18 .       

       FIG. 2B  illustrates an additional variant provided by the invention consisting in changing the control frequency in a manner substantially proportional to the acceleration or deceleration of the rotation speed of the steering wheel  3 . For reasons of precision, it is preferable that this frequency be not below 1000 Hz. 
     In addition to the applications that have just been illustrated with the aid of  FIG. 2 , the method according to the invention may have power supply frequencies that differ from those envisaged above. 
     As illustrated in  FIG. 2D , when no rotation is detected, the battery consumption is low. When a change in the position of the rotor is detected by the position sensor  13 , the means  9  generate a control signal to the module  18  at an active frequency that is strictly higher than the standby frequency and this has the effect of increasing battery consumption. This consumption is then reduced:
         when the position sensor  13  detects a deceleration;   at the end of a deceleration; or   when said sensor detects no rotation for a certain period.       

     It will be noted that the preferred field of application of the invention is that of vehicles. The method according to the invention may be applied to any type of vehicle fitted with a power-steering system requiring low consumption in order to ensure optimal power-supply life. Accordingly, the invention can be applied to buses, cars, trucks or any other type of vehicle.