FR2843085A1 - Compensation system for power steering uses calculation of correcting torque to compensate for road camber or cross wind - Google Patents

Abstract

Active compensation for the lateral pull on a vehicle is provided by the electric power assisted steering system. The direction of travel of the vehicle is determined, and a correctional torque calculated for the steering system. This is weighted according to steering wheel position and vehicle speed. The procedure provides active compensation for the lateral pull on a vehicle, due to the banking of the road surface on which the vehicle is travelling, or a side wind. A compensating torque is applied to the steering wheels by the electric power assisted steering system. It includes a first block (21) which identifies and provides a positive or negative output signal (22) according to whether the vehicle is travelling in a straight line. This is linked to a further block - a first processor (23) which calculates a compensating torque, the calculation being initiated when the first block provides a positive output. A second processing block (25) weights the torque according to values representing the operating conditions of the vehicle including the angular position of the steering wheel and the speed of the vehicle.

Description

1 1

  STEERING DRAW COMPENSATION

ELECTRIC ASSISTED

  The present invention relates to a method for obtaining an active compensation for a vehicle draft, on the slope of the road on

  which is driving a vehicle or a side wind.

  It is more particularly intended for the method of obtaining active compensation for a vehicle draft, in which a couple of

  1o compensation is applied to the wheels by an electric power steering.

  Indeed, when the driver of a vehicle exerts no action on

  the steering wheel, the vehicle tends not to adopt a straight path.

  On the one hand, the vehicle is subjected to external disturbances such as the wind or road irregularities. On the other hand, in the absence of these disturbances, the vehicles tend to deviate from their trajectory either to the right or to the left: the vehicle pulls to the right or to the left. The main cause is that the roads have a curved profile so as for example to evacuate rainwater. In countries where vehicles drive to the right of the road, the

  vehicles tend to deviate from their trajectory to the right.

  The drawing of the road profile is permanent. To maintain a straight path, the driver must apply permanent opposite torque to the steering wheel. This torque can be significant, it contributes to driver fatigue on long journeys. It appears advantageous to have a means to compensate for this permanent draw. Some manufacturers have installed mechanical devices on their vehicles for this purpose, such as a spring offset on the strut or installed between the wheel support and the

  lower suspension, or the specific location of the tires.

  However, these devices can only compensate for an average slope and impose a specific layout for roads where the direction of the draft is opposite. Publication EP1031492 presents to solve these problems a method consisting in calculating in real time a draft compensation torque applied by the DAE (used to designate an Electric Power Steering), thus ensuring active compensation of the draft. To calculate this compensation torque, the angle of rotation of the vehicle's steering wheel 1o is measured and, when the value of this angle is less than a fixed value of the order of a few degrees, the value of the steering wheel torque is integrated. measured for a few seconds. Depending on the sign of the integral thus found, the value of the pull compensation applied by is incremented or decremented.

the DAE.

  Such a method generates a very dynamic compensation torque, that is to say that it is applied very quickly and with a large amplitude, up to its maximum value. Such a torque thus creates asymmetries in the torque felt by the driver. For example, an over-effort is generated to exit a large curve on the highway and resume a rectilinear trajectory. In addition, draft compensation is applied regardless of the speed of the vehicle and in particular when stationary, while at low speed, the draft of the vehicle is not sensitive and therefore should not be compensated. Finally, this solution requires a very high precision in the measurement of the steering wheel angle and in particular a very good "zero setting" (a reading of O 'of the steering wheel rotation angle) of the sensor, while industrial dispersions make

this very difficult detection.

  To overcome these drawbacks, the invention provides a method for obtaining active compensation for the draft of a vehicle, on a slope of the roadway on which a vehicle is traveling or in a crosswind, in which a torque of compensation is applied to the wheels by an electric power steering, characterized in that it comprises a first identification block returning a positive or negative straight-line driving data output, a first block for calculating a compensation torque, the calculation being initiated when the first identification block returns positive data, and a second calculation block weighting the compensation torque, calculated

  1o previously, according to values representative of the state of the vehicle.

  According to a characteristic of the present invention, the data output from the first identification block is determined by the processing of at least two values representative of the state of the vehicle. This number of multiple inputs thus makes it possible to optimize the detection of running in a straight line. These representative values are advantageously measured values of the flying torque, the steering angle and the speed of the vehicle. In this case, the first block returns positive data when simultaneously, the speed is greater than a first determined threshold, the flywheel torque is less than a second determined threshold and the steering wheel angle is less than a third determined threshold. Representative vehicle condition values may also include measuring or estimating yaw speed and / or transverse acceleration. According to another characteristic of the invention, the first calculation block determines a compensation torque as a function of the measurement of the flywheel torque, of a constant Kt, this constant being chosen beforehand according to the sampling pitch of this first calculation block, and the value of the compensation torque at the previous step. The intrusion of this constant in the calculation makes it possible to obtain a very not very dynamic calculation. Beforehand, the couple of

  compensation can be set to a predetermined value.

  According to another characteristic of the invention, the compensation torque is weighted in the second calculation block according to the speed of the vehicle. An example of weighting can be that a factor of 100% is applied in the second calculation block to the torque of compensation of the draft when the vehicle speed is greater than 50 km / h, a factor of 0% is applied when the speed of the vehicle is less than 20 km / h, and, when the vehicle speed varies between 20 km / h and 50 km / h, the application factor

  varies linearly between 0% and 100%.

  Other characteristics and advantages of the invention will become apparent on

  reading of the detailed description which follows for the understanding of which

  reference will be made to the appended drawings in which: - Figure 1 is a block diagram representative of the principle of application of a pull compensation torque, - Figure 2 is a block diagram representative of the general algorithm of the method according to l invention, - FIG. 3 is a diagram of the first identification block according to the invention, - FIG. 4 is a diagram of the first calculation block according to the invention,

  - Figure 5 is a diagram of the second calculation block according to the invention.

  According to the diagram presented in FIG. 1, the electric power steering calculator calculates in real time a torque of assistance to be provided by the system as a function of various parameters, essentially the steering torque Cv, the steering angle Av and the vehicle speed. Vspd, other parameters can also be taken into account. The final assistance torque setpoint 10 is composed on the one hand of a theoretical assistance torque setpoint 11, determined by control laws 12, and on the other hand of a draft compensation torque setpoint 13, obtained by a calculation unit 14,

subject of the invention.

  The draft compensation torque setpoint according to the invention is obtained, as shown in FIG. 2, at the conclusion of three processing phases. Firstly, an identification block 21 of the driving conditions in a straight line identifies, from the measurement of values representative of the state of the vehicle, the will of the driver to maintain a rectilinear trajectory, and determines in time real a logic variable 22 representing the driving state in a straight line. In a second step, a first calculation block 23 gives in real time, as a function of the measurement of the flywheel torque Cv and of the state of the logic variable obtained in the previous identification block, the pull compensation torque 24 In a third step, a second calculation block 25 gives in real time the draft compensation torque to be applied by the DAE 13 as a function of the speed of the vehicle Vspd and of the draft compensation torque 24 calculated by the

first calculation block 23.

  According to a first embodiment shown in FIG. 3, the identification block 21 of the driving conditions in a straight line takes into account the input values which are the measurement of the steering wheel angle Av, the measurement of the steering wheel torque Cv and measuring the speed of the vehicle Vspd. The absolute value of these measurements is respectively compared to a threshold value. By way of nonlimiting example, the threshold corresponding to the measurement of the steering wheel angle is +/- 20, the threshold corresponding to the measurement of the flying torque is + / 1.5 Nm, and the threshold corresponding to the measurement of vehicle speed is

km / h.

  The driver's desire to drive in a straight line is detected, according to the present invention, by combined monitoring of the vehicle speed, the steering wheel torque and the steering wheel angle. Multiple monitoring thus makes it possible to stand out from the problem of zero setting, present when the detection of taxiing in a straight line is carried out on the sole information of the steering angle. The vehicle is thus assimilated as traveling in a straight line when on the one hand the vehicle speed is sufficient, this speed decreasing when the vehicle enters a marked turn, and when io on the other hand no effort or steering angle, capable of represent a

marked turn, is not detected.

  An embodiment of the identification method according to the invention is shown in FIG. 3. Information representative of the speed of the vehicle Vspd is obtained from a sensor, for example of the accelerometer type, and used as input to the identification method. This measurement is then compared with a threshold value 31 below which the vehicle speed is estimated to be insufficient to draw the conclusion of driving in a straight line. As long as the measured speed is lower than the comparison threshold, a loop return 32 is implemented and new speed values are compared with the corresponding threshold 31. When the vehicle speed is higher than the comparison threshold, information accordingly 33 is sent as input to a

collector 34.

  Two other inputs are connected to the collector 34, similarly. Information representative of the flywheel torque Cv and respectively of the flywheel angle Av is obtained from sensors connected to the steering column, for example from a force sensor and from an angular displacement sensor respectively, and used as inputs to the identification process. The absolute values of these measurements are then compared to a torque threshold value 31c and respectively to an angle threshold value 31a, above which the action exerted by the driver on the steering wheel of the vehicle is estimated to be sufficient to draw the conclusion therefrom. the vehicle is not driving in a straight line. As long as the absolute values of the measured flywheel torque and of the measured flywheel angle respectively are greater than the corresponding comparison threshold, a loop feedback 32c, respectively 32a is implemented and new torque and angle values respectively are then compared. When the absolute value of the steering wheel torque and of the steering wheel angle respectively is lower than the comparison threshold, information

  positive 33c, respectively 33a is sent to the input of a collector.

  The collector 34 is produced by means of an AND gate with triple input and double output. As long as positive information is received simultaneously at the three inputs of the collector, a time counter CI is incremented by a predetermined value dt. This counter C1 is compared with a threshold value 35

  equivalent, according to a preferred embodiment, to 2 seconds.

  The incrementation of the counter C1 then ends when this counter is greater than the corresponding threshold value, which is representative of a vehicle having specific characteristics of running in a straight line, and this for an estimated duration sufficient to ensure that this driving state 36. The incrementation of the counter CI also ends in cases where at least one of the input information is not positive, the collector then returning a negative response 37 concerning the driving state online

  right and resetting the Cl counter to zero.

  The information at the output of this taxi identification block 21 is therefore a YES / NO flag representative of the state of the variable "taxi state in a straight line". A YES flag therefore means that the vehicle is in a straight-line driving situation, and that a draft compensation torque must be applied. The torque value 24 corresponding to the pulling action exerted by the road is calculated in a first calculation block 23 shown in FIG. 4. At the input of this first calculation block 23, the pull compensation value obtained in step previous 24 'is firstly multiplied to a constant Kt dependent on the sampling step and secondly added to the measured value of the flywheel torque Cv. These two values are then processed by operational blocks, operating a division of the same constant Kt, in order to obtain the following relation io: Count (n) = Cv + Count (n- 1) + Compjtir (n- 1) * (Kt- 1) Kt Kt in which: Comp tir (n) denotes the pull compensation torque, Comptir (nl) denotes this torque at the previous step, Kt denotes a dynamic constant,

Cv designates the flying couple.

  A saturation block 41 is inserted at the output of this calculation block 23, in order to limit the compensation to a maximum value. This value is

  stored in memory until a new value has been calculated.

  According to a particular embodiment of the invention, the couple of

  draft compensation can be set initially to a predetermined value.

  An initial compensation is then generated and makes it possible to advantageously replace the mechanical drawdown compensation devices. Depending on the markets for which the vehicles are intended, and the associated traffic directions, the initial compensation may indeed be initially set "to the left" or "to the right". In addition, the initial setting of the compensation torque can easily be readjusted to adapt to new road conditions, or conversely be kept at a fixed value, not subject to the dispersions and wear that may present. mechanical parts. The first calculation block 23 previously described returns a pull compensation value 24 calculated as a function of the road and the vehicle. It is then in a second calculation block 25 to give the 1o draft compensation torque applied by the vehicle 13. By way of nonlimiting example, the second calculation block 25 represented in FIG. 5, takes into account the vehicle speed values to judge the application force of the draft compensation torque. An equivalence table 1, to which an input value of the speed of the vehicle Vspd is supplied, returns an application percentage as output. For example, at a speed between 0 and 20 km / h, corresponds to an application factor of 0%: the draft of the vehicle, which is not sensitive to the driver at these low speeds, has no to be compensated. Conversely, for speeds greater than km / h, the application factor is 100%. Finally, between the values of 20 to 50 km / h, the application factor varies linearly from 0 to 100%. This application as a function of the speed of the vehicle makes it possible to obtain an adaptive compensation, which does not cause the driver any feeling of

brutal correction.

  This objective is also achieved by the introduction of the constant Kt, which is a function of the sampling step of the first calculation block. This constant allows an adjustment of the time of convergence of computation. The value chosen directly influences the time necessary for the compensation of the draw to be complete. The higher the value of Kt, the longer the time for obtaining full compensation. This constant thus makes it possible to have a computation whose dynamics can be modulated and which one can therefore make less

  binary in order to obtain an adaptive draw compensation.

  The invention is in no way limited to the embodiment described and illustrated, which has been given only by way of example. It will indeed be understood that the device according to the invention may require knowledge in real time, in addition to the quantities explained above such as the torque and the steering wheel angle or the speed of the vehicle, of additional quantities such as, not only 1o comprehensive, measuring or estimating the yaw speed of the vehicle and / or

  the transverse acceleration of the vehicle.

Claims (9)

  1. Method for obtaining an active compensation for a vehicle draft, on a slope of the roadway on which a vehicle is traveling or in a side wind, in which a compensation torque is applied to the wheels by an electric power steering , characterized in that it comprises: * a first identification block returning a positive or negative straight line driving data output, e a first block for calculating a compensation torque, the calculation being initiated when the first identification block returns positive data, * a second calculation block weighting the compensation torque, calculated previously, according to values representative of the state of the vehicle.   2. Method for obtaining an active drawdown compensation according to claim 1, characterized in that the data output from the first identification block is determined by the processing of at least two values   representative of the condition of the vehicle.   3. Method for obtaining active draft compensation according to claim 2, characterized in that the values representative of the state of the vehicle are measured values of the steering wheel torque, of the steering wheel angle and vehicle speed.   4. Method for obtaining active draft compensation according to claim 3, characterized in that the first block returns positive data when simultaneously, the speed is greater than a first determined threshold, the flywheel torque is less than a second determined threshold and the flying angle is less than a third determined threshold. 5. Method of obtaining active drawdown compensation according to one of the   Claims 2 to 4, characterized in that the representative values of   vehicle condition include measuring or estimating the speed of   yaw and / or transverse acceleration.   6. Method for obtaining active draft compensation according to claim 1, characterized in that the first calculation block determines a compensation torque as a function of the measurement of the flywheel torque, of a constant Kt, this constant being chosen beforehand according to the sampling step of this first calculation block, and the value of the torque compensation at the previous step.   7. Method for obtaining active draft compensation according to claim 6, characterized in that the compensation torque can   be initially set to a predetermined value.   8. Method for obtaining active draft compensation according to claim 1, characterized in that the compensation torque is   weighted in the second calculation block according to the vehicle speed.   9. A method of obtaining active draft compensation according to claim 8, characterized in that a factor of 100% is applied in the second calculation block to the draft compensation torque when the vehicle speed is greater than 50 km / h, a factor of 0% is applied when the vehicle speed is less than 20 krn / h, and, when the vehicle speed varies between 20 km / h and 50 km / h, the factor   of application varies linearly between 0% and 100%.