FR2720699A1 - Control process for electric vehicle to improve comfort - Google Patents

Abstract

The control process operates on the drive signals applied to the motor current controller. The slope of the current versus time curve is held below a maximum rate determined by a comfort value. The comfort value is determined from an inverse function of the fluctuations in the current. The current change over a set time is determined to provide the comfort threshold value. The time span used to determine the rate of fluctuation is selected according to the sense of rotation of the motor and the sense of variation of torque of the motor, effectively allowing different threshold slopes depending on sense of rotation and acceleration or deceleration.

Description

Method for controlling a vehicle engine
with improved comfort
For driving a motor vehicle, the driver has driving devices to adjust the speed. If you consider a car, and in particular an electric car, the accelerator pedal regulates the amp and the current of the current flowing through the engine. In case of fast ~ -t fast or rapid release of this -idde, the engine had c immediately requested and applies to the car a sudden acceleration or deceleration. This variation in speed modifies the existing balance of the various elements of the kinematic chain extending from the engine to the wheels, which could at that time be relatively free to "float" with respect to each other, and involves them in an action of brutal cooperation.

 Each of the elements of the chain has a particular mechanical inertia which can delay its reaction the action mentioned above, so that this cooperation can only be established after a relatively long oscillating regime and which, above all, can shake the driver.

 It is known to limit the acceleration by fixing, still in the example of the electric car, a maximum limit to the time derivative of the current.

A time derivative expresses the slope of a curve representative of a function, in this case the function expressing the evolution of the current over time. A weak slope therefore corresponds to a weak acceleration, without jerks.

 This solution is not satisfactory because, even in the case of a relatively small current variation, therefore of short duration, jolts still occur.

 The present invention aims to reduce these tremors.

 To this end, the invention relates to a method for controlling an engine of a vehicle from vehicle driving members, the engine receiving at least one control signal generated by one of the driving members and capable of varying. , method in which the derivative over time is kept dw command signal below a maximum value, characterized in that the derivative over time of the control signal is kept below a comfort value determined in inverse function of signal variations.

 Thus, a slight variation in the control signal has a significant effect only after a duration determined by the comfort value, which corresponds to a maximum limit of acceleration, or deceleration, of the vehicle. As a result, the elements of the kinematic chain, which possibly floated relative to each other before the signal variation occurs, are only slightly requested to come to cooperate with each other and therefore do not tend to oscillate and to create jolts.

 If, in an electric car, the control signal is the supply current of the engine, in an internal combustion car it is the flow of oxidant sent to the engine.

 The invention will be better understood using the following description of the preferred embodiment of the control method of the invention, applied to an electric car, with reference to the appended drawing, in which: - Figure 1 illustrates the prior art method and - Figure 2 illustrates the method of the invention.

 FIG. 1 represents the amplitude of the armature current I of the rotary motor of the electric car, plotted on the ordinate, as a function of time t, plotted on the abscissa.

 It will be recalled that the armature current, supplied by the car battery, passes through the rotor of the motor to supply it with energy which is transformed into an engine torque. The speed of rotation of the rotor, and therefore the power of the motor, varies from ca in the same direction as the armature current.

 The engine speed control is carried out from an accelerator pedal, through a pedal stroke sensor creating a driving signal which increases the intensity of the motor armature current with the depressing of the pedal.

 When the accelerator pedal is depressed suddenly, the driving signal has a steep rising edge and the armature current I should have substantially an edge 1 of the same shape, between two bearings Il and I2.

 In the prior art, the steep front 1 was replaced by an inclined front 2, represented by a dotted line em, of slope, or time derivative, oIM / dt determined. The duration TO of edge 2 was therefore proportional to the difference ol = I2-I1 between the two armature current stages I1 and 12. Thus, whatever the variation oI of the armature current, the derivative over time of the control signal was kept below the maximum value oIM / dt.

 To illustrate the method of the invention, three alternations of the armature current I are shown in FIG. 2, as a function of time t.

 The first half-wave corresponds to an arbitrarily called positive armature current because it creates a motor or traction torque. Starting from a zero current, the first half-wave comprises three stages 12, 14 and 16 respectively preceded by two rising edges ll and 13 and a falling edge 15. A falling edge 17 follows the bearing 16 and reduces the current to zero.

 The second half-wave has, for negative currents creating a braking torque, substantially the same shape as the first half-wave and has bearings and fronts 21 to 27 homologous with the bearings and fronts 11 to 17.

 The representation of the third alternation 30, positive, has just started.

 To implement the method of the invention, the accelerator pedal stroke is monitored by the sensor to determine the current of the above bearings, its rest position corresponding to a predetermined negative engine braking current. , and its maximum depression corresponding to a predetermined motor current. In this example, the motor current varies linearly with the pedal travel between these two extreme current values.

Having thus determined, by interpolation, the value of the current I11 to be applied to the motor, the time slope Poil, or dI / dt, of the front il, is calculated, corresponding to the passage of the armature current from the value 0 to the value I11, by the formula
Pîl = dI / dt = oI / T1 with = = I11 - O and T1 = value of a minimum edge duration threshold 11.

 Expressed differently, we have the following relation: oI / (dI / dt) = constant.

 The time derivative Pîl represents a comfort value determined as an inverse function of the variation of the control signal.

 The duration T1 represents a determined comfort duration, which makes it possible to guarantee that any variation in the armature current will extend over at least this comfort duration, that is to say that the acceleration, positive or negative, will be limited and that jolts will be eliminated or at least reduced. In particular, the small variations in the armature current will correspond to a very small time derivative, therefore will not cause jolts.

 In this way the derivative of the control signal is maintained in time below the comfort value Poil, determined as an inverse function of the variations of the signal and the comfort value P11 is determined by making it correspond to a variation xI of the control signal of duration of comfort T1 determined. As a result, the comfort of the car is improved by reducing the jolts during acceleration and deceleration.

 A calculation block, connected to the position sensor, performs the calculations defining the current I, in order to control a known circuit for adjusting the armature current I of the motor.

The same is done for the edges 13 and 15. For the edge 17 of return to zero of the current, the threshold T1 is replaced by a threshold T2. This change in duration threshold value is due to the fact that it is adapted to the kinematic behavior of the elements of the car, whose time constant in oscillation depends on the accelerations they undergo. In particular, the transition to zero acceleration (current I = 0) modifies the amplitude and the resonant frequency of these elements. Thus, the duration of comfort, T1 or
T2, as a function of the direction of variation of the motor force and, here, as a function of the final value of the current, for which the acceleration decreases to a zero value.

 The method is applicable in the same way for the second half-wave, by replacing the pair of threshold values T1 and T2 by a pair of threshold values T3 and T4, to take account of the different behavior of the elements, under acceleration or under braking.

 In summary, the choice, for each alternation, between the values T1 and T2, in one case, and T3 and T4, in the other case, of the duration of comfort is, as explained above, a function of the direction of variation. of the force exerted by the motor.

 In addition, each alternation is associated with two specific values, T1, T2 and T3, T4, that is to say that the duration of comfort T1 or T2 and T3 or T4 is determined as a function of the direction of the force. exerted by the engine on the vehicle.

 The kinematic behavior of the elements of the car is thus taken into account precisely in the four configurations defined above.

 In this example, provision is also made to limit the temporal variation dI / dt of the armature current applied to the motor to the maximum temporal slope value oIM / dt, that is to say that the maximum value is substituted eIM / dt at the comfort value dIM / dt in the case where the latter is greater than the former, which would occur in the case of a significant variation in current CI.

 The invention is not limited to a rotary motor but can also be applied to a linear motor.

Claims (5)

1. A method of controlling an engine of a vehicle from vehicle driving members, the engine receiving at least one control signal generated by one of the driving members and capable of varying, method in which the derivative in time of the control signal (dI / dt) below a maximum value (dIM / dt), characteristic by the fact that the derivative is kept in the tenps Kdisit) of the control signal below a comfort value tdIM / dt) determined as an inverse function of the variations (oI) of the signal. 2. Method according to claim 1, in which the comfort value is determined (dIM / dt) by making it correspond to a variation of control signal (oI) of determined comfort duration (T1-T4). 3. Method according to one of claims 1 and 2, wherein said maximum value (CIM / dt) is substituted for the comfort value (dIM / dt) in the event that the latter (dI / dt) is greater than that one (CI / dt). 4. Method according to one of claims 2 and 3, wherein said comfort duration is determined (T1, T2; T3, T4) depending on the direction of the force exerted by the engine on the vehicle. 5. Method according to one of claims 2 to 4, wherein said comfort duration is determined (T1, T3; T2, T4) depending on the direction of variation of the motor force.