FR3131259A1 - Method for regulating the creep speed of an electric or hybrid vehicle - Google Patents

Abstract

This method for regulating the creep speed of a vehicle comprises the following steps: - Conversion (step 16) of a value representative (12; 18) of the depression of a brake pedal into a target speed (20 ) crawling; - Determination of a reference torque value (22) to obtain the target creep speed; - Calculation (step 28) of the difference between the target speed (20) obtained and the actual speed (26) of the vehicle; - Conversion (step 32) of the difference between the target speed (20) obtained and the actual speed (26) of the vehicle into a regulation torque (34); and - Sum (step 42) of the reference torque (22) with the regulation torque (34) to obtain a creep torque (44) intended to be applied to the wheels. Figure for abstract: Fig 4

Description

Method for regulating the crawl speed of an electric or hybrid vehicle

The present invention relates to the crawling of a motor vehicle with electric or hybrid traction or propulsion.

The invention relates more particularly to the regulation of the crawl speed as a function of disturbances applied to the vehicle, for example as a function of an increasing slope.

Previous techniques

An electric or hybrid vehicle is capable of crawling, that is, moving forward at a reduced speed when the accelerator pedal is raised, with the speed controlled by the brake. Crawling is possible on flat roads or with reduced speeds on rising slopes with a slope less than a threshold, for example of the order of 10%, the speeds being lower the higher the slopes. In particular, crawling also allows staying on site on rising slopes whose slope is equal to said threshold, for example of the order of 10%.

We represented on the a schematic mapping 2 of a torque coming from a vehicle engine, called creeping torque, imposed on the wheels of an electric or hybrid vehicle with automatic gearbox as a function of the speed of said vehicle when the accelerator pedal of the vehicle is raised, if the brake pedal is not depressed. This map 2 is for example contained in the on-board computer or in a vehicle recording medium and readable by the on-board computer.

The abscissa axis represents the speed V of the vehicle while the ordinate axis represents the creeping torque C applied to the wheels.

In portion 4 at high speed, and in the case where the accelerator pedal is not pressed, the instruction perceived by the on-board computer, reflecting the driver's wishes, is a slowdown of the vehicle, i.e. i.e. negative acceleration. The creeping torque is therefore negative in order to slow down the vehicle. In an electric vehicle, the electric motor can then enter an energy-generating mode, producing current while decelerating the vehicle, that is, braking it. This is a case of regenerative braking.

As a variant not shown, if the vehicle does not use regenerative braking, the creeping torque applied could also be zero when the speed of the vehicle is at high speed.

In portion 6 at low speed, which constitutes a portion strictly speaking of crawling since the speed of the vehicle is positive but while remaining low, which means that the vehicle is moving forward at moderate speed and that the torque of applied ramp is positive, that is to say it is a motor torque (positive and not negative as in the case of regenerative braking), a first operating point 8 exists in order to maintain a speed of the vehicle constant on a flat road, the creeping torque applied only serving to resist the friction forces induced among others by the air and the road (more precisely: to the resisting torque F that said friction forces apply to the wheels) .

A second operating point 10 exists at zero speed V and for a maximum creeping torque C. This concerns in particular the case in which the vehicle remains on site on an upward slope equal to a threshold, of approximately 10% for example. For a slope greater than said threshold, the torque from point 10 can no longer compensate for the higher load and the vehicle leaves in the opposite direction, in the direction of descent.

The passage from the first operating point 8 to the second operating point 10 is carried out for example during movement of the vehicle on an upward slope.

Conversely, the passage from the second operating point 10 to the first operating point 8 corresponds for example to starting and moving the vehicle on a flat road, in which the vehicle gradually gains speed as soon as release the brake pedal. As the speed increases, the creep torque applied to the wheels is reduced, and the vehicle speed stabilizes as soon as the crawl torque exactly compensates for the resisting torque F coming from the friction forces.

The on-board computer also allows you to manage the brakes when crawling.

We represented on the a schematic graph showing the ramp portion 6 at low speed of the , for different percentages of depression 12 of the brake pedal. The abscissa axis represents the speed V of the vehicle while the ordinate axis represents the creeping torque C applied.

When the brake pedal is not depressed, in other words for 0% depression, and the vehicle is at zero speed, the applied creep torque C is maximum. This allows in particular a hill start without rolling back. This also allows the vehicle to begin to accelerate under the effect of the crawl engine torque and gain speed.

Conversely, the more the brake pedal is pressed, the less the creeping torque C applied to the wheels is significant.

Thus, as soon as the brake pedal is completely released, the vehicle applies a torque equivalent to the second operating point 10, in other words, equivalent to the maximum crawling effort.

However, the maximum crawling effort currently only allows the vehicle to be kept on site on a slope lower than a predetermined threshold, for example a slope of 10%, or to move it forward on a lesser slope. Thus, the vehicle cannot crawl for rising slopes greater than this threshold, for example 10%.

A first solution consists of shifting upwards the mapping 2 illustrated in the , in other words to increase all the torque values corresponding to a given speed of the vehicle by a predetermined constant value, in order to have a maximum crawling effort allowing crawling up to higher slopes, for example of the order 15%, or even 30%.

We represented on the cartography 2 of the as well as a second mapping 14 including a shift towards larger couples.

However, this second mapping 14 has the effect of increasing the speed of the first operating point 8, namely the cruising speed of the vehicle on a flat road, without pressing any pedal (accelerator, brake). This poses a problem when starting the vehicle since the start of the vehicle will be more abrupt due to the greater torque applied to the wheels, which produces an unpleasant sensation of racing for the passengers.

A second problem is that of safety on a flat road, on which the crawling speed is then very high, increasing the risk of accidents.

In other words, the second mapping 14 improves the crawling performance on an upward slope for the passengers of the vehicle but deteriorates the crawling performance on a flat road.

A second known solution consists of determining the mass of the vehicle and the slope on which the vehicle is located, then modulating the torque map 2 accordingly in order to obtain a high torque for a steep upward slope of more than 10%.

However, at low cost, the methods of measuring and identifying slope or mass with current sensors, notably accelerometers, are unreliable, particularly when the vehicle is moving.

The present invention therefore aims to overcome the aforementioned drawbacks by allowing crawling on steep rising slopes while maintaining the current crawling performance on a flat road.

The subject of the present invention is a method for regulating the crawl speed of an electric or hybrid vehicle comprising a braking circuit and wheels, the method comprising the following steps:

- Conversion of a value representative of the depression of a brake pedal of the braking circuit into a target crawling speed of the vehicle

- Determination of a reference torque value to be applied to the wheels, as a function of said value representative of the depression of the brake pedal and the actual speed of the vehicle, to obtain said target crawling speed on a flat road;

- Calculation of the difference between the target speed obtained and the actual speed of the vehicle;

- Conversion of the difference between the target speed obtained and the actual speed of the vehicle into a regulation torque; And

- Sum of the reference torque value to be applied to the wheels to obtain the target crawl speed on a flat road with the regulation torque to obtain a crawl torque intended to be applied to the wheels.

Thus, whatever the inclination of a rising slope, for example in a non-limiting manner up to 15% or even 30%, the vehicle can move along this slope, regardless of the mass of the vehicle. . This process also makes it possible to have no setback, or at least to limit the setback to a few centimeters, when the vehicle is moving on a slope.

In a particular mode of implementation, the method further comprises a step of consolidating the ramp torque by applying a minimum limit and a maximum limit to the ramp torque.

Advantageously, the minimum limit is equal to the value of the torque to be applied to the wheels to obtain the target crawling speed on a flat road.

Advantageously, the maximum limit is equal to a torque value predefined by a vehicle safety module.

In a particular mode of implementation, the value representative of the depression of the brake pedal is a pressure value in the braking circuit of the vehicle.

Advantageously, the step of converting the difference between the target speed obtained and the actual speed of the vehicle into a regulating torque is carried out after a step of verifying the fact that no acceleration of the vehicle is requested by pressing the vehicle's accelerator pedal.

Advantageously, the step of converting the difference between the target speed obtained and the actual speed of the vehicle into a regulating torque is carried out after a step of verifying the fact that the actual speed of the vehicle is less than a predefined speed threshold .

In one mode of implementation, the predefined speed threshold corresponds to the maximum crawling speed of the vehicle, preferably less than 20 kilometers per hour.

The present invention also relates to a computer program configured to implement the method as defined above, when it is executed by the computer.

An object of the present invention is also a motor vehicle comprising a computer and a computer-readable recording medium, the recording medium comprising a computer program as defined above.

Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

which has already been mentioned, schematically illustrates a map of a creeping torque imposed on the wheels of an electric or automatic hybrid vehicle as a function of the speed of said vehicle when the brake pedal is not depressed;

which has already been mentioned, schematically illustrates a map of a portion of low-speed crawling for different percentages of depression of the brake pedal of a vehicle;

which has already been mentioned, schematically illustrates the cartography of the as well as a second mapping shifted towards larger couples;

schematically illustrates a method for regulating the crawl speed of a vehicle in the form of a control loop according to the invention; And

schematically illustrates an example of a relationship between a target speed of the vehicle and a value representative of the depression of the brake pedal.

Detailed presentation of at least one embodiment

We have shown schematically on the a method of regulating the crawl speed of a vehicle in the form of a control loop. This is for example an electric or hybrid automobile vehicle.

The vehicle comprises in particular a braking circuit comprising a brake pedal, an accelerator pedal, wheels and an on-board computer. The on-board computer is in particular a computer making it possible to read a recording medium included in the vehicle, the recording medium comprising a computer program configured to implement the method below when executed by the on-board computer.

In a first step 16, a value representative of the depression of the brake pedal 12 is converted, for example in a particular embodiment, the value of the pressure 18 in the braking circuit, into a value target speed 20 of vehicle crawling on flat road. As will be seen below, thanks to the method according to the invention, this crawling speed will be identical on a sloping road thanks to closed-loop regulation of the vehicle speed around a setpoint corresponding to the target speed.

The value of the pressure 18 in the braking circuit is for example obtained by direct measurement by a pressure sensor placed in the braking circuit of the vehicle.

This conversion step 16 is carried out for example by means of a theoretical or empirical map 24 included in the computer program. The mapping 24 used attributes in the form of a correspondence a desire for speed on the part of the driver of the vehicle to a value representative of the depression of the brake pedal 12, for example the braking pressure 18. For example, the cartography used may be similar to the graph illustrated in . This figure represents on the abscissa the actual depression of the brake pedal 12, the graduations corresponding to percentages of depression, in this example between 0% (0) and 25% (0.25). The graduation corresponding to the pressures has not been shown. On the ordinate, the graph of the represents the target speed 20 in kilometers per hour. In this example the graduation goes from 0 to 6 km/h.

When the brake pedal is not actuated, in other words when the value of the depression percentage 12 is 0%, the target speed 20 is the maximum crawl speed of the vehicle previously defined arbitrarily, preferably less than 20 kilometers per time for security reasons. On the example of the , this speed is 5.5 km/h.

During this same step 16 or separately, the value representative of the depression of the brake pedal 12 or 18 is used again in order to determine a reference torque value 22 to be applied to the wheels. More precisely, each reference torque value is determined as a function of the actual speed V 26 of the vehicle and this value representative of the depression of the brake pedal 12 or 18, from a calibration 23 corresponding to the . It makes it possible to obtain the target value of a reference crawling torque 22 on a flat road, as explained in support of the .

The reference torque 22 is a decreasing function of the value representative of the depression of the brake pedal 12 or 18.

In the case where no pressure on the brake pedal is observed, the reference torque 22 to be applied to the wheels according to the actual speed V 26 of the vehicle to obtain the target crawling speed on a flat road, once the torque of rampage exactly compensates the resistant torque F, is then at its maximum as illustrated on the map of the by the upper curve.

In reference to the , the target speed 20 corresponding to the maximum crawl speed can for example be maintained for light presses on the brake pedal, for example for a depression 12 of less than 1% (0.01 on the abscissa axis of the ). Then, preferably, the target speed 20 decreases linearly as the brake pedal is depressed. This allows the driver to control the vehicle's crawl speed using the braking system. This also prevents the engine from fighting against the braking force: when the driver brakes beyond 20% pressure 12 of the brake pedal, we understand that the driver's desire is to stop the vehicle, and no torque is present. is applied to the wheels.

After having recovered the value of the real speed 26 of the vehicle, in other words the instantaneous speed, a step 28 is carried out for calculating the difference between the value of the target speed 20 of vehicle crawling obtained in the previous step 16 and the real speed 26 of the vehicle.

In particular, the actual speed 26 of the vehicle can be obtained by direct measurement by a speed sensor.

The computer program includes for example a subtractor 28 intended to carry out step 28 in order to obtain at output a difference 30 between the value of the target speed 20 and the actual speed 26 of the vehicle.

Then, a step 32 is carried out for converting the difference 30 between the value of the target speed 20 and the actual speed 26 of the vehicle into a regulation torque 34. The regulation torque 34 corresponds to the additional torque to be applied to the wheels, in addition to the reference torque, to fill the speed gap determined previously. In particular, the difference 30 symbolizes an increasing slope which causes the actual speed 26 to drop relative to the target speed 20 and the regulating torque 34 therefore corresponds to the additional torque to be applied to compensate for the additional resisting torque induced by the increasing slope.

It is in a manner known per se a couple of the form m*g*sinα, formula in which m designates the mass of the vehicle, g the acceleration of gravity and sinα the sine of the positive angle α of the rising slope.

The computer program includes for example an integral proportional corrector 36 intended to carry out step 32 of converting the deviation 30 into a regulating torque 34.

Advantageously, step 32 is only carried out if the deviation 30 is non-zero, or greater than a predefined deviation, for example 3 kilometers per hour, which makes it possible to only request the integral proportional corrector 36 in a situation of rising slope or more generally a situation where the vehicle is slowed down by its environment.

In a particular mode of implementation, step 32 of converting the difference between the target speed 20 obtained and the actual speed 26 of the vehicle into a regulating torque 34 is only carried out after verification of certain conditions.

In particular, step 32 is carried out after a step 38 of checking that no acceleration of the vehicle is requested. This verification is for example carried out by direct measurement of the depression of the vehicle's accelerator pedal. This condition is fundamental to identify the driver's desire to crawl. This condition allows in particular the integral proportional corrector 36 not to conflict with the driver's desire to move forward. For example, with light pressure on the accelerator pedal, the driver might want to go beyond the crawl speed. In the event that this condition is not in place, the integral proportional corrector 36 would calculate a negative torque to be added at the driver's discretion in order to bring the vehicle speed back towards the crawl target, which goes against the desire of the driver.

Furthermore, in an implementation mode compatible with the previous condition, the step 32 of converting the difference between the target speed 20 obtained and the actual speed 26 of the vehicle into a regulating torque 34 is only carried out after a step 40 of verifying the fact that the actual speed 26 of the vehicle is less than a predefined speed threshold, the predefined speed threshold being for example the maximum crawling speed of the vehicle, preferably less than 20 kilometers per hour.

This condition allows the integral proportional corrector 36 to be activated only when the vehicle is already in a zone considered as a ramp portion 6. Indeed, during a long deceleration phase, too early activation of the integral proportional corrector 36 could introduce oscillations and instability when servoing. This harmful effect is greatly reduced with a predefined speed threshold.

We then carry out a step 42 of summing the reference torque 22, that is to say the torque to be applied to the wheels to obtain the target crawling speed on a flat road, with the regulating torque 34 in order to obtain a creeping torque 44 intended to be applied to the wheels.

The computer program includes for example an adder 46 intended to carry out step 42.

Optionally, the method further comprises a step 48 of consolidating the creep torque 44 by applying to the crawl torque a minimum limit 50 and a maximum limit 52 which can thus limit the extreme values of the creep torque 44 intended to be applied to the wheels.

In particular, the minimum limit 50 for the creeping torque 44 can be equal to the value of the reference torque 22.

In addition, the maximum limit 52 for the creep torque 44 can be equal to a torque value predefined by a vehicle safety module. The safety module defines, for example, as a maximum limit 52 the maximum crawling speed of the vehicle, preferably less than 20 kilometers per hour, or a maximum limit 52 which may depend on the inclination of the slope.

The computer program comprises, for example, a limitation means 53 intended to carry out step 48.

The conditions of this consolidation step 48 make it possible to guarantee that the method according to the invention will not degrade the driving performance on a flat road and will not endanger passengers with too high a crawling speed. We finally obtain a consolidated creeping torque 54.

Claims (10)

Method for regulating the crawl speed of an electric or hybrid vehicle comprising a braking circuit and wheels, characterized in that it comprises the following steps:

• Conversion (step 16) of a representative value (12; 18) of the depression of a brake pedal of the braking circuit into a target speed (20) of vehicle creep;
• Determination of a reference torque value (22) to be applied to the wheels, as a function of said representative value (12; 18) of the depression of the brake pedal and the actual speed of the vehicle, to obtain said target speed crawling on a flat road;
• Calculation (step 28) of the difference between the target speed (20) obtained and the actual speed (26) of the vehicle;
• Conversion (step 32) of the difference between the target speed (20) obtained and the actual speed (26) of the vehicle into a regulation torque (34); And
• Sum (step 42) of the reference torque value (22) to be applied to the wheels to obtain the target crawl speed on a flat road with the regulation torque (34) to obtain a crawl torque (44) intended to be applied to the wheels.

Method according to claim 1, further comprising a step (48) of consolidating the ramp torque (44) by applying to the ramp torque a minimum limit (50) and a maximum limit (52). Method according to claim 2, in which the minimum limit (50) is equal to the value of the reference torque (22) to be applied to the wheels to obtain the target crawling speed on a flat road. Method according to one of claims 2 and 3, in which the maximum limit (52) is equal to a torque value predefined by a vehicle safety module. Method according to any one of claims 1 to 4, in which the value representative of the depression of the brake pedal (12) is a pressure value (18) in the braking circuit of the vehicle. Method according to any one of claims 1 to 5, in which the step (32) of converting the difference between the target speed (20) obtained and the actual speed (26) of the vehicle into a regulating torque (34) is carried out after a step (38) of checking that no acceleration of the vehicle is requested. Method according to any one of claims 1 to 6, in which the step (32) of converting the difference between the target speed (20) obtained and the actual speed (26) of the vehicle into a regulating torque (34) is carried out after a step (40) of verifying that the actual speed (26) of the vehicle is lower than a predefined speed threshold. Method according to claim 7, in which the predefined speed threshold corresponds to the maximum crawling speed of the vehicle, preferably less than 20 kilometers per hour. Computer program configured to implement the method according to any one of claims 1 to 8, when executed by the computer. Motor vehicle comprising a computer and a computer-readable recording medium, the recording medium comprising a computer program according to claim 9.