FR3010031A1 - METHOD FOR CONTROLLING THE RECOVERABLE BRAKE RESISTANT TORQUE OF AN ELECTRIC MOTOR VEHICLE ACCORDING TO THE DECLIVATION OF THE ROAD - Google Patents

Abstract

The invention relates to a method for controlling the regenerative braking resistor torque of an automobile vehicle (10) driven by a rotating electric machine (14), the vehicle (10) comprising: the rotating electric machine (14) capable of operating in a "generator" mode in which a regenerative braking torque (Cr) opposes the rotation of the rotor; - means (22, 24, 26) for determining the gradient (D) down the road taken by the vehicle (10); - An electronic control unit (21) which is able to act on the rotating electric machine (14) to control the value of the regenerative braking torque (Cr); characterized in that the value of the regenerative braking resisting torque (Cr) is calculated as a function of the gradient (D) determined by the determining means (22, 24, 26).

Description

BACKGROUND OF THE INVENTION The invention relates to a method for controlling the regenerative braking resistor torque of a motor vehicle driven by a rotating electrical machine. . The invention relates more particularly to a method of controlling the regenerative braking resistor torque of a motor vehicle driven by a rotating electrical machine, the vehicle comprising: the rotating electrical machine which comprises a stator and a rotor linked in rotation with at least a driving wheel of the vehicle, the rotating electrical machine being able to operate in a so-called "generator" mode in which the rotor is rotated by the inertia of the vehicle to produce electrical energy, and wherein a resistive torque of regenerative braking opposes the rotation of the rotor; means for determining the slope downhill of the road taken by the vehicle; - An electronic control unit which is able to act on the rotating electrical machine to control the value of the regenerative braking resisting torque. Electric vehicles are driven by a rotating electric machine capable of operating in a "motor" mode in which the electrical energy supplying the rotating electrical machine is converted into a motor torque which drives the wheels of the vehicle via the rotor of the rotating electrical machine . The driver of the vehicle has an accelerator pedal to act on the electric motor and a brake pedal to act on a set of friction brakes that equip the vehicle wheels.

When the driver completely releases the accelerator pedal without applying the brake pedal, the vehicle is coasting. In this case, the rotor of the rotating electrical machine is rotated by the wheels under the effect of the inertia of the vehicle. The engine brake is then produced solely by the mechanical friction of the various elements of the drive train. Such engine braking results in the application of a negative friction resisting torque which opposes the rotation of the motor shaft. On electric motor vehicles, the friction-resistant torque is significantly lower than on combustion-engine vehicles. In order for the driving sensations of a motor vehicle to approach those of a motor vehicle with a heat engine, it is known to temporarily operate the rotating electrical machine in "generator" mode. In this "generator" mode, the mechanical energy that rotates the rotor is converted into electrical energy. The rotating electrical machine then produces a regenerative braking resisting torque which opposes the rotation of the motor shaft. This resistant regenerative braking torque comes to add up with the friction resisting torque to increase the engine brake. The operation of the rotating electrical machine in "generator" mode advantageously makes it possible to recharge the batteries of the vehicle in order to increase its autonomy. It is for this reason that this mode of operation is also known as "recuperative braking". The regenerative braking resistor torque is globally proportional to the electrical power produced by the rotating electrical machine in "generator" mode. The rotary electrical machine is for example formed by a synchronous motor with wound rotor. In this case, the regenerative braking resistor torque is controlled by varying the intensity of the magnetic field produced by the rotor. This is achieved by acting on the power supply of the rotor. According to a known solution of the state of the art, a rated electrical resistance torque is determined automatically. However, this solution does not anticipate road gradients in which the vehicle is likely to accelerate in the absence of regenerative braking resistant torque. According to another known solution, the driver can manually select a regenerative braking resisting torque. This solution is not satisfactory because the regenerative braking resistor torque is an additional parameter to be managed for the driver in addition to the acceleration and conventional braking of the vehicle. This does not promote a flexible driving of the vehicle. In addition, such a solution is not ergonomic to accurately choose the desired engine brake level because the driver can not intuitively determine the slowdown that the vehicle will suffer depending on the selected electrical resistor torque. The driver is indeed likely to go directly from the nominal resistance torque to a resisting torque too high compared to his wish. In particular to solve these problems, the invention proposes a method of the type described above, characterized in that the value of the regenerative braking resisting torque is calculated as a function of the slope determined by the determination means. According to other characteristics of the process: the value of the resistive resisting torque is proportional to the slope determined by the determination means; when the gradient is below a predetermined threshold, the value of the regenerative braking resistor torque is equal to a predetermined minimum value; the determination means comprise an automatic recognition device for the traffic signs announcing a dangerous descent; - The recognition device is able to identify the slope indicated on such a sign; the determination means comprise an electronic device for geolocating the vehicle, such as a "GPS", which comprises a database able to match information concerning the gradient of the roads with the geographical coordinates; the determination means comprise a sensor of the longitudinal attitude of the vehicle which is able to measure the angle of the longitudinal axis of the vehicle with respect to a horizontal plane; the value of the regenerative braking resistor torque is calculated cyclically, and when a new value of the regenerative braking resistor torque is calculated, the variation of the regenerative braking resistor torque is controlled so as to vary progressively from the current value to said new value; the regenerative braking resisting torque varies according to a predetermined slope. Other features and advantages of the invention will become apparent upon reading the following detailed description for the understanding of which reference will be made to the appended drawings in which: FIG. 1 is a diagrammatic view from above which represents a motor vehicle driven by a rotating electrical machine; FIG. 2 is a diagram which represents the intensity of the regenerative braking torque of the vehicle as a function of time; FIG. 3 is a diagram which represents the gradient of the road traveled by the vehicle according to the same time scale as that of FIG. 2. In the rest of the description, elements presenting an identical structure or functions analogues will be designated by the same reference. In the remainder of the description, longitudinal, vertical and transverse orientations indicated by the "L, V, T" trihedron of FIG. 1 will be adopted for the vehicle. For the description and the claims, the "slope" of a descending road as the sine of the angle formed between the road, in a longitudinal direction, and a horizontal plane. Thus, the steeper the road, the higher the value of the gradient. Conventionally, the slope of a road is given as a percentage corresponding to the difference between the maximum height and the minimum height of the descent divided by the distance traveled on the road between these two levels. FIG. 1 shows a motor vehicle 20 comprising four wheels 12A, 12B. Both 12A rear wheels are drive. They are rotatably mounted about a common transverse axis. The driving wheels 12A are capable of being rotated by a rotating electric machine 14 operating in "engine" mode. According to a not shown variant of the invention, the motor vehicle is a hybrid vehicle comprising a first electric motor formed by a rotating electrical machine and a second combustion engine for driving the front wheels 12B. In known manner the rotating electric machine 14 comprises a stator (not shown) wound within which a rotor (not shown) is rotatably mounted. In a nonlimiting manner, the rotating electric machine 14 is formed by a synchronous machine with wound rotor. The rotor of the rotating electric machine 14 is rotatably connected with at least the driving wheels 12A of the vehicle 10 via a longitudinal motor shaft 16. The motor shaft 16 rotates the drive wheels 12A through a torque transmission mechanism 18 such as a differential. The windings of the rotor and of the stator are supplied with electrical energy by an on-board traction battery 20 on board the vehicle 10. The rotating electric machine 14 is capable of operating in two modes: a first mode called "engine" in which the electrical energy supplying the rotating electric machine 14 is converted into a driving torque to drive the rotor in rotation to move the vehicle 10; a second mode called "generator" in which the rotor is rotated by the drive wheels 12A under the effect of the inertia of the vehicle to produce electrical energy. Thus, in "motor" mode, the rotating electric machine 14 consumes electrical energy, while in "generator" mode, it produces electrical energy. In known manner, in "generator" mode, a "Cr" resistant pair of regenerative braking opposes the rotation of the rotor, and thus of the driving wheels 12A. The value of the torque "Cr" resistant regenerative braking depends in particular on the power supply of the rotor. Indeed, the more powerful the magnetic field induced by the rotor, the greater the torque "Cr" resistant regenerative braking will be important. The vehicle 10 also comprises an electronic control unit 21 which is able to act on the supply of electricity to the rotating electric machine 14, in particular the rotor, to control the value of the "Cr" torque resistant to regenerative braking. The vehicle 10 further comprises means for determining the value of the gradient "D" down the road taken by the vehicle 10. The determination means determine the slope "D" either continuously or cyclically with a predetermined frequency. In the example shown in the figures, the vehicle 10 is equipped with a device 22 for automatic recognition of road signs. In known manner, such a device 22 comprises a camera, such as a camera (not shown), which is able to capture an image of the road ahead of the vehicle 10. The device 22 further comprises a unit electronic processing which is capable of analyzing the image to identify roadside signs present on the side of the road. The system 22 is particularly capable of recognizing signs announcing a dangerous descent. These panels are regulated by national standards which must be in accordance with the convention on road signs concluded in Vienna on November 8, 1968. Thus, according to the standards in force in France, dangerous hatches are codified under the reference "A16 "By the orders of June 6 and 7, 1977. Such a sign indicating the proximity of a dangerous descent includes an inscription indicating the gradient" D "of the road, generally in the form of a percentage. The recognition device 22 is able to identify the slope "D" indicated by the panel. The recognition device 22 is thus part of the means of determining the slope "D" of the road. The determination means also comprise a vehicle attitude sensor 24 which is capable of measuring the angle between the longitudinal axis of the vehicle 10 and a horizontal plane orthogonal to the direction of gravity. In known manner, such a sensor 24 is formed by a longitudinal acceleration sensor of the vehicle. Such a sensor 24 is for example used by a device (not shown) for electronic trajectory correction on board the vehicle 10. For example, it is a device of the "Electronic Stability Program" type, better known by its acronym. "ESP", or a device type "Electronic Stability Control", better known by its acronym "ESC".

The determining means also comprise an electronic device 26 for the geolocation of the vehicle, also known by the English name "Global Positioning System" or by its acronym "GPS". The geolocation device 26 has access to a cartographic background which is, for example, stored in a suitable medium, such as a random access memory or a read-only memory. The geolocation device 26 also has access to a database capable of matching information concerning the slope "D" of the roads with the geographical coordinates.

This is for example a three-dimensional cartography which at each geographic point of the cartographic background corresponds to an altitude. The geolocation device 26 is thus able to derive the slope "D" of the road in the direction of descent as a function of the difference in altitude between two points distant from the road. In the example shown in FIG. 1, the vehicle 10 thus comprises three means for determining the slope "D" of the road: the device 22 for automatic recognition of the road signs; the vehicle attitude sensor 24 of the vehicle 10; the geolocation device 26.

It should be noted that the recognition device 22 can determine an increase in the gradient of the road indicated by a traffic sign. On the other hand, there is no road sign to signal the end of a dangerous descent. Thus, to determine a return to a lower gradient, or zero, one of the other two means of determining the gradient must be used. The device 22 for automatic recognition of the panels, the attitude sensor 24 and the geolocation device 26 are able to communicate with the electronic control unit 21 to transmit the slope "D" of the road as soon as it has been determined. The communication is for example performed wired or radio frequency. The invention proposes a method for varying the regenerative braking torque "Cr" as a function of the slope "D" of the road determined by the determination means described above. The value of the regenerative braking resistor torque "Cr" is calculated, cyclically or continuously, by the electronic control unit 21 as a function of the slope "D" determined by at least one of the means 22, 24, 26 for determining . On a downhill road, the motor vehicle will tend to accelerate under the effect of gravity. The acceleration of the vehicle will be proportional to the slope "D" of the road. To prevent the driver from having to use conventional friction brakes, the value of the "Cr" resistant recuperative torque is calculated to vary in the same direction as the slope "D" determined by the determination means. Thus, the greater the slope "D", the more the torque "Cr" resistant regenerative regenerative braking will be high. Conversely, when the declivity "D" decreases, the torque "Cr" resistant regenerative regenerative braking also decreases.

This also makes it possible to take full advantage of the descent to recharge the traction battery 20 and thus increase the autonomy of the vehicle 10. When the gradient "D" is below a predetermined threshold "Dm", the value of the braking resisting torque recoverable is equal to a predetermined minimum "Crm" value. This is for example the value "Crm" which is applied in a standard way to vehicles 10 not implementing the method according to the invention. This threshold "Dm" predetermined ensures a braking identical to that of the engine brake for vehicles with combustion engine, even when the vehicle 10 rolls on a horizontal road. An example of application of the method is now described with reference to FIGS. 2 and 3.

During a first step "E1" of the method, at least one of the means 22, 24, 26 of determination determine the slope "D" of the road. If this gradient "D" is below the threshold "Dm" predetermined, the electronic control unit 21 sets the torque "Cr" resistant regenerative braking as being equal to its value "Crm" minimum. This is visible between the times "t0" and "tl" on the diagrams of FIGS. 2 and 3. The process is then reiterated. On the other hand, if the determined gradient "D1" is greater than the predetermined threshold "Dm", the electronic control unit 21 calculates for the pair "Cr" resistant regenerative braking a new value "Cri" greater than the value "Crm" minimum, as represented between times "t1" and "t2" in FIGS. 2 and 3.

If the latter condition is satisfied, a second "E2" command step is triggered. The second step "E2" of control is continued only when the conditions of a regenerative braking are satisfied, for example when the vehicle rolls forward and the driver does not request the accelerator. During this second control step, the electronic control unit 21 then acts on the power supply of the rotor of the rotating electric machine 14 in order to increase the power of the magnetic field induced to match the "Cr" pair. real regenerative braking resistor to the new value "Cr1" calculated by the electronic control unit 21. This makes it possible to increase the electric power produced by the rotating electric machine 14 in "generator" mode, while braking the descent of the vehicle 10. The process is then reiterated. The method is cyclically reiterated with a predetermined frequency in order to constantly adjust the value of the regenerative braking resistant "Cr" torque to the "D" gradient of the road. When, during a new iteration of the method, the declivity "D2" of the road increases again, as is the case between the times "t4" and "t5" of FIGS. 2 and 3, the electronic unit 21 The controller calculates a new value "Cr2" for the "Cr" regenerative braking torque in the first step "El". This makes it possible to take full advantage of the curves of the road to recharge the traction battery. It is preferable to avoid surprising the driver by varying too sharply the torque "Cr" resistant regenerative braking. To do this, the variation of the regenerative braking resistor torque "Cr" from a current value to a new value is progressively controlled from the current value to said new value. In the example shown in FIG. 2, the regenerative braking resistant torque "Cr" varies according to a predetermined slope, for example between the value "Cr1" and the value "Cr2" as it is visible from the instant " t4 ".

It will be understood, of course, that the invention is applicable to a vehicle also comprising one or a combination of two means for determining the gradient. Nevertheless, the multiplicity of the determination means makes it possible to obtain a more reliable method which resists in particular the deficiencies of one of the determination means. The method carried out according to the teachings of the invention makes it possible to take full advantage of the descents present on the vehicle path to recharge the traction battery and thus increase the range of the vehicle. In addition, the regenerative braking resisting torque is automatically adjusted to the gradient of the road. This prevents unintended acceleration of the vehicle on dangerous descents.

The level of adjustment is preferably determined during the design of the vehicle. Advantageously, the resistive torque can be increased, within the limits of the physical possibilities of the device, in order to respect a speed limitation coming either from the device 26 or from the recognition of a speed limitation panel by the device 22.

Claims (9)

REVENDICATIONS1. A method of controlling the regenerative braking resistor torque of an automobile vehicle (10) driven by a rotating electric machine (14), the vehicle (10) comprising: - the rotating electrical machine (14) having a stator and a rotor connected thereto in rotation with at least one wheel (12A) driving the vehicle, the machine (14) rotating electrical being capable of operating in a so-called "generator" mode in which the rotor is rotated by the inertia of the vehicle to produce power electrical energy, and in which a regenerative braking resistor torque (Cr) opposes the rotation of the rotor; - means (22, 24, 26) for determining the gradient (D) down the road taken by the vehicle (10); - An electronic control unit (21) which is able to act on the rotating electric machine (14) to control the value of the regenerative braking torque (Cr); characterized in that the value of the regenerative braking resisting torque (Cr) is calculated as a function of the gradient (D) determined by the determining means (22, 24, 26). 2. Method according to the preceding claim, characterized in that the value of the torque (Cr) resistant recuperative is proportional to the gradient (D) determined by the means (22, 24, 26) of determination. 3. Method according to the preceding claim, characterized in that when the slope (D) is less than a predetermined threshold (Dm), the value of the torque (Cr) resistant regenerative braking is equal to a predetermined minimum value (Crm). 4. Method according to any one of the preceding claims, characterized in that the determining means comprise a device (22) for automatic recognition of traffic signs announcing a dangerous descent. 5. Method according to the preceding claim, characterized in that the device (22) of recognition is able to identify the slope (D) indicated on such a sign. 6. Method according to any one of the preceding claims, characterized in that the determining means comprise an electronic device (26) for geolocation of the vehicle, such as a "GPS", which comprises a database suitable for matching information concerning the gradient (D) of roads with geographical coordinates. 7. Method according to any one of the preceding claims, characterized in that the determination means comprise a sensor (24) of the longitudinal attitude of the vehicle which is able to measure the angle of the longitudinal axis of the vehicle relative to to a horizontal plane. 8. Method according to any one of the preceding claims, characterized in that the value of the regenerative braking resistor torque (Cr) is calculated cyclically, and in that, when a new value of the regenerative braking resistor torque is calculated, the variation of the regenerative braking resistor torque (Cr) is controlled so as to vary progressively from the current value to said new value. 9. Method according to the preceding claim, characterized in that the torque (Cr) resistant regenerative braking varies according to a predetermined slope.