DEVICE AND METHOD FOR BRAKEING A MOTOR VEHICLE WITH AN ELECTRIC MACHINE

Description

[0001] This application relates to a braking device and method for a motor vehicle equipped with an electric machine.

[0002] Purely electric and hybrid electric vehicles are equipped with an electric drive motor. Most of the time, such vehicles are also equipped with an anti-lock braking system, also known by its English name "Antilock Braking System" or by the corresponding acronym "ABS".

[0003] An ABS system is an assistance system that limits wheel lock-up during periods of heavy braking. More specifically, during braking, the car decelerates because braking torque is applied to the wheel. This torque causes the wheel to lose speed, resulting in a decrease in the vehicle's speed. The wheel slip ratio (tx) is defined as the difference between the wheel's linear speed (V_wheel) and the vehicle's speed (V_veh), divided by the vehicle's speed (V_veh). tx = V roue − V veh V veh

[0004] Conventionally, an ABS system regulates the wheel slip rate (tx) to maintain it within an optimal range by adjusting the braking torque applied to the wheel. The frequency of this regulation is constrained by the ABS system's electronics, hydraulics, and mechanics. This results in regulation action frequencies between 5 Hz and 8 Hz.

[0005] When an ABS system is used in an electric or hybrid-electric vehicle, torsional oscillations of the drivetrain occur between the wheels and the electric motor during emergency braking. Specifically, the wheel speed oscillations caused by ABS regulation can excite the drivetrain at its natural frequency. This results in significant suspension travel, which can lead to the failure of tie rods, powertrain suspension components, or drivetrain elements such as transmission shafts or transmissions.

[0006] US 2006 / 025905 A1 discloses a system and method of active engine damping that mitigates oscillations in the drivetrain of a motor vehicle during ABS operation.

[0007] US 2012 / 262102 A1 discloses a method for damping the oscillations of a drivetrain in a vehicle.

[0008] In view of the above, the invention aims to limit the torsional oscillations of the kinematic chain rising from the wheels during emergency braking.

[0009] To this end, a braking device for a motor vehicle equipped with an electric machine is proposed, comprising a first actuation means capable of applying a braking torque on at least one wheel of the vehicle and a module for regulating a slip rate linked to said wheel.

[0010] According to the invention, this device comprises a determination module capable of determining a correction signal for a phase shift between oscillations of the rotational speed of said wheel and oscillations of the rotational speed of the electric machine and a second actuation means capable of controlling the electric machine with the correction signal.

[0011] By correcting the phase shift in this way, we avoid excitation of the kinematic chain between the wheel and the electric machine and we limit the risk of breakage of a suspension element, the powertrain or another mechanical element.

[0012] Preferably, the correction signal is a correction torque to be delivered by the electrical machine.

[0013] Furthermore, it can be predicted that the correction torque is positive when the braking torque is negative.

[0014] Such a correction torque allows the electric machine to accelerate and, as a result, allows the electric machine to catch up in phase with the wheel when the latter is braked.

[0015] Advantageously, the correction torque is proportional to the braking torque.

[0016] In one embodiment, a proportionality coefficient linking the braking torque and the correction torque is equal to the opposite of a mechanical transmission ratio between the electric machine and said wheel.

[0017] It can also be provided that the determination module is configured to deliver a zero or zero (0) correction torque when no regulation of the slip rate linked to said wheel is implemented by the regulation module.

[0018] It can also be provided that the determination module is configured to deliver a zero or converging zero (0) correction torque when the slip rate related to said wheel is less than a threshold between 10% and 15%.

[0019] Such a configuration of the determination module allows the correction to be implemented only when the regulation is likely to be active.

[0020] Preferably, the correction signal is calculated as a function of a time second derivative of an angular position of the electrical machine.

[0021] Advantageously, the correction signal is proportional to at least one parameter chosen from an equivalent moment of inertia of an assembly consisting of the electric machine and elements of the kinematic chain between the electric machine and said wheel, and a time second derivative of an angular position of the electric machine.

[0022] Such a calculation makes it possible to obtain a torque sized to compensate for the phase lag between the electric machine and the wheel.

[0023] According to another aspect, a propulsion and braking system for a motor vehicle is proposed, comprising an electric machine and a braking device as defined previously.

[0024] In one embodiment, the assembly includes a gearbox mechanically connected to the electric machine.

[0025] Preferably, the assembly includes an internal combustion engine mechanically connected to the gearbox.

[0026] According to the invention, a braking method for a motor vehicle equipped with an electric machine is proposed, comprising the application of a braking torque on at least one wheel of the vehicle and the regulation of a slip rate linked to said wheel.

[0027] According to one of its general characteristics, this process includes determining a correction signal for a phase shift between oscillations of the rotational speed of said wheel and oscillations of the rotational speed of the electric machine and controlling the electric machine with the correction signal.

[0028] Preferably, a torque of the electric machine is decreased when the control module decreases the braking torque on said wheel, and / or a torque of the electric machine is increased when the control module increases the braking torque on said wheel.

[0029] According to yet another aspect, a computer program is proposed comprising code configured to, when executed by a processor or electronic control unit, implement the process as defined above.

[0030] 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: [ Fig 1 ] schematically represents a propulsion and braking system according to a first embodiment of the invention, [ Fig 2 ] schematically represents a braking device incorporated into the whole of the figure 1 , [ Fig3 ] is a time graph of the rotational speeds of the wheels and the electric motor of a powertrain of the entire figure 1 . [ Fig 4 ] is a time graph of the braking torque and the regulating torque throughout the figure 1 . [ Fig 5A ], [ Fig 5B ] And [ Fig 5C ] are time graphs showing the oscillations of the kinematic chain during intense braking respectively without implementation of a correction, with virtual disengagement of the electric machine and with implementation of a correction, [ Fig 6 ] illustrates a propulsion and braking system according to a second embodiment of the invention, and [ Fig 7 ] illustrate a propulsion and braking system according to a third embodiment of the invention.

[0031] In reference to the figure 1 A propulsion and braking assembly 1 is schematically represented according to a first embodiment of the invention. Assembly 1 is intended to be incorporated into a motor vehicle.

[0032] Assembly 1 includes a powertrain 2. The function of the powertrain 2 is to provide propulsion for the motor vehicle. In this case, as will be explained later, the motor vehicle is purely electric. A purely electric vehicle is a vehicle whose propulsion is provided exclusively by an electric motor.

[0033] The powertrain 2 comprises an electric machine 4, a gearbox 6 and a differential 7. The electric machine 4 has the function of delivering mechanical power transmitted by the gearbox 6 and the differential 7 to shafts 8 and 9 respectively attached to two drive wheels 10 of the vehicle.

[0034] Assembly 1 includes a braking device 12. The function of device 12 is to brake the wheels 10 when the vehicle users wish the vehicle to slow down. The braking device 12 is shown in detail on the figure 2 .

[0035] The braking device 12 includes an actuation means 14 capable of applying a braking torque T to the wheels 12. For example, the actuation means 14 may include two brake discs (not shown) respectively attached to the shafts 8 and 9 and two calipers (not shown) respectively capable of exerting a frictional force on the brake discs.

[0036] The braking device 12 includes a control module 16. The function of the control module 16 is to prevent the wheels 10 from locking up during heavy braking. To this end, the control module 16 is configured to regulate the slip rate tx associated with each of the wheels 10, where the slip rate tx is calculated according to the equation below: tx = V roue − V veh V veh where V wheel is the linear speed of the wheel concerned and V veh is the speed of the vehicle.

[0037] In the illustrated example, the control module 16 is configured so that the slip rate associated with each of the wheels 10 remains within a range of 10% to 15%. Without departing from the scope of the invention, the control module 16 could be replaced by any other anti-lock braking device.

[0038] The braking device 12 includes a determining module 18. The function of the determining module 18 is to determine a way to correct a phase shift between oscillations of the rotational speed ω wheel of each of the wheels 10 and oscillations of the rotational speed ω me of the electric machine 4. In this way, the determining module 18 determines how to limit the torsional oscillations of the kinematic chain between the wheels 10 and the electric machine 4. In this respect, the determining module 18 determines a correction signal, in this case a correction torque T corr, to be generated by the electric machine 4.

[0039] Device 12 includes an actuation means 20. The actuation means 20 is capable of controlling the electrical machine 4 by taking into account the corr signal T determined by the determination module 18.

[0040] In reference to the figure 3 , the time graph of the rotational speed ω wheel is represented by a curve 24 and the time graph of the rotational speed ω me is represented by a curve 26. The reproduction of the curve 24 at the height of the curve 26 by the dotted curve 28 shows the presence of a phase shift 30 at the origin of the torsional oscillations of the kinematic chain.

[0041] During an interval schematically represented by arrow 32, the positive torque T corr is applied to the electric machine 4 to increase the rotational speed ω me. In the interval corresponding to arrow 32, the braking torque T bracing applied to the wheels 10 results in a decrease in the rotational speed ω wheel. This reduces the phase shift between curves 24 and 26.

[0042] Thus, by applying a strictly positive correction torque T corr to the electric machine 4 while the wheel rotational speed ω decreases, the phase shift is reduced. In other words, to reduce the phase shift between curves 24 and 26, a strictly positive correction torque T corr must be applied by the electric machine 4 when a negative braking torque T bracing is applied to the wheels 10.

[0043] More specifically, with reference to the figure 4 , we have schematically represented a time graph of the evolution of the braking torque T braking on the wheels 10 by the curve 34, and the time evolution of the correction torque T corr delivered by the electric machine 4 with the curve 36. The torque T braking being a braking torque, it can only be negative.

[0044] In view of the figure 4 The correction torque T corr is substantially proportional and opposite in sign to the braking torque T freins. More specifically, the proportionality coefficient k between the correction torque T corr and the braking torque T freins is equal to the negative of the mechanical transmission ratio between the electric machine 4 and the wheels 10: T corr = − k × T freinage

[0045] In this application, the expression "substantially proportional" means that, for any strictly negative braking torque T, the difference between the correction torque T corr (T) corresponding to the torque T and the product of the torque T by the coefficient -k is less than + / -5% of the product of the torque T by the coefficient -k: ∀ T < 0 , − k × 0,95 × T ≤ T corr T ≤ − k × 1,05 × T

[0046] In the illustrated example, the braking torque Tbraking is assumed to be identical for both wheels 10, and for the correction according to the invention, a value measured on one of the two wheels 10 is used, in this case, the wheel 10 mounted on the shaft 9. However, without departing from the scope of the invention, another method of determining the braking torque Tbraking can be considered. For example, the braking torque Tbraking of each wheel 10 can be considered separately, or the braking torque Tbraking can be considered as the average of the torques respectively associated with each of the wheels 10. The same applies to the slip rates tx associated with the wheels 10.

[0047] Still referring to figures 3 And 4 , whatever the period of oscillation of the rotational speed ω wheel , the following process is implemented.

[0048] At an initial instant, the slip rate tx related to the wheels 10 is less than the threshold value of 15%. The control module 16 is therefore inactive. As a result, the actuation means 14 applies a resisting torque on the axle 8 equal to or converging towards the maximum braking torque T.

[0049] At a certain point, the slip rate tx exceeds the threshold value of 15%. Module 16 implements slip rate regulation, which results in a progressive decrease in the braking torque T to zero (0). Simultaneously, the torque T corr to be applied by the electric machine 4 also progressively decreases to zero (0).

[0050] Next, the regulated slip rate tx falls below the threshold value of 10%. As a result, the regulation implemented by module 16 is terminated. The actuation means 14 progressively applies the converging braking torque Tbraking_max. Simultaneously, the determination module calculates the corr torque Tcorr to be applied by the electric machine 4. Consequently, the actuation means 20 drives the electric machine 4 to deliver the corr torque Tcorr.

[0051] In the illustrated example, two thresholds of 10% and 15% respectively are considered for regulating the slip rate tx and the correction according to the invention. Different values ​​and / or a different number of thresholds can be considered without departing from the scope of the invention.

[0052] THE figures 5A , 5B And 5C schematically illustrate the result obtained through the correction according to the invention. On the figures 5A ,5B And 5C , we have schematically represented by a thin line curve 38 the rotation speed ω wheel , and by a thick line curve 40 the rotation speed ω me .

[0053] On the figure 5A No correction is implemented to limit the phase shift between the oscillations of the wheel rotational speed ω and the oscillations of the me rotational speed ω. This results in a significant resonance of the me rotational speed ω. This resonance corresponds to the inertia of the electric motor 4 and the wheels 10 on the stiffness of the transmissions. This mode is strongly influenced by the high inertia of the electric motor 4, which, in the case of a purely electric or hybrid-electric vehicle, can be five (5) times greater than that of the wheels. This resonance can lead to excessive travel of the powertrain 2 on its suspension.

[0054] In reference to the figure 5B A schematic representation depicts a theoretical case in which the electric machine 4 is virtually disengaged. In other words, the mechanical link between the electric machine 4 and the wheels 10 has been opened. This is a purely theoretical consideration, given the absence of a clutch between the electric machine 4 and the wheels 10.

[0055] In the case of the figure 5B The rotational speed ωme is no longer subject to oscillations. The rotational speed ω wheel is subject to oscillations at a frequency between 5 Hz and 8 Hz. The resonance frequency is therefore lower and corresponds to that of a conventional anti-lock braking system.

[0056] In reference to the figure 5C The electric machine 4 is driven with the correction torque T corr determined by the determining modulus 18. As a result, the fluctuations in the velocity ω me, represented by curve 40, are greatly reduced compared to the fluctuations of the figure 5A .

[0057] The correction according to the invention therefore makes it possible to use the same physical system as in the case of the figure 5A with dynamic phase-lag compensation. This results in lower stresses on the input of powertrain 2 and on the vehicle.

[0058] The invention is not limited to the application of a correction torque as calculated according to the equation defined above. In particular, without departing from the scope of the invention, it is possible to calculate the correction torque T corr as a function of a second time derivative of the angular position θ me of the electrical machine 4. In such an example, the correction torque can be calculated in the form: T corr = J m × d 2 θ me dt 2 where J m is the equivalent moment of inertia of the assembly consisting of the rotor of the electric machine 4 and all the elements of the kinematic chain located between the electric machine 4 and the axle 8, including in particular the gears and shafts of the gearbox 6.

[0059] In reference to the figure 6 A schematic representation of assembly 41 is shown according to a second embodiment of the invention. Identical elements bear the same reference numerals.

[0060] Assembly 41 differs from assembly 1 in that it includes a powertrain 42 further equipped with an internal combustion engine 44 mechanically connected to the electrical machine 4 by means of a torque breaking means 46. In addition, the powertrain 42 includes an alternator 48 mechanically connected to the internal combustion engine 44.

[0061] In this embodiment, the motor vehicle is therefore a hybrid electric vehicle. A hybrid electric vehicle is a vehicle whose propulsion is provided by at least one electric drive motor. The aforementioned method can be implemented for braking the vehicle using device 12.

[0062] In reference to the figure 7 A schematic representation of assembly 49 according to a third embodiment of the invention is shown. Identical elements bear the same reference numerals. Assembly 49 comprises a powertrain 50.

[0063] Powertrain 50 differs from powertrain 2 in that it includes an internal combustion engine 52 mechanically connected to the gearbox 6. In this way, the gearbox 6 is both directly mechanically connected to the electric machine 4, and directly mechanically connected to the internal combustion engine 52. In addition, powertrain 50 includes a second electric machine 54 mechanically connected to the gearbox 6.

[0064] As in the second embodiment, the motor vehicle is hybrid electric powered and the aforementioned method can be implemented for braking the vehicle by means of device 12.

[0065] In this case, the braking method according to the invention can be implemented with respect to one of the two electrical machines 4 and 54, or with respect to both electrical machines 4 and 54.

[0066] In light of the foregoing, the braking device according to the invention makes it possible to limit the torsional oscillations of the drivetrain between the roads 10 and the electric motor 4 and / or 54, whether in a purely electric vehicle or a hybrid electric vehicle. This results in less travel of the powertrain on its suspension and a reduction in the risk of breakage of the connecting rods, the powertrain suspension components, or the drivetrain components.

Claims

1. Braking device (12) of a motor vehicle equipped with an electric machine (4, 54), comprising first actuating means (14) capable of applying a braking torque to at least one wheel (10) of the vehicle, and a module (16) for regulating a slip rate related to said wheel (10), characterized in that it comprises a determination module (18) capable of determining a correction signal for correcting a phase shift (30) between oscillations of the rotational speed of said wheel (10) and oscillations of the rotational speed of the electric machine (4, 54) and second actuating means (20) capable of controlling the electric machine (4, 54) using the correction signal.

2. Device (12) according to Claim 1, wherein the correction signal is a correction torque to be delivered by the electric machine (4, 54).

3. Device (12) according to Claim 2, wherein the correction torque is positive when the braking torque is negative.

4. Device (12) according to Claim 2 or 3, wherein the correction torque is substantially proportional to the braking torque, a coefficient of proportionality between the braking torque and the correction torque preferably being equal to the opposite of a mechanical transmission ratio between the electric machine (4, 54) and said wheel (10).

5. Device (12) according to any one of Claims 2 to 4, wherein the determination module (18) is configured to deliver a correction torque of zero or converging towards zero (0) when the slip rate related to said wheel (10) is not being regulated and / or when the slip rate related to said wheel (10) is less than a threshold of between 10% and 15%.

6. Device (12) according to any one of Claims 1 to 5, wherein the correction signal is calculated as a function of a second time derivative of an angular position of the electric machine (4, 54), the correction signal preferably being proportional to at least one parameter selected from an equivalent moment of inertia of an assembly consisting of the electric machine (4, 54) and driveline elements (6, 7) between the electric machine (4, 54) and said wheel (10), and a second time derivative of an angular position of the electric machine (4, 54).

7. Propulsion and braking assembly (1, 41, 49) for a motor vehicle comprising an electric machine (4, 54) and a braking device (12) according to any one of Claims 1 to 6.

8. Assembly (1, 41, 49) according to Claim 7, comprising a gearbox (6) mechanically connected to the electric machine (4, 54), the assembly (41, 49) preferably comprising an internal-combustion engine (44) mechanically connected to the gearbox (6).

9. Method for braking a motor vehicle equipped with an electric machine (4, 54), comprising applying a braking torque to at least one wheel (10) of the vehicle, and regulating a slip rate related to said wheel (10), characterized in that it comprises determining a correction signal for correcting a phase shift (30) between oscillations of the rotational speed of said wheel (10) and oscillations of the rotational speed of the electric machine (4, 54) and controlling the electric machine (4, 54) using the correction signal.

10. Computer program comprising code configured to implement, when executed by a processor or an electronic control unit, the method according to Claim 9.