METHOD FOR CONTROLLING A LOCKING SPEED DIFFERENTIAL OF A REAR WHEEL ASSEMBLY

Abstract

The invention relates to a method for controlling a traction architecture (10) of a motor vehicle comprising: - a first powertrain (11) of hybrid or electric type, - a second powertrain (15) of electric type, - the locking device (36) of the differential being initially in the unlocked state, in the case where one of the rear wheels (13.3, 13.4) loses grip or is no longer in contact with a road, said method comprises: - a step of controlling the electric motor (25) so as to reduce a speed difference between the rear wheels (13.3, 13.4), and - when the speed difference between the rear wheels (13.3, 13.4) becomes lower than a dog clutch threshold, the method comprises a step of controlling the locking device (36) of the differential in a locked state.

Description

Title of the invention: METHOD FOR CONTROLLING A LOCKING OF A SPEED DIFFERENTIAL OF A REAR WHEEL ASSEMBLY

[0001] The present invention relates to a method for controlling a locking of a speed differential of a rear wheel set. The invention finds a particularly advantageous application in the automotive field, with the traction architectures of four-wheel drive electric or hybrid motor vehicles.

[0002] In a manner known per se, a traction architecture of a motor vehicle may comprise a first hybrid or electric type powertrain mounted on a front wheel set and a second electric type powertrain mounted on a rear wheel set having a right rear wheel and a left rear wheel. The second powertrain comprises an electric motor associated with a speed reducer and a speed differential whose slip is biocable.

[0003] For this purpose, a locking device comprises a dog clutch arranged between a sun gear and a differential housing. The locking device is capable of selectively assuming a locked state in which the dog clutch provides a mechanical connection between the housing and the sun gear of the differential and an unlocked state in which the dog clutch separates the housing from the sun gear.

[0004] It may be desirable to operate a differential lock when one of the two rear wheels loses grip or is in the air (i.e. loses contact with the road) in order to stabilize the vehicle.

[0005] However, the locking device can only be activated if the sun gear rotates at the same speed as the differential gear housing. However, this is not the case when the two wheels connected to the differential have a speed difference between them. There is then a high risk that a "tooth against tooth" situation will prevent dog engagement and therefore the differential from locking.

[0006] The invention aims to effectively remedy this drawback by proposing a method for controlling a traction architecture of a motor vehicle comprising: - a first hybrid or electric powertrain mounted on a front wheel set, - a second electric type powertrain mounted on a rear wheel set having a right rear wheel and a left rear wheel, said second powertrain comprising an electric motor associated with a speed reducer, a speed differential comprising a housing and a sun gear, and a differential locking device provided with a dog clutch capable of selectively taking a locked state in in which the dog clutch provides a mechanical connection between the housing and the planetary gear of the differential and an unlocked state in which the dog clutch separates the housing from the planetary gear of the differential, - the differential locking device being initially in the unlocked state, in the event that one of the rear wheels loses grip or is no longer in contact with a road, said method comprises: - a step of controlling the electric motor in order to reduce a difference in speed between the rear wheels, and - when the speed difference between the rear wheels becomes lower than a dog clutch threshold, the method comprises a step of controlling the differential locking device in a locked state.

[0007] The invention thus makes it possible, thanks to the control of the electric motor, to ensure that the planetary gear rotates at substantially the same speed as the differential housing during the dog engagement phase to avoid any "tooth against tooth" situation likely to damage the differential locking device.

[0008] According to one implementation of the invention, a loss of grip or a loss of contact with a road of one of the rear wheels is detected when the speed difference between the rear wheels becomes greater than a loss of control threshold.

[0009] According to one implementation of the invention, the dog clutch threshold is much lower than the loss of control threshold.

[0010] According to one implementation of the invention, the electric motor is controlled at zero torque speed.

[0011] According to one implementation of the invention, said method is implemented when a speed of the motor vehicle is lower than a predefined speed threshold.

[0012] The invention also relates to a computer comprising a memory storing software instructions for implementing the method as previously defined.

[0013] According to one embodiment of the invention, the computer is an electronic stability control computer for the motor vehicle.

[0014] The invention further relates to a motor vehicle comprising a computer as defined above.

[0015] According to one embodiment of the invention, said motor vehicle comprises: - a first hybrid or electric powertrain mounted on a front wheel set, - a second electric powertrain mounted on a rear wheel set, said second powertrain comprising an electric motor associated with a speed reducer, a speed differential, and a differential locking device.

[0016] According to one embodiment of the invention, the locking device comprises a dog clutch capable of selectively assuming a locked state in which the dog clutch provides a mechanical connection between a housing and a sun gear of the differential and an unlocked state in which the dog clutch separates the housing from the sun gear of the differential.

[0017] The invention will be better understood upon reading the following description and examining the accompanying figures. These figures are given only for illustrative purposes but in no way limit the invention.

[0018] [Fig-1] [Fig.l] is a schematic representation of a traction architecture hybrid implementing the method according to the invention for controlling a lock of a speed differential mounted on a rear wheel set;

[0019] [Fig.2a][Fig.2b] Figures 2a and 2b are schematic representations of a device for locking a speed differential of a rear wheel set respectively in a locked state and in an unlocked state;

[0020] [Fig.3] [Fig.3] is a diagram of the steps of the method according to the invention of control of a differential speed lock mounted on a rear wheel set.

[0021] [Fig.l] shows a traction architecture 10 of a motor vehicle comprising a first powertrain 11 of hybrid type mounted on a front wheel set 12 having a right front wheel 13.1 and a left front wheel 13.2 as well as a second powertrain 15 of electric type mounted on a rear wheel set 16 having a right rear wheel 13.3 and a left rear wheel 13.4.

[0022] The first hybrid powertrain 11 comprises a heat engine 19, an electric motor 20 and a gearbox 21 connected to the wheels via a lowering axle. The gearbox 21 is preferably a dual-clutch gearbox. However, a single-clutch gearbox 21 may also be used.

[0023] A clutch 24 for connecting and disconnecting the heat engine 19 is arranged between the heat engine 19 and the electric motor 20. The clutch 24 is capable of selectively connecting the heat engine 19 to the gearbox 21 when said clutch 24 is in the closed state and of isolating the heat engine 19 from the gearbox 21 when said clutch 24 is in the open state. The isolation of the heat engine 19 from the gearbox 21 and therefore from the wheels 13.1-13.4 is required in particular when the vehicle is operating in a pure electric driving mode. The clutch 24 is associated with a flywheel 28 of the heat engine 19.

[0024] The second electric powertrain 15 comprises an electric motor 25 associated with a speed reducer 26 making it possible to make the high rotation speed of the electric motor 25 compatible with that of the wheels 13.1-13.4 of the motor vehicle. The electric motor 20 and the electric motor 25 are connected electrically to a traction battery 35. The electric motors 20, 25 are capable of operating in a motor mode in which the electric motors 20, 25 take electrical energy from the traction battery 35 to transform it into mechanical energy ensuring traction of the motor vehicle. The electric motor 20 and the electric motor 25 are also capable of operating in a generator mode, in particular during regenerative braking phases, in which the electric motors 20, 25 transform the mechanical energy of the vehicle into electrical energy making it possible to recharge the traction battery 35.

[0025] The second powertrain 15 also includes a speed differential 27 whose sliding is biocable.

[0026] More precisely, the speed differential 27 comprises a first toothed wheel 31 linked in rotation with the right rear wheel 13.3 and a second toothed wheel 32 linked in rotation with the left rear wheel 13.4. A sun gear 33 meshes on the one hand with the first toothed wheel 31 and on the other hand with the second toothed wheel 32. The sun gear 33 is linked in rotation about the axis of the wheels with a housing 34 driven in rotation by an output of the speed reducer 26.

[0027] Furthermore, a locking device 36 comprises a dog clutch 39 arranged between the sun gear 33 and the differential housing 34. The locking device 36 is capable of assuming a locked state in which the dog clutch 39 provides a mechanical connection between the housing 34 and the sun gear 33 of the differential (see [Fig. 2a]) and an unlocked state in which the dog clutch 39 separates the housing 34 from the sun gear 33 of the differential (see [Fig. 2b]).

[0028] A supervision computer 41 of the motor vehicle ensures supervision of the torque applied to the wheels 13.1-13.4.

[0029] A traction computer 42 manages a distribution of the torque between the front wheel set 12 and the rear wheel set 16 and is capable of controlling the torque of the thermal engine 19, the electric motor 20, the electric motor 25, as well as the torque level of the clutches.

[0030] An electronic stability control computer 43, called "ESC" computer (for "Electronic Stability Control" in English terminology), is capable of controlling hydraulic braking calipers 44.1-44.4 of the vehicle wheels so as to adapt a braking force applied to the different wheels 13.1-13.4 in the event of loss of control of the vehicle in order to re-establish a trajectory of the vehicle.

[0031] The electronic stability control computer 43 or a dedicated computer comprises a memory storing software instructions for implementing the method according to the invention described below with reference to [Fig. 3]. This method is advantageously implemented when a speed of the motor vehicle is lower than a predefined speed threshold, for example of the order of 5 km / h.

[0032] The differential locking device 36 being initially in the unlocked state, said method comprises a step 100 of measuring a speed difference Ereg between the right rear wheel 13.3 and the left rear wheel 13.4. For this purpose, the module M1 measures a difference between the rotation speed NI of the right rear wheel 13.3 and the rotation speed N2 of the left rear wheel 13.4.

[0033] If the speed difference Ereg becomes greater than a loss of control threshold SI (see condition 101), then it is detected that one of the rear wheels 13.3, 13.4 is losing grip or is no longer in contact with the road (the wheel is then said to be "in the air"). Advantageously, the loss of control threshold SI is of the order of 250 rpm. The automatic differential locking method is then triggered in a step 102.

[0034] The electric motor 25 is controlled, in a step 103, so as to reduce the speed difference Ereg between the right rear wheel 13.3 and the left rear wheel 13.4. The electric motor 25 is controlled at zero torque speed, that is to say that the torque of the electric motor 25 is intended solely to compensate for the drag torque of the electric motor 25 linked in particular to the inertia of the rotating elements and to the internal friction of the electric motor 25.

[0035] The speed difference Ereg between the right rear wheel 13.1 and the left rear wheel 13.4 is measured again in a step 104. In the case where the speed difference Ereg remains greater than a dog clutch threshold S2, the electric motor 25 is again controlled to reduce this speed difference Ereg during step 103.

[0036] In the case where the speed difference Ereg becomes lower than the dog clutch threshold S2, then the method comprises a step 105 of controlling the locking device 36 of the differential in a locked state. The dog clutch threshold S2 is much lower than the loss of control threshold SL. The dog clutch threshold S2 is for example of the order of 50 rpm.

[0037] Outside of the method, the speed differential 27 is not blocked unless this is requested by the driver via a dedicated control and the speed conditions of the rear wheels 13.3, 13.4 allow it.

[0038] Alternatively, the first power unit 11 is of the electric type and is therefore devoid of a thermal engine 19 and clutch 24.

Claims

Claims

1. Method for controlling a traction architecture (10) of a motor vehicle comprising: - a first powertrain (11) of hybrid or electric type mounted on a front wheel set (12), - a second powertrain (15) of electric type mounted on a rear wheel set (16) having a right rear wheel (13.3) and a left rear wheel (13.4), said second powertrain (15) comprising an electric motor (25) associated with a speed reducer (26), a speed differential (27) comprising a housing (34) and a sun gear (33), and a differential locking device (36) provided with a dog clutch (39) capable of selectively taking a locked state in which the dog clutch (39) provides a mechanical connection between the housing (34) and the sun gear (33) of the differential and an unlocked state in which the dog clutch (39) separates the housing (34) from the sun gear (33) of the differential, characterized in that, the differential locking device (36) being initially in the unlocked state, in the case where one of the rear wheels (13.3, 13.4) loses grip or is no longer in contact with a road, said method comprises: - a step of controlling the electric motor (25) so as to reduce a speed difference (Ereg) between the rear wheels (13.3, 13.4), and - when the speed difference (Ereg) between the rear wheels (13.3, 13.4) becomes lower than a dog clutch threshold (S2), the method comprises a step of controlling the locking device (36) of the differential in a locked state.

2. Method according to claim 1, characterized in that a loss of grip or a loss of contact with a road of one of the rear wheels (13.3, 13.4) is detected when the speed difference (Ereg) between the rear wheels (13.3, 13.4) becomes greater than a loss of control threshold (SI).

3. Method according to claim 2, characterized in that the clutch threshold (S2) is much lower than the loss of control threshold (SI).

4. Method according to any one of claims 1 to 3, characterized in that the electric motor (25) is driven at zero torque speed.

5. Method according to any one of claims 1 to 4, characterized in that it is implemented when a speed of the motor vehicle is below a predefined speed threshold.

6. Calculator (43) characterized in that it comprises a memory storing software instructions for implementing the method according to any one of the preceding claims.

7. Calculator according to claim 6, characterized in that the calculator (43) is an electronic stability control calculator for the motor vehicle.

8. Motor vehicle characterized in that it comprises a computer defined according to claim 6 or 7.

9. Motor vehicle according to claim 8, characterized in that it comprises: - a first powertrain (11) of hybrid or electric type mounted on a front wheel set (12), - a second powertrain (15) of electric type mounted on a rear wheel set (16), said second powertrain (15) comprising an electric motor (25) associated with a speed reducer (26), a speed differential (27), and a differential locking device (36).

10. Motor vehicle according to claim 9, characterized in that the locking device (36) comprises a dog clutch (39) capable of selectively taking a locked state in which the dog clutch (39) provides a mechanical connection between a housing (34) and a sun gear (33) of the differential and an unlocked state in which the dog clutch (39) separates the housing (34) from the sun gear (33) of the differential.

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