METHOD FOR CONTROLLING A REAR WHEEL AXLE SPEED DIFFERENTIAL LOCK

Abstract

The invention relates to a method for controlling a traction architecture (10) of a motor vehicle comprising: - a first powertrain (11) of the hybrid or electric type, - a second powertrain (15) of the electric type, - the differential locking device (36) being initially in the unlocked state, in the event that one of the rear wheels (13.3, 13.4) loses traction or is no longer in contact with the 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 less than a dog-engagement threshold, the method comprises a step of controlling the differential locking device (36) in a locked state. Figure 1

Description

Title of the invention: METHOD FOR CONTROLLING A REAR WHEEL AXLE SPEED DIFFERENTIAL LOCK

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

[0002] In a manner known per se, a traction architecture of a motor vehicle may comprise a first hybrid or electric powertrain mounted on a front axle and a second electric powertrain mounted on a rear axle 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 slippage is biocable.

[0003] To this end, a locking device comprises a dog clutch disposed between a planetary 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 planetary gear of the differential, and an unlocked state in which the dog clutch disengages the housing from the planetary gear.

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

[0005] However, the locking device can only be activated if the planetary gear rotates at the same speed as the differential housing. This is not the case when the two wheels connected to the differential have a difference in speed. There is then a high risk that a "tooth-on-tooth" situation will prevent the differential from engaging and therefore 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 axle, - a second electric powertrain mounted on a rear axle 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 planetary gear, and a differential locking device equipped with a dog clutch capable of selectively entering a locked state in in which the dog clutch provides a mechanical link between the housing and the differential planetary gear, and an unlocked state in which the dog clutch disconnects the housing from the differential planetary gear. - the differential locking device being initially in the unlocked state, in the event that one of the rear wheels loses traction or is no longer in contact with the road, said method comprises: - a step to control the electric motor in order to reduce the speed difference between the rear wheels, and - when the difference in speed between the rear wheels becomes less than a dog engagement threshold, the process includes a step of piloting the differential locking device into a locked state.

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

[0008] According to one embodiment of the invention, a loss of traction 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 embodiment of the invention, the dog clutch threshold is much lower than the loss of control threshold.

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

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

[0012] The invention also relates to a computer comprising a memory storing software instructions for the implementation of the process 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 previously defined.

[0015] According to one embodiment of the invention, said motor vehicle comprises: - a first hybrid or electric powertrain mounted on a front axle, - a second electric powertrain mounted on a rear wheel assembly, 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 taking a locked state in which the dog clutch ensures a mechanical link between a housing and a planetary gear of the differential and an unlocked state in which the dog clutch disengages the housing from the planetary 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 to illustrate, but in no way limit, the invention.

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

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

[0020] [Fig.3] Fig.3 is a diagram of the steps of the process according to the invention of control of a differential lock mounted on a rear axle.

[0021] Fig. 1 shows a traction architecture 10 of a motor vehicle comprising a first hybrid-type powertrain 11 mounted on a front wheel assembly 12 having a right front wheel 13.1 and a left front wheel 13.2 and a second electric-type powertrain 15 mounted on a rear wheel assembly 16 having a right rear wheel 13.3 and a left rear wheel 13.4.

[0022] The first hybrid-type powertrain 11 comprises a combustion engine 19, an electric motor 20, and a gearbox 21 connected to the wheels via a downshaft. 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 internal combustion engine 19 is disposed between the internal combustion engine 19 and the electric motor 20. The clutch 24 is capable of selectively connecting the internal combustion engine 19 to the gearbox 21 when said clutch 24 is in the closed state and of isolating the internal combustion engine 19 from the gearbox 21 when said clutch 24 is in the open state. Isolating the internal combustion 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 purely electric driving mode. The clutch 24 is associated with a flywheel 28 of the internal combustion engine 19.

[0024] The second electric powertrain 15 comprises an electric motor 25 associated with a speed reducer 26, making the high rotational 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 connected to a traction battery 35. The electric motors 20 and 25 are capable of operating in a motor mode in which they draw electrical energy from the traction battery 35 and convert it into mechanical energy to propel the vehicle. The electric motor 20 and electric motor 25 are also capable of operating in a generator mode, particularly during regenerative braking, in which they convert the vehicle's mechanical energy into electrical energy to recharge the traction battery 35.

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

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

[0027] In addition, a locking device 36 includes a dog clutch 39 disposed between the planetary gear 33 and the differential housing 34. The locking device 36 is capable of taking a locked state in which the dog clutch 39 provides a mechanical link between the housing 34 and the planetary gear 33 of the differential (see [Fig.2a]) and an unlocked state in which the dog clutch 39 disengages the housing 34 from the planetary gear 33 of the differential (see [Fig.2b]).

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

[0029] A traction computer 42 manages a distribution of torque between the front wheel assembly 12 and the rear wheel assembly 16 and is capable of controlling the torque of the internal combustion 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 an "ESC" computer (for "Electronic Stability Control" according to Anglo-Saxon terminology), is capable of controlling hydraulic brake calipers 44.1-44.4 of the vehicle's 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 restore a trajectory of the vehicle.

[0031] The electronic stability control unit 43 or a dedicated control unit includes 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 the speed of the motor vehicle is below a predefined speed threshold, for example, on the order of 5 km / h.

[0032] The differential locking device 36 being initially in the unlocked state, said method includes 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 rotational speed NI of the right rear wheel 13.3 and the rotational speed N2 of the left rear wheel 13.4.

[0033] If the engine speed deviation Ereg exceeds 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 traction 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 on the order of 250 rpm. The automatic differential locking process is then triggered in 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 only intended to compensate for the drag torque of the electric motor 25 related in particular to the inertia of the rotating elements and 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 event that the speed difference Ereg remains greater than a dog clutch threshold S2, the electric motor 25 is again driven to reduce this speed difference Ereg during the step 103.

[0036] If the engine speed difference Ereg falls below the engagement threshold S2, then the method includes a step 105 for controlling the differential locking device 36 in a locked state. The engagement threshold S2 is much lower than the loss of control threshold SL. The engagement threshold S2 is, for example, on the order of 50 rpm.

[0037] Apart from the process, the speed differential 27 is not locked unless requested by the driver via a dedicated control and the operating conditions of the rear wheels 13.3, 13.4 allow it.

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

Images