METHOD FOR MONITORING WHEEL NON-SLIP DURING REGENERATIVE BRAKING IN A 4x4 ELECTRIC MOTOR VEHICLE

Abstract

The invention relates to a method for monitoring wheel non-slip in an electric regenerative braking mode, a first electric machine engaged with wheel shafts of the front axle via a first transmission, having a first transmission ratio R1, and a second electric machine selectively engaged with wheel shafts of the rear axle via a second transmission, having a second transmission ratio R2, the method providing: an acquisition of the rotation speeds ω1 and ω2 of the electric machines, - if monitoring conditions are met, calculating the quantity to be monitored R1ω1-R2ω2, - if the quantity R1ω1-R2ω2 is greater than a first slip threshold (ωs1), then triggering a reconfiguration of the first type, - if the quantity R1ω1-R2ω2 is less than a second slip threshold (ωs2), negative, then triggering a reconfiguration of the second type. Figure 2

Description

Title of the invention: METHOD FOR MONITORING WHEEL NON-SLIP DURING RECOVERY BRAKING IN A 4x4 ELECTRIC MOTOR VEHICLE

[0001] The field of the invention relates to a method for monitoring wheel non-slip in an electric regenerative braking mode in an electrified motor vehicle having the possibility of operating in 4x4 mode.

[0002] The present invention also relates to a system implementing said method and also relates to a vehicle comprising such a system.

[0003] In recent motor vehicles, there is an increasingly marked need to be able to recover kinetic energy in the case of deceleration, downhill travel, and / or braking.

[0004] This function, called regenerative braking in the profession, is increasingly important in order to minimize average fuel consumption or electrical energy consumption, particularly on a reference route (WLTP or other).

[0005] We are particularly interested here in vehicles having two electrically powered axles, namely in practice a possibility of operating in so-called 4x4 mode with a first electric machine at the front and a second electric machine at the rear.

[0006] In particular here, the two axles are mechanically independently powered, i.e. there is no longitudinal shaft connecting the front axle to the rear axle.

[0007] In this document, the front axle designates the front axle and the rear axle designates the rear axle.

[0008] In the present context, and in the circumstances of deceleration and / or braking, it frequently happens that the front axle and the rear axle apply a torque to the wheels to decelerate and / or brake the vehicle. But it is also not excluded to have a situation where only one of the two axles, front or rear, applies a braking torque to the wheels to decelerate and / or brake, while the other of the two axles is freewheeling.

[0009] In a context where we seek to maximize the kinetic and / or potential energy recovered during braking or descent phases, we seek to apply the highest possible braking torque to the wheels.

[0010] However, care must still be taken to avoid a loss of grip of one of the vehicle's wheels, which is the subject of the present invention.

[0011] The person skilled in the art knows that under these conditions, the ABS anti-lock braking system cannot intervene; there is in fact no action on the vehicle's braking system under these circumstances.

[0012] The inventors therefore sought to propose an optimized solution to maximize energy recovery while avoiding slipping and / or loss of grip of one of the vehicle's wheels in the regenerative braking situation.

[0013] To this end, the present invention proposes a method for monitoring non-slip of wheels in an electric regenerative braking mode in a motor vehicle comprising a front axle and a rear axle, a first electric machine in selective engagement with wheel shafts of the front axle via a first transmission, having a first transmission ratio RI, and a second electric machine in selective engagement with wheel shafts of the rear axle via a second transmission, having a second transmission ratio R2, the method providing for an acquisition of a vehicle movement speed, an acquisition of a rotation speed col of the first electric machine, and an acquisition of a second rotation speed co2 of the second electric machine, characterized in that the method provides for the following steps: a- define conditions for monitoring the first and second rotation speeds, b- if the monitoring conditions are met, calculate the quantity to be monitored Rlcol-R2co2, the quantity to be monitored being signed, c- if the quantity Rlcol-R2co2 is greater than a first slip threshold for a first duration, then declare a first type fault and trigger a first type reconfiguration, d- if the quantity Rlcol-R2co2 is lower than a second slip threshold, negative, for a second duration, then declare a second type fault and trigger a second type reconfiguration.

[0014] Thanks to the provisions promoted above, it is possible to avoid a loss of grip on one of the wheels of the vehicle in a regenerative braking situation, and at the same time to maximize the energy recovered by regenerative braking or regenerative deceleration.

[0015] In other words, this process makes it possible to achieve the maximum possible regenerative braking while preserving the directional controllability of the vehicle.

[0016] From another angle, the method proposes to continuously check the consistency of the rotation speeds of the front and rear motors in the regenerative braking situation.

[0017] It must be understood that the speed values here are instantaneous values, that this either for the vehicle's travel speed, for example, delivered by the ABS anti-lock braking system, or for the rotation speeds of the first and second electric machines, measured respectively by an angular sensor signed on the rotors of the electric machines. It should be noted that the implementation of the method proposed here does not require any additional speed sensor compared to the equipment already existing on the vehicle.

[0018] It should be noted that, generally, the engagement of the first machine with the front axle is permanent, in the case of a vehicle that is essentially front-wheel drive. However, it is not excluded that this engagement is selective, e.g. controlled by a clutch or a dog clutch.

[0019] It is noted that it is not excluded that the electromotive group installed on the front axle comprises an internal combustion engine (hybrid vehicle configuration).

[0020] Advantageously, the method provides for a recurrent application of steps b- to d-, with very short cycle times, of the order of ten milliseconds maximum.

[0021] Step a- is also carried out recurrently, but not necessarily with the same frequency.

[0022] On both the first axle and the second axle, the drive train that connects the electric machine to the wheel shafts includes a differential, but this does not prevent the proposed method from working well as will be explained in detail later.

[0023] It is noted that in practice, there is always one of the wheels of an axle which begins to lose grip first, thus generating a difference which is used to advantage in the proposed method.

[0024] The first slip threshold and / or the second slip threshold can be expressed as an absolute value or as a relative value with respect to the reference rotation speed as will be seen later.

[0025] The first duration may be equal to or different from the second duration.

[0026] The functional distribution between various computing units involved in the method will be discussed later.

[0027] According to one embodiment, the method provides that a first type reconfiguration consists of canceling or dividing by at least four the torque applied by the second electric machine. In this case, it is a wheel of the rear axle which has started to slip.

[0028] As a result, the drastic reduction or cancellation of the torque on the rear axle will lead to the elimination of the slippage of the problematic wheel relative to the ground.

[0029] According to one embodiment, the method provides that a second type reconfiguration consists of cancelling or dividing by at least four the torque applied by the first electric machine. In this case, it was a wheel on the front axle that started to slip. Here too, drastically reducing or eliminating the torque on the front axle will eliminate the slippage of the problematic wheel relative to the ground.

[0030] According to one embodiment, the monitoring conditions comprise a condition on the speed of movement of the vehicle greater than a speed threshold, and a condition of braking torque applied to at least one of the first and second electrical machines.

[0031] As a result, the possibility of an inconsistency between the speed on the front axle and the speed on the rear axle is only monitored under the conditions of regenerative braking on at least one axle, and a fortiori on both axles at the same time.

[0032] According to one embodiment, the speed threshold is between 20 km / h and 35 km / h. For example, the speed threshold is a calibratable value chosen in the vicinity of 30 km / h. A wheel lock below such a speed threshold does not represent a real danger. Conversely, for speeds higher, or even much higher than this speed threshold, a wheel lock can cause a really problematic skid, hence the interest of the present invention.

[0033] According to one embodiment, the first slip threshold and / or the second slip threshold are calibratable values. For example, Icos2l < Icos 11 can be chosen if greater slippage on a rear wheel is to be tolerated. The slip threshold values in question can result from behavior tests on a representative vehicle platform. Furthermore, several differentiated thresholds can be provided depending on the dynamic scenarios, for example, straight line, curve, high speed, etc.

[0034] According to one embodiment, the first slip threshold and / or a second slip threshold are expressed as a percentage of a maximum of (Rlcol,R2co2).

[0035] For example, we can choose a difference threshold of 15% for the first slip threshold. In other words, cosl = 0.15 Rlcol and cos2 = - 0.15 R2co2. Optionally, we can choose cosl = 0.20 Rlcol, or cos2 = - 0.12 R2co2 if we want to tolerate a slightly greater slip on the rear axle.

[0036] Advantageously, the vehicle's travel speed is delivered by the ABS computer which takes the averages of the 2 or 3 fastest wheels, excluding any possible wheel that locks.

[0037] According to one embodiment, in the event of reconfiguration of the first or second type respectively, a respective fault code is recorded in the memory of a control unit involved.

[0038] According to one embodiment, it is provided that nominal operation is resumed after switching off the ignition and switching it back on.

[0039] This allows you to restart in a normal state after switching off the ignition. Only a residual trace is present in a computer memory.

[0040] The first duration and the second duration can be identical. For example, 330 ms can be chosen as the value. The first and second durations can also be different. These are preferably calibratable values.

[0041] The present invention also relates to a motor vehicle comprising a front axle and a rear axle, comprising a first electric machine in selective engagement with wheel shafts of the front axle via a first transmission, having a first transmission ratio, and a second electric machine in selective engagement with wheel shafts of the rear axle via a second transmission, having a second transmission ratio, and at least one control unit configured to implement the method as described previously.

[0042] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: [Fig.l] is a functional schematic representation of a motor vehicle where the method presented in the present invention can be implemented; [Fig.2] shows a timing diagram illustrating an operating sequence where the torques on the electrical machines become resistive and a wheel begins to lose grip; [Fig.3] schematically illustrates an example of steps of the method implemented.

[0043] In the different figures, the same references designate identical or similar elements.

[0044] In [Fig.l], a VHL vehicle is shown schematically, with a front axle AV with steered and driven wheels and a rear axle ARR with selectively driven wheels (in so-called '4x4' mode).

[0045] The vehicle in question may be a passenger vehicle, a utility vehicle, a van, a recreational vehicle, a minibus, a coach, a truck, etc.

[0046] The front axle is equipped with a first electric machine noted ML

[0047] The motor vehicle comprises a first TRI transmission.

[0048] The first electric machine Ml is engaged with the wheel shafts 21G, 21D of the front axle via the first TRI transmission.

[0049] As known per se and not described in detail, the first TRI transmission comprises a differential and a reducer which makes it possible to lower the rotation speed starting from the rotation speed of the electric machine denoted col up to the rotation speed of the front wheel shafts 21G, 21D.

[0050] A first transmission ratio RI is thus determined between the neck and the rotation speed of the front wheel shafts 21G, 21D, so that the rotation speed of the crown of the differential is equal to RI x col, also noted in compact form Rlcol.

[0051] The front axle electromotive group may include, where appropriate, an internal combustion engine designated MO (in the case of a hybrid vehicle).

[0052] The rear axle is equipped with a second electric machine marked M2.

[0053] The motor vehicle comprises a second transmission TR2.

[0054] The second electric machine M2 is in selective engagement with the wheel shafts 22G, 22D of the front axle via the second transmission TR2.

[0055] The selectivity of the engagement can be achieved by means of a clutch or a dog clutch, which makes it possible to link the second electric machine to the differential crown or to make them independent.

[0056] As known per se and not described in detail, the second transmission TR2 comprises a differential and a reducer which makes it possible to lower the rotation speed starting from the rotation speed of the electric machine denoted co2 to the rotation speed of the rear wheel shafts 22G, 22D.

[0057] A second transmission ratio R2 is thus determined between co2 and the rotation speed of the rear wheel shafts 22G, 22D, so that the rotation speed of the differential crown is equal to R2 x co2, also noted in compact form R2co2.

[0058] It is considered that the diameter of the front and rear wheels of the vehicle is identical. However, the proposed method works in the opposite case, provided that a possible difference in wheel diameter between the front and rear axles is taken into account.

[0059] In the normal case, the front axle rotates at the same speed as the rear axle, so we have Rlcol= R2co2.

[0060] This is also true in curves where the differential is stressed, even if the outer wheels turn faster than the inner wheels, the above equality remains true at the level of the differential crowns.

[0061] The first electrical machine M1 is controlled by a first control unit 11 via a power device called inverter INV1 (or 'inverter' in the jargon of the trade) which comprises power switches connected to the phases of the stator.

[0062] Similarly, the second electrical machine M2 is controlled by a second control unit 12 via a power device called inverter INV2.

[0063] In addition, a supervision unit also called supervisor 14 is provided, configured to coordinate the needs for positive traction and regenerative braking.

[0064] To communicate with each other, it is provided that the first control unit 11, the second control unit 12, the supervisor computer 14 and the battery management computer 13 communicate via a multiplexed network 15, for example a CAN type network, as known per se.

[0065] The vehicle is equipped with a BATT battery, otherwise called a traction battery, or still battery pack. In the context of the present invention, the BATT battery of the vehicle has sufficient capacity to admit a significant recharge current over a substantial duration during the regenerative braking phases of the vehicle.

[0066] The electrochemical technology of the battery may be any within the meaning of the present invention. It may be, for example, lithium-ion technology.

[0067] As known per se, a battery management computer 13 is provided, otherwise called in the trade BMS from the English 'Battery Management System', the functions of which are not detailed here.

[0068] The vehicle is equipped with a braking system with anti-lock function. For this purpose, a computer called ABS is provided which collects in particular the information coming from the wheel speed sensors, four in number, one on each wheel.

[0069] According to one embodiment, the speed of movement of the vehicle VV is delivered by the ABS computer which takes the averages of the 2 or 3 fastest wheels, excluding any possible wheel which locks.

[0070] According to an alternative embodiment, a reference speed could be calculated as an equivalent of the maximum of the values Rlcol, R2co2.

[0071] It is noted that the main function of the anti-lock braking system is to relieve or cancel a braking action; it is therefore understood that this function is of no help in the case of regenerative braking where the braking torque is applied by the electric machine. The ESP function (dynamic stability by selective braking) is also not usable in the circumstances of interest.

[0072] In [Fig.2], the first phase of the timing diagrams illustrates a positive motor situation up to time t0. The torque C1 delivered by the first electric machine is positive, the torque C2 delivered by the 2nd electric machine is also positive, they are located above the zero torque limit represented by CPL = 0.

[0073] From the beginning until time t0, we notice on the middle part at mid-height of the graph that the quantity Rlcol- R2co2 is very close to the value 0, materialized by the line Rlcol- R2co2 = 0.

[0074] Conditions for monitoring the first and second rotational speeds (col,co2) are defined, which relate to the circumstances of regenerative braking. In fact, we are interested here in the case where at least one electric machine produces a negative torque, i.e. exerts a braking torque on the wheels of the axle considered.

[0075] The monitoring conditions also include a condition on the speed of movement of the vehicle VV greater than a speed threshold VS1.

[0076] According to one embodiment, the speed threshold VS1 is between 20 km / h and 35 km / h. Preferably, the speed threshold is a calibratable value. The speed threshold VS1 can be chosen to be around 30 km / h.

[0077] The person skilled in the art knows that a wheel lock below such a speed threshold VS1 does not represent a real danger. Conversely, for speeds higher, or even much higher than this speed threshold, a wheel lock can cause a really problematic skid, which should be avoided.

[0078] The definition and monitoring of the monitoring conditions forms the step noted a- of the process.

[0079] As soon as the monitoring conditions prevail, the method provides for monitoring the quantity Rlcol-R2co2, this quantity to be monitored being signed. The calculation of the quantity Rlcol-R2co2 forms the step noted b- of the method.

[0080] The quantity Rlcol-R2co2 is compared iteratively to action trigger thresholds, also called sliding thresholds here.

[0081] It is noted that the calculation of the quantity Rlcol-R2co2 can be carried out permanently even when the monitoring conditions are not met.

[0082] A first positive cosl slip threshold and a second negative cos2 slip threshold are provided.

[0083] The method provides that if the quantity Rlcol-R2co2 is greater than the first slip threshold cosl for a first duration DTI, then the method provides for declaring a fault of the first type and triggering a reconfiguration of the first type. This forms the step noted c- of the method.

[0084] Furthermore, the method provides that if the quantity Rlcol-R2co2 is lower than the second slip threshold cos2, for a second duration DT2, then the method provides for declaring a second type fault and triggering a second type reconfiguration. This forms the step noted d- of the method.

[0085] A first type of reconfiguration consists of cancelling or dividing by at least four the torque C2 applied by the second electric machine M2. Indeed, in this case, it is a wheel of the rear axle which has started to slip, R2co2 then becomes significantly lower than RI col.

[0086] This is illustrated in [Fig.2] at the end of the time interval noted tt2, where we see that the torque C2 goes to 0 (time t21).

[0087] Later on the timeline of [Fig.2], after the interruption, the opposite case was illustrated.

[0088] A second type of reconfiguration consists of cancelling or dividing by at least four the torque applied Cl by the first electric machine ML. In fact, in this case, it is a wheel of the front axle which has started to slip, Rlcol then becomes significantly lower than R2co2.

[0089] This is illustrated in [Fig.2] at the end of the time interval denoted tt3, where we see that the couple Cl goes to 0 (time t22).

[0090] Cancelling the resistive torque on the axle where a wheel begins to slip or lock allows the wheel to be rotated again, thereby maintaining control of the vehicle's trajectory.

[0091] [Fig.2] also illustrates a case where a stealth blockage occurs, during the time interval noted ttl. However, as this time interval ttl is smaller than Dl, then the action of canceling the resistive torque is not undertaken.

[0092] In practice, the counting of the blocking duration only begins from the moment when the quantity Rlcol-R2co2 is greater than the first slip threshold cosl (where respectively Rlcol-R2co2 is less than the second slip threshold cos2).

[0093] The first slip threshold cosl is a calibratable value. The second slip threshold cos2 is a calibratable value.

[0094] For example, we can choose Icos2l < Icos 11 if we want to tolerate greater slippage on a rear wheel, or the opposite if we want to tolerate greater slippage on a front wheel.

[0095] For the thresholds, one can choose absolute values in revolutions per minute or thresholds in relative values.

[0096] For example, we can choose a difference threshold of 15% for the first slip threshold. In other words, cosl = 0.15 x Rlcol relevant for a rear wheel that slips and cos2 = - 0.15 x R2co2 relevant for a front wheel that slips.

[0097] Optionally, one can choose cosl = 0.20 x Rlcol, or cos2 = - 0.12 x R2co2 if one wants to tolerate a slightly greater slip on the rear axle.

[0098] The configurable values of thresholds cosl, cos2 can be obtained after behavior tests on a vehicle platform corresponding to the vehicle of interest here.

[0099] It may be provided that the configurable values cosl, cos2 depend on the situation of the vehicle, in particular its actual loading and a possible towing mode.

[0100] The configurable threshold values can also be made dependent on the dynamic driving situation of the vehicle, for example with specific values for the straight line and differentiated values for journeys in more or less pronounced curves.

[0101] The method provides that in the event of reconfiguration of the first or second type respectively, a respective fault code is recorded in the memory of a control unit involved, for example in the supervisor computer 14.

[0102] The method provides that nominal operation is resumed after switching off the ignition and switching on the ignition again. Switching off the ignition (key OFF) allows the fault to be reset to 0, only a trace remains in non-volatile memory but this does not light up preferably a fault indicator on the dashboard.

[0103] In the context of the above presentation, it is assumed that the BATT battery has sufficient recharge acceptance so as not to be the limiting factor of the regenerative braking function.

[0104] As known per se, the on-board computers, control units 11, 12 and supervisor computer 14 are each equipped with a microcontroller, which makes it possible to carry out calculations, to manage multiple tasks, and to store in non-volatile memory information recoverable via the diagnostic channel.

[0105] As visible in [Fig.3], steps b- to d- are subject to an L1 iteration served by a fast recurrence task, for example every 10 milliseconds. In the illustrated example, there is a loop at the upper level formed by the L2 iteration which may have a lower recurrence frequency. In another variant, there is a single iteration loop for the four steps a- to d-.

Claims

Claims

1. Method for monitoring non-slip of wheels in an electric regenerative braking mode, in a motor vehicle comprising a front axle and a rear axle, a first electric machine (Ml) in selective engagement with wheel shafts of the front axle via a first transmission, having a first transmission ratio RI, and a second electric machine (M2) in selective engagement with wheel shafts of the rear axle via a second transmission, having a second transmission ratio R2, the method providing an acquisition of a speed (VV) of movement of the vehicle, an acquisition of a rotation speed col of the first electric machine, and an acquisition of a second rotation speed co2 of the second electric machine, characterized in that the method provides the following steps: a- defining conditions for monitoring the first and second rotation speeds (col,co2),b- if the monitoring conditions are met, calculate the quantity to be monitored Rlcol-R2co2, the quantity to be monitored being signed, c- if the quantity Rlcol-R2co2 is greater than a first slip threshold (cosl) for a first duration (DTI), then declare a fault of the first type and trigger a reconfiguration of the first type, d- if the quantity Rlcol-R2co2 is less than a second slip threshold (cos2), negative, for a second duration (DT2), then declare a fault of the second type and trigger a reconfiguration of the second type.,

2. Method according to claim 1, characterized in that the method provides that a reconfiguration of the first type consists of canceling or dividing by at least four the torque applied by the second electrical machine.

3. Method according to claim 1, characterized in that the method provides that a second type reconfiguration consists of canceling or dividing by at least four the torque applied by the first electrical machine.

4. Method according to any one of claims 1 to 3, characterized in that the monitoring conditions comprise a condition on the speed of movement of the vehicle (VV) greater than a threshold of speed (SV1), and a braking torque condition applied to at least one of the first and second electrical machines.

5. Method according to any one of claims 1 to 4, characterized in that the speed threshold (SV1) is between 20 km / h and 35 km / h.

6. Method according to any one of claims 1 to 5, characterized in that the first slip threshold (cosl) and / or the second slip threshold (cos2) are calibratable values.

7. Method according to any one of claims 1 to 6, characterized in that the first slip threshold (cosl) and / or a second slip threshold (cos2) are expressed as a percentage of a maximum of (Rlœl,R2œ2).

8. Method according to any one of claims 1 to 7, characterized in that, in the event of reconfiguration of the first or second type respectively, a respective fault code is recorded in the memory of a control unit involved.

9. Method according to any one of claims 1 to 8, characterized in that nominal operation is resumed after switching off the contact and switching on the contact.

10. Motor vehicle comprising a front axle and a rear axle, comprising a first electric machine (Ml) in selective engagement with wheel shafts of the front axle via a first transmission, having a first transmission ratio, and a second electric machine (M2) in selective engagement with wheel shafts of the rear axle via a second transmission, having a second transmission ratio, and at least one control unit configured to implement the method according to one of claims 1 to 9.

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