METHOD FOR DETERMINING THE TORQUE TO BE APPLIED TO THE WHEELS IN A VEHICLE SPEED LIMITING FUNCTION

Abstract

A method for determining a motor torque (CMO) to be applied to the wheels of a driven axle, in a speed limiting function in a vehicle comprising driven and non-driven wheels, the speed limiting function managing a maximum advance speed (VP) and using as the current advance speed (VV) an advance speed based on the rotational speed (VRR1) of the driven wheels, the method providing that if a first difference between the maximum advance speed (VP) and the current advance speed (VV) is less than a first threshold (S1) and if a second difference between the rotational speed (VRR1) of the driven wheels and the rotational speed (VRR2) of the non-driven wheels is greater than a second threshold (S2), then the speed limiting function changes the basis for calculating the current advance speed, which becomes the rotational speed of the non-driven wheels. Figure 2

Description

Title of the invention: METHOD FOR DETERMINING A TORQUE TO BE APPLIED TO THE WHEELS IN A VEHICLE SPEED LIMITING FUNCTION

[0001] The present invention relates generally to the field of driver assistance systems in motor vehicles, and in particular the speed limitation function.

[0002] The vehicles concerned include electric or hybrid vehicles, but the present invention is equally applicable to vehicles with internal combustion engines.

[0003] We are particularly interested here in a speed limitation function, and in a speed restriction function.

[0004] We consider here motor vehicles comprising a motorized axle with driving wheels and a non-motorized axle with non-driving wheels.

[0005] The transmission of torque from the wheels to the ground depends on the coefficient of friction between the tire and the ground at the point of contact between the tire and the ground, which can also generally be called 'adhesion'.

[0006] It may happen that the coefficient of friction does not allow all the applied torque to be passed between the tire and the ground, in which case a wheel slip occurs.

[0007] Such a slip can occur in particular in the event of significant acceleration on a surface with little adhesion, for example on a wet road.

[0008] When the vehicle is equipped with an anti-slip function, also called 'ASR', this function intervenes as soon as the slip rate reaches a certain percentage (on the order of 10% or more, according to a non-limiting example), but it does not intervene for lighter slips. The percentage in question for 'triggering' an ASR intervention depends on the operating conditions and circumstances.

[0009] Such a slip can occur while the speed limiting function is engaged.

[0010] Generally, when the speed limitation function is engaged, the speed limitation function manages a maximum advance speed which must not be exceeded (except in very specific cases).

[0011] Furthermore, the speed limiting function generally uses as the current forward speed a forward speed based on the average rotational speed of the drive wheels.

[0012] It has been observed that when the speed limiting function intervenes to limit the torque requested by the driver while a slight slip condition exists on the drive wheels, this leads to a somewhat chaotic and turbulent feedback loop, which is felt by the driver. Indeed, one or more small oscillations are observed in the rotational speed of the drive wheels.

[0013] In this context, the inventors sought to propose a solution to eliminate the aforementioned servo turbulence, in order to improve driver feel and to improve vehicle stability.

[0014] To achieve this objective, the invention proposes a method for determining a motor torque to be applied to the wheels of a driven axle, in a speed limiting function in a motor vehicle comprising a driven axle with drive wheels and a non-driven axle with non-drive wheels, the speed limiting function managing a maximum advance speed and generally using as the current advance speed an advance speed based on the rotational speed of the drive wheels, the method providing that: a- if a first difference between the ceiling advance speed and the current advance speed is less than a first threshold, and if a second difference between the rotation speed of the driving wheels and the rotation speed of the non-driving wheels is greater than a second threshold, then the speed limitation function changes the calculation basis of the current advance speed which becomes the rotation speed of the non-driving wheels.

[0015] Thanks to these provisions, switching to the current forward speed calculated from the rotation speed of the non-driving wheels makes it possible to avoid the creation of undesirable oscillations.

[0016] It should be noted that in this document, the term "speed limiting function" encompasses both the classic speed limiter function and the speed restriction function.

[0017] Advantageously, the rotational speed of the non-driving wheels is more stable than that of the driving wheels, and the servo loop is then free of oscillations.

[0018] This helps to avoid small jolts that could be felt by the driver and occupants of the vehicle.

[0019] Of course, if the slip suddenly increases, the traction control regulation / feedback loop of the traction control system intervenes and then controls the engine torque control downwards.

[0020] It should be noted that in practice, one works with the half-sum of the wheel speeds of the axle in question. It is observed that, provided the average radius is known, of wheels, it is possible to transpose a wheel rotation speed into a vehicle forward speed.

[0021] According to an advantageous option, the method may further include: b- if the second difference between the rotational speed of the driving wheels and the rotational speed of the non-driving wheels becomes less than a third threshold, then the speed limiting function changes the basis for calculating the current forward speed, which becomes the rotational speed of the driving wheels again.

[0022] Whereupon, the speed limiting function then returns to its nominal operation. Thus, the use of the rotational speed of the non-driving wheels as the basis for calculating the current forward speed is only temporary and concerns the phase of approaching the maximum speed setpoint and reaching said setpoint.

[0023] According to a particular example, the basic loop of the process is executed iteratively with a frequency of at least 100 Hz, i.e., a loop period of 10 ms or less. This results in a very responsive system behavior, although, as will be seen later, for certain conditions to be verified, a confirmation over a certain confirmation time prevails.

[0024] According to one embodiment, the first threshold and / or the second threshold are parameterizable or calibrable thresholds.

[0025] The threshold values ​​can thus be adjusted after qualification tests. The threshold values ​​can be made dependent on the type of vehicle to which the process is applied.

[0026] According to a particular example, the calibration values ​​may depend on the vehicle load, the slope of their road, and so on.

[0027] The calibration table or matrix may have several dimensions as known in itself.

[0028] According to one embodiment, the third threshold is a parameterizable or calibrable threshold.

[0029] The speed of return to nominal operation for the speed limitation function can thus be chosen.

[0030] According to one embodiment, the conditions concerning the first deviation and the second deviation must be verified during respectively a first duration and a second confirmation duration, in order to be validated.

[0031] Each of the first and second confirmation durations can be on the order of a few tens of milliseconds. As a result, the function does not react to a very specific event, such as a wheel passing over a pothole.

[0032] The first and second confirmation durations may be identical or different.

[0033] According to one embodiment, the change of the calculation basis for the calculation of the current feed rate is achieved by a smooth transition without a jump.

[0034] The switch from one piece of information to the other is gradual, without any jump in the determination of the vehicle's forward speed. The behavior is sufficiently smooth, and the change is therefore not perceptible to the driver and / or the vehicle's occupants.

[0035] This applies on the one hand to the switching of the rotational speed of the driving wheels towards the rotational speed of the non-driving wheels and on the other hand to the switching of the rotational speed of the non-driving wheels towards the rotational speed of the driving wheels.

[0036] To achieve a smooth transition, weights that gradually reverse can be used. The time gradient of change can also be limited.

[0037] According to one embodiment, the use of the smooth transition is subject to calibration. The seamless transition function can thus be activated or deactivated.

[0038] If the calibration is such that the jumpless transition function is not activated, then a jump from VRR1 to VRR2, or vice versa from VRR2 to VRR1, can occur.

[0039] According to one embodiment, authorization of the process may be provided subject to calibration, or subject to manufacturer, fleet manager or end user parameterization.

[0040] It is therefore possible to activate or deactivate the function of switching the forward speed calculation based on the rotational speed of the non-drive wheels. This configuration can be included in the vehicle configuration settings.

[0041] The present invention also relates to a motor vehicle comprising at least one motorized axle with drive wheels and one non-motorized axle with non-drive wheels, a speed limiting function, and at least one computer involved in the speed limiting function and configured to implement the method as defined above.

[0042] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures illustrating variants of the invention, in which: - [Fig.l] schematically illustrates in top view a synoptic diagram of the vehicle equipped with the speed limitation function; - [Fig.2] represents an example of a chronogram of a situation in speed increase towards the advance speed capped by the speed limiting function; - [Fig.3] represents an example of a process flowchart.

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

[0044] In [Fig.1], a VHL vehicle is schematically represented, with a front axle ESS AV with steering and driving wheels and a rear axle ESS ARR with non-driving wheels.

[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 powered by a hybrid electric motor in the illustrated example. The electric motor consists of an electric machine, denoted ME1, and an internal combustion engine (ICE). Generally, the powertrain can be purely electric, hybrid, or conventionally powered.

[0047] The electric motor unit is engaged with the front axle wheel shafts via a TRI transmission.

[0048] As known in itself and not described in detail, the TRI transmission includes a differential and a reduction gear which allows the rotational speed to be lowered from the rotational speed of the powertrain output to the rotational speed of the front wheel shafts.

[0049] We are interested here in the speed limitation function designated here by the acronym FLV.

[0050] The vehicle in question includes at least one on-board computer responsible for the FLV speed limitation function. In practice, several computers may be involved. For the sake of simplicity, we will refer here to the FLV computer (designated CMM) even though the FLV function described may be distributed across two or more computers.

[0051] The CMM computer controls the torque produced in the electromotor group, via the INV inverter with regard to the electric machine ME1.

[0052] The vehicle is also equipped with a braking computer, otherwise generally called an ABS computer, which is responsible for determining the rotation speed of each wheel of the vehicle.

[0053] The ABS control unit can also implement the ASR traction control function.

[0054] To communicate with each other, the ABS computer and the CMM computer communicate via a multiplexed network 15, for example a CAN type network, as known per se.

[0055] The CAN network data rate is at least 500 kilobits / s. In practice, a CAN network with a data rate of 1 megabit / s can be used. If necessary, a private multiplexed network can be used to avoid any latency in the transmission of messages from the ASR computer to the engine control unit.

[0056] A rotation speed sensor, labeled WSS in [Fig. 1], is provided at each wheel. The four respective wheel rotation speed values ​​are acquired by the ABS control unit, which then transmits this information to the network to other computers. The ABS computer also calculates the average wheel rotation speed for each of the vehicle's axles.

[0057] VRR1 denotes the average rotational speed of the drive wheels of the axle with drive wheels, here the front axle ESS AV. VRR2 denotes the average rotational speed of the wheels of the axle with non-drive wheels, here the rear axle ESS ARR.

[0058] One or both of the computers involved know a ratio that allows the vehicle's forward speed to be calculated by simply multiplying the wheel rotation speed. This ratio is based primarily on the average wheel radius.

[0059] Among the driver assistance systems, there is the speed limitation function, abbreviated FLV, which helps the driver not to exceed a speed limit.

[0060] In the speed limit function, a maximum speed is set either by the driver or by another vehicle system, for example, a navigation system informed of speed limit zones. The speed limit can also be received in real time from a remote system via a wireless communication link.

[0061] This maximum speed instruction generally varies over time depending on driving circumstances, roads travelled, etc. This maximum speed instruction may also generally depend on the type of vehicle (trailer attached, van, heavy goods vehicle) and certain local restrictions (pollution, roadworks, etc.).

[0062] The speed limiting system is a variant of the speed restriction system, which consists of setting, according to the country of sale and / or local regulations, a maximum speed that the vehicle must not exceed. In this case, the setting is not intended to change over time; it is fixed.

[0063] Figure 2 illustrates a situation where the driver accelerates up to the pending speed limit in the FLV speed limitation function.

[0064] The line at the bottom of the timing diagram indicates the actual activation state of the speed limitation function.

[0065] The area above represents the field of velocities transposed into forward speed of the vehicle.

[0066] The ABS system acquires signals from the four WSS wheel speed sensors, one on each wheel. The ABS system calculates the average wheel rotation speed for each axle.

[0067] The average rotational speed of the front axle wheels (drive axle) is denoted RR1 (in revolutions per minute). The average rotational speed of the rear axle wheels (non-drive axle) is denoted RR2 (in revolutions per minute).

[0068] Given the knowledge of the average wheel radius, the wheel rotation speed is converted into the vehicle's forward speed, respectively VRR1 and VRR2 (in km / h). According to a general expression, we can write VRR1 = f(RR1) and VRR2 = f(RR2).

[0069] The current feed rate generally used by the FLV speed limiting function is the feed rate calculated based on the rotational speeds of the drive wheels, i.e., f(RRl). This allows for a reliable and precise dynamic control loop.

[0070] The limiting setpoint speed, also called the ceiling speed, is denoted VP. The current advance speed, taken as the variable to be controlled, is denoted VV. In the general case, VV = f(RRl).

[0071] At time t0, VRR2 = VRR1. Between t0 and t1, an increase in the current forward speed VV is observed, and a concomitant reduction in the difference VP-VV. A slight drift between the speed of the driving wheels and the speed of the non-driving wheels is also observed, i.e., VRR2-VRR1 increases.

[0072] When VP-VV is less than a first threshold SI, the FLV function is about to intervene. This first threshold SI is configurable or calibrable. We denote El = VP-VV, El being the first deviation, measuring the difference in current advance speed relative to the maximum setpoint (see downward arrow in [Fig.2]).

[0073] Furthermore, the difference E2 = VRR2 - VRR1 represents the effect of the drive wheels slipping on the road surface. The difference E2 is called the second deviation E2.

[0074] At time t1, the difference E2 = VRR2-VRR1 becomes greater than a second threshold S2. This second threshold, denoted S2, is parameterizable or calibrable.

[0075] It is noted that the second threshold can be expressed in km / h or in revolutions per minute, depending on whether one is working on an equivalent advance speed or on the source information of wheel rotation speed.

[0076] At time tl, according to the proposed method, the speed limiting function changes its source for calculating the current forward speed. From time tl onwards, it now uses the basis provided by the rotational speeds of the non-driving wheels VRR2 instead of using the basis provided by the rotational speeds of the driving wheels VRR1 as before.

[0077] This is symbolized on the highest curve of the graph in [Fig.2], where RMM denotes the mode with the basis provided by the rotational speeds of the driving wheels VRR1 and RNMO denotes the mode with the basis provided by the rotational speeds of the non-driving wheels VRR2.

[0078] The motor torque to be applied to the wheels of the driven axle is denoted CMO. It is shown just below in [Fig. 2]. Up to time t2, the motor torque corresponds to the driver's input, but from time t2 onwards, or even slightly thereafter, the torque is determined by the driver. Previously, the speed limitation function took over and imposed a lower engine torque so that the vehicle's forward speed did not exceed the VP ceiling.

[0079] Advantageously, thanks to the use of the rotational speed of the non-driving wheels as a reference, the control of the torque servo system on the ceiling speed is calm and does not exhibit oscillation.

[0080] At time t3, while the regulation provided by the speed limitation function is active, the gap E2 = VRR2-VRR1 becomes less than a third threshold S3.

[0081] This is the condition for switching back the calculation of the advance speed with the calculation based on the rotation speeds of the drive wheels VRR1.

[0082] This third threshold S3 is configurable or calibrable.

[0083] The proposed process therefore uses the following basic loop, as also visible in [Fig.3]:

[0084] a- if a first difference between the ceiling advance speed and the current advance speed El = VP - VV is less than the first threshold SI and if a second difference E2 between the rotation speed VRR1 of the driving wheels and the rotation speed VRR2 of the non-driving wheels, i.e. E2 = VRR1 - VRR2, is greater than the second threshold S2, then the speed limiting function FLV changes the calculation basis of the current advance speed VV which becomes the rotation speed VRR2 of the non-driving wheels.

[0085] b- if the second difference E2 between the rotational speed VRR1 of the driving wheels and the rotational speed VRR2 of the non-driving wheels ie E2 = VRR1 - VRR2, becomes less than the third threshold S3, then the speed limiting function changes the basis for calculating the current forward speed VV which becomes again the rotational speed VRR1 of the driving wheels.

[0086] This loop is repeated, as illustrated in [Fig.3], with a recurrence of at least 100 hertz.

[0087] According to an optional feature, a smooth transition is provided during a switch from one reference to another. For example, a calculation can be provided as follows: VV = Cl x VRR1 + C2 x VRR2, with the sum of the coefficients Cl + C2 = 1, and opposite variations, the complete variation being able to extend over a period of a few tens of milliseconds, or even one to two hundred milliseconds, or even a longer period without these values ​​being limiting.

[0088] According to an alternative solution, the temporal gradient of the velocity calculation can be limited below a value expressed in m / s2.

[0089] Generally speaking, we speak of a smooth transition when it is devoid of a jump.

[0090] It is noted that this smoothing function can be subject to the presence of an activation calibration of this smoothing function.

[0091] Furthermore, the entire function of switching to the reference provided by the non-driving wheels can also be subject to the presence of a calibration flag activating the entire function.

[0092] In addition, as already discussed above, the inequality conditions expressed above may require confirmation of several consecutive calculation loops, or may require confirmation over a determined storage period.

Claims

Demands

1. A method for determining a motor torque (CMO) to be applied to the wheels of a driven axle MMM, in a speed limiting function (FLV) in a motor vehicle comprising a driven axle with driving wheels and a non-driven axle with non-driving wheels, the speed limiting function managing a maximum advance speed (VP) and generally using as the current advance speed (VV) an advance speed based on the rotational speed (VRR1) of the driving wheels, the method providing that: a- if a first difference (E1) between the maximum advance speed (VAP) and the current advance speed (VV) is less than a first threshold (S1) and if a second difference (E2) between the rotational speed (VRR1) of the driving wheels and the rotational speed (VRR2) of the non-driving wheels is greater than a second threshold (S2),Then the speed limiting function changes the calculation basis for the current forward speed (VV), which becomes the rotational speed (VRR2) of the non-driving wheels.

2. Method according to claim 1, further comprising: b- if the second difference (E2) between the rotational speed (VRR1) of the driving wheels and the rotational speed (VRR2) of the non-driving wheels VRR1 - VRR2 becomes less than a third threshold (S3), then the speed limiting function changes the calculation basis of the current forward speed (VV) which becomes again the rotational speed (VRR1) of the driving wheels.

3. A method according to any one of claims 1 to 2, characterized in that the first threshold (SI) and / or the second threshold (S2) are parameterizable or calibrable thresholds.

4. Method according to claim 2, characterized in that the third threshold (S3) is a parameterizable or calibrable threshold.

5. A method according to any one of claims 1 to 4, characterized in that the conditions concerning the first deviation (E1) and the second deviation (E2) must be verified for a first and a second confirmation period respectively, in order to be validated.

6. A method according to any one of claims 1 to 4, characterized in that the change in the calculation basis for the calculation of

7.

8.

9. The current forward speed is achieved through a smooth transition without any jumps. Method according to claim 6, characterized in that the use of the smooth transition is subject to calibration. A process according to any one of claims 1 to 4, characterized in that it provides for authorization of the process subject to calibration, or subject to manufacturer, fleet manager or end user parameterization. Motor vehicle, comprising at least one powered axle with drive wheels and one non-powered axle with non-drive wheels, a speed limiting function, and at least one computer involved in the speed limiting function and configured to implement the method according to any one of claims 1 to 8.

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