Determination of the torque required of an electric prime mover of a vehicle in a limp home mode of travel

Abstract

The invention relates to a method implemented in a vehicle comprising a powertrain, including an electric prime mover supplying or recovering a required torque, and a limp home mode of travel at at least one target speed. This method comprises a step (10-60) in which, when the mode is set, the required torque is controlled as a function of the actual speed of the land vehicle and a first value representative of a difference between the target speed and the actual speed.

Description

[0001] DESCRIPTION

[0002] TITLE: DETERMINATION OF THE TORQUE REQUIRED FROM AN ELECTRIC DRIVE MACHINE OF A VEHICLE IN A DEGRADED TRAVEL MODE

[0003] The present invention claims priority from French application No. 2201030 filed on 07.02.2022, the content of which (text, drawings and claims) is incorporated herein by reference.

[0004] Technical field of the invention

[0005] The invention relates to land vehicles having a degraded travel mode (or emergency mode, or in English "limp home mode"), and more specifically to the control of the torque requested from the electric motor of the powertrain of such vehicles when the degraded travel mode is used.

[0006] State of the art

[0007] Certain land vehicles, possibly of the automobile type, include a powertrain (or GMP) comprising at least one electric motor and have a degraded travel mode (or emergency or limp home mode) which is established in the event of detection of a problem within the GMP or the main (or traction) battery associated with this electric motor.

[0008] It is recalled that the degraded mode of travel consists of imposing a movement of the land vehicle at a speed lower than or equal to a target speed, generally relatively low (typically between 15 km / h and 40 km / h), in order to avoid immediate immobilization which is a priori not essential at the time in question and therefore allow the driver to park his land vehicle in a secure place or to reach an after-sales service for an inspection.

[0009] Usually, in order for the (land) vehicle to be able to travel at the target speed in the degraded travel mode, the electric motor i is asked for a torque (positive or negative) which is a function of the current actual speed of the vehicle. For this purpose, a vehicle computer can, for example, store a table (or map) establishing a correspondence between speeds and torques, and obtained during testing or development phases.

[0010] A main disadvantage of this type of table (or mapping) is that each torque associated with a speed has been determined for a vehicle traveling on a flat (or without slope) traffic lane and with an average weight. Therefore, in the degraded travel mode the actual speed of the vehicle varies (and therefore is not constant) depending at least on the slope of the traffic lane taken by the vehicle, which can hinder its driver, for example when parking it. This results from the fact that when the vehicle travels on an uphill traffic lane it needs more torque than what is required of its electric motor to reach the target speed, while if the vehicle travels on a downhill traffic lane it needs less torque than what is required of its electric motor to reach the target speed.This disadvantage is all the more accentuated when the difference between the aforementioned average weight and the actual (current) weight of the vehicle is large.

[0011] The invention therefore aims in particular to improve the situation.

[0012] Presentation of the invention

[0013] For this purpose, it proposes in particular a control method intended to control the torque requested from an electric motor of a powertrain of a land vehicle having a degraded travel mode at at least one target speed.

[0014] This control method is characterized by the fact that it comprises a step in which, when the mode is established, the requested torque is controlled as a function of an actual speed of the land vehicle and a first value representative of a difference between the target speed and the actual speed.

[0015] Thanks to this mode of controlling the torque required from the electric motor, during the degraded travel mode, the actual speed of the land vehicle is substantially constant regardless of the gradient of the road on which it is traveling and regardless of its weight, which avoids disturbing the driver.

[0016] The control method according to the invention may include other characteristics which may be taken separately or in combination, and in particular:

[0017] - in its step, an absolute value of the difference (between the target speed and the actual speed) can be determined, then, when this determined absolute value is greater than a first chosen threshold, a second value representative of a percentage difference between the target speed and the actual speed can be determined, then the first value can be determined as a function of this second determined value, then the requested torque can be determined as a function of the actual speed and the first determined value;

[0018] - in the presence of the first option, in its step we can determine a first value equal to a result of a product between the second value and a chosen corrective coefficient;

[0019] - in the presence of the last sub-option, in its step the corrective coefficient can be chosen according to the actual speed and / or the percentage of deviation;

[0020] - also in the presence of the last sub-option, in its step we can determine the requested torque by multiplying a theoretical torque associated with the real speed and the first value increased by a value equal to one;

[0021] - also in the presence of the first sub-option, in its step, when the determined absolute value becomes lower than the first threshold at an instant, a theoretical torque associated with the actual speed can be determined and this determined theoretical torque can be used as the requested torque when a chosen duration has elapsed since this instant;

[0022] - in the presence of the last sub-option, in its step the duration can be chosen according to the actual speed and / or the percentage of deviation.

[0023] The invention also provides a computer program product comprising a set of instructions which, when executed by processing means, is capable of implementing the control method of the type presented above for controlling a torque requested from an electric motor of a powertrain of a land vehicle having a degraded travel mode at at least one target speed. The invention also provides a control device intended to equip a land vehicle comprising a powertrain, comprising an electric motor capable of providing or recovering a requested torque, and a degraded travel mode at at least one target speed.

[0024] This control device is characterized by the fact that it comprises at least one processor and at least one memory arranged to carry out the operations consisting, when the mode is established, of triggering a control of the requested torque as a function of an actual speed of the land vehicle and of a first value representative of a difference between the target speed and the actual speed.

[0025] The invention also proposes a land vehicle, possibly of the automobile type, and comprising a powertrain, comprising an electric motor capable of providing or recovering a requested torque, a degraded travel mode at at least one target speed, as well as a control device of the type presented above.

[0026] Brief description of the figures

[0027] Other characteristics and advantages of the invention will appear on examining the detailed description below, and the appended drawings, in which: [Fig. 1] illustrates schematically and functionally an exemplary embodiment of a land vehicle comprising an all-electric GMP and a supervision computer comprising a control device according to the invention,

[0028] [Fig. 2] schematically and functionally illustrates an exemplary embodiment of a GMP supervision calculator comprising an exemplary embodiment of a control device according to the invention, and

[0029] [Fig. 3] schematically illustrates an example of an algorithm implementing a control method according to the invention.

[0030] Detailed description of the invention

[0031] The invention aims in particular to propose a control method, and an associated DC control device, intended to enable the control of the torque requested from an electric motor MME of a powertrain (or GMP) of a land vehicle V when the degraded travel mode is used (or established).

[0032] In the following, it is considered, by way of non-limiting example, that the land vehicle V is of the automobile type. This is for example a car, as illustrated in Figure 1. But the invention is not limited to this type of land vehicle. It relates in fact to any type of land vehicle comprising a powertrain (or GMP) comprising at least one electric motor and having a degraded travel mode (or emergency or limp home mode). Thus, it relates, for example, to utility vehicles, camper vans, minibuses, coaches, trucks, motorcycles, leisure vehicles (snowmobiles, karts), tracked vehicles, road vehicles, construction vehicles, and agricultural vehicles, for example.

[0033] Furthermore, it is considered in the following, by way of non-limiting example, that the land vehicle V comprises a powertrain (or GMP) of the all-electric type (and therefore whose drive is provided exclusively by at least one electric motor MME). But the GMP could be hybrid since the degraded travel mode of its vehicle is carried out exclusively using the torque supplied or recovered by its electric motor.

[0034] It is again recalled that the degraded travel mode consists of imposing a movement of the (land) vehicle V at a speed which is less than or equal to a target speed vc by controlling the torque cd requested from the electric motor MME. It will be noted that in the degraded travel mode it is possible to provide first and second target speeds respectively for forward and reverse travel.

[0035] Figure 1 schematically shows a (land) vehicle V comprising an electric GMP transmission chain and a DC control device according to the invention.

[0036] The transmission chain has a GMP which is, here, purely electric and therefore which includes, in particular, an electric motor MME, a motor shaft AM, a main (or traction) battery BP and a transmission shaft AT. Here, the term "electric motor" means an electric machine arranged to provide or recover torque to move the vehicle V.

[0037] The operation of the GMP is supervised by a CS supervision computer.

[0038] The electric prime mover MME (here an electric motor) is coupled to the main (or traction) battery BP, in order to be supplied with electrical energy during a rolling phase, and to supply this main battery BP with regenerative (electric) current during a regenerative braking phase. It is coupled to the motor shaft AM, to provide it with torque by rotational drive. This motor shaft AM is here coupled to a reducer RD which is also coupled to the transmission shaft AT, itself coupled to a first train T1 (here of wheels), preferably via a differential D1. The operation of the electric prime mover MME is controlled by a machine computer CM, and supervised by the supervision computer CS.

[0039] This first train T1 is here located in the front part PW of the vehicle V. But in a variant this first train T1 could be the one which is here referenced T2 and which is located in the rear part PRV of the vehicle V.

[0040] The main battery BP may, for example, include electrical energy storage cells, possibly of the electrochemical type (for example of the lithium-ion (or Li-ion) or Ni-Mh or Ni-Cd type). It should be noted that the cells (for electrical energy storage) may possibly be grouped in modules that are identical or different from each other.

[0041] For example, the main BP battery can be of low voltage type (typically 450 V for illustration). But it could be of medium voltage or high voltage type.

[0042] It should be noted that the MME electric motor can also be coupled to an electrical energy generator which can, for example, be a converter and responsible for supplying electrical energy, from the main BP battery and converted, to a very low voltage service battery (in particular for recharging it) and an on-board network.

[0043] As mentioned above, the invention proposes in particular a control method intended to enable the control of the torque cd requested from the electric motor MME when the degraded travel mode is used (or established).

[0044] This (control) method can be implemented at least partially by the DC control device (illustrated in figures 1 and 2) which comprises for this purpose at least one processor PR1, for example a digital signal processor (or DSP ("Digital Signal Processor")) and at least one memory MD. This DC control device can therefore be implemented in the form of a combination of electrical or electronic circuits or components (or "hardware") and software modules (or "software"). For example, it can be a microcontroller.

[0045] The MD memory is RAM in order to store instructions for the implementation by the processor PR1 of at least part of the control method. The processor PR1 may comprise integrated (or printed) circuits, or several integrated (or printed) circuits connected by wired or wireless connections. An integrated (or printed) circuit is understood to mean any type of device capable of carrying out at least one electrical or electronic operation.

[0046] In the example illustrated non-limitingly in Figures 1 and 2, the DC control device is part of the CS supervision computer of the GMP. But this is not obligatory. Indeed, the DC control device could include its own computer, or it could be part of the CM machine computer, for example.

[0047] As illustrated non-limitingly in Figure 3, the (control) method according to the invention comprises at least one step 10-60 which is implemented each time the degraded travel mode is used (or established) in the vehicle V.

[0048] In this step 10-60, the (DC control device) controls the torque cd which is requested from the electric motor MME as a function of the actual (current) speed vr of the vehicle V and of a first value v1 which is representative of the difference ev between the (one) target speed (of the degraded travel mode) vc and this actual speed vr (i.e. ev = vc - vr). The actual speed vr is known permanently and precisely in the vehicle V, in particular by the supervision computer CS (for example, it may be provided by an ESP / ABS type function (ESP: "Electronic Stability Program"), ABS: "Anti-Blocking System").

[0049] This mode of controlling the requested torque cd is particularly advantageous because it makes it possible to have in the degraded travel mode an actual speed vr of the vehicle V which is substantially constant whatever the gradient (upward or downward or zero) of the traffic lane on which it is traveling and whatever its weight. Thus, the driver is not disturbed during the degraded travel mode, and in particular when parking his vehicle V.

[0050] It will be understood that it is at least the processor PR1 and memory MD of the DC control device which are arranged to carry out the operations consisting, when the degraded travel mode is used, in controlling the torque cd which is requested from the electric motor MME as a function of the actual speed vr of the vehicle V and of the first value v1 (representative of the difference ev between the target speed vc and the actual speed vr).

[0051] It will be noted that step 10-60 may comprise a sub-step 10 in which one (the DC control device) may begin by determining an absolute value vae of the deviation ev (i.e. vae = |ev| = |vc - vr|), and a sub-step 20 in which one (the DC control device) may compare this determined absolute value vae to a first chosen threshold s1.

[0052] Then, when this determined absolute value vae is greater than the first threshold s1 chosen (i.e. vae > s1), one (the DC control device) can determine, in a sub-step 30 step 10-60, a second value v2 which is representative of a percentage difference pe between the target speed vc and the actual speed vr, then determine the first value v1 as a function of this second value v2.

[0053] For example, the percentage deviation pe can be equal to the ratio between the deviation ev and the target speed vc (i.e. pe = ev / vc = (vc-vr) / vc (in %)). We can therefore have a negative or positive percentage deviation pe depending on whether vc is less than or greater than vr.

[0054] Also for example, the second value v2 can be equal to the percentage deviation pe (i.e. v2 = pe). But this is not mandatory.

[0055] Then, step 10-60 may comprise a sub-step 40 in which one (the DC control device) may determine the requested torque cd as a function of the actual speed vr and the first determined value v1 (function of v2).

[0056] It will be noted that, when in sub-step 20 the determined absolute value vae is less than or equal to the first threshold s1 chosen (i.e. vae < s1), one (the DC control device) can, for example, determine, in a sub-step 50 of step 10-60, a theoretical torque ct(vr) associated with the actual speed vr and use this determined theoretical torque ct(vr) as the requested torque cd.

[0057] For example, the theoretical torque ct(vr) can be determined within a table (or map) establishing a correspondence between (actual) speeds and (requested) torques, and determined during testing or development phases of a vehicle similar to the one concerned (V) for an average on-board load. It should be noted that one table (or map) can be used for forward travel and another table (or map) for reverse travel. It should also be noted that the (each) table (or map) can, for example, be stored in the DC control device. It should also be noted that instead of using a table (or map) one can use at least one mathematical formula (or equation) giving the requested torque cd as a function of the actual speed vr.

[0058] It will also be noted that in sub-step 30 the control device DC) can, for example, determine a first value v1 which is equal to the result of the product between the second value v2 (here equal to the percentage of deviation pe) and a chosen corrective coefficient cc (i.e. v1 = v2*cc (with here v2 = pe)). This corrective coefficient cc is intended to improve the accuracy of the determination of the requested torque cd. It will be noted that the percentage of deviation pe can be negative or positive, the first value v1 can therefore also be negative or positive.

[0059] For example, in sub-step 30 of step 10-60 the corrective coefficient cc can be chosen as a function of the actual speed vr and / or the percentage deviation pe. In this case, it is possible, for example, to use a law (or mapping) defining the evolution of the corrective coefficient cc as a function of the actual speed vr and / or the percentage deviation pe, and determined during testing and development phases of a vehicle similar to that concerned (V).

[0060] But this is not obligatory. Indeed, the corrective coefficient cc can be fixed (or constant) whatever the actual speed vr and / or whatever the percentage deviation pe.

[0061] Also for example, in sub-step 40 of step 10-60, one (the control device DC) can, for example, determine the requested torque cd by multiplying a theoretical torque ct(vr) which is associated with the actual speed vr and the first value v1 increased by a value equal to one (i.e. cd = ct(vr)*(1 + v1 )). Thus, when the first value v1 is negative the requested torque cd is less than the theoretical torque ct(vr), which is suitable for the case where the vehicle V is traveling on a descending slope, and when the first value v1 is positive the requested torque cd is greater than the theoretical torque ct(vr), which is suitable for the case where the vehicle V is traveling on an ascending slope.

[0062] As indicated above, the theoretical torque ct(vr) can be determined within the aforementioned table (or map), which establishes a correspondence between (actual) speeds and (requested) torques. It should be noted that here too one table (or map) can be used for forward travel and another table (or map) for reverse travel. It should also be noted that instead of using a table (or map) one can also use at least one mathematical formula (or equation) giving the requested torque cd as a function of the actual speed vr.

[0063] It will also be noted that a return to a conventional operating mode can be provided when the determined absolute value vae becomes permanently lower than the first threshold s1. For this purpose, when the determined absolute value vae becomes lower than the first threshold s1 at a time t (i.e. vae < s1 from t), one (the DC control device) can, for example, determine, in a sub-step 60 of step 10-60, a theoretical torque ct(vr) which is associated with the actual speed vr (and presented above), and use this determined theoretical torque ct(vr) as the requested torque cd when a chosen duration of has elapsed since this time t. This amounts to carrying out sub-step 50 when the duration of has elapsed.In order to implement this option, one (the DC control device) can trigger a time delay having the first chosen duration as soon as the determined absolute value vae becomes lower than the first threshold s1 at a time t, and when this time delay expires (and one still has vae < s1), one (the DC control device) uses the determined theoretical torque ct(vr) as the requested torque cd.

[0064] For example, in sub-step 60 of step 10-60 the duration of can be chosen as a function of the actual speed vr and / or the percentage of deviation pe. In this case, it is possible, for example, to use a law (or mapping) defining the revolution of the duration of as a function of the actual speed vr and / or the percentage of deviation pe, and determined during testing and development phases of a vehicle similar to that concerned (V).

[0065] But this is not obligatory. Indeed, the duration of can be fixed (or constant) whatever the actual speed vr and / or whatever the percentage deviation pe.

[0066] Limp Home mode is inhibited when the problem initially detected and which triggered its implementation is no longer present, for example after the driver has switched off the ignition of vehicle V and then switched the ignition back on.

[0067] However, it is also possible to provide an operating option in which the degraded travel mode is (at least) temporarily inhibited when the driver presses the brake pedal PF of the vehicle V in a certain way. For example, a percentage interval of depression of the brake pedal PF can be provided which induces a dosage of the requested torque cd, and beyond this interval the degraded travel mode is temporarily inhibited. For example, this interval can include the first ten percent of depression of the brake pedal PF, and its upper and lower limits are hereinafter called the second s2 and third s3 thresholds (with s3 different from 0%).

[0068] In this case, we can, for example, have the operation described below.

[0069] When the brake pedal PF is fully released (0%), the control method described above is implemented. When the brake pedal PF is depressed by a percentage that is greater than the second threshold s2, the degraded travel mode is temporarily inhibited. When the brake pedal PF is depressed by a percentage ppf that is between the second s2 and third s3 thresholds (i.e. s2 < ppf < s3), the requested torque cd can be determined (the DC control device), for example, by means of the formula: cd = ct(vr)*(1 +v1 )*cc'. cc' is another corrective coefficient that can, for example, be determined by the DC control device by means of the formula: cc' = (s2 - ppf) / s2.

[0070] It will also be noted, as illustrated non-limitingly in Figure 2, that the supervision computer CS (or the computer of the control device DC) can also comprise a mass memory MM1, in particular for storing the tables (or maps), the actual speeds and any percentages ppf of depression of the brake pedal PF, as well as any intermediate data involved in all its calculations and processing. Furthermore, this supervision computer CS (or the computer of the control device DC) can also comprise an input interface IE for receiving at least the actual speeds and any percentages ppf, to use them in calculations or processing, possibly after having formatted and / or demodulated and / or amplified them, in a manner known per se, by means of a digital signal processor PR2.In addition, this supervision calculator CS (or the calculator of the control device DC) can also include an output interface IS, in particular to deliver each requested torque cd having to control in real time the electric motor machine MME during the degraded travel mode, and a possible message (or order) of temporary inhibition of the degraded travel mode.

[0071] It will also be noted that the invention also proposes a computer program product (or computer program) comprising a set of instructions which, when executed by processing means of the electronic circuit (or hardware) type, such as for example the processor PR1, is capable of implementing the control method described above to control the torque cd requested from the electric motor MME of the GMP of the vehicle V during the degraded travel mode.

Claims

DEMANDS 1. Method for controlling the torque required by an electric drive machine (EDM) of a powertrain of a land vehicle (V) having a degraded mode of movement at least one target speed, characterized in that it includes a step (10-60) in which, when said mode is established, said torque required is controlled as a function of an actual speed of said land vehicle (V) and a first value representing a difference between said target speed and actual speed.

2. Method according to claim 1, characterized in that in said step (10-60) an absolute value of said deviation is determined, then, when said determined absolute value is greater than a first chosen threshold, a second value is determined representing a percentage of deviation between said actual speed and target speed, then, then the first value is determined as a function of said second determined value, then said required torque is determined as a function of said actual speed and said first determined value.

3. Method according to claim 2, characterized in that in said step (10-60) a first value is determined equal to a result of a product between said second value and a chosen correction coefficient.

4. Method according to claim 3, characterized in that in said step (10-60) said correction coefficient is chosen as a function of said actual speed and / or said percentage of deviation.

5. Method according to claim 3 or 4, characterized in that in said step (10-60) said required torque is determined by multiplying a theoretical torque associated with said actual speed and said first value increased by a value equal to one.

6. A method according to any one of claims 2 to 4, characterized in that in said step (10-60), when said determined absolute value becomes less than said first threshold at an instant, a theoretical torque associated with said actual speed is determined and this determined theoretical torque is used as the required torque when a chosen time has elapsed since said instant.

7. Method according to claim 6, characterized in that in said step (10-60) said duration is chosen as a function of said actual speed and / or said percentage of deviation.

8. Product computer program comprising a set of instructions which, when executed by processing means, is suitable for implementing the control method according to any one of claims 1 to 7 for controlling a torque requested to an electric motor machine (EMM) of a powertrain of a land vehicle (V) having a degraded mode of movement at least one target speed.

9. Control device (CD) for a land vehicle (V) comprising a powertrain, including an electric motor machine (EMM) suitable for supplying or recovering a required torque, and a degraded mode of movement at least one target speed, characterized in that it comprises at least one processor (PR1) and at least one memory (MD) arranged to perform the operations consisting, when said mode is established, of triggering a control of said required torque as a function of an actual speed of said land vehicle (V) and a first value representing a difference between said target speed and actual speed.

10. Land vehicle (V) comprising a powertrain, including an electric motive machine (EMM) capable of supplying or recovering required torque, and a degraded mode of movement at least at a target speed, characterized in that it further comprises a control device (CD) according to claim 9.

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