DETERMINATION OF THE TORQUE REQUIRED BY AN ELECTRIC POWERTRAIN OF A VEHICLE IN A DEGRADED MOTION MODE

Abstract

A method is implemented in a vehicle comprising a powertrain, including an electric motor supplying or recovering a required torque, and a degraded mode of travel at at least one target speed. This method includes a step (10-60) in which, when the mode is established, the required torque is controlled as a function of the actual speed of the land vehicle and a first representative value of a difference between the target speed and the actual speed. Figure 3

Description

Title of the invention: DETERMINATION OF THE TORQUE REQUIRED BY AN ELECTRIC POWER STEERING MACHINE OF A VEHICLE IN A DEGRADED MOTION MODE Technical field of the invention

[0001] The invention relates to land vehicles having a degraded (or emergency, or in English "limp home mode") mode of movement, and more specifically the control of the torque required from the electric drive machine of the powertrain of such vehicles when the degraded mode of movement is used. State of the art

[0002] Certain land vehicles, possibly of the motor vehicle type, include a powertrain (or PWM) comprising at least one electric motor and have a degraded (or backup or limp home) mode of movement which is established in the event of detection of a problem within the PWM or the main (or traction) battery associated with this electric motor.

[0003] It is recalled that the degraded mode of movement consists of imposing a movement of the land vehicle at a speed less than or equal to a target speed, generally relatively low (typically between 15 km / h and 40 km / h), in order to avoid an immediate immobilization which is not essential at the time in question and thus allow the driver to park his land vehicle in a secure place or to reach an after-sales service for an inspection.

[0004] Typically, in order for the (land) vehicle to travel at the target speed in degraded mode, the electric drive unit is required to apply a torque (positive or negative) that is a function of the vehicle's actual current speed. For this purpose, a vehicle computer can, for example, store a table (or map) establishing a correlation between speeds and torques, obtained during testing or development phases.

[0005] A major drawback of this type of table (or map) lies in the fact that each torque associated with a speed has been determined for a vehicle traveling on a flat (or level) road and with an average weight. Consequently, in degraded driving mode, the vehicle's actual speed varies (and is therefore not constant) depending at least on the slope of the road the vehicle is traveling on, which can be inconvenient for the driver, for example, when parking. This results from the fact that when the vehicle is traveling on an uphill road, it needs more torque than is required from its electric drive unit to reach the target speed, whereas if the vehicle is traveling on a downhill road It requires less torque than what is demanded of its electric drive unit to reach the target speed. This drawback is all the more pronounced when the difference between the aforementioned average weight and the actual (ongoing) weight of the vehicle is large.

[0006] The invention therefore aims in particular to improve the situation. Presentation of the invention

[0007] In particular, it proposes for this purpose a control method intended to control the torque required from an electric drive machine of a powertrain of a land vehicle having a degraded mode of movement at least at a target speed.

[0008] This control method is characterized by the fact that it includes a step in which, when the mode is established, the required torque is controlled as a function of an actual speed of the land vehicle and a first value representing a difference between the target speed and the actual speed.

[0009] Thanks to this method of controlling the torque requested from the electric drive machine, during the degraded movement mode, the actual speed of the land vehicle is substantially constant regardless of the slope of the road on which it travels and regardless of its weight, which avoids disturbing the driver.

[0010] The control method according to the invention may include other features which may be taken separately or in combination, and in particular:

[0011] - in its step one can determine an absolute value of the difference (between the speeds target and actual speed), then, when this determined absolute value is greater than a first chosen threshold, a second value can be determined representing a percentage difference between the target speed and actual speed, then the first value can be determined as a function of this second determined value, then the required torque can be determined as a function of the actual speed and the first determined value;

[0012] - in the presence of the first option, in its step one can determine a first value equal to the result of a product between the second value and a chosen correction coefficient;

[0013] - in the presence of the last sub-option, in its step the correction coefficient can to be chosen based on the actual speed and / or the percentage difference;

[0014] - also in the presence of the last sub-option, in its step one can determine the required torque by multiplying a theoretical torque associated with the actual speed and the first value increased by a value equal to one;

[0015] - also in the presence of the first sub-option, in its step, when the value If the absolute value of the determined value becomes less than the first threshold at a given instant, a theoretical torque associated with the actual velocity can be determined, and this theoretical torque can be used. determined as the requested pair when a chosen duration has elapsed since that moment;

[0016] - in the presence of the last sub-option, in its step the duration can be chosen in depending on the actual speed and / or the percentage difference.

[0017] The invention also proposes a computer program product comprising a set of instructions which, when executed by processing means, is suitable for implementing the control method of the type presented above to control a torque requested from an electric drive machine of a powertrain of a land vehicle having a degraded mode of movement at least at a target speed.

[0018] The invention also proposes a control device intended to equip a land vehicle comprising a powertrain, including an electric drive machine capable of supplying or recovering a required torque, and a degraded mode of movement at least at a target speed.

[0019] This control device is characterized by the fact that it includes at least one processor and at least one memory arranged to perform 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 a first value representative of a difference between the target speed and the actual speed.

[0020] The invention also proposes a land vehicle, possibly of the automobile type, comprising a powertrain, including an electric drive machine capable of supplying or recovering a required torque, a degraded mode of movement at least at a target speed, and a control device of the type presented above. Brief description of the figures

[0021] Other features and advantages of the invention will become apparent from an examination of the detailed description below, and the accompanying drawings, in which:

[0022] [Fig. 1] schematically and functionally illustrates an example of an embodiment of a land vehicle comprising an all-electric powertrain and a supervisory computer including a control device according to the invention,

[0023] [Fig.2] schematically and functionally illustrates an example of an embodiment of a powertrain monitoring computer comprising an example of an embodiment of a control device according to the invention, and

[0024] [Fig.3] schematically illustrates an example of an algorithm implementing a control method according to the invention. Detailed description of the invention

[0025] The invention aims in particular to provide a control method, and an associated DC control device, intended to allow control of the torque required from an electric drive machine MME of a powertrain (or GMP) of a land vehicle V when the degraded mode of movement is used (or established).

[0026] In what follows, the land vehicle V is considered, by way of non-limiting example, to be of the automobile type. This is, for example, a car, as illustrated in [Fig. 1]. However, the invention is not limited to this type of land vehicle. It relates to any type of land vehicle comprising a powertrain (or PWM) including at least one electric drive unit and having a degraded (or backup or limp home) mode of operation. Thus, it relates, for example, to commercial vehicles, motorhomes, minibuses, coaches, trucks, motorcycles, recreational vehicles (snowmobiles, go-karts), tracked vehicles, road maintenance vehicles, construction equipment, and agricultural vehicles, for example.

[0027] Furthermore, in what follows, by way of non-limiting example, the land vehicle V comprises an all-electric powertrain (or PMT) (and therefore whose propulsion is provided exclusively by at least one electric motor). However, the PMT could be hybrid provided that the degraded mode of movement of the vehicle is achieved exclusively using the torque supplied or recovered by its electric motor.

[0028] It is reiterated that the degraded mode of movement consists of imposing a speed on the (land) vehicle V that is less than or equal to a target speed vc by controlling the torque cd requested from the electric drive machine MME. It should be noted that in the degraded mode of movement, first and second target speeds can optionally be provided for forward and reverse movement, respectively.

[0029] A (land) vehicle V comprising an electric GMP transmission chain and a DC control device according to the invention is schematically represented in [Fig.1].

[0030] The transmission chain has a powertrain which, in this case, is purely electric and therefore includes, in particular, an electric drive machine MME, a drive shaft AM, a main (or traction) battery BP and a transmission shaft AT. Here, "electric drive machine" means an electric machine arranged to supply or recover torque to move the vehicle V.

[0031] The operation of the GMP is supervised by a CS supervisory computer.

[0032] The electric drive machine MME (here an electric motor) is coupled to the main (or traction) battery BP, in order to be supplied with electrical energy during a driving phase, and to supply this main battery BP with current (Electric) regenerative braking occurs during a regenerative braking phase. It is coupled to the drive shaft AM to provide torque through rotational drive. This drive shaft AM is coupled to a reduction gear RD, which is also coupled to the transmission shaft AT. The AT is itself coupled to a first set of wheels Tl, preferably via a differential Dl. The operation of the electric traction unit MME is controlled by a machine control computer CM and supervised by the supervisory control computer CS.

[0033] This first train Tl is located here in the front part PVV of the vehicle V. But in a variant this first train Tl could be the one which is here referenced T2 and which is located in the rear part PRV of the vehicle V.

[0034] The main battery BP may, for example, include electrical energy storage cells, possibly of the electrochemical type (for example, lithium-ion (or Li-ion) or Ni-MH or Ni-Cd type). It should be noted that the (electrical energy storage) cells may optionally be grouped into identical or different modules.

[0035] For example, the main battery BP may be of the low voltage type (typically 450 V by way of illustration). But it could be of the medium voltage or high voltage type.

[0036] It should be noted that the electric motive machine MME can also be coupled to an electric power generator which can, for example, be a converter and be responsible for supplying electrical power, from the main battery BP and converted, to a very low voltage auxiliary battery (in particular for recharging it) and an on-board network.

[0037] As mentioned above, the invention proposes in particular a control method intended to allow control of the torque cd requested from the electric drive machine MME when the degraded mode of movement is used (or established).

[0038] This (control) method can be implemented at least partially by the DC control device (illustrated in Figures 1 and 2), which for this purpose comprises at least one PR1 processor, for example a digital signal processor (or DSP), and at least one MD memory. This DC control device can therefore be implemented as a combination of electrical or electronic circuits or components (or "hardware") and software modules (or "software"). For example, it could be a microcontroller.

[0039] The MD memory is random access memory (RAM) to store instructions for the implementation by the PR1 processor of at least part of the control process. The PR1 processor may comprise integrated (or printed) circuits, or several integrated (or printed) circuits connected by wired or wireless connections. A circuit is defined as integrated (or printed) any type of device capable of performing at least one electrical or electronic operation.

[0040] In the example illustrated, but not limited to, in Figures 1 and 2, the DC control device is part of the powertrain control unit (CS). However, this is not mandatory. The DC control device could, for example, comprise its own control unit, or it could be part of the machine control unit (CM).

[0041] As illustrated non-limitingly in [Fig.3], the (control) method according to the invention comprises at least one step 10-60 which is implemented each time the degraded mode of travel is used (or established) in the vehicle V.

[0042] In this step 10-60, the DC control device controls the torque cd requested from the electric drive machine MME as a function of the actual (current) speed vr of the vehicle V and a first value vl which is representative of the difference ev between the target speed (of the degraded driving mode) vc and this actual speed vr (i.e., ev = vc - vr). The actual speed vr is known continuously and precisely in the vehicle V, in particular by the supervisory computer CS (for example, it may be provided by an ESP / ABS type function (ESP: "Electronic Stability Program"), ABS: "Anti-Blocking System").

[0043] This method of controlling the required torque cd is particularly advantageous because it allows the vehicle V to have a virtually constant actual speed vr in degraded driving mode, regardless of the slope (uphill, downhill, or flat) of the road on which it is traveling and regardless of its weight. Thus, the driver is not disturbed during degraded driving mode, and especially when parking the vehicle V.

[0044] It will be understood that at least the PR1 processor and MD memory of the DC control device are arranged to perform the operations consisting, when the degraded movement mode is used, of controlling the torque cd which is requested from the electric drive machine MME as a function of the actual speed vr of the vehicle V and the first value vl (representative of the difference ev between the target speed vc and the actual speed vr).

[0045] It will be noted that step 10-60 may include a substep 10 in which one (the DC control device) may start by determining an absolute value vae of the deviation ev (i.e. vae = levl = Ivc - vrl), and a substep 20 in which one (the DC control device) may compare this absolute value determined vae to a first threshold if chosen.

[0046] Then, when this determined absolute value vae is greater than the first threshold si chosen (i.e., vae > si), one (the DC control device) can determine, in a sub-step 30 of step 10-60, a second value v2 which is representative of a percentage of difference pe between the target speed vc and the actual speed vr, then determine the first value vl as a function of this second value v2.

[0047] 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 %)). Therefore, the percentage deviation pe can be negative or positive depending on whether vc is less than or greater than vr.

[0048] Also, for example, the second value v2 can be equal to the percentage difference pe (i.e., v2 = pe). But this is not mandatory.

[0049] Next, step 10-60 may include a substep 40 in which one (the DC control device) can determine the required torque cd as a function of the actual speed vr and the first determined value vl (function of v2).

[0050] It will be noted that, when in substep 20 the absolute value determined vae is less than or equal to the first threshold si chosen (i.e. vae < si), one (the DC control device) can, for example, determine, in a substep 50 of step 10-60, a theoretical torque ct(vr) associated with the actual speed vr and use this theoretical torque determined ct(vr) as the required torque cd.

[0051] For example, the theoretical torque ct(vr) can be determined from a table (or map) establishing a correspondence between (actual) speeds and (required) torques, and determined during testing or development phases of a vehicle similar to the one concerned (V) for an average onboard load. It should be noted that one table (or map) can be used for forward movement and another table (or map) for reverse movement. It should also be noted that 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), at least one mathematical formula (or equation) can be used to give the required torque cd as a function of the actual speed vr.

[0052] It should also be noted that in substep 30, the DC control device can, for example, determine a first value vl which is equal to the product of the second value v2 (here equal to the percentage deviation pe) and a chosen correction coefficient cc (i.e., vl = v2*cc (where v2 = pe here)). This correction coefficient cc is intended to improve the accuracy of determining the required torque cd. It should be noted that since the percentage deviation pe can be negative or positive, the first value vl can therefore also be negative or positive.

[0053] For example, in substep 30 of step 10-60 the correction coefficient cc can be chosen as a function of the actual speed vr and / or the percentage deviation pe. In this case, one can, for example, use a law (or map) defining the evolution of the correction 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 the one concerned (V).

[0054] But this is not mandatory. Indeed, the correction coefficient cc can be fixed (or constant) regardless of the actual speed vr and / or regardless of the percentage difference pe.

[0055] Also, for example, in substep 40 of step 10-60, the DC control device can, for example, determine the required torque cd by multiplying a theoretical torque ct(vr), which is associated with the actual speed vr, and the first value vl increased by a value equal to one (i.e., cd = ct(vr)*(l + vl)). Thus, when the first value vl is negative, the required torque cd is less than the theoretical torque ct(vr), which is suitable for the case where the vehicle V is traveling on a downward slope, and when the first value vl is positive, the required torque cd is greater than the theoretical torque ct(vr), which is suitable for the case where the vehicle V is traveling on an upward slope.

[0056] As indicated above, the theoretical torque ct(vr) can be determined from the aforementioned table (or map), which establishes a correspondence between (actual) speeds and (required) torques. It should be noted that one can also use a table (or map) for forward motion and another table (or map) for reverse motion. 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 required torque cd as a function of the actual speed vr.

[0057] It should also be noted that a return to a conventional operating mode can be anticipated when the determined absolute value vae falls permanently below the first threshold si. To this end, when the determined absolute value vae falls below the first threshold si at a time t (i.e., vae < si from t onwards), the DC control device can, for example, determine, in a substep 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 required torque cd when a chosen duration has elapsed since that time t. This is equivalent to performing substep 50 when the duration has elapsed.In order to implement this option, on (the DC control device) can trigger a timer with the first chosen duration as soon as the determined absolute value vae becomes less than the first threshold si at a time t, and when this timer expires (and we still have vae < si), on (the DC control device) uses the determined theoretical torque ct(vr) as the requested torque cd. .

[0058] For example, in substep 60 of step 10-60, the duration can be chosen as a function of the actual speed vr and / or the percentage deviation pe. In this case, one can, for example, use a law (or map) defining the evolution of the duration 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 the one concerned (V).

[0059] But this is not mandatory. Indeed, the duration of can be fixed (or constant) regardless of the actual speed vr and / or regardless of the percentage difference pe.

[0060] The degraded travel mode (or Limp Home mode) is inhibited when the problem initially detected and which triggered its establishment is no longer present, for example after the driver has switched off the ignition of vehicle V and then switched the ignition back on.

[0061] However, an operating option can also be provided in which the degraded driving mode is (at least) temporarily inhibited when the driver presses the brake pedal PF of vehicle V in a certain way. For example, a percentage range of brake pedal PF depressment can be provided that induces a specific torque application cd, and beyond this range the degraded driving mode is temporarily inhibited. By way of example, this range can include the first ten percent of brake pedal PF depressment, and its upper and lower bounds are hereinafter referred to as the second s2 and third s3 thresholds (with s3 not equal to 0%).

[0062] In this case, we can, for example, have the operation described below.

[0063] When the brake pedal PF is fully released (0%), the The control method described above. When the brake pedal PF is depressed by a percentage exceeding the second threshold s2, the degraded driving mode is temporarily inhibited. When the brake pedal PF is depressed by a percentage ppf between the second s2 and third s3 thresholds (i.e., s2 < ppf < s3), the DC control device can, for example, determine the required torque cd using the formula: cd = ct(vr)*(l+vl)*cc'. cc' is another correction coefficient that can, for example, be determined by the DC control device using the formula: cc' = (s2 - ppf) / s2.

[0064] It should also be noted, as illustrated but not limited to [Fig. 2], that the CS supervisory computer (or the DC control device computer) may also include a mass storage unit MM1, in particular for storing tables (or maps), actual speeds and any percentages ppf of brake pedal depressment PF, as well as any intermediate data involved in all its calculations and processing. Furthermore, this CS supervisory computer (or the DC control device computer) may also include an input interface IE for receiving at least the actual speeds and any percentages ppf, for use in calculations or processing, possibly after having been formatted and / or demodulated and / or amplified, in a manner known per se, by means of a digital signal processor PR2.In addition, this CS supervisory computer (or the DC control device computer) can also include an IS output interface, in particular to deliver each requested torque cd to be controlled in real time. the electric drive machine MME during the degraded travel mode, and a possible message (or order) to temporarily inhibit the degraded travel mode.

[0065] 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 type of electronic circuits (or hardware), such as for example the PR1 processor, is suitable for implementing the control method described above to control the torque cd requested from the electric drive machine MME of the vehicle V's GMP during the degraded travel mode.

Claims

Demands

1. A 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 at least one target speed, characterized in that it comprises a step (10-60) in which, when said mode is established, said torque 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 by determining an absolute value of said difference, then, when said determined absolute value is greater than a first chosen threshold, by determining a second value representing a difference between said target speed and actual speed divided by the target speed, then by determining the first value as a function of said second determined value, then by determining said torque required as a function of said actual speed and said first determined value,and when said determined absolute value falls below said first threshold at a given 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 duration has elapsed since said instant.

2. Method according to claim 1, 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.

3. Method according to claim 2, characterized in that in said step (10-60) said correction coefficient is chosen as a function of said actual speed and / or the difference between said target speed and actual speed divided by the target speed.

4. Method according to claim 2 or 3, 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.

5. A method according to any one of the preceding claims, characterized in that in said step (10-60) said duration is chosen as a function of said actual speed and / or the difference between said target speed and actual speed divided by the target speed.

6. Control device (CD) for a land vehicle (V) comprising a powertrain, including an electric motor (EM) suitable for supplying or recovering a required torque, and a degraded mode of movement at 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 control of said required torque as a function of an actual speed of said land vehicle (V) and a first representative value of a difference between said target speed and actual speed, by determining an absolute value of said difference, and then, when said determined absolute value is greater than a first chosen threshold, by determining a second representative value of a difference between said target speed and actual speed divided by the target speed,then by determining the first value as a function of the second determined value, then by determining the required torque as a function of the actual speed and the first determined value, and when the determined absolute value falls below the first threshold at a given instant, a theoretical torque associated with the actual speed is determined, and this determined theoretical torque is used as the required torque when a chosen duration has elapsed since that instant.

7. Product computer program comprising a set of instructions which, when executed by a control device according to claim 6, is suitable for implementing the control method according to any one of claims 1 to 5 to control a torque requested to an electric motive machine (EMM) of a powertrain of a land vehicle (V) having a degraded mode of movement at least at a target speed.

8. 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 6.

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