Method for determining the torque distribution between front and rear axle in a vehicle with an electric drive assembly

Abstract

A method is described for a vehicle (V) having an electric powertrain, for controlling the torque delivered by each electric motor (M3; M3, M4) of at least one drive unit associated with the front axle (FA) of the vehicle and the torque delivered by each electric motor (M1, M2; M3) of at least one drive unit associated with the rear axle (RA) of the vehicle (V), such that a torque distribution ratio (m) corresponds to the total torque (T) delivered by each electric motor (M3; M3, M4) of at least one drive unit of the front axle. FA The torque (T) delivered collectively by each motor (M1, M2; M3) of at least one drive unit on the rear axle (RA) and the torque delivered by each motor (M1, M2; M3) are collectively delivered. RA The ratio of ) can be kept at the minimum torque distribution ratio (m). MIN ) and maximum torque distribution ratio (m MAX The values ​​between ) are determined as a function of the thermal control of the drive unit.

Description

[0001] The text in this description Technical Field

[0002] This invention relates to vehicles with an electric powertrain, and more particularly to battery electric vehicles (BEVs). More specifically, the invention has been developed with reference to vehicles having an electric powertrain comprising at least one electric motor associated with each of the front and rear axles. Background Technology

[0003] In vehicles with an electric powertrain, the electric powertrain includes at least one drive unit associated with the front axle and at least one drive unit associated with the rear axle, wherein each drive unit includes an electric motor and the electric motor is operatively connected to the corresponding axle or the corresponding axle wheel. Control logic exists that instantaneously determines the torque delivery of the drive unit, thereby controlling the torque of the electric motor. If one axle is used more than the other, for example in the case of a very unbalanced torque distribution favoring that axle, the heat power rejected by (at least one) corresponding drive unit will be proportionally higher, leading to an uncontrolled rise in the temperature of the drive unit's components (electric motor, lubricant, inverter, etc.). The only available solution in the prior art to avoid overheating and the corresponding failure lies in applying a reduction in the delivered torque; however, this will be perceived by the driver because it is inconsistent with his desired vehicle dynamics goals.

[0004] Purpose of the invention

[0005] The present invention aims to solve the technical problems outlined above. Specifically, the object of the present invention is to provide a method for determining the torque distribution between the front and rear axles in a vehicle having an electric powertrain, wherein each of the front and rear axles includes at least one drive unit, the at least one drive unit including an electric motor and said electric motor being operatively connected to the corresponding axle or to the corresponding axle wheel, while the method effectively limits thermal fluctuations of the drive unit toward values ​​that may be dangerous to the integrity of the drive unit itself, and the method is imperceptible to the driver. Summary of the Invention

[0006] The object of the present invention is achieved by means of a method having the features set forth in the following claims, which form part of the technical disclosure provided herein in relation to the present invention. Detailed Implementation

[0007] As a general premise, the method according to the invention can be applied to a vehicle V having an electric powertrain including a front axle and a rear axle, wherein each of the front axle and the rear axle includes at least one drive unit, the drive unit including an electric motor and the electric motor being operatively connected to the respective axle or the respective axle wheel. Figures 1 to 4Examples illustrate the configuration of vehicle V, which can implement the method according to the invention, and the powertrain configurations differ from one another. Throughout the figures, reference numeral BT generally denotes the battery of vehicle V, which can be a single cell or a battery pack with a distributed arrangement and architecture. Reference numeral P followed by a subscript indicates the power flow delivered (solid arrow) or absorbed (dashed arrow) by the electric motor of the drive unit, the subscript being equal to the reference numeral used for the corresponding motor.

[0008] Figure 1 A vehicle V with an electric powertrain is shown, which includes a first drive unit and a second drive unit associated with the rear axle RA, and a third drive unit associated with the front axle FA.

[0009] The first drive unit includes a first electric motor M1 associated with the rear left wheel RL on the rear axle (in the same manner as the first drive unit as a whole), the second drive unit includes a second electric motor M2 associated with the rear right wheel RR on the rear axle (in the same manner as the second drive unit as a whole), and the third drive unit includes a third electric motor M3 associated with the front axle (in the same manner as the third drive unit as a whole). The mechanical connection between the motors M1 and M2 of the respective drive units and the wheels RL and RR is implemented by means of direct drive or by means of reduction gears, while the mechanical connection between the motor M3 of the third drive unit and the front axle is implemented by means of differential gears.

[0010] Figure 2 It shows the configuration relative to Figure 1 The vehicle is basically a mirror image of the electric powertrain vehicle V. Figure 2 The powertrain of the vehicle V includes a first drive unit and a second drive unit associated with the front axle FA and a third drive unit associated with the rear axle RA.

[0011] The first drive unit includes a first electric motor M1 associated with the front left wheel FL of the front axle (in the same manner as the first drive unit as a whole), the second drive unit includes a second electric motor M2 associated with the front right wheel FR of the front axle (in the same manner as the second drive unit as a whole), and the third drive unit includes a third electric motor M3 associated with the rear axle (in the same manner as the third drive unit as a whole). The mechanical connection between the motors M1 and M2 of the respective drive units and the wheels FL and FR is implemented by means of direct drive or by means of reduction gears, while the mechanical connection between the motor M3 of the third drive unit and the front axle is implemented by means of differential gears.

[0012] Figure 3 The vehicle V shown has an electric powertrain with a single drive unit on each axle. Figure 3The powertrain of the vehicle V includes a first drive unit associated with the rear axle RA and a second drive unit associated with the front axle FA.

[0013] The first drive unit includes a first electric motor M1 associated with the rear axle RA (in the same manner as the first drive unit as a whole), while the second drive unit includes a second electric motor M3 associated with the front axle FA (in the same manner as the second drive unit as a whole). The mechanical connection between the motors M1 and M3 of the respective drive units and the axles RA and FA is implemented by means of corresponding differential gears.

[0014] at last, Figure 4 A vehicle V with an electric powertrain is shown, which includes a first drive unit and a second drive unit associated with the rear axle RA, and a third drive unit and a fourth drive unit associated with the front axle FA.

[0015] The first drive unit includes a first electric motor M1 associated with the rear left wheel RL on the rear axle (in the same manner as the first drive unit as a whole), and the second drive unit includes a second electric motor M2 associated with the rear right wheel RR on the rear axle (in the same manner as the second drive unit as a whole). The third drive unit includes a third electric motor M3 associated with the front left wheel FL on the front axle (in the same manner as the third drive unit as a whole), and the fourth drive unit includes a fourth electric motor M4 associated with the front right wheel FR on the front axle (in the same manner as the fourth drive unit as a whole).

[0016] The mechanical connection between the motors M1, M2, M3, and M4 of the corresponding drive unit and the wheels RL, RR, FL, and FR is implemented by means of direct drive or by means of reduction gears.

[0017] In various embodiments of the present invention, reference is made to Figure 5 Regardless of the powertrain arrangement, the method—illustrated schematically by a flowchart associated with reference numeral 1—comprising:

[0018] - For each drive unit associated with the front axle FA, determine the limit value of the thermal power that can be rejected (block 2). Equal to the cooling power available for the drive unit and ultimate thermal energy Reference time interval t REF,n The sum of the ratios, wherein the limiting thermal energy Depends on the limiting temperature T of the drive unit LIM,n With the current temperature T of the drive unit ACT,n The difference between them; the subscript "n" of the above quantity identifies the corresponding drive unit (e.g., for...). Figure 1 and Figure 3 For n=3, Figure 2 For n=1, 2, for Figure 4 (n=3, 4)

[0019] - For each drive unit associated with the rear axle, determine (Block 4) the limit value of the heat power that can be rejected, equal to the cooling power available for the drive unit. and ultimate thermal energy Reference time interval t REF,n The sum of the ratios, where the limiting thermal energy depends on the limiting temperature T of the driving unit. LIM,n With the current temperature T of the drive unit ACT,n The difference between them; the subscript "n" of the above quantity identifies the corresponding drive unit (e.g., for...). Figure 1 and Figure 4 For n=1, 2, for Figure 2 For n=3, Figure 3 (n=1)

[0020] - For each drive unit associated with the front axle FA, the maximum mechanical power P that the drive unit can deliver will be... MEC,LIM,n Block 4 is determined as the limit of thermal power that the drive unit itself can reject. The function, and the maximum torque T that can be delivered by the drive unit. C,MAX,n The ultimate mechanical power P of the drive unit itself is determined. MEC,LIM,n The value and the corresponding front axle FA or front axle wheel speed n C The function; as mentioned above, the subscript "n" of the above quantity identifies the corresponding driving unit (e.g., for Figure 1 and Figure 3 For n=3, Figure 2 For n=1, 2, for Figure 4 (n=3, 4)

[0021] - For each drive unit associated with the rear axle RA, the ultimate mechanical power P that the drive unit can deliver will be... MEC,LIM,n The limit value of the thermal power that can be rejected by the drive unit itself is determined (block 6). The function, and the maximum torque T that can be delivered by the drive unit. C,MAX,n The ultimate mechanical power P of the drive unit itself is determined. MEC,LIM,n The value and the corresponding rotational speed n of the rear axle RA or the rear axle wheel RL or RR C The function,

[0022] - Target torque T T Determine (Block 8) the total torque T that can be delivered by each drive unit associated with the front axle FA. FA and the torque T that can be delivered in total by each drive unit associated with the rear axle RA. RAThe sum (therefore T) T =T FA +T RA Torque T T It is the so-called "center of gravity" torque, and therefore it corresponds to the torque to be delivered based on the vehicle driver's requirements;

[0023] - Minimum torque distribution ratio m MIN Determine (block 10) the minimum torque T that can be delivered to the front axle FA by at least one associated drive unit in general. FA,MIN The maximum torque T that can be delivered to the rear axle RA by at least one associated drive unit. RA,MAX The ratio, in which the minimum torque T that can be delivered to the front axle FA in general. FA,MIN Including target torque T T With the maximum torque T that can be delivered to the rear axle overall RA,MAX The difference between them

[0024] - Maximum torque distribution ratio m MAX Determine (block 10) the maximum torque T that can be delivered to the front axle by at least one associated drive unit in general. FA,MAX The minimum torque T that can be delivered to the rear axle by at least one associated drive unit in general. RA,MIN The ratio, where the minimum torque T that can be delivered to the rear axle overall. RA,MIN Including target torque T T The maximum torque T that can be delivered to the front axle FA in total FA,MAX The difference between them.

[0025] The determinations performed in blocks 2 through 10 will now be described in detail with reference to preferred embodiments of the invention.

[0026] Regarding Block 2, extreme thermal energy It can be calculated as ,in:

[0027] -C COMP,n It is the heat capacity of the drive unit (understood as the equivalent total heat capacity, and therefore determined based on the heat capacity of the motor and the mechanical connection between the motor and the axle or wheel).

[0028] -TEMP LIM,n It is the limit temperature of the drive unit.

[0029] - This is expressed as a safety margin for the temperature range; It can be optional in the calculation, but it's best to take it into account.

[0030] -TEMP ACT,nIt is the current temperature of the drive unit.

[0031] - The subscript "n" of the above quantity identifies the corresponding drive unit.

[0032] In this way, the maximum thermal power that can be rejected by the drive unit The expression becomes:

[0033] From it

[0034]

[0035] Time t REF,n This is a time interval of duration, equal to the time interval for controlling the delivery of torque by the corresponding drive unit to the forward or rear axle. The subscript n represents the drive unit and is typically referenced to time t. REF,n It can vary as a function of the driving unit and the manipulation itself.

[0036] Available cooling power It is a known data item in itself, and it depends on the characteristics of the cooling circuit associated with the drive unit.

[0037] Regarding block 4, the maximum mechanical power P that can be delivered by each drive unit is... MEC,LIM,n It is based on the mechanical efficiency of the drive unit. The calculation begins with the definition of , which is defined as follows:

[0038]

[0039] (The subscript "n" in the above quantities identifies the corresponding drive unit)

[0040] P MEC,MAX,n This is the ideal maximum mechanical power of the drive unit, corresponding to the (ideal) unit efficiency case. Furthermore, the power P... MEC,MAX,n It can be expressed as the limiting power P corresponding to the actual delivered power. MEC,LIM,n and the thermal power corresponding to the power dissipated in the form of heat The sum of .

[0041]

[0042] Therefore, mechanical efficiency It can be written as

[0043] , so that:

[0044] From it

[0045] And ultimately

[0046]

[0047] From power P MEC,LIM,n The calculations can yield the maximum torque T that can be delivered by each drive unit. C,MAX,n ,for:

[0048] If n C,n Expressed in rad / s, then

[0049] Or, if n C,n Expressed in RPM, it is

[0050] Where, n C,n It is the rotational speed of the axle or axle wheel associated with the drive unit (the subscript "n" in the above quantity identifies the drive unit itself).

[0051] T C,MAX,n The calculation enables the determination of the maximum torque T that can be delivered to the front axle FA and rear axle RA overall. RA,MAX T FA,MAX If a single drive unit is associated with an axle, the maximum torque T is... RA,MAX or T FA,MAX Equal to the torque T of the drive unit on the axle C,MAX,n (This applies to) Figure 1 The front axle in the middle, Figure 2 The rear axle and Figure 3 The two axles in the vehicle), wherein at least one of the front axle FA and the rear axle RA includes a first drive unit (which includes a first electric motor associated with the right wheel) and a second drive unit (which includes a second electric motor associated with the left wheel), and wherein - depending on the dynamic settings of the vehicle - a torque difference is provided between the right wheel and the left wheel. The delivery can then be made up to the maximum torque T of axle X (where X = FA, RA). X,MAX It is calculated in this way, considering the limitations imposed on components that are more critical to cooling, and can therefore be expressed as:

[0052]

[0053] (Assuming the torque T delivered to the right wheel) X,R Equal to the torque T delivered to the left wheel X,L Add the difference )

[0054] in:

[0055] -T X,L,MAX,n It is the maximum torque that can be delivered to the left wheel of axle X (where X = FA, RA); in the calculation, this corresponds to torque T. C,MAX,nWhere n equals - depending on the embodiment shown in the figure - the subscript of the drive unit associated with the left wheel of the axle (for Figure 1 , Figure 2 In the example, n=1, for Figure 4 In the example, n=1, 3).

[0056] -T X,R,MAX,n It is the maximum torque that can be delivered to the right wheel of axle X (where X = FA, RA); in the calculation, it corresponds to torque T. C,MAX,n Where n equals - depending on the embodiment shown in the figure - the subscript of the drive unit associated with the right wheel of the axle (for Figure 1 , Figure 2 In the example, n=2, for Figure 4 Examples of implementations, n=2, 4), and

[0057] - The subscript n of the above quantity identifies the driving unit.

[0058] refer to Figure 6 It corresponds to torque T on the X-axis. RA The torque T is on the Y-axis. FA The figure shows the relationship between m in a graphical way. MIN and m MAX Definition and T T The corresponding set of geometric trajectories, T T It is the target torque determined based on the driver's requirements (and secondly, on the vehicle's dynamic settings).

[0059] Corresponding to T T The defined geometric trajectory in plane T RA -T FA The line above corresponds to the line with a negative angle coefficient (T) FA =T T -T RA ), and m MIN and m MAX It is with axis T RA -T FA The angle coefficients of two lines that intersect at the origin (which are positive and in ascending order).

[0060] With angle coefficient m MIN and m MAX The straight line and the marked torque T T The intersection of the straight lines of the geometric trajectory defines segment S, which, according to the invention, contains the maximum total torque T delivered to the front axle FA and the rear axle RA. FA,MAX and T RA,MAX This is to keep the thermal control of the drive unit within its limits, and simultaneously to meet the requirements corresponding to the torque T. TThe driver's requirements. In other words, once the total target torque T... T Vehicle V has been fixed, and once the limit T is defined—by means of the thermal control considerations detailed above— FA,MAX and T RA,MAX And therefore the limit m MIN and m MAX Target torque T T It can be included by having endpoints (T) RA,MIN T FA,MAX ) and (T RA,MAX T FA,MIN The paired values ​​T within segment S) FA T RA deliver.

[0061] In other words, the method according to the invention includes controlling the total torque delivered by each motor of at least one drive unit of the front axle FA and the total torque delivered by each motor of at least one drive unit of the rear axle RA, such that the torque distribution ratio m (which corresponds to the total torque T delivered by each motor of at least one drive unit of the front axle FA) is such that... FA The total torque T delivered by each motor of at least one drive unit of the rear axle RA. RA The ratio) is kept at the minimum torque distribution ratio m MIN and maximum torque distribution ratio m MAX The values ​​included in this range ensure that the target torque T corresponding to the driver's requirements is met. T At the same time, and even while delivering maximum torque (T) to the axle FA,MAX T RA,MAX Even under these conditions, the limits of thermal control of the drive unit are always observed.

[0062] Of course, the details and embodiments of the implementation can vary considerably with respect to what has been described and shown herein, without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method for determining torque distribution between a front axle (FA) and a rear axle (RA) in a vehicle (V) having an electric powertrain, wherein each of the front axle (FA) and the rear axle (RA) includes at least one drive unit, the at least one drive unit including an electric motor (M1, M2, M3; M1, M3; M1, M2, M3, M4) and said electric motor (M1, M2, M3; M1, M3; M1, M2, M3, M4) operatively connected to the respective axle (FA, RA) or to the respective wheel of said axle (FA, RA), The method includes: - For each drive unit associated with the front axle (FA), determine the limit value of the thermal power that can be rejected. ) equals the cooling power available for the drive unit ( ) and limiting thermal energy ( ) and reference time interval (t) REF The sum of the ratios of the limiting thermal energy, wherein the limiting thermal energy depends on the limiting temperature (T) of the drive unit. LIM,n ) and the current temperature (T) of the drive unit ACT,n The difference between ) - For each drive unit associated with the rear axle, determine the limit value of the thermal power that can be rejected ( ) equals the cooling power that can be used for the drive unit ( ) and limiting thermal energy ( ) and reference time interval (t) REF The sum of the ratios of the limiting thermal energy, wherein the limiting thermal energy depends on the limiting temperature (T) of the drive unit. LIM,n ) and the current temperature (T) of the drive unit ACT,n The difference between ) - For each drive unit associated with the front axle (FA), the maximum mechanical power (P) that the drive unit can deliver will be... MEC,LIM,n The limit value of the thermal power that the drive unit itself can reject is determined to be ( The function of ), and the maximum torque (T) that the drive unit can deliver. C,MAX,n The limit mechanical power (P) of the drive unit itself is determined. MEC,LIM,n The value of ) and the corresponding front axle or front axle wheel speed (n) C,n The function of ) - For each drive unit associated with the rear axle (RA), the maximum mechanical power (P) that the drive unit can deliver will be... MEC,LIM,n The limit value of the thermal power that the drive unit itself can reject is determined to be ( The function of ), and the maximum torque (T) that the drive unit can deliver. C,MAX,n The limit mechanical power (P) of the drive unit itself is determined. MEC,LIM,n The value of ) and the corresponding rear axle (RA) or rear axle wheel speed (n) C,n The function of ) - determining a target torque (T T ) as the sum of the torque (T FA ) that each drive unit associated with the front axle (FA) is generally able to deliver and the torque (T RA ) that each drive unit associated with the rear axle (RA) is generally able to deliver, - determining a minimum torque distribution ratio (m MIN ) as a ratio between a minimum torque (T FA,MIN ) overall deliverable to the front axle (FA) by the at least one drive unit associated therewith and a maximum torque (T RA,MAX ) overall deliverable to the rear axle (RA) by the at least one drive unit associated therewith, wherein the minimum torque (T FA,MIN ) overall deliverable to the front axle (FA) comprises a difference between the target torque (T T ) and the maximum torque (T RA,MAX ) overall deliverable to the rear axle (RA), - determining a maximum torque distribution ratio (m MAX ) as the ratio of the maximum torque (T FA,MAX ) that can be delivered to the front axle by the at least one drive unit associated therewith and the minimum torque (T RA,MIN ) that can be delivered to the rear axle by the at least one drive unit associated therewith, wherein the minimum torque (T RA,MIN ) that can be delivered to the rear axle comprises the difference between the target torque (T T ) and the maximum torque (T FA,MAX ) that can be delivered to the front axle (FA).

2. The method of claim 1, comprising controlling the torque delivered by each motor (M3; M3, M4) of at least one drive unit of the front axle (FA) and the torque delivered by each motor (M1, M2; M3) of at least one drive unit of the rear axle (RA), such that the torque distribution ratio (m) is maintained at the minimum torque distribution ratio (m). MIN ) and the maximum torque distribution ratio (m MAX The torque distribution ratio corresponds to the total torque (T) delivered by each motor (M3; M3, M4) of at least one drive unit associated with the front axle. FA The torque (T) delivered collectively by each motor (M1, M2; M3) of at least one drive unit associated with the rear axle (RA) and the torque delivered by each motor in combination. RA The ratio between them, and such that the torque (T) delivered by each motor (M3; M3, M4) of at least one drive unit associated with the front axle is generally greater than that delivered by the front axle. FA The torque (T) delivered collectively by each motor (M1, M2; M3) of at least one drive unit associated with the rear axle (RA) and the torque delivered by each motor in combination. FA The sum of these is equal to the target torque (T). T ).

3. The method according to claim 1 or claim 2, wherein, At least one of the front axle (FA) and the rear axle (RA) includes a first drive unit and a second drive unit, the first drive unit including a first electric motor (M1) associated with the left wheel, and the second drive unit including a second electric motor (M2) associated with the right wheel, wherein the torque difference between the right wheel and the left wheel is... The maximum torque that can be delivered to the axle in total is provided and calculated as follows: in: -T X,MAX,n It is the maximum torque that can be delivered to axle X. -T X,L,MAX,n The maximum torque that the first electric motor can deliver to the left wheel of axle X is the maximum torque that can be delivered to the left wheel of axle X. -T X,R,MAX,n The maximum torque that the second electric motor can deliver to the right wheel of axle X is the maximum torque that can be delivered to the right wheel of axle X. -X specifies the front axle or the rear axle. - The subscript n of the above quantity identifies the driving unit.

4. The method according to any one of the preceding claims, wherein, The ultimate thermal energy ( ) was calculated as ,in: -C COMP,n It is the heat capacity of the drive unit. -TEMP LIM,n This is the limit temperature of the drive unit. - This is expressed as a safety margin for the temperature range. -TEMP ACT,n It is the current temperature of the drive unit. - The subscript n of the above quantity identifies the driving unit.

5. The method according to claim 4, wherein, The maximum mechanical power that each drive unit can deliver is calculated as follows: in: -P MEC,LIM,n It is the limit of the mechanical power that the drive unit can deliver. - This is the limit of the driving unit's ability to reject thermal power. -P MEC,LIM,n It is the ultimate mechanical power, - It is the mechanical efficiency of the drive unit. - The subscript n of the above quantity identifies the driving unit.

6. The method of claim 5, further comprising: [the method is described in the original text, but the provided text is incomplete and cannot be accurately translated without further context.] C,MAX The calculation is as follows: T C,MAX,n =P MEC,LIM,n / n C,n in: -n C,n It is the rotational speed of the axle or axle wheel associated with the drive unit. - The subscript n of the above quantity identifies the driving unit.

7. The method according to claim 4, wherein, The limit of thermal power that the drive unit can reject Calculated as: in: - It is the cooling power that can be used for the drive unit. - The subscript n of the above quantity identifies the driving unit.

8. The method according to any one of the preceding claims, wherein, The reference time (t) REF,n ) is a duration time interval, which is equal to the duration time interval of the manipulation to be controlled by delivering torque to the front axle or the rear axle by the corresponding at least one drive unit.

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