阅读说明：本技术 用于补偿电子限滑差速器中的离合器扭矩的方法 (Method for compensating clutch torque in an electronic limited slip differential ) 是由 安德鲁·N·埃德莱 约翰·A·格罗格 于 2018-04-14 设计创作，主要内容包括：本发明涉及一种确定车辆上的限滑差速器齿轮机构的离合器扭矩的方法,该方法包括获得估计的传动系扭矩。建立所需的偏置扭矩。确定实现所需偏置扭矩所需要的必要的离合器扭矩。基于估计的传动系扭矩来命令必要的离合器扭矩以实现所需的偏置扭矩。(A method of determining clutch torque of a limited slip differential gear mechanism on a vehicle includes obtaining an estimated driveline torque. The required biasing torque is established. A necessary clutch torque required to achieve the desired bias torque is determined. The necessary clutch torque is commanded based on the estimated driveline torque to achieve the desired bias torque.)

1. A method of determining clutch torque of a limited slip differential gear mechanism on a vehicle, the method comprising:

obtaining an estimated driveline torque;

establishing a desired bias torque;

determining a necessary clutch torque required to achieve the desired bias torque; and

commanding the requisite clutch torque based on the estimated driveline torque to achieve a desired bias torque.

2. The method of claim 1, further comprising:

determining whether the vehicle is turning left or right;

wherein determining the clutch torque is based on the determination of whether the vehicle is turning left or right.

3. The method of claim 2, further comprising:

a first set of equations is used to calculate clutch torque based on the vehicle turning left.

4. The method of claim 2, further comprising:

calculating clutch torque using a second set of equations different from the first set of equations based on the vehicle being turned right.

5. The method of claim 2, further comprising:

determining a left output shaft torque;

determining a right output shaft torque; and

calculating the bias torque based on the left output shaft torque and the right output shaft torque.

6. The method of claim 1, wherein the limited slip differential gear mechanism comprises a bevel gear set comprising pinions and side gears, wherein the bevel gear set generates a differential gear offset torque, and wherein determining a clutch torque required to achieve a desired offset torque is based on the differential gear offset torque.

7. The method of claim 1, wherein the commanded clutch torque is decreased when the driveline torque is increased.

8. A method of determining clutch torque of a limited slip differential gear mechanism on a vehicle, the method comprising:

obtaining an estimated driveline torque;

establishing a desired bias torque;

determining a differential gear bias torque provided by a bevel gear set in the limited slip differential gear mechanism;

determining a necessary clutch torque required to achieve a desired bias torque based on the differential gear bias torque; and

commanding the requisite clutch torque based on the estimated driveline torque to achieve a desired bias torque.

9. The method of claim 8, further comprising:

determining whether the vehicle is turning left or right;

wherein determining the clutch torque is based on the determination of whether the vehicle is turning left or right.

10. The method of claim 9, further comprising:

a first set of equations is used to calculate clutch torque based on the vehicle turning left.

11. The method of claim 9, further comprising:

calculating clutch torque using a second set of equations different from the first set of equations based on the vehicle being turned right.

12. The method of claim 9, further comprising:

determining a left output shaft torque;

determining a right output shaft torque; and

calculating the bias torque based on the left output shaft torque and the right output shaft torque.

13. The method of claim 8, wherein the commanded clutch torque is decreased when the driveline torque is increased.

14. A method of determining an output shaft torque for a limited slip differential gear mechanism, the method comprising:

determining a driveline torque;

determining a clutch torque; and

an output shaft torque is determined based on the driveline torque and the clutch torque.

15. The method of claim 14, wherein determining the clutch torque comprises determining a limited slip differential clutch torque.

16. The method of claim 15, wherein determining the limited slip differential clutch torque comprises determining an electronic limited slip differential clutch torque.

17. The method of claim 14, wherein determining the output shaft torque comprises:

determining a left output shaft torque; and

a right output shaft torque is determined.

18. The method of claim 14, further comprising:

determining a combined effect of friction between first and second side gears of the limited slip differential gear mechanism and a housing of the limited slip differential gear mechanism.

19. The method of claim 18, further comprising:

determining an average effective radius of the combined effect of friction.

20. The method of claim 19, wherein the determining the combined effect of friction comprises establishing a constant for a coefficient of cross-axis torque used as a cross-axis for the limited slip differential gear mechanism.

Technical Field

The present disclosure relates generally to differential gear mechanisms and, more particularly, to a method of providing Limited Slip Differential (LSD) clutch torque compensation for differential gear torque biasing as a function of driveline torque.

Background

A differential gear mechanism may be provided in the axle assembly and used to transfer torque from the drive shafts to the pair of output shafts. The drive shaft may drive the differential through the use of bevel gears that mesh with a ring gear mounted to the differential housing. In automotive applications, differentials allow tires mounted on either end of an axle assembly to rotate at different speeds. This is important when the vehicle is turning because the tire casing travels a greater distance in an arc than the tire casing. Therefore, the tire casing must rotate at a faster speed than the tire tube to compensate for the greater travel distance. The differential includes a differential case and gearing that allows torque to be transmitted from the drive shaft to the output shaft while allowing the output shaft to rotate at different speeds as desired. The gear arrangement may generally include a pair of side gears mounted for rotation with respective output shafts. A series of cross pins or pinion shafts are fixedly mounted to the differential case for rotation therewith. A corresponding plurality of pinion gears are mounted for rotation with the pinion shaft and in meshing relationship with the two side gears.

Some differential gear mechanisms include a traction adjusting differential. Typically, the clutch pack may be disposed between one of the side gears and an adjacent surface of the differential case. A clutch pack or locking mechanism is operable to limit relative rotation between the gearbox and one of the side gears. In such differentials, engaging the clutch pack or locking mechanism (delayed differentiation) is accomplished by one of several different methods. Some configurations include a piston that actuates to move the clutch pack between open, locked, and partially locked states. In some examples, it is challenging to configure the differential case to accommodate the required components while optimizing packaging space on the vehicle.

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

Disclosure of Invention

A method of determining clutch torque of a limited slip differential gear mechanism on a vehicle includes obtaining an estimated driveline torque. The required biasing torque is established. A necessary clutch torque required to achieve the desired bias torque is determined. The necessary clutch torque is commanded based on the estimated driveline torque to achieve the desired bias torque.

According to an additional feature, control determines whether the vehicle is turning left or right. The clutch torque is based on a determination of whether the vehicle is turning left or right. The clutch torque is calculated using a first set of equations based on the vehicle being turned left. Based on the vehicle turning to the right, a second set of equations, different from the first set of equations, is used to calculate clutch torque.

According to other features, a left output shaft torque is determined. A right output shaft torque is determined. The offset torque is calculated based on the left output shaft torque and the right output shaft torque. The limited slip differential gear mechanism includes a bevel gear set including pinion gears and side gears. The bevel gear set generates differential gear offset torque. The clutch torque required to achieve the desired bias torque is based on the differential gear bias torque. As the driveline torque increases, the commanded clutch torque decreases.

A method of determining clutch torque of a limited slip differential gear mechanism on a vehicle according to additional features of the present disclosure includes obtaining an estimated driveline torque. The required biasing torque is established. A differential gear bias torque provided by a bevel gear set in a limited slip differential gear mechanism is determined. A necessary clutch torque required to achieve the desired bias torque is determined. The necessary clutch torque is commanded based on the estimated driveline torque to achieve the desired bias torque.

According to an additional feature, control determines whether the vehicle is turning left or right. The clutch torque is based on a determination of whether the vehicle is turning left or right. The clutch torque is calculated using a first set of equations based on the vehicle being turned left. Based on the vehicle turning to the right, a second set of equations, different from the first set of equations, is used to calculate clutch torque.

According to other features, a left output shaft torque is determined. A right output shaft torque is determined. The offset torque is calculated based on the left output shaft torque and the right output shaft torque. As the driveline torque increases, the commanded clutch torque decreases.

A method of determining an output shaft torque of a limited slip differential gear mechanism according to additional features includes determining a driveline torque. A clutch torque is determined. The output shaft torque is determined based on the driveline torque and the clutch torque. Determining the clutch torque includes determining a limited slip differential clutch torque. Determining the limited slip differential clutch torque includes determining an electronic limited slip differential clutch torque. Determining the output shaft torque includes determining a left output shaft torque and a right output shaft torque. A combined effect of friction between the first and second side gears of the limited slip differential gear mechanism and a housing of the limited slip differential gear mechanism is determined. The average effective radius of the combined effect of friction is determined. Determining the combined effect of friction includes establishing a constant for the coefficient of cross-axis torque that serves as the cross-axis for the limited slip differential gear mechanism.

Drawings

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of an exemplary LSD constructed according to one example of the present disclosure; and is

Fig. 2 is a schematic diagram of an exemplary vehicle incorporating the LSD of fig. 1.

Detailed Description

Referring initially to FIG. 1, an exemplary vehicle drive train is shown and generally identified by reference numeral 10. The exemplary vehicle driveline 10 includes a Limited Slip Differential (LSD) assembly 30 having a clutch assembly 32 and a differential gear assembly 34. It should be understood that the following disclosure applies to mechanical LSD as well as electronic (eLSD) configurations. The limited slip differential assembly 30 is received in a housing 36 and is used to drive a pair of axle shafts 40 and 42 connected to drive wheels. Generally speaking, during normal operating conditions, the limited slip differential assembly 30 functions as a conventional open differential until an event occurs that requires biasing torque. When a loss of traction is detected or anticipated, the clutch assembly 32 may be selectively actuated to generate an optimal biasing ratio for that situation.

The differential gear assembly 34 includes a pair of side gears 60 and 62 mounted for rotation with the axle shafts 40 and 42 (and the first and second drive wheels), respectively. The side gears 60 and 62 define a first axle opening and a second axle opening. A plurality of cross pins or pinion shafts 66 are fixedly mounted to the differential case 64 for rotation therewith. A corresponding plurality of pinion gears 70 are mounted for rotation with the pinion shaft 66 and are in meshing relationship with the two side gears 60 and 62. The pinion gear 70 and the side gears 60, 62 together define a bevel gear set 80. Bevel gear set 80 generates a biasing torque in differential gear assembly 34. As will be understood below, the teachings of the present disclosure take into account the additional biasing torque (differential gear biasing torque) generated by the bevel gear set 80 when determining the clutch torque required to achieve the desired biasing torque between the left and right axle shafts 40, 42.

In the open configuration, described more fully below, the differential gear assembly 34 is used to allow the axle shafts 40 and 42 to rotate at different speeds.

The clutch assembly 32 may include any configuration, such as a clutch pack and a clutch actuator. The clutch pack includes a plurality of annular plates interleaved between a plurality of annular friction disks. A plurality of annular plates may be coupled for rotation with one of the differential case 64 and the differential gear assembly 34. A plurality of annular friction disks may be coupled for rotation with the other of the differential case 64 and the differential gear assembly 34. In one example, a plurality of annular plates are coupled for rotation to the differential case 64 (e.g., splined to an inner diameter of the differential case 64) and a plurality of annular friction disks are coupled for rotation with the differential gear assembly 34 (e.g., splined to an outer diameter of the side gear 60). It should be understood that the annular friction disks may be supported for rotation by either or both of the side gears 60 or 62.

The plurality of annular plates and annular friction disks are interleaved with one another and are adapted to rotate past one another in a substantially non-contacting relationship when the clutch assembly 32 is in its open position. However, those skilled in the art will appreciate that the term "non-contact" as used herein is relative and is not meant to necessarily indicate that the annular plate and annular friction disk are absolutely not in contact when the clutch assembly 32 is in the open state. The annular plate and the annular friction disks are axially movable into frictional engagement with respect to one another to reduce relative rotation between the annular plate and the annular friction disks when the clutch assembly 32 is in the closed or partially closed configuration. In this manner, the side gears 60 and 62 and the axle shafts 40 and 42 rotate with the drive wheels when the clutch assembly 32 is in its closed position.

The clutch assembly 32 may be operated in an open configuration to allow the side gears 60 and 62 to rotate independently of one another, e.g., at different speeds. The clutch assembly 32 may also be operated in a closed or partially closed configuration, wherein the side gears 60 and 62 rotate together or partially together (that is, not independently), e.g., at substantially the same speed. The clutch pack 32 may be, for example, a hydraulic clutch pack 32 that utilizes pressurized hydraulic fluid that may act on a piston to selectively actuate the clutch pack between an open configuration, a closed configuration, and a partially closed configuration.

According to the present disclosure, the LSD biasing torque is calculated using a static moment equation sum. Six equations are required in total. For left turns, the differential case requires a moment sum, which allows the cross-axis torque to be resolved. The lateral torque is the input to the sum of two subsequent moment equations for the left and right gears. The method of using three equations is repeated for the right turn.

According to the method of the present invention, a user may determine left and right output shaft torque values for a given driveline torque and a given LSD clutch torque. In addition, constants are used to represent the combined effect of friction between each side gear and the differential case and the average effective radius of the friction surface. This constant is used as a coefficient of torque divided by 2 on the abscissa. Representing the torque developed between the side gears and the differential case. A constant value of 0.13 will provide an open differential bias ratio of 1.3. The user may vary this factor to match the particular open differential bias ratio used. The actual open differential bias ratio may be determined experimentally using a test vehicle or in an axle dynamometer.

The following discussion relates to an LSD in which a clutch pack is splined between a left side gear and a differential case. If the clutch pack is splined between the right sides, the sum of the moment equations will change.

The input data will now be identified.

T_{Drive train}：＝1000N.m

T_{Drive train}Is estimated rear driveline torque on the CAN bus

C₁：＝0.09

C₁Is a constant representing the friction of the gear due to the separating force. The value 0.13 provides an open differential (clutch torque of 0) bias ratio of 1.3. A value of 0.046 provides a bias ratio of 1.1.

To estimate the offset torque output, a commanded clutch torque may be input.

T_{Clutch device}：＝400N.m

To estimate the required clutch torque, a commanded bias torque may be input.

Biasing: 400n.m

The calculations will now be identified.

Left turn (omega)_{Left side of}＜ω_{Right side})：

The sum of the moments on the differential case can be represented by the following equation:

T_{l gear}Left gear to differential case torque

T_{X axis}Differential cross axle torque

T_{R gear}Right gear to differential case torque

These equations represent the resulting torque between the side gears and the differential case due to the side gear separation force.

Thus, using the above equation:

T_{x axis}＝T_{Drive train}-T_{Clutch device}

The sum of the moments on the left hand gear can be represented by the following equation:

thus, using the above equation:

the sum of the moments on the right gear can be represented by the following equation:

T_{l right axis}Right output shaft torque while turning left

Thus, using the above equation:

Δ_{left side of}＝454·N·m

Simplified equation for delta torque (left turn):

|T_{clutch device}-C₁·T_{Clutch device}+C₁|T_{Drive train}||＝454·N·m

Clutch _ torque _ left: 341. N. m

Offset _ ratio_{Left side of}＝2.66

Right turn (omega)_{Left side of}＞ω_{Right side})：

Thus, using the above equation:

T_{x axis}＝T_{Drive train}+T_{Clutch device}

The sum of the moments on the left hand gear can be represented by the following equation:

thus, using the above equation:

the sum of the moments on the right-hand gear:

thus, using the above equation:

Δ_{right side}：＝|T_{R left shaft}-T_{R right axis}|

Δ_{Right side}＝526·N·m

Simplified equation for delta torque (right turn)

|-T_{Clutch device}-C₁·T_{Clutch device}-C₁·|T_{Drive train}||＝526·N·m

Clutch-torque-right-284. n.m

T_{R right axis}Right-goingRight output shaft torque during rotation

Offset-ratio_{Right side}＝3.22

The output data will now be identified:

if the bias torque is estimated based on the commanded clutch torque:

commanded clutch torque: t is_{Clutch device}＝400·N·m

Turning left: t is_{L left axle}＝727·N·m

T_{L right axis}＝273·N·m

Δ_{Left side of}＝454·N·m

Offset-ratio_{Left side of}＝2.66

And (3) turning to the right: t is_{R left shaft}＝237·N·m

T_{R right axis}＝763·N·m

Δ_{Right side}＝526·N·m

Offset-ratio_{Right side}＝3.22

Positive axle torque will be used to accelerate the vehicle in the forward direction. Negative axle torque will be used to accelerate the vehicle in the reverse direction.

If the desired clutch torque is estimated based on the commanded bias torque:

the commanded bias torque is then: offset is 400. N.m

Turning left: clutch _ torque _ left is 341 · N · m

And (3) turning to the right: clutch _ torque _ right is 284 · N · m

With continuing reference to FIG. 1 and with additional reference to FIG. 2, a method for determining clutch torque of a limited slip differential mechanism 34 on a vehicle 90 according to one example of the present disclosure will be described. T is_{Drive train}Is a desired estimated driveline torque value or target driveline torque for use in a particular vehicle 90. The requested bias torque is also established to be consistent with the particular vehicle 90. In some examples, the estimated driveline torque and the requested bias torque are output by a differential having a particular vehicle 90A customer offering of the required subset. As is known, the offset torque is the difference between the left axle torque 92 and the right axle torque 94. By way of example, if the requested offset torque is 2000Nm, the difference between the left axle torque 92 and the right axle torque 94 needs to be 2000 Nm. However, as described above, the actual required clutch torque from the clutch assembly 32 required to achieve 2000Nm may be less than 2000Nm due to the additional gear biasing torque provided by the bevel gear set 80.

In some prior art examples, it is assumed that the commanded clutch torque will be equal to the requested bias torque. Using the above example, the prior art assumes that a commanded clutch torque of 2000Nm will result in a bias torque of 2000 Nm. However, as described in this disclosure, this is an inaccurate assumption that results at least in part from the additional differential gear biasing torque implemented in the differential gear assembly 34. The above equation takes into account this additional differential gear offset. Thus, the controller 100 may command a more precise commanded clutch torque to the clutch assembly 32 to achieve the desired bias torque.

It should also be appreciated from the above equations that the direction (left or right) in which the vehicle is turning will affect the commanded clutch torque. Using the 2000Nm required offset torque example described above, if the vehicle 90 is turning left, the controller 100 may need to command 1500Nm of clutch torque to achieve the 2000Nm required offset torque. However, if the vehicle 90 is turning to the right, the controller 100 may need to command a clutch torque of less than 1500Nm to achieve the same 2000Nm required bias torque. This is due to the greater gear offset while the clutch assembly 32 is disposed to the left (to the left of bevel gear set 80, as viewed in FIG. 1) when turning to the right. It should also be understood that these torque values are merely exemplary, and that other values may be used. The driveline torque also contributes to the required commanded clutch torque. In this regard, if more driveline torque is input into the differential assembly 34, less commanded clutch torque is required to achieve the target bias torque. Thus, as the driveline torque increases, the commanded clutch torque decreases.

Additionally, it should be understood that the equation will vary based on the position of the clutch assembly 32. Further explained, the clutch assembly 32 disposed between the bevel gear set 80 and the right half-shaft 42 will have a different equation than that described above using the example shown in FIG. 1, wherein the clutch assembly 32 is disposed between the bevel gear set 80 and the left half-shaft 42. In addition, some differential gear assemblies 34 having other clutch assembly configurations (e.g., the clutches on opposite sides of the bevel gear set 80) will result in different differential gear biasing torques and require different equations.

The foregoing description of these examples has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular example are generally not limited to that particular example, but, where applicable, are interchangeable and can be used in a selected example, even if not specifically shown or described. The same can be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.