System and method for estimating clutch torque and tire longitudinal force of an electronic limited slip differential

Abstract

A system includes a clutch state module and a clutch torque module. The clutch state module is configured to determine whether a clutch of an electronic limited-slip differential is locked or unlocked. The electronic limited-slip differential couples an engine of a vehicle to left and right wheels of the vehicle. The clutch torque module is configured to estimate an actual torque transmitted by the clutch using a first clutch torque model when the electronic limited-slip differential is unlocked and to estimate the actual clutch torque using a second clutch torque model when the electronic limited-slip differential is locked. The second clutch torque model is different from the first clutch torque model.

Description

Technical Field

[0001] This invention relates to a system and method for estimating the clutch torque and tire longitudinal force of an electronic limited-slip differential. Background Technology

[0002] The information provided in this section is for the purpose of providing a general overview of the background of this disclosure. The work of the currently named inventors within the scope described in this section, and aspects of the description that may not otherwise conform to the prior art at the time of filing, are neither expressly nor implicitly regarded as prior art to this disclosure.

[0003] This disclosure relates to systems and methods for estimating clutch torque and tire longitudinal force in electronic limited-slip differentials.

[0004] A differential transmits torque from a vehicle's engine to its left and right wheels. A limited-slip differential allows the left and right wheels to rotate at different speeds while limiting the maximum speed difference between them. An electronic limited-slip differential includes an electronically controlled clutch that allows the left and right wheels to rotate at different speeds when the clutch is unlocked, and causes them to rotate at the same or nearly the same speed when the clutch is locked. Summary of the Invention

[0005] An example system according to this disclosure includes a clutch status module and a clutch torque module. The clutch status module is configured to determine whether the clutch of an electronic limited-slip differential is locked or unlocked. The electronic limited-slip differential connects the vehicle's engine to the left and right wheels of the vehicle. The clutch torque module is configured to estimate the actual torque transmitted by the clutch using a first clutch torque model when the electronic limited-slip differential is unlocked, and to estimate the actual clutch torque using a second clutch torque model when the electronic limited-slip differential is locked. The second clutch torque model differs from the first clutch torque model.

[0006] In one respect, the first clutch torque model includes a hyperbolic tangent function.

[0007] In one respect, the hyperbolic tangent function is a function of the speed difference between the left and right wheels.

[0008] In one respect, the first clutch torque model relates the required clutch torque and the speed difference between the left and right wheels to the actual clutch torque, and the required clutch torque is the amount of torque to be transmitted by the clutch.

[0009] In one respect, the second clutch torque model correlates the longitudinal tire forces at the left wheel and the right wheel with the actual clutch torque.

[0010] In one aspect, the system further includes a tire longitudinal force module configured to estimate the tire longitudinal forces at the left and right wheels using a first longitudinal force model when the electronic limited-slip differential is unlocked, and to estimate the tire longitudinal forces at the left and right wheels using a second longitudinal force model when the electronic limited-slip differential is locked. The second longitudinal force model differs from the first longitudinal force model.

[0011] In one respect, the first longitudinal force model correlates the actual clutch torque and axle input torque with the longitudinal forces of the tires at the left and right wheels, and the axle input torque is the amount of torque transmitted from the engine to the electronic limited-slip differential.

[0012] In one aspect, the second longitudinal force model includes a first relationship between the axle input torque and the longitudinal forces of the tires at the left and right wheels, and a second relationship between the vertical forces of the tires at the left and right wheels and the longitudinal forces of the tires at the left and right wheels, wherein the axle input torque is the amount of torque transmitted from the engine to the electronic limited-slip differential.

[0013] In one aspect, based on the slip ratios of the left and right wheels, the tire longitudinal force module selects a second relationship from several different relationships between the tire vertical force at the left and right wheels and the tire longitudinal force at the left and right wheels.

[0014] In one aspect, the clutch status module is configured to determine whether the clutch is locked or unlocked based on the speed difference between the left and right wheels and the clutch's torque capacity.

[0015] Another example of the system according to this disclosure includes a clutch status module and a tire longitudinal force module. The clutch status module is configured to determine whether the clutch of the electronic limited-slip differential is locked or unlocked. The electronic limited-slip differential connects the vehicle's engine to the left and right wheels of the vehicle. The tire longitudinal force module is configured to estimate the tire longitudinal forces at the left and right wheels using a first longitudinal force model when the electronic limited-slip differential is unlocked, and to estimate the tire longitudinal forces at the left and right wheels using a second longitudinal force model when the electronic limited-slip differential is locked. The second longitudinal force model is different from the first longitudinal force model.

[0016] In one aspect, the first longitudinal force model correlates the actual clutch torque and axle input torque with the longitudinal forces of the tires at the left and right wheels. The actual clutch torque is the actual torque transmitted by the clutch, and the axle input torque is the amount of torque transmitted from the engine to the electronic limited-slip differential.

[0017] In one aspect, the system further includes a clutch torque module configured to estimate the actual clutch torque using a first clutch torque model when the electronic limited-slip differential is unlocked, and to estimate the actual clutch torque using a second clutch torque model when the electronic limited-slip differential is locked. The second clutch torque model differs from the first clutch torque model.

[0018] In one respect, the first clutch torque model relates the required clutch torque and the speed difference between the left and right wheels to the actual clutch torque, and the required clutch torque is the amount of torque to be transmitted by the clutch.

[0019] In one respect, the second clutch torque model correlates the longitudinal tire forces at the left wheel and the right wheel with the actual clutch torque.

[0020] In one aspect, the second longitudinal force model includes a first relationship between the axle input torque and the longitudinal forces of the tires at the left and right wheels, and a second relationship between the vertical forces of the tires at the left and right wheels and the longitudinal forces of the tires at the left and right wheels, wherein the axle input torque is the amount of torque transmitted from the engine to the electronic limited-slip differential.

[0021] In one aspect, based on the slip ratios of the left and right wheels, the tire longitudinal force module selects a second relationship from several different relationships between the tire vertical force at the left and right wheels and the tire longitudinal force at the left and right wheels.

[0022] Another example of a system according to this disclosure includes a clutch status module, a clutch torque module, and a tire longitudinal force module. The clutch status module is configured to determine whether the clutch of the electronic limited-slip differential is locked or unlocked. The electronic limited-slip differential connects the vehicle's engine to the left and right wheels of the vehicle. The clutch torque module is configured to estimate the actual torque transmitted by the clutch using a first clutch torque model when the electronic limited-slip differential is unlocked, and to estimate the actual clutch torque using a second clutch torque model when the electronic limited-slip differential is locked. The second clutch torque model is different from the first clutch torque model. The tire longitudinal force module is configured to estimate the tire longitudinal forces at the left and right wheels using a first longitudinal force model when the electronic limited-slip differential is unlocked, and to estimate the tire longitudinal forces at the left and right wheels using a second longitudinal force model when the electronic limited-slip differential is locked. The second longitudinal force model is different from the first longitudinal force model.

[0023] In one aspect, the first clutch torque model includes a first-order transfer function that correlates the required clutch torque and the hyperbolic tangent of the speed difference between the left and right wheels with the actual clutch torque, which is the required amount of torque, and describes the transient dynamics of the clutch to be transmitted by the clutch. The second clutch torque model correlates the longitudinal tire forces at the left and right wheels with the actual clutch torque. The first longitudinal force model correlates the actual clutch torque and the axle input torque with the longitudinal tire forces at the left and right wheels, which is the amount of torque transmitted from the engine to the electronic limited-slip differential. The second longitudinal force model includes a first relationship between the axle input torque and the longitudinal tire forces at the left and right wheels, and a second relationship between the vertical tire forces at the left and right wheels and the longitudinal tire forces at the left and right wheels.

[0024] In one aspect, based on the slip ratios of the left and right wheels, the tire longitudinal force module selects a second relationship from several different relationships between the tire vertical force at the left and right wheels and the tire longitudinal force at the left and right wheels.

[0025] This invention provides the following technical solutions:

[0026] 1. A system comprising:

[0027] A clutch status module configured to determine whether the clutch of an electronic limited-slip differential is locked or unlocked, the electronic limited-slip differential connecting the vehicle's engine to the left and right wheels of the vehicle; and

[0028] The clutch torque module is configured as follows:

[0029] When the electronic limited-slip differential unlocks, the actual torque transmitted by the clutch is estimated using a first clutch torque model; and

[0030] When the electronic limited-slip differential is locked, the actual clutch torque is estimated using a second clutch torque model, wherein the second clutch torque model is different from the first clutch torque model.

[0031] 2. The system according to Scheme 1, wherein the torque model of the first clutch includes a hyperbolic tangent function.

[0032] 3. The system according to Scheme 2, wherein the hyperbolic tangent function is a function of the speed difference between the left wheel and the right wheel.

[0033] 4. The system according to Scheme 1, wherein:

[0034] The first clutch torque model correlates the required clutch torque and the speed difference between the left and right wheels with the actual clutch torque; and

[0035] The required clutch torque is the amount of torque that is to be transmitted by the clutch.

[0036] 5. The system according to Scheme 1, wherein the second clutch torque model relates the longitudinal tire force at the left wheel and the longitudinal tire force at the right wheel to the actual clutch torque.

[0037] 6. The system according to claim 5 further includes a tire longitudinal force module, which is configured to:

[0038] When the electronic limited-slip differential unlocks, the longitudinal forces on the tires at the left and right wheels are estimated using a first longitudinal force model; and

[0039] When the electronic limited-slip differential is locked, a second longitudinal force model is used to estimate the longitudinal forces on the tires at the left and right wheels, wherein the second longitudinal force model is different from the first longitudinal force model.

[0040] 7. The system according to Scheme 6, wherein:

[0041] The first longitudinal force model correlates the actual clutch torque and axle input torque with the tire longitudinal forces at the left and right wheels; and

[0042] The axle input torque is the amount of torque transmitted from the engine to the electronic limited-slip differential.

[0043] 8. The system according to Scheme 6, wherein:

[0044] The second longitudinal force model includes:

[0045] A first relationship between the axle input torque and the longitudinal force of the tires at the left and right wheels; and

[0046] The second relationship between the vertical force on the tires at the left and right wheels and the longitudinal force on the tires at the left and right wheels; and

[0047] The axle input torque is the amount of torque transmitted from the engine to the electronic limited-slip differential.

[0048] 9. The system according to Scheme 8, wherein, based on the slip ratio of the left wheel and the right wheel, the tire longitudinal force module selects the second relationship from a plurality of different relationships between the tire vertical force at the left wheel and the right wheel and the tire longitudinal force at the left wheel and the right wheel.

[0049] 10. The system according to claim 1, wherein the clutch status module is configured to determine whether the clutch is locked or unlocked based on the following factors:

[0050] The speed difference between the left wheel and the right wheel; and

[0051] The torque capacity of the clutch.

[0052] 11. A system comprising:

[0053] A clutch status module configured to determine whether the clutch of an electronic limited-slip differential is locked or unlocked, the electronic limited-slip differential connecting the vehicle's engine to the left and right wheels of the vehicle; and

[0054] The tire longitudinal force module is configured as follows:

[0055] When the electronic limited-slip differential unlocks, the longitudinal tire forces at the left and right wheels are estimated using a first longitudinal force model; and

[0056] When the electronic limited-slip differential is locked, a second longitudinal force model is used to estimate the longitudinal forces on the tires at the left and right wheels, wherein the second longitudinal force model is different from the first longitudinal force model.

[0057] 12. The system according to claim 11, wherein:

[0058] The first longitudinal force model correlates the actual clutch torque and axle input torque with the longitudinal tire forces at the left and right wheels;

[0059] The actual clutch torque is the actual torque transmitted by the clutch; and

[0060] The axle input torque is the amount of torque transmitted from the engine to the electronic limited-slip differential.

[0061] 13. The system according to claim 12 further includes a clutch torque module configured to:

[0062] When the electronic limited-slip differential unlocks, the actual clutch torque is estimated using a first clutch torque model; and

[0063] When the electronic limited-slip differential is locked, the actual clutch torque is estimated using a second clutch torque model, wherein the second clutch torque model is different from the first clutch torque model.

[0064] 14. The system according to claim 13, wherein:

[0065] The first clutch torque model correlates the required clutch torque and the speed difference between the left and right wheels with the actual clutch torque; and

[0066] The required clutch torque is the amount of torque that is to be transmitted by the clutch.

[0067] 15. The system according to Scheme 13, wherein the second clutch torque model relates the longitudinal tire force at the left wheel and the longitudinal tire force at the right wheel to the actual clutch torque.

[0068] 16. The system according to claim 11, wherein:

[0069] The second longitudinal force model includes:

[0070] A first relationship between the axle input torque and the longitudinal force of the tires at the left and right wheels; and

[0071] The second relationship between the vertical force on the tires at the left and right wheels and the longitudinal force on the tires at the left and right wheels; and

[0072] The axle input torque is the amount of torque transmitted from the engine to the electronic limited-slip differential.

[0073] 17. The system according to claim 16, wherein, based on the slip ratio of the left wheel and the right wheel, the tire longitudinal force module selects the second relationship from a plurality of different relationships between the tire vertical force at the left wheel and the right wheel and the tire longitudinal force at the left wheel and the right wheel.

[0074] 18. A system comprising:

[0075] A clutch status module is configured to determine whether the clutch of an electronic limited-slip differential is locked or unlocked, the electronic limited-slip differential connecting the vehicle's engine to the vehicle's left and right wheels;

[0076] The clutch torque module is configured as follows:

[0077] When the electronic limited-slip differential unlocks, the actual torque transmitted by the clutch is estimated using a first clutch torque model; and

[0078] When the electronic limited-slip differential is locked, the actual clutch torque is estimated using a second clutch torque model, wherein the second clutch torque model is different from the first clutch torque model; and

[0079] The tire longitudinal force module is configured as follows:

[0080] When the electronic limited-slip differential unlocks, the longitudinal tire forces at the left and right wheels are estimated using a first longitudinal force model; and

[0081] When the electronic limited-slip differential is locked, a second longitudinal force model is used to estimate the longitudinal forces on the tires at the left and right wheels, wherein the second longitudinal force model is different from the first longitudinal force model.

[0082] 19. The system according to claim 18, wherein:

[0083] The first clutch torque model includes a first-order transfer function that correlates the required clutch torque and the hyperbolic tangent function of the speed difference between the left and right wheels with the actual clutch torque.

[0084] The required clutch torque is the required torque amount, which also describes the transient dynamics of the clutch to be transmitted by the clutch.

[0085] The second clutch torque model correlates the longitudinal tire force at the left wheel and the longitudinal tire force at the right wheel with the actual clutch torque;

[0086] The first longitudinal force model correlates the actual clutch torque and axle input torque with the tire longitudinal forces at the left and right wheels;

[0087] The axle input torque is the amount of torque transmitted from the engine to the electronic limited-slip differential; and

[0088] The second longitudinal force model includes:

[0089] The first relationship between the axle input torque and the longitudinal force of the tires at the left and right wheels; and

[0090] The second relationship between the vertical force of the tires at the left and right wheels and the longitudinal force of the tires at the left and right wheels.

[0091] 20. The system according to claim 19, wherein, based on the slip ratio of the left wheel and the right wheel, the tire longitudinal force module selects the second relationship from a plurality of different relationships between the tire vertical force at the left wheel and the right wheel and the tire longitudinal force at the left wheel and the right wheel.

[0092] The further scope of this disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are intended for illustrative purposes only and are not intended to limit the scope of this disclosure. Attached Figure Description

[0093] This disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0094] Figure 1 This is a functional block diagram of an example vehicle based on this disclosure;

[0095] Figure 2 This is a functional block diagram of an example powertrain control module based on this disclosure;

[0096] Figure 3 This is a flowchart illustrating an example method for estimating the clutch torque and tire longitudinal force of an electronic limited-slip differential according to this disclosure; and

[0097] Figure 4 This is a graph showing an example relationship between the slip ratio of a wheel and the normalized longitudinal force according to this disclosure.

[0098] In the accompanying drawings, reference numerals may be reused to identify similar and / or identical elements. Detailed Implementation

[0099] The powertrain control system estimates the amount of torque transmitted by the clutch of the electronic limited-slip differential (eLSD) and controls the eLSD clutch based on the estimated clutch torque. In one example, the powertrain control system adjusts the pressure of the hydraulic fluid supplied to the clutch to minimize the difference between the required clutch torque and the estimated clutch torque. Therefore, estimating the clutch torque enables the powertrain control system to control the amount of torque transmitted by clutch 34 in a closed-loop manner.

[0100] The powertrain control system also estimates the longitudinal tire forces at the left and right wheels coupled to the eLSD and controls the engine's torque output based on these estimated forces. In one example, the powertrain control system determines a target longitudinal tire force to achieve a target vehicle acceleration and adjusts the engine's actuators to minimize the difference between the target and estimated longitudinal tire forces. Therefore, estimating the longitudinal tire forces allows the powertrain control system to control both the longitudinal tire forces (and vehicle acceleration) in a closed-loop manner.

[0101] The powertrain control system disclosed herein estimates the eLSD clutch torque and tire longitudinal force in an accurate manner, which improves closed-loop control of these parameters and thus improves vehicle performance. In one example, the powertrain control system uses a hyperbolic tangent function to model the behavior of the eLSD and uses this model to estimate the eLSD clutch torque when the eLSD clutch is disengaged. The hyperbolic tangent function illustrates the fact that the maximum torque capacity of the eLSD clutch is not always achievable as required.

[0102] In another example, the model used by the powertrain control system to estimate the clutch torque when the eLSD clutch is disengaged takes into account actuator delay. Consequently, the powertrain control system avoids the shuddering problem that could otherwise occur when the speed difference between the wheels engaged with the eLSD is close to zero. In yet another example, instead of simply setting the estimated clutch torque to zero, the powertrain control system uses a model to estimate the eLSD clutch torque when the eLSD clutch is engaged. As a result, the estimated clutch torque is more accurate when the eLSD clutch is engaged.

[0103] Now for reference Figure 1 The vehicle 10 includes an engine 12, a transmission 14, an eLSD 16, a battery 18, an electric motor 20, a front half-shaft 22, a rear half-shaft 24, a left front wheel 26, a right front wheel 28, a left rear wheel 30, and a right rear wheel 32. The engine 12 burns a mixture of air and fuel to produce drive torque. The transmission 14 transmits torque from the engine 12 to the eLSD 16 at one of several different gear ratios.

[0104] The eLSD 16 transmits torque from the transmission 14 to the left rear wheel 30 and the right rear wheel 32 via the rear half-shaft 24. The battery 18 powers the electric motor 20. The electric motor 20 rotates the left front wheel 26 and the right front wheel 28 via the front half-shaft 22.

[0105] The eLSD 16 includes a clutch 34 that transmits torque from the left rear wheel 30 to the right rear wheel 32 and vice versa. When the clutch 34 is disengaged, the eLSD 16 allows the left rear wheel 30 and the right rear wheel 32 to rotate at different speeds while limiting the maximum speed difference between them. When the clutch 34 is engaged, the eLSD 16 drives the left rear wheel 30 and the right rear wheel 32 at the same or nearly the same speed.

[0106] Vehicle 10 further includes a left front wheel speed sensor (WSS) 36, a right front wheel speed sensor (WSS) 38, a left rear wheel speed sensor (WSS) 40, a right rear wheel speed sensor (WSS) 42, a clutch pressure sensor 44, a vehicle motion sensor 46, a camera 48, and a powertrain control module 50. The left front wheel speed sensor (WSS) 36 measures the speed of the left front wheel 26. The right front wheel speed sensor (WSS) 38 measures the speed of the right front wheel 28. The left rear wheel speed sensor (WSS) 40 measures the speed of the left rear wheel 30. The right rear wheel speed sensor (WSS) 42 measures the speed of the right rear wheel 32.

[0107] Clutch pressure sensor 44 measures the pressure of the hydraulic fluid supplied to clutch 34 of eLSD 16. Vehicle motion sensor 46 measures the longitudinal (forward and backward) acceleration, lateral (rearward) acceleration, and yaw rate of vehicle 10. Vehicle motion sensor 46 may be an inertial measurement unit, comprising one or more accelerometers measuring the longitudinal and lateral acceleration of vehicle 10 and a gyroscope measuring the yaw rate of vehicle 10. Camera 48 captures images of the road surface on which vehicle 10 travels.

[0108] The powertrain control module 50 controls the engine 12, transmission 14, eLSD 16, and electric motor 20 based on inputs from sensors in the vehicle 10. In one example, the powertrain control module 50 uses sensor inputs to estimate the amount of torque transmitted by the clutch 34 of the eLSD 16 and the longitudinal tire forces at the left rear wheel 30 and right rear wheel 32. The powertrain control module 50 then controls the engine 12 and the clutch 34 of the eLSD 16 based on the estimated clutch torque and the estimated tire longitudinal forces.

[0109] The powertrain control module 50 adjusts how it estimates the amount of torque transmitted by the clutch 34 and / or the longitudinal tire forces at the left rear wheel 30 and right rear wheel 32 based on whether the clutch 34 is locked or unlocked. In one example, when the clutch 34 is unlocked, the powertrain control module 50 estimates the clutch torque using a first clutch torque model, and when the clutch 34 is locked, the powertrain control module 50 estimates the clutch torque using a second clutch torque model. The second clutch torque model differs from the first clutch torque model.

[0110] Now for reference Figure 2 An example implementation of the powertrain control module 50 includes a clutch torque capacity module 52, a slip ratio module 54, a clutch torque module 56, a tire longitudinal force module 58, an eLSD clutch control module 60, and an engine control module 62. The clutch torque capacity module 52 can estimate the torque capacity of the clutch 34 of the eLSD 16 using, for example, lookup tables and / or equations, based on the clutch pressure from the clutch pressure sensor 44. Alternatively, the torque capacity of the clutch 34 can be predetermined. The clutch torque capacity module 52 can increase the estimated clutch torque capacity as the clutch pressure increases, and vice versa. The clutch torque capacity module 52 outputs the estimated clutch torque capacity.

[0111] The slip ratio module 54 determines the slip ratio of the left rear wheel 30 and the slip ratio of the right rear wheel 32. The slip ratio module 54 determines the slip ratio of the left rear wheel 30 based on the speed of the left rear wheel 30 and the speed of the vehicle 10. For example, the slip ratio module 54 can use a relationship such as the following to determine the slip ratio of the left rear wheel 30.

[0112] (1) ,

[0113] Among them κ lr The slip ratio of the left rear wheel is 30, ω lr It is the speed (angular velocity) of the left rear wheel at 30, R eff,r It is the effective radius of the freely rolling tire on each of the left rear wheel 30 and the right rear wheel 32, and This is the translational speed at the center of the left rear wheel 30. The slip ratio module 54 can determine the translational speed at the center of the left rear wheel 30 using a relationship such as the following.

[0114] (2) ,

[0115] Where v x It is the longitudinal speed of vehicle 10, l w Here, r is the rear track width of vehicle 10, and r is the yaw rate of vehicle 10. Similarly, the slip ratio module 54 can determine the slip ratio of the right rear wheel 32 using the following relationship.

[0116] (3) ,

[0117] Among them κ rr It is the slip ratio of the right rear wheel, ω = 32. rr It is the speed (angular velocity) of the right rear wheel at 32, and This is the translational speed at the center of the right rear wheel 32. The slip ratio module 54 can determine the translational speed at the center of the right rear wheel 32 using a relationship such as the following.

[0118] (4) .

[0119] The slip ratio module 54 receives the speeds of the left rear wheel 30 and the right rear wheel 32 from the left rear WSS 40 and right rear WSS 42, respectively. The effective rolling tire radius can be predetermined or estimated in real time. The slip ratio module 54 can determine the speed of the vehicle 10 based on the wheel speeds from two or more of the wheel speed sensors 36, 38, 40, and 42 and the effective rolling tire radius. For example, the slip ratio module 54 can determine four values ​​of the vehicle speed corresponding to the wheel speeds from the wheel speed sensors 36, 38, 40, and 42, and then set the vehicle speed to be equal to the average of the four values. The slip ratio module 54 outputs the slip ratios of the left rear wheel 30 and the right rear wheel 32.

[0120] The clutch torque module 56 estimates the amount of torque transmitted by the clutch 34. As discussed in more detail below, when the clutch 34 is unlocked, the clutch torque module 56 estimates the clutch torque using a first clutch torque model, and when the clutch 34 is locked, the powertrain control module 50 estimates the clutch torque using a second clutch torque model. The second clutch torque model differs from the first clutch torque model. The clutch torque module 56 outputs the estimated clutch torque.

[0121] The tire longitudinal force module 58 estimates the tire longitudinal forces at the left rear wheel 30 and the right rear wheel 32. As discussed in more detail below, when the clutch 34 is unlocked, the tire longitudinal force module 58 uses a first longitudinal force model to estimate the tire longitudinal forces, and when the clutch 34 is locked, the tire longitudinal force module 58 uses a second longitudinal force model to estimate the clutch torque. The second longitudinal force model differs from the first longitudinal force model. The tire longitudinal force module 58 outputs the estimated tire longitudinal forces.

[0122] The eLSD clutch control module 60 controls the amount of torque transmitted by the clutch 34 of the eLSD 16. The eLSD clutch control module 60 achieves this by generating the required clutch torque based, for example, the yaw rate of the vehicle 10 and the slip ratios of the left rear wheel 30 and the right rear wheel 32. The required clutch torque is the desired (or target) amount of torque to be transmitted by the clutch 34. In one example, the eLSD clutch control module 60 identifies when the vehicle 10 is in an oversteer condition based on the vehicle yaw rate and slip ratio, and increases the required clutch torque to correct the oversteer condition. The eLSD clutch control module 60 outputs the required clutch torque and / or controls the clutch 34 to achieve the required clutch torque.

[0123] The eLSD clutch control module 60 also controls the clutch 34 based on the estimated clutch torque. In one example, the eLSD clutch control module 60 adjusts the pressure of the hydraulic fluid supplied to the clutch 34 to minimize the difference between the required clutch torque and the estimated clutch torque. Therefore, the estimated clutch torque allows the eLSD clutch control module 60 to control the amount of torque transmitted by the clutch 34 in a closed-loop manner. The eLSD clutch control module 60 can adjust the clutch pressure by adjusting the position of the pump and / or valve in the eLSD 16.

[0124] Engine control module 62 controls the torque output of engine 12 based on driver input (e.g., accelerator pedal position, cruise control setting speed). Engine control module 62 achieves this by generating the required engine torque based on driver input and adjusting the actuators of engine 12 (e.g., throttle valve, fuel injector, spark plugs) to achieve the required engine torque. In one example, engine control module 62 determines the target vehicle acceleration based on driver input and increases or decreases the required engine torque as the target vehicle acceleration increases or decreases. eLSD clutch control module 60 outputs the required engine torque and / or controls the actuators of engine 12 to achieve the required engine torque.

[0125] The engine control module 62 also controls the torque output of the engine 12 based on the tire longitudinal force. In one example, the engine control module 62 determines a target tire longitudinal force to achieve a target vehicle acceleration and adjusts the actuators of the engine 12 to minimize the difference between the target tire longitudinal force and the estimated tire longitudinal force. Therefore, the estimated tire longitudinal force enables the engine control module 62 to control the tire longitudinal force (and vehicle acceleration) in a closed-loop manner.

[0126] Now for reference Figure 3 The method for estimating the amount of torque transmitted by the clutch 34 of the eLSD 16 and the longitudinal tire forces at the left rear wheel 30 and right rear wheel 32 begins at point 64. In the description of this method presented below, Figure 2 The module that executes the steps of the method may be different from the one described below. Furthermore, or alternatively, one or more steps of the method may be executed independently of any module.

[0127] At point 66, the powertrain control module 50 monitors the operating parameters of the vehicle 10. The clutch torque capacity module 52 monitors the clutch pressure from the clutch pressure sensor 44. The slip ratio module 54 monitors the wheel speeds from the left front, right front, left rear, and right rear WSSs 36, 38, 40, and 42. The tire longitudinal force module 58 monitors the longitudinal vehicle acceleration, lateral vehicle acceleration, and vehicle yaw rate from the vehicle motion sensor 46.

[0128] At point 68, the clutch torque module 56 determines the state of the clutch 34 (i.e., whether the clutch 34 is locked or unlocked). The clutch torque module 56 may determine the state of the clutch 34 based on the speed difference between the left rear wheel 30 and the right rear wheel 32 and / or the torque capacity of the clutch 34. If the clutch 34 is locked, the method continues at point 70. Otherwise, the method continues at point 72. The clutch torque module 56 may be referred to as or include a clutch state module, which determines the state of the clutch 34 as described herein. Alternatively, the clutch state module may be detached from and communicate with the clutch torque module 56.

[0129] In one example, when the rear wheel speed difference is less than a slip threshold (e.g., 0.5 radians per second) and the clutch torque capacity is greater than a torque threshold (e.g., 100 Nm), the clutch torque module 56 determines that the clutch 34 is locked. Conversely, when the rear wheel speed difference is greater than or equal to the first threshold, the clutch torque module 56 determines that the clutch 34 is unlocked. The clutch torque module 56 receives the clutch torque capacity from the clutch torque capacity module 52.

[0130] At point 72, the clutch torque module 56 uses a first clutch torque model to estimate the actual amount of torque transmitted by the clutch 34 of the eLSD 16. This first clutch torque model can be referred to as the unlocking eLSD model. In one example, the first clutch torque model is represented by the following relationship:

[0131] (5) ,

[0132] Where T c_act It is the actual clutch torque, τ c τ is the time constant characterizing the behavior of clutch 34, s is a complex variable used for Laplace transform, p1, p2, and p3 are unitless constants characterizing the dynamic behavior of clutch 34, tanh is the hyperbolic tangent function, dω is the speed difference between the left rear wheel 30 and the right rear wheel 32, and Tc_rqst is the required clutch torque. Therefore, the first clutch torque model correlates the required clutch torque and the hyperbolic tangent function of the rear wheel speed difference with the actual clutch torque. Furthermore, the first clutch torque model uses a first-order transfer function to describe the transient dynamics of clutch 34. The clutch torque module 56 can determine the time constant τ, for example, using lookup tables and / or equations based on the clutch torque capacity or the required clutch torque. c The constants p1, p2, and p3 can be predetermined. The clutch torque module 56 receives the required clutch torque from the eLSD clutch control module 60.

[0133] At position 74, the tire longitudinal force module 58 uses a first longitudinal force model to estimate the tire longitudinal forces at the left rear wheel 30 and the right rear wheel 32. This first longitudinal force model can be referred to as the wheel dynamics model. In one example, the first longitudinal force model includes the following two relationships:

[0134] (6) ,as well as

[0135] (7) ,as well as

[0136] Where F xrl It is the longitudinal force of the tire at point 30 on the left rear wheel, F xrr It is the longitudinal force of the tire at point 32 on the right rear wheel, F roll,rl It is the rolling resistance of the left rear wheel, F. roll,rr It is the rolling resistance of the right rear wheel 32, T r_act This is the actual rear axle torque (i.e., the amount of torque transmitted from engine 12 to eLSD 16), I wr It is the moment of inertia of each of the left rear wheel 30 and the right rear wheel 32. It is the angular acceleration of the left rear wheel at 30 degrees, and It is the angular acceleration of the right rear wheel at 32.

[0137] The tire longitudinal force module 58 can reduce rolling resistance F roll,rl Set to be equal to the product of a constant (e.g., 0.01) and the vertical force of the tire at point 30 on the left rear wheel. The tire longitudinal force module 58 can control the rolling resistance F. roll,rr The longitudinal force module 58 is set to the product of a constant (e.g., 0.01) and the vertical force of the tire at the right rear wheel 32. The actual rear axle torque can be determined based on the actuator values ​​of the engine 12 (e.g., throttle position, fuel injection timing, spark timing) and the current gear ratio of the transmission 14. The moments of inertia of wheels 30, 32 can be predetermined. The longitudinal force module 58 can determine the angular accelerations of the left and right rear wheels by differentiating the velocities of the left and right rear wheels with respect to time.

[0138] At point 70, the tire longitudinal force module 58 uses a second longitudinal force model to estimate the tire longitudinal forces of the left rear wheel 30 and the right rear wheel 32. The second longitudinal force model includes an axle dynamics model, which is embodied in the following relationship:

[0139] (8) ,as well as

[0140] In addition, the second longitudinal force model includes one or more of the following relationships:

[0141] (9) ,

[0142] (10) ,as well as

[0143] (11) ,

[0144] Where F zrl It is the vertical force on the tire at point 30 on the left rear wheel, F zrr It is the vertical force on the tire at point 32 of the right rear wheel, μ rl It is the coefficient of friction of the road surface on which the left rear wheel travels at 30 km / h, in μ. rr K is the coefficient of friction of the road surface on which the right rear wheel (32) is traveling. norm It is the normalized longitudinal tire stiffness of each of the left rear wheel 30 and the right rear wheel 32, l w Here, r is the track width of vehicle 10, r is the yaw rate of vehicle 10, and K... rr This refers to the slip ratio of the right rear wheel 32. The tire longitudinal force module 58 can estimate the vertical tire forces at the left rear wheel 30 and right rear wheel 32 based on the longitudinal and lateral vehicle accelerations from the vehicle motion sensor 46. The tire longitudinal force module 58 can estimate the coefficients of friction at the left rear wheel 30 and right rear wheel 32 based on road images captured by the camera 48. The vehicle track width is predetermined. The tire longitudinal stiffness can be predetermined or determined by the tire longitudinal force module 58 based on the tire vertical forces.

[0145] The tire longitudinal force module 58 selects one of relations (9), (10), or (11) based on the slip ratios of the left rear wheel 30 and the right rear wheel 32 to be included in the second longitudinal force model. In one example, the tire longitudinal force module 58 selects one of relations (9), (10), or (11) based on (i) the slip ratios of the left rear wheel 30 and the right rear wheel 32 and (ii) the relationship between the normalized longitudinal force for the same wheel. More specifically, the tire longitudinal force module 58 selects one of relations (9), (10), or (11) based on whether the relationship between the slip ratio and the normalized longitudinal force is in a linear or nonlinear region. The normalized longitudinal force of the wheel is the ratio of the tire longitudinal force at the wheel to the product of the coefficient of friction at the wheel and the tire vertical force at the wheel.

[0146] Figure 4 The relationship 84 between (i) the slip ratio of one of the left rear wheel 30 and the right rear wheel 32 and (ii) the normalized longitudinal force for the same wheel is shown. Relationship 84 is plotted about the x-axis 86 representing the slip ratio and the y-axis 88 representing the normalized longitudinal force. Relationship 84 is linear in the first region 90, both linear and nonlinear in the second region 92, and nonlinear in the third region 94.

[0147] When the slip ratios of both the left rear wheel 30 and the right rear wheel 32 are in the linear region (e.g., the first region 90), the tire longitudinal force module 58 selects relation (9) to include it in the second longitudinal force model. When one of the slip ratios of the left rear wheel 30 and the right rear wheel 32 is in the linear region and the other slip ratio is in the nonlinear region, the tire longitudinal force module 58 selects relation (11) to include it in the second longitudinal force model. When the slip ratios of both the left rear wheel 30 and the right rear wheel 32 are in the nonlinear region (e.g., the third region 94), the tire longitudinal force module 58 selects relation (10) to include it in the second longitudinal force model.

[0148] Refer again Figure 3 At point 76, the clutch torque module 56 uses a second clutch torque model to estimate the actual amount of torque transmitted by clutch 34 of eLSD16. This second clutch torque model can be referred to as the locked eLSD model. In one example, the second clutch torque model is represented by the following relationship:

[0149] (12) .

[0150] Where F xrl and F xrr The longitudinal tire forces at the left rear wheel 30 and right rear wheel 32 are estimated using one of relations (8) and relations (9), (10) or (11). The method ends at 78.

[0151] The foregoing description is illustrative in nature and is in no way intended to limit this disclosure, its application, or its use. The broad teachings of this disclosure can be implemented in many forms. Therefore, although this disclosure includes particular examples, its true scope should not be so limited, as other modifications will become apparent upon examination of the drawings, specification, and appended claims. It should be understood that one or more steps within the method may be performed in a different order (or simultaneously) without altering the principles of this disclosure. Furthermore, although each of the embodiments described above has certain features, any one or more of those features described with respect to any embodiment of this disclosure may be implemented in any other embodiment and / or combined with features of any other embodiment, even if such combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and substitutions of one or more embodiments remain within the scope of this disclosure.

[0152] Spatial and functional relationships between components (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connection,” “joint,” “link,” “adjacent,” “next to,” “on top,” “above,” “below,” and “set.” Unless explicitly described as “direct,” when describing the relationship between the first and second components in the foregoing disclosure, the relationship can be a direct relationship in which no other intervening components exist between the first and second components, or it can be an indirect relationship (spatially or functionally) between the first and second components. As used herein, the phrase at least one of A, B, and C should be interpreted as meaning the use of a non-exclusive OR logic (A or B or C), and should not be interpreted as meaning “at least one of A, at least one of B, and at least one of C.”

[0153] In the accompanying drawings, the arrows generally indicate the flow of information (such as data or instructions) related to the illustration. For example, when components A and B exchange various types of information, but the information transmitted from component A to component B is related to the illustration, the arrow can point from component A to component B. This unidirectional arrow does not mean that no other information is transmitted from component B to component A. Furthermore, for information sent from component A to component B, component B can send a request for information or a receipt confirmation to component A.

[0154] In this application, including the following definitions, the term "module" or "controller" may be replaced by the term "circuit". The term "module" may refer to, be a part of, or include: application-specific integrated circuit (ASIC); digital, analog, or mixed-signal analog / digital discrete circuits; digital, analog, or mixed-signal analog / digital integrated circuits; combinational logic circuits; field-programmable gate arrays (FPGAs); processor circuitry (shared, dedicated, or grouped) that executes code; memory circuitry (shared, dedicated, or grouped) that stores code executed by the processor circuitry; other suitable hardware components that provide the described functionality; or combinations of some or all of the foregoing, such as in a system-on-a-chip.

[0155] This module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces connected to a local area network (LAN), the Internet, a wide area network (WAN), or a combination thereof. The functionality of any given module of this disclosure can be distributed among multiple modules connected via the interface circuits. For example, multiple modules can allow for load balancing. In a further example, a server (also referred to as a remote, or cloud) module may perform some functions on behalf of a client module.

[0156] As used above, the term "code" can include software, firmware, and / or microcode, and can refer to programs, routines, functions, classes, data structures, and / or objects. The term "shared processor circuitry" includes a single processor circuitry that executes some or all of the code from multiple modules. The term "group processor circuitry" includes processor circuitry combined with additional processor circuitry to execute some or all of the code from one or more modules. References to multiple processor circuitry include multiple processor circuitry on a discrete chip, multiple processor circuitry on a single chip, multiple cores of a single processor circuitry, multiple threads of a single processor circuitry, or combinations thereof. The term "shared memory circuitry" includes a single memory circuitry that stores some or all of the code from multiple modules. The term "group memory circuitry" includes memory circuitry combined with additional memory to store some or all of the code from one or more modules.

[0157] The term memory circuit is a subset of the term computer-readable medium. As used herein, the term computer-readable medium does not include transient electrical or electromagnetic signals propagated through a medium (such as on a carrier wave); therefore, the term computer-readable medium can be considered tangible and non-transient. Non-limiting examples of non-transient tangible computer-readable media are non-volatile memory circuits (such as flash memory circuits, erasable programmable read-only memory circuits, or masked read-only memory circuits), volatile memory circuits (such as static random access memory circuits or dynamic random access memory circuits), magnetic storage media (such as analog or digital magnetic tape or hard disk drives), and optical storage media (such as CDs, DVDs, or Blu-ray discs).

[0158] The apparatus and methods described in this application can be implemented, in whole or in part, by a special-purpose computer created by configuring a general-purpose computer to perform one or more special functions embodied in a computer program. The functional blocks, flowchart components, and other elements described above serve as software specifications that can be translated into a computer program through the routine work of skilled technicians or programmers.

[0159] A computer program includes processor-executable instructions stored on at least one non-transitory tangible computer-readable medium. A computer program may also include or depend on stored data. A computer program may include a basic input / output system (BIOS) that interacts with the hardware of a special-purpose computer, device drivers that interact with specific devices of the special-purpose computer, one or more operating systems, user applications, background services, background applications, etc.

[0160] Computer programs may include: (i) descriptive text to be parsed, such as HTML (Hypertext Markup Language), XML (Extensible Markup Language), or JSON (JavaScript Object Notation); (ii) assembly code; (iii) object code generated from source code by a compiler; (iv) source code for execution by an interpreter; and (v) source code for compilation and execution by a just-in-time compiler, etc. By way of example only, source code may be written using syntax from languages ​​including: C, C++, C#, Objective C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, JavaScript®, HTML5 (Hypertext Markup Language, Fifth Revision), Ada, ASP (Dynamic Server Pages), PHP (PHP: Hypertext Preprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, MATLAB, SIMULINK, and Python®.

Claims

1. A system for a vehicle, comprising: a clutch state module of the vehicle configured to determine whether a clutch of an electronic limited slip differential is locked or unlocked, the electronic limited slip differential coupling an engine of the vehicle to left and right wheels of the vehicle, wherein the clutch state module is configured to determine whether the clutch is locked or unlocked based on a speed difference of the left and right wheels and a torque capacity of the clutch, wherein the clutch state module determines that the clutch is locked when a speed difference of the rear wheels is less than a slip threshold and the torque capacity of the clutch is greater than a torque threshold, and the clutch state module determines that the clutch is unlocked when the speed difference of the rear wheels is greater than or equal to the slip threshold; a clutch torque module of the vehicle configured to: estimate an actual clutch torque transferred by the clutch using a first clutch torque model when the electronic limited slip differential is unlocked; and estimate the actual clutch torque using a second clutch torque model when the electronic limited slip differential is locked, wherein the second clutch torque model is different than the first clutch torque model.

2. The system of claim 1, wherein the first clutch torque model comprises a hyperbolic tangent function.

3. The system of claim 2, wherein the hyperbolic tangent function is a function of a speed difference of the left and right wheels.

4. The system of claim 1, wherein: the first clutch torque model relates a required clutch torque and the speed difference of the left and right wheels to the actual clutch torque; and the required clutch torque is an amount of torque required to be transferred by the clutch.

5. The system of claim 1, wherein the second clutch torque model relates tire longitudinal forces at the left wheel and tire longitudinal forces at the right wheel to the actual clutch torque.

6. The system of claim 5, further comprising a tire longitudinal force module configured to: estimate the tire longitudinal forces at the left and right wheels using a first longitudinal force model when the electronic limited slip differential is unlocked; and estimate the tire longitudinal forces at the left and right wheels using a second longitudinal force model when the electronic limited slip differential is locked, wherein the second longitudinal force model is different than the first longitudinal force model.

7. The system of claim 6, wherein: the first longitudinal force model relates the actual clutch torque and an axle input torque to the tire longitudinal forces at the left and right wheels; and the axle input torque is an amount of torque transferred from the engine to the electronic limited slip differential.

8. The system of claim 6, wherein: the second longitudinal force model comprises: a first relationship between an axle input torque and the tire longitudinal forces at the left and right wheels; and a second relationship between tire vertical forces at the left and right wheels and the tire longitudinal forces at the left and right wheels; and the first relationship is a function of a longitudinal slip ratio of the left and right wheels. The axle input torque is an amount of torque transferred from the engine to the electronic limited slip differential.

9. The system of claim 8, wherein the tire longitudinal force module selects the second relationship from a plurality of different relationships between the tire vertical force at the left and right wheels and the tire longitudinal force at the left and right wheels based on a slip ratio of the left and right wheels.

10. A system for a vehicle, comprising: a clutch state module of the vehicle configured to determine whether a clutch of an electronic limited slip differential is locked or unlocked, the electronic limited slip differential coupling an engine of the vehicle to left and right wheels of the vehicle, wherein the clutch state module is configured to determine whether the clutch is locked or unlocked based on a speed difference of the left and right wheels and a torque capacity of the clutch, wherein the clutch state module determines that the clutch is locked when the speed difference of the rear wheels is less than a slip threshold and the torque capacity of the clutch is greater than a torque threshold, and the clutch state module determines that the clutch is unlocked when the speed difference of the rear wheels is greater than or equal to the slip threshold; a tire longitudinal force module of the vehicle configured to: estimate tire longitudinal forces at the left and right wheels using a first longitudinal force model when the electronic limited slip differential is unlocked; and estimate the tire longitudinal forces at the left and right wheels using a second longitudinal force model when the electronic limited slip differential is locked, wherein the second longitudinal force model is different than the first longitudinal force model.

11. The system of claim 10, wherein: the first longitudinal force model relates an actual clutch torque and an axle input torque to the tire longitudinal forces at the left and right wheels; the actual clutch torque is an actual amount of torque transferred by the clutch; and the axle input torque is an amount of torque transferred from the engine to the electronic limited slip differential.

12. The system of claim 11, further comprising a clutch torque module configured to: estimate the actual clutch torque using a first clutch torque model when the electronic limited slip differential is unlocked; and estimate the actual clutch torque using a second clutch torque model when the electronic limited slip differential is locked, wherein the second clutch torque model is different than the first clutch torque model.

13. The system of claim 12, wherein: the first clutch torque model relates a required clutch torque and the speed difference of the left and right wheels to the actual clutch torque; and the required clutch torque is a required amount of torque to be transferred by the clutch.

14. The system of claim 12, wherein the second clutch torque model relates a tire longitudinal force at the left wheel and a tire longitudinal force at the right wheel to the actual clutch torque.

15. The system of claim 10, wherein: the second longitudinal force model comprises: a first relationship between an axle input torque and the tire longitudinal forces at the left and right wheels; and a second relationship between tire vertical forces at the left and right wheels and the tire longitudinal forces at the left and right wheels; and the axle input torque is an amount of torque transferred from the engine to the electronic limited slip differential.

16. The system of claim 15, wherein the tire longitudinal force module selects the second relationship from a plurality of different relationships between the tire vertical forces at the left and right wheels and the tire longitudinal forces at the left and right wheels based on a slip ratio of the left and right wheels.

17. A system for a vehicle, comprising: a clutch state module of the vehicle configured to determine whether a clutch of an electronic limited slip differential is locked or unlocked, the electronic limited slip differential coupling an engine of the vehicle to left and right wheels of the vehicle, wherein the clutch state module is configured to determine whether the clutch is locked or unlocked based on a speed difference of the left and right wheels and a torque capacity of the clutch, wherein the clutch state module determines that the clutch is locked when the speed difference of the rear wheels is less than a slip threshold and the torque capacity of the clutch is greater than a torque threshold, and the clutch state module determines that the clutch is unlocked when the speed difference of the rear wheels is greater than or equal to the slip threshold; a clutch torque module of the vehicle configured to: estimate an actual clutch torque transferred by the clutch using a first clutch torque model when the electronic limited slip differential is unlocked; and estimate the actual clutch torque using a second clutch torque model when the electronic limited slip differential is locked, wherein the second clutch torque model is different than the first clutch torque model; and a tire longitudinal force module of the vehicle configured to: estimate tire longitudinal forces at the left and right wheels using a first longitudinal force model when the electronic limited slip differential is unlocked; and estimate the tire longitudinal forces at the left and right wheels using a second longitudinal force model when the electronic limited slip differential is locked, wherein the second longitudinal force model is different than the first longitudinal force model.

18. The system of claim 17, wherein: the first clutch torque model comprises a first order transfer function that relates a hyperbolic tangent function of a demanded clutch torque and the speed difference of the left and right wheels to the actual clutch torque; the demanded clutch torque is an amount of demanded torque that accounts for transient dynamics of the clutch to be transferred by the clutch; the second clutch torque model relates tire longitudinal forces at the left wheel and tire longitudinal forces at the right wheel to the actual clutch torque; the first longitudinal force model relates the actual clutch torque and an axle input torque to the tire longitudinal forces at the left and right wheels; the axle input torque is an amount of torque transferred from the engine to the electronic limited slip differential; and ​ The second longitudinal force model includes: a first relationship between the axle input torque and the tire longitudinal forces at the left and right wheels; and a second relationship between tire vertical forces at the left and right wheels and the tire longitudinal forces at the left and right wheels.

19. The system of claim 18, wherein the tire longitudinal force module selects the second relationship from a plurality of different relationships between the tire vertical forces at the left and right wheels and the tire longitudinal forces at the left and right wheels based on slip ratios of the left and right wheels.

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