Control device for vehicle differential limiting clutch

Abstract

To provide a control device for a vehicle differential motion limiting device that suppresses sliding of a differential motion limiting clutch, and heat generation or durability reduction caused by such sliding.SOLUTION: With an electronic control device 60, when a differential motion occurs on right and left driving wheels 16, 18 because of occurence of sliding of a differential limitation clutch 46 exceeding a torque capacity of the differential motion limiting clutch 46, a pressing load (engagement pressure) on the differential motion limiting clutch 46 is reduced and a differential motion limiting torque is reduced during braking of either of the driving wheels 16, 18 with either of wheel brakes 52, 54. By doing so, sliding of the differential motion limitation clutch 46, heat generation and durability reduction caused by such sliding are suppressed when the driving wheel on the high torque side of the driving wheels 16, 18 is braked using either of the wheel brakes 52, 54.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a control device for a differential limiting clutch for a vehicle, which suppresses heat generation of the differential limiting clutch used to limit differential rotation in a differential gear device of a vehicle.

Background Art

[0002] In a vehicle provided with a differential gear device provided between left and right drive shafts and distributing the drive torque transmitted from a drive source to left and right drive wheels while allowing their differential rotation, a differential limiting clutch that limits the differential generated between the left and right drive wheels, and a wheel brake device that controls the rotational speeds of the drive wheels respectively, when the drive torque transmitted from the drive source to the differential gear device rapidly increases and slip occurs in the differential limiting clutch exceeding the torque capacity of the differential limiting clutch, a vehicle that enhances the straight-ahead stability of the vehicle by suppressing the drive torque transmitted to the drive wheel on the high-torque side among the drive wheels using the wheel brake has been proposed. For example, the vehicle described in Patent Document 1 is an example thereof.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as described above, when the drive torque transmitted to the high-torque drive wheel is suppressed using the wheel brake, the differential limiting clutch may slip, and this slip could lead to overheating and reduced durability of the differential limiting clutch. While it is thought that the slip of the differential limiting clutch decreases when the wheel brake is in operation, it does not become completely zero, and a slight amount of slip continues. Since a large drive torque exceeding the torque capacity of the differential limiting clutch is transmitted, causing slippage, even a slight amount of slippage has a relatively significant impact on the differential limiting clutch.

[0005] The present invention was made against the above circumstances, and its objective is to provide a control device for a vehicle differential limiting device that can suppress the sliding of the differential limiting clutch, and the resulting heat generation and deterioration of durability. [Means for solving the problem]

[0006] To achieve the above objectives, 1 The gist of the invention is a control device for a vehicle differential limiting clutch, comprising: (a) a differential gear device provided between left and right drive shafts for distributing drive torque transmitted from a drive source to the left and right drive wheels while allowing their rotational difference; a differential limiting clutch for limiting the differential between the left and right drive wheels; and a wheel brake device for controlling the rotational speed of each of the drive wheels, wherein when the differential limiting clutch slips due to exceeding the torque capacity of the differential limiting clutch and a differential occurs between the left and right drive wheels, the control device brakes the drive wheel on the higher torque side of the drive wheels using the wheel brake; and (b) during braking of the drive wheel by the wheel brake, the differential limiting torque of the differential limiting clutch is reduced. (c) The control device reduces the differential limiting torque of the differential limiting clutch when a differential rotation occurs that is equal to or greater than a preset differential rotation determination value while the drive wheel is being braked by the wheel brake, but does not reduce the differential limiting torque of the differential limiting clutch when a differential rotation occurs that is less than the preset differential rotation determination value. It is the matter. The gist of the second invention is a control device for a vehicle differential limiting clutch, which is provided in a vehicle equipped with a differential gear device provided between left and right drive shafts for distributing drive torque transmitted from a drive source to left and right drive wheels while allowing their rotational difference, a differential limiting clutch for limiting the differential occurring between the left and right drive wheels, and a wheel brake device for controlling the rotational speed of each of the drive wheels, wherein when the differential limiting clutch slips due to exceeding the torque capacity of the differential limiting clutch and a differential occurs between the left and right drive wheels, the control device brakes the drive wheel on the higher rotational side of the drive wheels using the wheel brake, wherein (b) the differential limiting torque of the differential limiting clutch is reduced while the drive wheel is being braked by the wheel brake, and (c) the control device reduces the differential limiting torque of the differential limiting clutch while the drive wheel is being braked by the wheel brake, provided that the temperature of the differential limiting clutch is above a preset clutch temperature determination value. The gist of the third invention is a control device for a vehicle differential limiting clutch, which is provided in a vehicle equipped with a differential gear device provided between left and right drive shafts for distributing drive torque transmitted from a drive source to left and right drive wheels while allowing their rotational difference, a differential limiting clutch for limiting the differential occurring between the left and right drive wheels, and a wheel brake device for controlling the rotational speed of each of the drive wheels, wherein when the differential limiting clutch slips due to exceeding the torque capacity of the differential limiting clutch and a differential occurs between the left and right drive wheels, the control device brakes the drive wheel on the higher rotational side of the drive wheels using the wheel brake, wherein (b) the differential limiting torque of the differential limiting clutch is reduced while the drive wheel is being braked by the wheel brake, and (c) the control device reduces the differential limiting torque of the differential limiting clutch on the condition that the elapsed time since the start of operation of the wheel brake exceeds a preset elapsed time determination threshold while the drive wheel is being braked by the wheel brake. The gist of the fourth invention is a control device for a vehicle differential limiting clutch, which comprises (a) a differential gear device provided between left and right drive shafts for distributing drive torque transmitted from a drive source to left and right drive wheels while allowing their rotational difference, a differential limiting clutch for limiting the differential occurring between the left and right drive wheels, and a wheel brake device for controlling the rotational speed of each of the drive wheels, wherein when the differential limiting clutch slips due to exceeding the torque capacity of the differential limiting clutch and a differential occurs between the left and right drive wheels, the control device brakes the drive wheel on the higher rotational side of the drive wheels using the wheel brake, and (b) reduces the differential limiting torque of the differential limiting clutch while the drive wheel is being braked by the wheel brake, and (c) when the differential rotation of the differential gear device is increasing while the drive wheel is being braked by the wheel brake, the control device preferentially reduces the differential limiting torque of the differential limiting clutch. [Effects of the Invention]

[0007] According to the first invention,When the torque capacity of the differential limiting clutch is exceeded and slippage occurs in the differential limiting clutch, causing a differential between the left and right drive wheels, the differential limiting torque of the differential limiting clutch is reduced while the drive wheels are being braked by the wheel brakes. This makes it possible to suppress the sliding of the differential limiting clutch, and the resulting heat generation and decrease in durability, when braking the drive wheel on the higher torque side of the drive wheels using the wheel brakes. Furthermore, according to the first invention, the control device reduces the differential limiting torque of the differential limiting clutch when a differential rotation occurs that is equal to or greater than a preset differential rotation determination value during braking of the drive wheels by the wheel brakes. However, if a differential rotation occurs that is less than the preset differential rotation determination value, the differential limiting torque of the differential limiting clutch is not reduced. As a result, since the differential limiting torque of the differential limiting clutch is not reduced when a differential rotation occurs that is less than the preset differential rotation determination value, operation can be continued without reducing the differential limiting torque of the differential limiting clutch, thus suppressing a sudden decrease in the transmitted driving force. According to the second invention, when the differential limiting clutch slips due to exceeding its torque capacity, causing a differential between the left and right drive wheels, the differential limiting torque of the differential limiting clutch is reduced while the drive wheels are being braked by the wheel brakes. This suppresses the sliding of the differential limiting clutch and the resulting heat generation and deterioration of durability when the high-torque drive wheel is being braked using the wheel brakes. Furthermore, according to the second invention, the control device reduces the differential limiting torque of the differential limiting clutch while the drive wheels are being braked by the wheel brakes, provided that the temperature of the differential limiting clutch is above a preset clutch temperature determination value. This suppresses overheating and deterioration of durability of the differential limiting clutch. According to the third invention, when the differential limiting clutch slips due to exceeding its torque capacity, causing a differential between the left and right drive wheels, the differential limiting torque of the differential limiting clutch is reduced while the drive wheels are being braked by the wheel brakes. This suppresses the sliding of the differential limiting clutch and the resulting heat generation and deterioration of durability when the high-torque drive wheel is being braked using the wheel brakes. Furthermore, according to the third invention, the control device reduces the differential limiting torque of the differential limiting clutch while the drive wheels are being braked by the wheel brakes, provided that the elapsed time since the start of operation of the wheel brakes exceeds a preset elapsed time threshold. This suppresses overheating and deterioration of durability of the differential limiting clutch. According to the fourth invention, when the differential limiting clutch slips due to exceeding its torque capacity, causing a differential between the left and right drive wheels, the differential limiting torque of the differential limiting clutch is reduced while the drive wheels are being braked by the wheel brakes. This makes it possible to suppress the sliding of the differential limiting clutch and the resulting heat generation and decrease in durability when braking the high-torque drive wheel using the wheel brakes. Furthermore, according to the fourth invention, if the differential rotation of the differential gear system is increasing while the drive wheels are being braked by the wheel brakes, the control device preferentially reduces the differential limiting torque of the differential limiting clutch. This prevents the combined time of control by the differential limiting clutch and control by the wheel brakes from becoming unnecessarily long or short depending on the differential rotation determination value and clutch temperature determination value, thereby reducing the opportunities for sliding of the differential limiting clutch and loss of driving force.

[0008] Preferably, the vehicle is equipped with multiple differential gears, and the control device identifies the differential gears in which differential action is occurring based on the rotational speed of the drive wheels, and reduces the differential limiting torque of the differential limiting clutch only for the differential gears in which differential action is occurring. This makes it possible to suppress the reduction in transmitted driving force caused by releasing unnecessary differential limiting clutches.

[0009] Preferably, the control device continuously or gradually reduces the differential limiting torque of the differential limiting clutch. This suppresses the generation of vehicle body vibrations and abnormal noises associated with the sudden release of the differential limiting clutch.

[0010] Preferably, when the control device reduces the differential limiting torque of the differential limiting clutch, it does not completely disengage the differential limiting clutch, but leaves a certain amount of differential limiting torque. This makes the sudden increase in differential and the change in wheel speed during the reduction of differential limiting torque gradual, so the operation of the wheel brakes used in conjunction with the differential becomes gradual, and the occurrence of discomfort is suppressed. [Brief explanation of the drawing]

[0015] [Figure 1] This figure illustrates the main components of a vehicle including a control device according to one embodiment of the present invention. [Figure 2] This is a flowchart illustrating the main parts of the control operation of the control device in the embodiment shown in Figure 1. [Figure 3] It is a time chart for explaining the main part of the control operation of the control device in FIG. 1. [Figure 4] It is a flowchart for explaining the main part of the control operation of the control device in another embodiment of the present invention. [Figure 5] It is a flowchart for explaining the main part of the control operation of the control device in another embodiment of the present invention. [Figure 6] It is a time chart for explaining the main part of the control operation of the control device in FIG. 5. [Figure 7] It is a time chart for explaining the control operation of the conventional control device in comparison with FIG. 6. [Figure 8] It is a time chart for explaining the main part of another control operation of the control device in FIG. 5. [Figure 9] It is a time chart for explaining the control operation of the conventional control device in comparison with FIG. 8.

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail while referring to the drawings. In the following embodiments, the drawings are appropriately simplified or modified, and the dimensional ratios and shapes of each part are not necessarily accurately drawn.

EXAMPLE

[0017] FIG. 1 is a diagram for explaining the main part of the vehicle 10 to which the present invention is applied, and is also a diagram for explaining the main part of the control system provided in the vehicle 10. The vehicle 10 is a FF vehicle, a FR vehicle, or a four-wheel drive vehicle.

[0018] In FIG. 1, the vehicle 10 includes a prime mover 12 such as an engine or a motor, a transmission 14 that changes the rotation of the prime mover 12, a pair of left and right drive wheels 16, 18, and a differential gear device 26 connected to the pair of left and right drive wheels 16, 18 via a pair of left and right drive shafts 20, 22.

[0019] The differential gear unit 26 includes a large-diameter bevel gear 30 that meshes with a small-diameter bevel gear 28 connected to the transmission 14 via a propeller shaft 24, a differential case 32 to which the large-diameter bevel gear 30 is fixed, and a pair of side gears 38 and 40 that mesh with each other via a pinion 36 provided inside the differential case 32 and rotatably supported by a pinion shaft 34. The differential gear unit 26 transmits the drive torque transmitted from the transmission 14 via the propeller shaft 24 to a pair of left and right drive wheels 16 and 18, which are respectively connected to the pair of side gears 38 and 40 via a pair of drive shafts 20 and 22, while allowing differential rotation between them.

[0020] The differential limiting clutch 46 is provided in the differential gear unit 26 and limits differential rotation between a pair of left and right drive shafts 20, 22 and a pair of left and right drive wheels 16, 18 connected thereto. The differential limiting clutch 46 is configured such that, for example, a plurality of fixed friction plates 48 that are not rotatable and mounted in the differential case 32 and rotating friction plates 50 that rotate with the drive shafts 22 are stacked alternately, and a pressing load is applied to the fixed friction plates 48 and rotating friction plates 50 by an electric actuator (not shown) using an electric motor, which presses them against each other.

[0021] The wheels of the vehicle 10, namely the drive wheels 16 and 18, are equipped with wheel brakes 52 and 54, respectively, to control their rotation. These wheel brakes 52 and 54, as well as the aforementioned differential limiting clutch 46, are controlled by an electronic control unit 60, which functions as a control device for the vehicle 10.

[0022] The electronic control unit 60 includes a so-called microcomputer, and input signals are processed according to a pre-stored program. Functionally, the electronic control unit 60 includes a differential limiting clutch slip determination unit 62, a differential limiting clutch control unit 64, and a wheel brake control unit 66.

[0023] The differential limiting clutch slip determination unit 62 calculates the differential rotation speed ΔNdf (rpm) of the differential gear unit 26, which is the difference between the rotation speeds of the left and right drive wheels 16 and 18 detected by the left and right wheel rotation sensors 68 and 70, respectively, and determines whether the differential rotation speed ΔNdf is equal to or greater than a preset clutch slip determination threshold ΔNdf1.

[0024] The differential limiting clutch control unit 64 performs differential limiting control (basic control) to limit the differential rotation of the pair of drive wheels 16 and 18 by applying a predetermined pressing load from an electric actuator to the fixed-side friction plate 48 and the rotating-side friction plate 50 of the differential limiting clutch 46, in order to prevent a decrease in the driving force of the pair of drive wheels 16 and 18 when one of the pair of drive wheels 16 and 18 slips while the vehicle 10 is traveling on an icy road or muddy road, etc.

[0025] During differential limiting control of the differential limiting clutch 46, if, for example, one of the drive wheels 16 or 18 slips and a large torque is transmitted to the other, resulting in a driving torque exceeding the torque capacity of the differential limiting clutch 46, the straight-line stability of the vehicle is impaired. Therefore, to suppress the torque of the other drive wheel, the wheel brake control unit 66 uses one of the wheel brakes 52 or 54 to suppress the torque of the other drive wheel. However, during such wheel brake control, slight slippage occurs in the differential limiting clutch 46, which could lead to overheating and reduced durability of the differential limiting clutch 46.

[0026] In contrast, if the differential limiting clutch slip determination unit 62 determines that slippage has occurred in the differential limiting clutch 46 during wheel brake control, and the wheel brake control unit 66 is using one of the wheel brakes 52 or 54 to suppress the rotation of the high-speed (high-torque) wheel of the pair of drive wheels 16 or 18, the differential limiting clutch control unit 64 restricts the differential limiting control of the differential limiting clutch 46. That is, it either releases the differential limiting clutch 46 or reduces the pressing load on the differential limiting clutch 46.

[0027] Figure 2 is a flowchart illustrating the main parts of the control operation of the electronic control unit 60. In Figure 2, step S1 (the steps are omitted hereafter) determines whether or not differential limiting control (LSD control) is being performed by the differential limiting clutch control unit 64. If the determination in S1 is denied, this routine is terminated. However, if it is affirmed, in S2, which corresponds to the differential limiting clutch slip determination unit 62, it is determined whether or not slippage has occurred in the differential limiting clutch 46 during differential limiting control, based on whether or not the differential rotational speed ΔNdf (rpm) of the differential gear unit 26 has become equal to or greater than a preset clutch slip determination threshold ΔNdf1. If the determination in S2 is denied, differential limiting control is continued in S3. However, if the determination in S3 is affirmed, it is determined whether or not the rotation of the high-speed (high-torque) wheel of the pair of drive wheels 16 and 18 is being suppressed using one of the wheel brakes 52 or 54. If the judgment in S3 is denied, the differential limiting control is continued in S3. However, if it is affirmed, in S5, the pressing load (engagement pressure) of the differential limiting clutch 46 is reduced, and the differential limiting control is restricted.

[0028] If the vehicle 10 is equipped with multiple differential gears 26, such as a 4WD vehicle, the pressing load of the differential limiting clutch 46 is reduced only for the differential gear 26 that is generating differential rotation during differential limiting control, thereby limiting the differential limiting control. This suppresses the reduction in transmitted driving force due to the unnecessary release of the differential limiting clutch 46. Furthermore, if the vehicle 10 is equipped with a differential gear 26 with a differential limiting clutch 46 only on the rear wheels, and brake control is activated due to differential rotation in the front wheel differential gear, this is detected, and the pressing load of the rear wheel differential limiting clutch 46 is not reduced, continuing normal clutch control. Also, if the vehicle 10 is equipped with differential gears 26 with differential limiting clutches 46 on both the front and rear wheels, and brake control is activated due to differential rotation in the front wheel differential gear, the pressing load of the differential limiting clutch 46 on the front wheel is reduced, but normal control continues on the rear wheel.

[0029] Figure 3 shows several control modes in which the pressing load of the differential limiting clutch 46 is reduced in S5. Time t2 in Figure 3 indicates the start of the reduction in the pressing load (engagement pressure) of the differential limiting clutch 46 in response to the suppression of the rotation of the high-speed (high-torque) wheel of the pair of drive wheels 16 and 18 using one of the wheel brakes 52 and 54. In Figure 3, the solid line shows an example in which the clutch pressing load during differential limiting control, which is shown as a constant value, is reduced to zero at time t2.

[0030] In contrast, the dashed line in Figure 3 shows an example in which the clutch pressing load during differential limiting control, which is shown as a constant value, is gradually reduced to a certain residual value at time t2. In this case, by reducing the clutch pressing load to a residual value within a range that does not cause problems with the sliding of the differential limiting clutch 46, the sudden decrease in the amount of driving torque transmitted and the change in wheel speed during the pressing load reduction control can be made gentler, thereby making the brake control operation of the wheel brake 52 or 54 used in conjunction with it gentler.

[0031] Furthermore, the dashed line in Figure 3 shows an example where the clutch pressing load during differential limiting control, which is shown as a constant value, is continuously reduced at a constant slope from time t2. In this case, the generation of vehicle body vibration and abnormal noise associated with the sudden release of the differential limiting clutch 46 is suppressed, as is the sudden change in vehicle body behavior due to the sudden loss of driving torque associated with the rapid increase in differential rotation of the differential limiting clutch 46, and the sudden change in vehicle body behavior and the generation of abnormal noise associated with the rapid increase in braking force of the brake control.

[0032] According to the electronic control device 60 of this embodiment, when the differential limiting clutch 46 slips due to exceeding its torque capacity and differential occurs between the left and right drive wheels 16 and 18, the pressing load (engagement pressure) of the differential limiting clutch 46 is reduced and the differential limiting torque is decreased when one of the drive wheels 16 and 18 is being braked using either the wheel brake 52 or 54. As a result, when the high-torque drive wheel of the drive wheels 16 and 18 is being braked using either the wheel brake 52 or 54, the sliding of the differential limiting clutch 46 and the resulting heat generation and decrease in durability are suppressed. [Examples]

[0033] Other embodiments of the present invention will be described below. In the following description, parts common to the previously described embodiments will be denoted by the same reference numerals and their descriptions will be omitted.

[0034] Figure 4 is a flowchart illustrating the other key aspects of the control operation of the electronic control unit 60. Figure 4 differs from the flowchart in Figure 2 in that S6, which is executed when the judgment in S4 is affirmed, is placed between S4 and S5; otherwise, it is the same. The differences will be explained below.

[0035] In Figure 4, in S6, prior to the reduction of the pressing load (engagement pressure) of the differential limiting clutch 46 in S5, it is determined whether or not a predetermined condition for executing the limitation of differential limiting control (LSD control) is satisfied (corresponding to the LSD control limitation condition). This predetermined start condition is one of (1) to (3). (1) The rotation of the high-speed (high-torque) wheel of the pair of drive wheels 16 and 18 is suppressed using one of the wheel brakes 52 or 54, but the differential rotation speed ΔNdf (rpm) of the differential gear unit 26 has become greater than or equal to a preset clutch slip detection threshold ΔNdf1. (2) The temperature Tc (°C) of the differential limiting clutch 46 has become equal to or greater than the preset overheating threshold Tc1. (3) The elapsed time te from the start of braking (brake control) of the wheel on the high rotation (high torque) side by one of the wheel brakes 52 or 54 has become equal to or greater than a preset elapsed time determination threshold te1.

[0036] If the judgment in S6 is denied, the differential limiting control is continued in S3. However, if it is affirmed, in S5, the pressing load (engagement pressure) of the differential limiting clutch 46 is reduced, and the differential limiting control is restricted.

[0037] According to the electronic control device 60 of this embodiment, in addition to obtaining the same effects as in the above-described embodiment 1, when the brake control is operating but the differential rotation speed ΔNdf (rpm) of the differential gear unit 26 falls below a preset clutch slip judgment threshold ΔNdf1, operation can be continued while continuing normal differential limiting control without reducing the pressing load of the differential limiting clutch 46, thus suppressing the reduction in transmitted driving force. [Examples]

[0038] Figure 5 is a flowchart illustrating the other key aspects of the control operation of the electronic control unit 60. Figure 5 differs from the flowchart in Figure 4 in that S7 and S8, which are executed when the judgment in S4 is affirmed, are placed between S4 and S5, and S9, which determines whether the differential rotational speed ΔNdf of the differential gear unit 26 is increasing, is placed between S4 and S5, and similarly S10, which determines whether the differential rotational speed ΔNdf of the differential gear unit 26 is increasing, is placed between S8 and S5. Otherwise, it is the same. The differences will be explained below.

[0039] In S7, it is determined whether a predetermined condition A for implementing the limitation of differential limiting control (LSD control) is satisfied (i.e., it corresponds to LSD control limitation condition A). Condition A is a condition that is not affected by the increase in the differential rotation speed ΔNdf of the differential gear unit 26 and transitions to differential limiting by the differential limiting clutch 46. For example, this is when the temperature Tc (°C) of the differential limiting clutch 46 becomes equal to or greater than a preset heating determination threshold Tc1. If the determination in S7 is affirmative, in S5, the pressing load (engagement pressure) of the differential limiting clutch 46 is reduced, and the differential limiting control is limited. However, if the determination in S7 is negative, in S8, it is determined whether a predetermined condition B for implementing the limitation of differential limiting control (LSD control) is satisfied (i.e., it corresponds to LSD control limitation condition B). Condition B is, for example, when the elapsed time te from the start of braking (brake control) of the high-rotation (high-torque) wheel by one of the wheel brakes 52 or 54 becomes equal to or greater than a preset elapsed time determination threshold te1. If the judgment in S8 is denied, S9 is executed; if it is affirmed, S10 is executed.

[0040] In S9, which is executed when S4 is denied and when S8 is denied, it is determined whether the differential rotational speed ΔNdf of the differential gear unit 26 is increasing. If the determination in S9 is denied, differential limiting control is continued in S3, but if it is confirmed, in S5 the pressing load (engagement pressure) of the differential limiting clutch 46 is reduced and differential limiting control is restricted. In S10, which is executed when S8 is confirmed, it is also determined whether the differential rotational speed ΔNdf of the differential gear unit 26 is increasing. If the determination in S10 is denied, differential limiting control is continued in S3, but if it is confirmed, in S5 the pressing load (engagement pressure) of the differential limiting clutch 46 is reduced and differential limiting control is restricted.

[0041] With the electronic control device 60 of this embodiment, in addition to obtaining the same effects as in the above-described embodiments 1 and 2, the determination of whether to continue differential limiting control or to perform differential limiting clutch 46 pressure reduction control is made, without relying on (and taking precedence over) other threshold determinations, depending on whether the differential rotation speed ΔNdf of the differential gear device 26 is increasing, thereby suppressing the sliding of the differential limiting clutch 46 and the loss of transmission driving force.

[0042] Furthermore, according to the electronic control device 60 of this embodiment, as shown in the time chart of Figure 6, even before the predetermined condition B for executing the limitation of differential limiting control (LSD control) is met (negation of S8), if it is determined that the differential rotation speed ΔNdf of the differential gear unit 26 is increasing (affirmation of S9), the control to reduce the pressing load of the differential limiting clutch 46 is executed (S5), thereby suppressing unnecessary sliding of the differential limiting clutch 46. In Figure 6, the solid line represents the differential rotation speed ΔNdf, the dashed line represents the pressing load of the differential limiting clutch 46, and the dashed line represents the temperature Tc of the differential limiting clutch 46. In Figure 6, after the start of differential limiting control of the differential gear unit 26 (time t0), brake control by one of the wheel brakes 52 or 54 is started (time t1), and before the elapsed time determination threshold te1, the reduction of the pressing load (engagement pressure) of the differential limiting clutch 46 is started (time t2), thus suppressing unnecessary sliding of the differential limiting clutch 46.

[0043] Incidentally, Figure 7 is a time chart illustrating the conventional control operation. In this case, the elapsed time determination threshold te1 and the starting point (time t2) of the reduction of the pressing load (engagement pressure) of the differential limiting clutch 46 are the same. Therefore, the sliding of the differential limiting clutch 46 continues until the elapsed time te from the start of braking (brake control) of the high-speed (high-torque) wheel by one of the wheel brakes 52 or 54 reaches the elapsed time determination threshold te1.

[0044] Furthermore, according to the electronic control device 60 of this embodiment, as shown in the time chart of Figure 8, if a decreasing trend in the differential rotation ΔNdf of the braking (brake control) of the wheel on the high-rotation (high-torque) side by one of the wheel brakes 52 or 54 is confirmed (negation of S10), the pressing load of the differential limiting clutch 46 is not reduced even if the elapsed time te exceeds the elapsed time determination threshold te1 (continuation of S3). As a result, stable operation of the vehicle 10 is prioritized, and the differential limiting control of the differential limiting clutch 46 is continued.

[0045] Incidentally, Figure 9 is a time chart illustrating the conventional control operation. In this case, as soon as the elapsed time te reaches the elapsed time determination threshold te1, the differential limiting control by the differential limiting clutch 46 ends and the pressing load of the differential limiting clutch 46 is reduced. As a result, the sliding of the differential limiting clutch 46 is suppressed, but the driving force of the vehicle 10 decreases, and vibrations of the vehicle 10 may occur as a result.

[0046] Although embodiments of the present invention have been described in detail above with reference to the drawings, the present invention is also applicable to other embodiments.

[0047] For example, in the embodiment described above, the differential limiting clutch 46 was provided between the differential case 32 and the drive shaft 22 of the differential gear unit 26, but it may also be provided between the differential case 32 and the drive shaft 20, or between the side gears 38 and 40, etc.

[0048] Furthermore, in the aforementioned differential limiting clutch 46, a pressing load was applied to the fixed friction plate 48 and the rotating friction plate 50 by an electric actuator, but the pressing load may also be applied by a hydraulic actuator.

[0049] Furthermore, the aforementioned vehicle 10 does not necessarily have to be equipped with a transmission 14.

[0050] It should be noted that the above-described embodiment is merely one example, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. [Explanation of Symbols]

[0051] 10: Vehicle, 12: Engine, 14: Transmission, 16, 18: Drive wheels, 20, 22: Drive shaft, 24: Propeller shaft, 26: Differential gear system, 28: Small diameter bevel gear, 30: Large diameter bevel gear, 32: Differential case, 34: Pinion shaft, 36: Pinion, 38, 40: Side gears, 46: Differential limiting clutch, 48: Fixed side friction plate, 50: Rotating side friction plate, 52, 54: Wheel brake, 60: Electronic control unit (control unit), 62: Differential limiting clutch slip detection unit, 64: Differential limiting clutch control unit, 66: Wheel brake control unit, 68, 70: Wheel rotation sensor

Claims

1. A vehicle comprising a differential gear system provided between the left and right drive shafts for distributing drive torque transmitted from a drive source to the left and right drive wheels while allowing for their rotational differences, a differential limiting clutch for limiting the differential between the left and right drive wheels, and a wheel brake system for controlling the rotational speed of each of the drive wheels, wherein when the differential limiting clutch slips due to exceeding its torque capacity and a differential occurs between the left and right drive wheels, the control device for a vehicle differential limiting clutch brakes the higher-rotating drive wheel using the wheel brake, During braking of the drive wheels by the aforementioned wheel brakes, the differential limiting torque of the differential limiting clutch is reduced. The control device reduces the differential limiting torque of the differential limiting clutch when the differential rotation exceeds a preset differential rotation threshold during braking of the drive wheels by the wheel brakes, but does not reduce the differential limiting torque of the differential limiting clutch when the differential rotation falls below the preset differential rotation threshold. A control device for a differential limiting clutch in a vehicle, characterized by the following features.

2. A vehicle comprising a differential gear device provided between left and right drive shafts for distributing drive torque transmitted from a drive source to left and right drive wheels while allowing their rotational difference, a differential limiting clutch for limiting the differential occurring between the left and right drive wheels, and a wheel brake device for controlling the rotational speed of each of the drive wheels, wherein when the differential limiting clutch slips due to exceeding the torque capacity of the differential limiting clutch and a differential occurs between the left and right drive wheels, a control device for a vehicle differential limiting clutch for braking the higher-rotating drive wheel of the drive wheels using the wheel brake, During braking of the drive wheels by the aforementioned wheel brakes, the differential limiting torque of the differential limiting clutch is reduced. The control device reduces the differential limiting torque of the differential limiting clutch, provided that the temperature of the differential limiting clutch is above a preset clutch temperature determination value while the drive wheels are being braked by the wheel brakes. A control device for a differential limiting clutch in a vehicle, characterized by the following features.

3. A vehicle comprising a differential gear device provided between left and right drive shafts for distributing drive torque transmitted from a drive source to left and right drive wheels while allowing their rotational difference, a differential limiting clutch for limiting the differential occurring between the left and right drive wheels, and a wheel brake device for controlling the rotational speed of each of the drive wheels, wherein when the differential limiting clutch slips due to exceeding the torque capacity of the differential limiting clutch and a differential occurs between the left and right drive wheels, the control device for a vehicle differential limiting clutch brakes the drive wheel on the higher rotational side of the drive wheels using the wheel brake, During braking of the drive wheels by the aforementioned wheel brakes, the differential limiting torque of the differential limiting clutch is reduced. The control device, while braking the drive wheels with the wheel brakes, reduces the differential limiting torque of the differential limiting clutch, provided that the elapsed time since the start of operation of the wheel brakes exceeds a preset elapsed time threshold. A control device for a differential limiting clutch in a vehicle, characterized by the following features.

4. A vehicle comprising a differential gear device provided between left and right drive shafts for distributing drive torque transmitted from a drive source to left and right drive wheels while allowing their rotational difference, a differential limiting clutch for limiting the differential occurring between the left and right drive wheels, and a wheel brake device for controlling the rotational speed of each of the drive wheels, wherein when the differential limiting clutch slips due to exceeding the torque capacity of the differential limiting clutch and a differential occurs between the left and right drive wheels, the control device for a vehicle differential limiting clutch brakes the drive wheel on the higher rotational side of the drive wheels using the wheel brake, During braking of the drive wheels by the aforementioned wheel brakes, the differential limiting torque of the differential limiting clutch is reduced. If the differential rotation of the differential gear unit is increasing while the drive wheels are being braked by the wheel brakes, the control device will preferentially reduce the differential limiting torque of the differential limiting clutch. A control device for a differential limiting clutch in a vehicle, characterized by the following features.

Images