JP7257196B2 - Vehicle drive system - Google Patents

Description

The present invention relates to a vehicle drive system that drives front and rear wheels.

As a vehicle drive system that drives the front and rear wheels, there is a fixed distribution type drive system that distributes driving force to the front and rear wheels at a fixed ratio, and a variable distribution type drive system that changes the distribution ratio of the driving force to the front and rear wheels. (See Patent Documents 1 to 3). A fixed distribution type drive device is provided with a differential mechanism composed of bevel gears and planetary gears, and is provided with a limited differential clutch for limiting the differential of the differential mechanism. Also, the variable distribution drive system is provided with a transfer clutch for transmitting driving force to the front wheels or the rear wheels.

JP 2016-16732 A Japanese Patent Application Laid-Open No. 2005-289160 Japanese Unexamined Patent Application Publication No. 2005-28913

By the way, when the differential limiting clutch and the transfer clutch are released, the difference in rotational speed between the front wheels and the rear wheels is allowed. The rotation speed difference with the wheel is limited. In this way, when there is a rotational speed difference between the front wheels and the rear wheels with the differential limiting clutch or transfer clutch engaged, internal circulation torque is generated and the energy efficiency of the vehicle is reduced. was a factor in the decline.

SUMMARY OF THE INVENTION An object of the present invention is to improve the energy efficiency of a vehicle.

A vehicle drive system according to the present invention is a vehicle drive system that drives front wheels and rear wheels, and includes a fastening state for limiting a rotational speed difference between the front wheels and the rear wheels, and a state of engagement between the front wheels and the rear wheels. When the rotational speed difference between the front wheels and the rear wheels exceeds a speed difference threshold during acceleration while the clutch is controlled to be in an engaged state, a clutch control unit that controls the clutch from an engaged state to a disengaged state, and the speed difference threshold value is set larger as the target driving force during acceleration increases.

A vehicle drive system according to the present invention is a vehicle drive system that drives front wheels and rear wheels, and includes a fastening state for limiting a rotational speed difference between the front wheels and the rear wheels, and a state of engagement between the front wheels and the rear wheels. When the rotational speed difference between one side and the other side of the clutch exceeds a speed difference threshold during acceleration while the clutch is controlled to be in a disengaged state that allows a rotational speed difference, and the clutch is controlled to be in an engaged state. and a clutch control unit for controlling the clutch from the engaged state to the disengaged state, and the speed difference threshold value is set larger as the target driving force during acceleration increases.

According to the present invention, the clutch is controlled from the engaged state to the disengaged state when the rotational speed difference exceeds the speed difference threshold. As a result, driving force can be efficiently transmitted, and energy efficiency can be improved.

1 is a diagram showing a configuration example of a vehicle provided with a vehicle drive system according to an embodiment of the invention; FIG. 4 is a flowchart showing an example of a procedure for executing clutch release control; It is a figure which shows an example of the relationship between front-back rotation difference and driving force. It is a figure which shows the rotation condition of a drive system, and the transmission condition of driving force. (A) and (B) are diagrams showing the rotation state of the driving system and the transmission state of the driving force. It is a figure which shows an example of the relationship between front-back rotation difference and driving force. FIG. 5 is a diagram showing an example of a relationship between a speed difference threshold and target driving force; (A) and (B) are diagrams simply showing the position of a transfer clutch. FIG. 10 is a diagram showing a configuration example of a vehicle provided with a vehicle drive system according to another embodiment of the present invention; (A) to (C) are diagrams simply showing the position of a differential limiting clutch.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Vehicle configuration]
FIG. 1 is a diagram showing a configuration example of a vehicle 11 provided with a vehicle drive system 10 according to one embodiment of the present invention. As shown in FIG. 1, a vehicle 11 that is an all-wheel drive vehicle is provided with a powertrain 14 comprising an engine 12 and a transmission 13 . A transmission 13 of the power train 14 is provided with a transfer clutch (clutch) 15 that constitutes a part of the vehicle drive device 10 . Further, the transmission 13 is provided with a transmission mechanism 16 such as an automatic transmission mechanism, and a transmission output shaft 17 of the transmission mechanism 16 is connected to a front wheel output shaft 19 via a gear train 18 . A front differential mechanism 20 is connected to the front wheel output shaft 19 , and left and right front wheels 22 are connected to a front drive shaft 21 extending from the front differential mechanism 20 . Furthermore, a rear wheel output shaft 23 is connected to the transmission output shaft 17 via a transfer clutch 15 . A rear differential mechanism 24 is connected to the rear wheel output shaft 23 , and left and right rear wheels 26 are connected to a rear drive shaft 25 extending from the rear differential mechanism 24 .

The driving force output from the engine 12 via the transmission mechanism 16 is transmitted to the front wheel output shaft 19 via the gear train 18, and then transmitted from the front wheel output shaft 19 to the front wheels 22 via the front differential mechanism 20 and the like. Further, the driving force output from the engine 12 via the transmission mechanism 16 is transmitted to the rear wheel output shaft 23 via the transfer clutch 15 and then transmitted from the rear wheel output shaft 23 to the rear wheels 26 via the rear differential mechanism 24 and the like. is transmitted to In this way, since the driving force is transmitted to the rear wheels 26 via the transfer clutch 15, the transfer clutch 15 is controlled to be in the engaged state during all-wheel drive in which the front wheels 22 and the rear wheels 26 are driven, while only the front wheels 22 are engaged. When driving the front wheels, the transfer clutch 15 is controlled to be released. By controlling the engagement force of the transfer clutch 15, which is a friction clutch, the driving force distributed to the rear wheels 26 can be increased or decreased, and the torque distribution ratio between the front wheels 22 and the rear wheels 26 can be freely controlled. be able to. In this manner, during all-wheel drive in which the front wheels 22 and the rear wheels 26 are driven, the transfer clutch 15 is controlled to the engaged state including the slip state.

[Control system]
Next, a control system for the powertrain 14 will be described. As shown in FIG. 1, the vehicle drive system 10 is provided with a controller 30 such as a microcomputer. The controller 30 has an engine control section 31 that controls the operating state of the engine 12, a shift control section 32 that controls the gear ratio of the transmission mechanism 16, and a clutch control section 33 that controls the engagement force of the transfer clutch 15. are doing. The controller 30 controls the operating state of the engine 12 by outputting control signals to injectors, throttle valves and the like (not shown) based on various information transmitted from various sensors. The controller 30 also outputs control signals to a valve unit 34 comprising a plurality of electromagnetic valves and oil passages based on various information transmitted from various sensors, thereby controlling the operating states of the speed change mechanism 16 and the transfer clutch 15. ing. Hydraulic oil discharged from an oil pump (not shown) is supplied to the transmission mechanism 16 and the oil chambers of the transfer clutch 15 via the valve unit 34 .

Various sensors connected to the controller 30 include an accelerator sensor 35 that detects the amount of operation of the accelerator pedal, a brake sensor 36 that detects the amount of operation of the brake pedal, and a vehicle speed sensor 37 that detects the vehicle speed. Various sensors connected to the controller 30 include an outside air temperature sensor 38 for detecting outside air temperature, a steering angle sensor 39 for detecting a steering angle (not shown), and acceleration in the longitudinal direction of the vehicle (hereinafter referred to as longitudinal acceleration). ), and a lateral acceleration sensor 41 for detecting acceleration in the vehicle width direction (hereinafter referred to as lateral acceleration). Further, various sensors connected to the controller 30 include a right front wheel speed sensor 42 that detects the rotational speed of the right front wheel 22, a left front wheel speed sensor 43 that detects the rotational speed of the left front wheel 22, and a right rear wheel 26 sensor. There is a right rear wheel speed sensor 44 that detects the rotational speed and a left rear wheel speed sensor 45 that detects the rotational speed of the left rear wheel 26 .

[Clutch release control]
As described above, during all-wheel drive in which the front wheels 22 and the rear wheels 26 are driven, the transfer clutch 15 is controlled to the engaged state including the slip state. In this way, when the transfer clutch 15 is controlled to be in the engaged state, the rotational speed difference between the front wheels 22 and the rear wheels 26 is limited. An internal circulating torque is generated in the system and the energy efficiency of the vehicle 11 is reduced. For example, when the diameter of the front wheels 22 or the rear wheels 26 is reduced due to a decrease in air pressure or the like, a difference in rotational speed occurs between the front and rear wheels 22 and 26 even when the vehicle is traveling straight ahead, resulting in internal circulation torque. Energy efficiency was declining. Therefore, from the viewpoint of improving the energy efficiency of the vehicle 11, the controller 30 executes clutch release control to release the transfer clutch 15 based on the rotational speed difference between the front wheels 22 and the rear wheels 26 during all-wheel drive.

FIG. 2 is a flow chart showing an example of a procedure for executing clutch release control. As shown in FIG. 2, in step S10, it is determined whether the outside air temperature is 0° C. or higher. When it is determined in step S10 that the outside air temperature is less than 0° C., the process proceeds to step S11, and the transfer clutch 15 is controlled to be in the engaged state. That is, when the outside air temperature is less than 0° C. and there is a risk of road surface freezing, the process proceeds to step S11, and the vehicle attitude is stabilized by executing all-wheel drive control.

If it is determined in step S10 that the outside air temperature is 0° C. or higher, the process proceeds to step S12, where the rotational speed difference between the front wheels 22 and the rear wheels 26 (hereinafter referred to as the front-rear rotational difference) It is determined whether or not it is below the threshold value a1. If it is determined in step S12 that the front-to-rear rotation difference is equal to or greater than the threshold value a1 (for example, several hundred rpm), that is, if it is determined that the front wheels 22 or the rear wheels 26 are slipping, the process proceeds to step S13, and the road surface is It is determined whether the resistance exceeds a predetermined threshold b1 (eg 0.3). If it is determined in step S13 that the road surface resistance is equal to or less than the threshold (resistance threshold) b1, that is, if it is determined that the front wheels 22 or the rear wheels 26 are slipping due to the slippery road surface, the process proceeds to step S11. , the vehicle attitude is stabilized by executing all-wheel drive control. In step S13, the road surface resistance is estimated based on the longitudinal acceleration, the longitudinal rotation difference, and the like. Further, the road surface resistance is the coefficient of friction between the running road surface and the tires.

If it is determined in step S12 that the front-rear rotation difference is less than the threshold a1, or if it is determined in step S13 that the road resistance exceeds the threshold b1, the process proceeds to step S14, and the steering angle is set to a predetermined threshold ( It is determined whether or not the steering angle threshold c1 is exceeded. If it is determined in step S14 that the steering angle is greater than or equal to the threshold value c1, that is, if it is determined that the vehicle 11 is turning, the process proceeds to step S11, and all-wheel drive control is executed to turn the vehicle. It stabilizes the vehicle posture while driving.

If it is determined in step S14 that the steering angle is below the threshold value c1, that is, if it is determined that the vehicle 11 is traveling straight ahead, the process proceeds to step S15, where the lateral acceleration of the vehicle 11 reaches a predetermined threshold value ( It is determined whether or not the acceleration threshold value) d1 is exceeded. In step S15, when it is determined that the lateral acceleration is equal to or greater than the threshold value d1, that is, when it is determined that the vehicle 11 is skidding, the process proceeds to step S11, and all-wheel drive control is executed. It stabilizes the vehicle posture during skidding.

If it is determined in step S15 that the lateral acceleration of the vehicle 11 is less than the threshold value d1, that is, if it is determined that the vehicle 11 is not skidding, the process proceeds to step S16, and the vehicle 11 is accelerating. It is determined whether there is If it is determined in step S16 that the vehicle 11 is accelerating, all of the preconditions for releasing the all-wheel drive control are satisfied. A condition is determined.

As described above, the situation in which it is determined that the vehicle is accelerating in step S16 through steps S10 and S12 to S15 is a situation in which the outside air temperature has risen to 0° C. or higher, and the road surface is slippery. The front wheels 22 or the rear wheels 26 are not slipping, the vehicle 11 is traveling forward, the vehicle 11 is not skidding, and the vehicle 11 is accelerating. It is a situation that we are doing. That is, even if the transfer clutch 15 is released to stop the all-wheel drive control, the vehicle attitude is stable, and the engine 12 consumes fuel. In this way, if it is determined through steps S10 and S12 to S16 that the preconditions for canceling the all-wheel drive control are established, the process proceeds to step S17, based on the front-rear rotation difference and the target driving force, It is determined whether or not the driving force on the negative side acts on the front wheels 22 or the rear wheels 26 .

Here, FIG. 3 is a diagram showing an example of the relationship between the front-rear rotation difference and the driving force. In FIG. 3, the vertical axis indicates the driving force, and the horizontal axis indicates the front-rear rotation difference. 3, the dashed line TF is the target driving force of the vehicle 11 output from the front and rear wheels 22 and 26, the solid line Ftm is the driving force output from the transmission mechanism 16, and the dashed line Ff is the output from the front wheels 22. The two-dot chain line Fr is the driving force output from the rear wheels 26 . An arrow α shown in FIG. 3 indicates the magnitude of internal circulation torque, which will be described later. 4 and 5 are diagrams showing the rotation state of the driving system and the transmission state of the driving force. FIG. 4 shows a situation where there is no front-rear rotation difference, and FIGS. 5A and 5B show situations where there is a front-rear rotation difference. 5(A) shows the situation of the front-rear rotation difference N1 shown in FIG. 3, and FIG. 5(B) shows the situation of the front-rear rotation difference N2 shown in FIG.

First, a situation in which there is no front-to-rear rotation difference will be described. As shown in FIG. 4 , part of the driving force Ftm output from the engine 12 via the transmission mechanism 16 is distributed from the gear train 18 to the front wheel output shaft 19 and output from the front wheels 22 as driving force Ff. Part of the driving force Ftm output from the engine 12 through the transmission mechanism 16 is distributed from the transfer clutch 15 to the rear wheel output shaft 23 and output from the rear wheels 26 as driving force Fr. In the example shown in FIG. 4, the rotational speeds NF, NR of the front and rear wheels 22, 26 are substantially the same, and the input rotational speed Ni and the output rotational speed No of the transfer clutch 15 are substantially the same. In other words, this is a situation in which internal circulation torque is not generated in the drive system, and driving force is efficiently transmitted from the transmission mechanism 16 to the front and rear wheels 22 and 26 . For this reason, as indicated by symbol Xa in FIG. They are almost identical.

Next, the situation in which the front-rear rotation difference occurs will be described. As shown in FIG. 5A, when the rotational speed NR of the rear wheels 26 becomes faster than the rotational speed NF of the front wheels 22 due to a decrease in the air pressure of the rear wheels 26, the output rotational speed of the transfer clutch 15 No becomes faster than the input rotation speed Ni. In this case, the driving force α1 flows from the rear wheel 26 side to the front wheel 22 side as internal circulating torque, and this driving force α1 is absorbed by slippage of the transfer clutch 15, torsion of various rotating shafts, and the like. When the driving force α1 flows from the rear wheel 26 side to the front wheel 22 side in this way, the driving force Fr1 output from the rear wheel 26 decreases, and the driving force Fr1 output from the front wheel 22 decreases, as indicated by the front-rear rotation difference N1 in FIG. The applied driving force Ff1 increases, and the total value Ftm1 of the driving force Ff1 and the driving force Fr1 becomes higher than the target driving force TF. That is, in order to obtain a driving force equivalent to the target driving force TF, it is necessary to increase the engine output.

3 and 5B, the air pressure of the rear wheels 26 is further reduced compared to the situation shown in FIG. When the rotational speed NF becomes higher than the rotational speed NF, the output rotational speed No of the transfer clutch 15 becomes higher than the input rotational speed Ni. That is, when the front-rear rotation difference increases to N2, the driving force α2 larger than the driving force α1 flows from the rear wheel 26 side to the front wheel 22 side as internal circulating torque, and this driving force α2 causes the transfer clutch 15 to slip. It is absorbed by torsion of various rotating shafts. In this way, when the front-rear rotation difference increases and the driving force α2 flows from the rear wheel 26 side to the front wheel 22 side, the negative side, that is, the resistance side driving force Fr2 acts on the rear wheel 26 and is output from the front wheel 22. As a result, the total value Ftm2 of the driving force Ff2 and the driving force Fr2 becomes higher than the target driving force TF. That is, in order to obtain a driving force equivalent to the target driving force TF, it is necessary to increase the engine output. Thus, in the example shown in FIG. 5(B), not only is the energy efficiency reduced by increasing the engine output, but the driving force Fr2 on the resistance side acts on the rear wheels 26 as well.

Therefore, as described in the flowchart of FIG. 2, the controller 30 included in the vehicle drive system 10 goes through steps S10 and S12 to S16, and when it determines that the preconditions for canceling the all-wheel drive control are satisfied, , the process proceeds to step S17, and it is determined whether or not the driving force on the negative side acts on the front wheels 22 or the rear wheels 26 based on the front-rear rotation difference and the target driving force. For example, as shown in FIG. 3, when the target drive force is set to "TF1" based on the accelerator pedal operation amount, vehicle speed, etc., the rotational speed NF of the front wheels 22 exceeds the rotational speed NR of the rear wheels 26. It is determined whether or not the driving force Ff on the negative side is acting on the front wheels 22 in the region where it exceeds. That is, when the target driving force is "TF1", the rotational speed NF of the front wheels 22 increases due to a decrease in air pressure or the like. is determined to be a situation in which Further, in a region where the rotation speed NR of the rear wheels 26 exceeds the rotation speed NF of the front wheels 22, it is determined whether or not the rear wheels 26 are in a situation where the driving force Fr on the negative side acts. That is, when the target driving force is "TF1", the rotation speed NR of the rear wheels 26 increases due to a decrease in air pressure, etc., and when the front-rear rotation difference exceeds the speed difference threshold value Nb1, the rear wheels 26 are driven to the negative side. It is determined that the situation is such that the force Fr acts.

In addition, the front-rear rotation difference at which the driving force on the negative side acts on the front wheels 22 or the rear wheels 26 changes according to the magnitude of the target driving force. Here, FIG. 6 is a diagram showing an example of the relationship between the front-rear rotation difference and the driving force. As shown in FIG. 6, when the target driving force is set to "TF2", which is larger than "TF1", the rotation speed NF of the front wheels 22 increases due to a decrease in air pressure, etc., and the front-rear rotation difference becomes greater than "Na1". When the speed difference threshold value Na2 is exceeded, it is determined that the driving force Ff on the negative side acts on the front wheels 22 . Further, when the target driving force is set to "TF2" which is larger than "TF1", the rotation speed NR of the rear wheels 26 increases due to the decrease in air pressure, etc., and the front-rear rotation difference becomes larger than "Nb1". When the threshold value Nb2 is exceeded, it is determined that the negative driving force Fr is acting on the rear wheels 26 . As shown in FIGS. 3 and 6, the speed difference threshold to be compared with the front-rear rotation difference increases or decreases according to the target driving force TF during acceleration. Here, FIG. 7 is a diagram showing an example of the relationship between the speed difference threshold and the target driving force. As shown in FIG. 7, the speed difference threshold to be compared with the front-rear rotation difference is set larger as the target driving force during acceleration increases. The speed difference threshold increases or decreases according to the target driving force, and is set within a range of, for example, several rpm to several tens of rpm.

As described above, when it is determined that the driving force on the negative side acts on the front wheels 22 or the rear wheels 26 based on the front-rear rotation difference and the target driving force, the flow chart shown in FIG. From step S18 to step S19, the transfer clutch 15 is controlled from the engaged state to the disengaged state. Thus, by disengaging the transfer clutch 15 and separating the front and rear wheels 22, 26, the generation of internal circulation torque can be stopped, and the energy efficiency of the vehicle 11 can be enhanced to improve the fuel efficiency. Furthermore, by stopping the generation of internal circulating torque, it is possible to eliminate excessive torsion of various rotating shafts, etc., and to prevent abnormal noise from occurring in the drive system.

In the above description, since the tire sizes of the front wheels 22 and the rear wheels 26 are the same, when the rotational speed difference between the front wheels 22 and the rear wheels 26 exceeds the speed difference threshold, the transfer clutch 15 is released from the engaged state. Although it is controlled in a released state, it is not limited to this. For example, the input rotational speed Ni of the transfer clutch 15 interlocked with the rotational speed NF of the front wheels 22 and the output rotational speed No of the transfer clutch 15 interlocked with the rotational speed NR of the rear wheels 26 may be used. That is, when the rotational speed difference between the input rotational speed Ni and the output rotational speed No exceeds the speed difference threshold value, that is, the rotational speed difference between the input side (one side) and the output side (other side) of the transfer clutch 15 is the speed difference. When the threshold value is exceeded, the transfer clutch 15 may be controlled from the engaged state to the disengaged state. As described above, even when the rotational speed difference between the input side and the output side of the transfer clutch 15 is used, the rotational speed difference between the input side and the output side of the transfer clutch 15 is calculated as in the example shown in FIG. is set larger as the target driving force during acceleration increases.

In the above description, the front wheels 22 and the rear wheels 26 have the same tire size. However, the present invention is not limited to this. , the present invention can be effectively applied. That is, even if the tire sizes of the front wheels 22 and the rear wheels 26 are different from each other, the gear train 18 and the differential gear are arranged so that the input rotation speed Ni and the output rotation speed No of the transfer clutch 15 match each other when traveling straight ahead. The gear ratios of mechanisms 20, 24 are designed. That is, even if the tire sizes of the front wheels 22 and the rear wheels 26 are different from each other, if the rotational speed of one of the front wheels 22 or the rear wheels 26 increases due to a decrease in the air pressure of the front wheels 22 or the rear wheels 26, the input rotational speed Ni and the An increase in the rotation speed difference from the output rotation speed No appears. Therefore, when the rotational speed difference between the input rotational speed Ni and the output rotational speed No exceeds the speed difference threshold, that is, when the rotational speed difference between the input side and the output side of the transfer clutch 15 exceeds the speed difference threshold, the transfer By controlling the clutch 15 from the engaged state to the disengaged state, the generation of internal circulation torque can be avoided.

Further, in the example shown in FIG. 1, the transfer clutch 15 that transmits the driving force toward the rear wheels 26 is provided, but the present invention is not limited to this, and the transfer clutch that transmits the driving force toward the front wheels 22 is provided. 50 may be provided. Here, FIGS. 8A and 8B are diagrams simply showing the positions of the transfer clutches 15 and 50. FIG. As shown in FIG. 8A, the transfer clutch 15 may be provided between the speed change output shaft 17 and the rear wheel output shaft 23, or may be provided between the front wheel output shaft 19 and the rear wheel output shaft 23. Also good. Further, as shown in FIG. 8B, a transfer clutch (clutch) 50 may be provided between the transmission output shaft 17 and the front wheel output shaft 19, and the front wheel output shaft 19 and the rear wheel output shaft 23 may be connected. You can set it in between. Thus, even when the transfer clutches 15, 50 are arranged, the difference in rotational speed between the front wheel 22 and the rear wheel 26 can be limited by engaging the transfer clutches 15, 50. By disengaging 50, the rotational speed difference between the front wheels 22 and the rear wheels 26 can be allowed.

[Other embodiments]
In the above description, the transfer clutches 15 and 50 provided between the front wheels 22 and the rear wheels 26 are used as the clutches for limiting the rotational speed difference between the front wheels 22 and the rear wheels 26, but this is not the only option. Alternatively, a differential limiting clutch 61 provided in the center differential mechanism 60 between the front wheels 22 and the rear wheels 26 may be used as the clutch for limiting the rotational speed difference between the front wheels 22 and the rear wheels 26 . Here, FIG. 9 is a diagram showing a configuration example of a vehicle 11 provided with a vehicle drive system 62 according to another embodiment of the present invention. 10A to 10C are diagrams simply showing the positions of the differential limiting clutches 61, 70, 71. FIG. In FIGS. 9 and 10, parts similar to those shown in FIGS. 1 and 8 are given the same reference numerals, and descriptions thereof are omitted.

As shown in FIG. 9 , the transmission 13 is provided with a center differential mechanism (differential mechanism) 60 that distributes driving force to the front wheels 22 and the rear wheels 26 . The compound planetary gear type center differential mechanism 60 includes a first sun gear 63 connected to the transmission output shaft 17, a second sun gear 64 connected to the rear wheel output shaft 23, and a front wheel output shaft 19 via a gear train 65. and a carrier 66 coupled to the carrier 66 . A carrier 66 of the center differential mechanism 60 rotatably supports a pinion 67 that meshes with the first and second sun gears 63 and 64 . By providing the center differential mechanism 60 between the front wheels 22 and the rear wheels 26, the driving force can be distributed between the front wheels 22 and the rear wheels 26 at a predetermined torque distribution ratio.

Further, the center differential mechanism 60 is provided with a limited differential clutch (clutch) 61 that limits the rotation of the pinion 67 . By controlling the differential limiting clutch 61 to be engaged, the differential rotation of the center differential mechanism 60 is limited and the rotational speed difference between the front wheels 22 and the rear wheels 26 is limited. On the other hand, by controlling the differential limiting clutch 61 to the released state, differential rotation of the center differential mechanism 60 is permitted, and a rotational speed difference between the front wheels 22 and the rear wheels 26 is permitted. Also, by controlling the engagement force of the differential limiting clutch 61, which is a friction clutch, the torque distribution ratio between the front wheels 22 and the rear wheels 26 is adjusted while limiting the rotational speed difference between the front wheels 22 and the rear wheels 26. can do In other words, the engagement state of the differential limiting clutch 61 includes the slip state.

As described above, even when the limited differential clutch 61 provided in the center differential mechanism 60 is used as the clutch for limiting the rotational speed difference between the front wheels 22 and the rear wheels 26, the above-described vehicle drive device 10 can function in the same way as That is, when the difference in rotational speed between the front wheels 22 and the rear wheels 26 exceeds the speed difference threshold during acceleration while the limited differential clutch 61 is controlled to be in the engaged state, the limited differential clutch 61 is changed from the engaged state to the released state. controlled. By disengaging the differential limiting clutch 61 and allowing the rotational speed difference between the front and rear wheels 22 and 26 in this manner, the generation of internal circulation torque can be stopped, and the energy efficiency of the vehicle 11 can be enhanced. . Furthermore, by stopping the generation of internal circulating torque, it is possible to eliminate excessive torsion of various rotating shafts, etc., and to prevent abnormal noise from occurring in the drive system. Also, when the rotational speed difference between the input side (one side) and the output side (other side) of the differential limiting clutch 61 exceeds the speed difference threshold during acceleration while the differential limiting clutch 61 is controlled to be in the engaged state. , the limited differential clutch 61 may be controlled from the engaged state to the disengaged state.

Here, FIGS. 10A to 10C are diagrams simply showing the positions of the differential limiting clutches 61, 70, 71. FIG. As a differential limiting clutch for limiting the rotational speed difference between the front wheels 22 and the rear wheels 26, as shown in FIG. It may be the clutch 61, or, as shown in FIG. 10(B), it may be a limited differential clutch 70 provided between the transmission output shaft 17 and the rear wheel output shaft 23, as shown in FIG. 10(C). 2, a limited differential clutch 71 provided between the transmission output shaft 17 and the front wheel output shaft 19 may be used. As described above, even when the differential limiting clutches 61, 70, 71 are provided in the center differential mechanism 60, the rotation of the front wheel 22 and the rear wheel 26 is prevented by engaging the differential limiting clutches 61, 70, 71. The speed difference can be limited, and the rotational speed difference between the front wheels 22 and the rear wheels 26 can be allowed by releasing the differential limiting clutches 61 , 70 , 71 .

It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. In the above description, hydraulic clutches controlled by hydraulic pressure are used as the transfer clutches 15, 50 and differential limiting clutches 61, 70, 71. A clutch may be used. Further, in the above description, an automatic transmission is exemplified as the transmission mechanism 16, but it is not limited to this, and a transmission mechanism such as a manual transmission or a continuously variable transmission may be provided. In the example shown in FIG. 2, clutch release control is executed in all vehicle speed ranges, but the present invention is not limited to this, and clutch release control is executed in a high vehicle speed range where internal circulation torque tends to increase. can be

In the above description, the engine 12 is used as the power source of the power train 14, but the power source is not limited to this, and an electric motor may be used as the power source. In the above description, a compound planetary gear type differential mechanism is used as the center differential mechanism 60. However, the present invention is not limited to this, and a simple planetary gear type differential mechanism or a bevel gear type differential mechanism may be used. It may be a mechanism.

10 vehicle driving device 11 vehicle 15 transfer clutch (clutch)
22 front wheel 26 rear wheel 33 clutch control unit 50 transfer clutch (clutch)
60 center differential mechanism (differential mechanism)
61 limited differential clutch (clutch)
62 vehicle drive device 70 limited differential clutch (clutch)
71 limited differential clutch (clutch)
Na1, Nb1, Na2, Nb2 Speed difference threshold TF, TF1, TF2 Target driving force b1 Threshold (resistance threshold)
c1 threshold (rudder angle threshold)
d1 threshold (acceleration threshold)

Claims (7)

A vehicle driving device for driving front wheels and rear wheels,
a clutch that is controlled into an engaged state that limits the rotational speed difference between the front wheels and the rear wheels and a disengaged state that allows the rotational speed difference between the front wheels and the rear wheels;
a clutch control unit that controls the clutch from the engaged state to the released state when the rotational speed difference between the front wheels and the rear wheels exceeds a speed difference threshold during acceleration while the clutch is controlled to the engaged state;
has
The speed difference threshold is set larger as the target driving force during acceleration increases.
Vehicle drive. In the vehicle drive system according to claim 1,
When the rotational speed difference between the front wheels and the rear wheels exceeds the speed difference threshold under the condition that the road surface resistance exceeds the resistance threshold during acceleration while the clutch is controlled to be in an engaged state, the clutch control unit and controlling the clutch from the engaged state to the disengaged state;
Vehicle drive. 3. In the vehicle drive system according to claim 1,
The clutch control unit controls the rotational speed difference between the front wheels and the rear wheels to exceed the speed difference threshold under a condition in which the steering angle is less than the steering angle threshold during acceleration while the clutch is controlled to be in an engaged state. controlling the clutch from the engaged state to the disengaged state when exceeding
Vehicle drive. In the vehicle drive device according to any one of claims 1 to 3,
When the clutch is controlled to be in an engaged state during acceleration, the clutch control unit detects a rotational speed difference between the front wheels and the rear wheels as a speed difference threshold under a condition in which acceleration in the vehicle width direction falls below an acceleration threshold. controlling the clutch from the engaged state to the disengaged state when exceeding
Vehicle drive. In the vehicle drive device according to any one of claims 1 to 4,
The clutch is a transfer clutch provided between the front wheel and the rear wheel,
Vehicle drive. In the vehicle drive device according to any one of claims 1 to 4,
The clutch is a limited differential clutch provided in a differential mechanism between the front wheel and the rear wheel,
Vehicle drive. A vehicle driving device for driving front wheels and rear wheels,
a clutch that is controlled into an engaged state that limits the rotational speed difference between the front wheels and the rear wheels and a disengaged state that allows the rotational speed difference between the front wheels and the rear wheels;
a clutch control unit that controls the clutch from the engaged state to the released state when a rotational speed difference between one side and the other side of the clutch exceeds a speed difference threshold during acceleration while the clutch is controlled to be in the engaged state; ,
has
The speed difference threshold is set larger as the target driving force during acceleration increases.
Vehicle drive.

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