Front and rear drive force distribution device for all-wheel drive vehicles

Abstract

To provide a front / rear drive force distribution device of an all wheel drive vehicle which prevents a main drive wheel from becoming a minus torque without lowering a precharge pressure of a transfer clutch in a travel state where front / rear rotation difference is generated at the time of driving, and a transfer input torque is less than a fastening torque, and can prevent deterioration of fuel consumption and drivability.SOLUTION: A front / rear drive force distribution device 1 includes: a one-way clutch 51 which transmits a drive torque input to a front drive shaft 43 side from a secondary shaft 37 side, and shuts off a coast torque input to the secondary shaft 37 side from the front drive shaft 43 side; and a connection / disconnection mechanism 52 which is arranged between the secondary shaft 37 and the transfer clutch 41, and connects / disconnects torque transmission between the front drive shaft 43 and a rear wheel transmission shaft 39. The connection / disconnection mechanism 52 is released when the drive torque is input, and is fastened when the coast torque is input.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a front-rear driving force distribution device for an all-wheel drive vehicle. [Background technology]

[0002] All-wheel drive (AWD) vehicles (or four-wheel drive (4WD) vehicles) that can distribute torque (driving force) to all (four) wheels and have excellent off-road performance and driving stability have been widely used. One known all-wheel drive vehicle is a so-called torque-split all-wheel drive vehicle that has primary drive wheels to which engine torque or the like is directly transmitted and secondary drive wheels to which engine torque or the like is transmitted via a transfer clutch, and that adjusts the distribution of driving force to the secondary drive wheels by controlling the fastening force of the transfer clutch according to the driving conditions, etc. (See, for example, Patent Document 1).

[0003] In a torque-split all-wheel drive vehicle, for example, when the main drive wheels (e.g., front wheels) slip, the fastening force of the transfer clutch is increased and torque distribution to the secondary drive wheels (e.g., rear wheels) is increased so that the differential rotation between the main drive wheels and the secondary drive wheels (e.g., rear wheels) is eliminated. Also, in a torque-split all-wheel drive vehicle, for example, a pre-charge pressure (preload) is constantly applied to the transfer clutch to improve response during driving, so that the torque transmitted to the rear wheels does not become zero. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-338456 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, when cornering at low vehicle speed and low torque, the front wheel rotation speed is greater than the rear wheel rotation speed due to the difference between the inside and outside wheels. In such a driving state, if the input torque of the transfer clutch is less than the engagement torque of the transfer clutch, the rear wheel torque is equal to the transfer clutch engagement torque, and torque flows from the faster front wheels to the rear wheels, resulting in negative torque at the front wheels. This negative front wheel torque during driving can lead to a deterioration in fuel economy and drivability (a feeling of being pushed out from the rear wheels when the front wheels are braked (uncomfortable feeling)).

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide a front / rear driving force distribution device for an all-wheel drive vehicle that can prevent the main drive wheel with a faster rotation speed from becoming negative torque without lowering the pre-charge pressure of the transfer clutch in a driving condition in which a front / rear rotation difference occurs during driving, such as when cornering at low vehicle speeds and with low torque, and the "input torque of the transfer clutch < the engagement torque of the transfer clutch" (a driving condition in which the main drive wheel with a faster rotation speed may become negative torque), thereby preventing a deterioration in fuel economy and drivability (causing the driver to feel uncomfortable) [Means for solving the problem]

[0007] A front / rear driving force distribution device for an all-wheel drive vehicle according to one aspect of the present invention is provided with a driving force transmission shaft connected to a driving force source so as to be torque transmissible and which transmits the driving force output from the driving force source, a main driving wheel transmission shaft connected to the driving force transmission shaft so as to be torque transmissible and which transmits the driving force transmitted by the driving force transmission shaft to main driving wheels, a subordinate driving wheel transmission shaft connected to the driving force transmission shaft so as to be torque transmissible and which transmits the driving force transmitted by the driving force transmission shaft to subordinate driving wheels, and a transfer clutch which adjusts the driving force transmitted by the subordinate driving wheel transmission shaft to the subordinate driving wheels in accordance with a fastening force. The driving force distribution device comprises a one-way clutch provided on a main drive wheel transmission shaft, which transmits drive torque, which is the driving force input from the drive force transmission shaft side to the main drive wheel transmission shaft side, and cuts off coast torque, which is the driving force input from the main drive wheel transmission shaft side to the drive force transmission shaft side, and a disconnecting mechanism disposed between the drive force transmission shaft and the transfer clutch, which connects and disconnects torque transmission between the main drive wheel transmission shaft and the slave drive wheel transmission shaft, the disconnecting mechanism being disengaged when driving, in which drive torque is input, and connected when coasting, in which coast torque is input. [Effects of the Invention]

[0008] According to the present invention, in a torque split all-wheel drive vehicle, for example, when cornering at low vehicle speeds and low torque, a front-rear rotation difference occurs during driving, and in a driving condition where the "input torque of the transfer clutch < the engagement torque of the transfer clutch" occurs (a driving condition in which the main drive wheel with a faster rotation speed may experience negative torque), it is possible to prevent the main drive wheel with a faster rotation speed from experiencing negative torque without lowering the pre-charge pressure of the transfer clutch, thereby preventing deterioration in fuel economy and drivability (which would cause the driver to feel uncomfortable). [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing an overall configuration of a front-rear driving force distribution device for an all-wheel drive vehicle according to an embodiment, and an all-wheel drive vehicle equipped with the front-rear driving force distribution device; [Figure 2]1 is an enlarged view showing a main part of a front / rear driving force distribution device for an all-wheel drive vehicle according to an embodiment of the present invention; [Figure 3] 1 is a diagram showing a state of a front / rear driving force distribution device for an all-wheel drive vehicle according to an embodiment when coasting; [Figure 4] 1 is a diagram showing a state of the front and rear driving force distribution device for an all-wheel drive vehicle according to an embodiment when the vehicle is driving (when transfer input torque<engagement torque). FIG. [Figure 5] 1 is a diagram showing a state of the front and rear driving force distribution device for an all-wheel drive vehicle according to an embodiment when the vehicle is driving (when transfer input torque>engagement torque). FIG. [Figure 6] FIG. 4 is a diagram showing the relationship between transfer input torque and front and rear torque (front wheel torque, rear wheel torque). DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be designated by the same reference numerals. In addition, the same elements will be designated by the same reference numerals in each drawing, and redundant explanations will be omitted.

[0011] First, the configuration of a front / rear driving force distribution device 1 for an all-wheel drive vehicle according to an embodiment will be described using Figures 1 and 2. Figure 1 is a diagram showing the overall configuration of the front / rear driving force distribution device 1 for an all-wheel drive vehicle and an all-wheel drive (AWD) vehicle 4 equipped with the front / rear driving force distribution device 1. Figure 2 is an enlarged view showing the main parts of the front / rear driving force distribution device 1 for an all-wheel drive vehicle.

[0012] The engine 20 (corresponding to the driving force source described in the claims) may be of any type, but may be, for example, a horizontally opposed, direct-injection, four-cylinder gasoline engine. In the engine 20, air drawn in through an air cleaner (not shown) is throttled by an electronically controlled throttle valve (hereinafter simply referred to as a "throttle valve") 85 provided in an intake pipe, passes through an intake manifold, and is drawn into each cylinder formed in the engine 20. The amount of air drawn in through the air cleaner is detected by an air flow meter. Furthermore, the throttle valve 85 is provided with a throttle opening sensor 83 that detects the opening of the throttle valve 85. Each cylinder is equipped with an injector that injects fuel. Each cylinder is also equipped with a spark plug that ignites the air-fuel mixture and a built-in igniter coil that applies high voltage to the spark plug. In each cylinder of the engine 20, the mixture of the drawn air and the fuel injected by the injector is ignited by the spark plug and combusted. After combustion, the exhaust gas is discharged through an exhaust pipe.

[0013] In addition to the air flow meter and throttle opening sensor 83 described above, a cam angle sensor 81 for identifying the cylinders of the engine 20 is attached near the camshaft of the engine 20. A crank angle sensor 82 for detecting the position of the crankshaft is also attached near the crankshaft of the engine 20. These sensors are connected to an engine control unit (hereinafter referred to as "ECU") 80. Also connected to the ECU 80 are various sensors such as an accelerator opening sensor 84 for detecting the amount of depression of the accelerator pedal, i.e., the opening of the accelerator pedal, and a water temperature sensor for detecting the temperature of the cooling water for the engine 20.

[0014] An output shaft (crankshaft) 21 of the engine 20 is connected to a torque converter 22 having a clutch function and a torque amplification function, and a continuously variable transmission 30 that converts and outputs the driving force from the engine 20 via a forward / reverse switching mechanism 27.

[0015] The torque converter 22 is mainly composed of a pump impeller 23, a turbine runner 24, and a stator 25. The pump impeller 23 connected to the output shaft 21 generates a flow of oil, and the turbine runner 24, which is disposed opposite the pump impeller 23, receives power from the engine 20 via the oil to drive the output shaft. The stator 25, located between the two, rectifies the discharge flow (return) from the turbine runner 24 and returns it to the pump impeller 23, thereby generating torque amplification.

[0016] Torque converter 22 also has a lock-up clutch 26 that directly couples the input and output. When lock-up clutch 26 is not engaged (in a non-lock-up state), torque converter 22 amplifies the driving force of engine 20 and transmits it to continuously variable transmission 30, and when lock-up clutch 26 is engaged (in a lock-up state), torque converter 22 directly transmits the driving force of engine 20 to continuously variable transmission 30. The rotation speed (turbine rotation speed) of turbine runner 24 that constitutes torque converter 22 is detected by a turbine rotation sensor 94. The detected turbine rotation speed is output to a transmission control unit (hereinafter referred to as "TCU") 70.

[0017] The forward / reverse switching mechanism 27 switches between forward and reverse rotation (forward and reverse movement of the vehicle) of the drive wheels 10 (left front wheel 10FL, right front wheel 10FR, left rear wheel 10RL, right rear wheel 10RR). The forward / reverse switching mechanism 27 mainly includes a double-pinion planetary gear train, a forward clutch (forward clutch) 28, and a reverse brake (reverse brake) 29. The forward / reverse switching mechanism 27 is configured to be able to switch the transmission path of the engine driving force by controlling the respective states of the forward clutch 28 and the reverse brake 29.

[0018] More specifically, when the D (drive) range is selected, the rotation of the turbine shaft 31 is transmitted directly to the primary shaft 32 (described later) by engaging the forward clutch 28 and disengaging the reverse brake 29, allowing the vehicle to travel forward. On the other hand, when the R (reverse) range is selected, the planetary gear train is operated by disengaging the forward clutch 28 and engaging the reverse brake 29, thereby reversing the rotation direction of the primary shaft 32 and allowing the vehicle to travel backward.

[0019] Furthermore, when the N (neutral) range or P (parking) range is selected, the forward clutch 28 and the reverse brake 29 are released, thereby separating the turbine shaft 31 from the primary shaft 32 (the transmission of engine driving force is interrupted), and the forward / reverse switching mechanism 27 is in a neutral state in which it does not transmit power to the primary shaft 32. The operations of the forward clutch 28 and the reverse brake 29 are controlled by the TCU 70 and the valve body (control valve) 60.

[0020] The continuously variable transmission 30 has a primary shaft 32 connected to a turbine shaft 31 of the torque converter 22 via the forward / reverse switching mechanism 27, and a secondary shaft 37 disposed in parallel to the primary shaft 32. The turbine shaft 31, primary shaft 32, and secondary shaft 37 correspond to the driving force transmission shafts described in the claims.

[0021] A primary pulley 34 is provided on the primary shaft 32. The primary pulley 34 has a fixed pulley 34a joined to the primary shaft 32 and a movable pulley 34b mounted opposite the fixed pulley 34a so as to be slidable in the axial direction of the primary shaft 32, and is configured so that the cone surface spacing between the pulleys 34a, 34b, i.e., the pulley groove width, can be changed. Meanwhile, a secondary pulley 35 is provided on the secondary shaft 37. The secondary pulley 35 has a fixed pulley 35a joined to the secondary shaft 37 and a movable pulley 35b mounted opposite the fixed pulley 35a so as to be slidable in the axial direction of the secondary shaft 37, and is configured so that the pulley groove width can be changed.

[0022] A chain 36 that transmits driving force is stretched between the primary pulley 34 and the secondary pulley 35. The gear ratio is continuously changed by changing the groove width of the primary pulley 34 and the secondary pulley 35 to change the ratio of the winding diameter of the chain 36 to each of the pulleys 34, 35 (pulley ratio). Here, if the winding diameter of the chain 36 around the primary pulley 34 is Rp and the winding diameter around the secondary pulley 35 is Rs, the gear ratio i is expressed as i = Rs / Rp. Therefore, the gear ratio i can be calculated by dividing the primary pulley rotation speed Np by the secondary pulley rotation speed Ns (i = Np / Ns).

[0023] Here, a hydraulic chamber 34c is formed in the primary pulley 34 (movable pulley 34b). On the other hand, a hydraulic chamber 35c is formed in the secondary pulley 35 (movable pulley 35b). The groove widths of the primary pulley 34 and the secondary pulley 35 are set or changed by adjusting the primary hydraulic pressure introduced into the hydraulic chamber 34c of the primary pulley 34 and the secondary hydraulic pressure introduced into the hydraulic chamber 35c of the secondary pulley 35.

[0024] The secondary shaft 37 of the continuously variable transmission 30 is connected to a front drive shaft 43 (corresponding to the main drive wheel transmission shaft described in the claims) via a reduction gear 38 consisting of a pair of gears (reduction drive gear 38a and reduction driven gear 38b) and a disconnecting mechanism 52 described later.

[0025] The driving force output to the secondary shaft 37 is transmitted to a front differential (hereinafter also referred to as "front diff") 44 via a reduction gear 38, a connecting / disconnecting mechanism 52 (described later), and a front drive shaft 43. The front differential 44 is, for example, a bevel gear type differential device. The driving force from the front differential 44 is transmitted to a left front wheel 10FL via a left front wheel drive shaft 45L, and to a right front wheel 10FR via a right front wheel drive shaft 45R. The left front wheel 10FL and the right front wheel 10FR correspond to the main drive wheels recited in the claims.

[0026] Here, the reduction driven gear 38b incorporates a one-way clutch 51 and a disengagement mechanism 52 that constitute the front / rear driving force distribution device 1. The one-way clutch 51 and the disengagement mechanism 52 will be described in detail later.

[0027] Further, a rear wheel transmission shaft 39 is connected to the reduction driven gear 38b via a connecting / disconnecting mechanism 52, and the rear end of the rear wheel transmission shaft 39 is connected to a propeller shaft 46 extending rearward of the vehicle via a transfer gear 42 consisting of a pair of gears (transfer drive gear, transfer driven gear). The rear wheel transmission shaft 39 and the propeller shaft 46 correspond to the driven wheel transmission shafts described in the claims.

[0028] A transfer clutch 41 is provided on the propeller shaft 46 to adjust the driving force transmitted to the rear differential 47. The transfer clutch 41 controls the engagement force (i.e., the torque distribution ratio to the rear wheels 10RL, 10RR) in accordance with the driving state of the four wheels (for example, the slip state of the front wheels 10FL, 10FR), engine torque, etc. Therefore, the driving force adjusted (distributed) by the transfer clutch 41 is transmitted to the rear differential 47 via the propeller shaft 46.

[0029] A left rear wheel drive shaft 48L and a right rear wheel drive shaft 48R are connected to the rear differential 47. Driving force from the rear differential 47 is transmitted to the left rear wheel 10RL via the left rear wheel drive shaft 48L and to the right rear wheel 10RR via the right rear wheel drive shaft 48R. The left rear wheel 10RL and the right rear wheel 10RR correspond to the driven wheels recited in the claims.

[0030] The front / rear driving force distribution device 1 for an all-wheel drive vehicle has a function of preventing the front wheels 10FL and 10FR, which have a faster rotation speed, from becoming negative torque without reducing the pre-charge pressure of the transfer clutch 41 in a driving state in which a front / rear rotation difference occurs during driving, such as during low-speed, low-torque cornering, resulting in "input torque of the transfer clutch 41 < engagement torque of the transfer clutch 41" (a driving state in which the front wheels 10FL and 10FR, which have a faster rotation speed, may become negative torque), thereby preventing a deterioration in fuel economy and drivability (a feeling of discomfort to the driver). Note that "input torque of the transfer clutch 41 = input torque of the continuously variable transmission 30 × torque ratio of the torque converter 22 × gear ratio × reduction gear ratio." Furthermore, when the front / rear rotation difference is "front wheels > rear wheels," such as during steering, "front wheel torque = input torque of the transfer clutch 41 - engagement torque of the transfer clutch 41" holds.

[0031] Therefore, the front / rear driving force distribution device 1 for an all-wheel drive vehicle mainly includes a one-way clutch 51 and a connecting / disconnecting mechanism (dog clutch) 52.

[0032] 2, the one-way clutch 51 is attached to one side surface of the reduction driven gear 38b (front drive shaft 43). For example, a cylindrical portion extending in the axial direction is formed on one side surface of the reduction driven gear 38b, and the one-way clutch 51 is incorporated inside the cylindrical portion. As the one-way clutch 51, for example, a known type such as a roller type, a cam type, or a sprag type can be used.

[0033] One-way clutch 51 transmits the driving force (torque) from secondary shaft 37 in one direction to front drive shaft 43. In other words, one-way clutch 51 transmits drive torque, which is the driving force (torque) input (transmitted) from secondary shaft 37 to front drive shaft 43, and blocks coast torque, which is the driving force (torque) input (transmitted) from front drive shaft 43 to secondary shaft 37, without transmitting it.

[0034] The disengagement mechanism (dog clutch) 52 is disposed on the other side surface of the reduction driven gear 38b (between the front drive shaft 43 and the transfer clutch 41). For example, a cylindrical portion extending in the axial direction is formed on the other side surface of the reduction driven gear 38b, and the disengagement mechanism 52 is incorporated inside the cylindrical portion. The disengagement mechanism 52 engages and disengages (releases / engages) torque transmission between the front drive shaft 43 and the rear wheel transmission shaft 39 and secondary shaft 37.

[0035] The disconnecting mechanism 52 is released during driving when drive torque is input (transmitted), that is, when drive force (torque) is input (transmitted) from the secondary shaft 37 side to the front drive shaft 43 and rear wheel transmission shaft 39 side. In other words, the front drive shaft 43 is disconnected from the rear wheel transmission shaft 39 and secondary shaft 37.

[0036] On the other hand, the disconnecting mechanism 52 is connected (fastened) when coasting (when coasting with the accelerator pedal released) in which coasting torque is input (transmitted), that is, when driving force (torque) is input (transmitted) from the front drive shaft 43 and rear wheel transmission shaft 39 side to the secondary shaft 37 side. In other words, the front drive shaft 43 is connected to the rear wheel transmission shaft 39 and secondary shaft 37.

[0037] More specifically, the disconnecting mechanism 52 is mainly composed of a sleeve 521, a torque cam 522, and a return spring 523 (corresponding to the biasing member described in the claims).

[0038] The sleeve 521 is formed in a cylindrical shape that can be fitted onto the external splines formed on the outer periphery of the end (synchronizer ring) of the front drive shaft 43 and the external splines formed on the outer periphery of the end (synchronizer ring) of the rear wheel transmission shaft 39, and has internal splines that extend in the axial direction along its inner circumferential surface. The sleeve 521 is configured to be slidable in the axial direction on the outer peripheries of the external splines formed on the outer periphery of the end of the front drive shaft 43 and the external splines formed on the outer periphery of the end of the rear wheel transmission shaft 39.

[0039] The front drive shaft 43 and the rear wheel transmission shaft 39 are arranged coaxially (on the same straight line), and one opening of the sleeve 521 can be spline-fitted with the front drive shaft 43, and the other opening is (always) spline-fitted with the rear wheel transmission shaft 39. The sleeve 521 switches (intermittently connects and disconnects) the connection state between the front drive shaft 43 and the rear wheel transmission shaft 39 and the secondary shaft 37 by moving in the axial direction (depending on the position).

[0040] The torque cam 522 slides the sleeve 521 in the axial direction, switching (connecting and disconnecting) the state of connection between the front drive shaft 43 and the rear wheel transmission shaft 39 and secondary shaft 37. For example, the torque cam 522 has a tapered surface that converts a circumferential differential movement into an axial movement (advancing or retreating) of the cam (ball) 522a, and during driving when drive torque is input (transmitted), the cam (ball) 522a is pushed out in the axial direction, causing the sleeve 521 to slide toward the rear wheel transmission shaft 39, thereby disconnecting the front drive shaft 43 from the rear wheel transmission shaft 39 and secondary shaft 37 (releasing the connection / disconnection mechanism 52).

[0041] On the other hand, when coasting and coast torque is input (transmitted), the torque cam 522 connects (fastens) the front drive shaft 43 to the rear wheel transmission shaft 39 and the secondary shaft 37 (fastens the disconnection mechanism 52) without pushing out the cam (ball) 522a (i.e., without sliding the sleeve 521).

[0042] The return spring 523 applies a biasing force to the sleeve 521 in a direction to connect the front drive shaft 43 with the rear wheel transmission shaft 39 and the secondary shaft 37 (a direction to fasten the disconnection mechanism 52). Therefore, when coasting and coasting torque is input (transmitted) (i.e., when the cam (ball) 522a is not pushed out), the biasing force of the return spring 523 causes the sleeve 521 to slide toward the front drive shaft 43, and the front drive shaft 43 is connected (fastened) with the rear wheel transmission shaft 39 and the secondary shaft 37 (the disconnection mechanism 52 is fastened).

[0043] Next, the operation of the front and rear driving force distribution device 1 of an all-wheel drive vehicle will be described with reference to Figures 3 to 6. Figure 3 is a diagram showing the state of the front and rear driving force distribution device 1 of an all-wheel drive vehicle when coasting. Figure 4 is a diagram showing the state of the front and rear driving force distribution device 1 of an all-wheel drive vehicle when driving (when transfer input torque < engagement torque). Figure 5 is a diagram showing the state of the front and rear driving force distribution device 1 of an all-wheel drive vehicle when driving (when transfer input torque > engagement torque). Figure 6 is a diagram showing the relationship between transfer input torque and front and rear torque (front wheel torque, rear wheel torque).

[0044] During coasting when coasting torque is input (transmitted) (when transfer input torque is in the coasting direction), as shown in FIG. 3, cam 522a is not pushed out (torque cam 522 is not activated), and sleeve 521 is pushed toward front drive shaft 43 by the biasing force of return spring 523, thereby engaging and disengaging mechanism 52. In other words, front drive shaft 43 is connected to rear wheel transmission shaft 39 and secondary shaft 37. Then, as shown by the dashed line in FIG. 3, coasting torque is transmitted via front drive shaft 43 and disengaging mechanism 52. Therefore, engine braking torque can be transmitted (see area (1) in FIG. 6).

[0045] During driving when drive torque is input (transmitted) (when transfer input torque is in the drive direction) and when "transfer input torque < fastening torque," as shown in Fig. 4, the drive torque causes differential movement between reduction driven gear 38b and the flange portion of sleeve 521, causing torque cam 522 to operate (circumferential force is converted into axial force by cam 522a), pushing cam 522a out in the axial direction, causing sleeve 521 to slide toward rear wheel transmission shaft 39, and disengaging mechanism 52. In other words, front drive shaft 43 is disconnected from rear wheel transmission shaft 39 and secondary shaft 37.

[0046] Therefore, as shown by the dashed line in Figure 4, the drive torque is transmitted to the propeller shaft 46 (rear wheels 10RL, 10RR) via the connection / disconnection mechanism 52 and the rear wheel transmission shaft 39. Here, the front drive shaft 43 and the rear wheel transmission shaft 39 are disconnected, and when the "transfer input torque < connection torque," the one-way clutch 51 spins idly (≒ 0 Nm), thereby blocking the flow of torque from the front wheels 10FL, 10FR to the rear wheels 10RL, 10RR. This prevents the front wheels 10FL, 10FR from experiencing negative torque (see area (2) in Figure 6).

[0047] During driving (when the transfer input torque is in the drive direction), as described above, the disconnecting mechanism 52 is released, and the front drive shaft 43 is disconnected from the rear wheel transmission shaft 39 and the secondary shaft 37. When the "transfer input torque > fastening torque," as shown by the dashed lines in Figure 5, the drive torque is transmitted to the rear wheels 10RL, 10RR via the disconnecting mechanism 52, the rear wheel transmission shaft 39, and the propeller shaft 46, and is also transmitted to the front wheels 10FL, 10FR via the one-way clutch 51 and the front drive shaft 43 (see area (3) in Figure 6).

[0048] As described above in detail, according to this embodiment, during coasting, the sleeve 521 is pushed toward the front drive shaft 43 by the biasing force of the return spring 523 without the cam 522a being pushed out (the torque cam 522 not being actuated), and the connecting / disconnecting mechanism 52 is engaged. In other words, the front drive shaft 43 is connected to the rear wheel transmission shaft 39 and the secondary shaft 37. Therefore, coasting torque can be transmitted via the front drive shaft 43 and the connecting / disconnecting mechanism 52. This makes it possible to transmit engine braking torque.

[0049] On the other hand, during driving (when transfer input torque<engagement torque), the drive torque causes the reduction driven gear 38b and the flange portion of the sleeve 521 to move differentially, actuating the torque cam 522 (the circumferential force is converted into an axial force by the cam 522a), pushing out the cam 522a, causing the sleeve 521 to slide toward the rear wheel transmission shaft 39, and disengaging the disengagement mechanism 52. In other words, the front drive shaft 43 is disconnected from the rear wheel transmission shaft 39 and the secondary shaft 37. Therefore, the drive torque is transmitted to the propeller shaft 46 (rear wheels 10RL, 10RR) via the disconnection mechanism 52 and the rear wheel transmission shaft 39. Here, because the front drive shaft 43 is disconnected from the rear wheel transmission shaft 39 and because the one-way clutch 51 spins idly (≈0 Nm) when "transfer input torque<engagement torque," the flow of torque from the front wheels 10FL, 10FR to the rear wheels 10RL, 10RR can be blocked. This prevents the front wheels 10FL and 10FR from becoming negative torque.

[0050] Furthermore, during driving (when the transfer input torque is greater than the engagement torque), the disconnecting mechanism 52 is released, and the front drive shaft 43 is disconnected from the rear wheel transmission shaft 39 and the secondary shaft 37. The drive torque is then transmitted to the rear wheels 10RL and 10RR via the disconnecting mechanism 52 and the rear wheel transmission shaft 39, and can also be transmitted to the front wheels 10FL and 10FR via the one-way clutch 51 and the front drive shaft 43.

[0051] As a result, in a torque split type all-wheel drive vehicle 4, for example, when cornering at low vehicle speeds and low torque, a difference in rotation between the front and rear wheels occurs during driving, and in a driving condition where the input torque of the transfer clutch 41 is less than the engagement torque of the transfer clutch 41 (a driving condition in which the front wheels 10FL, 10FR, which have a faster rotation speed, may become negative torque), it is possible to prevent the front wheels 10FL, 10FR, which have a faster rotation speed, from becoming negative torque without lowering the pre-charge pressure of the transfer clutch 41, thereby preventing a deterioration in fuel efficiency and drivability (which may cause the driver to feel uncomfortable) (and still transmit engine brake torque).

[0052] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and various modifications are possible. For example, in the above embodiments, the present invention is described as being applied to an all-wheel drive (AWD) vehicle 4 that uses an engine 20 as a driving force source, but the present invention can also be applied to, for example, an all-wheel drive hybrid vehicle (AWD-HEV) that uses an engine and an electric motor as a driving force source, or an all-wheel drive electric vehicle (AWD-BEV) that uses only an electric motor as a driving force source.

[0053] Furthermore, in the above embodiment, a dog clutch is used as the disconnecting mechanism 52, but instead of the dog clutch, for example, a multiple-plate or single-plate clutch having a facing (friction plate) may be used.

[0054] Furthermore, a synchronizing mechanism for synchronizing the rotation of the front drive shaft 43 and the sleeve 521 may be provided between the external spline formed on the end of the front drive shaft 43 and the internal spline of the sleeve 521 .

[0055] In the above embodiment, a chain-type continuously variable transmission (CVT) has been described as an example of an automatic transmission, but instead of the chain-type continuously variable transmission, for example, a belt-type continuously variable transmission or a toroidal continuously variable transmission may be used. Also, instead of the continuously variable transmission, a stepped automatic transmission (AT) or the like may be used.

[0056] Furthermore, the configuration of the driving force transmission system described above (for example, the configuration of the gear train, shafts, etc.) is an example, and is not limited to the above embodiment. [Explanation of symbols]

[0057] 1 Front and rear drive force distribution device for all-wheel drive vehicles 4 All-wheel drive (AWD) vehicles 10FL, 10FR Front wheels (main drive wheels) 10RL, 10RR rear wheels (secondary drive wheels) 20 Engine (power source) 22 Torque converter 24 Turbine runner 26 Lock-up clutch 27 Forward / reverse switching mechanism 28 Forward clutch 29 Reverse brake 30 Continuously variable transmission 32 Primary Axis 34 Primary pulley 35 Secondary pulley 36 Chain 37 Secondary Axis 38 Reduction gear 38a Reduction drive gear 38b Reduction driven gear 39 Rear wheel transmission shaft 41 Transfer clutch 43 Front drive shaft 46 Propeller shaft 51 One-way clutch 52 Dog clutch 521 Sleeve 522 Torque Cam 522a Cam (Ball) 523 Return spring (biasing member)

Claims

1. a driving force transmission shaft connected to a driving force source so as to be capable of transmitting torque and transmitting driving force output from the driving force source; a main drive wheel transmission shaft connected to the drive force transmission shaft so as to be able to transmit torque, and configured to transmit the drive force transmitted by the drive force transmission shaft to main drive wheels; a driven wheel transmission shaft connected to the driving force transmission shaft so as to be capable of transmitting torque, and configured to transmit the driving force transmitted by the driving force transmission shaft to a driven wheel; a transfer clutch that adjusts the driving force transmitted to the driven wheels by the driven drive wheel transmission shaft in accordance with a fastening force, a one-way clutch provided on the main drive wheel transmission shaft, which transmits drive torque, which is a driving force input from the drive force transmission shaft side to the main drive wheel transmission shaft side, and cuts off coast torque, which is a driving force input from the main drive wheel transmission shaft side to the drive force transmission shaft side; a connecting / disconnecting mechanism disposed between the driving force transmission shaft and the transfer clutch, for connecting / disconnecting torque transmission between the main drive wheel transmission shaft and the slave drive wheel transmission shaft, The disconnecting mechanism is released during driving when a drive torque is input, and is connected during coasting when a coast torque is input. A front and rear driving force distribution device for an all-wheel drive vehicle.

2. the disconnecting mechanism is capable of transmitting torque to the driving force transmission shaft, and includes a sleeve spline-fitted with each of the main drive wheel transmission shaft and the slave drive wheel transmission shaft, and is provided slidably in the axial direction; 2. The front-rear driving force distribution device for an all-wheel drive vehicle according to claim 1, wherein the sleeve slides toward the driven drive wheel transmission shaft during driving when drive torque is input, thereby disconnecting the main drive wheel transmission shaft from the driven drive wheel transmission shaft, and slides toward the main drive wheel transmission shaft during coasting when coast torque is input, thereby connecting the main drive wheel transmission shaft to the driven drive wheel transmission shaft.

3. 3. The front / rear driving force distribution device for an all-wheel drive vehicle according to claim 2, wherein the disconnecting mechanism includes a torque cam that, when driving and when drive torque is input, pushes a cam in the axial direction and slides the sleeve toward the driven drive wheel transmission shaft to disconnect the main drive wheel transmission shaft and the driven drive wheel transmission shaft, and, when coasting and when coasting and when coasting torque is input, slides the sleeve toward the main drive wheel transmission shaft without pushing out the cam to connect the main drive wheel transmission shaft and the driven drive wheel transmission shaft.

4. 4. The front and rear driving force distribution device for an all-wheel drive vehicle according to claim 3, wherein the disconnecting mechanism has a biasing member that applies a biasing force to the sleeve in a direction that connects the main drive wheel transmission shaft and the driving force transmission shaft.

5. the main drive wheel transmission shaft transmits driving force to the front wheels; 5. The front-rear driving force distribution device for an all-wheel drive vehicle according to claim 1, wherein the driven drive wheel transmission shaft transmits driving force to rear wheels.

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