Drive mode switching mechanism

Abstract

To switch between two-wheel drive and four-wheel drive after simplifying structure.SOLUTION: A drive mode switching mechanism comprises: a case which rotates integrally with an input shaft, and an inside space of which is formed as an oil filling space; a driven-side clutch part rotated integrally with the case in the oil filling space; a screw rotated by a driving force of a power source transmitted through an output shaft in the oil filling space, made movable in a direction to / from the output shaft, and moved in a direction separating away from the output shaft by the output shaft rotated at a specific speed higher than the input shaft; a drive-side clutch part rotated integrally with the screw in the oil filling space, and moved in a direction to / from the driven-side clutch part in response to a movement of the screw; and a transmission action part energizing the screw and the drive-side clutch part in a direction approaching the output shaft, and transmitting the driving force of the power source transmitted to the output shaft to the screw.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to the technical field of a drive mode switching mechanism for switching between two-wheel drive and four-wheel drive modes.

Background Art

[0002] For vehicles such as automobiles, there are two-wheel drive (mode) and four-wheel drive (mode) as methods for transmitting the power generated in a power source such as an engine or an electric motor to drive wheels. Two-wheel drive is a method of rotating one of the front wheels or the rear wheels by the driving force of the drive source, and four-wheel drive is a method of rotating both the front wheels and the rear wheels by the driving force of the drive source.

[0003] There is a type of vehicle that can switch between two-wheel drive and four-wheel drive (see, for example, Patent Document 1). In such a vehicle, the driving force of the drive source is transmitted to the drive wheels by a power transmission device, and a drive mode switching mechanism for switching between two-wheel drive and four-wheel drive is provided.

[0004] In such a vehicle that can switch between two-wheel drive and four-wheel drive, usually, driving is performed by two-wheel drive. However, for example, when the wheels spin during driving on a bad road such as a snowy road or a gravel road, the rotation speed difference between the front wheels and the rear wheels is detected by a sensor, the wheel spin state is detected, and based on the detection result, the drive mode switching mechanism is operated to switch from two-wheel drive to four-wheel drive.

[0005] When switching from two-wheel drive to four-wheel drive, the driving force from the drive source is transmitted to both the front wheels and the rear wheels, and even when one of the front wheels or the rear wheels is in a spinning state, a good driving state on a bad road or the like is ensured by the driving force transmitted to the other wheel.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] By the way, in a vehicle capable of switching between two-wheel drive and four-wheel drive as described above, a sensor for detecting the rotational speed difference between the front wheels and the rear wheels, each part such as a clutch operated based on the detection result of the sensor, and a control unit for controlling these parts are required, and the structure of the drive mode switching mechanism is complicated.

[0008] Therefore, an object of the present invention is to perform switching between two-wheel drive and four-wheel drive while simplifying the structure.

Means for Solving the Problems

[0009] First, the drive mode switching mechanism according to the present invention is a drive mode switching mechanism that switches between two-wheel drive and four-wheel drive, and includes an output shaft that is rotated by the driving force of a power source during two-wheel drive and four-wheel drive, an input shaft that is rotated in a state where the driving force of the power source is not transmitted during two-wheel drive, a case that rotates integrally with the input shaft and in which an internal space is formed as an oil filling space, a driven-side clutch portion that rotates integrally with the case in the oil filling space, and a driving force of the power source that is transmitted through the output shaft in the oil filling space. A screw that is rotated and is movable in a direction of approaching and separating from the output shaft, and the output shaft is moved in a direction of separating from the input shaft when the output shaft rotates at a speed higher than a certain level than the input shaft, and in the oil filling space, the screw A drive-side clutch portion that rotates integrally with the screw and is moved in a direction of approaching and separating from the driven-side clutch portion as the screw moves, and a transmission action portion that biases the screw and the drive-side clutch portion in a direction of approaching the output shaft and transmits the driving force of the power source transmitted to the output shaft to the screw. When the drive-side clutch portion is moved in a direction of approaching the driven-side clutch portion, the drive-side clutch portion and the driven-side clutch portion are engaged and switched from two-wheel drive to four-wheel drive. When the drive-side clutch portion is moved in a direction of separating from the driven-side clutch portion, the engagement between the drive-side clutch portion and the driven-side clutch portion is released and switched from four-wheel drive to two-wheel drive.

[0010] As a result, when the output shaft rotates at a speed higher than a certain level than the input shaft, the drive-side clutch portion is moved along with the screw that is moved in a direction of separating from the output shaft, so that the drive-side clutch portion and the driven-side clutch portion are engaged and switched from two-wheel drive to four-wheel drive.

Effect of the Invention

[0011] According to the present invention, when the output shaft rotates at a speed higher than a certain level than the input shaft, the driving-side clutch portion is moved along with a screw that moves in a direction away from the output shaft, so that the driving-side clutch portion and the driven-side clutch portion are engaged and switched from two-wheel drive to four-wheel drive. Therefore, it is possible to switch between two-wheel drive and four-wheel drive while simplifying the structure.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments for carrying out the drive mode switching mechanism of the present invention will be described with reference to the accompanying drawings. <Configuration of Vehicle> First, an outline of the configuration of a vehicle 100 provided with a drive mode switching mechanism 1 will be described (see FIG. 1).

[0014] Vehicle 100 is of a type capable of switching between two-wheel drive and four-wheel drive. For example, it has an engine (internal combustion engine) 101 as a drive source on the front end side, and a transmission 102 is connected to the engine 101 by a torque converter, a friction clutch, etc. not shown in the figure. In the case where the vehicle 100 is an electric vehicle, a hybrid electric vehicle, etc., a motor is provided as a drive source instead of the engine 101 or together with the engine 101.

[0015] The transmission 102 may be any of a manual transmission, an automatic transmission, or a semi-automatic transmission, and a planetary gear mechanism and an electronic control coupling 103 not shown in the figure are provided inside. In addition, a continuously variable transmission (CVT) may be used as the internal mechanism of the transmission 102.

[0016] A front differential 104 is connected to the transmission 102. Left and right front drive shafts 105 are connected to the front differential 104, and front wheels 106 are respectively connected to the front drive shafts 105. Therefore, the driving force of the engine 101 is transmitted to the front wheels 106 via the front differential 104 and the front drive shafts 105.

[0017] When the vehicle 100 is cornering, the front differential 104 absorbs the difference in the rotational speeds of the left and right front wheels 106, and the same torque is transmitted from the engine 101 to the front wheels 106.

[0018] A rear differential 107 is arranged on the rear end side of the vehicle 100. Left and right rear drive shafts 108 are connected to the rear differential 107, and rear wheels 109 are respectively connected to the rear drive shafts 108.

[0019] When the vehicle 100 is cornering, the rear differential 107 absorbs the difference in the rotational speeds of the left and right rear wheels 109, and the same torque is transmitted from the engine 101 to the rear wheels 109.

[0020] A drive mode switching mechanism 1 is arranged between the transmission 102 and the rear differential 107. The driving force transmitted from the engine 101 to the transmission 102 can be transmitted from the transmission 102 to the rear differential 107 via the drive mode switching mechanism 1. The driving force of the engine 101 transmitted to the rear differential 107 via the drive mode switching mechanism 1 is transmitted to the rear wheels 109 via the rear wheel drive shaft 108.

[0021] In the vehicle 100, normally, driving is performed by two-wheel drive, and the driving force transmitted from the engine 101 to the transmission 102 is not transmitted from the transmission 102 to the rear differential 107 via the drive mode switching mechanism 1. On the other hand, in the vehicle 100, when switching from two-wheel drive to four-wheel drive, the driving force transmitted from the engine 101 to the transmission 102 is transmitted from the transmission 102 to the rear differential 107 via the drive mode switching mechanism 1.

[0022] In addition, in the above, an example of the vehicle 100 in which front-wheel drive is performed in two-wheel drive is shown, but the vehicle 100 may be of a type in which rear-wheel drive is performed in two-wheel drive.

[0023] <Configuration of drive mode switching mechanism> The drive mode switching mechanism 1 will be described below (see FIGS. 2 and 3).

[0024] The drive mode switching mechanism 1 includes an output shaft 2 that is rotated in the axial direction by the driving force of the engine 101, an input shaft 3 that is located on the rear side of the output shaft 2 and is rotated in the axial direction, and a mechanism body 4 that is located between the output shaft 2 and the input shaft 3 and in which required components are arranged inside.

[0025] The output shaft 2 has its front end connected to the transmission 102, and the driving force of the engine 101 is transmitted to the output shaft 2 via the transmission 102. The driving force of the engine 101 is transmitted to the output shaft 2 during both two-wheel drive and four-wheel drive.

[0026] The input shaft 3 has its rear end connected to the rear differential 107 and is rotated in the axial direction along with the rotation of the rear wheels 109 during two-wheel drive. The driving force of the engine 101 is transmitted to the input shaft 3 via the output shaft 2 and the mechanism main body 4 during four-wheel drive, and the driving force of the engine 101 is not transmitted during two-wheel drive.

[0027] The mechanism main body 4 has a case 5 with the input shaft 3 connected to its rear end and various required parts arranged inside the case 5. The front end of the input shaft 3 is connected to the central part of the rear surface of the mechanism main body 4, and the mechanism main body 4 rotates integrally with the input shaft 3.

[0028] The case 5 has, for example, a cylindrical peripheral surface portion 6, a front surface portion 7 whose outer periphery is continuous with the front end portion of the peripheral surface portion 6, and a rear surface portion 8 whose outer periphery is continuous with the rear end portion of the peripheral surface portion 6. An insertion hole 7a penetrating in the front-rear direction is formed in the central part of the front surface portion 7. The internal space of the case 5 is formed as an oil-filled space 5a filled with oil 50.

[0029] A driven-side clutch portion 9 is provided on the inner surface (front surface) side of the rear surface portion 8. The driven-side clutch portion 9 has tooth portions 9a, 9a,... protruding forward from the rear surface portion 8, and the tooth portions 9a, 9a,... are spaced apart in the circumferential direction. An inclined surface is formed on the tooth portion 9a.

[0030] A support shaft 10 is rotatably supported on the front surface portion 7. The support shaft 10 has, for example, a substantially cylindrical support cylinder portion 11 extending in the front-rear direction and a connection base portion 12 attached to the front surface of the support cylinder portion 11, and the front-side opening of the support cylinder portion 11 is closed by the connection base portion 12. The diameter of the connection base portion 12 is larger than the diameter of the insertion hole 7a.

[0031] The support shaft 10 is rotatably supported by the front portion 7 with the support cylinder portion 11 inserted through the insertion hole 7a. The connection base portion 12 is located on the front side of the front portion 7, and the rear end portion of the output shaft 2 is connected to the connection base portion 12. Therefore, the support shaft 10 rotates integrally with the output shaft 2 in the axial direction, and the portion excluding the front end portion of the support cylinder portion 11 rotates in the oil filling space 5a.

[0032] A support space 13 is formed on the front side of the support cylinder portion 11, and the support space 13 is open forward in the support cylinder portion 11. An insertion space 14 is formed on the rear side of the support space 13 in the support cylinder portion 11. Spline grooves 14a, 14a extending in the front-rear direction are formed at positions 180 degrees opposite to each other in the insertion space 14 of the support cylinder portion 11. A shaft insertion hole 15 communicating with the support space 13 and the insertion space 14 is formed in the support cylinder portion 11. The diameter of the shaft insertion hole 15 is smaller than the diameters of the support space 13 and the insertion space 14. An oil flow hole 16 communicating with the support space 13 and the oil filling space 5a is formed in the support cylinder portion 11 in a state where the support shaft 10 is supported by the case 5.

[0033] A rotating body 17 is disposed in the oil filling space 5a. The rotating body 17 has a connecting shaft 18 extending in the front-rear direction, a screw 19 connected to the front end portion of the connecting shaft 18, a driving side clutch portion 20 connected to the rear end portion of the connecting shaft 18, and a spline shaft 21 protruding forward from the central portion of the screw 19.

[0034] When the screw 19 rotates in one direction, a propulsive force in the direction of moving the rotating body 17 rearward is generated. Therefore, when the screw 19 is rotated in one direction, a moving force is generated in the rotating body 17 in the direction of approaching the driven side clutch portion 9 by the driving side clutch portion 20.

[0035] The driving side clutch portion 20 has a substantially disc-shaped clutch base 20a facing in the front-rear direction and tooth portions 20b, 20b,... protruding rearward from the outer peripheral portion of the clutch base 20a, and the tooth portions 20b, 20b,... are spaced apart in the circumferential direction. An inclined surface is formed on the tooth portion 20b.

[0036] The dog clutch 22 is constituted by the driving-side clutch portion 20 and the driven-side clutch portion 9. Different from a friction clutch in which flat plates are pressed against each other and fastened by frictional force, the dog clutch 22 is fastened by engaging the inclined surfaces of the tooth portions 9a, 9a,... and the inclined surfaces of the tooth portions 20b, 20b,... with each other, and is a clutch that maintains a high fastening force.

[0037] The spline shaft 21 is provided with spline protrusions 21a, 21a that extend back and forth at positions 180 degrees opposite to each other.

[0038] The rotating body 17 has the spline shaft 21 inserted into the insertion space 14 from the rear, and the spline shaft 21 has the spline protrusions 21a, 21a inserted into the spline grooves 14a, 14a, respectively. Accordingly, the rotating body 17 is rotated integrally with the support shaft 10 and is movable in the front-rear direction with respect to the support shaft 10. Accordingly, since the support shaft 10 and the output shaft 2 are rotated integrally, the output shaft 2, the support shaft 10, and the rotating body 17 are rotated integrally.

[0039] A piston 23 is connected to the spline shaft 21. The piston 23 has a shaft portion 23a whose rear end is connected to the front end of the spline shaft 21 and a pressing plate portion 23b attached to the front end of the shaft portion 23a.

[0040] The piston 23 is inserted into the support space 13 from the insertion space 14 through the shaft insertion hole 15 in a state where the spline shaft 21 is inserted into the insertion space 14, and the pressing plate portion 23b is positioned in the support space 13.

[0041] A coil spring 24 is disposed on the rear side of the pressing plate portion 23b in the support space 13. The coil spring 24 is a compression coil spring and is pressed against the pressing plate portion 23b from the rear side. Accordingly, the biasing force of the coil spring 24 is transmitted to the rotating body 17 by the piston 23, and the rotating body 17 is biased forward.

[0042] The above-described support shaft 10, spline shaft 21, and coil spring 24 function as a transmission acting portion 25 that biases the screw 19 in a direction approaching the output shaft 2 and transmits the driving force of the engine 101 transmitted to the output shaft 2 to the screw 19.

[0043] A control valve 26 is disposed in the oil flow hole 16 of the support shaft 10. The control valve 26 controls the inflow rate of the oil 50 from the oil filling space 5a to the support space 13 and the outflow rate of the oil 50 from the support space 13 to the oil filling space 5a at different rates. Specifically, the control valve 26 controls the outflow rate of the oil 50 from the support space 13 to the oil filling space 5a to be faster than the inflow rate of the oil 50 from the oil filling space 5a to the support space 13.

[0044] <Operation of the drive mode switching mechanism> The operation of the above-described drive mode switching mechanism 1 will be described below (see FIGS. 2 to 5).

[0045] In a non-running state of the vehicle 100, the driving side clutch portion 20 is positioned in front of the driven side clutch portion 9 by the biasing force forward of the rotating body 17 by the coil spring 24, and the dog clutch 22 is in a non-engaged state.

[0046] When the vehicle 100 starts running, the driving force of the engine 101 is transmitted to the output shaft 2. The vehicle 100 is normally set in a running state by two-wheel drive with good fuel efficiency (see FIGS. 2 and 3).

[0047] In two-wheel drive, the output shaft 2 is rotated by the driving force of the engine 101, the input shaft 3 is rotated as the rear wheel 109 rotates, and the rotational speeds of the output shaft 2 and the input shaft 3 are made substantially the same. Therefore, the rotational speeds of the support shaft 10 and the rotating body 17 that rotate integrally with the output shaft 2 are also made substantially the same as the rotational speeds of the case 5 and the driven side clutch portion 9 that rotate integrally with the input shaft 3.

[0048] At this time, due to the forward biasing force of the coil spring 24, the rotating body 17 is not moved backward, the driving clutch portion 20 is held in a state of being positioned in front of the driven clutch portion 9, and the non-engaged state of the dog clutch 22 is maintained.

[0049] When the vehicle 100 is traveling in two-wheel drive, for example, when the front wheel 106 spins on a bad road such as a snowy road or a gravel road, the rotational speed of the front wheel 106 becomes faster than the rotational speed of the rear wheel 109. Therefore, the output shaft 2 rotates at a high speed with respect to the input shaft 3, and the rotational speeds of the support shaft 10 and the rotating body 17 that rotate integrally with the output shaft 2 become faster than the rotational speed of the input shaft 3.

[0050] When the rotational speed of the rotating body 17 increases, the propulsive force in the backward movement direction generated in the rotating body 17 by the screw 19 rotating at a high speed increases, and the rotating body 17 moves backward against the biasing force of the coil spring 24 (see FIGS. 4 and 5). As the rotating body 17 moves backward, the driving clutch portion 20 is engaged with the driven clutch portion 9 and the dog clutch 22 is brought into an engaged state.

[0051] When the dog clutch 22 is brought into an engaged state, the driving force of the engine 101 transmitted to the output shaft 2 is transmitted from the output shaft 2 to the case 5 and the input shaft 3 via the support shaft 10 and the rotating body 17, the output shaft 2 and the input shaft 3 rotate integrally at the same speed, and the rear wheel 109 is rotated by the driving force of the engine 101 and switched to four-wheel drive.

[0052] When switched from two-wheel drive to four-wheel drive, the output shaft 2 and the input shaft 3 rotate at the same speed and the propulsion amount by the screw 19 does not occur. At this time, since the inclined surface formed on the tooth portion 20b of the driving clutch portion 20 and the inclined surface formed on the tooth portion 9a of the driven clutch portion 9 are engaged and the engaging force of the dog clutch 22 is increased, the engaged state of the driving clutch portion 20 and the driven clutch portion 9 is not immediately released.

[0053] On one hand, when a force that acts to release the engagement of the dog clutch 22, such as the driving force of the engine 101 or the biasing force of the coil spring 24, becomes greater than the engagement force of the dog clutch 22, the engaged state of the dog clutch 22 is released, and the rotating body 17 is moved forward by the biasing force of the coil spring 24 (see FIGS. 2 and 3). Accordingly, the dog clutch 22 is brought into a released state, and the vehicle is switched from four-wheel drive to two-wheel drive.

[0054] By switching from four-wheel drive to two-wheel drive, the output shaft 2 is rotated by the driving force of the engine 101, and the input shaft 3 is rotated along with the rotation of the rear wheels 109.

[0055] In addition, in the above description, an example of the drive mode switching mechanism 1 provided in the vehicle 100 in which two-wheel drive is performed by front-wheel drive has been shown. However, in the case of the drive mode switching mechanism 1 provided in the vehicle 100 in which two-wheel drive is performed by rear-wheel drive, the positional relationship of each part is set to be the reverse front-back positional relationship compared to the above case.

[0056] Therefore, in the drive mode switching mechanism 1 provided in the vehicle 100 in which two-wheel drive is performed by rear-wheel drive, the input shaft 3 is positioned in front of the output shaft 2, and the driven side clutch portion 9, the rotating body 17, and the support shaft 10 are arranged in order from the front side inside the case 5. When the rotating body 17 biased rearward by the coil spring 24 is moved forward, the dog clutch 22 is engaged, and the vehicle is switched from two-wheel drive to four-wheel drive.

[0057] <Summary> As described above, in the drive mode switching mechanism 1, there are a driven clutch portion 9 that rotates integrally with the case 5, a screw 19 that is moved in a direction away from the output shaft 2 when the output shaft 2 rotates at a speed equal to or higher than a certain speed than the input shaft 3, a drive clutch portion 20 that is moved in a direction of approaching or separating from the driven clutch portion 9 as the screw 19 moves, and a transmission acting portion 25 that transmits the driving force of the power source transmitted to the output shaft 2 to the screw 19. When the drive clutch portion 20 is moved in a direction approaching the driven clutch portion 9, the drive clutch portion 20 and the driven clutch portion 9 are fastened and switched from two-wheel drive to four-wheel drive. When the drive clutch portion 20 is moved in a direction away from the driven clutch portion 9, the fastening between the drive clutch portion 20 and the driven clutch portion 9 is released and switched from four-wheel drive to two-wheel drive.

[0058] Therefore, as the screw 19 that is moved in a direction away from the output shaft 2 when the output shaft 2 rotates at a speed equal to or higher than a certain speed than the input shaft 3, the drive clutch portion 20 is moved, and the drive clutch portion 20 and the driven clutch portion 9 are fastened and switched from two-wheel drive to four-wheel drive. Thus, it is possible to switch between two-wheel drive and four-wheel drive while simplifying the structure.

[0059] In particular, it is possible to switch between two-wheel drive and four-wheel drive without the need for a sensor for detecting the rotational speeds of the front wheels 106 and the rear wheels 109, a control unit for controlling each part, etc., and it is possible to switch between two-wheel drive and four-wheel drive without complicating the structure of the drive mode switching mechanism 1.

[0060] Further, since the dog clutch 22 is constituted by the drive clutch portion 20 and the driven clutch portion 9, the fastening state is stabilized by the dog clutch 22 when the drive clutch portion 20 and the driven clutch portion 9 are fastened.

[0061] Therefore, the fastening state of the driving-side clutch portion 20 and the driven-side clutch portion 9 is not unintentionally released by external forces such as vibrations generated in the vehicle 100 or the biasing force of the transmission acting portion 25, and stable running performance of the vehicle 100 by four-wheel drive can be continuously ensured.

[0062] Furthermore, the transmission acting portion 25 includes a support shaft 10, a coil spring 24, and a spline shaft 21. The support shaft 10 is connected to the output shaft 2 and rotates integrally with the output shaft 2. The coil spring 24 is disposed in the support space 13, and the spline shaft 21 is inserted into the insertion space 14.

[0063] Therefore, since each part of the transmission acting portion 25 is arranged or supported on the support shaft 10, it is possible to switch between two-wheel drive and four-wheel drive while simplifying the structure.

[0064] Furthermore, an oil flow hole 16 communicating with the support space 13 and the oil filling space 5a is formed in the support shaft 10. A control valve 26 for controlling the flow rate of the oil 50 is disposed in the oil flow hole 16. The control valve 26 controls the flow rate of the oil 50 flowing from the oil filling space 5a to the support space 13 and the flow rate of the oil 50 flowing from the support space 13 to the oil filling space 5a at different speeds.

[0065] Therefore, the expansion and contraction speed of the coil spring 24 is controlled by the flow rate of the oil 50 controlled by the control valve 26, and the moving speed when the driving-side clutch portion 20 moves in the direction approaching the driven-side clutch portion 9 can be made faster than the moving speed when the driving-side clutch portion 20 moves in the direction away from the driven-side clutch portion 9, enabling a quick switch from two-wheel drive to four-wheel drive.

[0066] In addition, the screw 19 and the driving-side clutch portion 20 are connected by a connecting shaft 18, and the spline shaft 21 protrudes from the central portion of the screw 19.

[0067] Therefore, since the screw 19, the drive-side clutch portion 20, and the spline shaft 21 are not configured to rotate separately, it is possible to rotate the screw 19, the drive-side clutch portion 20, and the spline shaft 21 integrally while simplifying the structure.

Explanation of Signs

[0068] 100 Vehicle 101 Engine 1 Drive mode switching mechanism 2 Output shaft 3 Input shaft 5 Case 5a Oil filling space 9 Driven-side clutch portion 10 Support shaft 13 Support space 14 Insertion space 16 Oil flow hole 18 Connecting shaft 19 Screw 20 Drive-side clutch portion 21 Spline shaft 22 Dog clutch 24 Coil spring 25 Transmission acting portion 26 Control valve

Claims

1. A drive mode switching mechanism for switching between two-wheel drive and four-wheel drive, comprising: An output shaft rotated by the driving force of a power source during two-wheel drive and four-wheel drive; An input shaft rotated in a state where the driving force of the power source is not transmitted during two-wheel drive; A case that rotates integrally with the input shaft and has an internal space formed as an oil filling space; A driven clutch portion that rotates integrally with the case in the oil filling space; A screw that is rotated by the driving force of the power source transmitted through the output shaft in the oil filling space, is movable in a direction of approaching and separating from the output shaft, and is moved in a direction of separating from the output shaft when the output shaft rotates at a speed higher than a certain level than the input shaft; A driving clutch portion that rotates integrally with the screw in the oil filling space and is moved in a direction of approaching and separating from the driven clutch portion as the screw moves; A transmission acting portion that biases the screw and the driving clutch portion in a direction of approaching the output shaft and transmits the driving force of the power source transmitted to the output shaft to the screw; When the driving clutch portion is moved in a direction of approaching the driven clutch portion, the driving clutch portion and the driven clutch portion are engaged and switched from two-wheel drive to four-wheel drive; When the driving clutch portion is moved in a direction of separating from the driven clutch portion, the engagement between the driving clutch portion and the driven clutch portion is released and switched from four-wheel drive to two-wheel drive. A drive mode switching mechanism.

2. The drive mode switching mechanism according to claim 1, wherein a dog clutch is constituted by the driving clutch portion and the driven clutch portion. The drive mode switching mechanism according to claim 1.

3. The transmission acting portion includes a support shaft having a support space and an insertion space, a coil spring that biases the screw in a direction of approaching the output shaft, and a spline shaft that is supported by the support shaft so as to be axially movable, The support shaft is connected to the output shaft and rotates integrally with the output shaft; The coil spring is disposed in the support space; The spline shaft is inserted into the insertion space. The drive mode switching mechanism according to claim 1 or claim 2.

4. An oil flow hole communicating the support space and the oil filling space is formed in the support shaft; A control valve for controlling the flow rate of oil is disposed in the oil flow hole. The flow rate of oil from the oil filling space to the support space and the flow rate of oil from the support space to the oil filling space are controlled to different rates by the control valve. The drive mode switching mechanism according to claim 3.

5. The screw and the drive side clutch portion are connected by a connecting shaft. The spline shaft protrudes from the central portion of the screw. The drive mode switching mechanism according to claim 3 or claim 4.

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