JP2002276561A - Vane pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent damage of a vane pump when the volume of hydraulic oil is so much expanded by abnormally high temperature of the vane pump that the hydraulic oil cannot be absorbed in a reservoir. SOLUTION: The vane pump P has side plates 30 and 32, a cam ring 31, and a rotor 35 stored in a casing 19. The reservoir 55 consists of a piston 57 slidably engaged inside a through hole 27a bored through a rotor shaft 27 for supporting the rotor 35 in the axial direction, and a coil spring 59 for energizing the piston 57. When the temperature of the vane pump P is abnormally high and the volume of the hydraulic oil is largely expanded, the piston 57 engaged with the through hole 27a of the rotor shaft 27 is moved over a relief groove 27b and the hydraulic oil inside the reservoir 55 is discharged out of the through hole 27, so that the damage of the vane pump is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vane pump in which a rotor having a large number of radially arranged vanes is rotatably housed in a space surrounded by a cam ring and side plates.

[0002]

2. Description of the Related Art In such a vane pump, hydraulic oil thermally expands and contracts due to a temperature difference between an operation and a stop. Therefore, when the hydraulic oil expanded due to a rise in temperature contracts due to a decrease in temperature, it is sucked into the casing. There is a problem that the trapped air mixes with the hydraulic oil. In order to absorb a change in the volume of hydraulic oil based on a temperature difference, a vane pump casing provided with a variable volume reservoir is disclosed in Japanese Patent Application Laid-Open No. 7-125.
It is known from US Pat.

[0003]

By the way, in the above-mentioned conventional apparatus, a cover constituting a part of the casing of the vane pump is slidably supported via a disc spring and a seal member, and the inside of the cover is used as a reservoir. However, when the temperature of the vane pump becomes abnormally high and the volume of the hydraulic oil expands significantly, the expansion of the hydraulic oil cannot be absorbed by the reservoir, and the vane pump may be damaged.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to reliably prevent damage to a vane pump when the volume of hydraulic oil is greatly expanded due to an abnormally high temperature of the vane pump and cannot be absorbed by a reservoir. Aim.

[0005]

According to the first aspect of the present invention, a rotor is rotatably housed in a space surrounded by a cam ring and a side plate. A radially outer end of each of the vanes slidably supported by the plurality of radially formed vane grooves is brought into contact with the inner peripheral surface of the cam ring, and a reservoir is provided in a hollow portion of a rotor shaft supporting the rotor; The vane pump is characterized in that the reservoir includes a piston slidably fitted in the hollow portion of the rotor shaft, and relief means for communicating the hollow portion of the rotor shaft with the atmosphere as the piston slides. Suggested.

According to the above construction, since the reservoir provided in the hollow portion of the rotor shaft supporting the rotor is provided with the piston slidably fitted in the hollow portion, the hydraulic oil in the casing due to a rise in temperature. When the piston expands, the volume of the reservoir decreases by moving the piston in one direction, and when the hydraulic oil in the casing contracts due to a temperature drop, the piston moves in the other direction to increase the volume of the reservoir. Air can be reliably prevented from being mixed into the hydraulic oil. Moreover, when the volume of the hydraulic oil expands significantly due to the abnormally high temperature of the vane pump and cannot be completely absorbed by the reservoir, the relief means communicates the hollow portion of the rotor shaft to the atmosphere and discharges the hydraulic oil to the outside.
Damage to the vane pump due to abnormal expansion of the hydraulic oil can be reliably prevented. Further, since the reservoir is housed in the hollow portion of the rotor shaft, the reservoir can be compactly arranged while avoiding the influence of the discharge pressure of the vane pump.

The through holes 27a of the embodiment correspond to the hollow portions of the present invention, and the first side plates 30, 30 of the embodiment.
L, 30R and the second side plate 32 correspond to the side plate of the present invention, and the relief grooves 27b, 2 of the embodiment.
7b and the communication holes 27c, 27c correspond to the relief means of the present invention.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on embodiments of the present invention shown in the accompanying drawings.

1 to 9 show a first embodiment of the present invention. FIG. 1 is a skeleton diagram of a power transmission device of a four-wheel drive vehicle, and FIG. 2 is a longitudinal sectional view of a hydraulic coupling device. 3 is a sectional view taken along line 3-3 in FIG. 2, and FIG.
5 is a sectional view taken along line 5-5 in FIG. 4, FIG. 6 is a sectional view taken along line 6-6 in FIG. 4, FIG. 7 is a sectional view taken along line 7-7 in FIG. 4, and FIG. FIG. 9 is a hydraulic circuit diagram of the hydraulic coupling device.

As shown in FIG. 1, a four-wheel drive vehicle V has an engine E disposed horizontally at the front of the vehicle body, and an engine E
And a transmission M coupled to the right side surface of the transmission.
First power transmission system D1 that transmits the driving force of transmission M to left and right front wheels WFL and WFR as main driving wheels.
Is composed of a first spur gear 2 provided on the output shaft 1 of the transmission M, a second spur gear 3 meshing with the first spur gear 2, a bevel gear type front differential 4 driven by the second spur gear 3, and a front differential 4. The vehicle includes left and right axles 5L and 5R extending left and right and connected to front wheels WFL and WFR as main drive wheels.

A second power transmission system D for transmitting the driving force of the first power transmission system D1 to rear wheels WRL and WRR as auxiliary driving wheels.
Reference numeral 2 denotes a third spur gear 6 provided in a differential box of the front differential 4, a fourth spur gear 7 meshing with the third spur gear 6, a first bevel gear 8 rotating integrally with the fourth spur gear 7, and a first bevel gear 8 A second bevel gear 9 meshing with a propeller shaft 10 having a second bevel gear 9 at the front end and extending rearward of the vehicle body; a third bevel gear 11 provided at the rear end of the propeller shaft 10;
A fourth bevel gear 12 meshing with the bevel gear 11;
The vehicle includes a hydraulic coupling device H driven by the bevel gear 12, and left and right axles 13L, 13R extending right and left from the hydraulic coupling device H and connected to rear wheels WRL, WRR.

Next, the structure of the hydraulic coupling device H will be described with reference to FIG.

The hydraulic coupling device H includes a left vane pump PL and a right vane pump PR which are symmetrically arranged. The left and right vane pumps PL, PR
The vehicle includes a left first side plate 30L, a left cam ring 31L, a second side plate 32, a right cam ring 31R, and a right first side plate 30R, which are integrally connected by six bolts 21. At this time, the left first side plate 30L, the left cam ring 31L, the second side plate 32, the right cam ring 31R, and the right first side plate 30R are positioned in the rotation direction through the knock pins (not shown), and are left inside. Cam ring 31L,
The right end face of the left first side plate 30L is superimposed on the left end face of the cylindrical casing 19 that houses the second side plate 32, the right cam ring 31R, and the right first side plate 30R, and a plurality of pieces together with the fourth bevel gear 12 are provided. They are connected by bolts 22. Second side plate 32
Is a central center plate 37 formed of a thin steel plate.
A pair of left and right sintered metal valve plates 38
L, 38R are superposed. The joint surface between the left first side plate 30L and the casing 19 is sealed with an O-ring 23, and the joint surface between the right first side plate 30R and the casing 19 is sealed with an O-ring 24.

An outer peripheral surface of an annular support portion 30a protruding from the left side surface of the left first side plate 30L is supported by the housing 20 with a ball bearing 25, and an inner peripheral surface of the support portion 30a is hereinafter described with a ball bearing 26. It is supported by the left rotor shaft 27L. The outer peripheral surface of an annular support portion 30a protruding from the right side surface of the right first side plate 30R is supported by the housing 20 with a ball bearing 25, and the inner peripheral surface of the support portion 30a is formed by a ball bearing 26 with a right rotor described later. It is supported by the shaft 27R.

An axle 13b of the left rear wheel WRL is splined to the axle 13L and a shaft hole 30b of the first left side plate 30L.
Is sealed by an O-ring 29 supported by the shaft hole 30b, is splined to the axle 13R of the right rear wheel WRR, and penetrates the shaft hole 30b of the right first side plate 30R. The outer periphery of the right rotor shaft 27R is sealed by an O-ring 29 supported by the shaft hole 30b. Therefore, the four O-rings 23, 24, 29, 29 prevent the hydraulic oil from leaking to the outside of the left and right vane pumps PL, PR, and allow air to enter the inside of the left and right vane pumps PL, PR. Is prevented.

The left rotor 35L splined to the left rotor shaft 27L is connected to the left first side plate 3
0L, left cam ring 31L and second side plate 3
The right rotor 3 rotatably housed in a space surrounded by the right rotor shaft 2 and splined to the right rotor shaft 27R.
5R is the right first side plate 30R, the right cam ring 3
It is rotatably housed in a space surrounded by the 1R and the second side plate 32. The second side plate 32 is a component common to the left vane pump PL and the right vane pump PR, and has an inner peripheral surface in the radial direction via needle bearings 36, 36 and an outer periphery of a facing portion of the left rotor shaft 27L and the right rotor shaft 27R. Are supported so as to be relatively rotatable.

Next, the structure of the right vane pump PR will be described in detail with reference to FIGS. Note that the structure of the left vane pump PL is mirror-symmetrical to the structure of the right vane pump PR with respect to the left and right, and therefore, redundant description will be omitted. Corresponding components of the right vane pump PR and the left vane pump PL have the same reference numerals with the suffixes "R" and "L", respectively.

The inner peripheral surface of the right cam ring 31R has a substantially triangular shape, and a circular right rotor 3 housed therein is formed.
5R, three working chambers 40R... Spaced apart by 120 ° in the circumferential direction are formed. Plate-shaped vanes 41 are slidably supported by eight vane grooves 35a radially formed on the right rotor 35R, and radially outer ends of the vanes 41 are formed on the inner periphery of the right cam ring 31R. Sliding on the surface. Each vane 4 is provided on both sides of the right rotor 35R.
Annular vane push-up ports 35b, 35b are formed so that the outer end of the first cam ring 1 is brought into close contact with the inner peripheral surface of the right cam ring 31R. The vane lifting ports 35b communicate with the bottoms of the eight vane grooves 35a of the right rotor 35R. Also, the vane groove 35a is formed so that the radial outer end of each vane 41 is in close contact with the inner peripheral surface of the right cam ring 31R.
The coil spring 42 is contracted between the bottom of the vane 41 and the radially inner end of the vane 41.

As clearly shown in FIGS. 3 to 7, on the outer surface of the right valve plate 38R of the second side plate 32 (the surface facing the right cam ring 31R and the right rotor 35R), three right vane pumps PR are provided. Three suction ports 43R and three discharge ports 44R that face the circumferential ends of the working chambers 40R are recessed. The suction port 43R and the discharge port 44R are formed with a communication hole h1 penetrating the right valve plate 38R, a communication groove g1 recessed in an inner surface (a surface facing the center plate 37) of the right valve plate 38R, and a right. Through a communication hole h2 penetrating the valve plate 38R, the vane lifting port 35b.
Communicate with A stepped valve seat 45 is formed in the communication hole h1, and a check ball 46 attached to the communication hole h1 from the inner side of the right valve plate 38R and the valve seat 4 are formed.
5 constitute check valves 47R.
The check valves 47R are connected to the vane lifting ports 35b from the suction port 43R and the discharge port 44R.
Has the function of permitting the flow of hydraulic oil to the outside and preventing the flow of hydraulic oil in the opposite direction. The check balls 46 are prevented from falling off from the communication holes h1 by the center plate 37.

Therefore, when the vehicle is traveling forward, the discharge port 4
When the pressure of the suction ports 43R becomes low, the discharge pressure of the discharge ports 44R on the high pressure side is transmitted to the vane lifting port 35b. When the suction port 43R is at a high pressure and the discharge port 44R is at a low pressure during reverse running of the vehicle, the discharge pressure of the suction port 43R on the high pressure side is transmitted to the vane lifting port 35b.

Three suction ports 43R... And three discharge ports 44 recessed on the outer surface of the right valve plate 38R.
R ... are communication holes h3 penetrating the right valve plate 38R.
, A communication groove g2 recessed in the inner surface of the right valve plate 38R, and a communication hole h passing through the right valve plate 38R.
4 communicates with the outer peripheral portion of the right rotor shaft 27R. Stepped valve seats 48 are formed in the communication holes h3, and the communication holes h3 are formed from the outer surface side of the right valve plate 38R.
Check ball 49 attached to 3 ... and valve seat 48 ...
The check valves 50R. The check valves 50R have a function of preventing the flow of hydraulic oil from the suction port 43R and the discharge port 44R to the outer peripheral portion of the right rotor shaft 27R, and permitting the flow of hydraulic oil in the opposite direction.

Six L-shaped communication grooves g3 are formed in the inner surface of the right valve plate 38R. One end of each of the communication grooves g3 is connected to the suction port 43R and the suction port 43R through the communication hole h3. The discharge ports 44R communicate with each other. Also, three communication grooves g4 are recessed on the outer surface of the right valve plate 38R, and both ends of each communication groove g4 are formed in the L-shape through communication holes h5 penetrating the right valve plate 38R. It communicates with the other end of the communication groove g3.

As clearly shown in FIG. 7, the communication holes h5 are provided with first orifices 51R, 51R, respectively. The first orifices 51R, 51R have directionality, and a large pressure loss occurs when the hydraulic oil flows in the direction indicated by the arrow in FIG. 7 during forward running of the vehicle, and the hydraulic oil reverses during reverse running of the vehicle. A small pressure loss occurs when flowing in the direction. 3, 4 and 6
As shown in FIG. 7, the second orifices 52 penetrate the center plate 37 so that the suction ports 43L, 43R and the discharge ports 44L, 44R of the left and right valve plates 38L, 38R communicate with each other.
Is formed.

As shown in FIG. 2, through holes 27a, 27a extending in the axial direction and opening at both ends are formed inside the left and right rotor shafts 27L, 27R, and a pair of left and right reservoirs 55L, 55R are formed therein. Is provided. Each of the reservoirs 55L, 55R has a piston 57, which is slidably fitted into the through hole 27a, 27a via an O-ring 56, 56.
57, plugs 58, 58 for closing the outer ends of the through holes 27a, 27a, and the plugs 58, 58 and the piston 57,
And coil springs 59, 59 disposed between the coil springs.
In the vicinity of the plugs 58, 58, the through holes 27a, 27
a, two relief grooves 27b, 27b are formed in the inner circumferential surface in the axial direction, and these relief grooves 27b, 27b
Communicates with the atmosphere through the communication holes 27c, 27c. Through holes 58a, 58 inside plugs 58, 58 so that the movement of pistons 57, 57 is not hindered by the trapping of air.
a penetrates in the axial direction.

When the hydraulic oil inside the vane pumps PL, PR expands and contracts in response to a change in temperature, the volumes of the reservoirs 55L, 55R change to absorb the change in the volume of the hydraulic oil. Air can be prevented from being mixed into the air. That is, when the hydraulic oil expands due to a rise in temperature, the pistons 57, 57 compress the coil springs 59, 59 and move in directions away from each other, and the reservoirs 55L, 55
Since the volume of 5R increases, the expansion of the hydraulic oil can be absorbed. Conversely, when the hydraulic oil contracts due to a temperature drop, the pistons 57 move in the direction approaching each other due to the elastic force of the coil springs 59, 59, and the reservoirs 55L, 55
Since the volume of the 5R is reduced, it is possible to absorb the contraction of the hydraulic oil and prevent the air from being sucked into the pump.

If the temperature of the hydraulic oil rises abnormally for some reason, the pistons 57, 57
59 moves largely in the direction away from each other while compressing, and the ends thereof communicate with the relief grooves 27b, 27b of the through holes 27a, 27a of the left and right rotor shafts 27L, 27R. As a result, the inner space of the vane pumps PL, PR is filled with the through holes 27a, 2 of the rotor shafts 27L, 27R.
7a, relief grooves 27b, 27b and communication holes 27c,
The hydraulic oil is communicated with the atmosphere via the opening 27c, and the expanded hydraulic oil is discharged to the outside through the communication holes 27c, 27c, thereby preventing the hydraulic coupling device H from being damaged.

When the suction ports 43L, 43R (or the discharge ports 44L, 44R ...) become negative with the operation of the vane pumps PL, PR, the check valves 50L, 50R ... Open the suction ports 43L, 43R (or discharge ports 44L,
44R) are communicated with the reservoirs 55L and 55R, so that it is possible to prevent the occurrence of cavitation due to excessive negative pressure. At this time, the coil springs 59, 5
Since the hydraulic oil is pressurized by the pistons 57, 57 urged in 9, the cavitation can be more effectively prevented. Moreover, the rotor shafts 27L, 27
Using the R through holes 27a, 27a, the reservoir 55L,
Since the 55R is disposed, it is possible not only to avoid the influence of the discharge pressure of the vane pumps PL and PR, but also to provide the vane pump P by providing the reservoirs 55L and 55R.
Enlargement of L and PR can be avoided. In addition, since the reservoirs 55L and 55R are located at the rotation center of the vane pumps PL and PR, they are less affected by centrifugal oil pressure. Can be suppressed.

The second side plate 32 is constituted by a center plate 37 at the center and left and right valve plates 38L and 38R arranged so as to sandwich both sides thereof, and a communication hole penetrating the left and right valve plates 38L and 38R. , h2, h3, h4, h5, communication grooves g1,..., g3,... formed in the inner surfaces of the left and right valve plates 38L, 38R, and the left and right valve plates 3.
Since all the oil passages of the left and right vane pumps PL and PR are constituted by the communication grooves g4 formed on the outer surfaces of the 8L and 38R, these oil passages are concentrated on the second side plate 32, and the left and right first passages are arranged. Not only can the side plates 30L and 30R be made of simple plates, but also the oil passage can be shortened and the number of assembly steps can be reduced by subassembly of the second side plate 32. The size of the coupling device H can be reduced.

The check valves 47L, 47R are arranged inside the communication holes h1 of the left and right valve plates 38L, 38R, and the check valves 50L, 50R,.
To the communication holes h4 of the left and right valve plates 38L, 38R.
The check valves 47L
, 47R ...; 50L ..., 50R ... can be compactly assembled to the left and right valve plates 38L, 38R, and the leakage of hydraulic oil can be effectively suppressed. In particular, the check valves 47L ..., 47 are provided by switching valves facing the side surfaces of the rotors 35L, 35R.
As compared with the conventional one having the function of R.
The amount of leakage of hydraulic oil from the side surfaces of L and 35R can be significantly reduced.

Further, the left and right valve plates 38L, 38
, H2, h3, h4, h5, and the communication grooves g1, g2, g3, g4,... Are all formed in the thickness direction (the direction of the rotor shafts 27L, 27R). Therefore, the valve plates 38L and 38R can be manufactured by sintering, which can contribute to cost reduction. The left and right valve plates 38
Since the suction ports 43L, 43R and the discharge ports 44L, 44R of the L, 38R communicate with each other through the second orifices 52, the second orifices 52 are connected to the suction ports 43L, 43R and A special oil passage communicating with the discharge ports 44L, 44R is not required, which can contribute to a reduction in the number of processing steps.

Since the first orifices 51L, 51R are arranged in series two by two, the required pressure loss can be generated even if the diameter of the orifices 51L is increased, and the first orifices 51L,. Not only can be effectively prevented from clogging, but also drilling is easy and productivity can be improved.

While the structure of the right vane pump PR has been mainly described above, the structure of the left vane pump PL is mirror-symmetrical to that of the right vane pump PR, and the two structures are substantially the same.

FIG. 9 shows a hydraulic circuit of the hydraulic coupling device H. As can be seen from the figure, the suction port 43L and the discharge port 44L of the left vane pump PL are provided on the left valve plate 38L of the second side plate 32, for a total of three pairs of first orifices 5L.
1L, and the suction port 43R and the discharge port 44R of the right vane pump PR communicate with each other through a total of three pairs of first orifices 51R provided on the right valve plate 38R of the second side plate 32. . The suction ports 43L, 43R of the left and right vane pumps PL, PR communicate with each other through second orifices 52, which penetrate the center plate 37 of the second side plate 32.
The discharge ports 44L, 44R of the PR communicate with each other by second orifices 52, which penetrate the center plate 37 of the second side plate 32. Center plate 3
7 is a thin plate, so that the second orifices 52 can be easily formed. Further, by assembling a center plate 37 having a different hole diameter from the second orifices 52, L
It becomes possible to change the SD effect.

The suction port 43L of the left vane pump PL ...
Any one of the high pressure sides of the discharge ports 44L communicates with the vane push-up port 35b via a check valve 47L provided on the left valve plate 38L of the second side plate 32, and the suction port 43R of the right vane pump PR and discharge. One of the high pressure sides of the ports 44R communicates with the vane lifting port 35b via a check valve 47R provided on the right valve plate 38R. Left vane pump P
The low-pressure side of any one of the suction port 43L and the discharge port 44L of the L is connected to the reservoirs 55L and 55R via check valves 50L provided on the left valve plate 38L of the second side plate 32, and the right vane pump PR
Of the suction port 43R and the discharge port 44R of the second side plate 32 communicate with the reservoirs 55L and 55R via check valves 50R provided on the right valve plate 38R of the second side plate 32.

Further, a relief valve 61 is provided between the vane lifting ports 35b, 35b and the reservoirs 55L, 55R.
L, 61R and chokes 62L, 62R are provided. The relief valves 61L and 61R are virtual, and are generated between the left and right rotors 35L and 35R when the left and right first side plates 30L and 30R are bent by hydraulic pressure or when the bolts 21 are extended. It is constituted by a gap. The chokes 62L, 62R
Is also virtual, and the left and right first side plates 30L,
30R or the gap between the sliding portions of the second side plate 32 and the left and right rotors 35L, 35R.

Next, the operation of the first embodiment of the present invention having the above configuration will be described.

When the vehicle V is traveling at a constant speed, the driving force of the engine E is transmitted from the output shaft 1 to the left and right front wheels WFL via the first spur gear 2, the second spur gear 3, the front differential 4, and the left and right axles 5L and 5R. , WFR. At this time, the rotation of the third spur gear 6 of the front differential 4 is controlled by the rotation of the fourth spur gear 7, the first bevel gear 8, the second bevel gear 9, and the propeller shaft 1.
0, the vane pumps PL, PR of the hydraulic coupling device H via the third bevel gear 11 and the fourth bevel gear 12 (that is, the left and right cam rings 31L, 31R).
To rotate. On the other hand, the rotation of the rear wheels WRL, WRR driven by the frictional force received from the road surface as the vehicle V travels,
Rotor shaft 27 from left and right axles 13L, 13R
Rotor 35L of left vane pump PL via L, 27R
And it is transmitted to the rotor 35R of the right vane pump PR. No slip has occurred on the front wheels WFL, WFR,
Therefore, when the rotation speeds of the front wheels WFL, WFR and the rear wheels WRL, WRR are equal, the left and right cam rings 31L, 3L
The rotation speed of 1R matches the rotation speed of the left and right rotors 35L, 35R, and no relative rotation occurs. As a result, the hydraulic coupling device H does not transmit the driving force because the left and right vane pumps PL, PR do not discharge the hydraulic oil, and the vehicle V is in the front wheel drive state.

The front wheels WFL, WFR to which the driving force of the engine E directly acts upon starting or sudden acceleration on a low friction road.
Slips, the cam rings 31L of the left and right vane pumps PL, PR interlocked with the rotation of the front wheels WFL, WFR.
A relative rotation in the forward direction occurs between the left and right vane pumps P, 31R and the rotors 35L, 35R of the left and right vane pumps PL, PR interlocked with the rotation of the rear wheels WRL, WRR.
L, PR suck the hydraulic oil discharged from the discharge ports 44L, 44R through the suction ports 43L, 43R.
The hydraulic oil discharged from the discharge ports 44L, 44R passes through the first left and right orifices 51L, 51R and returns to the suction ports 43L, 43R, but the flow resistance at that time causes the left and right vane pumps PL to return. , PR, and this load is used as driving force by the left and right rear wheels WRL, WR.
It is transmitted to R. Thus, when the front wheels WFL, WFR slip, the vehicle is in the four-wheel drive state, and the traction of the vehicle V can be increased. At this time, the first orifice 5
As the diameter of 1L..., 51R... Decreases, the load on the left and right vane pumps PL, PR increases, and the rear wheels WRL, WRR
The driving force transmitted to the motor increases.

When the vehicle V makes a tight turn at low speed,
Since the average radius of the turning trajectory of the left and right rear wheels WRL, WRR is smaller than the average radius of the turning trajectory of the left and right front wheels WFL, WFR, the left and right cam rings 31L, 31R connected to the front wheels WFL, WFR, and the rear wheel. Relative rotation occurs between the left and right rotors 35L, 35R connected to WRL, WRR. Moreover, since the radius of the turning trajectory of the left and right rear wheels WRL, WRR is large in the turning outer wheel and small in the turning inner wheel, the magnitude of the relative rotation differs between the left and right vane pumps PL, PR. At this time, the hydraulic oil discharged from the discharge ports 44L, 44R of the left and right vane pumps PL, PR is supplied to the left and right first orifices 51L, 51L.
R flows back to the suction ports 43L, 43R through R ... and the difference between the hydraulic oil discharged by the left and right vane pumps PL, PR is offset by going back and forth through the second orifices 52 ..., so that both vane pumps PL , PR is prevented from generating a large load. As a result, when the four-wheel drive vehicle V makes a tight turn at low speed, it is possible to reduce the yaw moment in the direction that hinders the turn caused by the difference in radius of the turning locus of each wheel.

For example, the left and right front wheels W excluding the left rear wheel WRL
When the FL, WFR and the right rear wheel WRR get stuck in mud, when the cam rings 31L, 31R rotate in conjunction with the slipping front wheels WFL, WFR, the right rear wheel WRR, which is stuck in mud and has reduced friction, also moves. , Cam ring 31R
, The vehicle 41 slips due to the driving force transmitted via the rotor 35R and the rotor shaft 27R. However, the left rear wheel WRL riding on a road surface having a high friction coefficient has a vane 41.
Since driving force is transmitted via the rotor 35L and the rotor shaft 27L, escape from mud becomes possible by the driving force. That is, according to the hydraulic coupling device H of the present embodiment, the function of a so-called differential limiting mechanism (LSD) can be exhibited. At this time, the smaller the diameter of the second orifices 52 is, the stronger the differential limiting function can be.

As described above, when starting or suddenly accelerating on a low friction road, the rotational speeds of the front wheels WFL, WFR are changed to the rear wheels WRL, WRL.
If the rotational speed exceeds the WRR, the rotors 35L, 35L
R relatively rotates in the forward direction (the direction of arrow A in FIG. 3), hydraulic oil is sucked in from suction ports 43L, 43R, and hydraulic oil is discharged from discharge ports 44L, 44R,. As a result, the check valves 47L ..., 47R ... connected to the high pressure side discharge ports 44L ..., 44R ... open.
The high pressure side discharge ports 44L ..., 44R ... communicate with the vane push-up ports 35b, 35b, and the vane push-up ports 35b, 35b and the low pressure side suction ports 43L ..., 4
The communication with 3R is shut off by check valves 47L, 47R connected to the suction ports 43L, 43R. Thus, the vanes 41 can be urged radially outward by the hydraulic pressure transmitted to the vane lifting ports 35b, 35b, and their tips can be pressed against the inner peripheral surfaces of the cam rings 31L, 31R.

On the other hand, when the vehicle performs sudden braking, AB
The front wheels WFL, WFR are controlled by controlling the locked state of the wheels by S (antilock brake system) or the like.
Are locked before the rear wheels WRL, WRR, so that the vehicle behavior is stabilized. When the rotational speeds of the rear wheels WRL, WRR exceed the rotational speeds of the front wheels WFL, WFR due to the rapid braking, the rotors 35L, 35R rotate in the reverse direction (FIG. 3).
, And the discharge ports 44L.
Hydraulic oil is sucked from 4R ... and suction ports 43L ..., 4
Hydraulic oil is discharged from 3R. As a result, the check valves 4 connected to the suction ports 43L, 43R,.
7L ..., 47R ... are opened, the suction ports 43L ..., 43R ... on the high pressure side become vane push-up ports 35b, 35b.
And the vane push-up ports 35b, 35b
The communication between the low pressure side discharge ports 44L, 44R, and the like is blocked by check valves 47L, 47R, which are connected to the discharge ports 44L, 44R. Thus, the vanes 41 can be urged radially outward by the hydraulic pressure transmitted to the vane lifting ports 35b, 35b, and their tips can be pressed against the inner peripheral surfaces of the cam rings 31L, 31R.

Incidentally, in the four-wheel drive vehicle V equipped with the hydraulic coupling device H, the front wheels WFL, WFR
The left and right vane pumps PL, PR generate a load according to the relative rotational speed difference between the rear wheels WRL, WRR, and the front wheels WF
The driving force is transmitted from the side where the rotation speeds of L, WFR and rear wheels WRL, WRR are high to the side where the rotation speeds are low. Therefore, the control of the braking force at the time of sudden braking causes the front wheels WFL,
If WFR tries to lock first, the rear wheels WRL, WR
When the rotation speed of R exceeds the rotation speed of front wheels WFL and WFR, driving force is transmitted from rear wheels WRL and WRR to front wheels WFL and WFR, and the locking of front wheels WFL and WFR is suppressed, and rear wheels WRL and WFR are suppressed. In the worst case, the front wheels WFL and WFR and the rear wheels WR
There is a possibility that L and WRR are locked simultaneously and the vehicle behavior becomes unstable.

In order to avoid this, in this embodiment, the front wheels WF
The magnitude of the load generated by the vane pumps PL and PR differs depending on the direction of the relative rotation of the rear wheels LRL and WFR and the rear wheels WRL and WRR. That is, when the rotation speeds of the front wheels WFL, WFR exceed the rotation speeds of the rear wheels WRL, WRR, such as when starting or suddenly accelerating on the low friction road described above,
The rotors 35L, 35R relatively rotate in the direction of arrow A in FIG. 3, and the operating oil is supplied to the pair of first orifices 51L, 51R,.
Flows in the direction indicated by the arrow in FIG. 7 to generate a large pressure loss. As a result, the vane pumps PL and PR generate a large load and move from the front wheels WFL and WFR to the rear wheels WRL and WRR.
(See the solid line in FIG. 8A).

On the other hand, as in the case of sudden braking described above, the rear wheels WR
When the rotation speeds of L and WRR exceed the rotation speeds of front wheels WFL and WFR, rotors 35L and 35R rotate relative to each other in the direction of arrow B in FIG. 3, and hydraulic oil is supplied to a pair of first orifices 51L.
, 51R in the direction opposite to the direction indicated by the arrow in FIG. 7 to generate a small pressure loss. As a result, the vane pump P
L and PR generate a small load, and the driving force transmitted from the rear wheels WRL and WRR to the front wheels WFL and WFR decreases (see the broken line (B) in FIG. 8). Thus, the front wheel W
The FL and WFR can be locked prior to the rear wheels WRL and WRR to prevent vehicle behavior from becoming unstable.

10 to 12 show a second embodiment of the present invention. FIG. 10 is a skeleton diagram of a power transmission device of a four-wheel drive vehicle, and FIG. 11 is a longitudinal sectional view of a hydraulic coupling device. 12 is a hydraulic circuit diagram of the hydraulic coupling device.

As is apparent from a comparison between FIG. 10 and FIG. 1, the second embodiment differs from the first embodiment in the structure of the second power transmission system D2. That is, the second power transmission system D2 of the second embodiment includes a hydraulic coupling device H between the rear end of the propeller shaft 10 and the bevel gear type rear differential 14, and this hydraulic coupling device H Is a single vane pump P
Is provided.

Next, the structure of the hydraulic coupling device H will be described with reference to FIG. The vane pump P of the hydraulic coupling device H is the first pump shown in FIG.
It has substantially the same configuration as the right vane pump PR of the hydraulic coupling device H of the embodiment. Basically, the reference numerals of the components of the vane pump P are the same as those of the corresponding components of the right vane pump PR, or The same reference numerals are used for components without the suffix "R".

The vane pump P is connected to the first side plate 3
0, a cam ring 31, a second side plate 32, and an end plate 71, which are positioned in the rotational direction through a knock pin (not shown).
The two bolts 21 are integrally connected. The second side plate 32 has the same structure as the valve plate 38R of the first embodiment, and the end plate 71 has the same function as the center plate 37 of the first embodiment. However,
The end plate 71 does not include the second orifices 52 of the center plate 37 (see FIG. 6). The cylindrical casing 19 that covers the outside of the first side plate 30, the cam ring 31, the second side plate 32, and the end plate 71 is locked to the end plate 71 by the clip 72.

The housing 73 of the rear differential 14 (see FIG. 10) has a third bevel gear 11 (see FIG. 10).
) Is supported via a roller bearing 74, and the shaft 11a of the third bevel gear 11 is splined 77 to a coupling 78 fixed to the end plate 71 with bolts 75. Fixed at.

A rotor shaft 27 is supported on the first side plate 30 and the second side plate 32 via ball bearings 26 and needle bearings 36, respectively. A coupling 80 which is splined 79 to the front end of the rotor shaft 27 is provided. Are connected to the rear end of the propeller shaft 10 by bolts 81. A rotor 35 splined to the rotor shaft 27 is rotatably housed in a space surrounded by the first side plate 30, the cam ring 31, and the second side plate 32. Eight vane grooves 3 radially formed in the rotor 35
Each of the plate-shaped vanes 41 is slidably supported by 5 a. The radially outer ends of the vanes 41 slide on the inner peripheral surface of the cam ring 31.

End plate 71 and casing 19
The space is sealed with an O-ring 23 and the first side plate 30
By sealing the space between the casing 19 and the O-ring 24 with the O-ring 24 and further sealing the outer periphery of the rotor shaft 27 passing through the shaft hole 30b of the first side plate 30 with the O-ring 29, leakage of hydraulic oil to the outside of the vane pump P , And the intrusion of air into the vane pump P is prevented.

Since the internal structure of the vane pump P and the structure of the oil passage and the like are the same as those of the right vane pump PR of the first embodiment described with reference to FIGS. 3 to 5, the overlapping description will be omitted. However, as is clear from the comparison of the hydraulic circuit diagram of FIG. 12 with the hydraulic circuit diagram of FIG. 9 (first embodiment), the second embodiment includes only a single vane pump P, so that the left and right vane pumps PL, PR Are eliminated from each other.

As shown in FIG. 11, the rotor shaft 27
Through hole 27a extending in the axial direction and opening at both ends
Is formed, and the reservoir 55 is provided therein.
The reservoir 55 includes a piston 57 slidably fitted to the through hole 27a via an O-ring 56, a plug 58 for closing the outer end of the through hole 27a, and a coil spring disposed between the plug 58 and the piston 57. 59. In the vicinity of the plug 58, two relief grooves 27b, 27b are formed in the inner peripheral surface of the through hole 27a in the axial direction, and the relief grooves 27b, 27b communicate with the atmosphere through the communication holes 27c, 27c. . A through hole 58a penetrates the plug 58 in the axial direction so as not to hinder the movement of the piston 57.

When the hydraulic oil inside the vane pump P expands and contracts in accordance with the temperature change, the volume of the reservoir 55 changes to absorb the change in the volume of the hydraulic oil. Contamination can be prevented.
That is, when the hydraulic oil expands due to a temperature rise, the piston 5
7 compresses the coil springs 59 and moves in a direction away from each other to increase the volume of the reservoir 55, so that the expansion of the hydraulic oil can be absorbed. Conversely, when the hydraulic oil contracts due to a temperature drop, the piston 57 moves in a direction approaching each other due to the elastic force of the coil spring 59 and the volume of the reservoir 55 decreases, so that the contraction of the hydraulic oil is absorbed, Inhalation of air into the pump can be prevented.

If the temperature of the hydraulic oil rises abnormally for some reason, the piston 57 moves largely rightward in the figure while compressing the coil spring 59, and its tip is formed in the relief groove of the through hole 27 a of the rotor shaft 27. 27b, 27b
Communicate with As a result, the inner space of the vane pump P is filled with the through holes 27a of the rotor shaft 27 and the relief grooves 27.
The hydraulic coupling device H is prevented from being damaged by communicating with the atmosphere through the communication holes 27c and 27c and discharging the expanded hydraulic oil to the outside through the communication holes 27c and 27c.

When the suction port 43 (or the discharge port 44) becomes a negative pressure with the operation of the vane pump P, the check valve 50 is opened by the negative pressure, and the suction port 43 (or the discharge port) is discharged. Since the ports 44 communicate with the reservoir 55, cavitation due to excessive negative pressure can be prevented. At this time, since the hydraulic oil is pressurized by the piston 57 biased by the coil spring 59, the cavitation can be more effectively prevented. Moreover, the rotor shaft 2
Since the reservoir 55 is disposed using the through-hole 27a of the seventh embodiment, not only can the influence of the discharge pressure of the vane pump P be avoided, but also the enlargement of the vane pump P due to the provision of the reservoir 55 is avoided. be able to.

The left and right vane pumps P of the first embodiment
L and PR are provided on the left and right axles 13L and 13R, whereas the vane pump P of the second embodiment is provided with the axle 1
Propeller shaft 10 speeded up for 3L, 13R
, The vane pump P can be used at a relatively high rotation speed and a low torque, and the capacity of the vane pump P can be reduced to achieve downsizing and cost reduction.

Further, as an effect peculiar to this embodiment, the rotor shaft 27 of the vane pump P has the front wheel W as the main driving wheel.
Driven by the propeller shaft 10 linked to the FL and WFR, the rotor 35 rotates at the same time as the front wheels WFL and WFR slip and centrifugal force acts on the vanes 41. The responsiveness can be improved by increasing the sealing property between them.

Next, the operation of the second embodiment of the present invention having the above-described configuration will be described.

When the vehicle V is traveling at a constant speed, the driving force of the engine E is transmitted from the output shaft 1 to the left and right front wheels WFL via the first spur gear 2, the second spur gear 3, the front differential 4, and the left and right axles 5L and 5R. , WFR. At this time, the rotation of the third spur gear 6 of the front differential 4 rotates the rotor shaft 27 of the vane pump P of the hydraulic coupling device H via the fourth spur gear 7, the first bevel gear 8, the second bevel gear 9, and the propeller shaft 10. The rotor 35 is rotated. On the other hand, the rear wheels WRL, WRR driven by the frictional force received from the road surface as the vehicle V travels rotate from the left and right axles 13L, 13R to the rear differential 1.
4. The cam ring 31 of the vane pump P is rotated via the fourth bevel gear 12 and the third bevel gear 11. When no slip occurs in the front wheels WFL, WFR, and therefore, when the rotation speeds of the front wheels WFL, WFR and the rear wheels WRL, WRR are equal, the rotation speed of the rotor 35 and the cam ring 3
The number of rotations is equal to 1 and no relative rotation occurs. As a result, the hydraulic coupling device H does not transmit the driving force because the vane pump P does not discharge the hydraulic oil,
The vehicle V enters the front wheel drive state.

The front wheels WFL, WFR to which the driving force of the engine E directly acts when starting or suddenly accelerating on a low friction road.
Slips, the rotor 35 of the vane pump P interlocked with the rotation of the front wheels WFL, WFR, and the rear wheels WRL, WRR
The rotation of the vane pump P relative to the cam ring 31 is interlocked with the rotation of the vane pump P, and the vane pump P receives the hydraulic oil discharged from the discharge ports 44.
More inhalation. Hydraulic oil discharged from the discharge ports 44 passes through the first orifices 51 and returns to the suction ports 43. At this time, a flow resistance causes a load on the vane pump P, and this load acts as a driving force. Rear wheel WR
L, WRR. Thus, the front wheels WFL, WFR
When the vehicle slips, the vehicle is in a four-wheel drive state, and the traction of the vehicle V can be increased. At this time, as the diameter of the first orifices 51 decreases, the load on the vane pump P increases, and the driving force transmitted to the rear wheels WRL, WRR increases.

As described above, when starting or suddenly accelerating on a low friction road, the rotational speeds of the front wheels WFL, WFR are changed to the rear wheels WRL, WRL.
When the rotation speed exceeds the rotation speed of the WRR, the rotor 35 relatively rotates in the normal rotation direction, hydraulic oil is sucked from the suction ports 43, and hydraulic oil is discharged from the discharge ports 44. As a result, the check valves 47 connected to the high-pressure discharge ports 44 are opened, so that the high-pressure discharge ports 44 communicate with the vane push-up port 35b, and the vane push-up port 35b and the low-pressure suction port 43. Are interrupted by check valves 47 connected to the suction ports 43. Thus, the hydraulic pressure transmitted to the vane lifting port 35b urges the vanes 41 radially outward, so that the tips of the vanes 41 can be pressed against the inner peripheral surface of the cam ring 31.

On the other hand, when the vehicle performs sudden braking, AB
The front wheels WFL, WFR are controlled by controlling the locked state of the wheels by S (anti-lock brake system) or the like.
Are locked before the rear wheels WRL, WRR, so that the vehicle behavior is stabilized. When the rotational speeds of the rear wheels WRL, WRR exceed the rotational speeds of the front wheels WFL, WFR due to the rapid braking, the rotor 35 relatively rotates in the reverse direction, and the operating oil is sucked from the discharge ports 44.
The hydraulic oil is discharged from. As a result, the check valves 47 connected to the high pressure side suction ports 43 are opened, so that the high pressure side suction ports 43 are connected to the vane lifting port 35.
b, and the communication between the vane lifting port 35b and the discharge ports 44 on the low pressure side is shut off by the check valves 47 connected to the discharge ports 44. Thus, the vanes 41 can be urged radially outward by the hydraulic pressure transmitted to the vane push-up port 35 b, and their tips can be pressed against the inner peripheral surface of the cam ring 31.

Also in the second embodiment, the front wheels WF
The magnitude of the load generated by the vane pumps PL and PR differs depending on the direction of the relative rotation of the rear wheels LRL and WFR and the rear wheels WRL and WRR. That is, when the rotation speeds of the front wheels WFL, WFR exceed the rotation speeds of the rear wheels WRL, WRR, such as when starting or suddenly accelerating on the low friction road described above,
The hydraulic oil flows through the pair of first orifices 51 in the direction indicated by the arrow in FIG. 7 to generate a large pressure loss. as a result,
The vane pump P generates a large load and the front wheels WFL, W
The driving force transmitted from the FR to the rear wheels WRL, WRR increases (see the solid line in FIG. 8A).

On the other hand, as in the case of the sudden braking described above, the rear wheels WR
When the rotational speeds of L and WRR exceed the rotational speeds of front wheels WFL and WFR, hydraulic oil flows through the pair of first orifices 51 in a direction opposite to the direction shown by the arrow in FIG. . As a result, the vane pump P generates a small load, and the driving force transmitted from the rear wheels WRL, WRR to the front wheels WFL, WFR decreases (see the broken line (B) in FIG. 8). Thus, the front wheels WFL and WFR are
Locking can be performed before RL and WRR to prevent the vehicle behavior from becoming unstable.

FIG. 13 shows a third embodiment of the present invention, and corresponds to FIG. 12 showing the second embodiment.

In the third embodiment, the mounting direction of the vane pump P is opposite to that of the second embodiment, and the first side plate 30, the cam ring 31, the second side plate 32 and the end plate 71 are connected to the propeller shaft 10. The rotor shaft 27 and the rotor 35 are connected to the third bevel gear 11 side. That is, the propeller shaft 10 is connected to the end plate 71 with bolts 81.
The shaft portion 11a of the third bevel gear 11 is
7, coupling 76, bolt 75 ..., coupling 8
0 and the rotor shaft 2 via the spline connection 79
7.

Also in this embodiment, the cam ring 31 and the rotor 35 are rotated relative to each other by the relative rotation of the front wheels WFL, WFR and the rear wheels WRL, WRR, so that the vane pump P operates. As in the first embodiment, the four-wheel drive function can be exhibited, and the effect of the reservoir 55 and the effect of providing the vane pump P on the propeller shaft 10 are the same as those of the first embodiment. However, the following special effects can be obtained by mounting the vane pump P upside down with respect to the second embodiment.

In other words, when a plurality of centrifugal valves are provided radially on the rotor 35 and the rotation of the rotor 35 increases during high-speed running, the centrifugal valve opens to switch the vane pump P to a no-load state. In order to open the centrifugal valve, the rotation speed of the rotor 35 is set to the front wheel W which is the main drive wheel.
It is necessary not to be affected by the slip of FL and WFR. Therefore, if the rotor 35 is assumed to be the front wheels WFL, WF
R, the front wheels W even if the vehicle speed is lower than the set vehicle speed
There is a problem that the centrifugal valve opens when the rotation speed increases due to slippage of the FL and WFR. However, as in the third embodiment, the rear wheels WRL and WRR in which the rotor 35 is the auxiliary drive wheel are used.
The above problem can be solved if the connection is made.

Although the embodiments of the present invention have been described in detail, various design changes can be made in the present invention without departing from the gist thereof.

For example, the hydraulic coupling device H of the embodiment has the first side plates 30, 30L, 30
R, the cam rings 31, 31L, 31R and the second side plate 32 are accommodated in the casing 19, but the present invention does not include the casing 19, and the first side plates 30, 30L, 30R, the cam rings 31, 31L, 31
The present invention can also be applied to the hydraulic coupling device H in which the R and the second side plate 32 are directly exposed.

The rotor shafts 27, 27L, 27R
Grooves 27b, 27b formed in through holes 27a
Can be set as appropriate, and a spiral groove can be used instead of a linear groove.

[0074]

As described above, according to the first aspect of the present invention, the reservoir provided in the hollow portion of the rotor shaft supporting the rotor includes the piston which is slidably fitted in the hollow portion. Therefore, when hydraulic oil in the casing expands due to temperature rise, the piston moves in one direction to reduce the volume of the reservoir, and when hydraulic oil in the casing contracts due to temperature decrease, the piston moves in the other direction. And the volume of the reservoir is increased, so that the intrusion of air into the hydraulic oil can be reliably prevented.
Moreover, when the volume of the hydraulic oil expands significantly due to the abnormally high temperature of the vane pump and cannot be absorbed by the reservoir, the relief means communicates the hollow portion of the rotor shaft to the atmosphere and discharges the hydraulic oil to the outside. Damage to the vane pump due to abnormal expansion can be reliably prevented.
Further, since the reservoir is housed in the hollow portion of the rotor shaft, the reservoir can be compactly arranged while avoiding the influence of the discharge pressure of the vane pump.

[Brief description of the drawings]

FIG. 1 is a skeleton diagram of a power transmission device of a four-wheel drive vehicle.

FIG. 2 is a longitudinal sectional view of a hydraulic coupling device.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 2;

FIG. 6 is a sectional view taken along line 6-6 in FIG. 4;

FIG. 7 is a sectional view taken along line 7-7 of FIG. 4;

FIG. 8 is a graph illustrating the operation of an orifice plate.

FIG. 9 is a hydraulic circuit diagram of a hydraulic coupling device.

FIG. 10 is a skeleton diagram of a power transmission device of a four-wheel drive vehicle according to a second embodiment.

FIG. 11 is a longitudinal sectional view of a hydraulic coupling device.

FIG. 12 is a hydraulic circuit diagram of a hydraulic coupling device.

FIG. 13 is a longitudinal sectional view of a hydraulic coupling device according to a third embodiment.

[Explanation of symbols]

 27 rotor shaft 27L rotor shaft 27R rotor shaft 27a through hole (hollow portion) 27b relief groove (relief means) 27c communication hole (relief means) 30 first side plate (side plate) 30L first side plate (side plate) 30R first 1 side plate (side plate) 31 cam ring 31L cam ring 31R cam ring 32 second side plate (side plate) 35 rotor 35L rotor 35R rotor 35a vane groove 41 vane 55 reservoir 55L reservoir 55R reservoir 57 piston

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takuya Kurokawa 19, Matsuyamacho, Moka-shi, Tochigi Prefecture Honda Motor Co., Ltd.Tochigi Seisakusho Co., Ltd. (72) Inventor Takeshi Mochizuki 19 Matsuyamacho, Moka-shi, Tochigi Pref. (72) Inventor Toru Mabuchi 19, Matsuyama-cho, Moka-shi, Tochigi F-term (reference) in Honda Motor Co., Ltd. Tochigi Seisakusho Co., Ltd. CC19 CC21 DD01 DD07 DD09 DD21 DD24 DD35 DD40

Claims (1)

[Claims] 1. A rotor (35, 35L, 35R) is rotatably housed in a space surrounded by cam rings (31, 31L, 31R) and side plates (30, 30L, 30R, 32). , 35L, 35
R), a radially outer end of a vane (41) slidably supported by a plurality of vane grooves (35a) radially formed on the inner peripheral surface of the cam ring (31, 31L, 31R), (35, 35L, 35R) supporting the hollow portion (27) of the rotor shaft (27, 27L, 27R).
a) is provided with a reservoir (55, 55L, 55R), and the reservoir (55, 55L, 55R) is slidably fitted to the hollow portion (27a) of the rotor shaft (27, 27L, 27R). The piston (57) and the rotor shaft (27, 27)
A relief pump (27b, 27c) for communicating a hollow portion (27a) of the airbag (L, 27R) with the atmosphere.