JP2554813Y2 - Drive coupling device for four-wheel drive - Google Patents

Description

[Detailed description of the invention]

[0001]

This invention realizes a four-wheel drive state by transmitting the driving force from one side of the front and rear wheels to the other side by the hydraulic pressure generated by a hydraulic pump interposed between the two. Do 4
The present invention relates to a drive coupling device for wheel drive.

[0002]

2. Description of the Related Art A four-wheel drive vehicle that travels by transmitting the driving force of an engine to both front and rear wheels can realize stable traveling irrespective of natural conditions such as weather and road surface conditions and traveling conditions. It is in the spotlight as a thing.

In recent years, four-wheel drive vehicles have a drive connection in which a drive force distribution to both wheels is automatically changed in accordance with a rotational speed difference generated between the two wheels in a transmission system to front and rear wheels. The mainstream is a full-time four-wheel drive vehicle configured to obtain a substantially four-wheel drive state by interposing devices, and one of the drive coupling devices that performs such operation is a hydraulic pump. There is known a device that utilizes generated hydraulic pressure.

[0004] This is a hydraulic pump (generally a vane pump) constructed by coaxially combining a rotor and a casing, which are separately and interlocked with a transmission shaft to each of a front wheel and a rear wheel. With this configuration, a relative rotation corresponding to the rotational speed difference between the front and rear wheels is generated between the rotor and the casing, and the relative rotation, that is, between the front and rear wheels, is formed in a pump chamber formed therebetween. A hydraulic pressure is generated in accordance with the rotational speed difference between the front and rear wheels, and torque is transmitted from one of the front and rear wheels to the other through the hydraulic pressure acting between the rotor and the casing to suppress relative rotation between the two. A four-wheel drive state is realized.

[0005] The transmission characteristics required of a four-wheel drive vehicle differ depending on the traveling state, and the occurrence of tight corner braking caused by the difference in the turning radii of the front and rear wheels during turning is suppressed. Therefore, in a relatively small rotation speed difference range that is expected to occur during turning, the rate of change of the transmission torque with respect to the rotation speed difference is small,
It is desirable that a loose connection between the front and rear wheels be obtained. On the other hand, when one of the front and rear wheels falls into an idling state due to entry into a snow puddle, a sand puddle, etc. Sufficient torque transmission to the non-idling side is required to enable escape, and in the range where the rotational speed difference between the front and rear wheels is large, conversely, the rate of change of the transmission torque with respect to the rotational speed difference is large, rigid connection It is desirable that a state be obtained.

[0006] In the above-mentioned drive coupling device using a hydraulic pump, the hydraulic pressure that acts as a medium for transmitting the driving force is such that the oil discharged from the hydraulic pump is supplied to the low-pressure portion in accordance with the rotational speed difference between the front and rear wheels. It is generated against the flow resistance of the discharge-side oil passage until reflux occurs. The applicant of the present application has paid attention to this fact, and has disclosed a drive coupling device for four-wheel drive capable of obtaining desired transmission characteristics as described above in Japanese Patent Application Laid-Open No. H2-120521 and Japanese Utility Model Application Laid-Open No. 2-122228.
No. each proposed. FIGS. 4 and 5 are enlarged cross-sectional views of a main part showing a configuration of a characteristic portion of the four-wheel drive drive coupling device proposed in Japanese Utility Model Laid-Open No. 2-122228.

This four-wheel drive drive coupling device is provided with a throttle means which operates in the middle of the discharge oil passage 42 of the hydraulic pump to reduce the oil passage area of the oil passage 42 with an increase in the hydraulic pressure generated inside the hydraulic pump. The throttle means 6 is configured to store the generated hydraulic pressure in a spool chamber 43 formed by increasing the diameter of the communication side (upper side in the figure) of the discharge oil passage 42 to the low-pressure portion. A cylindrical throttle spool 60 with a bottom that slides upon receiving pressure, and limiting members 61 and 62 that limit the sliding range of the throttle spool 60 are provided.

The one limiting member 61 is press-fitted and fixed to the inner rear end of the spool chamber 43, and is slidably fitted on a guide rod 61b provided upright at the axial center of the limiting member 61. The throttle spool 60 has a pressure guide hole 6 penetrating the axis of the guide rod 61b.
The hydraulic pressure generated by the hydraulic pump introduced via 1c is received on the inner bottom surface, and is pressed toward the communication side with the low pressure portion. In addition, the other limiting member 62, which has a cylindrical shape with a short thin wall and a bottom,
The bottom part is fitted into the spool chamber 43 with the low pressure part side,
The movement toward the low pressure portion is restrained by a snap ring 63 engaged near the communication end of the spool chamber 43 with the low pressure portion, and the throttle spool 60 is interposed between the restriction member 62 and the throttle member 60. The coil spring 64 is urged toward the communication side (lower side in the figure) with the discharge oil passage 42.

In the throttle means 6, the throttle spool 60 slides due to the balance between the hydraulic pressure generated inside the hydraulic pump and the urging force of the coil spring 64, and the sliding causes the peripheral wall of the throttle spool 60 to move inside and outside. The communication area between the oil passage hole 60a penetrating through the inner wall and the oil passage hole 61a penetrating the peripheral wall of the guide rod 61b in and out changes.

That is, the generated hydraulic pressure inside the hydraulic pump is low,
When the throttle spool 60 is pressed against the restricting member 61, as shown in FIG. 4, the oil passage holes 60a and 61a communicate over substantially the entire surface, and the oil passage resistance of the entire discharge oil passage 42 is minimized. . Conversely, if the generated oil pressure inside the hydraulic pump is high and the spool 60 receiving the oil pressure slides against the urging force of the coil spring 64 and is pressed against the other limiting member 62, As a result of the communication between the holes 60a and 61a being substantially completely closed as shown in FIG. 5, the oil flow resistance of the entire discharge oil passage 42 is maximized. At this time, the flow of the hydraulic oil to the low-pressure portion is generated via a small-diameter throttle hole 60b formed in the center of the bottom surface of the throttle spool 60.

Therefore, in the four-wheel drive drive coupling device provided with the throttle means 6, the rotational speed difference between the front and rear wheels is small, and the throttle spool is generated by the hydraulic pressure generated inside the hydraulic pump.
Placed in a range where the pressing force of 60 is less than the biasing force of the coil spring 64
Te is the small becomes oil passing resistance of the discharge oil passage 42, before the portion transmitted torque from one of the rear wheels to the other is increased gradually to increase the rotational speed difference (first gradually increasing section) is revealing I do. Further, the hydraulic pressure generated spool 60 squeezed beyond the urging force of the coil spring 64 starts sliding, Oite between <br/> until abuts against the limiting member 62 is discharged in accordance with the increase in the hydraulic pressure generated The oil passage resistance of the oil passage 42 increases, and this increase in the oil passage resistance promotes an increase in the generated oil pressure, and a portion (sudden increase portion) where the transmission torque suddenly increases with the increase in the rotational speed difference appears. Furthermore, Oite after the contact by passing oil holes 60a, the communicating portion between 61a is fully closed, a portion that increases a rate of increase determined by oil passing area of the throttle hole 60b relatively slowly (the 2) . This
As a result, it a Rukoto such transmission characteristics can be obtained is shown in FIG. 6
As described above , such a characteristic is a desired transmission characteristic in the four-wheel drive drive coupling device.

[0012]

However, the hydraulic pressure generated by the hydraulic pump generally includes a pulsating component.
Since the throttle spool 60 receiving the generated hydraulic pressure exhibits unstable behavior due to the action of the pulsating component during the above-described sliding, the portion where the transmission torque suddenly increases during this sliding is not stable, Fluctuations in the transmission torque that occur under a constant rotational speed difference may cause the driver to feel uncomfortable.

Further, since the throttle spool 60 receives the high pressure generated inside the hydraulic pump, a transition point between the portion where the transmission torque sharply increases and the first and second gradually increasing portions occurs at a desired rotational speed difference. In order to obtain the transmission characteristics as shown in FIG. 6, it is necessary to process each part of the throttle means 6 with high dimensional accuracy, such as the area of the pressure receiving surface of the throttle spool 60, the clearance of the fitting portion with the guide rod 61b, and the like. However, there is a disadvantage that the number of processing steps is increased.

The present invention has been made in view of such circumstances, and further develops the four-wheel drive drive coupling device disclosed in Japanese Utility Model Laid-Open No. 2-122228 to provide a hydraulic pump discharge side oil passage.
Oite of the throttle means arranged in the middle, calling of the hydraulic pump
The movement of the throttle spool that receives the raw oil pressure occurs stably
Thus, an object of the present invention is to provide a four-wheel drive drive coupling device capable of stably obtaining desired transmission characteristics.

[0015]

SUMMARY OF THE INVENTION A drive coupling device for a four-wheel drive according to the present invention generates a hydraulic pressure according to a rotational speed difference between a front wheel and a rear wheel and discharges a hydraulic pump for coupling the two wheels. the middle of the side oil passage, it includes a throttle means for reducing the oil passage area of the discharge-side oil passage by the movement of the diaphragm spool caused by pressure generated hydraulic pressure of the hydraulic pump, the with increasing the hydraulic pressure generated A structure that increases the oil flow resistance of the discharge-side oil passage 4
In the drive coupling device for a wheel drive, the discharge-side oil passage is disposed upstream of the throttle unit, and the generated hydraulic pressure is reduced by the throttle.
The pressure is reduced before receiving the spool pressure, and
It is characterized by having a fixed throttle for reducing a pulsating component contained therein .

[0016]

[Action] In the present invention, the occurrence hydraulic internal hydraulic pump diaphragm is reduced pulsation components by passage of the fixed throttle arranged on the upstream side of the unit, also stop <br/> in a state of being reduced to an appropriate Acts on the spool . As a result, the unstable operation of the aperture spool is suppressed, and the processing accuracy in each part of the aperture means can be reduced, thereby reducing the number of processing steps.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing an embodiment thereof. FIG. 1 is a longitudinal sectional view of a four-wheel drive drive connection device (hereinafter referred to as the device of the present invention) according to the present invention.

In the figure, reference numeral 1 denotes an input shaft that rotates in conjunction with one of the front and rear wheels, and 2 denotes an output shaft that rotates in conjunction with the other. The vane pump 3 is a hydraulic pump that generates a hydraulic pressure between the input shaft 1 and the output shaft 2 according to the rotational speed difference between the two shafts 1 and 2, ie, the rotational speed difference generated between the front and rear wheels. And the driving force is transmitted from the input shaft 1 side to the output shaft 2 side through the hydraulic pressure generated inside the vane pump 3.

As is well known, the rotor 30 of the vane pump 3 is provided with a plurality of rectangular flat vanes 30a, 30a... Which can be moved back and forth in the radial direction, and these vanes 30a, 30a. A short cylindrical member urged outward by 30b. The casing of the vane pump 3 is
A cylindrical cam ring 31 with the same thickness as the rotor 30 and a pressure plate 32 in the form of a thick hollow disk, and a short cylinder coaxially connected to the inner peripheral side of the hollow disk Side plate 33 and a holding plate 34 having the same shape.The cylindrical portion of the holding plate 34 is externally fitted to the cylindrical portion of the side plate 33 to integrate them, and these and the pressure plate
32 are coaxially positioned on both sides of the cam ring 31, and a plurality of fixing bolts 35 which penetrate the disc portions of the holding plate 34 and the side plate 33 and the cam ring 31 in the thickness direction and are screwed to the pressure plate 32. , 35,..., Are all integrally connected.

The rotor shaft 4, which is the rotating shaft of the rotor 30, is inserted into the hollow portion of the side plate 33 and the hollow portion of the pressure plate 32 from the side plate 33 side, and is fitted to the hollow portion of the pressure plate 32. As shown in the figure, both sides of the cam ring 31 are supported by a ball bearing and a needle roller bearing fitted inside the cylindrical portion of the side plate 33.

The rotor 30 is housed in a cavity formed inside the cam ring 31 with both sides sandwiched by a pressure plate 32 and a side plate 33, and is spline-connected to the rotor shaft 4 between the above-described bearing positions. The rotation of the rotor shaft 4 causes the cam ring 31 to rotate coaxially inside the cam ring 31. The inner circumference of the cam ring 31 has an axial cross-sectional shape in which a plurality of recesses are formed around a circle, and a plurality of chambers surrounded by the outer circumference of the rotor 30 are formed at positions where the respective recesses are formed. Each of these chambers is
It functions as a pump chamber that generates hydraulic pressure in accordance with the relative rotation generated between the cam ring 31 and the cam ring 31 as described later.

The input shaft 1 is flanged to the end of the rotor shaft 4 projecting toward the side plate 33, and the output shaft 2 is flanged to the outer surface of the pressure plate 32. As a result, the rotor 30 rotates in conjunction with the rotation of the input shaft 1, and the casing including the pressure plate 33 as a part thereof rotates in conjunction with the rotation of the output shaft 2.
A relative rotation corresponding to a rotation speed difference between the input shaft 1 and the output shaft 2, that is, a rotation speed difference between the front and rear wheels, is generated between the casing 30 and the casing.

A thin cylinder 36 is fitted on the outside of the casing, and hydraulic oil for the vane pump 3 is supplied to the inside of an oil tank T formed in an annular shape between the cylinder 36 and the outer periphery of the casing. It is enclosed in. The plurality of pump chambers inside the cam ring 31 each penetrate the disc portion of the holding plate 34 and the side plate 33 in the thickness direction, and a check valve that allows only inflow to each pump chamber is fitted in the middle thereof. .. (Only one is shown) are connected to the oil tank T.

On the other hand, one end of each of the pump chambers is opened in the pressure plate 32, and the pressure plate 32 is turned radially inward to communicate with the base of the vanes 30a, 30a,. .. (Only one is shown) formed by fitting a check valve which allows only outflow from the chamber in the middle thereof, and these are provided on the discharge side of each pump chamber. The bases of the vanes 30a, 30a,..., Which are collectively connected, are connected to the oil tank T outside the casing via a discharge oil passage.

As shown in the figure, the discharge oil passage 42 has one end opened at a position corresponding to the base of the vanes 30a on the inner surface of the pressure plate 32, and has an appropriate depth in the thickness direction of the pressure plate 32. And a hole formed at an appropriate depth radially inward from the outer peripheral surface of the pressure plate 32 so as to intersect at a substantially right angle. The throttle means 5 is provided on the side of the oil passage 42 communicating with the oil tank T.

FIGS. 2 and 3 are enlarged sectional views of the vicinity of the diaphragm means 5, which is a characteristic part of the apparatus of the present invention. The aperture means 5 is
As with the conventional throttle means 6 shown in FIGS.
42 communicating side of the oil tank T, i.e., the inside of the spool chamber 43 to the downstream side is formed by increasing the diameter of the discharge passage 42, the vane
A throttle spool 50 that slides by receiving hydraulic pressure generated in the discharge oil passage 42 by the operation of the pump 3 is provided.

The throttle spool 50 having a cylindrical shape with a bottom is
The bottom of the spool chamber 43 is loosely fitted in the spool chamber 43 with the bottom facing inward, and is slidably externally fitted on a guide rod 51b erected at the axial center of the limiting member 51 fitted on the opening side of the spool chamber 43. It is urged toward the inner side, that is, the side communicating with the discharge oil passage 42, by a coil spring 54 interposed between the restriction member 51 and the coil spring 54. The restriction member 51 is connected to the oil tank T by a snap ring 53 attached near the end of the spool chamber 43 communicating with the oil tank T.
Side movement, the spring force of the coil spring 54 acts to press the throttle spool 50 against the bottom of the spool chamber 43. At this time, as shown in FIG. The entire surface of the communication end of the chamber 43 with the discharge oil passage 42 that opens to the bottom is closed, and the closed surface receives the internal pressure of the discharge oil passage 42 and slides against the spring force of the coil spring 54.

The throttle spool 50 is provided with an oil passage hole 50a penetrating a predetermined position of the peripheral wall in and out, and a small-diameter throttle hole 50b penetrating the center of the bottom surface in and out. The guide rod 51b for guiding the sliding includes an oil guide hole 51c penetrating the shaft center portion, and an oil passage hole 51a penetrating a predetermined position of the peripheral wall in and out. Oil passage hole on the throttle spool 50 side
50a and the oil passage hole 51a on the guide rod 51b side
2 is located at a position where the opening end of the discharge oil passage 42 is fully closed.
As shown in FIG. 3, the communication is formed over substantially the entire surface, and the communication area is reduced as shown in FIG.

In the apparatus according to the present invention, the aperture means 5
The fixed throttle 7 is arranged in the middle of the discharge oil passage 42 formed at the downstream end. The fixed throttle 7 is located in the middle of the discharge oil passage 42 that constitutes the discharge-side oil passage of the vane pump 3 and may be arranged at any position on the upstream side of the throttle means 5. It is reasonable to arrange it downstream of the merged position of the discharge oils from the plurality of pump chambers.

The fixed throttle 7 is formed by forming a small-diameter throttle hole 71 penetrating in the axial direction in the axial center portion of a short cylindrical throttle member 70. For example, as shown in FIGS. 2 and 3, the restricting member 70 is inserted into a fitting hole 44 having a circular cross section formed by increasing the diameter of the communication end of the discharge oil passage 42 with the inner surface of the pressure plate 32. This is realized by fitting.

In the apparatus of the present invention configured as described above,
When a rotation speed difference occurs between the input shaft 1 and the output shaft 2, that is, between the front and rear wheels, the relative rotation at a speed corresponding to this rotation speed difference causes the rotor 30 of the vane pump 3 and the cam ring 31 to rotate. Hydraulic oil sealed in the oil tank T is introduced into the pump chambers formed between them and formed between the two via the suction oil passages 40 that open to the upstream side in the respective relative rotation directions.

In each of the pump chambers of the vane pump 3, the vanes 30a, 30a.
The hydraulic fluid introduced into the pump chamber is pressed against the inner peripheral surface of the cam ring 31 by the urging of the vanes 30b and 30b, and introduced into the pump chamber.
It is sealed between 0a and 30a, and is rotated together with them to increase the pressure. At this time, the hydraulic pressure generated in each pump chamber acts between the rotor 30 and the cam ring 31 so as to suppress the relative rotation between them, and from the input shaft 1 to the output shaft 2, that is, from one of the front and rear wheels. On the other hand, torque is transmitted via the hydraulic pressure, and a four-wheel drive state is realized.

The oil that has been pressurized in each pump chamber passes through the oil guide passage 41 that opens to the downstream side in the relative rotation direction, so that the vanes 30a, 30a
., And presses each of the vanes 30a, 30a... Outward by a synergistic action with the urging force of the coil springs 30b, 30b.
It returns to the oil tank T via the discharge oil passage 42. The recirculated oil is sucked into the pump chambers of the vane pump 3 again and used for circulation.

In the operation as described above, the pressure is generated in each pump chamber in accordance with the relative rotation between the rotor 30 and the cam ring 31,
The hydraulic pressure that acts as a medium for transmitting the drive torque is generated against the oil flow resistance in the circulation of the hydraulic oil as described above, mainly against the oil flow resistance in the discharge oil passage 42. The oil flow resistance of the discharge oil passage 42 is
It depends on the oil flow resistance in the throttle means 5 operating as described above and the fixed throttle 7 arranged upstream of the throttle means 5.

When the throttle spool 50 of the throttle means 5 is at the position shown in FIG. 2, the oil passage in the throttle means 5 is limited to only the throttle hole 50b formed on the bottom surface of the throttle spool 50. Although it has a large oil flow resistance, when a hydraulic pressure is generated inside the vane pump 3 and acts through the fixed throttle 7, the throttle spool 50 rises against the spring force of the coil spring 54 due to the pressure received by this hydraulic pressure, Between the bottom of the spool chamber 43 and the inside of the spool chamber 42,
An oil passage indicated by an arrow in FIG. 3 is formed by a communication portion between the oil passage holes 50a and 51a and an oil passage hole 51c inside the guide rod 51b.

As described above, the communication area between the oil passage holes 50a and 51a decreases as the sliding amount of the throttle spool 50 increases, and the amount of sliding of the throttle spool 50 corresponds to the level of the hydraulic pressure acting on it. . Therefore, when the hydraulic pressure generated inside the pump chamber is low and the throttle spool 50 is slightly floating, the communication portion between the oil passage holes 50a and 51a is substantially fully opened, and the oil passage resistance in the throttle means 5 is reduced. Since it is small, the rate of increase in the transmission driving force with the increase in the rotational speed difference is kept small,
The first gradually increasing portion shown in FIG. 6 is obtained.

As the difference in rotation speed increases, the generated oil pressure increases, the sliding amount of the throttle spool 50 that receives the oil pressure via the fixed throttle 7 increases, and the communication area between the oil passage holes 50a and 51a decreases. In this case, the hydraulic pressure generated inside the vane pump 3 increases in accordance with the increase in the oil flow resistance in the throttle means 5, and the sliding amount of the throttle spool 50 increases in accordance with this.
As a result, the rate of increase of the transmission torque with respect to the increase in the rotational speed difference is very large until the communication between the oil passage holes 50a and 51a is completely closed. As shown in FIG.

Further, after the communication between the oil passage holes 50a and 51a is completely closed, the oil path of the return oil to the oil tank T is limited to only the throttle hole 50c on the bottom surface of the throttle spool 50. From this, the oil flow resistance of the subsequent throttle means 5 is kept constant,
A second gradually increasing portion shown in FIG. 6 in which the transmission torque increases with a rate of change determined by the combined resistance of this and the fixed throttle 7 is obtained.

The transmission characteristics obtained as described above are desirable in a four-wheel drive vehicle. However, in order to realize the transmission characteristics stably, it is necessary that the sliding of the throttle spool 50 occurs stably. It is. In the device of the present invention, the operating pressure on the throttle spool 50 is not the hydraulic pressure itself generated inside the vane pump 3 as described above, but the hydraulic pressure in which the pulsation component is reduced by passing through the throttle hole 71 of the fixed throttle 7. There is no danger that the sliding position of the spool 50 will fluctuate due to the action of the pulsating component . Working pressure on the throttle spool 50
With the hydraulic pressure appropriately reduced by passing through the throttle hole 71.
Because of this, the sudden increase in the transmission torque shown in FIG.
In order to obtain the transition point between the second incremental portion and the desired rotational speed difference, the area of the pressure receiving surface of the throttle spool 50, the guide rod
Extremely high dimensional accuracy is not required for each part of the drawing means 5 such as a gap between the fitting part and the fitting part 51b, and the number of processing steps can be reduced.

The structure of the restricting means 5 is not limited to that shown in the present embodiment, and, similarly to the restricting means 6 shown in FIGS. 4 and 5, a restricting member is disposed on each side of the restricting spool 50. Needless to say, the mode of forming the discharge oil passage 42 is not limited to that shown in this embodiment.

[0041]

[Effect of the Invention] As described in detail above, in the device of the present invention,
Upstream of the throttle means arranged in the middle of the discharge-side oil passage of the hydraulic pump
Side with a fixed throttle.
Min while being mitigate, grain oil pressure is reduced appropriately said
Since the configuration acts on the aperture spool of the aperture means, unstable operation during movement of the aperture spool can be suppressed, a desired transmission characteristic can be obtained stably, and the required accuracy in each section of the aperture means is relaxed. The present invention has excellent effects such as a reduction in the number of processing steps.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing the entire configuration of the device of the present invention.

FIG. 2 is an enlarged sectional view of a characteristic portion of the device of the present invention.

FIG. 3 is an enlarged sectional view of a characteristic portion of the device of the present invention.

FIG. 4 is an enlarged sectional view of a main part of a conventional drive coupling device for four-wheel drive.

FIG. 5 is an enlarged sectional view of a main part of a conventional drive coupling device for four-wheel drive.

FIG. 6 is a graph showing desirable transmission characteristics.

[Explanation of symbols]

 Reference Signs List 1 input shaft 2 output shaft 3 vane pump 5 throttle means 7 fixed throttle 30 rotor 31 cam ring 32 pressure plate 33 side plate 42 discharge oil passage 50 throttle spool 51 restricting member 50a oil passage hole 51a oil passage hole 51b guide rod T oil tank

Claims (1)

(57) [Scope of request for utility model registration] 1. A discharge side of a hydraulic pump for connecting both wheels by generating a hydraulic pressure according to a rotational speed difference between front and rear wheels therein.
The middle of the oil passage, it includes a throttle means for reducing the oil passage area of the discharge-side oil passage by the movement of the diaphragm spool caused by pressure generated hydraulic pressure of the hydraulic pump, the discharge with the rise of the hydraulic pressure generated In the four-wheel drive drive coupling device configured to increase the oil flow resistance of the side oil passage, the discharge oil passage is disposed upstream of the throttle means, and the generated oil pressure is reduced by the throttle.
The pressure is reduced before the spool receives pressure, and is included in the generated hydraulic pressure.
A four-wheel drive drive coupling device, comprising: a fixed throttle that reduces a pulsating component to be generated.