Hydraulic shock absorber

A hydraulic shock absorber includes: a cylinder that has an opening portion in a side wall surface on an axle side thereof; a reservoir that stores oil; a control unit that generates a damping force; and a movement prevention member at least a part of which is disposed outside the cylinder and on a vehicle body side of the opening portion, and that obstructs the oil from moving from the axle side to the vehicle body side.

FIELD OF THE INVENTION

The present invention relates to a hydraulic shock absorber that buffers an impact from a road surface.

BACKGROUND OF THE INVENTION

As a suspension device for suspending a wheel in a straddle-type vehicle such as a two-wheeled vehicle and a three-wheeled vehicle, for example, there is known a hydraulic shock absorber described in Patent Literature 1 in which a vehicle body-side tube and a wheel-side tube are formed telescopically. In the hydraulic shock absorber of Patent Literature 1, when an impact due to unevenness of the road surface is received by the wheel, the wheel-side tube telescopically moves in and out of the vehicle body-side tube.

However, in the hydraulic shock absorber of Patent Literature 1, when a straddle-type vehicle in which the hydraulic shock absorber is mounted vibrates in an upper-lower direction, oil inside a reservoir may move upward and may not stay in a vicinity of an opening portion leading from the reservoir to an interior of a cylinder. When the hydraulic shock absorber is rapidly extended in this situation, an amount of oil supplied to the interior of the cylinder may be insufficient, and air may be mixed with the oil flowing into a damping force generator to cause air biting. When air biting occurs, a desired damping force cannot be generated.

SUMMARY OF THE INVENTION

An object of an aspect of the present invention is to provide a hydraulic shock absorber which can stably generate a damping force.

In order to solve the above problems, a hydraulic shock absorber of an aspect of the present invention includes: a vehicle body-side tube that is disposed on a vehicle body side; an axle-side tube that is disposed on an axle side; a cylinder that is provided in the axle-side tube and has at least one opening portion in an axle-side side wall surface; a reservoir that is defined at an outer side of the cylinder and stores oil; a rod that is provided in the vehicle body-side tube; a piston that is provided on an axle side of the rod, and slides relative to an inner peripheral surface of the cylinder; a damping force generating unit that generates a damping force by oil flow due to a movement of the piston; and a movement prevention member at least a part of which is disposed outside the cylinder and on a vehicle body side of the opening portion, and that obstructs oil from moving from the axle side to the vehicle body side.

According to the aspect of the present invention, a damping force can be stably generated.

DETAILED DESCRIPTION OF THE INVENTION

An example of a front fork as an embodiment of a hydraulic shock absorber of the present invention will be described below.

FIG.1is a cross-sectional view showing a configuration of a hydraulic shock absorber according to an embodiment of the present invention. A hydraulic shock absorber1is a device that is attached in pair to both left and right sides of a wheel (not shown) in a saddle-type vehicle such as a two-wheeled vehicle or a three-wheeled vehicle, and functions as a suspension device for suspending the wheel.

As shown inFIG.1, the hydraulic shock absorber1is of a telescopic type, and includes a cylindrical tube11(vehicle body-side tube) connected to a vehicle body-side bracket (not shown) and a cylindrical tube12(axle-side tube) connected to an axle-side bracket13. The tube12moves relative to the tube11with a rod16as an axis and moves in and out of the tube11. Inside the tube12, a coil spring14that urges the tube11and the tube12in an extension direction is disposed. In the present embodiment, the hydraulic shock absorber1forms a pair of front forks in combination with another suspension device (not shown) having a coil spring14and no built-in damper. As another embodiment, front forks configured with suspension devices having built-in dampers on both left and right sides may be provided.

In the hydraulic shock absorber1, when an impact due to unevenness of a road surface is received by the wheel (not shown), the tube12telescopically moves in and out of the tube11. A process of compressing the hydraulic shock absorber1is referred to as a compression stroke, and a process of extending the hydraulic shock absorber1is referred to as an extension stroke. In the present embodiment, the inverted-type hydraulic shock absorber1in which the tube12moves in and out of the tube11is described, but the hydraulic shock absorber1can also be of an upright type in which the tube11moves in and out of the tube12.

The hydraulic shock absorber1includes a cylinder15attached to an axle side of the tube12with a central axis C1as an axis, and a rod16attached to a vehicle body side of the tube11with the central axis C1as an axis. A direction in which the central axis C1extends is referred to as an axial direction.

A vehicle body-side opening portion of the cylinder15is closed by a rod guide17, and an axle side of the rod16penetrates the rod guide17. The rod guide17slidably supports the rod16, and a rebound spring18that generates a reaction force when the tube11and the tube12are fully extended is disposed on an axle side of the rod guide17.

An interior of the cylinder15is filled with oil (hydraulic oil), and a piston19provided on the axle side of the rod16slides with respect to an inner peripheral surface of the cylinder15when the tube11and the tube12extend and contract. The piston19divides the cylinder15into a lower chamber20and an upper chamber21.

As shown inFIG.1, the rod16is a hollow shaft member having a flow path22through which the oil flows. The rod16has an opening portion23that opens in an axle-side end portion thereof and an opening portion24that opens in a vehicle body-side end portion thereof. In the present embodiment, the opening portion23is located inside the upper chamber21in the cylinder15. The upper chamber21is a vehicle body-side oil chamber in the oil chambers defined by the piston19sliding inside the cylinder15.

In the hydraulic shock absorber1, during both the compression stroke and the extension stroke, the oil flows from the upper chamber21into the flow path22, flows through an interior of the flow path22from an axle side thereof toward a vehicle body side thereof, and passes through a control unit10disposed on a vehicle body side of the rod16.

A base valve27is disposed at an axle-side end portion of the cylinder15, and the control unit10(damping force generating unit) is disposed on a cap member25that is disposed on the vehicle body side of the tube11. The control unit10is a damping force generator that generates a damping force by flow of the oil flowing out from the opening portion24of the rod16(that is, flow of the oil generated due to the movement of the piston19), and electronically controls an opening area of a variable throttle valve so as to control magnitude of the damping force generated when the oil passes through the variable throttle valve.

The control unit10provided in the hydraulic shock absorber1does not have to be an electronically controlled damping force generator, and a damping force generator that manually adjusts the damping force may be provided in the hydraulic shock absorber1. The damping force generator provided in the hydraulic shock absorber1does not have to be a device formed as a unit on the vehicle body side of the tube11. The hydraulic shock absorber1may be provided with a known substitutable damping force generator.

A vehicle body-side opening of the tube11is closed by the cap member25, and an axle-side opening of the tube12is closed by the axle-side bracket13. In order to prevent gas and oil enclosed inside the tube11and the tube12from leaking out, a tubular gap formed in an overlapping portion between the tube11and the tube12is closed with an oil seal or the like.

In the hydraulic shock absorber1, the oil is stored in a reservoir26that is a space at an outer side of the cylinder15surrounded by the tube11and the tube12. That is, the reservoir26is an oil chamber that stores oil and is defined at an outer side of the cylinder15and an inner side of the tube11and the tube12. Since the reservoir26is not completely filled with oil, an air chamber occupied by a gas such as air from a liquid level (not shown) of the stored oil is formed on the vehicle body side. The reservoir26compensates for a volume of oil that enters the cylinder15when the rod16enters the cylinder15and a volume change of oil caused by a temperature change.

FIG.2is a cross-sectional view showing a configuration of an axle-side end portion of the hydraulic shock absorber1. As shown inFIG.2, an opening portion43is formed in a side wall surface of the cylinder15on the axle-side thereof. At least one opening portion43is formed, for example, four opening portions43are formed. The opening portion43is an opening portion for the oil stored in the reservoir26to flow into the interior of the cylinder15. These opening portions43are formed closer to the axle side than a multilayer valve33of the base valve27. An opening central axis C2of the opening portion43is orthogonal to the central axis C1.

Outside of the cylinder15(that is, an interior of the reservoir26), a movement prevention member41that obstructs oil from moving from the axle side to the vehicle body side in the reservoir26is provided. The movement prevention member41includes a spring receiving portion41A (axle-side surface) that receives one end of the coil spring14, and a leg portion41B that extends from the spring receiving portion41A toward the axle side. The spring receiving portion41A is located closer to the vehicle body side than the opening portions43. It is sufficient that at least a part of the movement prevention member41is disposed on the vehicle body side of the opening portions43.

An axle-side end portion of the leg portion41B is abutted with a step portion13A formed on an inner wall surface of the axle-side bracket13, and an oil sump chamber42is defined by the movement prevention member41, the inner wall surface of the axle-side bracket13, and an outer wall surface of the cylinder15.

FIG.3is a top view of the movement prevention member41when viewed from the axial direction. InFIG.3, members other than the movement prevention member41and the cylinder15are omitted. As shown inFIG.3, the spring receiving portion41A has a substantially circular outer edge, and the leg portion41B is formed in a tubular shape along the outer edge. An opening portion41C for receiving the cylinder15is formed in the center of the spring receiving portion41A. Since a diameter of the opening portion41C is larger than an outer diameter of the cylinder15, an annular gap50is formed between the opening portion41C and the outer wall surface of the cylinder15.

As shown by a solid arrow inFIG.2, the oil in the reservoir26normally moves from the vehicle body side to the axle side through the gap50and then flows into the interior of the cylinder15through the opening portions43. Therefore, it can be said that the movement prevention member41defines the gap50that allows the oil to flow from the vehicle body side to the axle side.

Since gas exists on the vehicle body side of the reservoir26as described above, when the hydraulic shock absorber1vibrates in the upper-lower direction, the oil inside the reservoir26moves to the vehicle body side, and no oil exists in a vicinity of the opening portions43. When the hydraulic shock absorber1is rapidly extended in such a state, the oil supplied to the interior of the cylinder15is insufficient. As a result, air is mixed into the oil supplied to the control unit10through the flow path22of the rod16, and a phenomenon called air biting occurs in which the damping force is not generated. When air biting occurs, the ride quality and maneuverability of the vehicle deteriorate.

The movement prevention member41is provided to prevent such a phenomenon. That is, as the hydraulic shock absorber1vibrates in the upper-lower direction, the oil on the axle side of the reservoir26moves to the vehicle body side as shown by a broken line arrow inFIG.2. In the movement prevention member41, a part of the oil flow is obstructed by the spring receiving portion41A, and the oil is retained in the oil sump chamber42. As a result, the oil can stay in the vicinity of the opening portions43, and supply of the oil to the interior of the cylinder15can be prevented from being interrupted. An axle-side surface41E of the spring receiving portion41A corresponds to an axle-side surface of the movement prevention member41that obstructs a movement of the oil toward the vehicle body side.

In this way, in order to make the oil whose movement is obstructed by the spring receiving portion41A efficiently flows into the interior of the cylinder15from the opening portions43, it is preferable that a portion of the opening43closest to the vehicle body side is substantially the same in position with the surface41E of the spring receiving portion41A. In the example shown inFIG.2, the surface41E of the spring receiving portion41A is flat, and the surface41E and the portion of the opening portion43closest to the vehicle body side are adjacent to each other in the axial direction of the hydraulic shock absorber1. For example, a position of the surface41E in the axial direction and a position of the portion of the opening portion43closet to the vehicle body side in the axial direction are substantially the same within a range in consideration of a design error.

However, the position of the movement prevention member41, particularly the position of the surface41E, is not limited to that shown inFIG.2, and the position of the surface41E in the axial direction may overlap with that of the opening portion43or the surface41E may be located closer to the vehicle body side than the opening portion43. Further, as to be shown in an example in Embodiment 2, the surface41E does not have to be flat.

It is preferable that an opening area of the gap50is equal to or larger than a sum of opening areas of the plurality of opening portions43. This is because when the opening area of the gap50is smaller than the sum of the opening areas of the plurality of opening portions43, a flow path resistance of the oil passing through the gap50increases, and inflow of the oil into the interior of cylinder15is obstructed.

Further, as shown inFIGS.2and3, the movement prevention member41has an inclined surface41D between the vehicle body-side surface of the spring receiving portion41A and the opening portion41C. If the inclined surface41D is regarded as a part of the opening portion41C, a diameter of the opening portion41C formed in the movement prevention member41is larger on the vehicle body side than on the axle side.

Therefore, the oil flowing from the vehicle body side toward the axle side efficiently passes through the opening portion41C, but the oil flowing from the axle side toward the vehicle body side tends to be obstructed.

(Flow of Oil in Hydraulic Shock Absorber1)

In the compression stroke, as a volume of the upper chamber21(with reference toFIG.1) increases, the oil flows from the lower chamber20toward the upper chamber21. Then, an amount of oil in the lower chamber20corresponding to an infiltrated volume of the rod16is surplus, so that the surplus oil passes through the opening portions43and flows out to the reservoir26.

Meanwhile, in the extension stroke, as a volume of the lower chamber20increases, the oil in the reservoir26passes through the opening portions43and flows into the cylinder15.

Overview

As described above, the hydraulic shock absorber1includes: the tube11on the vehicle body side; the tube12on the axle side; the cylinder15that is provided in the tube11and has at least one opening portion43in the axle-side side wall surface; the reservoir26that is defined at an outer side of the cylinder15and stores oil; the rod16that is provided on the tube11; the piston19that is provided on the axle side of the rod16and slides with respect to the inner peripheral surface of the cylinder15; the control unit10that generates a damping force by oil flow due to movement of the piston19; and the movement prevention member41at least a part of which is disposed outside the cylinder15and on the vehicle body side of the opening portion43, and that obstructs the oil from moving from the axle side to the vehicle body side.

According to the configuration, even when the vehicle on which the hydraulic shock absorber1is mounted vibrates in the upper-lower direction, the oil stays in the vicinity of the opening portion43since the movement prevention member41obstructs the upward movement of the oil in the reservoir26.

Therefore, even when the hydraulic shock absorber1is rapidly extended, since the oil is supplied to the interior of the cylinder15, air is not mixed into the oil flowing into the control unit10, and therefore, the damping force can be stably generated.

The axle-side surface41E of the movement prevention member41and the portion of the opening portion43closest to the vehicle body side are adjacent to each other in the axial direction of the hydraulic shock absorber1. Therefore, the oil whose movement is obstructed by the surface41E of the movement prevention member41can efficiently flow into the opening portion43.

The movement prevention member41defines a gap50, that allows the oil to flow from the vehicle body side to the axle side, between the movement prevention member41and the side wall surface of the cylinder15. The oil in the reservoir26moves from the vehicle body side to the axle side through the gap50. By setting the gap between the movement prevention member41and the side wall surface of the cylinder15as a flow path of the oil, the flow path can be formed more easily than in a case where the flow path is formed in another portion of the movement prevention member41.

Further, by forming the gap50along at least a part of a periphery of the side wall surface of the cylinder15, the oil in the reservoir26can move from the vehicle body side to the axle side.

Further, the opening area of the gap50is equal to or larger than a sum of an opening area of the at least one opening portion43. With the configuration, the flow path resistance of the oil passing through the gap50is reduced, and obstruction on supply of the oil to the interior of the cylinder15can be prevented.

The coil spring14is provided inside the reservoir26, and the movement prevention member41includes the spring receiving portion41A that receives the coil spring14, and the leg portion41B that extends from the spring receiving portion41A toward the axle side. With the configuration, the movement prevention member41can also function as a spring receiving portion that receives the coil spring14inside the reservoir26.

Another embodiment of the present invention will be described below. For convenience of description, members having the same functions as those described in the above embodiment are denoted by the same reference numerals, and description thereof will not be repeated.

FIG.4is a cross-sectional view showing a configuration of an axle-side end portion of a hydraulic shock absorber1A according to the present embodiment. As shown inFIG.4, similarly to the movement prevention member41, a movement prevention member51provided in the hydraulic shock absorber1A includes a spring receiving portion51A, a leg portion51B, an opening portion MC, and an inclined surface MD. The movement prevention member51is different from the movement prevention member41in that the movement prevention member51has a recess portion51E, that is recessed toward the vehicle body side, on an axle-side surface of the spring receiving portion51A. Therefore, a portion of the recess portion51E closest to the vehicle body side (bottom of the recess portion) is located closer to the vehicle body side than a portion of the opening portion43closest to the vehicle body side.

An axle-side surface of a portion forming the opening portion51C is substantially the same in position with a portion of the opening portion43closest to the vehicle body side. This point is the same as the movement prevention member41of Embodiment 1.

Another embodiment of the present invention will be described below. The movement prevention member51can also be applied to a modification of the present embodiment.

The gap50formed by the movement prevention member41does not necessarily have to be formed over an entire periphery of the side wall surface of the cylinder15, and may be formed along at least a part of the side wall surface.

The spring receiving portion for receiving the coil spring14may be provided separately from the movement prevention member41, and the movement prevention member41without the leg portion41B may be disposed on the vehicle body side of the opening portion43.

The spring receiving portion41A may have an opening portion as an alternative of the gap50, which allows the oil to flow from the vehicle body side to the axle side, at a position away from the side wall surface of the cylinder15. Further, the opening portion may have a structure or a shape that allows flow of the oil from the vehicle body side to the axle side and restricts flow of the oil from the axle side to the vehicle body side.

For example, an opening portion may be formed in the spring receiving portion41A, and a check valve that allows flow of the oil from the vehicle body side to the axle side, and restricts flow of the oil from the axle side to the vehicle body side may be provided in the opening portion.

The present invention is not limited to the embodiments described above, various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention.

REFERENCE SIGNS LIST