Patent Description:
A hydraulic shock absorber provided with a piston moving in an axial direction of a piston rod in response to extension/compression of an elastic body has been disclosed in PTL <NUM>. The piston is pressed so that one end surface of the piston can be contacted with or separated from a damping valve by the elastic body.

A shock absorber in which a first piston mounted on a piston rod is inserted into a cup-like component inside a cylinder has been disclosed in PTL <NUM>. In the shock absorber, the first piston is inserted into an internal space of the cup-like component so that different damping force from that in a case where the first piston is positioned outside the internal space occurs.

<CIT> shows a single cylinder type hydraulic shock absorber including a cylinder in which a piston and a free piston are slidably provided. The piston is provided with attenuating force generating means, and a piston rod so as to penetrate the piston and move forward/backward in the cylinder. Furthermore, an oil lock mechanism is provided including a first member provided at an end portion of the piston rod, and a second member penetrating the free piston. During compression, an oil lock member of the second member enters an oil lock cap of the first member, and pressurizes oil held between the oil lock cap and the oil lock member to ease compression force.

<CIT> shows a positioning strut for motor vehicle door comprising a piston with a rod and a valve to control fluid flow between the two working chambers. The piston has a ring and a sealing ring formed integrally, so that each movement of the piston ring is synchronized with movement of the sealing ring.

<CIT> shows a shock absorber assembly including a pressure tube having an upper end and a lower end and defining an interior, a rod guide disposed adjacent the upper end, a first compression valve assembly adjacent the lower end, a rod operatively coupled to the pressure tube having a first end and a second end, an extender coupled to the second end of the rod, a piston assembly coupled to the extender between the rod guide and the first compression valve assembly with the piston assembly disposed within the interior and slideably coupled to the pressure tube, with the piston assembly dividing the interior into an upper and a lower working chamber, a second compression valve assembly coupled to the extender between the piston assembly and the first compression valve assembly, and a cup disposed within the lower working chamber and defining a bore shaped to receive the second compression valve assembly.

PTL <NUM>: Japanese Unexamined Patent Application Publication "<CIT>)".

According to the invention of PTL <NUM>, the magnitude of occurring damping force cannot be changed in accordance with the position of the piston.

According to the invention of PTL <NUM>, when the first piston enters the cup-like component, working oil flows through a flow path formed in the first piston so that the damping force occurs.

An object of the present invention is to provide a hydraulic shock absorber which can use a different mechanism from the background art to generate damping force dependent on the position of a piston.

In order to solve the foregoing problem, according to an aspect of the present invention, there is provided a hydraulic shock absorber including: a cylinder; a piston rod that is inserted into the cylinder, and on which a first piston, a valve, and a second piston configured to slide against the cylinder are disposed sequentially from one end side; and an oil lock portion that is disposed on the one end side inside the cylinder, and that forms a gap flow path between the oil lock portion and an outer circumferential surface of the first piston when the first piston is inserted into the oil lock portion; wherein: the first piston has a piston internal flow path through which the one end side and the other end side that is an opposite side to the one end side communicate with each other, and the first piston is displaceable in an axial direction of the piston rod; and when the piston rod moves toward the one end side, the first piston relatively moves toward the other end side and the other end side of the first piston abuts against the valve, so that due to a flow of working oil passing through the piston internal flow path, the valve bends to generate damping force.

In addition, according to another aspect of the present invention, there is provided a hydraulic shock absorber including: a cylinder in which an opening portion for letting out working oil is formed in a one end side wall portion; and a piston rod that is inserted into the cylinder and on which a first piston, a valve and a second piston are disposed sequentially from the one end side; wherein: the first piston has a large diameter portion that is larger in diameter than any other portion of the first piston and that forms a gap flow path between the large diameter portion and an inner surface of the cylinder; the first piston further has a piston internal flow path through which the one end side and the other end side that is an opposite side to the one end side communicate with each other, and the first piston is displaceable in an axial direction of the piston rod; and when the piston rod moves toward the one end side, the first piston moves toward the other end side and the other end side of the first piston abuts against the valve, so that due to a flow of working oil passing through the piston internal flow path, the valve bends to generate damping force.

In addition, according to a further aspect of the present invention, there is provided a hydraulic shock absorber including: a cylinder; a piston rod that is inserted into the cylinder, and on which a first piston, a valve, and a second piston configured to slide against the cylinder are disposed sequentially from one end side; and an oil lock portion that is disposed on the one end side inside the cylinder, and that forms a gap flow path between the oil lock portion and an outer circumferential surface of the first piston when the first piston is inserted into the oil lock portion; wherein: the first piston has a piston internal flow path through which the one end side and the other end side communicate with each other, and is displaceable in an axial direction of the piston rod; and when the piston rod moves toward the one end side, the first piston relatively moves toward the other end side with respect to the piston rod and the other end side of the first piston abuts against the valve, so that due to a flow of working oil passing through the piston internal flow path, the valve bends to generate damping force.

According to an aspect of the present invention, it is possible to provide a hydraulic shock absorber which can generate damping force dependent on the position of a piston.

An embodiment of the present invention will be described below in detail.

(Configuration of Hydraulic Shock Absorber <NUM>).

<FIG> is a view showing an overall configuration of an extended state of a hydraulic shock absorber <NUM> according to the present embodiment. <FIG> is a view showing an overall configuration of a state halfway through a compression stroke of the hydraulic shock absorber <NUM> according to the present embodiment. The hydraulic shock absorber <NUM> is a shock absorber used for rear cushion etc. of a motorcycle. The vehicle in which the hydraulic shock absorber <NUM> is mounted is not limited particularly but may be a two-wheeled vehicle or a four-wheeled vehicle. As shown in <FIG> and <FIG>, the hydraulic shock absorber <NUM> is provided with a cylinder <NUM>, a piston rod <NUM>, a damping force generating portion <NUM>, a sub tank <NUM>, an outer tube <NUM>, and a suspension spring <NUM>.

The cylinder <NUM> is a tubular member whose vehicle body side (one end side) end portion is fixed to a mounting member <NUM>, and which is internally filled with working oil. The mounting member <NUM> is a member for mounting the hydraulic shock absorber <NUM> on the vehicle body. A plurality of hole portions <NUM> are formed in a vehicle body side portion of the cylinder <NUM> so that the inside of the cylinder <NUM> and the damping force generating portion <NUM> can communicate with each other through the hole portions <NUM>. In addition, a plurality of hole portions <NUM> are formed in an axle side portion of the cylinder <NUM> so that the inside of the cylinder <NUM> and the damping force generating portion <NUM> communicate with each other through the hole portions <NUM>.

An oil lock portion <NUM> shaped like a tube whose axle side (the other end side) is opened is disposed on the vehicle body side inside the cylinder <NUM>. A first piston <NUM> which will be described later is inserted into the oil lock portion <NUM> so that the working oil present between the oil lock portion <NUM> and the first piston <NUM> is compressed. Thus, it is possible to obtain an effect that bottoming of the hydraulic shock absorber <NUM> can be prevented. The aforementioned effect will be hereinafter called "oil lock effect".

The piston rod <NUM> is a rod-like member which is inserted into the cylinder <NUM> from the axle side. <FIG> is a sectional view showing a member which is disposed on a vehicle body side leading end portion of the piston rod <NUM>. More specifically, <FIG> is a sectional view of the hydraulic shock absorber <NUM> taken along a plane including a central axis C of the piston rod <NUM>. As shown in <FIG>, the first piston <NUM>, a valve <NUM>, and a second piston <NUM> are disposed on the vehicle body side leading end portion of the piston rod <NUM> sequentially from the vehicle body side.

The second piston <NUM> is a piston sliding against the cylinder <NUM>. By the second piston <NUM>, an internal space of the cylinder <NUM> is sectioned into a first oil chamber S1 which is positioned on the vehicle body side, and a second oil chamber S2 which is positioned on the axle side. The second piston <NUM> makes contact with the cylinder <NUM> through an O-ring 23a provided in an outer circumferential surface of the second piston <NUM>.

The first piston <NUM> is a piston which is disposed on a vehicle body side end portion of the piston rod <NUM> and which is shaped like a cylinder opened on the vehicle body side.

The first piston <NUM> is inserted into the oil lock portion <NUM> in a compressed state of the hydraulic shock absorber <NUM>. Consequently, a small oil chamber S0 is formed between the oil lock portion <NUM> and the first piston <NUM> to thereby generate an oil lock effect.

An outer diameter of the first piston <NUM> is smaller than an inner diameter of the oil lock portion <NUM> so that a gap flow path 11a is formed between an outer circumferential surface of the first piston <NUM> and an inner circumferential surface of the oil lock portion <NUM>. When working oil of the small oil chamber S0 is compressed in a compression side stroke, the working oil in the small oil chamber S0 passes through the gap flow path 11a and flows out of the small oil chamber S0. On this occasion, damping force occurs in the gap flow path 11a.

The first piston <NUM> has a flow path (piston internal flow path) 21a on the axle side so that the inside and the outside of the first piston <NUM> can communicate with each other through the flow path 21a. The valve <NUM> in which a plurality of plate valves are laminated is disposed on the axle side of the first piston <NUM>. The valve <NUM> is a damping valve which bends against a flow of working oil to thereby generate damping force and which has a shape and a size large enough to close an axle side opening portion of the flow path 21a.

The first piston <NUM> is displaceable in an axial direction of the piston rod <NUM> with respect to the piston rod <NUM>. When the piston rod <NUM> moves toward the vehicle body side in the compression side stroke, the first piston <NUM> relatively moves toward the axle side with respect to the piston rod <NUM>. On the contrary, when the piston rod <NUM> moves toward the axle side in an extension side stroke, the first piston <NUM> relatively moves toward the vehicle body side with respect to the piston rod <NUM>.

Specifically, the first piston <NUM> has a small diameter portion <NUM> on the axle side. The small diameter portion <NUM> is smaller in inner diameter than any other portion of the first piston <NUM>. The aforementioned flow path 21a is formed to penetrate the small diameter portion <NUM> axially. A spacer 27shaped like a tube is disposed on an outer circumferential surface of the piston rod <NUM>. The spacer <NUM> has a small diameter portion <NUM> and a large diameter portion <NUM>. The large diameter portion <NUM> having an outer diameter larger than an outer diameter of the small diameter portion <NUM> is positioned on the vehicle body side with respect to the small diameter portion <NUM>. The small diameter portion <NUM> of the first piston <NUM> is disposed on a radially outer side of the small diameter portion <NUM>.

An axle side end portion of the spacer <NUM> abuts against the valve <NUM>. A vehicle body side end portion of the spacer <NUM> abuts against a stopper <NUM> provided on a vehicle body side end portion of the piston rod <NUM>. Therefore, the spacer <NUM> is not displaced axially. The stopper <NUM> may be, for example, a nut engaged with a screw groove provided in the vehicle body side end portion of the piston rod <NUM>.

A length of the small diameter portion <NUM> of the spacer <NUM> is axially longer than a length of the small diameter portion <NUM> of the first piston <NUM>. Therefore, the first piston <NUM> can be axially displaced between the large diameter portion <NUM> of the spacer <NUM> and the valve <NUM>.

In addition, a valve spring <NUM> urging the first piston <NUM> toward the axle side, i.e. toward the side where the valve <NUM> is positioned is disposed between the small diameter portion <NUM> and the large diameter portion <NUM> in the axial direction. The valve spring <NUM> is an annular member having elasticity, such as a coil spring etc..

In a situation that oil pressure is not applied to the first piston <NUM>, the first piston <NUM> is displaced toward the axle side by elastic force of the valve spring <NUM> to abut against the valve <NUM>. In addition, in the compression side stroke, the first piston <NUM> abuts against the valve <NUM> more intensely due to resistance of the working oil received because the first piston <NUM> moves toward the vehicle body side, in addition to the elastic force of the valve spring <NUM>. On the other hand, in the extension side stroke, oil pressure in the small oil chamber S0 decreases temporarily because the first piston <NUM> moves toward the axle side. Due to a difference in oil pressure between the small oil diameter S0 and the first oil diameter S1 generated on this occasion, the first piston <NUM> is displaced toward the vehicle body side against the elastic force of the valve spring <NUM>.

<FIG> is a sectional view showing a positional relation between the first piston <NUM> and the valve <NUM> in the compression side stroke. <FIG> is a sectional view showing a positional relation between the first piston <NUM> and the valve <NUM> in the extension side stroke.

In the compression side stroke, an axle side end surface of the first piston <NUM> and the valve <NUM> abut against each other, as shown in <FIG>. When the first piston <NUM> enters the oil lock portion <NUM> in this state, the oil pressure in the small oil chamber S0 increases so that a portion of the working oil in the small oil chamber S0 passes through the flow path 21a to bend the valve <NUM> so as to flow out to the first oil chamber S1. Due to the valve <NUM> bending on this occasion, damping force occurs. At the same time, another portion of the working oil in the small oil chamber S0 flows through the gap flow path 11a. On this occasion, damping force also occurs in the gap flow path 11a.

On the other hand, in the extension side stroke, the axle side end surface of the first piston <NUM> and the valve <NUM> are separated from each other, as shown in <FIG>. Therefore, in the extension side stroke, the axle side opening portion of the flow path 21a is opened so that the working oil can flow into the small oil chamber S0 through the flow path 21a. Therefore, it is possible to prevent the small oil chamber S0 from becoming negative pressure in accordance with the relative movement of the first piston <NUM> toward the axle side.

In addition, an external diameter of the small diameter portion <NUM> of the spacer <NUM> is smaller slightly (e.g. by <NUM>) than an internal diameter of the small diameter portion <NUM> of the first piston <NUM>. Therefore, the first piston <NUM> can be also displaced in a radial direction of the piston rod <NUM>. In addition, a vehicle body side end portion of the first piston <NUM> is tapered. Therefore, it is possible to realize a configuration in which even when accuracy of positioning between the first piston <NUM> and the oil lock portion <NUM> is not increased, the vehicle body side end portion of the first piston <NUM> can be guided by an axle side end portion of the oil lock portion <NUM> so that the first piston <NUM> can be inserted into the oil lock portion <NUM>.

Incidentally, the first piston <NUM> does not have to be always shaped like a cylinder, but may be shaped like a tube having another section than a circular section, such as a quadrangular prism section. In this case, the shape of the section of the oil lock portion <NUM> is also a shape fitted to the shape of the section of the first piston <NUM>. However, when the section of the first piston <NUM> is circular, it is unnecessary to perform angular alignment between the first piston <NUM> and the oil lock portion <NUM>. Therefore, it is preferable that each of the first piston <NUM> and the oil lock portion <NUM> has a circular shape in section.

As shown in <FIG> and <FIG>, a mounting member <NUM> for mounting the hydraulic shock absorber <NUM> on the axle, and a spring bearing <NUM> against which the suspension spring <NUM> abuts are provided on the axle side of the piston rod <NUM>.

A bump rubber <NUM> is disposed on a vehicle body side of the mounting member <NUM>. The bump rubber <NUM> absorbs shock when a rod guide <NUM> and the mounting member <NUM> are in contact with each other in the compression side stroke of the hydraulic shock absorber <NUM>.

The damping force generating portion <NUM> communicates with the first oil chamber S1 and the second oil chamber S2. The damping force generating portion <NUM> generates damping force in accordance with the flow of the working oil generated due to the movement of the piston rod <NUM>. Incidentally, a specific configuration of the damping force generating portion <NUM> will not be shown because it is irrelevant to the present invention.

The sub tank <NUM> compensates for working oil corresponding to a volume change amount inside the cylinder <NUM> due to displacement of the piston rod <NUM> with respect to the cylinder <NUM>. The sub tank <NUM> communicates with the first oil chamber S1 and the second oil chamber S2 through the damping force generating portion <NUM>.

The outer cylinder <NUM> is a tubular member provided on an outer side of the cylinder <NUM>. The outer cylinder <NUM> is disposed coaxially with the cylinder <NUM>. An annular flow path 50a is formed between an inner circumferential surface of the outer tube <NUM> and an outer circumferential surface of the cylinder <NUM> so that the damping force generating portion <NUM> and the second oil chamber S2 can be made to communicate with each other through the annular flow path 50a. A vehicle body side spring bearing <NUM> against which the suspension spring <NUM> abuts is provided on an outer circumference of the outer tube <NUM>.

In addition, a rod guide <NUM> which the piston rod <NUM> penetrates is disposed in the vicinity of an axle side end portion of the outer tube <NUM>. The rod guide <NUM> is a member which is generally shaped like a thick cylinder. The rod guide <NUM> makes contact with the inner circumferential surface of the outer tube <NUM> through an O-ring 52a. In addition, the rod guide <NUM> supports the piston rod <NUM> so that the piston rod <NUM> can axially move in an inner hole of the rod guide <NUM> through an oil seal 52b, a bush 52c, and a dust seal 52d.

In addition, a rebound rubber 52e is disposed on a vehicle body side of the rod guide <NUM>. The rebound rubber 52e absorbs shock caused by contact of the second piston <NUM> with a vehicle body side surface of the rod guide <NUM> when the hydraulic shock absorber <NUM> is most extended.

The suspension spring <NUM> is compressed to absorb vibration caused by unevenness of a road surface. A vehicle body side end portion of the suspension spring <NUM> abuts against the vehicle body side spring bearing <NUM> and an axle side end portion of the suspension spring <NUM> abuts against the axle side spring bearing <NUM>. In this manner, the positions of the opposite ends of the suspension spring <NUM> are regulated.

The flow of the working oil in the hydraulic shock absorber <NUM> will be described with reference to <FIG> and <FIG>. In <FIG> and <FIG>, the flow of the working oil in the compression side stroke is designated by a solid line and the flow of the working oil in the extension side stroke is designed by a broken line.

In the compression side stroke, the working oil flows from the first oil chamber S1 into the damping force generating portion <NUM> through the hole portions <NUM> in accordance with movement of the piston rod <NUM> toward the vehicle body side, as shown in <FIG>. Of the working oil flowing into the damping force generating portion <NUM>, some working oil corresponding to an entry volume of the piston rod <NUM> flows into the sub tank <NUM>, and the remaining working oil flows into the second oil chamber S2 through the annular flow path 50a and the hole portions <NUM>.

Further, in a state the first piston <NUM> is inserted into the oil lock portion <NUM> (a trailing end of a stroke) in the compression side stroke, the working oil in the small oil chamber S0 flows into the first oil chamber S1 through the gap flow path 11a, as shown in <FIG>. Damping force occurs due to the flow of the working oil. In addition, since the working oil in the small chamber S0 bends the valve <NUM> from the flow path 21a to flow into the first oil chamber S1, damping force also occurs. Accordingly, the damping force can be generated in accordance with the position of the first piston <NUM>, i.e. a depth of the stroke of the hydraulic shock absorber <NUM>.

When the first piston <NUM> moves toward the outside of the oil lock portion <NUM> in the extension side stroke, a portion of the working oil in the first oil chamber S1 flows from the gap flow path 11a and the flow path 21a into the small oil chamber S0, as shown in <FIG>.

In addition, the working oil in the second oil chamber S2 flows into the damping force generating portion <NUM> through the hole portions <NUM> on the axle side of the cylinder <NUM> and the annular flow path 50a in accordance with the movement of the second piston <NUM> toward the axle side. The working oil which has generated the damping force in the damping force generating portion <NUM> flows into the first oil chamber S1. Further, working oil corresponding to a retraction volume of the piston rod <NUM> flows from the sub tank <NUM> into the first oil chamber S1.

As described above, the hydraulic shock absorber <NUM> according to the present embodiment is provided with the cylinder <NUM>, the piston rod <NUM>, and the oil lock portion <NUM>. The piston rod <NUM> is inserted into the cylinder <NUM>. The first piston <NUM>, the valve <NUM>, and the second piston <NUM> sliding against the cylinder <NUM> are disposed on the piston rod <NUM> sequentially from the vehicle body side. The oil lock portion <NUM> is disposed on the vehicle body side inside the cylinder <NUM>. When the first piston <NUM> is inserted into the oil lock portion <NUM>, the gap flow path 11a is formed between the oil lock portion <NUM> and the outer circumferential surface of the first piston <NUM>. The first piston <NUM> has the flow path 21a through which the vehicle body side and the axle side communicate with each other. At the same time, the first piston <NUM> is displaceable in the axial direction of the piston rod <NUM>. When the piston rod <NUM> moves toward the vehicle body side, the first piston <NUM> relatively moves toward the axle side with respect to the piston rod <NUM>. As a result, the axle side of the first piston <NUM> abuts against the valve <NUM>. Due to the valve <NUM> bent by the flow of the working oil passing through the flow path 21a, the damping force is generated.

According to the aforementioned configuration, when the piston rod <NUM> has arrived at the vehicle body side of the cylinder <NUM>, the first piston <NUM> is inserted into the oil lock portion <NUM> so that the axle side end surface of the first piston <NUM> abuts against the valve <NUM>. When the first piston <NUM> enters the oil lock portion <NUM> in this state, the oil pressure in the small oil chamber S0 increases so that a portion of the working oil in the small oil chamber S0 passes through the flow path 21a to bend the valve <NUM> to thereby flow out to the first oil chamber S1. Due to the valve <NUM> bent on this occasion, damping force occurs. In addition, the flow of the working oil passing through the flow path 21a is partially restricted by the valve <NUM>. Thus, pressure of the working oil in the small oil chamber S0 increases. Due to the working oil flowing through the gap flow path 11a formed between the outer circumferential surface of the first piston <NUM> and an inner surface of the oil lock portion <NUM>, damping force also occurs. Accordingly, the hydraulic shock absorber <NUM> can efficiently generate damping force dependent on the position of the first piston <NUM>.

When the piston rod <NUM> moves toward the axle side, the first piston <NUM> moves toward the vehicle body side so that the opening portion of the flow path 21a is opened. Accordingly, the working oil flows into the small oil chamber S0 through the flow path 21a. Therefore, it is possible to prevent the small oil chamber S0 from becoming negative pressure so that it is possible to make the hydraulic shock absorber <NUM> work stably.

In addition, in the hydraulic shock absorber <NUM>, the first piston <NUM> is displaceable in the radial direction of the piston rod <NUM>. Accordingly, it is possible to realize a configuration in which the first piston <NUM> can be inserted into the oil lock portion <NUM> even when the accuracy of the positioning between the first piston <NUM> and the oil lock portion <NUM> is not increased.

In addition, in the hydraulic shock absorber <NUM>, the first piston <NUM> has a tubular shape opened on the vehicle body side, and has the flow path 21a on the axle side. Thus, the first piston <NUM> is shaped like a tube. Accordingly, it is possible to reduce the weight of the first piston <NUM> while securing the length of the gap flow path 11a.

Another embodiment of the present invention will be described below. Incidentally, for convenience of explanation, members having the same functions as the members described in the aforementioned embodiment will be referred to by the same signs correspondingly and respectively, and description thereof will be omitted.

<FIG> is a sectional view showing a configuration of an important part of a hydraulic shock absorber 1A according to the present embodiment. The hydraulic shock absorber 1A is different from the hydraulic shock absorber <NUM> in that the hydraulic shock absorber 1A is (i) provided with a valve <NUM> in place of the valve <NUM>, (ii) provided with a second piston <NUM> in place of the second piston <NUM>, and (iii) further provided with damping valves 23c and 23d (damping force generating valves).

The valve <NUM> is not a valve for generating damping but a valve for restricting a flow of working oil passing through a flow path 21a. In a compression side stroke of the hydraulic shock absorber 1A, an axle side opening portion of the flow path 21a is closed by the valve <NUM>. Accordingly, the working oil is retrained from flowing through the flow path 21a. Therefore, in comparison with the hydraulic shock absorber <NUM>, an amount of the working oil flowing through a gap flow path 11a increases, and damping force occurring in the gap flow path 11a increases.

The second piston <NUM> has a flow path (second piston internal flow path) 23b through which a vehicle body side and an axle side communicate with each other. The damping valves 23c and 23d are disposed on a vehicle body side opening portion and an axle side opening portion of the flow path 23b respectively. The working oil passes through the flow path 23b in accordance with movement of the second piston <NUM> through a first oil chamber S1 in a compression side stroke and an extension side stroke. Due to the damping valve 23c or 23d bending on this occasion, damping force occurs. Therefore, it is possible to also generate damping force in the second piston <NUM> in the hydraulic shock absorber 1A.

Another embodiment of the present invention will be described below. Incidentally, for convenience of explanation, members having the same functions as the members described in the aforementioned embodiments will be referred to by the same signs correspondingly and respectively, and description thereof will be omitted.

<FIG> is a conceptual view showing a configuration of an important part of a hydraulic shock absorber <NUM> according to the present embodiment, i.e. a partial sectional view showing a state in which a first piston 21D is positioned on an axle side with respect to an opening portion 10b of a cylinder 10A in a compression side stroke. <FIG> is a conceptual view showing the configuration of the important part of the hydraulic shock absorber <NUM> according to the present embodiment, i.e. a partial sectional view showing a state in which the first piston 21D is positioned on a vehicle body side with respect to the opening portion 10b in the compression side stroke. <FIG> is a conceptual view showing the configuration of the important part of the hydraulic shock absorber <NUM> according to the present embodiment, i.e. a partial sectional view showing a state in which the first piston 21D is positioned on the vehicle body side with respect to the opening portion 10b in an extension side stroke. In <FIG>, a positional relation between a member such as the first piston 21D disposed on a vehicle body side end portion of a piston rod <NUM> and the opening portion 10b is schematically shown, but description about other members is omitted. A flow of working oil in the compression side stroke is designated by a solid line and the flow of the working oil in the extension side stroke is designated by a broken line.

As shown in <FIG>, the hydraulic shock absorber <NUM> is different from the hydraulic shock absorber <NUM> in that the hydraulic shock absorber <NUM> is provided with the cylinder 10A in place of the cylinder <NUM>, and provided with the first piston 21D in place of the first piston <NUM>. In addition, the hydraulic shock absorber <NUM> is different from the hydraulic shock absorber <NUM> in that the hydraulic shock absorber <NUM> is not provided with any oil lock portion <NUM> but the opening portion 10b for letting out the working oil is formed in a vehicle body side wall portion.

The first piston 21D is different from the first piston <NUM> in that the first piston 21D has a large diameter portion 21b forming a gap flow path 21c between the large diameter portion 21b and an inner surface of the cylinder 10A. In the present embodiment, a space provided on the vehicle body side with respect to the large diameter portion 21b inside the cylinder 10A is a small oil chamber S0. A space between the large diameter portion 21b and a second piston <NUM> is a first oil chamber S1.

In the example shown in <FIG>, the whole of the first piston 21D serves as the large diameter portion 21b. However, the large diameter portion 21b may be formed as a portion of the first piston 21D. A thickness of the large diameter portion 21b in an axial direction of the piston rod <NUM> is larger than an aperture of the opening portion 10b. That is, the large diameter portion 21b has a thickness large enough to cover the opening portion 10b.

In addition, a spring bearing <NUM> is provided in the vicinity of a vehicle body side end portion of the piston rod <NUM> in the present embodiment. The position of a vehicle body side end portion of a valve spring <NUM> is regulated by the spring bearing <NUM>.

In addition, the first piston 21D has a flow path (piston internal flow path) 21a in a similar manner to or the same manner as the first piston <NUM>. At the same time, the first piston 21D is displaceable in the axial direction of the piston rod <NUM>. In addition, a tubular retention member <NUM> having a step in the axial direction is disposed on an outer circumferential surface of the piston rod <NUM> between the first piston 21D and the second piston <NUM>. A valve <NUM> in the present embodiment is retained in the vicinity of the first piston 21D by the retention member <NUM>.

In the compression side stroke, the working oil in the small oil chamber S0 flows into a damping force generating portion <NUM> from hole portions <NUM> to thereby generate damping force. Then, some working oil corresponding to an entry volume of the piston rod <NUM> flows into a sub tank <NUM> and the remaining working oil flows into a second oil chamber S2.

Further, in a state in which the first piston 21D is positioned on the axle side with respect to the opening portion 10b, a portion of the working oil in the small oil chamber S0 flows from the opening portion 10b into the second oil chamber S2 via an annular flow path 50a, as shown in <FIG>. When the first piston 21D arrives at the vehicle body side with respect to the opening portion 10b, working oil flowing out of the opening portion 10b decreases, and working oil flowing through the gap flow path 21c increases, as shown in <FIG>. On this occasion, damping force occurs due to the flow of the working oil passing through the gap flow path 21c.

In the extension side stroke, the working oil in the second oil chamber S2 flows into the damping force generating portion <NUM> to generate damping force, and the working oil then flows into the small oil chamber S0. In addition, a portion of the working oil from the second oil chamber S2 flows into the first oil chamber S1 through the opening portion 10b. In addition, some working oil corresponding to a retraction volume of the piston rod <NUM> flows from the sub tank <NUM> into the small oil chamber S0.

Further, as shown in <FIG>, the first piston <NUM> moves toward the axle side in the extension side stroke so that oil pressure in the small oil chamber S0 temporarily decreases. Due to a difference in oil pressure between the small oil chamber S0 and the first oil chamber S1 generated on this occasion, the first piston <NUM> is displaced toward the vehicle body side against elastic force of the valve spring <NUM>. On this occasion, an axle side opening portion of the flow path 21a is opened. Accordingly, the working oil in the first oil chamber S1 flows into the small oil chamber S0 through the flow path 21a.

Incidentally, a flow path 23b and damping valves 23c and 23d of the second piston <NUM> are not shown in <FIG>. However, also in the present embodiment, the second piston <NUM> may have the flow path 23b and the damping valves 23c and 23d in a similar manner to or the same manner as the hydraulic shock absorber 1A in the embodiment <NUM>.

As described above, the hydraulic shock absorber <NUM> in the present embodiment is provided with the cylinder 10A and the piston rod <NUM>. In the cylinder 10A, the opening portion 10b for letting out the working oil is formed in the vehicle body side wall portion. The piston rod <NUM> is inserted into the cylinder 10A. The first piston 21D, the valve <NUM> and the second piston <NUM> are disposed on the piston rod <NUM> sequentially from the vehicle body side. The first piston 21D has the large diameter portion 21b which is larger in diameter than any other portion of the first piston 21D, and which has the gap flow path 21c formed between the large diameter portion 21b and the inner surface of the cylinder 10A. Further, the first piston 21D has the flow path 21a through which the vehicle body side and the axle side communicate with each other. At the same time, the first piston 21D is displaceable in the axial direction of the piston rod <NUM>. When the piston rod <NUM> moves toward the vehicle body side, the first piston 21D moves toward the axle side so that an axle side of the first piston 21D abuts against the valve <NUM>, and due to the flow of the working oil passing through the flow path 21a, the valve <NUM> bends to generate damping force.

According to the aforementioned configuration, when the first piston 21D moves toward the vehicle body side with respect to the opening portion 10b of the cylinder 10A, pressure of the working oil present on the vehicle body side with respect to the opening portion 10b increases. On this occasion, the working oil flows through the gap flow path 21c between the inner surface of the cylinder 10A and an outer circumferential surface of the large diameter portion 21b. As a result, the damping force occurs. Moreover, on this occasion, the axle side of the first piston 21D abuts against the valve <NUM>, and the valve <NUM> bends due to the flow of the working oil passing through the flow path 21a. As a result, the damping force also occurs. Accordingly, damping force dependent on the position of the first piston 21D can be generated efficiently.

When the piston rod <NUM> then moves toward the axle side, the first piston 21D moves toward the vehicle body side, and the opening portion of the flow path 21a is opened. Therefore, the working oil flows into the small oil chamber S0 through the flow path 21a. The small oil chamber S0 is formed by the cylinder <NUM> and the first piston 21D. Therefore, it is possible to prevent the small oil chamber S0 from becoming negative pressure so that it is possible to make the hydraulic shock absorber <NUM> work stably.

Claim 1:
A hydraulic shock absorber (<NUM>) comprising
a cylinder (<NUM>);
a piston rod (<NUM>) that is inserted into the cylinder, and on which a first piston (<NUM>), a valve (<NUM>), and a second piston (<NUM>) configured to slide against the cylinder are disposed sequentially from one end side; and
an oil lock portion (<NUM>) that is disposed on the one end side inside the cylinder, and that forms a gap flow path (11a) between the oil lock portion and an outer circumferential
surface of the first piston when the first piston is inserted into the oil lock portion;
wherein:
the first piston has a piston internal flow path (21a) through which the one end side
and the other end side communicate with each other, and is displaceable in an axial direction of the piston rod; and
when the piston rod moves toward the one end side in the axial direction, the first piston relatively moves toward the other end side with respect to the piston rod in the axial direction, and the other end side of the first piston abuts against the valve, so that due to a flow of working oil passing through the piston internal flow path, the valve bends to generate damping force.