JP2000337425A - Damping force developing structure for hydraulic buffer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a damping force on the compression side when the piston of a hydraulic damper is thrust into the lower limit area of a stroke to a value higher than an ordinary stroke region. SOLUTION: A free piston 32 having a base end part energized upward through the force of a spring 34 supported at a damping valve BV on the pressure side and having a through-hole 32A extending through a central part is slidably mounted on the lower chamber B of a cylinder 31. At the ordinary area Su of a stroke at which the through-hole of the free piston is released, a flow rate obtained by multiplying the sectional area of the piston rod 1 with the lowering speed of the piston rod is fed to the damping valve on the pressure side to generate a damping force on the pressure side at an ordinary area. When the piston rod is thrust into the lower limit area Sd of a stroke, a piston nut 18 coupled to the lower end of the piston rod is brought into contact with the through-hole of the free piston to close the through-hole, and the free piston is pressed down at the same lowering speed as that of the piston rod. A high flow rate obtained by multiplying the sectional area of the free piston with a lowering speed is fed to the damping valve on the pressure side and the damping force on the pressure side higher than that at the ordinary area of a stroke is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a damping force generating structure for a hydraulic shock absorber which suppresses vibration of a vehicle body such as a suspension system of an automobile, and more particularly to a pressure side damping force when a piston enters a lower limit range of a stroke. It is about structure.

[0002]

2. Description of the Related Art As this type of hydraulic shock absorber, for example, the one shown in FIG. 4 is known. First, an outline of the structure will be described with reference to the drawings. The hydraulic shock absorber mounted between the vehicle body and the wheels via a coupling member includes a piston rod 1
The piston 2 and the piston valve PV are assembled to each other, and the slidable housing is accommodated therein. The cylinder 2 having the base valve BV mounted at the lower end is housed in the outer cylinder 3 to seal the outside air and the rod guide 5. After the gasket case 6 accommodating therein is inserted from above the outer cylinder 3, the upper end of the outer cylinder 3 is hermetically sealed by welding all around. A tank chamber D is formed between the cylinder 2 and the outer cylinder 3.

[0003] When the piston rod 1 rises in the cylinder 2 filled with hydraulic oil, the hydraulic oil in the closed upper chamber A flows out to the lower chamber B via the piston valve PV. The passage resistance becomes the extension side damping force. Hydraulic oil corresponding to the piston rod withdrawal volume that is insufficient due to the rise of the piston rod 1 is replenished from the bottom chamber C connected to the tank chamber D via a base valve BV disposed at the lower end of the cylinder 2.

Next, the piston valve P of the hydraulic shock absorber
V will be described. A lower end portion of the piston rod 1 is provided with a spigot portion 1A having a diameter smaller than that of an upper portion. A piston band 13 slidingly contacting the inside of the cylinder is mounted on the outer surface of the piston 12, and an outer ring portion is cut on the back surface of the piston 12. A check valve consisting of a notched leaf valve 11 provided with a notch 11A and a perforated leaf valve 10 superimposed on the notch 11A, a ring seat 9 having an outer periphery serving as a support diameter of the deflection of the check valve, and the check valve from the back. A leaf spring 8 to be urged and a valve stopper 7 for restricting the maximum deflection of the check valve are inserted in a superposed manner.

Next, a washer-shaped leaf valve 14 whose inner peripheral side is fixed, and a ring seat 15 whose outer periphery is a support diameter for bending of the leaf valve 14 are fitted and inserted.
4 and a spring 17 for urging the spring seat 16 from the rear side
Is screwed on with a piston nut 18 that guides the piston vertically. Finally, the piston valve PV is formed by fastening the piston nut 18 to the spigot portion 1A with a specified tightening torque.

An outer peripheral port 12A communicating with the lower chamber B and an inner peripheral port 12B communicating with the upper chamber A are formed in the piston 12 which divides the inside of the cylinder 2 into an upper chamber A and a lower chamber B. Above the outer peripheral port 12A, an annular opening window 12F formed by the outer seat surface 12C and the intermediate seat surface 12D is provided, and above the inner peripheral port 12B, the intermediate seat surface 12D and the inner cylindrical portion 12E are provided. An annular opening window 12G to be formed is provided. A check valve composed of a notched leaf valve 11 having a notch 11A and a perforated leaf valve 10 superposed thereon is seated in the opening windows 12F and 12G, and connects the upper chamber A and the lower chamber B. Orifice passage 11 consisting of notch
A is formed.

The upper chamber A and the lower chamber B have low piston speeds.
In a so-called very low speed to low speed range in which the pressure difference is small, the outer periphery of the leaf valve 14 urged by the spring 17 covers the opening window 12H on the lower surface of the piston. For this reason, the pressure oil in the upper chamber A is released to the lower chamber B via the orifice passage 11A, and a damping force in a very low to low speed range is generated by the passage resistance at this time.

As the piston speed increases, the flow rate passing through the orifice passage 11A also increases, and the pressure difference between before and after the orifice passage also increases. As the piston speed approaches the middle speed range, the pressure difference between the upper chamber A and the lower chamber B increases,
The outer periphery of the leaf valve 14 urged by the spring 17 overcomes the urging force of the spring 17 and the combined flexural rigidity of the extension damping valve composed of the leaf valve 14, and is pushed open from the opening window 12H on the lower surface of the piston. Then, the hydraulic oil flows out into the lower chamber B, and the passage resistance at this time generates the extension damping force in the middle speed range and thereafter.

The above description is based on the cylinder 2 filled with hydraulic oil.
When the piston rod 1 descends, on the contrary, when the piston rod 1 descends, the hydraulic oil in the sealed lower chamber B is supplied to the outer peripheral port 12 of the piston 12.
Through A, the check valves 10 and 11 urged by the leaf spring 8 are pushed open, and replenished to the upper chamber A which becomes negative pressure. The hydraulic oil in the lower chamber B excluding this portion flows out from the lower chamber B to a bottom chamber C connected to the tank chamber D via a base valve BV attached to the lower end of the cylinder 2, and the passage resistance at this time is reduced. Is the compression damping force.

A cylinder 2 forming a hydraulic chamber of a hydraulic shock absorber
A valve case 27 is fitted to the lower end of the valve case. This valve case has an outer peripheral port 2 communicating with the bottom chamber C.
An inner peripheral port 27B communicating with 7A and the lower chamber B is formed. An annular opening window 27F formed by the outer seat surface 27C and the intermediate seat surface 27D is provided above the outer peripheral port 27A, and the intermediate seat surface 27D and the inner cylindrical portion 27E are provided above the inner peripheral port 27B. An annular opening window 27G to be formed is provided. In the opening windows 27F and 27G, there are seated a suction valve including a notch leaf valve 26 having a notch 26A and a perforated leaf valve 25 overlapping the notch leaf valve 26, and a notch communicating the lower chamber B and the bottom chamber C. Orifice passage 26 consisting of
A is formed.

Next, the configuration of the base valve BV will be described. First, a valve case 27 fitted to the lower end portion of the cylinder 2 on the shaft portion 21A of the guide 21, a notched leaf valve 26 provided with a notch 26A in an outer ring portion on the back surface of the valve case 27, and a superimposed on this. Perforated leaf valve 2
5, a ring seat 24 whose outer periphery is the support diameter of the deflection of the suction valve, a leaf spring 23 for urging the suction valve from the back, and a valve stopper 22 for regulating the maximum deflection of the suction valve. And insert it.

Subsequently, the lower opening window 2 of the valve case 27
7H, the washer-shaped leaf valve 28 is opposed to the lower surface of the leaf valve 28,
The ring seat 29 and the valve stopper 30 that regulates the maximum amount of deflection of the leaf valve 28, which are the support diameters of the deflection, are sequentially inserted.
The nut 31 is screwed. Finally, the base valve BV is formed by fastening the nut 31 to the lower end of the guide 21 with a specified tightening torque.

In the low-speed range of the piston speed at which the piston rod 1 descends, an orifice passage 26A formed by a notch of a notch leaf valve facing the opening window 27F.
Above the middle speed region where the piston speed increases, the hydraulic oil flowing into the lower opening window 27H through the inner peripheral port 27B of the base valve case is compressed by the pressure side damper formed by the leaf valve 28 whose inner peripheral side is fixed. The outer peripheral side of the valve is pushed open to discharge the working oil corresponding to the entering volume of the piston rod 1 from the lower chamber B to the bottom chamber C connected to the tank chamber D, and a pressure-side damping force is generated by the passage resistance at that time.

Conversely, when the piston rod 1 is lifted, the suction valves 25 and 26 urged by the non-return spring 23 are pushed open by passing through the outer peripheral port 27A of the base valve case, and the rebound volume of the piston rod 1 is removed. The hydraulic oil is replenished from the bottom chamber C to the lower chamber B.

As described in detail above, the piston valve P
V is mounted at the lower end of the piston rod, and the base valve BV is mounted at the lower end of the cylinder. The shaft diameter of the mounting part is about the piston rod spigot part and the latter is about the shaft part of the guide. The operation and effect of the stop valve (pressure side: suction valve) and the damping valve are based on the piston valve PV,
The same applies to the base valve BV.

[0016]

As described above, in the low-speed range of the piston speed, the hydraulic oil on the upstream side passes through the notch of the cut-out leaf valve, which is partially cut off on the outer peripheral side, and also in the middle-speed range. In the following, in addition to this passage, the notched leaf valve and the inner peripheral side of the leaf valve superposed thereon are pushed open to flow downstream, and a damping force is generated by the passage resistance at this time. This damping force is substantially constant over the entire stroke range as shown by the solid line in FIG. If the compression-side damping force is reduced to improve the ride comfort of the vehicle, the damping of large-amplitude vertical vibrations when passing through the undulation of the road is insufficient, so that the piston approaches the lower limit of the stroke, so-called. A bottom bump occurs, which adversely affects the riding comfort of the vehicle.

The present invention has been made in view of the above circumstances, and an object of the present invention is to increase the pressure-side damping force when the piston enters the lower limit range of the stroke, so as to be higher than that in a normal stroke region. It is to provide a hydraulic shock absorber which can be used.

[0018]

SUMMARY OF THE INVENTION According to the present invention, there is provided a fuel cell system, comprising: a cylinder housed in an outer cylinder divided into an upper chamber and a lower chamber;
The extension damping valve provided on the piston slidably guided in the cylinder is connected to the lower end of the piston rod by a piston nut to control the extension damping force when the piston rod extends, A hydraulic shock absorber that controls the compression damping force when the piston rod contracts by fitting a compression damping valve that partitions the inside into a lower chamber and a bottom chamber that communicates with the tank chamber at the lower end of the cylinder. Things.

In order to solve the problem, a means adopted by the present invention is to provide a free piston having a base end portion upwardly urged by a spring supported by the compression-side damping valve and having a through hole penetrating the center portion. In the normal range of the stroke in which the through hole of the free piston is opened slidably in the lower chamber of the cylinder, the flow rate obtained by multiplying the cross-sectional area of the piston rod by the descending speed of the piston rod is damped on the pressure side. While supplying the pressure to the valve to generate a compression side damping force in the normal range, when the piston rod enters the lower limit range of the stroke, the piston nut coupled to the lower end of the piston rod causes the free piston to rotate. By contacting the through hole and closing it, and pushing down the free piston at the same descending speed as the piston rod, the sectional area of the free piston is reduced. The high flow rate multiplied by the lowering speed is supplied to the compression side damping valve is possible to generate a greater compression side damping force than normal range of the stroke. " In the lower limit range of the stroke, the side hole of the cylinder that replenishes the upper chamber that becomes a negative pressure with the hydraulic oil from the tank chamber may be covered by the free piston in the normal range of the stroke, or may be formed on the inner surface of the cylinder. The hole may be covered by a fitted check seal.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A hydraulic shock absorber according to the present invention has the same basic structure as the prior art shown in FIG.
Is movably inserted into the cylinder 31 via the expansion-side damping valve PV mounted on the lower end thereof, and the expansion-side damping valve PV partitions the upper chamber A and the lower chamber B. Further, a pressure-side damping valve BV is provided at a lower end portion of the cylinder 31 and similarly partitions a lower chamber B and a bottom chamber C.

In order to solve the above-mentioned problems of the prior art, the lower limit damping force when the piston 12 enters the lower limit range Sd of the stroke during the contraction stroke, as shown by the broken line in FIG. And the lowering speed may be reduced as the stroke approaches the lower limit Z of the stroke. Hereinafter, the present invention is shown in FIG.
Based on the first embodiment shown in FIG. 1, only portions different from those of the related art will be denoted by different reference numerals and described.

The difference from the hydraulic shock absorber described in the prior art is that the base end is supported by the valve stopper 22 of the compression side damping valve BV on the inner surface of the lower chamber side of the cylinder 31 to which the compression side damping valve BV is fitted. The free piston 32 urged upward by the spring 34 is slidably mounted. When the piston 12 moves up and down in the normal stroke area Su, the free piston 32 having the cushioning member 33 such as a rubber sheet fitted on the upper surface is locked to the inner surface of the cylinder 31 by press fitting or the like, and the stroke lower limit area Sd Is stopped at the upper limit of the lower limit area Sd.

In this state, the free piston 32
Since the lower chamber B and the auxiliary chamber F communicate with each other through the through hole 32A formed in the piston rod 1, the flow rate is calculated by multiplying the cross-sectional area of the piston rod 1 by the piston speed in a so-called contraction stroke in which the piston rod 1 descends. The oil is supplied from the lower chamber B to the pressure-side damping valve BV through the through hole 32A and the auxiliary chamber F, and flows out to the bottom chamber C connected to the tank chamber D.
The normal compression side damping force shown by the solid line is generated.

When the piston 12 enters the lower limit range Sd of the stroke, the flange portion 18A of the piston nut 18, which connects the piston valve PV to the piston rod 1, comes into contact with the cushioning member 33 fitted on the upper surface of the free piston. The passage between the chamber B and the auxiliary chamber F is shut off. When the piston rod 1 further descends, the free piston 32 is pushed down at the same speed as the piston rod 1, so that the free piston 3
2 is multiplied by the piston speed to supply a large flow rate of hydraulic oil to the compression side damping valve BV. At this time, as shown by a broken line in FIG. Generate force.

The lowering range damping force and the repulsive force of the spring, which increase with the lowering of the free piston 32, are applied to the piston rod 1 as a reaction force, so that the lowering speed of the piston rod 1 is rapidly reduced. When the free piston 32 is lowered, the side hole 31A of the cylinder is opened and the tank chamber D and the lower chamber B communicate with each other. Of the piston valve PV through the side hole 31A and the lower chamber B
The check valves 10 and 11 are pushed open to replenish the hydraulic oil.

Assuming that the outer diameter of the piston rod 1 is Dr and the inner diameter of the cylinder 31 is Dc, the flow rate Qd passing through the compression-side damping valve BV in the stroke lower limit area Sd is smaller than the flow rate Qu in the normal stroke area Su by Qd. = Qu (Dc
/ Dr) ² = Qu × k, that is, k ｛= (Dc / D
r) ² ｝ times. When the general-purpose size of the hydraulic shock absorber is Dr = 18 mm and Dc = 25 mm, k = 1.
93.

The fact that the flow rate Qd in the stroke lower limit area becomes k times the flow rate Qu in the normal area corresponds to the fact that the piston speed has increased k times. Therefore, the lower limit for lowering the stroke lower limit area Sd at the piston speed V is obtained. The area damping force is equal to the damping force at a piston speed of V × k times the normal damping force curve shown by the solid line in FIG. 2, and becomes larger than the normal damping force as shown by the broken line in FIG.

When the piston rod 1 extends from the lower limit range Sd of the stroke, the free piston 32 urged by the spring 34 rises following the piston rod 1 and enters the auxiliary chamber F, which becomes a negative pressure. , Compression side damping valve B
Hydraulic oil is replenished from the tank chamber D via the V suction valves 25 and 26.

In the first embodiment, when the piston rod 1 enters the lower limit range Sd of the stroke, the free piston 32 is slightly pushed down, and then the cylinder 31 is moved downward.
The opening of the side hole 31A causes a delay in the replenishment of the hydraulic oil from the tank chamber D to the upper chamber A, which becomes a negative pressure with the lowering of the free piston 32, and may cause abnormal noise. The second embodiment shown in FIG. 3 improves this point.

In the second embodiment, as in the first embodiment, a free piston 32 urged upward by a spring 34 is provided on the inner surface of the lower chamber side of the cylinder 41 on which the compression side damping valve BV is mounted. Mount slidably. When the piston 12 moves up and down in the normal stroke range Su, the free piston 3 with the cushioning member 33 fitted on the upper surface is used.
2 abuts against a stopper 45 that is locked to the inner surface of the cylinder 41 by press fitting or the like and that defines a lower limit region Sd of the stroke,
It stops at the upper limit of the lower limit area Sd.

Above the stopper 45, a check seal 46 made of an elastic material such as rubber provided with a clearance to the inner diameter of the cylinder 41 is held by the stopper 45 to be locked. When the piston 12 moves up and down in the normal stroke range Su, the check seal 46 covers the side hole 41A of the cylinder 41 from inside. When the piston 12 enters the lower limit range Sd of the stroke, the flange 18A of the piston nut 8 comes into contact with the cushioning member 33 fitted on the upper surface of the free piston, and shuts off the passage between the lower chamber B and the auxiliary chamber F.

When the piston rod 1 descends from this state, the free piston 32 is pushed down at the same speed as the piston rod 1, so that a large amount of hydraulic oil obtained by multiplying the cross-sectional area of the cylinder 41 by the piston speed is supplied to the pressure-side damping valve BV.
And a lower limit damping force larger than the normal stroke range Su is generated by the passage resistance at this time. The lower chamber B, which communicates with the upper chamber A, which becomes a negative pressure as the free piston 32 descends through the check valves 10 and 11 of the piston valve PV, covers the side hole 41A of the cylinder 41. When the seal 46 is pushed open, the hydraulic oil is replenished from the tank chamber D without delay.

[0033]

As described in detail above, according to the first embodiment of the present invention, when the piston rod enters the lower limit range of the stroke, the lower flange of the piston nut is attached to the buffer member fitted to the upper surface of the free piston. Abuts and blocks the passage between the lower chamber and the auxiliary chamber. When the free piston descends, the cylinder side hole opens and the tank chamber and the auxiliary chamber communicate with each other, so the upper chamber, which becomes negative pressure as the free piston descends, operates from the tank chamber through the cylinder side hole. Oil is replenished. Further, according to the second embodiment of the present invention, when the piston rod enters the lower limit region of the stroke, the lower flange of the piston nut comes into contact with the cushioning member fitted on the upper surface of the free piston, and the lower chamber and the auxiliary chamber. Block the passage between them. When the piston rod descends from this state, a check seal covering the side hole of the cylinder is pushed and opened in the upper chamber, which becomes negative pressure as the free piston descends, and hydraulic oil flows from the tank chamber without delay. Be replenished. In any of the above embodiments, when the piston rod enters the lower limit range of the stroke, the free piston is pushed down at the same speed as the piston rod, so that a large flow of hydraulic oil obtained by multiplying the cross-sectional area of the cylinder by the piston speed causes a compression damping. The damping force is supplied to the valve, and the passage resistance at this time generates a lower limit damping force larger than the normal stroke range. For this reason, the descending speed of the piston rod, which has descended to the lower limit range of the stroke, is quickly reduced, so that the bottom of the hydraulic shock absorber is prevented and the riding comfort of the vehicle can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a hydraulic shock absorber according to a first embodiment of the present invention.

FIG. 2 shows damping force characteristics in a normal range and a lower limit range of the hydraulic shock absorber according to the present invention.

FIG. 3 is a sectional view of a main part of a hydraulic shock absorber according to a second embodiment of the present invention.

FIG. 4A is a longitudinal sectional view of a hydraulic shock absorber according to the related art. (B) It is a top view of the perforated leaf valve which concerns on a prior art. (C) It is a top view of the notch leaf valve based on a prior art.

[Explanation of symbols]

 Reference Signs List A Upper chamber B Lower chamber C Bottom chamber D Tank chamber PV Extension damping valve BV Pressure damping valve Sd Lower limit range of stroke Su Normal range of stroke 1 Piston rod 18 Piston nut 31, 41 Cylinder 31A, 41A (Cylinder) side hole 22 outer cylinder 32 free piston 32A through hole (of free piston) 34 spring

Claims (3)

[Claims] An interior of a cylinder housed in an outer cylinder is divided into an upper chamber and a lower chamber, and an expansion damping valve provided on a piston slidably guided in the cylinder is provided with a piston rod by a piston nut. To control the extension-side damping force when the piston rod extends, and fit the compression-side damping valve, which partitions the inside of the cylinder into a lower chamber and a bottom chamber that communicates with the tank chamber, at the cylinder lower end. A hydraulic shock absorber for controlling a compression side damping force when the piston rod is contracted when the piston rod is contracted, comprising a through hole which is urged upward at a base end by a spring supported by the compression side damping valve and penetrates a central portion. The free piston is slidably mounted in the lower chamber of the cylinder, and in a normal region of the stroke in which the through hole of the free piston is open, the cross-sectional area of the piston rod is While supplying the flow rate multiplied by the lowering speed of the rod to the compression side damping valve to generate a compression side damping force in the normal range, when the piston rod enters the lower limit range of the stroke,
The piston nut connected to the lower end of the piston rod abuts and closes the through hole of the free piston, and pushes down the free piston at the same descent speed as the piston rod, thereby reducing the free piston. A damping force generating structure for a hydraulic shock absorber, characterized in that a large flow rate obtained by multiplying the cross-sectional area by the descending speed is supplied to a pressure-side damping valve to generate a pressure-side damping force larger than a normal stroke region. 2. A side hole of a cylinder for replenishing the upper chamber, which becomes a negative pressure, with hydraulic oil from the tank chamber in a lower limit range of a stroke, is covered by the free piston in a normal range. The damping force generating structure for a hydraulic shock absorber according to claim 1. 3. In the lower limit range of the stroke, a side hole of a cylinder for refilling the upper chamber, which becomes a negative pressure, with hydraulic oil from the tank chamber is covered by a check seal fitted to an inner surface of the cylinder in a normal range. The damping force generating structure for a hydraulic shock absorber according to claim 1, wherein the damping force generating structure is provided with holes.