GB2111168A

GB2111168A - Hydraulic damper with bypass

Info

Publication number: GB2111168A
Application number: GB08231310A
Authority: GB
Inventors: Masahiro Ashiba
Original assignee: Tokico Ltd
Current assignee: Hitachi Ltd
Priority date: 1981-11-06
Filing date: 1982-11-02
Publication date: 1983-06-29
Also published as: GB2111168B; DE3240984A1; KR860001691B1; KR840002501A; DE3240984C3; DE3240984C2; BR8206430A

Abstract

A hydraulic damper for use in a suspension system of a vehicle, comprises a cylinder 2 receiving therein hydraulic liquid, a piston 13 working in the cylinder and partitioning the interior of the cylinder into two liquid chambers 17, 18, a piston rod 15 secured to the piston and extending to the outside through one end of the cylinder, and valve or valves 24,32 mounted on the piston and generating a damping force in the extension and contraction strokes of the damper. A by-pass passage 46, 19,21 is provided to connect the two chambers by-passing the valve device on the piston, and a check valve (22) is provided in the by-pass passage for changing the liquid flow in the passage between the extension and contraction strokes. The passage may be open for both directions of flow, the check valve merely altering the available cross-section. The passage may also be adjustable by means of an adjusting rod 41 extending through the piston rod and a rotary valve member 43. <IMAGE>

Description

SPECIFICATION Hydraulic damper This invention relates to a hydraulic damper and, particularly to a hydraulic damper of the kind including a cylinder receiving therein hydraulic liquid, a piston working in the cylinder and partitioning the interior of the cylinder into first and second chambers, a piston rod secured to the piston and extending through the first chamber to the outside of the damper, and a damping force generating valve device mounted on the piston for generating damping force in the extension and contraction strokes of the damper.

The damping force generating device may be a single valve acting in both of the extension and contraction strokes or may be formed of two separate valves acting respectively in the extension and contraction strokes and preventing the liquid flow in the reverse direction.

The hydraulic damper of the aforementioned kind is widely used in vehicles such as automobiles. The projecting end of the piston rod is usually connected to a sprung mass of the vehicle such as the chassis and the lower end of the cylinder is secured to an unsprung mass such as a wheel axle.

It is preferable to adjust the damping force of the damper such that the damping force is reduced when the vehicle is running on a smooth road thereby improving the comfortableness in the driving condition and that the damping force is increased when the vehicle is running on a rough road condition thereby preventing excessive vertical movement of the chassis and preventing the bottoming phenomenon.

For the end, there has been proposed to provide a by-pass passage for connecting the first and second chambers by-passing the damping force generating valve or valves on the piston, and an adjustable valve operable from the outside of the damper to adjust the effective area of the bypass passage. Embodically, a longitudinally extending bore is formed through the piston rod with the lower end thereof opening to the second chamber and the bore is connected to the first chamber through a radial hole formed in the piston rod to constitute the by-pass passage. The adjusting valve is actuated by an actuating rod which extends through the bore in the piston rod and projects from the projecting end of the piston rod.The damper operates generally satisfactorily, however, there is another requirement in the hydraulic damper for use in the suspension system of the vehicle, that the damping force in the contraction stroke should be small enough as compared with that of the extension stroke with respect to the same piston speed. Usually, the damping force in the contraction stroke is about one half to one third (1/2-1/3) of the damping force in the extension stroke.

When the adjusting valve is adjusted to increase the passage area of the by-pass passage, the damping force decreases both in the extension and contraction strokes, whereby, the desired ratio between the damping forces in the contraction and extension strokes cannot be maintained, and the decrease in the damping force in the extension stroke deteriorates the stability in the driving characteristics. It has been experienced that when the damping force of the damper is too small or the characteristic of the damper is too soft and the vehicle is running at a high speed it is difficult to control or maintain the direction of the vehicle.

The present invention has been made in view of the aforesaid circumstances and, according to the invention, the hydraulic damper of the aforementioned kind is provided with a by-pass passage for connecting the first and second chambers by-passing the valve or valves on the piston, and a check valve to change the liquid flow in the by-pass passage between the extension and contraction strokes of the damper, particularly, to reduce the liquid flow in the extension stroke as compared with the liquid flow in the contraction stroke.

Preferably, the by-pass passage is constituted of a coaxial bore in the piston rod, with the inner end of the bore opening the second chamber, and the bore is connected to the first chamber through a radial hole in the piston rod.

Further objects and advantages of the invention will become apparent from the following detailed description taken with reference to accompanying drawings exemplifying some preferred embodiments of the invention, in which: Fig. 1 is a longitudinal sectional view of a hydraulic damper according to the invention; Fig. 2 is an enlarged partial view of Fig. 1; Fig. 3 is a sectional view taken along line Ill- 111 in Fig. 1 and showing an adjustable valve; Fig. 4 is a view similar to Fig. 3 but showing the adjustable valve being opened condition; Fig. 5 is a diagram showing the relationship between the damping force in the extension and contraction strokes and the piston speed according to the invention; Fig. 6 is a view similar to Fig. 2 but showing a modified form;; Fig. 7 is a partial longitudinal sectional view of a hydraulic damper according to a second embodiment of the invention; Fig. 8 is a partial enlarged view of Fig. 7 at the location encircled by a circle VIII in Fig. 7; and Fig. 9 is a partial longitudinal sectional view of a hydraulic damper according to a third embodiment of the invention.

The hydraulic damper shown in Fig. 1-Fig. 4 comprises a tubular main body 1 consisting of an outer tube 2, an inner tube 3 constituting the cylinder according to the invention a bottom cap 4 closing the lower end of the outer tube 2, and an upper cap 5 closing the upper end of the outer tube 2. The inner and outer tubes 2 and 3 define therebetween an annular space serving as a reservoir 6. The reservoir 6 communicates with the interior of the inner tube 3 through a connecting hole 7 provided in the lower end portion of the inner tube 3. A mounting ring 8 is secured to the bottom cap 4. A rod guide 9 closes the upper end of the inner tube 3 and slidably guides a piston rod 1 5 which will hereinafter be explained.An annular seal 12, a seal 11 serving as a check valve encircling the piston rod 1 5 and normally seating on the rod guide 9 to allow the fluid flow only in the radially outward direction with respect to the piston rod and toward the reservoir 6, and a spring 10 are disposed between the upper cap 5 and the rod guide 9.

A piston 13 is slidably fitted in the inner tube 3, and a coaxial bore 14 is formed in the piston 13 for fitting with the piston rod 1 5. The piston rod 1 5 is secured to the piston 13 with a reduced diameter portion of the piston rod 1 5 fitting with the bore 14, and a hollow nut 1 6 screwthreadingly engaging with the tip end of the small diameter portion. The piston 13 partitions the interior of the inner tube 3 into a first chamber or the upper chamber 17 and a second or the lower chamber 18. The piston rod 1 5 extends through the upper chamber 17, slidably through the rod guide 9 and the seal 12 to the outside of the damper.The chambers 1 7 and 18, and the lower portion of the reservoir 6 contain therein hydraulic liquid such as oil, and the upper portion of the reservoir 6 contains therein gas under pressure.

A coaxial bore 29 extends through the piston rod 1 5 with the lower end thereof opening to the interior of the hollow nut 1 6. There are provided radial holes 21 and 23, as shown in Fig. 2, to connect the bore 20 with the upper chamber 17.

The interior of the hollow nut 1 6 is connectable to the lower chamber 1 8 through a radial hole 46.

Thus, the radial holes 21 and 23 in the piston rod, the coaxial bore 20 in the piston rod, and the radial hole 46 in the hollow nut 1 6 constitute a by-pass passage 1 9 according to the invention which communicates the upper and lower chambers 17 and 18 by-passing damping force generating valves mounted on the piston which will be explained hereinafter.

As shown in Fig. 2, the radial hole 23 is normally closed by a check valve 22 according to the invention. The check valve 22 consists of a casing 22b screw-threadingly secured to the piston rod 15 and having an opening 22a, a valve body 22c, and a spring 22d which normally urges the valve body 22c to seat on a valve seat defined on the outer end of the radial hole 21. Thus, the check valve 22 permits the liquid flow only from the lower chamber 18 to the upper chamber 17.

Annular grooves 24 and 25 are respectively formed in the upper and lower end surfaces of the piston 13, and the grooves 24 and 25 are respectively permanently connected to the lower and upper chambers 18 and 17 through a plurality of connecting holes 27 and 26 respectively (although only one each is shown in Fig. 1). On the upper side of the piston 13, a damping force generating.valve 28 for the contraction stroke cooperates with the annular groove 24. The damping force generating valve 28 consists of a valve disc 29 consisting of two or more mutually overlapping annular sheets normally covering the annular groove 24, an annular retainer 30 acting as a fulcrum of the deflection of the valve disc 29, and a retainer 31 having an increased diameter for preventing the excessive deflection of the valve disc 29.The valve disc 29 and the retainers 30 and 31 are clamped between the piston 1 3 and a shoulder 15a which is formed on the piston rod 15.

Similarly, a damping force generating valve 32 for the extension stroke is provided on the lower side groove 25. The valve 32 consists of a valve disc 33 normally covering the annular groove 25 in the piston 13, a retainer 34 serving as a fulcrum of the deflection of the valve disc 33, and a retainer 35 having an increased diameter for preventing the excessive deflection of the valve disc 33. The valve disc 33 and the retainers 34 and 35 are clamped between the piston 13 and the hollow nut 16.

An actuating rod 41 extends loosely through the bore 20 in the piston rod 1 5. The upper end of the rod 41 projects from the upper end of the piston rod 15. A seal 42 is provided between the rod 41 and the upper end portion of the bore 20 for allowing the rotation of the rod 41 around the longitudinal axis thereof but preventing the leakage of the hydraulic liquid. The lower or the inner end of the rod 41 projects from the piston rod 1 5 and is secured to a closure member 43.

The closure member 43 comprises a disc shaped portion having a substantial thickness and slidably and rotatably engaging with the inner peripheral surface of the hollow nut 16, and a partially cylindrical portion slidably engaging with the inner peripheral surface of the nut 16. A plurality of communicating holes 51 are formed in the disc shaped portion of the closure member 43. A stop 47 is provided in the hollow nut 1 6 to restrict the range of the relative rotation between the closure member 43 and the nut 16. As shown in Figs. 3 and 4, the partially cylindrical portion of the closure member 43 selectively opens and closes the radial hole 46 in the nut 1 6 in response to the rotation of the closure member 43.A plurality of rings 48 are disposed between the closure member 43 and a shoulder 1 6a formed in the nut 16, and a spring 50 is disposed between the closure member 43 and a cap 49 closing the lower end of the hollow nut 16. The spring 50 urges the closure member 43 against the rings 48 to maintain the relative vertical position of the closure member 43 with respect to the hollow nut 16.

The upper end of the piston rod 15 is inserted through the chassis 52 (only a portion thereof is shown in Fig. 1) of a vehicle such as an automobile and is secured thereto through a nut 53 screw-threadingly engaging with the upper end portion of the piston rod 1 5. Incidentally, the mounting ring 8 is secured to such as a wheel shaft.

The hydraulic damper having the constitution as described heretofore operates as follows. Fig. 5 is a diagram showing the damping force characteristics wherein damping force W1 in the extension stroke and damping force W2 in the contraction stroke are shown with reference to piston speed V. Firstly, it is assumed that the closure member 43 takes the condition shown in Fig. 3 with the radial hole 46 in the hollow nut 16 being closed. In the extension stroke, the piston 13 and the piston rod 1 5 move upward or in the arrow A direction in Fig. 1. The liquid in the upper chamber 17 flows into the lower chamber 18 deflecting the valve disc 32 around the radially outer periphery of the retainer 34. The liquid flows through connecting holes 26 and the annular groove 25 from the upper chamber 17 to the lower chamber 18.Further, an amount of the liquid corresponding to the ingress of the piston rod 1 5 into the inner tube 3 flows through the connecting hole 7 from the lower chamber 7 to the reservoir 6. The damping force W1 at this condition is shown as line D, D in Fig. 5. It will be noted that the line 0 D1 in Fig. 5 is mainly determined by a fixed orifice which is provided according to conventional technique such as by providing one or more restricted cut-outs in the outer periphery of either of the valve discs 29 and 33, by providing one more cut-outs or orifices in the annular wall defining either of the annular grooves 24 and 25, or by providing an orifice in the wall of the hollow nut 16 or in the cap 49.

In the contraction stroke, the damping force generating valve 28 on the piston 1 3 determines the damping force d1 d as shown in Fig. 5, and the damping force in the low piston speed condition is determined by the fixed orifice and is depicted by line 0 d in Fig. 5. It will be understood that the dampintrce W, in the extension stroke as depicted by line D D is solely determined by the characteristics of the valve 32 and the damping force W2 in the contraction stroke as depicted by line d1 d in Fig. 5 is solely determined by the characteristics of the valve 28, and which are determined as desired by suitably selecting the design of each valves.

Next, the actuating rod 41 is rotated by a suitable rotating device (not shown) so that the closure member opens the radial hole 46 as shown in Fig. 4. In the extension stroke of the damper, the check valve 22 is closed, but the upper chamber 17 and the lower chamber 18 are connected by an additional passage consisting of the radial hole 23, the bore 20, the communicating holes 51,the interior of the nut 16, and the radial hole 21. Therefore, the communication of the upper and lower chambers 17 and 18 is easier than the closing condition of the adjusting valve 43. As the result, the damping force W1 is determined by line E in Fig. 5.

While in the contraction stroke, the check-valve 22 opens thereby further increasing the effective area of the passage 19 consisting of radial holes 21 and 23, the bore 26, the communicating holes 51, the interior of the hollow nut 16 and the radial hole 46. As the result, the damping force W2 in the contraction stroke is determined by line e in Fig. 5.

It will be understood that when the check valve 22 and the radial hole 21 are not provided as taught by prior art technique, the damping force in the contraction stroke is depicted by line fin Fig. 5 whereby the ratio between the damping force in the extension stroke and that in the contraction stroke cannot be maintained as compared with the valve closed condition (line D and line d).

In other words, the effective area of the passage 1 9 in the valve open condition is determined to provide the damping force W2 in the contraction stroke as depicted by line e according to prior art technique wherein the check valve 22 is not provided, then, the damping force in the extension stroke would decrease substantially as depicted by line F in Fig. 5.

Therefore, according to the invention, it is possible to maintain the desired ratio between the damping force in the extension and contraction strokes irrespective to the adjustment therefor, thus, it is possible to assure desired comfortable driving conditions in rough road and smooth road conditions without deteriorizing the steering characteristics.

Figs. 7 and 8 show the second embodiment of the invention, wherein the hollow nut 1 6 in the first embodiment is substituted by a nut 72 of conventionai type and the lower end of the hollow piston rod 1 5 receives therein a check valve 70.

The check valve 70 consists of a valve body 71 normally seating a valve seat defined on the inner periphery of an opening 75 in a plug 74 which closes the lower end of the bore 20 in the piston rod 1 5. A spring 78 acts between the valve body 71 and a spring retainer 76 which is also secured to the inner wall of the bore 20. An orifice opening 73 is formed in the valve body 71.

Further, the actuating rod 41 does not extend to the lower end of the bore 20 and terminates adjacent to the radial hole 21. A closure member 80 is secured to the lower end of the actuating rod 41 for opening or closing the radial hole 21 in response to the rotational movement of the actuating rod 41. Alternatively, the closure member 80 opens or closes the radial hole 21 in response to the vertical movement of the actuating rod 41.

The operation and the effects of the second embodiment is substantially similar to the first embodiment, since, when the adjusting valve (43 in the first embodiment, and 80 in the second embodiment) is fully closed, no liquid flow generates in the by-pass passage and the damping force characteristics are depicted by lines 0 D and 0 d which are determined by the characteristics of damping force generating valves 28 and 32 and the fixed orifice. In the second embodiment shown in Fig. 7, the fixed orifice is constituted of a plurality of circumferential cut-outs formed in the valve disc 29.When the adjusting valve is actuated, the check valve (22 in the first embodiment, and 70 in the second embodiment) opens in the contraction stroke to establish a large amount of the by-pass flow and, in the extension stroke, the check valve closes but a small amount of the by pass flow is established by a small hole (23 in the first embodiment, and 73 in the second embodiment). The characteristics in the adjusting valve open condition is depicted by lines 0 E and in in Fig. 5.

Fig. 9 shows the third embodiment of the invention. The embodiment differs from the first embodiment in that the check valve 22 in the first embodiment is substituted by a check valve 60 which is disposed in the hollow nut 16. The check valve 60 consists of a valve member 64, a central opening 63 formed in a cap 62 closing the lower end of the hollow nut 16, and a spring 61 extending between the valve member 64 and the closure member 43. Further, the radial hole 23 is omitted since the radial hole 23 acts to permanently connect the upper chamber 1 7 with the bore 20 in the piston rod 1 5.

The operation of the third embodiment slightly differs from the first embodiment. Namely, the check valve 60 opens in the contraction stroke even though the adjusting valve 43 is in the closed condition. Therefore, the damping force characteristics of the third embodiment is depicted by line 0 d,' d' in Fig. 1 in the contraction stroke with the adjusting valve 43 being closed, as compared with the line 0 d, d in the first and second embodiment. Thus, the damping force in the contraction stroke can further be decreased as compared with the first and second embodiment, whereby when the hydraulic damper is utilized in a vehicle suspension system, the driving feeling can further be improved, and it is possible to maintain good stability in the directional control.

it will be understood that the invention is not limited to the embodiments disclosed and various modification can easily be applied for those skilled in the art within the technical scope of the invention, for example, the hydraulic damper is not limited to the dual-tube type shown in the drawing, and the invention may be applied to single tube type hydraulic dampers. Further, the damping force generating valve device mounted on the piston may be of any desired type provided that the valve can generate substantial part of the damping force in both of the extension and contraction strokes. Further, in the embodiments, the check valve acts to decrease the damping force in the contraction stroke as compared with the extension stroke, however, the direction of the check valve may be reversed whereby the damping force in the extension stroke decreases as compared with the contraction stroke.

The spring force of the spring acting on the check valve may be determined as desired. When the spring force is reduced the angle of the inclination of the rising up portion such as O d1, (Fig. 5) can be decreased.

Claims

1. A hydraulic damper including a cylinder receiving therein hydraulic liquid, a piston working in the cylinder and partitioning the interior thereof into first and second chambers, a piston rod secured to the piston and extending through the first chamber to the outside of the cylinder, and damping force generating valve means mounted on the piston for generating damping force in the extension and contraction strokes of the damper, characterized by a by-pass passage for connecting said two chambers by-passing said valve means on the piston, and a check valve for changing the liquid flow in said by-pass passage between the extension and contraction strokes of the damper.

2. A hydraulic damper according to Claim 1, wherein said by-pass passage is constituted of a coaxial bore and a radial hole formed respectively in the piston rod.

3. A hydraulic damper according to Claim 2, wherein there is provided a valve for controlling the effective area of said by-pass passage, and said valve is secured to an operating rod extending through said bore and operable from the outside of the damper.

4. A hydraulic damper as set forth in Claim 2, wherein said check valve is provided in the first chamber for normally closing said radial hole in the piston rod, and said valve opens in the contraction stroke of the damper.

5. A hydraulic damper as set forth in Claim 2, wherein said check valve normally receives the liquid pressure in the second chamber and opens in the contraction stroke of the damper.

6. A hydraulic damper substantially as hereinbefore described with reference to, and as illustrated in, Figs. 1 to 5; or Fig. 2 when modified by Fig. 6; or Figs. 7 and 8, or Fig. 9 of the accompanying drawings.