GB2199921A

GB2199921A - Shock-absorber with hydraulic - mechanical draw stop

Info

Publication number: GB2199921A
Application number: GB08800762A
Authority: GB
Inventors: Gunther Handke; Peter Ullmer; Ernst Prozeller
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1987-01-16
Filing date: 1988-01-14
Publication date: 1988-07-20
Anticipated expiration: 2008-01-14
Also published as: GB2199921B; DE8700703U1; GB8800762D0

Abstract

A hydraulic-mechanical draw stop situated in the annular working chamber defined by piston rod 6 and cylinder 3 comprises a stop ring 10 secured on the piston rod which co-operates with a damping ring 14 guided under initial stress on the cylinder wall and with a one-piece damping ring carrier and bush member 12, 13. The member 12, 3 is subject to the action of a stop spring 11 made fast in the region of the piston rod end of the cylinder. A corrugation 15 in the cylinder wall can provide for a less sudden increase in damping when the stop ring 10 contacts the damping ring 14. The ring 14 has a gap 14a which allows limited fluid flow once the corrugation is passed. <IMAGE>

Description

TITLE: Vibration damper or combination shock-absorber spring unit with hydraulic-mechanical draw stop The invention relates to a vibration damper or a combination shock-absorber spring unit with hydraulicmechanical draw stop according to the opening statement of Claim 1.

It is known to arrange such a hydraulic-mechanical draw stop in the interior of the cylinder between its inner wall and the piston rod. In this case this draw stop comprises a stop ring secured on the piston rod and co-operting with a damping ring and a damping ring carrier. This damping ring carrier lies for one part on the damping ring and for the other part on a stop spring made fast in the region of the piston rod guide, the damping ring being guided under initial stress on the cylinder wall. Moreover a distance bush is provided which acts for the one part upon the stop ring and for the other upon the stop spring.In the insertion of the draw stop this distance bush passes through the damping ring and comes to abut on the damping ring carrier, whereby the damping ring itself, on further pushing out of the piston rod, rests on the stop ring of the latter.

The parts forming the hydraulic-mechanical draw stop must be produced very exactly, so that jamming of the damping ring carrier on the piston rod and thus jamming of the damping ring on the inner wall of the cylinder does not take place a aresult of oblique placing of the damping ring carrier.

This presumes that both the abutment face of the damping ring carrier facing the stop spring and the abutment face for the damping ring are produced extremely exactly parallel with one another and also the stop spring exerts upon the damping ring carrier no force distributed varyingly over the circumference It is the problem of the present invention to produce a hydraulic-mechanical draw stop which, while being simple to produce, renders eas assembly possible and guarantees good guidance on the piston rod so that a jamming effect caused by oblique positioning and the consequent wear are avoided.

In accordance with the invention this problem is avoided in that the darping ring carrier is made in one piece with the distance bush, the external diameter of which is smaller than the internal diameter of the damning ring and the axial length of which limits the axial mobility of the damping ring in relation to the damping ring carrier. The one-piece form ration of the damning ring carrier with the distance bush guarantees that this unit possess good guidance on the piston rod. The one-piece formation also has the advantage that the abutment faces for spring and damping ring are substantially easier to produce and an oblique positioning of the damping ring is avoided.The one-piece formation of darping rlg carrier and distance bush also facilitates assembly Er. renders possible an irprovement of the strength -rcLerties of this part, and lower demands can be made of the manufacturing tolerance of the spring, since a slightly differing spring force upon the damping ring carrier does not set the latter askew, as a result of the long guidance.

In further development of the invention the damping ring carrier with distance bush is made as a sintered part.

This formation as sintered part effects especially good running properties on the chromium-plated piston rod and permits problem-free, accurately dimensioned, reasonably priced production. As shown by one feature of the invention, such a construction without subsequent work can be arranged with slight play on the piston rod, so that the satisfactory function of the draw stop is guaranteed.

A further advantageous form of embodiment is obtained in that the damping ring carrier comprises in the region of the internal diameter an extension piece of sleeve form serving for the centring of the stop spring. Such a form of embodiment is especially suitable in the case of vibration dampers where the radial distance between piston rod and inner wall of the cylinder is relatively great.

The fitting of the dvav stop is here especially simple, as the stop spring is connected with the damping ring carrier before installation in the cylinder, and at the same time a satisfactory centring of the lower end of this stop spring is prouced.

-0n especially advantageous form of embodiment of the draw stop is obtained in accordance with the inventiczlin that the damping ring, in the autment-free condition of the distance bush, is arranged with the stop ring in the region of at least oce axial corrugation of the cylinder. Such a draw stop effects a stroke-dependently acting hydraulic damping, where the cross-section of the axial corrugation of the cylinder can be made steplessly variable with increasing outward thrust movement of the piston rod, whereby an impact-type action of the hydraulic draw stop is avoided.

In order to guarantee a satisfactory transfer flow of the hydraulic fluid the damping ring carrier is provided in accordance with the invention on its external diameter with several recesses distributed uniformly over the circumference.

The invention Till be explained in greater detail below by reference to the forra of embodiment as represented in the drawing, wherein : FIGURE 1 shows a combination shock-absorber spring unit insert in partial longitucina section; FIGURE 2 shows the damming ring carrier made in one piece with the distance bush, according to Figure 1, in enlarged representation; FIGURE 3 shows a plan view of the damping ring carrier according to Figure 2; FIGLTS 4 shows a damping ring carrier made with an extension piece for the centring of the stop spring and FIGURE 5 shows an enlarged representation of the mechanical-hydraulic draw stop.

In Figure 1 the vibration damper formed as Wombination shock-absorber spring unit 1 is provided with a container 2 in which a cylinder 3 is clamped and centred with radial spacing by means of a piston rod guide 4 and a bottom valve.

A piston rod 6 guided in the piston rod guide 4 and sealed to the exterior by a piston rod seal 5 carries the piston 7 provided with damping devices, which divides the fluidfilled interior of the cylinder 3 into a working chamber 8 beneath and a working chamber 9 above the piston 7. The two working chambers 8 and 9 are in communication with one another by way of the damping devices of the piston 7, while the working chamber 8 is connected by way of the bottom valve with the compensating chamber formed by the container 2 and cylinder 3. This compensating chamber has a gas and fluid filling. The hvdraulic-mechanical draw stop is arranged in the annular working chamber 9.This stop possesses a stop ring 10 secured on the piston rod 6, which ring, as from a specific outward movement distance of the piston rod 6, comes to abut on a distance bush 13 made in one piece with the damping ring carrier 12. A stop spring 11 is made fast in the cylinder 3 at the upper end, that is in the region of the piston rod guide 4, and acts with the lower end upon the damping ring carrier 12. L: damping ring 14 lies under initial stress upon the inner wall of the cylinder 3, the initial stress being so great that it exerts a retaining force for the component consisting of damping ring carrier 12 and distance bush 13, so that when the draw stop is not acting the damping ring carrier 12 does not lift away from the stop spring 11.

When the draw stop is in the position as illustrated the damping ring 14 lies in the region of at leest one axial corrugation 15 of the cylinder 3. This axial corrugation 15 has the effect that when the draw stop comes into action the hydraulic damping of outward movement does not start suddenly, but increases continuously over a pre-determined distance of outward movement of the piston rod. This is achieved in that the axial corrugations 15 form with the damping ring 14 a stroke-dependently acting variable passage cross-section. After the axial corrugation is passed only the passage cross-section formed by the gap of the damping rmg14aEs as constriction serving for damping The component produced in one piece from damping ring carrier 12 and distance bush 13 is represented in enlarged manner in Figure 2.This component possesses an abutment face 16 for the stop spring 11 and an abutment face 17 for the damping ring 14. As shown by the plan view of the damping ring carrier 12 according to Figure 3, this also comprises recesses 18 distributed over the circumference, in order to guarantee a satisfactory through-flow of the damning fluid. This component consisting of damping ring carrier 12 and distance bush 13 is advanta{reously formed as a sintered part, whereby, without subsequent working, the internal diameter forms the movement play with the chromiumplated piston rod, while the abutment faces 16 and 17 can be produced in this way exactly parallel with one another.

As a result of the relatively great axial length of the component consisting of damping ring carrier 12 and distance bush 13, good guidance on the piston rod is achieved, while the formation as wintered part guarantees low-friction running on the piston rod.

The form of embodiment according to Figure 4 shows a one-piece formation of the damping ring carrier 12 with the distance bush 13 and an extension piece 19 of sleeve form.

This extension piece 19 of sleeve form serves for the securing of the part on the stop spring and for the centring of this stop spring.

In rigure 5 there is seen an enlarged illustration of the middle region of Figure 1, the container 2 being omitted for the sake of simplicity. The sto p ring 10 is secured on the piston rod 6 in that a prolongation 10a of the stop ring 10 is pressed into a groove 6a of the piston rod 6. The damping ring carrier 12 is guided displaceably with the distance bush 13 formed in one piece on it and the centring extension piece 19 likewise fitted on it according to Figure 4 - on the piston rod 6. The helical compression spring 11, which is axially supported according to Figure 1 on the piston rod guide 4, engages with its lower end on the abutment face 16 of the damping ring carrier 12 and is centred by the centring extension piece 19 of sleeve form.The damping ring 14 lies under elastic initial stress against the internal circumferential surface 3a of the cylinder 3, so that there is a friction between the damping ring 14 and the internal circumferential surface 3a. The damping ring 14 is slit once and has a gap 14a. The damping ring 14 rests on the abutment face 17 of the damping ring carrier 12. The damping ring carrier 12 together with the distance bush 13 and the centring extension piece 1 is produced in one piece as a sintered part, the internal circumferential surface 12a of the sintered part being formed for slide-favouring guidance on the piston rod dand the abutment faces 16 and 17 being arranged exactly parallel with one another and perpendicular to the axis of the piston rod 6.In the cylinder 3 the axial corrugation 15 can be seen, the cross-section of which decreases towards the piston rod guide 4. When the piston rod 6 travels far out in relation to the cylinder 3 as a result of a heavy impact, the stop ring 10 firstly strikes upon the lower end of the distance bush 13 and shifts the distance bush 13 together with the damping ring carrier 12 and the centring extension piece 19 upwards, so that the helical compression spring 11 is compressed.The damping ring 14 at first does not accompany the upward movement, since it bears with friction under elastic initial stress on the internal circumferential surface 3a, and with its internal circumferential surface possesses a small spacing from the external circumferential surface of the distance bush 13. Cnly when the stop ring 10 comes to abut against the damping ring 14 does the damping ring 14 also accompany the upward movement.As a result of the tapering of the axial corrugation 15 the through-flow cross-section for the fluid contained in the upper part chamber 8a becomes the smaller, the further the damping ring 14 moves upwards. When the damping ring 14 reaches the upper end 15a of the axial corrugation 15, only the gap formed between the two ends of the slit damping ring 14, facing one another in the region of the gap 14a, is avail- able as outflow cross-secticn for the fluid contained in the upper r?7t chamber Sa.

VMen the piston rod 6 travels downwards again, the helical compressicn spring 11 expands and the stop ring 10 finally lifts away again from the lower end of the distance bush 13. Since the damping ring 14 rests with friction under initial stress on the inner circumferential surface 3a, the damping ring 14 remains in the position as shown in Figure 5, even after lifting away of the stop ring 10, so that the damping ring carrier 12 also retains the position as shown in Figure 5. It should.also be remarked that in Figure 5 again the damping ring carrier 12 is provided with recesses 18 on its external circumference, as represented in Figu-e 3, so that the damping ring carrier does not impede the throughflow of fluid.

Claims

1.) Vibration damper or combination shock-absorber spring unit with hydraulic-mechanical draw stop, in which a piston connected with a piston rod and comprising damping devices is axially movably arranged in a damping-fluidfilled clinder and divides the cylinder interior into two working chambers, while the piston rod is guided and sealed to the exterior at one cylinder end and the hydraulicmechanical draw stop is situated in the annular working chamber defined by piston rod and cylinder, this draw stop comprises a stop ring secured on the piston rod which cooperates with a damping ring guided under initial stress on the cylinder wal anQ with a damping ring carrier, and this damping ring carrier is subject to the action of a stop spring made fast in the region of the piston rod guide, while a distance bush acts for the one part upon the stop ring and for the other part upon the stop spring, charcteriaed In that the damping ring carrier (12) is made in one piece with the distance bush ( 13), the external diameter of which is smaller than the internal diameter of the damping ring (14) and the axial length of which limits the axial mobility of the damping ring (14) in relation to the damping ring carrier (12).

2.) Vibration damper or combination shock-absorber string unit according to Claim 1, characterised in that the damping ring carrier (12) and the distance bush (13) are made as a sintered part.

3.) Vibration damper or combination shock-absorber spring unit according to Claims 1 and 2, characterised in that the distance bush (13) is arranged with slight play on the piston rod (6).

4.) Vibration damper or combination shock-absorber spring unit according to Claims 1 to 3, characterised in that the damping ring carrier (12) comprises an extension piece (19) ofsleeve form, serving for the centring of the stop spring (11), in the region of the internal diameter.

5.) Vibration damper or combination shock-absorber spring unit according to Claims 1 to 4, characterised in that when the distance bush (13) is inthe stop-free state the damping ring (14) is arranged with the stop ring (10) in the region of at least one axial corru:gation (15) of the cylinder (3).

6.) Vibration damper or combination shock-absorber spring unit according to Claims 1 to 5, characterised in that the damping ring carrier (12) comprises on its external diameter a plurality of recesses (18) uniformly distributed over the circumference.

7.) Vibration damper substantially as described with reference to the accompanying drawings.