GB2131120A

GB2131120A - Hydraulic damper with temperature- compensated throttle

Info

Publication number: GB2131120A
Application number: GB08323764A
Authority: GB
Inventors: Rudolf Schmidt
Original assignee: Boge GmbH
Current assignee: ZF Boge GmbH
Priority date: 1982-11-27
Filing date: 1983-09-05
Publication date: 1984-06-13
Also published as: GB8323764D0; GB2131120B; IT8323764A0; DE3243995C2; DE3243995A1; FR2536811A1; IT1166986B; IT8323578V0

Abstract

A hydraulic damper with a damping piston 22 secured on a hollow piston rod 10 has inside the piston rod a throttle member comprising respectively a throttle passage and an axially displaceable control element 5' varying the cross-section of the throttle passage, the control element 5' being acted upon through a control piston 5 by a temperature responsive varying volume of fluid present in a chamber 3. According to the invention the control element, the control piston and the chamber form a self contained unit 1. This piston rod insert 1 operates independently of piston rod length and diameter and of the volume of working fluid trapped in the piston rod. Such a unit is a component which is independent of the design details of the respective types of damper, and by use of which in addition a reduction in weight is further possible. <IMAGE>

Description

SPECIFICATION Hydraulic damper The invention relates to a hydraulic damper with a piston secured to a hollow piston rod and a throttle member mounted inside the piston rod comprising a throttle passage and an axially displaceable control member which varies the cross-section of the throttle passage, the control element being acted upon through a control piston by a fluid present in a chamber and varying in volume with changes in temperature.

In such dampers the temperature-dependent viscosity, and accordingly the changes in density, of the damping fluid is allowed for by the control element by which the throttling crosssection in the throttle member can be altered.

The aim of this is to achieve, as far as possible, constant or indeed over-compensated damping forces over as wide a temperature range as possible.

Dampers of this kind are known (e.g. German Patent Specification DE-OS 31 06 766) in which a volume of fluid is trapped in a hollow piston rod, the temperature-dependent changes in volume of the fluid displacing the control piston axially, so that different damping forces are produced by the change in the cross-sectional area for flow. A drawback in such constructions is that a large and, from the weight-saving point of view disadvantageous, volume must be present in the piston rod. Moreover, piston rods differing in length and diameter must also have different fluid volumes and thereby different lengths of control piston travel, so that a corresponding number of components is required. Furthermore, the overall internal surface of the piston rod must be machined using expensive workhandling methods, so that dynamic sealing of the control piston can be achieved.

Taken this as its starting point, the aim of the invention is to construct a damper so that, independently of the length and diameter of the piston rod and of the volume of oil trapped in the piston rod, a temperaturedependent control of the damping force is achieved, capable of being introduced universally and furthermore achieving a reduction in weight without loss of function.

According to the invention we provide an hydraulic damper having a piston secured to a hollow piston rod, a throttle member being mounted inside the piston rod and comprising a throttle passage and an axially displaceable control element which varies the cross-section of the throttle passage, the control element being acted upon by a control piston in turn acted upon by a fluid of volume variable with temperature which is present in a chamber, in which the chamber, the control element and control piston form a unit, the unit being received within the piston rod.

With this construction a compact and accordingly weight-saving unit is provided, which in conjunction with the small trapped volume of oil can perform the necessary relatively large control movements. Moreover the unit can be introduced universally in piston rods of different lengths and diameters by the use of unit components.

In a preferred embodiment the throttle passage is in communication with an orifice in the wall of the piston rod by way of a flow opening provided in the wall of the unit.

To achieve trouble-free location of the unit in the cavity of the piston-rod the unit is in one embodiment provided with a screw-thread engaging in a corresponding thread on a piston rod sleeve. Alternatively the lower end of the unit could be pressed into a drawn-in portion of the piston rod and the unit and piston rod secured together by a roll pin or by means of corrugations. In this arrangement the threaded sleeve in the piston rod is omitted, with a saving in cost.

The outside wall of the chamber is preferably sealed with respect to the cylindrical inside wall of the piston rod. In such an arrangement it is of advantage that the cavity in the piston rod does not have to contain an unnecessary quantity of fluid which would have an adverse effect on the overall weight of the damper. The quantity of fluid required for the temperature-controlled valve arrangement is also a component of the chamber of the unit portion.

An embodiment of the invention will now be described, by way of example only with reference to the accompanying drawings, of which: Figure 1 is a section through a piston rod of a telescopic vibration damper according to the invention with a unit screwed into place; and Figure 2 is an elevation of the unit shown in Fig. 1.

The hollow piston rod 10 shown in Fig. 1 has in its cavity the cartridge-like piston rod insert 1, formed as a unit. The piston rod insert 1 comprises an outside wall 2, in the chamber 3 defined by which there is trapped a quantity of fluid. A control piston 5, preloaded by the spring 4 and pressing against the fluid in the chamber 3, is sealed with respect to the trapped fluid by means of an 0ring 6. The spring 4 abuts at its lower end a disc 7 which in turn bears against the outside wall 2. At its upper end it abuts a security disc 8 which in turn bears against the control piston 5. In an outward direction the outside wall 2 is statically sealed by means of O-ring 9 with respect to the inside wall of the piston rod 10 and by means of a female screwthread 11 its lower end is screwed over a screw-threaded sleeve 1 2 forcibly connected to the piston rod 10.The upper end of the outside wall 2 is beaded against a cover 13, an O-ring 1 5 forming a seal trapped between the cover 1 3 and a disc 14.

The lower end of the control piston 5 is in the form of a control pin 5' which with its double-conical surface shape forms a valve opening with an annular collar 1 6 on the outside wall 2. Through a flow opening 1 7 in the piston rod 10, an outer annular space 1 8, a passage 19, and an inner annular space 20 in the outside wall 2, the damping fluid flows through the valve opening via a bore 21 in the lower end of the piston rod and thereby flows from the working chamber above the piston 22 to the working chamber below the piston 22.

According to the change in volume, responsive to temperature, of the body of fluid trapped in the chamber 3 and corresponding axial displacement of the control pin 5', the consequent different cross-sectional opening areas produce higher or lower damping forces in the lower velocity range. Compensation of the temperature-dependent damping forces, and furthermore under-or over-compensation can accordingly be achieved. In the higher velocity range the damping forces are produced mainly by the valve devices on the piston 22.

In Fig. 2 a piston rod insert 1 is shown in elevation. Such a piston rod unit 1 can be manufactured as a unitary assembly and mounted in the cavity of widely different piston rods, and a respective matching of the damping forces can be obtained by alteration of the shape of the control pin 5'. In piston rods of larger diameter the lower region of the piston rod is more markedly drawn in and matched to correspond to the diameter of the unit.

Claims

1. An hydraulic damper having a piston secured to a hollow piston rod, a throttle member being mounted inside the piston rod and comprising a throttle passage and an axially displaceable control element which varies the cross-section of the throttle passage, the control element being acted upon by a control piston in turn acted upon by a fluid of volume variable with temperature which is present in a chamber, in which the chamber, the control element and control piston form a unit, the unit being received within the piston rod.

2. An hydraulic damper according to claim 1 in which the throttle passage is in communication with an orifice in the wall of the piston rod by way of a flow opening provided in the wall of the unit.

3. An hydraulic damper according to claim 1 or claim 2 in which the unit is engaged with a sleeve which is received within the piston rod.

4. An hydraulic damper according to any preceding claim in which the outside wall of the unit is sealed with respect to the inside wall of the piston rod.

5. An hydraulic damper substantially as described with reference to and as illustrated in the accompanying drawings.