GB2103159A

GB2103159A - Pneumatically cushioned vehicle seat

Info

Publication number: GB2103159A
Application number: GB08217227A
Authority: GB
Inventors: Helge Pietsch
Original assignee: Isringhausen GmbH and Co KG
Current assignee: Isringhausen GmbH and Co KG
Priority date: 1981-06-16
Filing date: 1982-06-14
Publication date: 1983-02-16
Also published as: SE450559B; JPS584512A; FR2507551A1; SE8203715L; FR2507551B1; GB2103159B; AU8489282A; DE3124072A1

Abstract

In a spring-loaded vehicle seat in which a seat frame 3 is supported on an under frame 7 by means of lovers 4, 5 arranged on said seat frame and an interposed pneumatic cushioning device 6, to produce as low a characteristic frequency as possible and to maintain the seat in its unloaded state in its uppermost vibrational position the seat has a metal spring 15 in addition to the pneumatic cushioning device and arranged in parallel with the device. <IMAGE>

Description

SPECIFICATION Pneumatically cushioned vehicle seat The invention relates to a pneumatically cushioned vehicle seat in which a seat frame, which carries the seat cushion, is supported on an under frame by levers and a pneumatic cushioning device interposed between the seat frame and under frame.

A distinction should be made between levers arranged in parallel and levers which intersect one another in the form of a scissors linkage and which are pivotally joined together at their points of intersection. In both cases an air bellows cushioning device, hereinafter called a pneumatic cushioning device, is arranged between the levers and a frame, usually the under frame, and the load capacity of the pneumatic cushioning device depends on the elastic force of the cushioning system itself and on the leverage ratio of the lever.

In order to be able to alter the load capacity of the pneumatic cushioning device in a convenient manner, the pneumatic cushioning device in known pneumatic seats is attached to a supply of compressed air for the vehicle and is supplied with the necessary internal pressure for pneumatic cushioning via control or pilot valves, so that any user of the seat is seated at exactly the specified statistical height of the vibration system, that is in the mean position which the seat occupies when at rest and about which it performs vibrations when bumps occur on the road.

Undesired large vibrations about the statistical height will then arise if the frequency of excitation coincides with the characteristic frequency of the seat. The excitation frequency depends on the particular type of vehicle and on road conditions as well as on the velocitv of travel, however, according to experience, the frequencies all lie above a limiting value and it is the aim of seat builders to construct seats whose characteristic frequencies, as far as possible, lie below the said limiting value so that, when driving, the excitation frequencies and the characteristic frequency of the seat do not coincide.

Another aim of seat builders is to ensure that the unladen seat remains fixed in its uppermost position. Normally the unladen seat is forced up into its uppermost position by the internal pressure of the pneumatic cushioning. However, the control or pilot valve of the pneumatic cushioning device may be activated in such a way that compressed air is discharged until the seat has sunk down its statistical height or even to its lowest vibrational position. Proposals for ensuring that the uppermost vibrational position of the seat in its unloaded state is kept by using a pneumatic relief valve are in many cases too costly because of the necessary accuracy of adjustment of the relief valve and because of the expense of assembly and of permanent maintenance of the valve.

An object of the invention is to provide a pneumatically cushioned vehicle seat of the type referred to with a low characteristic frequency which remains fixed in its uppermost vibrational position in the unloaded state.

According to the invention a spring-loaded vehicle seat comprises a seat frame, for carrying a seat cushion, supported on an under frame by levers attached to said seat frame, an interposed pneumatic cushioning device, and by a metal spring arranged in parallel with the pneumatic cushioning device.

The metallic spring is conveniently in the form of a tension spring and in one embodiment of the invention the metallic spring has a leverage ratio different from that of the pneumatic cushioning device.

The arrangement of a metal spring in parallel with the pneumatic cushioning device has resulted, entirely unexpectedly, in a lowering of the characteristic frequency of the seat which can be explained as follows, according to preliminary investigations by the applicant: With reference to the pneumatic cushioning device it holds that, within the operational range of the vibrating seats, the characteristic or C-value alters according to the internal pressure of the pneumatic cushioning device, that is if the pneumatic cushioning device is in a compressed condition and has as increased internal pressure a higher C-value is produced and, on the contrary, if the pneumatic cushioning device is extended and has a correspondingly decreased internal pressure, a lower C-value is produced.In comparison to this metal springs are normally manufactured in such a way that they have a defined (constant) C-value.

By arranging a pneumatic cushioning device and a metal spring in parallel the pneumatic cushioning device is supported, or in other words slightly extended, in such a way that the pneumatic cushioning device is unloaded and its internal pressure falls. Owing to this the C-value of the pneumatic cushioning device also decreases more than proportionally so that the pure addition of the constant C-value of the pneumatic spring, decreased owing to the reduction in the internal pressure, is in total less than the C-value given by the sole use of pneumatic cushioning. Since, at constant mass, the characteristic frequency is determined by the C-value there is thus obtained without noteworthy expense, solely the parallel arrangement of a metal spring which is relatively cheap to manufacture, the desired reduction in the characteristic frequency of the pneumatic seat.

At the same time the metal spring, arranged in parallel with the pneumatic cushioning device, acts as a supporting spring which, with suitable dimensions, can be arranged to lift the unladen seat into its uppermost vibrational position. In comparision with the proposals already put forward of incorporating an additional relief valve into the air system of the vibrating seat this is an important proposal, more favourable as to cost, which also ensures a robust, maintenance free, operation of the seat not liable to interference.

An additional advantage of a pneumatic seat according to the invention arises from the fact that the metal supporting spring also reduces the internal operating pressure of the pneumatic cushioning device required to guarantee the carrying capacity of the whole system in relation to the weight of a user of the seat. A reduction in the internal operating pressure of the pneumatic cushioning is advantageous in all those cases in which the compressed air supply system of the vehicle is unable to produce the maximum desired pressure. This is true, in particular, for vehicles which have a lower dashboard pressure for the braking system than is provided in vehicles in some countries, for example, in Germany. As a result a pneumatic seat with a metal supporting spring is more universally applicable.

Embodiments of the invention are now described in more detail with reference to the drawings, in which: Figure 1 is a schematic representation showing in side view a vibrational system of a pneumatic seat having scissors levers, and Figure 2 is a schematic representation showing in side view a vibrational system of a pneumatic seat having parallelogram levers.

The vibrational system illustrated in Figure 1 has a seat frame 3 which carries the seat cushion (not illustrated) and which is supported on an under frame 7 by means of scissors levers 4 and 5 attached to it with an interposed pneumatic cushioning device 6.

The scissors levers 4 and 5 are, in each case, pivotally attached to the frame 3 and 7 in known manner by means of fixed pivots 8 and 9 and movable or free pivots 10 and 11. A pneumatic cushioning device 6 is arranged in known manner between a base plate 12 and a pressure stirrup 1 3. The pressure stirrup 1 3 extends and is firmly fixed between two scissors levers 4 of similarform arranged at the sides of the vibrational system and the base plate 12 is firmly welded on the base frame 7.

A pin 14 to which one end of the tension spring 1 5 is pivotally attached is attached to the base plate 12. The other end of the tension spring 1 5 is pivotally attached to a pin 1 6 which is connected to the two scissors levers 5, of similar design, and which follow the adjustment movement of the movable pivot 11 during vibration of the seat.

Thus the tension force of the tension spring 1 5 is arranged to be in parallel with the compression force of the pneumatic cushioning device 6.

Figure 2 shows a vibration system for a pneumatic seat with parallelogram levers 1 7 and 1 8 which are pivotally attached to pivot bearings 19, 20, 21 and 22, to an under frame 23 and to a seat frame 24 which carries the seat cushion (not illustrated).

A pneumatic cushioning device 25 is clamped between a base plate 26 firmly welded to the under frame 23 and a pressure stirrup 27. The pressure stirrup 27 is firmly attached to the parallelogram lever 18.

In order to arrange a tension spring 28 in parallel with the device 25 the upper parallelogram lever 17 is lengthened beyond its pivot 19 by means of an extension piece 29 to which one end of the tension spring 28 is attached. The other end of the tension spring is pivotally attached to a pin 30 fixed in the under frame 23.

Claims

1. A spring-loaded vehicle seat, comprising a seat frame, for carrying a seat cushion, supported on an under frame by levers attached to said seat frame, an interposed pneumatic cushioning device, and by a metal spring arranged in parallel with the pneumatic cushioning device.

2. A vehicle seat according to Claim 1, wherein the metal spring is in the form of a tension spring.

3. A vehicle seat according to Claim 1 or 2, wherein the metal spring is arranged to have a leverage ratio different from that of the pneumatic cushioning device.

4. A vehicle seat substantially as described with reference to Fig. 1 or Fig. 2 of the drawings.