GB2272499A

GB2272499A - An air spring unit

Info

Publication number: GB2272499A
Application number: GB9322938A
Authority: GB
Inventors: Emanuel Groll; Jochen Horwath; Hans-Christian Pflug; Klaus Russ; Dieter Ziegler
Original assignee: Daimler Benz AG; Mercedes Benz AG
Current assignee: Daimler Benz AG
Priority date: 1992-11-17
Filing date: 1993-11-08
Publication date: 1994-05-18
Anticipated expiration: 2013-11-08
Also published as: GB2272499B; ITRM930743A1; DE4238790C2; IT1262428B; FR2698143B1; ITRM930743A0; DE4238790A1; GB9322938D0; FR2698143A1

Abstract

An air spring unit with a main chamber F (or 4) which varies in its volume during movements of the spring also has an additional chamber K (or 7) which exhibits an essentially constant volume and which, by means of a valve 6, can be connected to or disconnected from the main chamber F to vary the progressivity of the suspension. This valve 6 exhibits a virtually unthrottled opening position, from which it can be rapidly closed; on the other hand, the opening of the valve is performed with a delay, in that initially it runs through a pre-opening phase, permitting only small flows, to delay pressure equalization between chambers F and K. The valve is controlled by pressure applied in chamber 17. <IMAGE>

Description

2272499 1 An Air SDrincr Unit The invention relates to an air spring unit

with a main chamber which varies in its volume during movement, that is extension or retraction, of the spring, for example an air spring bellows, which by means of a valve adapted to be connected to an additional chamber, having an essentially constant volume, or can be blocked off with respect to this chamber, for varying the progressivity of the spring forces of the air spring unit.

Air spring units are used on motor vehicles, in particular also on trucks, whenever particularly great comfort is to be ensured and, in some cases, it is also additionally to be made possible to change the ground clearance of the vehicle to adapt to different operating conditions. Changing of the ground clearance is usually performed by introducing additional air into the air spring unit or letting air out of the spring unit. The feeding in or letting out of air is usually also used for varying the progressivity of the spring forces, by for example increasing the air pressure in the spring unit in the case of considerable spring compression excursions and reducing it in the case of excessive rebound excursions.

However, it must be accepted in this case that a relatively high amount of energy is required during driving.

In order to keep this energy expenditure as low as possible, it is known in principle to combine in the way specified at the beginning a main chamber of the air spring unit which is variable in its volume during operation of the spring with an additional chamber which exhibits an essentially constant volume and to control the connection between the two chambers by means of a valve. The additional chamber, which can be blocked off with respect to the main chamber, offers the possibility of varying the springeffective air volume. If the said valve between main chamber and additional chamber assumes its opened end position, a large overall volume is available, which changes only 2 relatively little during suspension excursions of the air spring unit, since the change in volume is only relatively small in comparison with the size of the overall volume. This means that the air pressure when the valve is open changes only relatively moderately during the suspension movement and the air spring unit exhibits a spring characteristic with relatively low progressivity. Consequently, particularly comfortable driving is made possible. If need be - for example if a spring compression stroke exceeds a predetermined threshold value - the additional chamber can be blocked off rapidly with respect to the main chamber, so that then only the air volume in the main chamber is spring- effective. This is synonymous to saying that the ratio between the changes in the springeffective air volume occurring between suspension movement and the overall volume in the main chamber reaches a relatively great value and the air spring unit correspondingly operates with distinctly increased progressivity, i.e. with increasing spring compression movement a distinctly increasing supporting force of the spring unit is achieved.

In addition, the spring characteristic when the valve is closed can be varied comparatively considerably by feeding into the main chamber or letting out of the main chamber comparatively small amounts of air. corresponding air spring units are described, for example, in the following printed publications: JP-A 61-180034, DE-A 40 18 712, DE-A 34 44 577, DE-B 10 81 780, DE-B 11 44 127, DE-A 15 30 632 and EP-A 01 66 702.

According to the printed publication mentioned last, the valve may be designed either as a simple change-over valve or as a controllable throttle valve. In the first case, only a comparatively rapid change-over between the completely opened state and the completely closed state is possible. In the latter case, the air throughput of the valve can be controlled.

In the case of a throttled opening position of the 3 valve, it must be taken into consideration however that the influence of the additional chamber on the progressivity of the spring characteristic may be very small, because the dynamic pressure changes occurring in the main chamber during suspension excursions cannot propagate virtually at all any longer to the additional chamber. Rather, the additional chamber is dynamically "isolated" from the main chamber when the connection path is throttled.

US-A 48 44 428 discloses an air spring unit in which a main chamber and an additional chamber are constantly connected via a throttled line and there is arranged between the two chambers a displaceable piston, the adjustment of which respectively effects an increase in the volume of one chamber and at the same tine a decrease in the volume of the other chamber. A variation of the progressivity of the spring characteristic can also be achieved in this way.

With regard to good suspension comfort, it is desirable to be able to control the connecting path between main chamber and additional chamber asymmetrically, in such a way that on the one hand rapid closing of this path and on the other hand delayed opening are made possible. By rapid closing, the suspension can, if need be, be hardened without jolting and without any appreciable power consumption, since on the one hand the spring-effective air volume changes rapidly and on the other hand no pressure change in the main chamber occurs solely due to the closing of the connecting path. By the delayed opening of the connecting path it is taken into account that, when the connecting path is closed, there may occur - depending on the suspension movement relatively great differences in pressure between main chamber and additional chamber, which can cause abrupt forces if the connecting path is opened suddenly without any throttling.

For such controlling of the connecting path, until now no constructionally simple possibilities have been presented.

DE-C 35 44 474 does admittedly show a valve for which 4 the characteristic reproducing the opening cross-section as a function of the valve stroke has a markedly kinked shape such that, upon leaving the closed position, as the opening stroke increases an initially only small and slightly increasing opening cross-section is exposed, which does not increase greatly until after the opening phase. However, the controlling of a valve which is to be fitted in the connection between main chamber and additional chamber of an air spring unit of the type specif ied - at the beginning is difficult, and that is so irrespective of the valve design. This is due to the fact that, when the valve is closed, very greatly changing differences in pressure between main chamber and additional chamber can occur on account of suspension movements. Consequently, however, the opening behaviour of the valve may be subject to correspondingly great fluctuations.

Therefore, the present invention seeks to improve the operating behaviour of an air spring unit of the type mentioned at the beginning by new measures for controlling the connection between main chamber and additional chamber.

According to the present invention there is provided an air spring unit with a main chamber which varies in its volume during movements of the spring, which by means of a valve is- adapted to be connected to an additional chamber, having an essentially constant volume, or to be blocked off with respect to this additional chamber for varying the progressivity of the spring forces of the air spring unit, wherein the valve has a valve body, acted upon by the pressure of the main chamber in a direction to close the valve and by the pressure-of the additional chamber in the direction to open the valve, and also a piston, which is connected to the valve body via a rod and has one effective surf ace acted upon by the pressure of the additional chamber and another effective surface which can be acted upon by a controllable pneumatic pressure (pS), the said one effective surface of the piston being greater than the cross-section of the valve body acted upon by the pressure of the additional chamber.

Thus, the arrangement according to the invention ensures that the pressure of the additional chamber always exerts a closing force on the valve, to be precise irrespective of whether the pressure of the main chamber is higher or lower than the pressure of the additional chamber.

Consequently, the greatly changing operating states of the air spring unit, and in particular the greatly fluctuating differences in pressure between main chamber and additional chamber, even in the case of an arrangement of a seat-controlled valve, are now of only entirely secondary importance for the opening behaviour of the latter.

This offers the possibility of using the simplest design measures for controlling the valve.

In this respect, according to a preferred embodiment of the invention it is provided that a control chamber, on the side of the piston which can be acted upon by the controllable pneumatic pressure, can be connected to a pneumatic pressure source via a throttled path and can be connected to an air outlet via an unthrottled path.

The unthrottled air outlet makes rapid closing of the valve possible. The throttled connection between control chamber and pressure source allows on the one hand a rapid pressure increase in the control chamber when the valve is closed, because the volume of the said chamber does not change as long as the valve is still in the closed position. As soon as the valve begins to open when the control pressure increases further, a comparatively large amount of pneumatic medium is required for a further pressure increase in the control chamber, because then the volume of the control chamber increases analogously to the opening stroke of the valve. Here the throttle thus prevents rapid feeding of relatively large amounts of pneumatic medium, so that the opening stroke of the valve can take place only with a delay or at lower speed.

This operating behaviour of the valve occurs necessarily, that is without any regulating of the pressure 6 in the control chamber. Rather, it is sufficient to connect the control chamber to the air outlet for closing the valve in unthrottled mode and to connect it to the pneumatic pressure source for slowly opening the valve in throttled mode.

In addition, it may expediently be provided that the controlling of the valve is performed fluidically, in particular pneumatically, to be precise in such a way that a fluidic positive-displacement unit serves for controlling the valve, which unit is subjected to fluid pressure for opening the valve or is relieved of fluid pressure for closing the valve, the pressure admission taking place via a throttled line and the pressure relief taking place via an unthrottled line. In this way, the opening stroke of the valve is slowed down. Nevertheless, rapid closing remains possible.

A preferred embodiment of the invention will now be described by way of example with reference to the drawings, in which:- Fig. I shows a schematicized sectional view of an air spring unit according to the invention, Fig. 2 shows a schematicized sectional view of a pneumatically controlled valve for the connection between main additional chamber, Fig. 3 shows a sectional view of the sealing surf aces of seat and valve body -of the abovementioned valve, and Fig. 4 shows a circuit-like representation of the control of the abovementioned valve.

According to Fig. 1, between a sprung mass 1, which in the case of a vehicle is f ormed by the vehicle body, and an unsprung mass 2, which in the case of a vehicle is f ormed by wheel or axle guiding elements and the like, there is arranged an air spring unit 3, which essentially comprises, in a way known in principle, a spring bellows 4 arranged on the sprung mass 1 and a rolling piston 5 which chamber and 7 can be pushed in therein and which is arranged on the unsprung mass 2.

During suspension movements, the volume of the spring bellows 4 changes, so that the air pressure in the spring bellows 4 increases during spring compression movements and decreases during rebound movements.

By means of a control valve (not shown), compressed air from a pressure source (not shown), for example from a compressor, can be introduced into the spring bellows 4 or let out to the outside. In this way, an additional pressure increase or pressure reduction can be achieved in the spring bellows 4.

The interior of the spring bellows 4 forms a volumevariable main chamber of the spring unit 3, which can be connected by means of a valve 6, which in the fully opened state exposes a large flow cross-section, to an additional chamber 7, which exhibits an essentially constant volume and is accommodated in cavities of the rolling piston 5 or cavities of the unsprung mass 2 which communicate with the said rolling piston.

By a further identical valve 8, if appropriate a further additional chamber 9 can also be connected.

When both valves 6 and 8 are open, a large springeffective air volume is available, the overall volume being changed only relatively little during suspension movements. Accordingly, the pressure changes of the air enclosed in the spring bellows 4 and in the additional chambers 7 and 9 caused by the suspension movements are relatively small, i.e. the air spring unit 3 operates with low progressivity. Depending on whether only the valve 8 or the valve 6 is closed, the spring-effective air volume can be reduced to a greater or lesser extent, with the consequence that the changes of the spring-effective air volume caused by suspension movements are correspondingly great in comparison with the overall spring-effective air volume and the air spring unit operates with greater progressivity.

In Fig. 2, the valve 6 is shown schematically.

8 According to Fig. 2, the valve 6 controls an opening 10 of large crosssection in a wall between the interior F of the spring bellows 4 and the interior K of the part of the additional chamber 7 accommodated in the rolling piston 5.

For this purpose the valve 6 has a cup-shaped valve body 11, which, in the closed state shown, rests on a valve seat 12 arranged on the rim of the opening 10.

By means of a rod 14, which is guided in a slidingly displaceable manner in a guide 13, the valve body 11 is connected to a cup-like piston, which is guided in a slidingly displaceable manner in a- corresponding cylinder and, on its side facing the valve body 11, is acted upon by the pressure PK in the additional chamber 7 and, on its side facing away from the valve body 11, is acted upon by a control pressure pS in a control chamber 17.

The effective area of the piston 15 facing the valve body 11 is larger than the end f ace of the valve body 11 f acing the piston 15. which end f ace is acted upon by the pressure pK in the additional chamber in the closed state of the valve 6. Consequently, the pressure PK always effects a force in the closing direction of the valve body 11.

The other side of the valve body 11 is acted upon by the pressure p. in the interior of the spring bellows 4. When the valve 6 is completely open, this pressure PF is virtually equal to the pressure pK.

When the control pressure pS in the control chamber 17 has reached an adequately great value, piston 15 and valve body 11 are raised from the position shown in Fig. 2, so that the valve 6 opens. If the pressure in the control chamber 17 falls by an adequate amount below the pressure PK in the additional chamber 7 or the pressure pF in the spring bellows 4, the valve 6 closes.

The control circuit shown in Fig. 4 serves for controlling the pressure in the control chamber 17. Depending on the switching position of a change-over valve 18, the control chamber 17 is connected to a pneumatic pressure source, or a compressor 19, or - as shown in Fig. 4 - to an 9 air outlet 20. Between change-over valve 18 and control chamber 17 there are arranged parallel to each other a throttle 21 and a non-return valve 22, which is opened by the pressure in the control chamber 17 as soon as the change-over valve 18 is brought into the position shown. Consequently, the control chamber 17 can be relieved of pneumatic pressure virtually without any throttling as soon as the change-over valve 18 is brought into the position shown. If, on the other hand, the change-over valve 18 is switched into its other position, the non-return valve 22 closes, and the compressed air from the pressure source 19 can only flow via the throttle 21 into the control chamber 17. Accordingly, the pressure built- up in the control chamber 17 is delayed.

It is accordingly achieved by the arrangement shown in Fig. 4 that, upon switching over of the change-over valve 18 into its position which is not shown, the valve 6 opens relatively slowly, but upon switching over the change-over valve 18 into the position shown it can close rapidly.

This achieves on the one hand rapid closing and on the other hand delayed opening of the valve 6, with a preopening phase in which, of the valve body 11, only an at most small opening cross-section is exposed, so that initially only a throttled connection is released between the additional chamber 7 and the main chamber 4 and a slow pressure equalization between these two chambers is made possible.

The control of the change-over valve 18 constantly checks itself for correct functioning. In the event that malfunctioning is detected, the change-over valve 18 is disconnected from its energy supply, for example an electric power source, so that it is brought by a restoring spring or the like necessarily into the position shown, in which the control chamber 17 remains virtually pressureless. Consequently, the valve 6 necessarily assumes its closed position, so that in such cases only the air volume in the spring bellows 4 is spring-effective and the spring unit 3 operates with correspondingly great progressivity. Consequently, in every case reliable operating behaviour of the air spring unit 3 is ensured - even if with reduced comfort.

According to Fig. 3, the valve body 11 and the valve seat 12 of the valve 6 may have sealing rings 23 and 24, respectively, which axially overlap each other in the closed position of this valve 6 and which are designed in such a way that, when the opening stroke of the valve body 11 is beginning, initially only a very narrow gap with a pronounced throttling effect is opened. It is ensured in this way that, upon opening of the valve 6, only a delayed pressure equalization between the interiors F and K is made possible.

In the case of the example shown in Fig. 3, the sealing ring 23, which is arranged as part of the valve seat 12, is designed as a metal ring which is screwed to a supporting part. The sealing - ring 24 on the valve body 11 consists of an elastomer material and is inserted in a groove of the valve body 11. A ring washer 25 and a retaining ring 26 serve for securing and fixing the sealing ring 24. To avoid air being enclosed by the sealing ring 24 inside the groove receiving it in the valve body 11, which air could then hinder the correct seating of the sealing ring 24 in the groove, a plurality of small bores 27 are arranged in the valve body 11 for venting the said groove.

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Claims

Clains

1. An air spring unit with a main chamber which varies in its volume during movements of the spring, which by means of a valve is adapted to be connected to an additional chamber, having an essentially constant volume, or to be blocked off with respect to this additional chamber for varying the progressivity of the spring forces of the air spring unit, wherein the valve has a valve body, acted upon by the pressure of the main chamber in a direction to close the valve and by the pressure of the additional chamber in the direction to open the valve, and also a piston, which is connected to the valve body via a rod and has one effective surface acted upon by the pressure of the additional chamber and another effective surface which can be acted upon by a controllable pneumatic pressure (pS), the said one effective surface of the piston being greater than the cross-section of the valve body acted upon by the pressure of the additional chamber.

2. An air spring unit according to Claim 1, wherein the valve is adapted to be driven in such a way as to open in a pulsed manner.

3. An air spring unit according to Claim 1 or 2, wherein the valve comprises a seat valve and on the seat and also on the valve body there are arranged closely over lapping sealing surfaces or sealing rings, which when the opening stroke begins initially expose only a throttling gap.

4. Air spring unit according to any one of Claims 1 to 3, wherein the piston blocks off a control chamber with respect to the additional chamber and the pressure (pS) in the control chamber is controllable in such a way that the control chamber can be connected for pressure admission via a throttled line to a pressure source and for pressure relief via an unthrottled line to an outlet.

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5. An air spring unit according to any one of Claims 1 to 4, wherein the unit comprises an air spring bellows.

6. An air spring unit according to any one of Claims 1 to 5, wherein the additional chamber is arranged in the piston of an air spring bellows or in cavities which can be connected to or communicate with the piston.

7. An air spring unit with a main chamber which varies in its volume during movements of the spring, substantially as described herein with reference to and as illustrated in the accompanying drawings.

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