AIR SPRING DEVICE FOR LOAD-CARRYING VEHICLES

Abstract: The invention relates to an air spring for transport vehicles comprising a vessel ("piston") (10) of rigid, pressure-resistant material, such as steel, and a bellows (9), fitted onto the vessel ("piston") (10), of e.g. nylon-reinforced rubber, being in pneumatic connection with the "piston" (10) and connected to a source of compressed air. The invention is characterised by the "piston" (10) being provided with an air shut-off valve (13) in the opening (12) towards the bellows (9).

Description: AIR SPRING DEVICE FOR LOAD-CARRYING VEHICLES TECHNICAL FIELD The present invention is a modification and an improvement of as such known air springs used for suspension of the chassis in heavy transport vehicles. Such air springs, being connected between the chassis and the wheel axle, generally comprise a lower vessel, called a piston, made of a rigid, pressure-resistant material such as steel, and an upper bellows, mounted on the vessel, made of e.g. nylon- reinforced rubber and being in pneumatic connection with the piston. BACKGROUND ART Today, air springs are commonly used for transportation vehicles of various sizes. Depending on the size and weight of the vehicle, from two up to eight air spring units are used, which may be arranged in pairs on a bogie. The air pressure in these air springs is in the order of 8 bar, and the air spring pressure is maintained by means of one or more valves in a piping system connected to a pressurised tank receiving its compressed air from a compressor driven by the vehicle engine. The same air spring principle is also used for the cab suspension. As the upper part of the air spring consists of a bellows, this entails that the top cover of the bellows, facing upwards and supporting the chassis, will be pushed upwards by a higher pressure and will be lowered by a lower pressure. In this manner, the height of the vehicle above ground level may be controlled, and it is also possible to tilt the vehicle in relation to the ground by using different pressure levels in the air springs on different sides of the vehicle. An inclination of the vehicle towards one side, caused by uneven load, may also be adjusted by using different pressure levels in the air springs on both sides of the vehicle. A level regulator, sensing and controlling the level of the vehicle in relation to the ground, is arranged on the chassis, and this regulator, supplying air to, or discharging air from, the air springs, can sense the level of the chassis in relation to the wheel axle or the ground. A major advantage of the air springs, besides having excellent suspension properties, is that the height of the vehicle above ground level can be adjusted. This for example allows the vehicle to be lowered, and to be adjusted to a correct height suitable for the height of a loading ramp, or to be run in under a trailer and then be raised, to carry the load to be transported. A simple electric control box for such lowering and raising is provided in connection with the driver's cab, making it very simple for the driver to perform this raising and lowering. TECHNICAL PROBLEM To lower and raise the vehicle chassis by means of the air springs, means on the one hand that a large amount of air must be discharged to the environment when the chassis is lowered, and on the other that air has to be forced in again, from the pressurised air tank, when the chassis is raised. As the amount of air being under pressure, or to be pressurised, and being accommodated in the air springs, is rather large, this means a substantial waiting time for the driver who wants to lower or raise the vehicle, especially in case of repeated height adjustments, e.g. when shunting several trailers or demountables, a waiting time that cannot be used for other activities. Particularly if the vehicle is without load and is to be lowered by its own weight, a rather long waiting time may occur. Consequently, there has for a long time existed a strong desire to reduce this waiting time. SOLUTION Thus, according to the present invention, an air spring for transport vehicles is provided, comprising a vessel ("piston") made of rigid, pressure-resistant material, such as steel, and a bellows fitted onto the vessel ("piston"), made of e.g. nylon-reinforced rubber, being in pneumatic connection with the "piston" and connected to a source of compressed air, said air spring being characterised by the "piston" being provided with an air shut-off valve in the opening towards the bellows. According to the invention, the valve may consist of, or be located in, a partition wall between the "piston" and the bellows. The valve may, according to the invention, consist of a rotary valve, which is closed and opened by a rotating motion. According to the invention, the valve may also consist of a seat/poppet valve, the poppet being raised and lowered by means of a piston in a separate cylinder inside the "piston", arranged to shut off the air inside the "piston", in a lowered position, while air is being discharged from or fed into the bellows, and to be open between the "piston" and the bellows, in a raised position, when air is neither discharged from or fed into the bellows. DESCRIPTION OF DRAWINGS The invention will be described in further detail below, with reference to the drawings, wherein Fig. 1 shows, schematically, the location of an air valve according to the invention, as well as a level control valve controlling the amount of air in the air springs, and Fig. 2 shows a cross-section of an air spring with a shut-off valve for separating the air volume in the "piston" from that in the bellows. MODE FOR CARRYING OUT THE INVENTION Fig. 1 illustrates part of a frame 1 being suspended by an air valve, generally desig- nated 2, which air spring 2 in turn is suspended by an element 3 that may be part of a bogie and constitutes an assembly together with the wheel axle 4. A level control valve 5 is bolted to the frame 1. This valve is actuated by a lever 6 and a rod 7, which is flexibly connected to the lever 6, said lever 7 having a perpendicular direction and abutting against the axle 4. As the frame 1 is vertically displaced in relation to the axle 4, a rotary motion will thus be created in the level control valve 5. The level control valve, which has a not shown piped connection to the top plate 8 of the bellows 9 of the air spring 2, is connected via piping to a pressurised tank receiving compressed air from a compressor driven by the vehicle engine. The lower part of the air spring 2 is generally comprised of a cylindrical pressure vessel, 10 made of a rigid material such as steel, whereas the bellows 9, normally consisting of nylon-reinforced rubber, is compressible. In the position shown in Fig. 1, when the lever 6 is in a horizontal position, the level control valve is closed, but if the frame 1, for example through loading of the vehicle, compresses the bellows 9, the level control valve 5 is opened so as to allow compressed air to enter the bellows and restore the desired position. If, however, the frame is raised excessively, for example through unloading of the vehicle, the level control valve 5 will discharge air from the bellows 10, allowing the frame 1 to be lowered to the desired position. The pressure in the air spring 2 and the volume thereof is thus controlled by inject- ing and discharging air. Thus, substantial amounts of air have to be discharged or injected into the air valve 2, and this may require rather a long time, as the pressure is the same in the entire air volume inside the air spring. One part of this air spring, i.e. the vessel 10, in technical jargon called the "piston", is however rigid and will not change its volume in dependence of its internal air pressure. According to the inven- tion, it is therefore preferred to close off this rigid component 10 during injection of air into, or discharge of air from, the air spring, in order thus to be able to control the pressure in the bellows 9 with a much smaller amount of air. Fig. 2 shows, in a vertical cross-section, an example of an air spring according to the invention, comprising a top plate 8 and a bellows 9 arranged on the so-called "piston" 10. According to the invention, a separation wall 11 has been provided between the inside of the bellows 9 and the inside of the "piston" 10. In this separation wall 11, there is an aperture 12 that can be closed by means of a valve poppet 13. When the valve poppet 13 is in its upper position, as shown in the figure, the aperture 12 is not closed and the air inside the "piston" 10 as well as that inside the bellows 9 has the same pressure, as there are openings 14 in the cylinder 15 delimiting the aperture 12 on its lower side. The position of the valve poppet 13 is governed by a compression spring 16, situ- ated below a piston 17 connected to the valve poppet 13, and by an air pressure P 2 supplied through the opening 18. When the pressure P 2 drops to zero through the action of a shut-off valve, the valve poppet 13 will move downwards, as the pressure inside the "piston" 10, which is the same as the pressure inside the bellows 9, will act on the top side of the piston 17 through the opening 19. This force acting on the top side of the piston 17 will be stronger than the force of the spring 16 acting in the opposite direction. When the valve poppet 13 is closed, the pressure inside the bellows will also add to the downward force on the valve and thus contribute to a correct closing thereof. When the pressure P 2 is introduced again, the valve will be opened, as the pressure P 2 is higher than, or as high as, the pressure inside the bellows, and as the bottom surface area of the piston 17 is larger than the top area of the valve poppet 13. A pipe connection 20 in the top plate 8 is shown in the figure, being connected to the level control valve 5 discussed above, for injecting and discharging air into/from the bellows 9. As will be apparent from the figure, the cylinder 15 in the "piston" 10 is made integrally with, or fixedly secured to, the bottom of the "piston" 10 and the separation wall 11. The cylinder 15 will thus provide a reinforcement against the vertical force that will be applied onto the "piston" when the valve poppet 13 is closed and the pressure inside the bellows will act upon the separation wall 11. As can be gathered from Fig. 2, the volume of the "piston" 10 is almost half of the entire volume of the air valve 2. At that pressure, around 8 bar, which is commonly used in such air springs, a substantially smaller amount of air will have to be sup- plied to, or be discharged from, the air spring 2 during lifting or lowering of the vehicle frame 1. The invention is not limited to the illustrated embodiment, but may be varied in different ways within the scope of the patent claims.

Claims: CLAIMS 1. An air spring for transport vehicles comprising a vessel ("piston") (10) of rigid, pressure-resistant material, such as steel, and a bellows (9), fitted onto the vessel ("piston") (10), of e.g. nylon-reinforced rubber, being in pneumatic connection with the "piston" (10) and connected to a source of compressed air, characterised by the "piston" (10) being provided with an air shut-off valve (13) in the opening (12) towards the bellows (9). 2. An air spring according to claim ^characterised in that the valve (13) consists of, or is located in, a partition wall (11) between the "piston" (10) and the bellows (9). 3. An air spring according to claim 2, characterised in that the valve (13) is a rotary valve, which is closed and opened by a rotary motion. 4. An air spring according to claim 2, characterised in that the valve (13) is a seat/poppet valve, the poppet being raised and lowered by means of a valve piston (17) in a separate cylinder (15) inside the "piston" (10), and being arranged, in a first position, to shut off the air inside the "piston" (10), while air is being discharged from or fed into the bellows (9) and, in a second position, to be open between the "piston" (10) and the bellows (9).

Inventors: JAEBERG BJOERN, JAEBERG, BJOERN
Applicants: JAEBERG BJOERN, VOLVO LASTVAGNAR AB, JAEBERG, BJOERN
Application year: 1998
Main classification: B60G11
IPC codes: B60G11, B60G17, F16F9