VALVE ARRANGEMENT FOR CONTROLLING AN AIR SUSPENSION, A VALVE UNIT, AND A VEHICLE PROVIDED WITH SUCH DEVICES

Abstract: Valve arrangement for multi-axle vehicles having air suspension, which vehicle is provided with at least one axle (1, 2, 3) having two or more air suspension elements (4, 5, 6, 7, 8, 9, 30) which can be pressurised by means of a source of compressed air (10), valves (13, 14, 15, 16, 17, 18) for pressurising or venting said air suspension elements, and a control unit (25) for controlling opening and closing of said valves. The invention also relates to a valve unit provided for each air suspension element, which valve unit comprises a first valve (15a, 16a, 44) between the source of compressed air (10) and the air suspension element (4, 5, 6, 7, 8, 9, 30), for pressurising said air suspension element, and a second valve (15b, 16b, 49) connected between the first valve and the air suspension element, for venting said air suspension element, which valves are normally closed. The invention further relates to a valve unit for said valve arrangement and a vehicle provided with such a valve arrangement.

Description: VALVE ARRANGEMENT FOR CONTROLLING AN AIR SUSPENSION, A VALVE UNIT, AND A VEHICLE PROVIDED WITH SUCH DEVICES TECHNICAL FIELD The invention relates to a valve arrangement for vehicles provided with air suspension, a valve unit for such an arrangement and a vehicle provided with such a valve arrangement. BACKGROUND ART Vehicles with air suspension are usually provided with a pair of air suspension elements, such as bellows, for each suspended axle. The volume of the air suspension elements can be varied with respect to the load on the vehicle or the height relative to the vehicle frame or ground-level. A conventional method of achieving this is to connect each air suspension element to a pair of valves, wherein one valve is used for pressurising and one is used for venting the air suspension element. A known system is known from WO-A1 -9305972, which discloses a valve arrangement for a vehicle having four bellows. The purpose of this arrangement is to minimise the number of valves in the system, as multiple valves often involves a complex control system. A disadvantage with this system is that all valves have been assembled into a single valve block or valve manifold. In present day vehicles, such valve blocks are often heavy and very complex structures. In order to avoid too many connections, with corresponding conduits, between the individual valves, these have been assembled into compact units. The different units making up a valve block will therefore comprise several different valves, each with its own specific function. As disclosed by the WO-document the different valves are connected to a central manifold chamber that can be pressurised or vented, which makes it impossible to pressurise one of the bellows at the same time as another is vented. A similar system is disclosed by DE-A1-38 15 612. In this document, Figure 1 shows a valve block 20 comprising three valves, which valve block controls the air suspension for one axle. The complex structure of a valve block is not apparent from schematic figures of this type. However, a cross-section of an actual valve block of this type is shown in Figure 1 of this application. Using the reference numbers of the German document, Figure 1 shows three solenoid valves 25-27 provided with plungers. A first valve 25 is normally connected to the atmosphere, but is also provided with a connection 21 to a pressure source. The remaining two valves 26, 27 are normally closed, but may be connected to their respective bellows via the connections 31 and 32 respectively, for venting of said bellows. As in the previous case, it is not possible to pressurise one bellows while venting the other. The unit is further provided with a connection 29, which may be connected to further units in the valve block. The function of the said valves will not be described in detail. Hence, a problem with current solutions is that the valve blocks are heavy, complex, and therefore expensive, components. In addition each valve block itself contains a number of units comprising -complex and often specially designed valves, each with its own specific function. Repairing or replacing one or more units in a valve block will therefore give rise to further problems. Apart form the complexities of the replacement, it is also necessary for the workshop in question to have one or more specific valve units in stock. As each model of a vehicle is usually provided with two or more different valve units, which may vary in design both between different models and within a models series, even a branded garage will need to keep a large number of different units in stock. DISCLOSURE OF INVENTION The purpose of the invention is to provide a valve unit that can replace all different types of valve units used in current air suspensions. A valve unit according to the invention can be installed separately in proximity to each air suspension element on every axle or centrally in a. valve block. By using identical valve units, installed separately or in combination, service and replacement of parts will be significantly simplified. In the long term the effect will be that only one kind of valve unit needs to be kept in stock with retail dealers and garages. This purpose is achieved by means of a valve arrangement according to claims 1-9 and a valve unit according to claims 10-14. The invention relates to a valve arrangement for vehicles having two or more axles with air suspension. The vehicle would be provided with at least one axle provided with two or more air suspension elements that can be pressurised by means of a source of compressed air, valves for pressurising or venting said air suspension element, and a control unit for controlling the opening and closing of the above valves. Each air suspension element has a first valve connected between the source of compressed air and said air suspension element, and a second valve connected between the first valve and the air suspension element for venting said air suspension element. Both these valves are normally closed. By means of this arrangement it is possible to control all valves separately, which enables complete individual control. This is particularly suitable for e.g. buses with a lowering function, wherein lowering of one side or alternatively one corner of the vehicle is required. Since a single valve according to the invention can replace a lowering valve that typically may comprise six or more valves, a significant cost reduction and simplification of the system is achieved. Said first and second valves are of the same type and are preferably, but not necessarily, assembled to a valve unit. This combination of the first and second valves is preferably used for all air suspension elements of the vehicle. By using identical valves for all air suspension elements, the structure of the system is significantly simplified. Apart from making service and replacement of parts simpler and quicker, only one type of valve has to be kept in stock. The valve units can either be installed adjacent each of the respective air suspension elements or be assembled in a central valve block. In order to allow for simple manoeuvring of the valve units, using for instance a central control unit, a suitable type of valve for this purpose is solenoid valves. In contrast to current valve units using slide valves, the preferred valves according to the invention are diaphragm valves. Diaphragm valves weigh less, are easier to manufacture and maintain, and are often more reliable than conventional slide valves. A valve unit used in the valve arrangement principally meant for use in connection with air suspension elements in a vehicle, but may also be used in other kinds of compressed air systems. A valve unit comprises a valve body with a connection from a source of compressed air and a connection to a compressed air consumer, as well as a connection for venting the compressed air consumer. In addition, the valve unit is provided with a first valve between the source of compressed air and the compressed air consumer, and a second valve for venting the compressed air consumer. Both valves are normally in a closed position. Each valve is provided with a solenoid for individual opening of either valve using an electronic control unit. It is not possible to open both valves simultaneously, as this would mean venting the source of compressed air. Venting of an air suspension element using said second valve is suitably done to the atmosphere. In order to achieve further weight savings, the valve body can be made from a plastic material. In addition, an injection moulded valve body is simpler to manufacture and required less subsequent machining than a corresponding body made from a metallic material. BRIEF DESCRIPTION OF DRAWINGS Figure 1 Shows a schematic cross-section of a known valve unit; Figure 2 Shows a schematic diagram for an embodiment of the invention comprising a vehicle with three axles; Figure 3 Shows a schematic diagram for the driving axle from Figure 2; Figure 4 Shows a schematic representation of a valve unit with two valves according to the invention; Figure 5 Shows a schematic cross-section of a valve unit with two valves according to the invention. MODE(S) FOR CARRYING OUT THE INVENTION Figure 2 shows a schematic diagram for an embodiment intended for a vehicle with three axles; a front axle 1 , a driving axle 2 and a further axle 3. In this case the invention is intended for a heavy vehicle in the form of a tractor unit with one driving axle, and may be applied to the driving axle, the driving axle and the further axle or on all three axles. Other combinations, for instance using several driving axles, are of course possible. Common for all embodiments is that one type of valve unit can be used for all axles with air suspension. The air suspension is achieved by means of air suspension elements in the form of bellows. According to the embodiment of Figure 2, all axles 1 , 2, 3 are provided with bellows 4, 5; 6, 7; 8,9 arranged in pairs on each axle. The bellows are placed between the chassis of the vehicle and each respective wheel axle. By controlling the pressurisation or venting of the bellows it is possible to achieve a desired height above ground level or to control the pressure difference between two bellows on the same axle. In this way the vehicle may, for instance, be raised when travelling on an uneven surface and be lowered when travelling on a motorway, when disengaging a trailer or when adjusting the height to a loading bay. It may also be desirable to control the pressure so that the driving axle takes a larger load than the bogie axle, in order to improve the gripping power of the tyres. The term bogie axle denotes a first driving axle that can be combined with a further axle, such as a lifting axle, a trailing axle, a second driving axle or a pusher axle. According to the invention a source of compressed air 10 delivers a pressure to an accumulator 11 , which is connected to a supply conduit 12. The supply conduit 12 supplies a number of valve units 13, 14; 15, 16; 17, 18, which in turn are connected to a corresponding number of bellows 4, 5; 6, 7; 8, 9. Each bellows is provided with a pressure sensor 19, 20; 21 , 22; 23, 24 for measuring the pressure in the respective bellows, and for transmitting signals corresponding to the pressure levels to a control unit 25. The bellows of the further axle 3 is controlled by a single valve unit 17. As the pressure in these bellows is equal, it can be measured by a single pressure sensor 23. In addition, the front axle 1 and the driving axle 2 are provided with level sensors 26; 27, 28, which measures the distance between the bellows and the chassis. As the front axle 1 carried less load, it is only provided with a single level sensor 26 between the bellows 4, 5. The driving axle that takes up a considerably larger load is provided with level sensors 27, 28 on either side of the vehicle adjacent each bellows. Signals representing the distance between chassis and axle are sent from the level sensors 26; 27, 28 to the control unit 25. The further axle 3 lacks a level sensor, as it only take up that part of the load which can not be taken up by the driving axle 2. However, the further axle is provided with an additional bellows 30, in order to lift the axle when required, e.g. for reducing the turning radius of the tractor unit and/or to reduce wear on the tires. This bellows is controlled by a separate valve unit 18. The function of the valve units and the wiring of the sensors to the control unit 25 will now be described in detail, with reference to Figures 3 and 4. Figure 3 shows a selected section of Figure 2, including the driving axle 2 only. When the pressure in a bellows 6, 7 needs to be adjusted, the control unit 25 evaluates the signals from the pressure sensors 21 , 22 and the level sensors 27, 28. Should a situation occur requiring an increased pressure in the left bellows 6 of the driving axle 2, then a signal is transmitted from the control unit 25 to the valve unit of that bellows 6. The signal actuates a solenoid 31 in the valve 15a of the valve unit 15, connecting the source of compressed air 10 with the bellows 6. This valve 15a comprises a normally closed two-position valve, which is caused to open by means of the solenoid in order to pressurise the bellows 6. Upon achieving the desired pressure level, the control unit 25 will cut the current to the solenoid 31 and the valve 15a will close. The pressure level is monitored by the control unit 25 by means of the pressure sensor 21. The same method can be used for raising the vehicle using the bellows 6 and 7. In this case the control unit 25 will also use the level sensors 27, 28 when opening and closing the valves 15a, 16a of the respective valve units. In order to vent either of the bellows 6, 7 or to lower the vehicle, a pair of second valves 15b, 16b in the respective valve units are used. These valves are connected to the conduits 35 and 36 respectively, between the above first valves 15a and 16a and the bellows 6 and 7 respectively. The control unit 25 transmits a signal to the solenoids 32, 34 of one or both valves 15b, 16b in order to open said valves, whereby one or both bellows 6, 7 are vented. Lowering the vehicle by venting the bellows is desirable for instance when the vehicle is travelling at higher speeds, or when depositing or picking up a trailer, an exchangeable platform or a container. An advantage over current systems is that it is possible to control all bellows individually and simultaneously. It is for instance possible to pressurise a bellows on one side of the vehicle at the same time as the bellows on the opposite side is being vented. Since only one valve needs to be controlled to pressurise or vent the bellows, the system gives a faster response to signals from the control unit. In addition to common control strategies for controlling the pressure in the bellows, a system of this type allows rapid pressurisation of one side combined with venting of the opposite side, in order to achieve a temporary displacement of the centre of gravity to counteract or prevent the vehicle from overturning. It is also possible to raise or lower one side or one corner of the vehicle through individual control of the bellows in connection to the respective side or corner. This is desirable for buses having a lowering function, whereby the height of the instep is controlled by raising or lowering the section of the vehicle adjacent the door. During boarding it is for instance possible to lower a bellows associated with the front corner of the bus, in order to reduce to height of the instep. Figure 4 shows a schematic representation of a valve unit according to the invention. The valve unit 40 is provided with a connection 41 to the source of compressed air, a connection 42 to a bellows and a connection 43 for venting to a tank or to the atmosphere. The first valve 44 is spring loaded towards a closed position, but can be moved to an open position for pressurisation of the bellows by means of a solenoid 45. The solenoid is controlled by a control unit (not shown) by means of a pair of electrical wires 46 and 47. When the current to the solenoid is interrupted by the control unit, the valve 44 will close. A second valve 49, of the same type as the first valve 44, is connected to a conduit between the first valve.44 and the connection 42 to the bellows. The second valve 49 is also spring loaded towards a closed position, but can be moved to an open position by means, of a solenoid 50. The solenoid 50 is connected to the control unit by means of a pair of electrical wires 47, 48, wherein one of said wires 47 is a ground connection which is used in common with the first solenoid 45. When a signal is transmitted from the control unit, the second valve 49 opens to vent the bellows. It is of course possible to use the wire 47 for positive or negative feeding of the solenoids. A schematic cross-section of a valve unit that can be used in a system according to the invention is shown in Figures 5A and 5B. Figure 5A shows a valve unit 51 that is provided with a connection 52 for compressed air which discharges into a first chamber 53 on one side of a diaphragm valve 54. Compressed air from the connection 52 is conducted through a first conduit 55 to the opposite side of said diaphragm valve 54. Hence the pressure is equal on both sides of the valve 54, which is provided with a spring 56 for spring loading the valve 54 against a seat 57. In this way the valve is normally in a closed position. In order to open the diaphragm valve 54 a first solenoid 58a (Fig. 5b) is used, which when actuated will act on a piston 59 that closes the connection between the source of compressed air 52 and the first conduit 55. The pressure in the first chamber 53 will cause the diaphragm valve 54 to lift from the seat 57 against the returning force of the first spring 56 only. Pressurised air will then flow from the first chamber 53, past the first diaphragm valve 54, into a second chamber 60, and out through a connection 61 to the bellows to be pressurised. As soon as the current to the first solenoid 58a is interrupted, the pressure is restored in the first conduit 55. With an equalised pressure on both sides of the diaphragm in the first valve 54, the valve will be closed by the return spring 56. The valve unit 51 is provided with a second diaphragm valve 62, which has a similar function for venting the bellows. The connection 61 to the bellows leads into the second chamber 60 and further into a third chamber 63 on one side of the second diaphragm valve 62. The connection for pressurised air 52 is connected via a second solenoid 58b to a conduit 64 that exits on the opposite side of the valve 62. As the pressure is equal on both sides, alternatively somewhat larger in the conduit 64, the diaphragm valve 62 is held in a closed position by the pressure and/or a spring 65. In order to vent the bellows a second solenoid is used, which when actuated will act on a piston 66 that closes the connection between the connection 52 and the i conduit 64. The conduit 64 is then vented to the atmosphere via a silencer 68. The pressure in the third chamber 63 will then cause the diaphragm of the valve to lift from its seat 67, whereby pressurised air will flow past the valve 62 via a conduit (not shown) that is vented to the atmosphere through an outlet that exits in the silencer 68. It is also possible to lead pressurised air from the bellows from the chamber 60 via the second solenoid 58b to the conduit 64 (connection not shown). The air pressure on both sides of the second diaphragm valve 62 will then be equalised, until the solenoid 58b is activated for venting of the bellows. A suitable valve for this purpose can be a standard valve used for anti- locking pneumatic brakes (ABS). An ABS-valve can be modified by reversing one of its solenoids and by re-boring/machining certain conduits and seats. This is done to achieve a normally closed valve, as the original valve is normally open. By starting from a valve unit having a valve body that after minor modifications can be used for multiple purposes, several advantages are achieved in view of rationalisation and reduced costs. In the above the valve unit has been described in connection with valve arrangements for air suspension for vehicles. It is of course possible to use the valve unit for compressed air systems having different applications.

Claims: CLAIMS 1. Valve arrangement for multi-axle vehicles having air suspension, which vehicle is provided with at least one axle (1, 2, 3) having two or more air suspension elements (4, 5, 6, 7, 8, 9, 30) which can be pressurised by means of a source of compressed air (10), valves (13, 14, 15, 16, 17, 18) for pressurising or venting said air suspension elements, and a control unit (25) for controlling opening and closing of said valves, characterized in that each air suspension element is provided with a first valve (15a, 16a, 44) between the source of compressed air (10) and the air suspension element (4, 5, 6, 7, 8, 9, 30), for pressurising said air suspension element, and a second valve (15b, 16b, 49) connected between the first valve and the air suspension element, for venting said air suspension element, which valves are normally closed. 2. Valve arrangement according to claim 1, characterized in that said first and second valves (15a, 15b, 16a, 16b, 44, 49) are of the same type. 3. Valve arrangement according to claim 1 or 2, characterized in that said first and second valves are attached together into a single valve unit (13, 14, 15, 16, 17, 18,40). 4. Valve arrangement according to the claims 1-3, characterized in that a valve unit (13, 14, 15, 16, 17, 18, 40) in the shape of a combination of the first and the second valves (15a, 15b, 16a, .16b, 44, 49) is used for all air suspension elements in the vehicle. 5. Valve arrangement according to any one of the claims 1-4, characterized in that the valve units are mounted adjacent its respective air suspension element. 6. Valve arrangement according to any one of the claims 1-4, characterized in that the valves are mounted together in a valve block. 7. Valve arrangement according to any one of the above claims, characterized in that the valves are solenoid valves. 8. Valve arrangement according to any one of the above claims, characterized in that the valves are diaphragm valves. 9. Valve arrangement according to any one of the above claims, characterized in that said second valve is vented to the atmosphere. 10. Valve unit for use in a pneumatic system, which unit comprises a valve body (51) with a connection (52) to a source of compressed air, a connection (61) compressed air consumer, and an outlet (68) for venting of the compressed air consumer, characterized in that the valve unit has a first valve (54), for pressurisation, between the source of compressed air and compressed air consumer, and a second valve (62), for venting, connected between the first valve (54) and the compressed air consumer, wherein both valves (54, 62) are normally closed. 11. Valve unit according to claim 10, characterized in that each valve is provided with a solenoid (58) for individual opening of either valve. 12. Valve unit according to claim 10 or 11, characterized in that the valves are diaphragm valves. 13. Valve unit according to any one of the claims 10-12, characterized in that said second valve is vented to the atmosphere. 14. Valve unit according to any one of the claims 10-13, characterized in that the valve body is made from a plastic material. 15. Vehicle with air suspension comprising valve arrangements according to claim 1, which vehicle has at least one axle (1-3) provided with two or more air suspension elements (4, 5, 6, 7, 8, 9, 30) which can be pressurised by means of a source of compressed air (10), valves (13, 14, 15, 16, 17, 18) for pressurising or venting said air suspension element, and a control unit (25) for controlling opening and closing of said valves, characterized in that each air suspension element (4, 5, 6, 7, 8, 9, 30) is provided with said valve arrangement (13, 14, 15, 16, 17, 18), which valves can be pressurised or vented individually and independently of each other by the control unit (25). 16. Vehicle according to claim 15, characterized in that one or more valve arrangements on one side of the vehicle can be controlled to achieve a lowering function.

Inventors: DEN HARTOG JAMES, DEN HARTOG, JAMES
Applicants: DEN HARTOG JAMES, VOLVO LASTVAGNAR AB, DEN HARTOG, JAMES
Application year: 2001
Main classification: B60G17
IPC codes: B60G17