Vehicle suspension with linked air bags

An air suspension system for a load carrying vehicle has multiple air bags associated with selected vehicle wheels to at least assist supporting the load and to control relative movement between the respective wheel and a supporting frame structure of the vehicle. A high flow-rate air tube connected to at least one air bag receives air from the connected air bag when air pressure in the air bag increases above that in the air tube. Air flows from the high flow rate air tube to a connected air bag when the air pressure in the air tube is above that of the air bag. The flow rate of air from the air tube to the air bag is controlled by the structure of the fittings between the respective air bags and the high flow-rate air tubes. A height valve maintains a predetermined pressure in the air bags when the vehicle is at rest.

FIELD OF THE INVENTION

This invention relates to a vehicle suspension incorporating linked air bags and relates particularly to a suspension system, which can be used for load transport vehicles, such as trucks, trailers, coaches and other road vehicles. However, the principles of the invention may be adapted for use with any wheeled vehicle, including tracked vehicles.

BACKGROUND OF THE INVENTION

Suspension systems incorporating air bags have previously been proposed. Air bag suspensions have been used on trucks, trailers, buses, coaches and the like for many years, and they generally provide an improved ride on highway surfaces, particularly relatively smooth highway surfaces.

When used on multi-axle vehicles, or when multiple air bags are used in conjunction with single axles on vehicles, it has previously been proposed to provide air bags on each side of the vehicle with the air bags connected by a tube or other connector of relatively small cross sectional area which restricts the flow of air between the tubes to a relatively low flow rate. The tube enables the air bags to be inflated relatively equally to provide an even height for the suspension of the vehicle above the ground.

Previously proposed air bag systems, however, have been shown to experience difficulty in providing adequate vehicle suspension when the vehicle is driven over rough terrain, particularly when such suspension systems have been used in conjunction with multi-wheeled, multi-axled vehicles. For example, for a coach having a multi-axle, rear suspension system, passing over a kerb, raised road section or the like, movement of the forward set of wheels over the impediment causes a consequent movement of the rear wheels lifting the rear wheels off the ground surface. Naturally, if drive is provided to the rear wheels of the dual rear axle suspension system, the vehicle can be stranded. A similar problem can arise with trucks or other vehicles with lazy axles when travelling over uneven roads, or when traversing relatively rough terrain. This may occur, for example, with farm related vehicles such as in attempting to load livestock or handling relatively large quantities of hay, straw, farming equipment, earthmoving equipment or the like.

With previously proposed air bag suspension systems, the air bags are generally supplied with air from an air tank using a relatively small diameter, low flow rate air tube connecting the tank to the air bags. This whole purpose of the connecting tube is to enable the air bags to be inflated and deflated, to vary the height of the vehicle above the ground depending on load conditions. The low flow rate air tubes are not designed or constructed to transfer air between air bags in response to sudden changes in pressure within the air bags and they do not quickly equalise the pressure within and between the air bags. This can cause difficulties, particularly with air bag suspension systems used in multi-axle vehicles, where it can be difficult to drive onto a ramp or the like as the valve, which is set to control the vehicle height, will react to the relative movement of one axle to thereby cause air to flow into the air bags thus causing one set of wheels to be lifted off the ramp. If that set of wheels is the set of driving wheels, further progress along the ramp may be prevented.

Another difficulty encountered with previously known air bag suspension systems is known as “tramp”. When a multi-axle vehicle encounters a rough or uneven road surface, such as a railway crossing, a cattle grid or the like, the vehicle suspension is caused to oscillate (tramp) for a substantial period of time. Such oscillation may cause damage to the road's surface as well as unduly stress a fully loaded vehicle.

Attempts have been made to overcome known difficulties using air bags for vehicle suspension systems. Australian Patent No 567664 discloses an air bag suspension whereby an air tank is mounted in the vehicle chassis directly above the air bags, and short, large diameter air ducts connect each air bag to the air tank. This system has as its aim to maintain the air pressure in each air bag relatively constant irrespective of the position of the vehicle axle to thereby reduce excessive vehicle body movement. The specification also discloses the elimination of restricting flow air lines connecting the air bags to the air tank. Each side of the vehicle has its own air tank connected to the air bags on that side of the vehicle, with the air tanks optionally being connected.

However, this proposal does not solve the problems referred to above as, when a vehicle axle moves upwardly due to an irregularity in a road surface, air in the air bag and the air tank is compressed. When the irregularity in the road surface has been passed, the pressure in the air tank and air bag forces the axle downwardly with great speed thereby forcing the vehicle tyre onto the road surface with a great impact. Because of the resilience of the vehicle pneumatic tyre, the rebound is sufficient to again compress air in the air bag and air tank, thereby commencing a cycle of tramping. Shock absorbers or dampers are thereby required in such a system to counteract the effects of the tramping. Such shock absorbers or dampers add to the vehicle suspension costs and provide further stress points in the vehicle suspension.

Australian Patent Application No 69220/87 proposes the damping of shock loads on the suspension system by providing a secondary air tank mounted within the primary air tank and communicating through a restrictive opening. The secondary air tank and restrictive opening combine to assist in the dampening of shock loads on the suspension. However, with the speed of operation, the large volume of air in the air tank and the large size of openings between the air bags to the air tank means that no effective dampening of tramping occurs and the system is unable to cope with uneven loads and uneven terrain.

U.S. Pat. No. 3,063,732 discloses a vehicle suspension system incorporating both leaf and air spring assemblies in combination. The specification discloses the use of air bags on a dual axle suspension with front and rear air bags connected by a hollow sub-frame to serve as pneumatic reservoirs. The system is also provided with height control valves on each side of the suspension so that the air bags on each side are independently inflated in accordance with load conditions. The air suspension is used in conjunction with leaf springs on each end of each axle. However, this suspension system does not provide means for controlling tramp or otherwise damping suspension oscillations.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the present invention there is provided an air suspension system for selected wheels of a vehicle comprising:

at least one air bag operatively associated with each selected vehicle wheel to control relative movement between the wheel and a supporting frame structure of the vehicle,

a high flow-rate air tube connected to the at least one air bag,

air flow controlling means between the high flow-rate air tube and the air bag,

the air flow controlling means regulating air flow from the high flow-rate air tube into the air bag generally fractionally proportional to a pressure differential between the high flow-rate air tube and the air bag whereby air flow rate increases at a lesser rate than an increase in differential pressure,

said air flow controlling means thereby controlling the rate of air pressure build-up in the air bag when air flows into the air bag,

the high flow-rate air tube forming a manifold to which air is passed in a manner that is substantially un-regulated by the air-flow controlling means when air pressure in the air bag increases above that in the manifold, and

air pressurising/exhausting means connected to the manifold through a low flow-rate air tube to maintain a required pressure therein to thereby maintain a selected, predetermined vehicle ride height.

In one embodiment of the invention, the selected wheels are a single pair of wheels on opposite sides of the vehicle. The high flow rate air tubes associated with each opposed air bag are interconnected by a low flow rate connection to restrict flow of air between the high flow rate air tubes. Air is able to flow to and from the air bags to the manifold as a result of a sudden pressure increase in a respective air bag resulting, for example, from a vehicle wheel encountering a bump in a road surface. Such sudden pressure increase, however, is not passed from one manifold to the other due to the low flow rate connection restricting air flow between manifolds.

In another embodiment of the invention, two selected wheels are mounted on adjacent, multiple axles of the vehicle, and the air bags associated with wheels on one side of the vehicle are connected by a manifold formed by the high flow rate air tube common to both air bags. In a further embodiment applicable to a tri-axle vehicle, at least one air bag is associated with each wheel, the airbags on one side of the vehicle being connected by a single manifold formed by a high flow-rate air tube.

Preferably, the air flow controlling means comprises a reduced diameter connection at one end, or each end, of the manifold, or at the connection of the manifold with the respective air bags, which is shaped to provide the proportional control of air flow. In a particular form, the air flow controlling means comprises the end wall of the manifold defining a shoulder between the manifold wall and the connection to the respective air bag. Such a shoulder acts to regulate the flow of air entering the connection from the manifold. It is believed that the regulation is as a result of turbulence developed, and the turbulence is fractionally proportional to the pressure differential that gives rise to the flow rate of air into the respective connection such that the regulation is proportional to the pressure difference between that of the air bag to which air is flowing and the manifold. Such regulation enables the system of the invention to react appropriately to road surface irregularities at any given vehicle speed. It is found that the rate of increase in pressure in one air bag and the transference of air from that air bag to the manifold and thus to the other air bag together with the controlled rate of flow of the air to the other air bag stabilises the rate of inflation of the other air bag to either totally obviate tramp or to substantially minimise rebound. Still further, it is found that the controlled rate of transference of air from the manifold to an air bag avoids development of suspension harmonic vibrations and/or oscillations which can give rise to unstable vehicle operation.

In one form of the invention, the pressurising means includes a height valve to admit pressurised air from a tank, air pump or the like, to the air bags or to exhaust air from the air bags to maintain an air pressure in the manifold(s) commensurate with maintaining a selected predetermined vehicle ride height when the vehicle is stationery. The pressurising means is unresponsive to sudden pressure changes in the manifold pressure during vehicle operation, and is used primarily to control the ride height of the vehicle and its load within predetermined limits. Thus, when the vehicle is lightly loaded, the ride height of the vehicle is maintained at a predetermined height by reducing the pressure in the manifold(s) to that which will enable the air bags to support the vehicle at the desired, predetermined height. When a load is added to the vehicle, and the vehicle height lowers as a result of the load compressing and increasing the pressure in the air bags, the vehicle height is restored to the selected, predetermined level by increasing the air pressure in the system to that pressure that gives the required ride height. The ride height may be relatively fixed, or it may be able to be changed by the vehicle operator changing the height valve actuating system.

In a preferred form of the invention, the height valve is actuated by a link connected to a rocker member which extends between front and rear axles of a dual axle set of the vehicle. The link is connected to the rocker member at a point approximately mid way along the length of the rocker member whereby only relative movement between the midway connection point and the vehicle supporting frame structure causes actuation of the valve. This means that normal movement of the suspension during vehicle operation will generally not result in operation of the height valve.

The air suspension system of the present invention is adapted to be installed in existing vehicles as well as being incorporated into vehicles during manufacture. For incorporation into existing vehicles, an air suspension kit is provided comprising the necessary number of air bags, the appropriate high flow rate air tubes to connect to the respective air bags, the connectors to connect the high flow rate air tubes to the air bags, and system pressurising means incorporating an air tank or the like and a height control valve. The height control valve is connected to the high flow rate air tubes by a low flow rate connection so that changes in air pressure in the manifolds is not transferred between the manifolds.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings,FIG. 1shows one embodiment of the present invention for use with a vehicle having a pair of adjacent axles22mounting front and rear wheels12and14. The vehicle incorporates a chassis member10on each side of the vehicle carrying a suspension mounting16for the front and rear axle and wheel sets. A trailing suspension arm18is mounted to each mounting bracket16by respective pivot pins20. The axle22of each wheel set is mounted to the opposed suspension arms18. Each suspension arm18is Z-shaped and engages over the respective axle22to form a mounting for respective front and rear air bags24and25which engage between the suspension arm18and the chassis10. The nature and operation of air bags in vehicle suspensions is well known and will not be described in further detail.

In this embodiment, a high flow rate air tube26extends between the respective front and rear air bags24and25and is connected thereto by connectors27. The high flow rate air tubes26on each side of the vehicle enable air to be transferred between the respective front and rear air bags in the event that the front and rear wheels12and14move upwardly or downwardly with respect to the chassis10. Thus, if the front wheel12moves upwardly relative to the chassis10, through the tire encountering a bump in a road surface, the air bag24is compressed increasing the pressure of air in that air bag. Air is then able to move from that air bag to the rear air bag25through the high flow rate air tube26. Similarly, if the rear wheel14moves upwardly relative to the chassis10increasing the pressure in the rear air bag25, air moves through the high flow rate air tube26into the front air bag24.

This movement of air between the respective front and rear air bags is independent on each side of the vehicle, and enables all wheels of the vehicle structure to carry loads substantially equally, even when wheels are moving upwardly and downwardly relative to the chassis due to road irregularities and the like. If either or both of the front and rear wheel pairs12and14are driven wheels, the air bag system of this embodiment ensures that the appropriate downward pressure on the suspension arms18, and thus the axles22, enable the wheel sets12and14to have appropriate traction on the ground surface. In this way, it is possible for both wheel sets12and14to retain positive contact with the ground surface. The high flow rate air tube26is capable of transferring a relatively large volume of air relatively quickly between the respective front and rear air bags24and25, thereby decreasing load on the vehicle suspension system, including vehicle shock absorbers, if fitted.

As indicated, the passage of air through the high flow rate air tube26occurs in both directions, depending on which of the front and rear air bags24and25has the greater or lesser internal pressure resulting from relative movement of the vehicle wheels12and14. The high flow rate air tube26is connected to the respective air bags by connectors27which, together with the high flow rate air tube26, controls the rate of flow through the high flow rate air tube26. In this embodiment, the diameter of the high flow rate air tube26is approximately 2 inches and the diameter of the connectors27is between one half inch and one and one half inches. These relative dimensions, however, will vary with different embodiments of the invention, different air bag structures and sizes and the number of air bags used in an air suspension system.

As shown inFIG. 2, the high flow rate air tubes26on each side of the vehicle are interconnected by a low flow rate air tube28which is connected via low flow rate tube31to a height valve29mounted on the vehicle chassis10. A rocker member32extends between the front and rear axles22, and a vertically extending link33is connected between the rocker member32and the height valve29. With this arrangement, any change in height between the mid point of the rocker member, to which the link33is connected, and the height valve29results in movement of the link33to actuate the height valve. An air tank34, supplied with air from an air pump (not shown) through the inlet tube36contains air under pressure for pressurising the air bags. Movement of the link33causes the height valve29to either admit air into the air bag system through the low flow rate line31and low flow rate interconnecting tube28, or to exhaust air from the system. Thus, if the height between the mid point of the rocker member32and the valve29decreases, as a result of an increase in load on the vehicle chassis10, the valve actuates to increase the pressure in the air bags24to restore the height to the predetermined set position. The pressure in the air bags24and25is, therefore, automatically adjusted in accordance with the vehicle mass and load to that required to maintain the selected vehicle ride height. However, because the low flow rate air tube28and air supply tube31conveys air at a low flow rate, minimal transference of air occurs between the high flow rate air tubes26on opposite sides of the vehicle due to relative movement of the vehicle wheels and chassis during operation of the vehicle. Further, by placing the connection of the link33to the mid point of the rocker member32, up and down movements of the front and rear wheel sets over a road bump or the like does not effect the relative position of the mid point link connection sufficiently to cause actuation of the valve29.

Referring toFIG. 3, the arrangement shown is similar to that ofFIGS. 1 and 2except that each axle222is associated with two air bags224,225. With this arrangement, each of the front and rear air bags224and225are interconnected by a high flow rate air tube226, with the end bags being connected to the tube226by connectors215and217whilst the intermediate bags of each pair224,225are connected to the tube by connectors228and230, respectively. It will be understood that relative vertical movement of the front and rear wheel sets212and214results in a transference of air from one of the pairs of air bags224,225to the other, but only half the air transferred passes through the section of high flow rate air tubes226interconnecting those air bags of each pair. In this embodiment, a suspension saddle218connects the respective air bags with the front and rear axles222. Air fittings215and217are used to connect the high flow rate air tube226to the respective air bags224,225. The air fittings215,217act to regulate the flow of air to prevent uncontrolled air flow between the air bags, to obviate resonant or harmonic pressure transference through the system.

The air bags shown in this embodiment are pressurised in a manner similar to that shown in the previous embodiment.

Referring toFIG. 4, the vehicle chassis310is carried by front and rear wheel sets312,314utilising an air bag system according to either of the previous embodiments. In the arrangement illustrated, the wheels312,314are driven through differentials319,321with drive shafts323and327.

A height valve rocker member333is connected between the differential319and321. The height valve334is carried on to cross member313and serves to automatically control the inflation of both front and rear air bag systems as previously described. The valve334is actuated by a link336which is connected mid point of a rocker member333mounted between the differentials319and321. If the wheels312,314pass along a sloping ramp in a reversing mode, rear wheels314lift but front wheels314lower. Therefore, there is little or no movement of the center of the rocker member333. The valve may be arranged so that minimal movement of the mid point of the rocker member333may cause minimal movement of the link336but insufficiently to actuate the valve334. Otherwise, air bags may be inflated or deflated inappropriately as a result of movement of a vehicle on or off a ramp or the like. By using the mid point between the axles of the front and rear wheel sets312and314, the valve334is not actuated inappropriately. However, if both differentials,319,321move up and down in relative unison, the rocker member333will cause the valve334to be actuated as required so that air is either added to or removed from the air bag system.

FIGS. 5 and 6illustrate an embodiment of the invention where an air bag suspension system is fitted to a front, steering axle of a vehicle. In this embodiment, vehicle chassis rails410on each side of the vehicle have mounting brackets435carrying springs437using mounting pins438. An axle422is mounted to each of the springs437, which are of a somewhat wedge shape, being at their greatest width where they are attached to the axle422. With this arrangement, the springs437absorb a significant amount of torsion and tension developed by movement of the axle422thereby eliminating the need for a separate stabiliser bar.

Each spring437supports an air bag424,425on each side of the vehicle, respectively. Each air bag424,425is connected to a high flow rate tube426through connectors427and429, respectively. The other ends of each of the high flow rate air tubes426are interconnected by a low flow rate connector or tube441. A height valve442mounted on the vehicle frame410is connected to one of the springs437by a link436. A low flow rate air tube443connects the valve442to a source of air under pressure, such as the tank34as shown inFIG. 2. The air in each air bag424,425, when the vehicle is stationary, is under substantially similar pressures governed by the height valve442. If an increase occurs in the load on the vehicle, the resulting reduction in height between the axle422and the chassis frame410causes the link436to actuate the valve442. Air under pressure from line443passes through the valve442to the low flow rate air tube440and into the air bags424and425through the air interconnection441and high flow rate air tubes426. If the load on the vehicle is reduced, air pressure in the air bags is released by the valve442releasing air to atmosphere.

Thus, air under pressure is supplied to and received from air bags224,225by the large diameter air tubes426and the connector441extending therebetween. The fittings427and429connecting the high flow air tubes426to the respective air bags424and425are of reduced diameter when compared to the tube426so as to provide a constriction. For example, tube426may be a two inch diameter tube with fittings427,429being three quarters of an inch in diameter, thus providing or being a controlling orifice.

Air under pressure is supplied to the high air flow tube426from the air hose440. The connector441is an in line tube and has a reduced diameter, of the order of one quarter of an inch, to provide a constriction between the air bags424and425.

By having air tube426of much larger diameter than connector441and the fittings427and429, air tube426on each side also acts as a manifold. In this embodiment, air in each of the air bags424,425may be forced into the respective high air flow air tube426by an upward movement of the associated wheel carried by the axle422. The high air flow air tubes426act as a manifold to receive the transferred air, but when the pressure is decreased in the air bags224,225, air flow from the manifold back into the respective air bags is controlled by reason of the fittings427and429. If the compression in air bags424,425is different, the connector441will allow a small amount of air flow therebetween at a controlled rate so as to equalise the pressure, the controlled rate of air flow acting to dampen any oscillations and minimise or eliminate tramping of opposite wheels.

Referring toFIG. 7, there is illustrated a high flow rate air tube452which is adapted to be used with any of the embodiments of the invention but which will be described with reference to its use in the embodiment shown inFIGS. 1 and 2.

The high flow rate air tube452of this embodiment is formed from a relatively flexible, pressure hose, such as a hydraulic hose. In the embodiment illustrated, the hydraulic hose is of two inches diameter and is preformed with crimped ends joined to the smaller diameter connector tubes27which connect the high flow rate air tube452to the respective front and rear air bags24and25on each side of the vehicle. The connector tubes may have a diameter of between about 0.25 and 0.8 times the diameter of the high flow rate air tube. A hydraulic hose is a preferred form of high flow rate air tube as it is designed and constructed to resist collapsing if the outside pressure exceeds the inside pressure.

The hydraulic hose, being flexible, is also able to be located relative to a vehicle chassis10so as to be positioned over and around structural members, suspension arms and the like. The relatively large diameter, high flow rate air tube452constitutes a manifold450with the smaller diameter end connectors27through which air is passed from one or other of the air bags24,25during vehicle operation. The change in diameter between the large diameter manifold450and the smaller diameter connections27forms a shoulder453at each end of the manifold450. Air flow through the manifold, indicated by flow lines458, becomes turbulent where it strikes a shoulder453and the air is forced to flow back on itself as it abuts the shoulder453. This air flow back results in a control or regulation of the air flow from the manifold450into the end connector27and the air bag25, when air is flowing in the direction as shown. The control or regulation of the air flow is generally fractionally proportional to the rate at which the air pressure differential changes whereby the air flow rate increases at a lesser rate than an increase in pressure differential. Thus, as the air flow rate increases with increasing pressure differential, the flow back also increases to effectively restrict the rate of increase in the air flow. However, the flow of air out of an air bag into the manifold is substantially unregulated and is more or less directly proportional to the pressure differential.

Further, the air flow through the manifold450is generally proportional to the pressure difference between the air bags24and25, such as that caused by the front vehicle wheels12moving upwardly relative to the chassis10as a result of a bump in the road surface. However, the flow rate through the manifold450and out into the air bag25is regulated by the back flow of air impeding the flow of air out of the manifold450, as described above. Such impeding of the flow of air flowing into the air bag25prevents rapid transferral of air from one air bag to the other and therefore provides a damping effect to significantly reduce or eliminate tramping by reducing the rate of rise of pressure in air bag25. The control or regulation also prevents over transfer of air between air bags that could otherwise result in the air pressure in the air bag to which air is transferred rising above that of the other air bag. Such over transfer can give rise to oscillations, whereby air moves backward and forward between the air bags through the high flow air tube which sometimes resonates causing uncontrolled vehicle pitching.

It will be understood that when the air pressure in the air bag25becomes greater than that in the air bag24, air flows in the reverse direction to that shown inFIG. 7. It will also be understood that the back flow of air caused by the shoulder453when air flows out of the manifold450in one direction or the other provides a variable regulation of the air flow in accordance with the air flow rate through the manifold. The regulation enables the system of the invention to react appropriately to road surface irregularities at any given vehicle speed. The rate of increase in pressure in one air bag and the rate of transference of air from that air bag to the manifold and thus to the other air bag together with the controlled rate of flow of the air to the other air bag stabilises the rate of inflation of the other air bag to either totally obviate tramp or to substantially minimise rebound.

A port456may be formed at one or other end of the high flow rate air tube452to facilitate connection of the tube452with the low flow rate air tube28providing pressurised air to the system, as shown inFIG. 2. Alternatively, such a port may be positioned approximately centrally along the length of the flexible high flow rate tube452.

With the present invention, it may be possible to use an air bag suspension system without the use of normal dampers or shock absorbers. Alternatively, reduced capacity dampers or shock absorbers may be used thus significantly reducing costs of suspension component. The damping effect resulting from use of the present invention dramatically reduces suspension oscillation or resonance. Therefore, suspension components, including springs, mounting points and the like are subjected to less stress than would otherwise occur over the life of a vehicle.