PRIORITY DOCUMENT

[0001] The present application claims priority from Australian Provisional Patent Application No. 2021900447 tided “AIR SPRING FOR A VEHICLE” and filed on 19 February 2021, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present invention relates to an air spring for a vehicle. In a particular form, the present invention relates to a variable volume air spring for a vehicle.

BACKGROUND

[0003] Air springs, also known as air bags have long been known as an alternative to standard steel springs in a variety of automotive suspension applications. Air springs are sometimes favoured over steel springs due to their ease of adjustability, by simply increasing or decreasing pressure in the spring to effect a change in ride height and quality.

[0004] Air springs are also favoured by 4x4 and SUV users, where they are often used in association with towing trailers and caravans, when heavily loaded for outback or long distance travel, when requiring increased ground clearance when travelling over uneven terrain, or when requiring reduced ride height when entering height restricted areas, such as car parks.

[0005] When the air spring undergoes bump (also known as compression) the air bag compresses, increasing the internal pressure of the air bag and increasing the spring rate. In long travel suspension systems it is difficult to achieve target spring rates and natural frequencies, and the amount that the air spring compresses can be substantial, resulting in undesirably high pressures in the system.

[0006] In order to maximise service life of the air bag, manufacturers specify a maximum operating pressure. Therefore, in order to still provide air suspension in long travel suspension systems, the size of the air bag has to be increased, however doing so may not be possible or practical due to vehicle packaging requirements or the need to package the air spring along with other suspension components, which may limit the amount of space available to accommodate the air spring.

[0007] It is against this background that the present disclosure has been developed. SUMMARY

[0008] According to a first aspect, there is provided an air spring comprising a first chamber defined by a moveable pneumatic piston and a first compressible volume, wherein the position of the pneumatic piston may be changed in order to vary the first compressible volume.

[0009] In one form, the pneumatic piston is biased against movement when the air spring is compressed.

[0010] In one form, the pneumatic piston is biased by a second chamber defined by the pneumatic piston and a second compressible volume.

[0011] In one form, the first and second chambers are divided by the pneumatic piston and wherein the second chamber is of a higher pressure than the first chamber, such that as the air spring is compressed, the first chamber preferentially compresses until the pressures of the respective chambers equalise, at which point any further compression causes the pneumatic piston to move and the first and second chambers to compress in unison.

[0012] In one form, the first chamber is defined by the pneumatic piston and a diaphragm attached with respect to a spring top at one end and to a generally cylindrical rolling sleeve at a second end.

[0013] In one form, the second chamber is defined by the pneumatic piston and an internal cylindrical volume provided by an internal blind bore of the rolling sleeve.

[0014] In one form, the pressure in both the first and second chambers is able to be independently and actively adjusted.

[0015] In one form, the position of the pneumatic piston is actively controlled by an actuator.

[0016] According to a second aspect, there is provided an air spring for a vehicle, comprising first and second chambers of low and high pressure divided by a pneumatic piston, wherein as the air spring is compressed, the first chamber preferentially compresses until the pressures of the respective chambers equalise, at which point any further compression causes the pneumatic piston to move and the first and second chambers to compress in unison.

[0017] According to a third aspect, there is provided a suspension stmt for a vehicle, comprising a hydraulic damper comprising a damper cylinder, a hydraulic piston slidably retained with the damper cylinder, and a piston rod for driving the hydraulic piston within the damper cylinder in compression and rebound; and an air spring attached with respect to the damper cylinder at a first end and with respect to the piston rod at a second end and comprising first and second chambers of low and high pressure divided by a pneumatic piston, wherein as the damper and the spring undergo compression, the first chamber preferentially compresses until the pressures of the respective chambers equalise, at which point any further compression causes the pneumatic piston to move and the first and second chambers to compress in unison.

[0018] According to a fourth aspect, there is provided a suspension system for a vehicle, comprising a plurality of air springs as described, a compressor, an accumulator, pipework, valving and a control system for selectively pressurising and depressurising the first and second chambers of each air spring.

BRIEF DESCRIPTION OF DRAWINGS

[0019] Embodiments of the present invention will be discussed with reference to the accompanying drawings wherein:

[0020] Figure 1 is a perspective view of a variable volume air spring, according to an embodiment;

[0021] Figure 2 is a cross-sectional view of the variable volume air spring of Figure 1;

[0022] Figure 3 is a cross-sectional view of the variable volume air spring of Figure 1; where both the first and second air chambers are undergoing compression;

[0023] Figure 4 is a volume vs displacement graph comparing the properties of a conventional air spring with the variable volume air spring of Figure 1 ;

[0024] Figure 5 is a pressure vs displacement graph comparing the properties of a conventional air spring with the variable volume air spring of Figure 1 ;

[0025] Figure 6 is a perspective view of a suspension strut comprising a variable volume air spring, according to an alternate embodiment; and

[0026] Figure 7 is a partial cross-sectional view of the suspension stmt of Figure 6.

DESCRIPTION OF EMBODIMENTS

[0027] Referring now to Figures 1 to 3, where there is shown an air spring 100, according to an embodiment for mounting between the chassis and the unsprung mass of a vehicle. The air spring 100 comprises a first chamber 110 defined by a moveable pneumatic piston 160 and a first compressible volume, wherein the position of the pneumatic piston 160 may be changed in order to vary the compressible volume. [0028] The pneumatic piston 160 is biased against movement when the air spring 100 is compressed by a second chamber 120 defined by the pneumatic piston 160 and a second compressible volume, wherein the first and second chambers 110, 120 are divided by the pneumatic piston 160, and wherein the second chamber is of a higher pressure than the first chamber, such that as the air spring 100 is compressed, the first chamber 110 preferentially compresses until the pressure of the first and second chambers 110, 120 equalises, at which point any further compression causes the pneumatic piston 160 to move and the first and second chambers 110, 120 to compress in unison (as best shown in Figure 3).

[0029] As best shown in Figures 2 and 3, it can be seen that the first chamber 110 is defined by the pneumatic piston 160 and a diaphragm 130, in particular a rolling lobe or sleeve diaphragm, attached with respect to a spring top 140 at one end and to an open end of a cylindrical rolling sleeve 150 at a second end, and the pneumatic piston 160. The second chamber is defined by an internal cylindrical volume provided by an internal blind bore 151 of the rolling sleeve 150.

[0030] It can be seen that the first end 131 of the diaphragm 130 has ahead 133, which interlocks with a respective channel 142 formed in the spring top 140 to form an airtight seal. The second end 132 of the diaphragm 130 is connected to the rolling sleeve 150, where it is crimped between an engaging surface on the rolling sleeve 150 and a crimping ring (not shown) to form an airtight seal.

[0031] As is also shown in Figures 2 and 3, the pneumatic piston 160 is retained in the rolling sleeve 150 by a snap ring 170 located in a groove 153 in the internal perimeter of the rolling sleeve 150. The pneumatic piston 160 comprises at least one sealing ring (not shown), retained in a groove 161 in the pneumatic piston 160, which forms a sealing relationship between the inner surface 154 of the rolling sleeve 150 and the pneumatic piston 160. It will be appreciated that it is by virtue of the snap ring 170 retaining the pneumatic piston 160 in the rolling sleeve 150, that the second chamber 120 is able to be pressurised at a higher rate than the first chamber 110. It will also be appreciated that as the air spring 100 undergoes expansion, the pneumatic piston 160 will expand until it is retained by the snap ring 170, restoring pressure in the second chamber 120 to what it was pre-compression.

[0032] It will therefore be appreciated that as the air spring 100 expands, the first and second chambers 110, 120 will expand in unison, until the pressure of the first chamber 110 reduces to below the original pressure of the second chamber 120, at which point, any further expansion occurs only in the first chamber 110. It will further be appreciated that the air spring 100 is able to return to its initial state with no change in spring rate or volume and maintaining vehicle ride height.

[0033] The spring top 140 is configured to receive an air fitting or pneumatic connector and features an internal conduit 141, providing passage for air as it is supplied to and withdrawn from the first chamber 110. It can also be seen that the rolling sleeve 150 is also configured to receive an air fitting or pneumatic connector and features an internal conduit 152, providing passage for air as it is supplied to and withdrawn from the second chamber 120.

[0034] Assembly of the air spring will be described below:

[0035] The pneumatic piston 160 is fitted with a sealing ring and installed in the blind bore 151 of the rolling sleeve 150. The first and second ends 131, 132 of the diaphragm 130 are then secured to the spring top 140 and rolling sleeve 150 respectively.

[0036] Referring now to Figure 4, where there is shown a volume vs displacement graph comparing the properties of a conventional single chamber air spring with the air spring 100 of the present invention. It can be seen that in a conventional air spring, as the spring undergoes compression (also known as negative displacement) the volume of the chamber reduces in a substantially linear fashion. In comparison, it can be seen that the volume of the air spring of the present invention also reduces in a substantially linear fashion, until such time as the pressure in the first and second chambers equalises, and the volume of the second chamber increases the available compressible volume. It will be appreciated that the point at which the compressible volume of the second chamber is made available can be adjusted by varying the pressure in the second chamber.

[0037] Referring now to Figure 5, where there is shown a pressure vs displacement graph comparing the properties of a conventional single chamber air spring with the air spring 100 of the present invention. It can be seen that in a conventional air spring, as the spring undergoes compression, internal pressure build up within the air spring increases in an exponential manner. In comparison, it can be seen that the internal pressure build up within the air spring of the present invention also increases in a similar manner until such time as the pressure in the first and second chambers equalises, and the volume of the second chamber increases the available compressible volume, resulting in a reduction in the rate at which pressure increases. It will again be appreciated that the point at which the compressible volume of the second chamber is made available can be adjusted by varying the pressure in the second chamber.

[0038] It will also be appreciated that by varying the respective pressures in the first and second chambers that the overall performance characteristics of the air spring can be adjusted to suit dynamic conditions.

[0039] Referring now to Figures 6 and 7, where there is shown a suspension stmt 200, according to an embodiment, for mounting between the chassis and the unsprung mass of a vehicle. The stmt 200 comprises a hydraulic damper 300 and an air spring 400. The hydraulic damper 300 comprises a damper cylinder 310, a hydraulic piston (not shown) slidably retained within the damper cylinder 310 and a piston rod 320 for driving the piston within the damper cylinder in compression (also known as bump) and rebound (also known as extension). The stmt 200 further comprises an air spring 400 attached with respect to the damper cylinder 310 at a first end and with respect to the piston rod 320 at a second end and comprising a diaphragm or airbag 430 attached with respect to the damper cylinder at a first end 431 and to the piston rod 320 at a second end 432 and comprising first and second chambers 410, 420 of low and high pressure divided by a pneumatic piston 460, wherein as the damper 300 and the spring 400 undergo compression, the first chamber 410 preferentially compresses until the pressures of the respective chambers equalise, at which point further compression causes the pneumatic piston 460 to move and the first and second chambers 410, 420 to compress in unison.

[0040] Again, it will be appreciated that as the damper and air spring 300, 400 move in rebound, the first and second chambers 410, 420 will expand in unison, until the pressure of the first chamber 410 reduces to below the original pressure of the second chamber 420, at which point, any further expansion occurs only in the first chamber 410. It will further be appreciated that the air spring 400 is able to return to its initial state with no change in spring rate or volume and maintaining vehicle ride height. While in the embodiment shown, a monotube damper 300 is employed, it will be appreciated that alternative dampers could be employed, such as twin-tube or remote reservoir dampers.

[0041] Referring now to Figure 7, it can be seen that the first chamber 410 of the air spring 400 is defined by a diaphragm 430 attached with respect to an upper chassis mount 440 at one end and to a generally cylindrical rolling sleeve 450 at a second end, and the pneumatic piston 460. The second chamber 420 is defined by an annular volume between the internal cylindrical volume of the rolling sleeve, the damper cylinder 310 and the pneumatic piston 460. It will be appreciated that where the air spring 400 of this embodiment differs from the air spring 100 of the first embodiment is that this air spring 400 has a portion of the damper cylinder 310 and piston rod 320 extending through it.

[0042] It can also be seen that the first end 431 of the diaphragm 430 is connected to an upper chassis mount 440, where it is crimped between an engaging surface on the upper chassis mount and a crimping ring (not shown) to form an airtight seal. The upper chassis mount 440 features a central aperture 442 through which a threaded section 330 of the piston rod 320 extends and is secured by a nut 340, configured to be retained by the upper chassis mount 440.

[0043] Referring again to Figure 7, it can be seen that the second end 432 of the diaphragm 430 is connected to the generally cylindrical rolling sleeve 450, where it is crimped between an engaging surface on the rolling sleeve 450 and a crimping ring (not shown) to form an airtight seal. The closed end 455 of the rolling sleeve 450 has an aperture 456 via which the rolling sleeve 450 is located over and attached to the damper cylinder 310 in a manner that forms an airtight seal between the rolling sleeve 450 and the damper cylinder 310. [0044] As is also shown in Figure 7, the pneumatic piston 460 is retained in the rolling sleeve by a snap ring 470 located in a groove 453 in the internal perimeter of the rolling sleeve 450. The pneumatic piston 460 comprises at least one external sealing ring (not shown), retained in an external groove 461 in the piston 460, which forms a sealing relationship between the inner surface 454 of the rolling sleeve 450 and the pneumatic piston 460. The pneumatic piston 460 also comprises at least one internal sealing ring (not shown), retained in an internal groove 462 formed in a central bore of the pneumatic piston 460, sized to accommodate the damper cylinder 310, wherein the at least one internal sealing ring forms a sealing relationship between the outer surface of the hydraulic cylinder 310 and the pneumatic piston 460.

[0045] As best shown in Figures 6 and 7, the stmt 200 also features a protective sleeve 480 which locates over the outside of the diaphragm 430, acting to protect the diaphragm 430 from accidental damage and to improve the working life and pressure rating of the diaphragm 430. The protective sleeve 480 is load bearing when the diaphragm 430 is inflated, preventing the diaphragm 430 from stretching or tearing due to over inflation.

[0046] It can also be seen that the inner surface 454 of the rolling sleeve 450 features an inner step 457 which acts as a barrier to the pneumatic piston 460, preventing further compression of the second chamber 420 beyond this point. It will be appreciated that this is an optional feature that may be employed to tune the performance of the air spring 400 and results in a third stage, where the overall available compressible volume of the air spring 400 is reduced, leaving only the volume of the first chamber 410 available for compression.

[0047] The upper chassis mount is configured to receive an air fitting or pneumatic connector and features an internal conduit, providing passage for air as it is supplied to and withdrawn from the first chamber. The rolling sleeve is also configured to receive an air fitting or pneumatic connector and features an internal conduit, providing passage for air as it is supplied to and withdrawn from the second chamber.

[0048] Assembly of the stmt will be described below:

[0049] The pneumatic piston 460 is fitted with internal and external sealing rings and is installed in the blind bore 451 of the rolling sleeve 450. The first and second ends 431, 432 of the diaphragm 430 are then secured to the upper chassis mount 440 and rolling sleeve 450 respectively. The protective sleeve 480 is then secured over the outside of the diaphragm 430.

[0050] The damper cylinder 310 and piston rod 320 of the damper 300 are then inserted through the aperture 456 formed in the closed end 455 of the rolling sleeve 450, and through the pneumatic piston 460 until the threaded section 330 of the piston rod 320 emerges through the central aperture 442 in the upper chassis mount 440, where the nut 340 is used to secure the piston rod 320 to the upper chassis mount 440, and the rolling sleeve 450 is secured to the damper cylinder 310.

[0051] While in the embodiments shown and described, the first chamber is in the form of a rolling sleeve diaphragm, whereby compression and expansion of the first chamber is by virtue of the compression and expansion of the diaphragm, it will be appreciated that in alternate embodiments, different types of diaphragms, or in fact, different types of air springs may be employed, such as bellow type air springs or piston and cylinder type air springs.

[0052] In the embodiments shown and described, the second chambers are formed within the respective rolling sleeves of both air springs, offering a compact packaging solution. It will however be appreciated that in alternative embodiments, the second chamber may be located remotely from the rolling sleeves, for example in a remote reservoir.

[0053] While not shown in either embodiment, it is also possible that an additional biasing means could also be used in conjunction with the second chamber and pneumatic piston to tune the rate at which the second chamber increases the available compressible volume. For example, a biasing means in the form of a compression spring could be located within the second chamber of the first embodiment, bearing against the pneumatic piston such that the pressure in the first chamber has to overcome not only the pressure in the second chamber but the force exerted against the pneumatic piston by the compression spring.

[0054] It will be appreciated that the air spring or the suspension stmt with air spring may be used as part of a suspension system comprising a plurality or combination of the springs or stmts, an air compressor, an accumulator, pipework, valving and a control system for selectively pressurising and depressurising the first and second chambers of each air spring. For example, a suspension system in a vehicle may comprise a pair of front stmts connecting the chassis to the front wheels, and a pair of rear air springs connecting the chassis to the rear wheels in parallel with separate dampers.

[0055] It will further be appreciated that the air springs or stmts with air springs may be part of passive systems, where the respective pressures in the first and second chambers are pre-set and not capable of adjustment. They may also be part of adjustable systems, where the respective pressures in the first and second chambers are user adjustable, allowing for changes in ride height and suspension characteristics. Further still, they may be part of active systems, where the respective pressures in one or both of the first and second chambers are actively adjusted in response to driving conditions.

[0056] In yet a further embodiment, not shown, there may be provided an air spring for mounting between the chassis and unspmng mass of a vehicle, the air spring comprising a chamber defined by a diaphragm attached with respect to a spring top at one end and an open end of a cylindrical rolling sleeve at another end, and a pneumatic piston slidably retained within the rolling sleeve, where the pneumatic piston is biased against pressure build up in the first chamber by a compression spring acting on the pneumatic piston.

[0057] While in the embodiments shown and described, the position of the pneumatic piston and resultant available compressible volume is determined by the resistive force of the second compressible volume and/or compression spring, it will be appreciated that in alternate embodiments, the position of the pneumatic piston may instead be controlled through means of an actuator, for example, a hydraulic actuator, where the position of the pneumatic piston is controlled by supplying / withdrawing a volume of hydraulic fluid in a second chamber, or alternatively, an electro mechanical actuator. In both instances, the position of the pneumatic piston and therefore the compressible volume of the first chamber may be quickly and accurately adjusted.

[0058] Throughout the specification and the claims that follow, unless the context requires otherwise, the words “comprise” and “include” and variations such as “comprising” and “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0059] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0060] In some cases, a single embodiment may, for succinctness and/or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.

[0061] It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.