AU7187600A - Steerable axle suspension with adjustable caster angle - Google Patents

Description

l

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): HOLLAND NEWAY INTERNATIONAL, INC.

Invention Title: STEERABLE AXLE SUSPENSION WITH ADJUSTABLE CASTER

ANGLE

The following statement is a full description of this invention, including the best method of performing it known to me/us: 00 0 0:0.0 00 0 STEERABLE AXLE SUSPENSION WITH ADJUSTABLE CASTER ANGLE RELATED APPLICATION This application claims priority under 35 U.S.C. 119 on U.S. provisional application 60/168,554, filed on December 2, 1999.

BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a vehicle steerable axle suspension. In one of its aspects, the invention relates to a vehicle steerable axle having an adjustable caster angle for forward and backward movement of a vehicle.

Description of the Related Art Trailing arm suspensions are commonly used in heavy-duty vehicles, such as tractor-trailer configurations. The trailing arm suspension typically comprises a hanger bracket depending from a vehicle frame and connected to an axle by one or more trailing or control arms, extending between the hanger bracket and axle.

15 Typically, the trailing arms are pivotally connected to the hanger bracket and the axle ooeo to control the relative rotation of the axle with respect to the hanger bracket as the axle moves in jounce and rebound. An air spring is positioned between the axle and the •vehicle frame to resist the relative rotation of the axle with respect to the hanger oo.o bracket.

S .20 The suspension can mount steerable or non-steerable axles depending on the need. Steerable axles are designed with a predetermined caster angle to permit the wheels of the steerable axle to self-steer in either the forward or backwards direction, .eeo•i typically the forward direction. In most suspensions, the caster angle is the angle between the kingpin pivot axis projected onto a vertical plane parallel to the forward 25 direction of travel and a vertical line in the plane. When the kingpin pivot axis is canted forwardly of the vehicle, the caster angle is said to be positive. Similarly, when the kingpin pivot axis is canted rearwardly of the vehicle, the angle is said to be negative. Positive caster angle results in tracking of the wheels in a forward direction and negative caster angle results in tracking of the wheels in a rearward direction.

One disadvantage of having a caster angle is that if the vehicle is operated in a direction opposite that for which the caster angle is designed, the wheels will no longer track and will rotate randomly about the kingpin joint pivot axis, adversely affecting operation of the vehicle in the direction opposite to the direction for which the caster angle is designed. Prior solutions to the loss of self-steering fall into three main categories: lift axle suspensions, lock-out devices, and caster angle adjustment.

The lift axle suspensions solve the problem by lifting the wheels out of contact with the ground during reverse operation. They have the disadvantage that the repeated lifting of the suspension can fully exhaust the pressurized air reservoir supplying air to the lift bags, requiring that the operator wait for the reservoir to recharge. The exhaustion of the air reservoir can happen very quickly, within two iterations of reverse and forward movement of the vehicle, and can take more than two minutes to recharge, which is very undesirable for the vehicle operator. The lock-out devices rotate and lock the wheels in a "straight-ahead" position. The caster angle adjustment solutions adjust the caster angle between positive and negative as needed.

Prior caster angle adjustment solutions were accomplished by using a •pneumatic, hydraulic or manual actuator between the hanger bracket or frame and the axle to selectively pivot the axle between positive and negative caster angles.

Steerable axle assemblies with pneumatic or hydraulic caster angle adjustment of this type are disclosed in U.S. Patent No's. 5,018,756, issued May 28, 1991; 5,015,004, issued May 14, 1991; and 5,816,605, issued October 6, 1998. An example ofa manually adjustable link for caster angle adjustment is shown in U.S. Patent No.

5,230,528, issued July 27, 1993.

All the previous caster angle adjustment solutions have the common disadvantage of requiring an additional actuator, be it pneumatic, hydraulic, or ."manual, to pivot the axle or axle assembly relative to the trailing arm to adjust the caster angle. The addition of the extra component adds substantial weight to the suspension, especially when it is understood that there are multiple steerable axles on a tractor or trailer, or the combination of both. The addition of weight in a trailing arm suspension is highly undesirable as it reduces the ultimate load carrying capacity of the vehicle. The extra component has the additional disadvantages of increasing the complexity of the trailing arm suspension, increasing the maintenance requirements, and increasing the likelihood of a failure of one or more suspension components.

SUMMARY OF THE INVENTION The invention relates to an improved trailing arm suspension comprising a pair of trailing arm assemblies adapted to mount to spaced frame rails of a vehicle. Each of the trailing arm assemblies comprises a trailing arm that is adapted to pivotally mount at one end to a vehicle frame, typically through a hanger bracket, for relative movement of the trailing arm with respect to the vehicle frame. Another end portion of the trailing arm is pivotally mounted to an axle bracket that forms a part of an axle assembly for rotation about a first pivot axis. A control arm, positioned above the trailing arm, is adapted to pivotally mount at one end to the vehicle frame, typically through the hanger bracket, for movement relative thereto. Another end portion of the control arm is pivotally mounted to the axle bracket for rotation about a second pivot •axis. The axle assembly includes an axle that mounts ground-engaging wheels. An t inflatable air spring, mounted to the axle assembly and adapted to mount to the vehicle frame, yieldably resists the vertical movement of the axle assembly relative to the frame. The inflatable air spring is operable between an inflated and deflated condition and applies a force between the vehicle frame and the axle assembly along a first force line when the air spring is inflated. An inflatable lift bag, which is operable between an inflated and deflated condition, is operably connected between the trailing arm or the control arm and the axle assembly to apply a force between the trailing arm (or control arm) and the axle assembly along a second force line to move the trailing arm from a design height toward the vehicle frame when the lift bag is inflated.

According to the invention, the control arm is mounted to the axle assembly or to a hanger bracket for relative fore and aft movement of the axle assembly to thereby pivot the axle assembly about the first pivot axis when the trailing arm is at the design height to change the caster angle between positive and negative angles.

In one embodiment of the invention, the control arm is connected to the axle assembly for relative movement of the axle assembly with respect to the other end of the control arm. In another embodiment, the control arm is movably mounted to the hanger bracket for relative movement of the control arm and the axle assembly with respect to the hanger bracket.

Preferably, the mounting between the axle assembly and the other end portion of the control arm is limited to movement between a forward caster position and a rearward caster position. In the forward caster position, the wheels mounted to the axle assembly will follow the vehicle when the vehicle is moving forward. In the rearward caster position, the wheels will follow the vehicle when the vehicle is moving rearward. The movable mounting preferably comprises a slot formed in the axle assembly, with the slot having first and second stops. The control armnn preferably includes a pin that extends into the slot and abuts the first stop when the control arm is in the forward caster position and abuts the second stop when the control arm is in the rearward caster position. The slot can comprise a forward end defining the second stop and rearward end defining the first stop.

The movable mounting can also include a link that extends between and is rotatably connected to both of the trailing arm and the control arm. A portion of the oo••• link can pivot relative to the axle for optional movement of the axle fore and aft between the rearward caster position and the forward caster position, respectively.

The lift bag is preferably positioned relative to the pivot point such that when the lift bag is inflated it applies a first moment in a first direction about the pivot point to rotate the axle assembly from one of the fore and aft positions to the other of the fore and aft positions. It is preferred that when the lift bag is in the inflated condition, the axle assembly is rotated from the aft to the fore position. The air spring is S"preferably positioned relative to the pivot point such that when the air spring is S"inflated it applies a second moment in a second direction, opposite the first direction, about the pivot point, to rotate the axle assembly from the other of the fore and aft positions to the one of the fore and aft positions when the lift bag is deflated. The second force line associated with the lift bag is preferably positioned a sufficient distance from the pivot axis to define a lift arm moment arm such that the first moment generated by the force of lift bag applied along the second force line moves the axle assembly from the second fore to the aft position when the lift bag and the air spring are inflated.

The axle assembly can comprise an axle bracket to which the trailing arm and the control arm are pivotally mounted and the lift bag extends between the trailing arm and the axle bracket.

The movable mounting between the hanger bracket or the axle assembly and the control arm is limited to a forward caster position and a rearward caster position.

In the forward caster position, the wheels will follow the vehicle when the vehicle is moving forward. In the rearward caster position, the wheels will follow the vehicle when the vehicle is moving rearward.

The movable mounting preferably comprises a slot formed in one of the hanger bracket and the axle assembly. The slot can have first and second stops and the control arm can have a pin extending into the slots. When the pin abuts the first stop, the control arm is in the forward caster position. Similarly, when the pin abuts the second stop, the control arm is in the rearward caster position. The slot can comprise a first end that defines the first stop and a second end that defines the second stop.

The movable mounting can also include a link that extends between and is rotatably connected to both of the trailing arm and the control arm. A portion of the link is free to pivot relative to the axle to permit the axle to move fore and aft between the rearward caster position and the forward caster position, respectively.

A catch mechanism is preferably provided for holding the pin in one of the forward and rearward caster positions. Preferably, the catch is movable between a hold position and a release position. In the hold position, the pin is held in the S•forward caster position. In the release position, the pin can move to the rearward position. The catch preferably comprises a fork having two spaced prongs in-between which the pin is received when the catch is in the hold position.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a side view of a trailing arm lift axle suspension according to the invention with a steerable axle assembly and illustrating the suspension ina lowered position and the axle at a positive caster angle for forward operation; FIG. 2 is a side view, like FIG. 1, of the suspension of FIG. 1 and illustrating the suspension in a lowered position and the axle at a negative caster angle for reverse operation; FIG. 3 illustrates a side view of the trailing arm lift axle suspension of FIG. 1 with the suspension in the raised position; FIG. 4 illustrates a second embodiment of a trailing arm lift axle suspension with a steerable axle according to the invention with the suspension in the raised position and the axle at a positive caster angle for forward operation; FIG. 5 is a perspective view of a portion of the trailing arm lift axle suspension illustrated in FIG. 4 with the axle in the positive caster angle position; FIG. 6 is a side view of a trailing arm lift axle suspension similar to FIG. 1 having an alternative construction for the achieving the caster angle adjustment S* "illustrating the suspension in a lowered position and the axle at a positive caster angle .:.oe for forward operation; and FIG. 7 is a side view of the suspension of FIG. 6 and illustrating the S .suspension in a lowered position and the axle at a negative caster angle for rearward operation.

o 0o•00°o .=ooo DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a trailing arm suspension 10 rotatably connecting a steerable axle 12 to a vehicle frame 14. Typically, a complete trailing arm suspension comprises a pair of trailing arm suspension assemblies 13 mounted on opposite sides of the vehicle. Only one of the trailing arm suspension assemblies 13 will be described in detail with it being understood that the description applies equally to both.

The trailing arm suspension assembly 13 comprises a hanger bracket depending from the vehicle frame 14 and an axle-mounting bracket 16, both of which are rotatably connected together by parallel trailing arm 18 and control arm 20. The axle mounting bracket 16 is also connected to the steerable axle 12, forming an axle assembly.

Rotatable connections 19, 21 rotatably connect one end of each the trailing arm and control arm to the hanger bracket. The rotatably connector 19 is preferably a bushed connector, but can be a simple pin, bolt or other rotatable connector. The traditional bushed connector has the advantage of providing some rotational resistance ""to the rotation of the arms and rotation of the arms along their longintudinal axis and lateral movement, unlike the pin or bolt.

Rotatable connections 23, 25 rotatably connect the other end of the arms to the axle mounting bracket 16. With this construction, any force imparted to the steerable axle 12 through contact with a road surface, results in rotation of the steerable axle 12 and axle bracket 16 relative to the hanger bracket. The rotatable connection 23 of the lower trailing arm 18 to the axle mounting bracket 16 is preferably accomplished by a bushed connector.

The rotatable connection 25 of the control arm 20 preferably comprises a pin 22 within an elongated, arcuate slot 24 in the axle mounting bracket. The arcuate slot 24 has a first end 24A, located forwardly of the vehicle, and a second end, 24B, located rearwardly of the vehicle. The first end 24A functions as a first stop and the second end functions as a second stop 24B. The pin 22 can rotate relative to the slot 24 to enable the relative rotation of the control arm and the axle bracket 16. Since the slot 24 is longer than the diameter of the pin 22, the pin 22 can also moved within the slot, permitting the fore and after relative movement of the axle bracket 16 and the control arm, effectively forming a moveable connection between the axle bracket 16 and the control arm Since the trailing arm is rotatably mounted to the axle bracket 16 and the control arm is rotatably and movably mounted to the control arm 20, the axle mounting bracket and steerable axle 12 (collectively the axle assembly) can pivot fore and aft relative to the vehicle about a pivot axis P, which is generally coaxial with the rotational axis of rotatable connection 23, while the control arm 20 and axle assembly rotate relative to each other. The range of pivotal fore and aft movement is limited by the length of the slot since the pivoting stops when the pin contacts either end 24A, 24B of the slot. The relative pivoting of the axle assembly alters the caster angle of the wheels.

They symbol in FIGS. 1 and 2 illustrates the angle the axle centerline forms relative to the vertical in a plane that is parallel to the vehicle direction of travel. In the suspension, the axle centerline forms a predetermined angle relative to the caster ~angle of the wheels. Thus, the change in is representative of the change in the caster angle, but is not necessarily the caster angle.

•oooo The impact of the axle assembly pivoting about the pivot point P can be seen by examining the pivot extremes illustrated in FIGS. 1 and 2 and the corresponding Schange in the angle As seen in FIG. 1, when the pin is abutting the first end 24A, the axle assembly is rotated to its aft most position relative to pivot point P and the angle is maximized. In this position the wheels supported by the axle have a positive caster angle and will track/follow the forward movement of the vehicle. As seen in FIG. 2, when the pin is abutting the second end 24B, the axle assembly is rotated to is most ."fore position relative to pivot point P and the angle is minimized. In this position the S°wheel supported by the axle have a negative caster angle and will track/follow the rearward movement of the vehicle. When the axle is oriented for tracking in the forward or reverse directions, the control arm position and axle assembly position can correspondingly be identified as being in the forward or reverse caster angle position.

To complete the suspension, an air spring 28 extends between the vehicle frame 14 and a portion of the axle mounting bracket 16. The air spring 28 includes a ride bag 30 and a piston 31, which is connects the ride bag to the axle bracket 16. The ride bag 30 is connected to the frame through a bracket 38 in the traditional manner.

The ride bag 30 dampens the rotational movement of the steerable axle assembly 12 relative to the hanger bracket 15. Pressurized air can be introduced and exhausted from the ride bag 30 to control the force applied by the air spring 28 against the axle mounting bracket 16. The center line A of the air bag indicates the line along which the force of the air bag is applied. As can be seen in FIG. 1, the force line A of the air bag lies in front (relative to the vehicle) of the pivotal connection between the lower trailing arm 18 and the axle bracket 16.

A lift bag 32 is disposed between the lower trailing arm 18 and the axle mounting bracket 16. Like the ride bag, pressurized air can be introduced and exhausted from the lift bag 32. The vertical component of the force applied by the lift bag 32 on the suspension is illustrated by the force line B. As with the force line A of the ride bag 30, the force line B of the lift bag also lies in front of the axle pivot point

P.

The ride bag 30 and lift bag 32 are generally circular in cross section, with the ride bag 30 typically having a much larger diameter than the lift bag 32, resulting in a greater cross-sectional area for the ride bag 30 than the lift bag 32. Since the ride bag and lift bag are typically supplied by the same source of pressurized air, each bag will 9oe be pressurized to the pressure of the common air source, resulting in the ride bag se@: applying a greater force because of its greater cross-sectional area along force line A 9..

than the lift bag 32 will apply along force line B.

o 5 A shock absorber 34 extends between the axle bracket 16 and the hanger bracket 15. Each end of the shock absorber 34 is mounted by a rotatable connection S° 36 to the frame bracket and the axle bracket.

The operation of the suspension, according to the invention, has four basic operational conditions. The lift axle suspension is either in the raised or lowered position and the caster angle is either positive or negative. In the raised position, the /0 caster angle is not relevant since the wheels are not touching the ground. It should be noted that the caster angle is considered positive when the wheels carried by the axle will track or follow the vehicle as it is moved in the forward direction. Conversely, the caster angle is considered negative when the wheels track or follow the vehicle as it is moved in the rearward direction. A positive caster angle may not necessarily indicate that the axle forms a positive angle relative to the vertical. Similarly, a negative caster angle may not necessarily indicate that the axle forms a negative angle relative to the vertical.

The lift positions will not be discussed in detail as they are discussed in corresponding U.S. application 09/116,366, filed July 16, 1998, which is incorporated by reference. It is sufficient for this description to know that when the suspension is raised, the air is exhausted from the ride bag 30 and air is introduced into the lift bag 32. When it is desired to have the lift axle suspension in contact with the ground and operate the vehicle in the forward direction, pressurized air is exhausted fromthe lift bag 32 to lower the lift axle suspension.

In the lowered position, pressurized air is introduced into the ride bag 30 in a sufficient amount for the trailing arm suspension tosupport the vehicle in a normal .manner. The ride bag 30 applies a force along force line A that induces a counterclockwise moment when viewed from FIG. 1, tending to pivot the axle assembly into •"20 a negative caster angle, which is inappropriate for forward operation.

To obtain the positive caster angle required for forward movement, pressurized air is introduced into the lift bag 32, resulting in the application of a force along force line B. The force from the lift bag acting along force line B results in a clockwise moment (as seen in FIG. 1) about the pivot point P that rotates the axle assembly •25 clockwise until the pin 22 of the upper control arm 20 abuts the forward or first end S"24A of the elongated arcuate slot 24, thereby limiting further rotation of the steerable S. .axle. The location and angular orientation of the forward end of the slot 24 effectively !defines the maximum positive caster angle obtainable by rotation of the axle assembly.

The magnitude of the moment induced by the lift bag 32 about pivot point P, must be great enough to overcome the moment induced by the air spring and the inherent pivotal resistant of the axle assembly. In the preferred embodiment, the greater moment attributable to the lift bag 32 is accomplished by the lift bag moment arm (the perpendicular distance between pivot point P and the force line B) is much greater than the ride bag moment arm (the perpendicular distance between pivot point P and the force line Thus, although the force applied by the ride bag 30 is much greater than the force applied by the lift bag 32, the greater moment arm for the lift bag 32 yields a greater moment that is sufficient to overcome the moment from the ride bag. The greater moment arm is advantageous in that force applied by the lift bag is not great enough to impair the normal operation of the ride bag When the vehicle is to be operated in reverse with the trailing arm suspension in the lower position, the caster angle must be adjusted from a positive caster angle to a negative caster angle. To obtain a negative caster angle, the air in the lift bag 32 is exhausted, substantially reducing or eliminating the application of a force along force line B. The ride bag 30 of the air spring 28 still applies a force to the axle assembly along force line A downwardly onto the axle bracket 16, which imparts a i' counterclockwise moment to the axle assembly about pivot point P. The counterclockwise moment will pivot the axle mounting bracket 16 and the steerable axle 12 from a positive caster angle to a negative caster angle, which is illustrated in FIG. 2. The pivoting of the axle bracket in the counterclockwise direction about point P is arrested when the pin 22 contacts the rearward end 24B of the elongated and S" "arcuate slot 24. As with the forward end of the slot 24, the rearward end of the slot 24 defines the maximum negative caster angle obtainable by the axle assembly.

25 If, for any reason, upon the exhaustion of the pressurized air from the lift bag 32, the pressurized air contained in the ride bag 30 of the air spring 28 is not sufficient to overcome the inherent rotational resistance of the axle mounting bracket and steerable axle, pressurized air need only be introduced into the ride bag 30 until the inherent resistance is overcome and the axle assembly rotates to the negative caster angle position.

In essence, the inflation and deflation of the lift bag controls the adjustment of the caster angle. Since the lift bag has a much smaller volume than the ride bag, the lift bag can be cycled between inflation and deflation many more times than the ride bag without exhausting all of the air from the air reservoir, reducing the likelihood that the operation of the vehicle will be interrupted or halted while the air reservoir repressurizes, which is a great improvement over merely lifting the suspension.

Referring to FIG. 3, when the trailing arm suspension 10 is not needed and it is desired to lift the suspension out of ground engaging contact, pressurized air is exhausted from the ride bag 30 and pressurized air is introduced into the lift bag 32.

As the lift bag 32 expands and applies a force between the lower trailing arm 18 and the axle bracket 16, the force tends to "open-up" the angle between the lower trailing arm 18 and the axle bracket 16 by pivoting the axle bracket 16 clockwise about pivot point 16, resulting in the relative movement between the axle bracket 16 and the pin 22, until the pin 22 abuts the forward end of the elongated, arcuate slot 24. Once the pin 22 abuts the forward end of the slot 24, the continued application of the force by the lift bag 32 pivots the axle assembly upwardly or counterclockwise with respect to the hanger bracket 15 to raise the steerable axle 12 offthe ground.

.Since the rotation of the axle is accomplished by the differences in the moments applied by the ride bag 30 and lift bag 32, and the corresponding moments are attributable to both the force and moment arm of the ride bag 30 and lift bag 32, it is within the scope of the invention for the size and location of the ride bag 30 and lift bag 32 to vary with respect to the pivot point P. It is important that the ride bag S and lift bag 32 be sized and oriented in such a manner to rotate the axle assembly for adjusting the caster angle as required for forward and rearward operation. Also, the 25 ride and lift bags need not necessarily be located relative to the suspension as shown in the drawings as long as the appropriate moments are applied to pivot the axle between the positive and negative caster angles for reverse and forward movement. It is also preferred that the magnitude of the force applied by the lift bag not interfere with the normal operation of the suspension. However, some interference is tolerable since the vehicle is not normally operated in the reverse direction for a long time or at high speeds.

FIGS. 4 and 5 illustrate a second embodiment of the trailing arm lift axle suspension with a steerable axle having caster angle adjustment according to the invention. The second embodiment 40 is substantially identical to the first embodiment 10, except that the steerable axle is a hollow beam fabricated from sheet metal rather than the solid T-shaped beam illustrated in FIGS. 1-3. Therefore, given that many of the parts are substantially identical between the two embodiments, like parts in the second embodiment will be identified by like numerals.

The trailing arm suspension 40 comprises a hanger bracket 15 depending from the vehicle frame 14. A pair of trailing arms 18, 20 rotatably mount a fabricated axle 42 to the hanger bracket 15. An air spring 28 is disposed between the vehicle frame 14 and a plate extending from the fabricated axle 42. A lift bag 32 has one end mounted to the lower trailing arm 18 and the other end mounted to the plate 44 extending from the fabricated axle 42.

The fabricated axle 42 includes a kingpin collar 46 adapted to mount a knuckle supporting the spindle of a traditional steerable axle. The centerline 48 of the kingpin •.collar 46 defines the rotation axis of the wheels for the steerable axle assembly.

Therefore, the angle of the centerline 48 formed with respect to the vertical defines the "i 20 caster angle E for the second embodiment.

The fabricated axle 42 further includes a pivot-adjusting rod 50 that is pivotally connected to the fabricated axle 42 through a bracket 54 and a pin 56 to define a pivot point P of the fabricated axle 42. The upper end of the pivot-adjusting rod 50 is pivotally connected to the end of the upper control arm 20 through a clevis 25 mounting 62 and a pin 64. A pivot restraint bracket 52 is rigidly mounted to the fabricated axle 42 and circumscribes the pivot-adjusting rod 50. The bracket 52 limits the degree of rotation of the pivot-adjusting rod 50 about the point P. The bracket 52 o. in combination with the link or rod 50 effectively performs the same function as the slot and pin of the first embodiment. The lower trailing arm 18 is pivotally mounted to the axle 42 through a U-shaped bracket 58 which is rigidly mounted to the axle 43 and a pin 60. The pivot axis P extends through the pin 60 as well as through the pin 56 as illustrated in FIG. The operation of the second embodiment is substantially identical to the operation of the first embodiment. When it is desired to lower the lift suspension and operate the vehicle in the forward direction, the air is substantially exhausted from the lift bag 32 to lower the fabricated axle 42 into ground-engaging contact. Pressurized air is then introduced into the ride bag 30 to a predetermined level suitable to dampen the road-induced lifting forces on the fabricated axle 42. The lift bag 32 is pressurized a sufficient amount so that the clockwise moment applied by the lift bag 32 about the pivot point P overcomes the counterclockwise moment applied by the ride bag about the pivot point P, resulting in the clockwise rotation of the fabricated axle 42 until the pivot adjusting rod 50 contacts the bracket 52, thereby limiting the positive caster angle (FIG. When it is desired to operate the suspension of FIGS. 4 and 5 in a reverse direction, the pressurized air is exhausted from the lift bag 32, substantially reducing or eliminating the clockwise moment acting on the fabricated axle 42 about point P.

The counterclockwise moment acting on the fabricated axle 42 as induced by the force °applied by the ride bag 30 rotates the fabricated axle 42 until it, contacts the pivot adjusting rod to rotate the axle to a negative caster angle suitable for reverse •20 operation.

Referring to FIGS. 6 and 7, there is shown a trailing arm suspension substantially identical to the suspension shown in FIGS. 1 and 2, except for the alternative construction of the caster angle adjustment mechanism. Therefore, like numerals will be used to identify like parts.

25 The suspension 10 of FIGS. 6 and 7 locates the slot 24' on the frame bracket instead of on the axle bracket 16. Correspondingly, the pin 22' is located on the frame bracket end of the control arm 20 and extends through the slot 24'. The control arm 24 is rotatably mounted to the axle bracket 16. Thus, in operation, the movement of the axle from the negative to positive caster angle (FIG. 6) by the inflation and deflation of the lift bag 32, results in the pin contacting a first end 24A' of the slot 24 to limit the angular rotation or pivoting of the axle bracket 16 relative to the pivot point P. Similarly, the movement of the axle from the positive to negative caster angle (FIG. results in the pin contacting a second end 24B' of the slot 24 to limit the angular rotation or pivoting of the axle bracket 16 relative to the pivot point P.

The suspension of FIGS. 6 and 7 also includes a pin lock 80 that locks or holds the pin 22' in the positive caster angle position (FIG. 6) to ensure that the axle bracket 16 does not pivot to the negative caster angle position (FIG. 7) when the vehicle is stopped after moving forward. The pin lock 80 preferably comprising a pneumatic actuator having a housing 82 from which extends a reciprocating arm 84, which is reciprocated between extended (FIG. 6) and retracted (FIG. 7) positions relative to the housing by the introduction and exhaustion of pressurized air from the housing 82. A fork 86 having spaced prongs 88 is mounted to the end of arm 84. Support plates extend away from the frame bracket 15 and are positioned on opposite sides of the pin 22' when the pin 22' abuts the end 24A' of the slot 24'. The pin 22' is received between the prongs 88 and the prongs are received between the support plates when the arm is in the extended position, whereby the prongs 88 hold the pin in place 1 and the support plates brace the fork.

~The actuation of the arm 86 is preferably controlled by the same air system that introduces and exhausts air from the lift bag 32 and the ride bag 30. The arm is •20 moved to the extended position after the air is introduced into the lift bag to hold the pin and thus the axle bracket in the positive caster angle position. Similarly, the arm is retracted prior to the air being exhausted from the lift bag to permit the pivoting of the axle bracket about the pivot point P.

The suspension system of the invention represents a substantial improvement oooeo 25 over prior art suspensions having caster angle adjustment. The suspension system of the invention does not require any extra or task specific devices to pivot the steerable S. axle between a negative and positive caster angle. The invention advantageously uses the ride bag and lift bags already used in a lift axle suspension and positions them so that by controlling the pressurized air introduced and exhausted from the ride bag and lift bag, the caster angle can be adjusted between a negative and positive position.

The invention dramatically reduces the weight of a trailing arm suspension with a steerable axle having caster angle adjustment along with reducing the complexity of the suspensions.

While the invention has been specifically described in connection with certain specific embodimentsthereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the forgoing disclosure without departing from the spirit of the invention.

While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

For the purposes of this specification it will be clearly understood that the word "comprising" means "including but not limited to", and that the word "comprises" has a corresponding meaning.

Claims (21)

1. In a trailing arm suspension comprising a pair of trailing arm assemblies adapted to be connected to spaced-apart vehicle frame members, each of the trailing arm assemblies comprising: an axle assembly adapted to mount ground engaging wheels; a trailing arm that is adapted to pivotally mount at one end portion to a vehicle frame for relative movement of the trailing arm with respect to the vehicle frame and at another end portion is pivotally mounted to the axle assembly for rotation about a first pivot axis; a control arm, positioned above the trailing arm, adapted to pivotally mount at one end portion to the vehicle frame for pivotal movement relative thereto, and, at another end portion, is pivotally mounted to the axle assembly for rotation about a second pivot axis; an inflatable air spring, mounted to the axle assembly and adapted to mount to the vehicle frame, for yieldably resisting the vertical movement of the axle assembly relative to the frame and operable between an inflated and deflated condition, "applying a force between the vehicle frame and the axle assembly along a first force line when the air spring is inflated; an inflatable lift bag, operable between an inflated and deflated condition, operably connected between the trailing arm and the axle assembly to apply a force between the trailing arm or control arm and the axle assembly along a second force line to move the trailing arm from a design height toward the vehicle frame to a lift oo position when the lift bag is inflated; the improvement which comprises: the control arm is mounted to the axle assembly for relative fore and aft movement of the axle assembly to thereby pivot the axle assembly about the first S" pivot axis when the trailing arm is at the design height to change the caster angle between positive and negative caster angles for forward and reward movement of a vehicle to which the suspension system is mounted.

2. The trailing arm suspension according to claim 1, wherein the moveable mounting between the axle assembly and the other end portion of the control arm is limited to a forward caster position and a rearward caster position wherein, in the forward caster position, the wheels will follow the vehicle when the vehicle is moving forward, and in the rearward caster position, the wheels will follow the vehicle when the vehicle is moving rearward.

3. The trailing arm suspension according to claim 2, wherein the moveable mounting comprises a slot formed in the axle assembly, with the slot having first and second stops, and the control arm has a pin extending into the slot, wherein, when the pin abuts the first stop, the control arm is in the forward caster position, and when the pin abuts the second stop, the control arm is in the rearward caster position.

4. The trailing arm suspension according to claim 3, wherein the slot comprises a forward end defining the second stop and a rearward end defining the first stop.

5. The trailing arm suspension according to claim 2, wherein the axle assembly comprises an axle and a link, the link extends between and is rotatably mounted to the other end portions of both the control arm and the trailing arm, the rotatable connection of one of the trailing arm and control arm with the link is connected to the axle, the other of the rotatable connection of the trailing arm and control arm with the link is pivotal relative to the axle to form the moveable mounting.

6. The trailing arm suspension according to claim 1, wherein the lift bag is positioned relative to the pivot point such that when the lift bag is inflated it applies a first moment in a first direction about the pivot point to rotate the axle assembly from one of the fore and aft positions to the other of the fore and aft positions.

7. The trailing arm suspension according to claim 6, wherein when the lift bag is inflated, the axle assembly is rotated from the aft to the fore position. U /q

8. The trailing arm suspension according to claim 7, wherein the moveable mounting comprises a slot formed in the axle assembly, with the slot having first and second stops, and the control arm has a pin extending into the slot, wherein, when the pin abuts the first stop, the control arm is in a forward caster position where the wheels mounted to axle assembly will follow the vehicle when the vehicle is moving forward, and when the pin abuts the second stop, the control arm is in the rearward caster position where the wheels mounted to the axle assembly will follow the vehicle when the vehicle is moving rearward.

9. The trailing arm suspension according to claim 7, wherein the air Sspring is positioned relative to the pivot point such that when the air spring is inflated it applies a second moment in a second direction, opposite the first direction, about the pivot point to rotate the axle assembly from the other of the fore and aft positions to the one of the fore and aft positions when the lift bag is deflated. The trailing arm suspension according to claim 9, wherein the second force line is positioned a sufficient distance from the pivot axis to define a lift arm •moment arm such that the first moment generated by the force of the lift bag applied •along the second force line moves the axle assembly from the fore to the aft position when the lift bag and the air spring are inflated.

OV.: S

"11. The trailing arm suspension according to claim 9, wherein the axle assembly comprises an axle bracket to which the trailing arm and the control arm are pivotally mounted and the lift bag extends between the trailing arm and the axle bracket.

12. In a trailing arm suspension comprising: a hanger bracket adapted to mount to a vehicle frame; an axle assembly adapted to mount an axle with ground engaging wheels; 0. a trailing arm pivotally mounted at one end portion to the hanger bracket for relative pivotal movement of the trailing arm to the vehicle frame and pivotally mounted at another end portion to the axle assembly for rotation about a first axis; 4 to a control arm, positioned above the trailing arm, and pivotally mounted at one end portion to the frame bracket for relative pivotal movement of the control arm to the vehicle frame, and at another end portion pivotally mounted to the axle assembly for rotation about a second axis; an inflatable air spring, operable between an inflated and deflated condition, mounted to the axle assembly and adapted to mount to the vehicle frame to yieldably resist the relative vertical movement of the axle assembly toward the vehicle frame, the inflatable air spring is adapted to apply a force to the axle assembly along a first force line when the air spring is inflated; an inflatable lift bag, operable between and inflated and deflated conditions, and operably connected to the trailing arm to apply a force to the trailing arm along a second force line to move the trailing arm from a design height toward the vehicle to a lift position when the lift bag is inflated; the improvement comprising: the control arm is movably mounted to one of the hanger bracket and the axle assembly for relative fore and aft movement of the axle assembly relative to the hanger bracket to thereby rotate the axle assembly about the first axis when the trailing arm is at the design height.

13. The trailing arm suspension according to claim 12, wherein the moveable mounting between the one of the hanger bracket and the axle assembly and the control arm is limited to a forward caster position and a rearward caster position wherein, in the forward caster position, the wheels will follow the vehicle when the 000o vehicle is moving forward, and in the rearward caster position, the wheels will follow the vehicle when the vehicle is moving rearward. 000000

14. The trailing arm suspension according to claim 13, wherein the e 0 moveable mounting comprises a slot formed in the one of the hanger bracket and the axle assembly, with the slot having first and second stops, and the control arm has a pin extending into the slot, wherein, when the pin abuts the first stop, the control arm 4 (I is in the forward caster position, and when the pin abuts the second stop, the control arm is in the rearward caster position.

The trailing arm suspension according to claim 14, wherein the slot comprises a first end defining the first stop and a second end defining the second stop.

16. The trailing arm suspension according to claim 15 and further comprising a catch for holding the pin in one of the forward and rearward caster positions.

17. The trailing arm suspension according to claim 16, wherein the catch is moveable between a hold position and a release position, in the hold position the pin is held in the forward caster position, and in the release position, the pin is free to move.

18. The trailing arm suspension according to claim 17, wherein the catch comprises a fork having two spaced prongs and the pin is received between the prongs when the catch is in the hold position.

19. The trailing arm suspension according to claim 11, wherein the lift bag t.:I is positioned relative to the first axis such that when the lift bag is inflated it applies a •s first moment in a first direction about the first axis to rotate the axle assembly from one of the fore and aft positions to the other of the fore and aft positions.

20. The trailing arm suspension according to claim 19, wherein when the lift bag is inflated, the axle assembly is rotated from the aft to the fore position about the first axis.

21. The trailing arm suspension according to claim 20, wherein the air spring is positioned relative to the first axis such that when the air spring is inflated it applies a second moment in a second direction, opposite the first direction, about the first axis to rotate the axle assembly from the other of the fore and aft positions to the one of the fore and aft positions when the lift bag is deflated. Dated this 28th day of November 2000 HOLLAND NEWAY INTERNATIONAL, INC. By their Patent Attorneys: GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia 2L/