FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, rule 13]
“A SELF-STEER AXLE ASSEMBLY FOR VEHICLES”
NAME AND ADDRESS OF THE APPLICANT:
TATA MOTORS LIMITED, an Indian company having its registered office at Bombay
house, 24 Homi Mody Street, Hutatma Chowk, Mumbai 400 001, Maharashtra, INDIA.
Nationality: Indian
The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD
The present invention generally relates to axles of automobiles and more particularly relates to a self-steer axle assembly of an automobile.
BACKGROUND OF THE DISCLOSURE
Heavy load carrying vehicles, such as commercial vehicles, large trailers and the like, often employ a self-steer axle assembly, such as a pusher or tag axle assembly, in order to distribute load over more wheels. Unlike in a positively steer axle assembly where at least one wheel may get turning movement from a steering wheel, in the self-steered axle assembly the turning moment of the wheels is generated when a thrust line of the vehicle and a longitudinal axis of the wheel comes at an angle to each other, for example, when the vehicle negotiates a turn.
Conventionally, each of the self-steer axle assembly and the positively steer axle assembly employ a tie rod that transfers an equivalent turning movement from one wheel to another wheel. Further, when the vehicle encounters road undulation or unwanted lateral forces, the tie rod also transfers forces from one wheel to the other wheel.
Furthermore, during movement of the vehicles, the wheels of the self-steering axle assembly experience wheel wobble, also known as “Wheel Shimmy.” Wheel shimmy is a condition in which the wheels oscillate about the king pin axis and typically it is observed more when the vehicle speed is high. Various concepts have been proposed in the art for reducing or eliminating wheel shimmy. For example, hydraulic shimmy dampers have been used to damp wheel shimmy. Typically, such shimmy dampers consist of hydraulic shock absorbers mounted on the axle beam. The hydraulic shock absorbers generally consist of hollow tubes filled with oil. A rod and piston move through the fluid to generate velocity-dependent, viscous-damping forces. However, such designs require frequent maintenance, and temperature increases can reduce damping efficiency.

OBJECTS OF THE INVENTION
The objective of invention is to provide a self-steering axle assembly for a vehicle, wherein each wheel of the self-steering axle assembly is capable of turning independently.
Another object of the invention is to provide a self-steering axle assembly which another object of the invention is to provide a self-steering eliminates the need of having a tie rod mechanism.
Yet axle assembly which is simple, employs fewer components, and is lighter in weight.
Yet another object of the invention is to lock the steering when the vehicle has reached a predetermined speed to avoid shimmy.
Further objects and features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.
SUMMARY OF THE INVENTION
The various embodiments of the present invention, disclose an axle assembly for a vehicle. The axle assembly includes an axle beam, and a knuckle having a first arm, a second arm and a body member carrying the first arm and the second arm. The axle assembly further includes a kingpin for connecting knuckle to the axle beam and at least one resilient member engaged with the kingpin and the knuckle. The knuckle is rotatably engaged with the kingpin such that the resilient member applies a resilient force against a movement of the knuckle about the kingpin.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 illustrates a perspective view of an axle assembly, according to an embodiment of the invention,
FIG. 2 illustrates an exploded view of the axle assembly of FIG. 1, according to an embodiment of the invention,

FIG. 3 illustrates a sectional view of the axle assembly of FIG. 1, according to an embodiment of the invention, and
FIG. 4 illustrates a perspective view of a lock actuator assembly of the axle assembly of FIG. 1, according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same.
It is to be noted at this point that all of the above described components, whether alone or in any combination, are claimed as being essential to the disclosure, in particular the details depicted in the drawings and reference numerals in the drawings are as given below.
An axle assembly 100, in accordance with the present invention is illustrated in FIGS. 1-3. The axle assembly 100 may be a stationary self-steer axle assembly fixedly supported from a vehicle frame or an auxiliary axle assembly pivotally supported from the vehicle frame which can be raised and lowered. Typically, the vehicle frame includes a left and a right vehicle beam (not shown) extending longitudinally from a front to a rear of the vehicle, in a known manner. The axle assembly 100 is adapted to be attached to both the left and right vehicle beams.
The axle assembly 100 includes an axle beam 102 having end portions 104, 106 and an elongated body portion 108 joining the end portions 104, 106. The axle assembly 100 may be secured to the vehicle by mounting flanges (not illustrated) projecting preferably inwardly from an upper surface of the elongated body 106.
A cylindrical bore 110 is provided at the end portion 104 of the axle beam 102. Similarly, a cylindrical bore is also provided at the end portion 106 of the axle beam 102. For the purpose of brevity the subsequent description will only be with reference to one side of the axle beam 102 i.e. towards the end portion 104, as it shall be apparent to those skilled in the art that similar components may be present on the opposite side of the axle beam 102 i.e. towards the end portion 106.

The axle assembly 100 further include a kingpin unit 120 connected to the axle beam 102 at the end portion 104. The kingpin unit 120 includes a kingpin 122 having a cylindrical configuration. The kingpin 122 may be configured to be received within the cylindrical bore 110 on the axle beam 102, such that a first end portion 124 and a second end portion 126 of the kingpin 122 are positioned out of the cylindrical bore 110. The kingpin unit 120 may further include a threaded cotter pin (not shown) configured to be inserted through the end portion 104 for engaging with the kingpin 122 and resisting rotating movement of the kingpin 122 with respect to the axle beam 102. Further, one or more bearing members, such as a thrust bearing, may be provided on the first end portion 124 and the second end portion 126 of the kingpin 122.
The axle assembly 100 further includes at least one resilient member. The at least one resilient member may be mounted on the kingpin 122. In accordance to the disclosed embodiment of the present invention, best shown in FIG. 2, the axle assembly 100 includes a first resilient member 130 and a second resilient member 132. The first resilient member 130 is configured to be mounted on the first end portion 124 of the kingpin 122 and the second resilient member 132 is configured to be mounted on the second end portion 126 of the kingpin 122.
In an embodiment of the present invention the first resilient member 130 and the second resilient member 132 are volute springs. The volute springs being made from a strip of Silico Manganese (SiMn) rolled spirally, in the way that the turns make a cone. In other embodiments of the present invention the first resilient member 130 and the second resilient member 132 may alternatively be torsion springs, helical springs, spiral springs, or the like, without deviating from the spirit of the present invention.
An inner end portion of the first resilient member 130 and the second resilient member 132 may be fixedly connected to the first end portion 124 and the second end portion 126 of the kingpin 122 respectively, while coiled portions of the first resilient member 130 and the second resilient member 132 may circumferentially enclose the first end portion 124 and the second end portion 126 of the kingpin 122. The mechanical properties, such as stiffness, of both the first resilient member 130 and the second resilient member 132

are similar. In an embodiment of the present invention, the first resilient member 130 positioned in an inverted relationship with respect to the second resilient member 132.
Referring again to the FIG. 1-3, the axle assembly 100 further includes a knuckle 140 rotatably engaged with the kingpin unit 120. More specifically, the knuckle 140 includes a first arm 142, a second arm 144 and a body member 146 carrying the first arm 142 and the second arm 144. The first arm 142 and the second arm 144 extend towards one side of the body member 146 while a wheel hub carrying the wheel (not illustrated) may be detachably mounted on an opposite of the body member 146.
The first arm 142 of the knuckle 140 is configured to be rotatably engaged with the first end portion 124 of the kingpin 122. In an embodiment of the present invention as shown in FIG. 2, the first arm 142 includes a hollow cylindrical portion 148 having an internal diameter bigger than the diameter of the cylindrical first end portion 124 of the kingpin 122. Particularly, the internal diameter of the hollow cylindrical portion 148 of the first arm 142 is such that it receives the first end portion 124 of the kingpin 122 along with the first resilient member 130.
A stopper member formed at an inner surface of the hollow cylindrical portion 148. The stopper member engages with an outer end portion of the first resilient member 130, when the first end portion 124 of the kingpin 122 is received within the first arm 142 of the knuckle 140. Due to such connection of the stopper member with the first resilient member 130, the first resilient member 130 applies a resilient force against a clockwise movement of the knuckle 140 about the kingpin 122.
The second arm 144 of the knuckle 140 is configured to be rotatably engaged with the second end portion 126 of the kingpin 122. In an embodiment of the present invention as shown in FIG. 2, the second arm 144 includes a hollow cylindrical portion 150 having an internal diameter bigger than the diameter of the cylindrical second end portion 126 of the kingpin 122. Particularly, the internal diameter of the hollow cylindrical portion 150 of the second arm 144 is such that it receives the second end portion 126 of the kingpin 122 along with the second resilient member 132.

A stopper member is provided at an inner surface of the hollow cylindrical portion 150. The stopper member engages with an outer end portion of the second resilient member 132, when the second end portion 126 of the kingpin 122 is received within the second arm 144 of the knuckle 140. Due to such connection of the stopper member with the second resilient member 132, the second resilient member 132 applies a resilient force against an anti-clockwise movement of the knuckle 140 about the kingpin 122.
Referring now to FIGS. 1 to 3, which illustrate perspective views of the axle assembly 100 in conjunction with FIG. 4 which illustrates a perspective view of a lock actuator assembly. As shown in FIG. 1 and 2, the axle assembly 100 further includes a lock actuator assembly 160 carried by the to the axle beam 102. The lock actuator assembly 160 configured to selectively lock the movement of the knuckle 140 with respect to the axle beam 102.
The lock actuator assembly 160 includes a housing 162 carried by the axle beam 102. The housing 162 may be detachably connected to the axle beam 102 by a mounting bracket 164, connected to the axle beam 102 by fasteners. The lock actuator assembly 160 further include an actuator rod 166 associated with the housing 162. The housing 162 is configured to receive a continuous hydraulic or pneumatic input, and an ECU (Electronic Control Unit) regulates the supply of the hydraulic or pneumatic input to the housing. Based on the input from the sensor to the housing 162, the actuator rod 166 extends and retracts with respect to the housing 162. A lock bracket 168 (shown in FIG. 2) may be connected to the knuckle 140. In an embodiment of the present invention, the lock bracket 168 a C-block bolted to the first arm 142 of the knuckle 140, as illustrated. The lock bracket 168 positioned with respect to the actuator rod 166 such that the lock bracket 168 may receive a portion of the actuator rod 166 when the actuator rod 166 has extended. Such receiving of the actuator rod 166 within the lock bracket 168 may lock the movement of the knuckle 140 with respect to the axle beam 102.
During operation of a vehicle having the axle assembly 100, when the vehicle negotiates a turn, i.e. when the vehicle corners, the vehicle thrust line comes at an angle with respect to the longitudinal axis of the wheels. Resultantly, a moment is generated at each of the

wheels which may force the wheels to displace from an original straight orientation and align with the vehicle thrust line. In accordance with the present invention, when the wheels turn, the knuckle 140 moves about the kingpin 122. Such movement of the knuckle 140 is against the resilient force of one of the first resilient member 130 and the second resilient member 132.
In an embodiment of the present invention, the right turn of the vehicle will cause a clockwise movement of the knuckle 140, which is against the resilient force of the first resilient member 130 and the left turn of the vehicle will cause anti-clockwise movement of the knuckle 140, which is against the resilient force of the second resilient member 132. The effect of the first resilient member 130 and the second resilient member 132, depending upon which side the vehicle turns, will subsequently bring the knuckle 140 and thus the wheel, in the original straight orientation. In a similar manner the wheel on the other side of the axle assembly 100 will also turn and return to the original straight orientation, when the vehicle negotiates a turn. Accordingly since the wheels are not connected by a tie rod, each wheel is free to turn independently. Moreover since the need of having a tie rod mechanism i.e. tie rod, tie rod arm, stabilizer etc, is eliminated, the disadvantages associated therewith, such as Ackermann error, are also eliminated. Furthermore, the absence of the tie rod also eliminates the likelihood of a drive shaft fouling with the tie rod. In addition, the absence of a tie rod also means that the axle assembly 100 is lighter in weight, as compared to a conventional axle assembly.
Further, during the operation of a vehicle, at high speeds it may be required to restrict the turning of the wheels, for safety purposes. The lock actuator assembly 160 of the present invention is provided to selectively lock the movement of the knuckle 140 with respect to the axle beam 102. Particularly, ECU (Electronic Control Unit) upon sensing that a threshold speed limit has been reached, actuate the lock actuator assembly 160 to alter the hydraulic or pneumatic input to the housing which will extend the actuator rod 166 and engage with the lock bracket 168 (best shown in FIG. 3). In an embodiment of the present invention the ECU actuates the lock actuator assembly 160 preferably at 60 kmph (kilometers per hour). In an alternative embodiment of the present invention the actuation the lock actuator assembly 160 can also be done manually.

The foregoing description provides specific embodiments of the present invention. It should be appreciated that these embodiment are described for purpose of illustration only, and that numerous other alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

Referral Numerals Description
100 Axle assembly
102 Axle beam
104 End portion of axle beam 102
106 End portion of axle beam 102
108 Elongated body portion of axle beam 102
110 Cylindrical bore
120 Kingpin unit
122 Kingpin
124 First end portion of the kingpin 122
126 Second end portion of the kingpin 122
130 First resilient member
132 Second resilient member
140 Knuckle
142 First arm
144 Second arm
146 Body member
148 Hollow cylindrical portion of the first arm 142
150 Hollow cylindrical portion of the second arm 144
160 Lock actuator assembly
162 Housing
164 Mounting bracket
166 Actuator rod
168 Lock bracket

We claim:
1 A self-steer axle assembly (100) for a vehicle, the axle assembly (100) comprising:
an axle beam (102);
a knuckle (140) having a first arm (142), a second arm (144) and a body member (146) carrying said first arm (142) and second arm (144); said axle beam (102) and said knuckle arms (142, 144) pivotally connected through a king pin (122); characterized in that,
at least one resilient member having a first end portion (124) connected to the kingpin (122) and a second end portion (126) connected to one of the arm of the knuckle (140), the knuckle (140) being rotatably engaged with the kingpin (122) such that said resilient member applies a resilient force against a movement of the knuckle (140) about the kingpin (122).
2. The self-steer axle assembly (100) as claimed in claim 1, wherein a first resilient member (130) and a second resilient member (132) connected to said first and second arm (142, 144) respectively.
3. The self-steer axle assembly (100) as claimed in claim 2, wherein the first resilient member (130) and the second resilient member (132) are volute springs.
4. The self-steer axle assembly (100) as claimed in claim 2, wherein the first resilient member (130) and the second resilient member (132) applies a resilient force against the clockwise and anti-clockwise movement of the knuckle respectively.
5. The self-steer axle assembly (100) as claimed in claim 1, further comprising a lock actuator assembly (160) adapted to selectively lock the movement of the knuckle (140) with respect to the axle beam (102).
6. The self-steer axle assembly (100) as claimed in claim 5, wherein said lock actuator assembly (160) controlled by an electronic controller based on the speed of the vehicle.

7. The self-steer axle assembly (100) as claimed in claim 5, wherein the lock
actuator assembly 160 includes
a housing (162) carried by the axle beam (102),
a solenoid operated actuator rod (166) associated with the housing (162), the actuator rod (166) configured to extend and retract with respect to the housing (162), and
a lock bracket (168) connected to the knuckle (140), the lock bracket (168) being capable of receiving a portion of the actuator rod (166) to selectively lock the movement of the knuckle (140) with respect to the axle beam (102).
8. The self-steer axle assembly (100) as claimed in claim 1, wherein the arm of said knuckle (140) includes a hollow cylindrical portion (148) configured to substantially receive an end portion (124) of the kingpin (122) along with said resilient member.
9. The self-steer axle assembly (100) as claimed in claim 6, wherein said hollow cylindrical portion (148) of the first arm (142) of the knuckle (140) includes a stopper member, and said resilient member engage with said stopper member.
10. A self-steer axle assembly (100) for a vehicle, the axle assembly (100) comprising:
an axle beam (102);
a knuckle (140) having a first arm (142), a second arm (144) and a body member (146) carrying said first arm (142) and second arm (144); a kingpin (122) pivotally connected to said axle beam (102) and knuckle arms (142, 144); characterized in that,
a first resilient member (130) having a first end portion connected to the first end portion (124) of the kingpin (122) and a second end portion configured to engage with the first arm (142) of the knuckle (140), such that the first resilient member (130) applies a resilient force against a clockwise movement of the knuckle (140) about the kingpin (122);
a second resilient member (132) having a first end portion connected to the second end portion (126) of the kingpin (122) and a second end portion configured to engage with the second arm (144) of the knuckle (140), such that the second resilient

member (132) applies a resilient force against an anti-clockwise movement of the knuckle (140) about the kingpin (122); and
a lock actuator assembly (160) adapted to selectively lock the movement of the knuckle (140) about the kingpin (122).