Wheel assembly for a vehicle

BACKGROUND OF THE INVENTION

This invention relates to a wheel assembly for a vehicle, and more specifically, the invention relates to a wheel assembly particularly useful for vehicles which frequently make tight turns.

Axle assemblies having dual wheels on either end have been used to increase the load bearing capability of heavy duty vehicles. Typically the pair of wheels on each end of the axle assembly are secured together so that they rotate together about an axis. Some heavy duty vehicles, such as lift trucks, undergo numerous turning maneuvers which wear the tires significantly. The tire wear is caused when the tires scrub, or drag, since the wheels that are secured together must travel different distances at the inside and outside of the turning radius. Sharper turns cause increased tire scrub. This problem is compounded because wheels with very large tires have a wide footprint. Different portions of the tire's footprint must travel different distances throughout the turning radius. That is, the outside of the tire must rotate a greater distance than the inside of the tire.

Tire wear and maintenance on heavy duty lift trucks due to scrub cost thousands of dollars annually per vehicle. A dual wheel assembly design has been proposed that uses hydraulic motors to independently drive each wheel. However, the design uses the operation of the suspension to reduce scrubbing and is not suitable for heavy vehicle applications. Furthermore, the hydraulic motors are not individually controlled so that the wheels cannot be rotatingly driven at different speeds relative to one another to travel along different radial distances and reduce scrubbing during vehicle turns. Therefore, what is needed is a wheel assembly with independently rotatable wheels that is also capable of reducing scrubbing across the width of each tire.

SUMMARY OF THE INVENTION AND ADVANTAGES

The present invention provides a multi-disc wheel assembly for a vehicle that includes a plurality of narrow discs assemblies that form a wheel assembly. The plurality of narrow disc assemblies include first and second narrow disc assemblies. A first independent drive mechanism applies a rotational force to the first narrow disc assembly to produce a first speed. A second independent drive mechanism applies a rotational force to the second narrow disc assembly to produce a second speed unequal to the first speed during a vehicle turn to minimize wheel assembly scrub.

Accordingly, the above invention provides a wheel assembly with independently rotatable wheels that is also capable of reducing scrubbing across the width of each tire.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1

is a front view of a vehicle utilizing one embodiment of the present invention wheel assembly; and

FIG. 2

is a schematic view of another embodiment of the present invention wheels assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A multi-disc wheel assembly

10

for a vehicle

12

, such as a heavy lift truck, is shown in FIG.

1

. Heavy lift trucks

12

, like the one shown, have a lift mechanism

13

and are used for lifting very heavy loads, such as a sea container

14

. Heavy lift trucks

10

typically have a rather wide wheel base with wide, non-steerable front wheels for supporting the load on a road surface

16

. The multi-disc wheel assemblies

10

of the present invention are an improvement over conventional wheel assemblies, which experience a significant amount of tire wear due to scrub. Preferably, the wheel assembly

10

has a width that is approximately equal to a conventional wheel assembly width for a heavy lift truck. It should be appreciated that the present invention wheel assembly

10

may be suitable for any vehicle application having wide tires that undergo a significant amount of turning.

The vehicle

10

has an axle assembly

18

with opposing ends

20

that may support multiple wheel assemblies

10

depending upon the load requirements of the particular vehicle. The axle assembly

18

may be one unitary structure or two separate stub axles. The axle assembly

18

has at least one wheel assembly

10

supported on each of the ends

20

. A plurality of narrow discs assemblies

22

form each wheel assembly

10

. The wheel assemblies

10

shown in

FIG. 1

each include a first

22

a

and second

22

b

narrow disc assemblies.

Referring now to

FIG. 2

, a wheel assembly

10

is shown having first

22

a,

second

22

b,

third

22

c,

and fourth

22

d

narrow disc assemblies supported on an axle

18

. The second narrow disc assembly

22

b

is interposed between the first

22

a

and third

22

c

narrow disc assemblies, and the third narrow disc assembly

22

c

is interposed between the second

22

b

and fourth

22

d

narrow disc assemblies. Preferably, the four narrow disc assemblies together are approximately the width of a conventional wheel. It is to be understood that any number of narrow disc assemblies

22

may be used.

Each disc assembly

22

has an independent drive mechanism

26

, preferably an electric motor and even more preferably an induction motor, for driving the disc assemblies

22

at slightly different speeds during a vehicle turn to reduce scrub. Preferably, the induction motors

26

are also used as the primary drive mechanisms for the vehicle. The induction motors

26

have a stator

28

and a rotor

30

that has a rim

32

with a tire

34

. An internal combustion engine may generate the electric power needed for the induction motors. Each rim

32

and tire is driven by its respective independent drive mechanism

26

so that different speeds may be obtained. Scrubbing across the width of each tire

34

is reduced compared to a conventional wheel and tire because the present invention tires

34

are narrower. Scrubbing is further reduced by independently driving each tire

34

at the speed needed to travel the distance along its radial path.

The vehicle turn has an inner R

i

and outer R

o

radius, and the first

22

a

and fourth

22

d

narrow disc assemblies are arranged at the inner R

i

and outer R

o

radii, respectively. The second

22

b

and third

22

c

narrow disc assemblies also have a turning radius, which is not shown for clarity. In operation, the independent drive mechanisms

26

for each narrow disc assembly

22

a,

22

b,

22

c,

22

d

apply a rotational force to is respective narrow disc assembly to produce first, second, third, and fourth speeds, respectively. The second speed is greater than the first speed, the third speed is greater than the second speed, and the fourth speed is greater than the third speed for the vehicle turn, shown in FIG.

2

. In this manner, each narrow disc assembly

22

may rotate at the speed needed to travel the distance along its radial path so that tire wear from scrubbing is reduced.

The multi-disc wheel assembly

10

may also include a controller

38

connected to the induction motors

26

and a sensor

40

connected to the controller

38

for sensing a vehicle turning radius. The sensor

40

sends a turning radius signal

42

to the controller

38

and the controller

38

produces a speed request signal

44

to the induction motors

26

for producing the desired speeds for each narrow disc assembly

22

. The sensor

40

may measure the vehicle turning radius at a steering input device, or in any other suitable manner.

The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.