U.S. patent number RE34,057 [Application Number 07/736,853] was granted by the patent office on 1992-09-08 for steering mechanism for a zero turning radius vehicle.
This patent grant is currently assigned to Simplicity Manufacturing, Inc.. Invention is credited to Tommy A. Middlesworth.
United States Patent |
RE34,057 |
Middlesworth |
September 8, 1992 |
**Please see images for:
( Certificate of Correction ) ** |
Steering mechanism for a zero turning radius vehicle
Abstract
A driving and steering mechanism for a vehicle having a pair of
driving wheels includes a steering wheel rotatably mounted to the
vehicle and an accelerator foot pedal pivotably mounted to the
vehicle. Transmissions associated with the driving wheels include a
pivotable control arm for controlling the operation of the
transmission, which independently controls the speed and direction
of rotation of the associated wheel. The vehicle is turned by
causing one wheel to rotate faster than the other wheel. A zero
turning radius turn can be effected by causing the driving wheels
to rotate in opposite directions. The driving and steering
mechanism includes a pair of floating links pivotably connected at
one end to a respective transmission control arm. Steering links,
associated with the steering wheel, are pivotably connected to a
respective floating link distal the connection to the control link.
Accelerator links, associated with the accelerator foot pedal, are
pivotably connected to a respective floating link at a point
between the control arm and steering link pivot points. The
floating links operate to integrate outputs from the steering wheel
and the accelerator foot pedal into a pair of outputs applied to
the pair of control arms, thereby controlling the speed and
direction of rotation of a respective driving wheel in response to
the prescribed steerage and speed.
Inventors: |
Middlesworth; Tommy A.
(Sheboygan Falls, WI) |
Assignee: |
Simplicity Manufacturing, Inc.
(Port Washington, WI)
|
Family
ID: |
26861685 |
Appl.
No.: |
07/736,853 |
Filed: |
December 12, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
165760 |
Mar 9, 1988 |
4790399 |
Dec 13, 1988 |
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Current U.S.
Class: |
180/6.2; 180/236;
180/6.28; 180/6.32; 180/6.5; 280/771; 74/471XY |
Current CPC
Class: |
B62D
9/00 (20130101); B62D 11/02 (20130101); Y10T
74/20201 (20150115) |
Current International
Class: |
B62D
9/00 (20060101); B62D 11/02 (20060101); B62D
006/00 () |
Field of
Search: |
;280/771
;180/6.2,6.24,6.26,6.28,6.32,6.34,6.36,236,6.48,6.50
;74/471R,471XY |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Advertisement for Grasshopper Zero-Turning Radius Mower. .
Advertisement for Dixon Zero Turning Radius Mower..
|
Primary Examiner: Rice; Kenneth R.
Attorney, Agent or Firm: Reinhart, Boerner, Van Deuren,
Norris & Rieselbach
Claims
What is claimed is:
1. A driving and steering mechanism for a vehicle having a pair of
driving wheels, comprising:
reversible motor means for driving each one of said pair of driving
wheels, including control means for controlling the speed and
direction of rotation of each one of said pair of driving wheels
independently of the other, thereby controlling the actual speed
and actual steerage of the vehicle;
a steering mechanism operable by the operator of the vehicle to
prescribe a steerage for the vehicle and having a first output
representing said prescribed steerage;
an accelerator mechanism operable by the operator of the vehicle to
prescribe a speed for the vehicle and having a second output
representing said prescribed speed; and
integrator linkage means, disposed between said control means and
said first and second outputs, for integrating said first and
second outputs into a third output, said third output being applied
to said control means to coordinate the speed and direction of
rotation of each of said reversible motor means in response to said
prescribed steerage and said prescribed speed, and including means
for reducing said actual vehicle steerage relative to said
prescribed steerage as said prescribed speed is increased.
2. The driving and steering mechanism of claim 1, wherein:
said control means includes left and right transmissions
controlling one each of said pair of driving wheels, each of said
transmissions including a rotatable control rod, the direction and
amount of rotation of which controls the speed and direction of
rotation of an associated one of said pair of driving wheels, and a
control link affixed at one end to said control rod having an input
point at the other end of said control link; and
said integrator linkage means includes left and right integrator
linkages associated with a respective one of said left and right
transmissions, and said third output comprises a left component
output and a right component output associated with a corresponding
one of said left and right integrator linkages, each one of said
left and right integrator linkages including;
a floating link pivotably attached to said input point of said
control link at said component output at one end of said floating
link, and including a first pivot distal said component output and
a second pivot situated between said component output and said
first pivot;
a steering link pivotably connected at one end to said first output
and at its other end to said first pivot; and
an accelerator link pivotably connected at one end to said second
output and its other end to said second pivot;
wherein, said means for reducing said actual steering includes said
floating link.
3. The driving and steering mechanism of claim 2, wherein:
each of said left and right transmissions has a neutral state in
which each of said pair of driving wheels is idle;
said accelerator mechanism includes means for biasing said
mechanism to a neutral position; and
each of said accelerator links associated with a corresponding on
of said left and right integrator linkages includes adjustment
means for adjusting the length of said accelerator link so that
when said accelerator mechanism is in said neutral position each of
said left and right transmissions is in said neutral state.
4. The driving and steering mechanism of claim 1, wherein:
said accelerator mechanism includes a foot pedal pivotably mounted
to said vehicle, said foot pedal having a first portion at one end
of said pedal and a second portion at the other end of said pedal,
wherein when said first portion is depressed said second output
from said accelerator means corresponds to forward motion of the
vehicle when integrated by said integrator linkage means, and when
said second portion is depressed said second output corresponds to
reverse motion of the vehicle when integrated by said integrator
linkage means.
5. A driving and steering mechanism for a vehicle having a pair of
driving wheels, comprising:
reversible motor means for driving each one of said pair of driving
wheels, including control means for controlling the speed and
direction of rotation of each one of said pair of driving wheels
independently of the other, thereby controlling the actual speed
and actual steerage of the vehicle;
a steering mechanism operable by the operator of the vehicle to
prescribe a steerage for the vehicle and having a first output
corresponding to said prescribed steerage;
an accelerator mechanism .Iadd.separate from said steering
mechanism and .Iaddend.operable by the operator of the vehicle to
prescribe a speed for the vehicle and having a second output
corresponding to said prescribed speed, said accelerator mechanism
also having a neutral position in which no speed is prescribed;
integrator linkage means, disposed between said control means and
said first and second outputs, for integrating said first and
second outputs into an input for said control means;
wherein when said steering mechanism and said accelerator mechanism
are in a first state, said control means, in response to a first
integrated input corresponding to said first state, operates to
proportion the relative speeds of said pair of driving wheels,
and
when said steering mechanism and accelerator mechanism are in a
second state in which said accelerator mechanism is in said neutral
position, said control means in response to a second integrated
input corresponding to said second state, operates to produce
opposite directions of rotation for each of said pair of driving
wheels.
6. The driving and steering mechanism of claim 5, wherein:
said control means includes left and right transmissions
controlling one each of said pair of driving wheels, each of said
transmissions including a rotatable control rod, the direction and
amount of rotation of which controls the speed and direction of
rotation of an associated one of said pair of driving wheels, and a
control link affixed at one end to said control rod having an input
point at the other end of said control link; and
said integrator linkage means includes left and right integrator
linkages associated with a respective one of said left and right
transmissions, and said third output comprises a left component
output and a right component output associated with a corresponding
one of said left and right integrator linkages, each one of said
left and right integrator linkages including;
a floating link pivotably attached to said input point of said
control link at said component output at one end of said floating
link, and including a first pivot distal said component output and
a second pivot situated between said component output and said
first pivot;
a steering link pivotably connected at one end to said first output
and its other end to said first pivot; and
an accelerator link pivotably connected at one end to said second
output and its other end to said second pivot.
7. The driving and steering mechanism of claim 6, wherein:
said integrator linkage means further includes means for reducing
said actual vehicle steerage relative to said prescribed steerage
as said prescribed speed is increased, said steerage reducing means
including each of said floating links associated with a
corresponding one of said left and right integrator linkages.
8. The driving and steering mechanism of claim 7, wherein:
said steering mechanism includes a steering shaft rotatably mounted
in said vehicle and having a steering wheel affixed at one end,
said steering wheel being operable by the operator of the vehicle
to apply a .[.displacement.]. .Iadd.steerage input to provide
.Iaddend.to said first output;
said accelerator mechanism includes a foot pedal pivotably mounted
in said vehicle, said foot pedal being operable by the operator of
the vehicle to apply a .[.displacement.]. .Iadd.second speed input
to provide .Iaddend.to said second output;
said steering wheel and said foot pedal being operable to
simultaneously vary said first output and said second output to
produce continuous changes in said actual speed and said actual
steering when said first and second outputs are integrated through
said left and right integrator linkages.
9. A driving .Iadd.mechanism .Iaddend.and .Iadd.independent
.Iaddend.steering mechanism for a vehicle having a pair of driving
wheels, comprising:
reversible motor means for driving each one of said pair of driving
wheels, including control means for controlling the speed and
direction of rotation of each one of said pair of driving wheels
independently of the other, thereby controlling the forward/reverse
motion, actual speed, and actual steerage of the vehicle;
a steering mechanism operable by the operator of the vehicle to
prescribe a steerage .Iadd.input .Iaddend.for the vehicle and
having a first output corresponding to said prescribed steerage
.Iadd.input.Iaddend.;
an accelerator mechanism operable by the operator of the vehicle to
simultaneously prescribe a speed .Iadd.input .Iaddend.and a
forward-reverse direction for the vehicle and having a second
output corresponding to said prescribed speed .Iadd.speed
.Iaddend.and forward-reverse direction; and
integrator linkage means for integrating said .[.first and second
outputs.]. .Iadd.steerage and speed inputs .Iaddend.into .[.an.].
.Iadd.a control .Iaddend.input for said control means, whereby said
control means coordinates operation of said motor means such that
the speed and direction of rotation of each one of said pair of
driving wheels is proportioned according to said .Iadd.control
.Iaddend.input to produce .[.said.]. actual speed, .[.said.].
actual steerage and .[.said.]. forward/reverse motion of the
vehicle.
10. The driving and steering mechanism of claim 9, wherein:
said accelerator mechanism includes a foot pedal pivotably mounted
to said vehicle, said foot pedal having a first portion at one end
of said pedal and a second portion at the other end of said pedal,
wherein said first portion is depressed .Iadd.to provide said speed
input, .Iaddend.said second output from said accelerator means
corresponds to forward motion of the vehicle .Iadd.when said speed
input is .Iaddend.integrated by said integrator linkage means, and
when said second portion is depressed said second output
corresponds to reverse motion of the vehicle .Iadd.when said speed
input is .Iaddend.integrated by said integrator linkage means.
11. The driving and steering mechanism of claim 9, wherein:
said control means includes left and right transmissions
controlling one each of said pair of driving wheels, each of said
transmissions including a rotatable control rod, the direction and
amount of rotation of which controls the speed and direction of
rotation of an associated one of said pair of driving wheels, and a
control link affixed at one end to said control rod having an input
point at a first length from said one end of said control link;
and
said integrator linkage means includes;
left and right floating links pivotably attached at one end to said
input point of a respective one of said control links associated
with said left and right transmissions, each of said left and right
floating links having a first pivot at a second length from said
input point and a second pivot situated between said input point
and said first pivot at a third length from said input point;
first means for connecting said first output of said steering
mechanism to said first pivot on each of said left and right
floating links; and
second means for connecting said second output from said
accelerator mechanism to said second pivot of each of said left and
right floating links;
wherein, displacements imposed on said first output by said
steering mechanism and on said second output by said accelerator
mechanism cause said first pivot and said second pivot on each of
said left and right floating links to move in curvilinear paths
geometrically defined by said first, second and third lengths,
resulting in a corresponding rotation of each of said control rods
associated with said left and right transmissions; and
further wherein rotation of each of said control rods in one
direction produces forward motion of the vehicle, and rotation of
each of said control rods in another direction produces reverse
motion of the vehicle.
12. The driving and steering mechanism of claim 11, wherein:
rotation of each of said control rods through different angles
produces said actual steerage; and
rotation of each of said control rods in opposite directions also
produces said actual steerage in which the vehicle moves in a zero
radius turn.
13. A driving and steering mechanism for a vehicle having a pair of
driving wheels, comprising:
reversible motor means for driving each one of said pair of driving
wheels, including control means for controlling the speed and
direction of rotation of each one of said pair of driving wheels
independently of the other, thereby controlling the forward/reverse
motion, actual speed and actual steerage of the vehicle;
a steering mechanism, including a rotatable steering wheel,
operable by the operator of the vehicle to prescribe a steerage
.Iadd.input .Iaddend.for the vehicle and having a first output
corresponding to said prescribed steerage .Iadd.input.Iaddend.;
an accelerator mechanism, including a pivotable foot pedal, for
prescribing a speed .Iadd.input .Iaddend.for the vehicle and
including a second output corresponding to said prescribed speed
.Iadd.input.Iaddend.;
integrator means for integrating said first and second .[.outputs
.Iadd.inputs and said resulting first and second outputs
.Iaddend.into a third output, said third output being applied to
said control means, said integrator means being continuously
operable while the vehicle is in motion to provide changes in the
forward/reverse motion, actual speed and actual steerage of the
vehicle while said steering wheel and said foot pedal are
.Iadd.capable of being .Iaddend.simultaneously .Iadd.and
independently .Iaddend.operated by the operator of the vehicle, and
including means for preventing tipping of the vehicle by reducing
said actual steerage relative to said prescribed steerage as said
prescribed speed is increased, and by limiting the prescribed speed
to a predetermined maximum value for each prescribed steerage such
that said predetermined maximum speed value is decreased as the
prescribed steerage is increased.
14. In a vehicle having a pair of driving wheels, the improvement
comprising:
a steering mechanism rotatably mounted to the vehicle and rotatable
by the operator of the vehicle to prescribe a steerage for the
vehicle, said steering mechanism including a plate rotatable with
said mechanism and having a pair of ends;
an accelerator mechanism pivotably mounted to said vehicle and
pivotable by the operator of the vehicle to prescribe a speed for
the vehicle, said accelerator mechanism including a bracket
pivotable with said mechanism and having a pair of ends;
an independent driving and steering mechanism for each one of said
driving wheels, each of said driving and steering mechanisms
including:
a reversible motor for driving said driving wheel;
a transmission operably associated with said reversible motor for
controlling the speed and direction of rotation of said motor;
a control arm pivotably mounted at one end to said transmission and
operable to control said transmission, said control arm having an
input point;
a floating link pivotably attached to said input point of said
control arm at a control pivot at one end of said floating link,
and having a first pivot distal said control pivot and a second
pivot between said control pivot and said first pivot, wherein
alternatively one of said first pivot and second pivot operates as
a temporary fixed pivot axis for said floating link such that a
displacement imposed on the other of said first pivot and second
pivot causes said floating link to pivot about said temporary fixed
pivot axis;
a first link pivotably connected at one end of said first link to
one of said first or said second pivots and pivotably connected at
its other end to one of said pair of ends of said steering
mechanism link, whereby rotation of said steering mechanism link
causes said first link to translate, thereby imposing a
displacement on said one of said first or said second pivots;
and
a second link pivotably connected at one end of said second link to
the other of said first or said second pivots and pivotably
connected at its other end to one of said pair of ends of said
accelerator mechanism bracket, whereby pivoting of said accelerator
mechanism bracket causes said second link to translate, thereby
imposing a displacement on said other of said first or said second
pivots.
15. In the vehicle according to claim 14, the improvement
wherein:
for each of said driving and steering mechanisms;
said first link is connected at its one end to said first pivot and
said second link is connected at its one end to said second
pivot;
said input point on said control arm is at a first length from said
one end of said control arm;
said first pivot on said floating link is at a second length from
said control pivot;
said second pivot on said floating link is at a third length from
said control pivot;
wherein, displacements imposed on said first link by said steering
mechanism and on said second link by said accelerator mechanism
cause said first pivot and said second pivot on each of said
floating link to move in cirvilinear paths geometrically defined by
said first, second and third lengths, resulting in a corresponding
rotation of each of said control arm associated with said
transmission; and
further wherein rotation of said control arms associated with each
one of the driving wheels in one direction produces forward motion
of the vehicle, and rotation of said control arms in another
direction produces reverse motion of the vehicle.
16. In the vehicle according to claim 14, the improvement
wherein:
rotation of said control arms associated with each one of the
driving wheels through different angles produces steerage for the
vehicle; and
rotation of said control rods associated with each one of the
driving wheels in opposite directions also produces steerage for
the vehicle in which the vehicle moves in a zero radius turn.
17. In the vehicle according to claim 14, the improvement
wherein:
said transmissions associated with each one of the driving wheels
has a neutral state in which the driving wheel is idle;
said accelerator mechanism includes means for biasing said
mechanism to a neutral position; and
for each of said driving and steering mechanisms, said second link
includes a turnbuckle having a variable length for adjusting the
length of said second link so that when said accelerator mechanism
is in said neutral position said transmission is in said neutral
state. .Iadd.
18. A driving mechanism and an independent steering mechanism for a
vehicle having a pair of driving wheels, comprising:
reversible motor means for driving each one of said pair of driving
wheels, including control means for controlling the speed and
direction of rotation of each one of said pair of driving wheels
independently of the other, thereby controlling the actual speed
and actual steerage of the vehicle;
a steering mechanism operable by the operator of the vehicle to
prescribe a steerage for the vehicle and having a first output
representing said prescribed steerage;
an accelerator mechanism operable by the operator of the vehicle to
prescribe a speed for the vehicle and having a second output
representing said prescribed speed with said accelerator mechanism
mechanically independent of said steering mechanism; and
integrator linkage means, disposed between said control means and
first and second outputs, for integrating said first and second
outputs into a third output, said third output being applied to
said control means to coordinate the speed and direction of
rotation of each of said reversible motor means in response to said
prescribed steerage and said prescribed speed, and including means
for reducing said actual vehicle steerage relative to said
prescribed steerage as said prescribed speed is increased.
.Iaddend. .Iadd.
19. A driving and steering mechanism for a vehicle having a pair of
driving wheels, comprising:
reversible motor means for driving each one of said pair of driving
wheels, including control means for controlling the speed and
direction of rotation of each one of said pair of driving wheels
independently of the other, thereby controlling the actual speed
and actual steerage of the vehicle;
a steering mechanism operable by the operator of the vehicle to
prescribe a steerage for the vehicle and having a first output
corresponding to said prescribed steerage input;
an accelerator mechanism having a speed input and operable by the
operator of the vehicle to prescribe a speed for the vehicle and
having a second output with said accelerator mechanism mechanically
independent of said steering mechanism such that said steerage
input is provided by mechanical components different from those
components providing said accelerator input and having a second
output corresponding to said prescribed speed, said accelerator
mechanism also having a neutral position in which no speed is
prescribed;
integrator linkage means, disposed between said control means and
said first and second inputs, for integrating said first and second
outputs into an input for said control means;
wherein when said steering mechanism and said accelerator mechanism
are in a first state, said control means, in response to a first
integrated input corresponding to said first state, operates to
proportion the relative speeds of said pair of driving wheels;
and
when said steering mechanism and accelerator mechanism are in a
second state in which said accelerator mechanism is in said neutral
position, said control means in response to a second integrated
input to said control means corresponding to said second state,
operates to produce opposite directions of rotation for each of
said pair of driving wheels. .Iaddend. .Iadd.
20. A driving mechanism and an independent steering mechanism for a
vehicle having a pair of driving wheels, comprising:
a steering mechanism operable by the operator of the vehicle to
prescribe a steerage input for the vehicle and having a first
output corresponding to said prescribed steerage input;
an accelerator mechanism operable by the vehicle operator to
simultaneously prescribe a speed input and having a second output
corresponding to said prescribed speed input; and
integrator means for integrating said steerage input and said speed
input into a control input for said control means, whereby said
control means coordinates operation of said motor means such that
the speed and direction of rotation of each one of said pair of
driving wheels is proportioned according to said control input to
product the actual speed, the actual steerage and said
forward/reverse motion of the vehicle. .Iaddend. .Iadd.
21. A lawn maintenance vehicle having a pair of driving wheels,
comprising:
a pair of hydraulic motors for independently driving the driving
wheels, each of said hydraulic motors including a steering wheel
and rotatable control shaft for controlling the speed and direction
of rotation of said motor;
a steering wheel assembly including a rotatable steering shaft;
a speed control mechanism including a user-actuable speed control
member mounted for rotation around a substantially horizontal pivot
axis; and
an integrator linkage coupled to said rotatable steering shaft,
said speed control member and each of said control shafts for
integrating independent movements of said steering shaft and said
speed control member into a combined movement of said control
shafts so that pivoting movement of said speed control member
results in substantially similar changes in the operating speeds of
said hydraulic motors while rotational movement of said steering
shaft results in dissimilar changes in the operating speeds of said
hydraulic motors. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a steering mechanism for vehicles,
and particularly to vehicles employing a sharp turning radius. The
present invention also relates to steering mechanisms for vehicles
which employ a pair of independently controlled driving wheels.
A variety of motor driven vehicles applications require that the
vehicle be capable of negotiating sharp turns, such as a garden
tractor or a riding lawnmower. In vehicles of this sort, a pair of
drive wheels powered by a small horsepower motor provide the motive
force for the vehicle. In order to provide steerage for the
vehicle, the driving wheels are provided with independent controls
and with independent hydrostatic or variable speed mechanical
transmissions.
In one example of a vehicle of the type described, a steering
mechanism, such as that described in the patent to Tsuji, et al.,
U.S. Pat. No. 4,154,314, provides independent control of the speed
of each of the driving wheels, such that in negotiating a turn, one
wheel is slowly braked while the speed of the other wheel is
increased. The Tsuji, et al. steering mechanism uses a control
lever corresponding to each of the driving wheels. Lever-type
controls of this nature have several problems - for instance, they
may be difficult to control around the neutral position, that is, a
hopping action may result around neutral when the operator and/or
the control lever is moving in one direction and the vehicle is
moving in the opposite direction. Another problem is that a typical
consumer using a riding lawn mower may find it confusing to use a
lever that controls both the vehicle speed and the steering. A
steering wheel is more natural to the average consumer who has not
had much exposure to machines controlled by levers. Finally,
although the Tsuji, et al. device provides for a small turning
radius, it does not provide for a zero turning radius - that is, a
vehicle turn effectively made about the midpoint of the driving
wheel axis.
One device described in a patent to Davis, et al., U.S. Pat. No.
3,362,493, provides the capability of performing a zero turn radius
by the vehicle. However, the Davis, et al. device is a complicated
assemblage of cams, levers and linkages. In addition, a separate
forward-reverse direction control is required to change the
direction of motion of the vehicle. Finally, although the Davis, et
al. device can produce a zero turning radius, there is no provision
in Davis, et al. for a reduction in vehicle speed as the vehicle
steerage is increased. That is, when the vehicle is moving at a
zero turning radius, there is no provision for reducing or limiting
the speed the vehicle moves around the turn, thus creating a risk
of tipping the vehicle during a sharp turn.
SUMMARY OF THE INVENTION
A driving and steering mechanism for a vehicle having a pair of
driving wheels comprises a pair of reversible motors, one for each
one of the driving wheels. Each of the reversible motors includes a
mechanism for controlling the speed and direction of rotation of
each one of the driving wheels independently of the other, thereby
controlling the actual speed and actual steerage of the vehicle. A
steering mechanism is included, operable by the operator of the
vehicle to prescribe a steerage for the vehicle and having a first
output representing the prescribed steerage. An accelerator
mechanism associated with the vehicle is also operable by the
operator of the vehicle to prescribe a speed for and the
forward/reverse direction of the vehicle and has a second output
representing this prescribed speed and direction. An integrator
linkage integrates the first and second outputs into a third output
applied to the motor controlling mechanism to coordinate the speed
and direction of rotation of each of the reversible motors in
response to the prescribed steerage and the prescribed speed. The
integrator linkage is also operable to reduce the actual vehicle
steerage relative to the prescribed steerage as the prescribed
speed is increased.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a steering mechanism according
to the preferred embodiment of the present invention.
FIG. 2 is a top elevational view of the steering mechanism shown in
FIG. 1.
FIG. 3 is a top schematic view of the positions of the control arms
and floating links of the steering mechanism of FIG. 1, shown for
several prescribed speeds, turning radii and directions of vehicle
travel.
DESCRIPTION OF THE PREFERRED EMBODIMENT
For the purposes of promoting an understanding of the principles of
the invention, reference will now be made to the embodiment
illustrated in the drawings and specific language will be used to
describe the same. It will nevertheless be understood that no
limitation of the scope of the invention is thereby intended, such
alterations and further modifications in the illustrated device,
and such further applications of the principles of the invention as
illustrated therein being contemplated as would normally occur to
one skilled in the art to which the invention relates.
Referring to FIGS. 1 and 2, a vehicle steering mechanism is shown
in detail as comprising a steering mechanism 10 and an accelerator
mechanism 20 that provides input to a pair of transmissions 50R and
50L. The transmissions 50R and 50L, respectively, provide power
input to a corresponding pair of right and left driving wheels, not
shown in the figures, such as driving wheels for a typical garden
tractor. The transmissions 50R and 50L operate independently of
each other, and each may comprise a hydrostatic transmission or a
variable speed mechanical transmission, as are commonly available
in the market.
The vehicle steering system is symmetric about the vehicle
centerline, thus the system includes right and left-hand
components. Right-hand components are identified by the suffix "R"
and left-hand components by the suffix "L". For simplicity, only
the right-hand component will be described, it being understood
that the left-hand counterpart is of identical, albeit mirrored,
design.
Steering mechanism 10 includes a steering wheel 11 mounted atop a
steering shaft 12 that is rotatably mounted to the vehicle body in
a conventional fashion. The steering shaft 12 terminates distal the
steering wheel in a steering shaft plate 13. A centering plate 14
is affixed to the steering shaft plate 13, and a centering spring
15 is mounted between the vehicle body and the centering plate 14
by a conventional means, such as a peg or other similar spring
retaining device. The spring 15, in the preferred embodiment, is a
helical tension spring that has a spring constant sufficiently
strong to overcome the mechanical resistance of the steering system
herein described, in order to restore the centering plate and
steering shaft plate to its original neutral position. However, the
centering spring 15 is not so strong that the operator would be
required to exert a great deal of force in order to turn the
steering wheel 11. The centering spring 15 and centering plate 15
operate to restore the steering mechanism to the neutral steerage
position, that is, with the vehicle moving in a straight line
rather than in a turning radius.
Accelerator mechanism 20 includes a foot pedal 21 integral with a
pedal side plate 22. Pedal side plate 22 is affixed to accelerator
bracket 24 by a pedal pivot axle 23R. A second pedal pivot axle 23L
is affixed to the left-hand side of accelerator bracket 24. Both
pedal pivot axles 23R and 23L are bearingly mounted to the vehicle
body in a conventional fashion. The accelerator mechanism 20 is
spring-loaded to a neutral position so that the vehicle remains
stationary when no pressure is applied to the foot pedal 21.
In the preferred embodiment, the pedal is spring-loaded using a
neutral spring 25, which can be a single coil helical torsion
spring that is mounted over the pedal pivot axle 23R. The free ends
of the neutral spring 25 react against restoring pins 26 and 27.
Pin 26 is secured to the side plate 22 and moves with the foot
pedal 21. Pin 27 is fixed to the vehicle frame and does not move.
As the foot pedal 21 is rotated, the restoring pins 26 and 27 force
the free ends of the neutral spring 25 apart. When the foot pedal
21 is released, the torsional stiffness of the neutral spring 25
forces the restoring pins 26 and 27 into the vertical alignment, as
shown in FIG. 1.
The foot pedal 21 includes pedal sections 21A and 21B. When
pressure is applied to pedal sections 21A, the foot pedal 21
rotates in a clockwise direction around pedal pivot axle 23, which
corresponds to a forward direction of operation for the vehicle, as
translated through the linkage system, to be described herein. On
the other hand, when pressure is applied to pedal section 21B, foot
pedal 21 rotates in a counterclockwise direction, which corresponds
to a reverse direction of operation for the vehicle. Thus, the
accelerator mechanism 20 not only provides speed control for the
vehicle, but it also provides forward/reverse direction control.
Pedal sections 21A and 21B can be sloped upwardly as shown in FIG.
1, or they may be generally flat, depending upon which
configuration is most comfortable for the vehicle operator.
Each of the transmissions 50R and 50L include a vertical control
shaft, 51R and 51L, respectively. The vertical control shafts 51R
and 51L are rotated to provide control of the transmission
direction and speed of rotation. In the preferred embodiment, a
counterclockwise rotation of the right vertical control shaft 51R
(as viewed from FIG. 2) produces a forward rotation of the
transmission 50R and the corresponding right-hand drive wheel. On
the other hand, a clockwise rotation of control shaft 51L provides
for forward operation of the corresponding left-hand drive wheel.
Operation of the drive wheels in reverse is accomplished by
opposite-hand rotations of the respective control shafts.
The speed of the drive wheel is controlled by the amount of
rotation of the vertical control shaft 51R - the greater the
angular rotation of the vertical control shaft, the greater the
rotational velocity of the transmission 50R and the right drive
wheel. Since the transmissions 50R and 50L, and their respective
right and left drive wheels, are independent of each other, each
may rotate at a different rotational speed and direction. Turning
the vehicle is accomplished by causing the right and left drive
wheels to rotate at different rotational speeds. For instance, for
a gradual right-hand turn, both transmissions 50R and 50L, and
their respective drive wheels, are rotating in the same direction
corresponding to the forward direction of travel for the vehicle.
However the left transmission 50L, and left drive wheel, rotate at
a faster rotational speed than their right-hand counterparts, The
amount of steerage, or the sharpness of the turn, is dictated by
the speed differential between the right and left-hand transmission
50R and 50L and associated drive wheels. The larger the speed
differential between the right and left-hand drive wheels, the
sharper the turn.
The vehicle can be caused to turn about one of the drive wheels by
stopping the rotation of that drive wheel and driving the opposite
drive wheel. In a typical lawn tractor, this type of turn is the
sharpest turn permitted by the steering system for the vehicle.
However, greater steerage or sharper turn angles are desirable and
beneficial. In order to effect sharper turn angles, the right and
left-hand drive wheels must rotate in opposite directions. When the
drive wheels are oppositely rotating, the vehicle turns about a
point along the centerline of the vehicle intersecting the axis of
the drive wheels. In the preferred embodiment, this "zero turn
radius" is generated by rotating the right-hand vertical control
shaft 51R in one direction and the left-hand vertical control shaft
51L in the other direction, which causes the respective
transmissions 50R and 50L to rotate in opposite directions as well
as their associated drive wheels. In order to accommodate the sharp
turning angles, the vehicle of the preferred embodiment includes
caster-type ground-engaging wheels, other than the drive wheels.
These caster-type wheels, not shown in the figures, are capable of
a 360.degree. rotation so as not to interfere with the vehicle
turning action.
The rotation of the vertical control shaft 51R (as well as control
shaft 51L) and, consequently, the direction and speed of rotation
of the transmission 50R (and 50L) and the associated drive wheel,
is controlled by a set of linkages and links, shown in detail in
FIG. 2. A control arm 30R is affixed to vertical control shaft 51R
and rotates with that shaft to control the manner of operation of
transmission 50R. A floating link 32R is pivotably attached to
control arm 30R at control pivot point 31R. The floating link 32R
is "floating" in the sense that it is not connected to a fixed
pivot point, that is, a pivot point fixed in the vehicle, such as
the pivot point for control arm 30R (i.e., vertical control shaft
51R). As will be described herein, floating link 32R rotates about
a variety of temporary pivot points depending upon the state of the
steering mechanism 10 and the accelerator mechanism 20.
Foot pedal link 40R attaches to floating link 32R at accelerator
pivot point 33R. Foot pedal link 40R spans between floating link
32R and the accelerator mechanism 20, connecting to a spanner
bracket 43R which is pivotably mounted to accelerator bracket 24 at
front pivot point 44R. Thus, as the foot pedal 21 is depressed, the
pedal rotates around pedal pivot axle 23R, which in turn causes
accelerator bracket 24 to rotate about the same axle. As the
accelerator bracket 24 rotates, it imparts a fore and aft motion
(as designated by the heavy arrows in FIG. 2) to the spanner
bracket 43R and the foot pedal link 40R. Since the front pivot
point 44R moves along an arc as the accelerator bracket 24 is
rotated, the spanner bracket 43R pivots relative to the accelerator
bracket 24 to allow the foot pedal link 40R to remain unbent during
the operation of the accelerator mechanism. As the foot pedal 21 is
depressed, the foot pedal link 40R moves either fore or aft,
depending upon which section 21A or 21B of the foot pedal is
depressed. As the foot pedal link 40R moves fore and aft, the
accelerator pivot point 33R on floating link 32R also moves fore
and aft. The ultimate effect of this fore and aft motion of
accelerator pivot point 33R on the motion of control arm 30R can
only be determined with reference to the actuation state of the
steering mechanism 10.
Actuation of the steering mechanism 10 provides input into the
steering system through a steering link 46R that is pivotably
attached to floating link 32R at steering pivot point 34R situated
at the end of the floating link distal the control pivot point 31R.
The steering wheel link 46R also attaches to steering shaft plate
13 at steering front point 47R. With this arrangement, as steering
wheel 11 and steering shaft 12 are rotated, steering front pivot
point 47R moves fore and aft about an arc relative to the axis of
the steering shaft 12. As the steering front pivot point 47R
rotates, steering wheel link 46R is moved either fore or aft,
depending upon the direction of rotation of the steering wheel
11.
As steering link 46R moves fore and aft, steering pivot point 34R
on floating link 32R also moves fore and aft. Like the foot pedal
link 40R, the steering link 46R is pivotably mounted to the
floating link and the steering shaft, to prevent any bending of the
steering link during operation of the steering mechanism. It will
be noted that with both the foot pedal link 40R and the steering
link 46R each will translate somewhat within their respective
horizontal planes, while moving fore and aft, in response to
operation of the respective accelerator and steering
mechanisms.
In the present invention, floating link 32R acts as an integrator
to combine the inputs from the steering mechanism 10 and the
accelerator mechanism 20. The floating link 32R senses the steering
and accelerator inputs, as prescribed by the vehicle operator, and
integrates the two inputs into a single output at the control pivot
point 31R. This output at control pivot point 31R controls the
rotation of control arm 30R and, consequently, the rotation of
vertical control shaft 51R. The operation of this linkage
mechanism, and, in particular the floating link 32R, is described
with reference to the state diagrams shown in FIG. 3. In the state
diagrams, both the right and left-hand portions of the steering
system are shown, since, as previously described, the vehicle
steerage is determined by the relative speed and direction of
rotation of the right and left drive wheels.
In the neutral state, represented by "State 1" in FIG. 3, the
control arms 30R and 30L and floating links 32R and 32L are in
linear alignment generally parallel to the axle of the drive
wheels. The phantom line 37 corresponds to the accelerator pivot
neutral position and is aligned with the neutral position of
accelerator pivot point 33R as shown in "State 1". Likewise,
phantom line 38 represents the steering pivot neutral position and
is aligned with the neutral position of steering pivot 34R in
"State 1". These phantom lines are provided to clearly illustrate
the displacement of the pivot points 33R and 34R during the
operation of the steering linkage system.
"State 2" in FIG. 3 represents the forward straight-ahead motion of
the vehicle. In this state, the steering mechanism is maintained in
its neutral position, while the foot pedal 21 of the accelerator
mechanism 20 is depressed at the forward portion 21A. Since the
steering mechanism is not being utilized, steering pivot point 34R
acts as a temporary pivot point for the floating link 32R. Thus, as
the accelerator foot pedal 21 is depressed, the foot pedal link 40R
and 40L move aft, thereby displacing the accelerator pivot points
33R and 33L aft. As these pivot points are moved aft, the floating
link 32R rotates about steering pivot point 34R, causing the
control pivot point 31R to be displaced in the aft direction. As a
result, control arm 30R is rotated in the counterclockwise
direction which causes vertical control shaft 51R to rotate in the
counterclockwise direction leading to a forward rotation of the
right drive wheel. Similarly, the left control arm 30L is rotated
in the clockwise direction, corresponding to a forward rotation of
the left drive wheel.
When a forward right turn is prescribed by the operator of the
vehicle, the steering shaft 12 of the steering mechanism 10 is
rotated, causing the steering wheel plate 13 to rotate. As the
steering wheel plate 13 rotates, the right steering link 46R moves
aft while the left steering wheel link 46L moves forward, which
causes the right steering pivot point 34R to move aft and the left
steering pivot point 34L to move forward, as shown in "State 3" in
FIG. 3. If the foot pedal 21 is maintained at a constant prescribed
speed orientation, accelerator pivot points 33R and 33L will act as
temporary pivot points for the floating links 32R and 32L as input
is received from the steering mechanism 10. It is seen in the
diagram for "State 3" that is a right turn prescribed by the
steering mechanism 10 causes the control pivot point 31L in the
left-hand side of the system to move farther aft than the control
pivot point 31R of the right-hand portion of the system. As
described above, this causes a speed differential between the right
and left drive wheels, with the left-hand drive wheel rotating
faster than the right-hand drive wheel. Conversely, a forward
left-hand turn is effected by turning the steering mechanism
steering wheel 11 in the opposite direction, that is,
counterclockwise, which ultimately causes the right drive wheel to
rotate faster than the left drive wheel.
In reverse operation, as illustrated in "State 5", the vehicle
operator depresses the reverse portion 21B of the foot pedal 21.
This, in turn, causes the right and left foot pedal links 40R and
40L to move in the forward direction. If no steerage is applied to
steering mechanism 10, steering pivot points 34R and 34L operate as
temporary pivot points for floating link 32R and 32L, to translate
the input from the accelerator mechanism 20 to a forward
displacement of control arms 30R and 30L and vertical control
shafts 51R and 51L. The resulting clockwise and counterclockwise
rotations of the vertical control shafts 51R and 51L, respectively,
cause the transmissions 50R and 50L to move the drive wheels
concurrently in their reverse directions.
A zero turning radius turn is represented by "State 6" and "State
7" in FIG. 3. In a zero turning radius turn, as used in the present
disclosure, the vehicle turns about a point at the midpoint of the
drive wheel axis. That is, the vehicle turns about the point Z as
defined by FIG. 2. In these states, the steering wheel 11 of the
steering mechanism 10 is rotated sharply in either the clockwise or
counterclockwise directions, depending upon the direction of turn
desired. It can be noted, upon an examination of "States 6" and "7"
in FIG. 3, that the accelerator pivot points 33R and 33L are
exactly oriented upon the accelerator pivot neutral line 37. Thus,
it is apparent that the speed and direction control of the right
and left-hand transmissions 50R and 50L are determined solely by
input from the steering mechanism 10. The accelerator pivot points
33R and 33L act as temporary pivot points for the floating links
32R and 32L as the steering pivots 34R and 34L are moved fore and
aft by the steering links 46R and 46L, respectively. Thus, as
steering wheel 11 is rotated fully to the clockwise direction, for
instance, to cause a zero radius right-hand turn, as represented by
"State 6" in FIG. 3, the left steering link 46L is moved forward
while the right steering link 46R is moved aft to the fullest
extents possible given that the steering pivot points 34R and 34L
are, for all intents and purposes, fixed relative to the
vehicle.
In the preferred embodiment, accelerator pivot point 33R is
situated on floating link 32R between control pivot point 31R at
the outboard end of link 32R and the steering pivot point 34R at
the inboard end of the floating link. The distance between control
pivot point 31R and accelerator pivot point 33R is roughly
one-fourth the distance between control pivot point 31R and the
steering pivot point 34R, in the preferred embodiment.
Consequently, movement of the accelerator pivot point 33R (with the
steering pivot point temporarily fixed) translates to a rotation of
control arm 30R through an angle approximately four times larger
than for an equal movement of the steering pivot point 34R (with
the accelerator pivot point temporarily fixed), as is apparent from
the application of simple geometric principles.
The present invention also contemplates switching the locations of
the accelerator and steering pivot points on floating link 32R, as
changing the distances of these pivot points from the control pivot
point 31R. Changes of this nature will alter the manner in which
the speed and steerage prescribed by the vehicle operator is
translated by the floating link 32R and control arm 30R into actual
vehicle motion. For instance, moving the steering pivot point 34R
closer to the control pivot point 31R will increase the effect of
movement of the accelerator and steering pivot points and will
reduce the difference in control arm rotation due to equal
movements of the accelerator pivot point and the steering pivot
point.
It is seen from the state diagrams in FIG. 3 that the floating
links 32R and 32L play a primary role in controlling the speed and
direction of rotation of the left and right-hand transmissions 50R
and 50L and the respective left and right-hand drive wheels. The
floating links 32R and 32L act as integrators to receive the input
from the steering mechanism 10 and the accelerator mechanism 20. In
addition, the use of the floating links 32R and 32L helps to limit
the amount of steerage available when the accelerator pedal is
fully depressed, and to force a reduction in the speed prescribed
by the operator on the accelerator pedal when increased steerage is
desired. In other words, the steering system of the present
invention operates to prevent an excessive combination of actual
speed and actual steerage, as a safety precaution to prevent
tipping the vehicle in a high speed turn.
Referring to FIG. 3, and in particular, "State 2" illustrated in
FIG. 3, when a forward motion has been prescribed by the
accelerator mechanism 20, control arm 30 is situated at an angle
.alpha. relative to its neutral position. When the steering
mechanism 10 is actuated, the angle of the control arm 30R relative
to its neutral position is reduced to an angle .beta.- that is,
angle .beta. is less than angle .alpha.. Likewise, at the left-hand
component of the steering system, the control arm 30L moves to an
angle .gamma., which represents an increase from the neutral angle
.alpha. that equals the change in angle for control arm 30R (i.e.,
.alpha.-.beta.). The changes in angles of the control arms 30R and
30L from their neutral steering angles .alpha. correspond directly
to a reduction in the rotational speed of the transmission 50R and
the right drive wheel and an increase in the rotational speed of
the transmission 50L and the left drive wheel. As previously
explained, this speed differential between the right and left drive
wheels, which is equivalent to the difference between the angles of
the two control arms (i.e., .gamma.-.beta.), causes the vehicle to
turn through a certain radius corresponding to the amount of
steerage selected. As the vehicle speed is increased, the neutral
angle .alpha. of the control arms 30R and 30L is increased and, for
the same prescribed steerage, the angles .beta. and .gamma. are
increased. However, the difference between the control arm angles,
.gamma.-.beta., is decreased due to the geometry of the links,
which translates directly to a reduction in actual steerage of the
vehicle.
The geometry of the steering linkage of the present invention also
serves to force a reduction in prescribed speed when a sharper
turning radius, or greater steerage, is desired by the operator. At
a given prescribed steerage, the lengths of the control arm 30R,
floating link 32R, steering link 46R and accelerator link 40R
geometrically restricts the amount of fore and aft motion possible
for the accelerator link 40R. Moreover, in a zero radius turn, such
as shown in `State 6` in FIG. 3, the vehicle speed is dictated
solely by the movement of the steering mechanism 10, with the
accelerator mechanism 20 situated in its neutral position. Any
prescribed speed will move the accelerator pivot points 33R and 33L
aft, which will move the control arms 30R and 30L counterclockwise
and clockwise, respectively. With enough counterclockwise motion,
control arm 30R will rotate from the orientation in `State 6`,
corresponding to a reverse rotation of the right drive wheel, to an
orientation such as shown in `State 2`, corresponding to a forward
rotation of the right drive wheel. At this point, both drive wheels
are rotating in the forward direction and the zero radius turn has
been eliminated. In order to restore the zero radius turn, the
vehicle operator must reduce the prescribed acceleration applied to
the accelerator mechanism 20. From the foregoing description of the
operation of the steering system, it is apparent that the linkage
mechanism provides a significant safety feature to prevent a
combination of high speed and sharp turning radius, which reduces
the risk of the vehicle tipping over or of the operator losing
control of the vehicle.
The foot pedal links 40R and 40L are each provided with a
turnbuckle 41R and 41L, respectively, to adjust the effective
length of the foot pedal links. The turnbuckles 41R and 41L are
rotated to adjust the neutral position of the control arms 30R and
30L when the spring-loaded accelerator foot pedal 21 is in its
neutral position. Alternatively, spanner brackets 43R and 43L can
be L-shaped with a bore through one leg of the L-shape. The foot
pedal links 40R and 40L can be provided with a threaded end that is
secured through the bore in the spanner bracket by threaded nuts on
either side of the bracket. Thus, the length of the foot pedal
links 40R and 40L can be adjusted by threading the threaded end of
the pedal link further onto the threaded nuts.
In addition, the accelerator bracket 24 is provided with adjusting
slots 28R and 28L within which front pivot points 44R and 44L
reside. Thus, when the front pivot points 44R and 44L are moved
upward in slots 28R and 28L, the maximum input provided by the
accelerator mechanism 20 is reduced relative to when the front
pivot points are at the lower end of the adjusting slots. The
adjusting slots 28R and 28L can be used to compensate for
variations in the transmission output.
In the preferred embodiment, the front pivot points 47R and 47L of
the right and left steering links 46R and 46L, are shown in FIG. 2
as comprising a post extending through a bore in the steering shaft
plate 13. In another aspect of the present invention, the front
pivot points 47R and 47L can include a ball joint, rather than the
post. The ball joints allow the entire steering mechanism 10 to be
rotated fore and aft, in the manner of a tilt steering wheel, to
make it easier for the operator to get on and off the machine, and
to allow the operator to place the steering wheel at more
comfortable orientation. The use of a ball joint ensures that the
steering shaft plate 13 will continue to operate even when the
steering mechanism 10 has been tilted fore or aft.
The steering mechanism of the present invention provides
significant advantages over the steering mechanisms of the prior
art devices. One benefit is that the steerage, speed, and direction
of operation of the vehicle is controlled entirely through a
steering wheel and an accelerator foot pedal, mechanism that are
familiar to most operators of the vehicle. Another benefit is that
the direction of operation, that is, forward or reverse, is
controlled by the foot pedal, rather than by a separate shifting
mechanism. This feature not only simplifies the mechanical
apparatus required for the present steering mechanism, it also
simplifies the operation of the vehicle from the operator's point
of view. Another principal benefit, as described more fully above,
is the safety feature provided by the linkage mechanism, and
particularly the floating link, that prevents a potentially
dangerous combination of actual vehicle speed and actual steerage,
regardless of the prescribed speed and steerage requested by the
vehicle operator. Yet another benefit of the present invention is
that a zero turning radius can be provided by the steering
mechanism without any intervention from the operator other than
prescribing a maximum steering angle on the steering mechanism.
Moreover, the speed and steerage changes can be simultaneous, which
enhances the maneuverability of the vehicle within which this
steering mechanism is contained.
While the invention has been illustrated and described in detail in
the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only the preferred embodiment has been shown
and described an that all changes and modifications that come
within the spirit of the invention are desired to be protected.
* * * * *