Land vehicles – Body elevation or tilt – Terrain slope compensation
Reexamination Certificate
1999-01-27
2001-03-06
Dickson, Paul N. (Department: 3618)
Land vehicles
Body elevation or tilt
Terrain slope compensation
C280S006157, C280S124161
Reexamination Certificate
active
06196555
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a roll-resistant hydraulic suspension system for a load handling vehicle.
2. Description of Related Art
In recent years, large load carrying vehicles, such as ore carriers, have become even larger so that they carry increasingly heavy loads. At the same time, such vehicles have become equipped with larger engines, giving the vehicles the capacity to operate at relatively high speeds. These greater loads and higher speeds have accentuated a shock-dampening problem. In particular, it has been found that such vehicles when heavily loaded and operated at high speeds on rough terrain, have a tendency to roll or tilt to one side, especially in turns.
More specifically,
FIGS. 1-7
and
10
depict schematically a conventional heavy load carrying vehicle
10
, such as an articulated underground mining vehicle for carrying heavy ore loads, for which the present invention is intended to be used. As best shown in
FIG. 1
, the vehicle includes a front vehicle or tractor portion
10
a,
and a rear load-carrying portion
10
b
interconnected at a steerable vertical hinge axis
11
.
Front vehicle portion
10
a
includes a pair of wheels
12
a
,
12
b
(
FIG. 3
) mounted at the opposite ends of an axle
14
carried by a generally V-shaped subframe
16
. Subframe
16
is connected to the main vehicle chassis
17
(see
FIGS. 3-7
) at a spherical bearing
18
such that the subframe
16
is effectively cantilevered forward from and beneath chassis
17
. A pair of hydraulic suspension cylinders
26
a
,
26
b
interconnect the free ends of the subframe
16
and main chassis
17
to isolate the chassis from shock loads transmitted to the subframe from the ground and to control the height of the chassis
17
above the subframe. By adjusting the hydraulic pressure and/or volume at the top ends of cylinders
26
a
and
26
b
, the height of the chassis
17
above the subframe
16
can be adjusted. Such height adjustments are numerous during operation of the vehicle because of the large weight difference between a loaded and unloaded vehicle and the need to maintain appropriate clearance between the subframe
16
and chassis
17
during all phases of loading and unloading of the vehicle.
Because of the spherical bearing-mounting of subframe
16
relative to chassis
17
, the subframel
6
, as viewed in elevation (FIG.
5
), can pivot vertically in the directions of arrow
20
about spherical bearing
18
. Similarly, as viewed from the front, as shown in
FIGS. 6 and 7
, any force encountered by one wheel, such as wheel
12
a
traveling over a rock, urges that wheel upwardly relative to the chassis, causing axle
14
to pivot in the directions of arrows
22
about the longitudinal axis
19
of the vehicle through spherical bearing
18
, thus urging opposite wheel
12
b
downwardly relative to the chassis about the same axis. Suspension cylinders
26
a
and
26
b
when hydraulically-coupled to accumulators
28
a
,
28
b
are intended to dampen such vertical movements of the axle and subframe caused by the vehicle traveling over rough, uneven terrain.
One known hydraulic circuit
39
for such suspension systems is shown schematically in FIG.
10
. The pressure sides of both hydraulic cylinders
26
a
,
26
b
are continuously hydraulically interconnected and share common pressure from accumulators
28
a
,
28
b
though hydraulic lines
43
. Similarly, the exhaust sides of both cylinders are hydraulically interconnected through hydraulic lines
45
. The system also includes a pressure bleed down valve
60
for de-pressurizing the system for maintenance.
A suspension height sensor
25
(see
FIGS. 8 and 9
) commands the leveling valve
46
. When height sensor
25
senses that the height of the vehicle's chassis relative to its subframe is at an optimal height, leveling valve
46
is spring-centered in its neutral position shown in
FIG. 10
to isolate the hydraulic lines
43
from pressure source
54
, thereby maintaining the same pressure and volume in the pressure sides of both hydraulic cylinders
26
a
,
26
b
to maintain the optimal height.
Should the sensed height of the vehicle be too high, the leveling valve
46
is mechanically-commanded to the left in
FIG. 10
to a position that connects hydraulic lines
43
with storage tank
56
, thereby allowing fluid in lines
43
to vent to the tank
56
and reducing pressure at the top ends of both cylinders and in accumulators
28
a
,
28
b
to lower the chassis relative to the subframe until the chassis is at the desired height as sensed by the height sensor
25
, at which point valve
46
returns to its spring-centered neutral position.
Should the sensed height of the vehicle be too low, the leveling valve
46
is mechanically-commanded to the right in
FIG. 10
to a position that connects hydraulic lines
43
with a hydraulic pressure source
54
, allowing hydraulic fluid under pressure to be transmitted thorough hydraulic lines
43
to the top ends of both cylinders
26
a
,
26
b
and to the accumulators
28
a
,
28
b
. This causes the cylinders to extend to raise the chassis to the desired level as sensed by the height sensor
25
, at which position leveling valve
46
returns to its spring-centered neutral position. Thus, although pressure in the hydraulic cylinders and accumulators, and thus the height of the chassis, can be modulated with the existing circuit, the hydraulic cylinders
26
a
,
26
b
and the respective accumulators
28
a
,
28
b
remain hydraulically interconnected during normal operation of the vehicle.
To illustrate, when a heavily loaded such vehicle turns at high speed, or when one wheel hits a bump, the force generated has a tendency to cause the chassis to roll or tilt to one side relative to the axle and subframe (see FIG.
7
). With a conventional hydraulic circuit for the suspension system, this tendency to roll is accentuated because the pressure sides of both suspension cylinders are hydraulically interconnected and share a common source of pressure fluid, such as accumulators
28
a
,
28
b
. Similarly, the exhaust sides of both cylinders are interconnected. Thus, for example and as shown in
FIG. 7
, when chassis
17
begins to roll to the right (or the right wheel
12
b
moves upward relative to the chassis) as shown, it tends to retract cylinder
26
b
, displacing fluid from the pressure side of that cylinder
26
b
. This displaced fluid is transmitted to the pressure or top side of the other suspension cylinder
26
b
, which tends to extend that cylinder as shown, and thereby accentuating the tendency of the chassis to roll to the right.
U.S. Pat. No. 5,443,283 to Hawkins discloses an independent swing arm suspension with one leveling valve for each wheel. In the Hawkins suspension, each wheel is independently suspended at all times and requires its own leveling valve. Thus, the two cylinders corresponding to each of an opposing pair of wheels can not be operated together to adjust the height of the vehicle uniformly.
U.S. Pat. No. 4,971,353 to Buma, U.S. Pat. No. 4,593,931 to Shiratori, and U.S. Pat. No. 5,642,282 disclose various independent suspension systems. U.S. Pat. No. 2,964,333 discloses a conventional leveling valve construction.
None of these prior systems reflects an appreciation of the roll problem. The suspension system having a hydraulic circuit according to the present invention, described below with reference to
FIGS. 8
,
9
, and
11
-
13
overcomes this problem by resisting the tendency of the chassis to roll relative to the subframe.
SUMMARY OF THE INVENTION
Fulfilling the foregoing need is the primary objective of the invention. More specific objectives of the invention are to provide a roll-resistant hydraulic suspension system for a load handling vehicle in which the hydraulic circuit:
(1) hydraulically isolates from one another the hydraulic suspension cylinders suspending opposite sides of the vehicle chassis from a common axle during normal vehicle operation to resist any tendency of the chassis to roll
Atlas Copco Wagner, Inc.
Dickson Paul N.
Klarquist Sparkman Campbell & Leigh & Whinston, LLP
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