Note: Descriptions are shown in the official language in which they were submitted.
e--~
This invention relates to suspension systems for tilt cab trucks.
Specifically, it relates to ~he shock absorber and spring components of such
systems.
This tilt cab suspension system according to this invention comprises
integral shock absorber and air spring assemblies located between the truck
frame and the cab. Integral shock absorber and air spring assemblies according
to the invention can be located at either the front or the rear of the cab.
An embodiment of integral shock absorber and air spring assembly speci-
fically adapted to be located at the front of the cab features a hydraulic lock
which locks the suspension system in the full down position for the entire tilt
cycle. At the start of a cab tilt cycle~ the vertical component of force from
the tilt cylinder~s) lifts the cab to the top of the suspension members' stroke.
In this position the cab is unstable and, as more weight is transferred to the
suspension members, there is a danger that one or both sides of the cab may fall
through the stroke of the cab suspension. This is particularly likely to occur
when the cab is being pulled back from the over-center position, since the tilt
cylinders have a force component that pulls down on the suspension members during
that portion of the tilt cycle. Damage to the cab and to truck chassis compon-
ents such as the radiator is likely to occur if the cab falls in this manner.
The integral shock absorber and air spring assembly disclosed herein eliminates
this problem~
Summary of the Invention
The invention provides an integral shock absorber and spring assembly
comprising:
(a) a first base;
~b~ a rod projecting from said first base;
(c) a second base;
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a cylinder projeeting from said seeond base, said
eylinder being closed at the end remo-te frorn said seeond base by a
cap through which said rod slidingly projects;
a piston carried by said rod within said eylinder, said
piston dividing the interior spaee of said eylinder into a firs-t
bore whieh deereases in volume during the upstroke of said piston
in said eylinder and a second bore which decreases in volume during
the downstroke of said piston in said cylinder;
a hydraulic fluid circuit comprising a reservoir for
hydraulie fluid, a first path of fluid eommunieation through said
piston; a second path of fluid communication through said cylinder
and posit~oned near an end of said cylinder towards which said
piston is direeted during an ups-troke and operably eonneeted -to
said reservoir, said second path of fluid communication having a
plurality of axially-spaced openings whereby -the effeetive eross-
seetional area of the sum of said openings is redueed as said
piston nears the end of an upstroke, said seeond pa-ths of fluid
eommunieation permitting a slower flow rate than said first pa-th of
fluid eommunieation, and a third path of fluid eommunieation through
said eylinder and positioned near an end of said eylinder -towards
whieh the piston is direeted during a downstroke and operably eon-
neeted to said reservoir, said third path of fluid eommunication
having a plurality of axially spaeed openings whereby the effeetive
eross-seetional area of the sum of said third path of fluid eommuni--
eation is redueed as said piston nears the end of i-ts downs-troke,
and wherein said third pa-th of fluid eomrnunieation permits a slower
flow rate during -the downstroke of said piston -than said first path
o fluid communication so -that during an ups-troke fluid will be
directed from said firs-t fluid pathway through said second :Eluid
pathway to said reservoir and from said reservoir through said
third pathway or fluid communication and into said second bore,
and during a piston downstroke, fluid exi-ts said second bore
through said first path of fluid communica-tion in said piston;
a one-way valve posi-tioned in said first path of fluid
communication which permits Elow toward said firs-t bore but does
not permit flow in the opposite direc-tion;
a remotely adjustable control valve positioned in said
hydraulic fluid circuit; and
a spring surrounding said rod and said cylinder connected
a-t one end to said first base and disposed to hold said piston at
an intermediate position in said cylinder.
Brief Descri tion of the Drawin s
P g~
Figure 1 is a side view of a -tilt cab truck incorporating
the present invention.
Figure 2 is a fragmentary side view of one type of prior
art which the present invention improves on.
Figure 3 is a schematic drawing of a first embodiment of
the integral shock absorber and air spring assemblies.
Figure 4 is a sectional view oE the shock absorber and
air spring assembly shown in Figure 3.
Figure 5 is a view along the lines of 5 - 5 in E'igure 4.
Figure 6 is a bottom plan view of Figure 4.
Figure 7 is a sectlonal view of the shock absorber sub-
assembly of a second embodiment of the subjec~ invention, showing
the piston in upward travel.
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Figure 8 is a sectional view of the second embodiment showing the
piston in downward travel.
Figure 9 is a sectional view similar to P;gure 7 of a ~hird embodiment
of the subject invention.
Figure lO is a sectional view similar to Figure 7 of a fourth embodi-
ment of the subject invention.
Figure 11 is a cross-sectional view of a fifth embodiment of a shock
absorber and air spring assembly according to the invention in the upstroke
mode.
Figure 12 is a view along the line 2 - 2 in Figure 11.
Figure 13 is a cross-sectional view similar to Figure 11, but in the
downstro]ce mode.
Figure 1~ is a view along the line ~ - 4 in Figure 13.
Detailed Description of the Presently Preferred Embodiments
Figure 1 shows a conventional tilt cab truck comprising an elongated
chassis member 10, a cab member 12 mounted on the chassis member 10 for pivotal
movement about an axis 1~ transverse to the longitudinal axis of the chassis
member 10 from a lowered first position (shown in Figure 1) to a raised second
position. An integral shock absorber and air spring assembly 16 as shown in
detail in Figures 3 - 6 is located at each of the front corners between the
chassis member 10 and the cab member 12. An integral shock absorber and air
spring assembly 18 as shown in detail in Figure 10 is located at each of the
rear corners between the chassis member 10 and the cab member 12, and a latch
mechanism 20 as shown in detail in our co-pending Canadian application serial
nurnber , filed
6~
is located at each of the rear corners between the assembly 18 and
the chassis member 10.
Structure of the First Embodiment
Turning to Figures 4 - 6, it will be seen that the shock
absorber and air spring assembly 16 comprises a first base 22 adapted to
be attached to the cam member 12 by a plurality of bolt holes 24, a second
base 26 adapted to be attached to the chassis member 10 by a plurality of
bolt holes 28, a shock absorber sub-assembly 30, and an air spring sub-
assembly 32.
The shock absorber sub-assembly 30 comprises a rod 34 projecting
from the first base 22, a cylinder 36 projecting from the second base
26 and containing a bore 38 closed at ~he end remote from the second
base 26 by a cap 40 through which the rod 34 slidingly projects, and
a piston 42 carried by the rod 34 within the bore 38. The
piston 42 is preferably in sealing contact with the bore
3~3, but a ~irst path of fluid communication 44 leads
through the piston 42. A reservoir 46 for hydraulic
fluids is located in the second base 26, and a second
path of fluid communication 48 leads through the cylinder
36 between the reservoir 46 and the bore 38 near the
lower end of the stroke of the piston 42.
The air spring sub assembly 32 comprises an a.r bag
52 surrounding the rod 34 and the cylinder 36 and a fourth
path of fluid communications 54 for communicating air
under pressure to and from the air bag 52. The air bag
52 is connected at its upper end to the first base 22 and
at its lower end to the second base 26. Alterna~ively,
the air bag 52 could be connected at its lower end to the
cylinder 36, but, in this embodiment, the second base 26
comprises an upper component 56 threadedly mounted at 58
on a lower component 60, the air bag 52 is connected to
the upper component 56, and the cylinder 36 is mounted on
the lower component 60. This configuration permits the
lower component 60 and the cylinder 36 to be removed
separately for maintenance without distur~ing the air
spring sub-assembly 32. In the presently preferred
embodiment, the fourth path of fluid communication 54
passes through the first base 22 and leads to an external
source 62 of high pressure air (shown only in Figure 3).
Since the assembly 16 is disclosed in the context of
a tilt cab truck, the rod 34 is mounted on the first base
22 by means of a universal joint 64 to permit the first
base 22 to pivot relative to the rod 34 as the cab member
12 pivots relative to the chassis member 10. However, it
will be appreciated that, if the assembly 16 is used in a
context where the first base 22 and the second base 26
move only vertically relative to each other, the universal
joint 64 can be dispensed with.
The first path of fluid communication 44 has a small
cross-sectional area, which restricts the passage of
hydraulic Eluid through it to a slower flow rate than is
possible through the second and third paths of fluid
commun cation 48 and 50. Additionally, a one-way valve
66 which permits upwards flow but which prevents downwards
flow is located in the first path of fluid communication 44.
The second path of fluid communication 48 starts
with a plurality of axially spaced passageways 68 leading
through the cylinder 36 to an annular chamber 70 between
the cylinder 36 and the upper component 56 of the second
base 26. The purpose of having a plurality of axially
spaced passageways 68 is to affect the reaction
characteristics of the shock absorber sub-assembly 30.
When the piston 42 begins an upwards stroke, all of the
passageways 68 are obstructed by the piston 42, and the
lS flow of the hydraulic fluid becomes much more restricted.
It will be noted that the cross~sectional area of
the passageway 68 closer to the cap 40 is smaller than
the cross-sectional areas of the passageways 68 farther
away from the cap 40, which also contributes to the
differential and progressive nature of the damping.
Moreover, it will be noted that the uppermost passageway
68 is spaced from the cap 40~ so that the incompressible
hydraulic fluid will be trapped in the bore 38 above the
piston 42 when the piston 42 cuts off the uppermost
passageway 68, preventing the piston 42 from striking the
cap 40.
The annular chamber 70 communicates with a passageway
72 in the lower component 60 of the second base 26, and
the passageway 72 leads to the reservoir 46. A selectively
operable valve 74 is located in the passageway 72. Air
pilot pressure is communicated to the valve 74 through a
passageway 76 in the second base 26, opening the valve 74
against the urging of a spring 78 and permitting flow of
hydraulic fluid through the second path of fluid communi-
cation 48. However, when the air pilot pressure isturned off, the spring 78 closes the valve 74, bloclciny
the second path of fluid communication 48.
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The third path of fluid communication 50 also com-
prises a plurality of small axially spaced passageways
80 leading through the cylinder 36 from the bore 38, and
their axial spacing accomplishes the same purpose as the
axial spacing of the passageways 68. However, in this
casel another much larger passageway 82 containing a one-
way flapper valve 84 which permits upwards flow but which
prevents downwards flow is also provided. (It should be
noted that the passageways 80 are open even ~hen the
passage~ay 82 is closed by the one-way valve 84~) The
passageways 80 and 82 join in a single passageway 86
which leads to the reservoir 46.
A further optional feature of the shock absorber
sub-assembly 30 is a selectively operable variable orifice
mechanism 88 (shown only in Figure 5) in the second path
of fluid communication 48. The mechanism 88 can, for
instance, comprise a conical valve actuation of which is
under the controL of the truck driver, thus permitting
the truck driver to control the stiffness of the shock
absorber sub-assemb]y 30.
The second base 26 is formed with an external neck
90 adjacent to the air bag 52, and the air bag 52 is
designed so that, when it expands, it expands into the
neck 90. This construction permits the external, or
radial, dimensions of the air bag 52 to remain approxi-
mately uniform as the air bag 52 expands and contracts.
A resilient pad 92 is provided on top of the upper
component 56 to cushion the jar when the first base 22
contacts the upper component of the second base 26.
Operatlon of the First Embodiment
When the truck is travelling over the road, the air
bag 52 is inflated, tending to hold the piston 42 in the
middle of the bore 38. Air pilot pressure is communicated
to the valve 74 through the passageway 76, and the second
path of fluid communication 48 is open.
_ 9 _
When an unevenness in the road causes the piston 42
to move upwardly in the bore 38, the one-way valve 66 in
the first path of fluid communication 44 is closed by
hydraulic pressure. Hydraulic fluid e~its the bore 38
above the piston 42 through the second path of Eluid
communication 48 and Elows to the reservoir 4~. At the
same time, fluid from the reservoir 46 flows through the
third path of communication 50 (including the passageways
80, 82, and 86) to the bore 38 beneath the piston 42.
When the piston 42 moves downwardly in the bore 38,
the one-way valve 66 in the first path of fluid communica-
tion 44 is opened by hydraulic pressure. Accordingly,
hydraulic fluid exits the bore 38 below the piston 42
both through the first path of fluid communication 44
leadin~ to the bore 38 above the piston 42 and through
the third path of fluid communication 50 leading to the
reservoir 46. ~owever, downward movement of the piston
42 causes hydraulic pressure to close the one-way valve
84 in the third path of fluid communication 50, which
means that hydraulic ~luid exits the bore 38 beneath the
piston 42 only through first means of fluid communication
44 and passageways 80, both of which are restricted.
Since the effective cross-sectional areas of the passage-
ways 80 is much smaller than the effective cross-
sectional area of the first path of fluid communication44, most of the flow from the bore 38 beneath the piston
42 is through the first path of fluid communication 44
to the bore 38 above the piston 42, and, since the rod
34 is coming into the bore 38 above the piston 42, the
available volume of the bore 38 be~eath the piston 42
decreases faster than the available volume of the bore
38 above the piston 42 increases. The net effect is
that hydraulic fluid exits the bore 38 above the piston
42 when the piston 42 is moving downwardly as well as
when it moves upwardly. In other words, there is a
constant counter-clockwise flow through the circuit (as
seen in Figures 3 and 4); the flow is never clockwise.
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Since the effective cross-sectional areas of the
second path of fluid communication 48 is smaller than the
effective cross-sectional area of the first path of fluid
cornmunication 4~ (when the one-way valve 66 is open) plus
the cross-sectional area of the third path of fluid
communication 50 when the one-way valve 84 is closed, the
shock-absorber sub-assembly 30 has a larger damping effect
when the piston 42 is moving upwardly than when the
piston ~2 is moving downwardly.
When it is desired to tilt the cab member 12 relative
to the chassis member 10, air is drained from the air bag
52/ allowing the piston 42 to sink to the bottom of the
bore 38, and the air pilot pressure is turned off, allowing
the valve 74 to close. Closing the valve 74 blocks the
second path of fluid communication 48 and traps hydraulic
fluid in the bore 38 above the piston 42. At the same
time, the hydraulic fluid in the bore 38 beneath piston
42 forces open the one-way valve 66, filling the gradua~ly
increasing volume of the bore 38 above the piston 42.
Hydraulic fluid which will not fit in the bore 38 above
the piston 42 drains slowly to the reservoir 46 through
the passageways 80, the hydraulic pressure having closed
the one-way valve 84 in the passageway 82. Since the
reservoir 46 must be large enough to accomodate hydraulic
fluid displaced by entry of the rod 34 into the bore 38
during the over-the-road travel, there is room in the
reservoir 46 for all the hydraulic fluid displaced by the
gradùal downward movement or the piston ~2. Thus, when
the piston 42 comes to rest on the bottom of the cylinder
36, the entire bore 38 above the piston 42 and the second
passageway 48 above the valve 74 are both filled with
hydraulic fluid.
After the piston 42 has come to rest on the bottom
of the cylinder 36, the tilt cylinders (not shown) are
actuated. As explained previously, in prior art devices
actuation of the tilt cylinders lifts the cab member to
the top of the suspension members' strokes, thus creating
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92~i
a dangerous situation. AS will be readily appreciated,
however, the incompressable volume of hydraulic fluid
locked above the piston 42 in the present device prevents
this from happening.
Structure of the Second Embodiment
-
Figures 7 and 8 show only the shock absorber and air
spring assembly 100 of a second embodiment of the subject
invention.
The shock absorber sub-assembly 100 comprises a rod
102 projecting from th0 first base (not shown), a cylinder
104 projecting from the second base (not shown) and
containing a bore 106 closed at the end remote from the
second base by a cap 108 through which the rod 102
slidingly projects, and a piston 110 carried by the rod
102 within the bore 106. The piston 110 is preferably in
loosely sliding contact with the bore 106, permitting
some peripheral leakage around the piston 110 in either
direction of motion of that piston. Additionally, a
first path of fluid communication 112 leads through the
piston 110.
A reservoir 114 for hydraulic fluid surrounds the
cylinder 104 near its lower end, and a reservoir 116 for
hydraulic fluid surrounds the cylinder 104 near its upper
end. A second path of fluid communication 118 leads from
the bore 106 near the cap 108 through the cylinder 104 to
the reservoir 116 and through a series of spring operated
check valves 120 to the reservoir 114. A third path of
fluid communication 122 leads from the reservoir 114 to
the bore 106 near the end of the bore 106 remote from the
cap 108.
The cylinder 104 is mounted in a lower housing 124
which, together with the exterior of the cylinder 10~,
defines the reservoir 114, and the cap 108 is mounted in
an upper housing 126 which, together with the ex-terior of
the cylinder 104, define the reservoir 116.
The first path of fluid communication 112 has a
small cross-sectional area, which restricts the passage
of hydraulic fluid through it to a slower flow rate than
is possible through the second and third paths of fluid
communication 113 and 122. Additionally, a one-way valve
128 which permits upward flow but which prevents downward
flow is located in the first path of fluid cornmunication
112.
The second path of fluld communication 118 starts
with a plurality of axially spaced passageways 130 leading
through the cylinder 10~ to the reservoir 116 between the
cylinder 10~ and the upper housing 126. As with the
first embodiment, the purpose of having a plurality of
axially spaced passageways 130 is to affect the reaction
characteristics of the shock absorber sub-assembly 100.
When the piston 110 begins an upwards stroke, all of the
passageways 130 are unobstructed, and the flow of hydraulic
fluid through the passageways 130 is relatively free.
However, towards the end oE an upwards stroke, the lower
passageways are obstructed by the piston 110, and the
flow of the hydraulic fluid becomes much more restricted.
It will be noted that, as with the first embodiment,
the cross-sectional area of the passageways 130 closer to
the cap 108 is smaller than the cross-sectional areas of
the passageways 130 farther away from the cap 108, which
also contributes to the differential and progressive
nature of the damping. Moreover, it will be noted that
the uppermost passageway 130 is again spaced from the cap
108, so that incompressible hydraulic fluid will be
trapped in the bore 106 above the piston 110 when the
piston 110 cuts off the uppermost passageway 130. While
there is some peripheral leakage around the piston 110,
it is a very small flow, and upperward surges are of very
short duration, so that, in practice, the piston 110 is
again prevented from striking the cap 108 by the locked
hydraulic fluid.
The plurality of spring operated check valves 120
are rnounted in the second path of fluid communication 118
where it enters the lower housing 124. The check valves
120 permit hydraulic fluid to ~Elow downwards into the
reservoir 11~, but do not permit hydraulic fluid to flow
upwards from the reservoir 114 into the reservoir 116.
As with the ~irst embodiment, a resilient padding
132 is provided on top of the upper housing 126 to cushion
the jar when the first base (not shown) contacts the
upper housing 126 (which is fixedly mounted on the second
base by means not shown).
Ope~ation of the Second Embodiment
__
In operation, when an upstroke is caused by a jarring
of the truck as it rides over an obstruction, the fluid
paths are as shown by the arrows in Figure 7. That is,
hydraulic fluid from the bore 106 above the piston 110 is
forced around the piston 110 to the bore 106 beneath the
piston 110 to some degree, but it is mostly forced through
the passageways 130, the reservoir 116, the check valves
120, the reservoir 114, and the third path of fluid
communication 122 to the bore 106 beneath the piston 110.
When the upstroke is completed and the rod 102 begins
to settle back down under the force of gravity, the check
valves 120 close, and communication from the bore 106
beneath the piston 110 to the bore 106 above the piston
110 is limited to the first path of fluid communication
112 and to peripheral leakage around the piston 110.
Since the rod 102 is re-entering the bore 106 during this
phase of the operation, the volume of hydraulic fluid
which exits the bore 106 beneath the piston 110 exceeds
the volume which becomes available for it in the bore 106
above the piston 110, and the excess is forced out through
the passageways 130 into the reservoir 116 as indicated
by the arrows in Figure 8.
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6~;
Third Embodiment
The third embodiment, shown in Figure 9, is identical
to the embodiments shown in Figures 7 and 8 except that
the air bag 52, whlch functions as a spring, has been
replaced with a mechanical spring 134. In this embodiment,
means (not shown) must be provided to bring the first
base into contact with the second base against the urgings
of the spring 134 when it is desired to lock the assembly
in the down position prior to tilting the cab member 12.
Fourth Embodiment
~ fourth embodiment, particularly adapted for use at
the rear corners of the cab, is shown in Figure 10. It
comprises a first base 136 adapted to be attached to the
cab member 12 by a plurality of bolt holes 138, a second
base 140 adapted to be attached to the latch mechanism 20
by a bolt 142, a shock absorber sub-assembly 144, and an
air spring sub-assembly 146.
The shock absorber sub-assembly 14~ comprises a rod
148 projecting from the first base 136, a cylinder 150
projecting from the second base 140 and containing a bore
152 closed at the end remote from the second base 140 by
a cap 154 through which the rod 148 slidingly projects,
and a piston 156 carried by the rod 148 within the bore
152. The piston 156 is preferably in sealing contact
with the bore 152, but a first path of fluid communication
158 leads through the piston 156~ A reservoir 160 for
hydraulic fluids surrounds the cylinder 150, and a second
path oE fluid communicatioon 162 leads through the cylinder
150 between the reser~oir 160 and the bore 152 near the
upper end of the stroke of piston 156. ~ third path of
fluid communication 164 leads through the cylinder 150
between the reservoir 160 and the bore 156 near the lower
end of the stroke of the piston 156.
The air spring sub-assembly 146 cornprises an air bag
166 surrounding the rod 1~8 and the cylinder 150 and a
fourth path of fluid communications 168 for communicating
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air under pressure to and from the air bag 166. The air
bag 166 is connected at its upper end to the first base
136 and at its lower end to the second base 140.
Alternatively, the air bag 166 could be connected at its
lower end to the cylinder 150, but, in this embodiment,
the second base 140 comprises an upper component 168
threadedly mounted at 170 on a lower component 172, the
air bag 166 is connected to the upper component 168, and
the cylinder 150 is mounted on the lower component 172.
This configuration permits the lower component 172 and
the cylinder 150 to be removed separately for maintenance
without disturbing the air spring sub-assembly 1~6. In
the presently preferred embodiment, the fourth path of
fluid communication 168 passes through the first base 136
and leads to an external source of high pressure air (not
shown~.
Since the assembly 18 is disclosed in the context of
a tilt cab truck, the rod 148 is mounted on the first
base 136 by means of a universal joint 174 to permit the
first base 136 to pivot relative to the rod 148 as the
cab member 12 pivots relative to the chassis member 10.
However, it will be appreciated that, if the assembly 18
is used in a context where the first member 136 and the
second member 140 move only vertically relative to each
other, the universal joint 174 can be dispensed with.
The first path of fluid communication 158 has a
small cross-sectional area, which restricts the passage
of hydraulic fluid through it to a slower flow rate than
is possible through the second and third paths of fluid
communication 162 and 164. Additionally, a one-way valve
176 which permits upwards flow but which prevents downwards
flow is located in the first path of fluid communication
158.
The second path of fluid communication 162 comprises
a plurality of axially spaced passageways leading through
the cylinder 150 to the reservoir 160. The purpose of
having a plurality of axially spaced passageways is to
- i6 -
26~
affect the reaction characteristics of the shock absorber
sub-assembly 144. When the piston 156 begins an upwards
stroke, all of the passageways are unobstructed, and the
flow of hydraulic fluid out of the passageways 162 is
relatively free. However, towards the end of an upwards
stroke, the lower passageways are obstructed by the piston
156, and the flow of the hydraulic fluid becomes much
more restricted.
It will be noted that the cross-sectional area of
the passageways comprising the second path of fluid
communication 162 close to the cap 154 are smaller than
the cross-sectional areas of the passageways farther away
from the cap 154, which also contributes to the differen-
tial and progressive nature of the damping. Moreover,
it will be noted that the uppermost passageway is spaced
from the cap 154, so that incompressible hydraulic fluid
will be trapped in the bore 152 above the piston 156
when tha piston 156 cuts off the uppermost passageway,
preventing the piston 156 from striking the cap 154.
The third path o~ fluid communication 164 also
comprises a plurality of small axially spaced passageways
leading through the cylinder 150 from the bore 152, and
their axial spacing accomplishes the same purpose as the
axial spacing of the passageways comprising the second
path of fluid communication 162.
The se~ond base 140 is fo~med with an external neck
178 adjacent to the air bag 166, and the air bag 166 is
designed so that, when it expands, it expands into the
neck 178. This construction permits the external, or
radial, dimensions of the air bag 166 to remain
approximately uniform as the air bag 166 expands and
contracts.
An elastomeric pad 180 i5 provided at the top of the
upper component 168 of the second base 1~0 to cushion the
jar if the first base 136 comes into contact with the
second base 140.
- 17 -
Operation of the Assembly 18
When the truck is travelling over the road, the air
bag 166 is inflated, tending to hold the piston 156 in
the middle of the bore 152. When an unevenness in the
road causes the piston 156 to move upwardly in the bore
152, the one-way valve 176 is closed by hydraulic pressure.
Hydraulic fluid exits the bore 152 above the piston 156
through the second path of fluid communication 162 and
flows into the reservoir 160. At the same time, fluid
flows Erom the reservoir 160 through the third path of
fluid communication 164 into the bore 152 beneath the
piston 156. Conversely, when an unevenness in the road
causes the piston 156 to move downwardly in the bore 152,
the one-way valve 17Ç is opened by hydraulic pressure.
Hydraulic fluid exits the bore 152 beneath the piston 156
through the first path of fluid communication 158. Since
the effective volume of the bore 152 beneath the piston
156 is decreased faster than the effec~ive volume of the
bore 152 above the piston 156 is increased (due to the
presence of the rod 148 in the latter), hydraulic fluid
from the bore 152 above the piston 156 is forced through
the second path of fluid communication 162 as the piston
156 moves downwardly, causing a counter-clockwise flow
(in Figure 10) of the hydraulic fluid regardless of the
direction of motion of the piston 1560
Fifth Embodiment
The shock absorber sub-assembly 216 comprises a rod
220 projecting from the first base 210, a cylinder 222
projecting from the second base 212 and containlng a bore
224 closed at the end remote from the second base 212 by
a cap 226 through which the rod 220 slidingly projects,
and a piston 228 carried by the rod 220 within the bore
224. The piston 228 is not in sealing contact with the
bore 224, but permits a small amount of restricted flow
in either direction, as indicated by the arrows in Figures
11 and 13. In addition, a conduit 230 leads through the
- 18 -
piston 228~ ~he conduit 230 contains a one-way valve 232
which permits flow from beneath the piston 228 to above
the piston 228, but prevents flow in the opposite direc-
tion.
An annular reservoir 234 is contained in the second
base 212 surrounding the cylinder 222. The second base
212 comprises an upper component 236 and a lower component
238. The upper componen-t 236 is a cup-shaped member
which has an axial bore 240 which receives the cap 226.
The upper component is threadedly mounted on the lower
component 238 at 241 so that the lower component 238 and
- the cylinder 222 can be removed separately for maintenance
without disturbing the air spring sub-assembly 218. The
reservoir 234 extends into both the upper component 236
and the lower component 238.
One or a plurality of a~ially spaced conduits 242
lead from the bore 224 near the cap 226 to a conduit 244
in the cylinder 222. The purpose of having a plurality
of axially spaced conduits 242 is to gradually affect the
reaction characteristics of the shock absorber sub-
assembly 216. When the piston 228 begins an upward
stroke, all of the conduits 242 are unobstructed, and
the flow of hydraulic fluid out of the conduits 242 is
relatively free. However, towards the end of an upward
stroke, the lower conduits 242 are obstructed by the
piston 228, and the flow of the hydraulic fluid becomes
much more restricted.
It has been found in practice that having a single
conduit 242 near the top of the stroke works best.
Moreover, it should be noted that, if a plurality of
conduits 2~2 are used, the lowest conduit 242 should not
be rnore than one piston width from the top of the stroke,
since otherwise leakage may occur from above the piston
directly to the chamber below the piston, rendering the
adjustable orifice useless.
It will be noted that the uppermost conduit 242 is
spaced from the cap 226. Accordingly, incompressible
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~! 9~
hydraulic fluid will be trapped in the bore 224 above
the piston 228 when the piston 228 cuts off the uppermost
conduit 242 except for the severely restricted clearance
around the piston 228. This configuration greatly slows
upward travel of the piston 228 at the end of its stroke
and prevents contact between the piston 228 and the cap
226 in all but the most extreme cases.
The conduit 244 communicates with an annular groove
246 in the end of the cylinder 222 which abuts the second
base 212. The purpose of the annular groove 246 is to
make the angular orientation of the cylinder 222 relative
to the second base 212 irrelevant. The annular groove
246 in turn communicates with a longitudinal blind bore
248 which extends vertically from the face of the second
lS base 212 which abuts with the cylinder 222. The blind
bore 248 communicates with a stepped radial bore 250
which contains a needle valve 252 described hereinafter.
The stepped radial bore 250 communicates with an axial
blind bore 254 which extends vertically from the face of
the second base 212 which defines the bottom of the bore
224. However, the bore 254 is plugged at 256. The axial
bore 254 communicates with another radial bore 258 (plugged
at 260), and the radial bore 258 communicates with another
blind longitudinal bore 262 which, finally, com~unicates
with the reservoir 234.
Turning to Figures 12 and 14, it will be seen that
the reservoir 234 also communicates with two stepped
bores 264 which are plugged at 266 and which contain one-
way valves 268. ~ngled bore 270 provides communication
between the stepped bores 264 and the lower face of the
bore 224, and the one~way valve 268 permit flow from the
reservoir 234 through the stepped bores 264 and the angled
bores 270 to the bore 224, but prevent flow in the opposite
direction.
Returning to the needle valve 252 (shown in Figures
11 and 13), it will be seen that it partially obstructs
the radial bore 250. ~owever, its position in the radial
- 20 -
bore 250 is under the control of the operator of the
truck via a cable 272, which permits the operator of the
truck to control the hardness of the ride.
In the downstroke mode, flow through the damper
piston keeps the chamber above the damper piston full.
Accordingly, damping of the piston in the downstroke mode
is altered by the adjustable orifice (i.e., the conduits
242) to the extent that the volume of hydraulic fluid
displaced by the rod must pass through the adjustable
orifice. Thus, the adjustable orifice controls damping
of the piston in both directions, although it controls
downstroke damping to a lesser extent than it controls
upstroke damping.
It should also be noted that the ratio of rod size
to bore size (i.e., the width of the annular clearance
between the piston and the cylinder) can be altered to
increase or decrease the amount of downstroke damping
that is affected by the adjustable orifice.
The Air Spring Sub Ass bly 218
The air spring sub-assembly 218 comprises an air bag
280 surrounding the rod 223 and the cylinder 222. A
conduit (not shown) communicates air under pressure to
and from the air bag 280. The air bag 280 is connected
at its upper end to the first base 210 and at its lower
25 end to the upper component 236 of the second base 212.
Alternatively, the air bag 280 could be connected at its
lower end to the lower component 238 of the second base
212, but the illustrated configuration facilitates dis-
assembly for maintenance.
Since the subject shock absorber and air spring
assembly is particularly well adopted for use on a tilt
cab truck, the rod 220 is mounted on the first base 210
by means of a universal joint 282. However, it will be
appreciated that, if the assembly is used in a context
35 ~here the first base 210 and the second base 212 move
only vertically relative to each other, the universal
2~;
joint 286 can be dispensed with.
The lower component 238 of the second base 212 is
formed with an external neck 284 adjacent to the air bag
280, and the air bag 280 is designed so that, when it
expands, it expands into the neck 284.
Operatio _ of the Shock Absorber and Air Spring Assembly
When a truck incorporating the subject shock absorber
and air spring assembly is travelling over the road, the
air bag 280 is inflated to a pressure controlled by a
levelling valve, tending to hold the piston 228 in the
middle of the bore 224.
When an unevenness in the road causes the piston 228
to move upwardly in the bore 224 (as shown in Figures 11
and 12), the one-way valve 232 in the conduit 230 is
closed by hydraulic pressure. Some hydraulic fluid leaks
around the piston 228, but most of the hydraulic fluid
above the piston 228 exits the bore 224 through the
conduits 242. From the conduits 242 it flows through the
conduit 244, the groove 246, the bore 248, the bore 250,
20 around the needle valve 252, and through the bore 252,
the bore 258, and the bore 262 to the reservoir 234.
From the reservoir 234 it flows through the bores 264
(unseating the one-way valve 268) and the bores 270 to
the bore 224 beneath the piston 228.
When an unevenness in the road causes the piston 228
to move downwardly in the bore 224 (as shown in Figures 13
and 14)~ the one-way valves 268 are closed by hydraulic
pressure, but the one-way valve 232 is opened. Thus,
hydraulic fluid from the bore 224 beneath the piston 228
flows upwardly through the conduit 230 (as well as around
the piston 228) to the bore 224 above the piston 228.
From there it flows through the conduits 242, the conduit
244, the groove 246, the bore 248, the bore 250, around
the needle valve 252, and through the bore 254, the bore
258, and the bore 262 to the reservoir 234 as before.
Since the decrease in volume in the bore 224 beneath
- 22 -
the piston 228 is greater than the increase ln volume in
the bore 224 above the piston 228 due to the presence of
the rod in the latter, the bore 224 above the piston 228
remains filled with hydraulic fluid as the piston 228
moves downwardly.
It should be noted that the cross-sectional area of
the conduit 230 below the one-way valve 232 is preferably
significantly smaller than the total cross-sectional
areas oE the conduits 242, so t:hat the downward stroke of
the piston 228 is initially much more damped than its
upward stroke.
Caveat
While the present invention has been illustrated by
a detailed description of several preferred embodiments
thereof, it will be obvious to those skilled in the art
that various changes in form and detail can be made
therein without departing from the true scope of the
invention. For that reason, the invention must be measured
b~ the claims appended hereto and not by the foregoing
preferred embodiments.
