Background of the Invention
1. Field of the Invention
The present invention relates to suspension systems for wheeled motor
vehicles and, more specifically to a suspension system incorporating new and improved
control rod linkage configurations.
The present invention finds particular utility in the heavy duty
truck and trailer industry. In this industry, the use of air suspension systems
has become quite popular due to their softer ride characteristics. In these suspensions,
equivalents of air springs, such as hydraulic cylinders with accumulators, are
sometimes alternatively used. Air suspension systems in common use typically utilize
trailing arms, also called main support members, that are rigidly attached to the
vehicle axles to support the vehicle frames upon the vehicle wheels. The trailing
arms are pivotally attached at one end to the vehicle frames with air springs mounted
between the frames and the other end of the trailing arms.
The trailing arms may take the form of gooseneck shaped Z-springs.
U.S. Pat. Nos. 4,693,486, 3,547,215, 4,858,949 and 5,346,247 provide examples of
such trailing arm suspensions. Alternatively, in some common designs, the trailing
arm may take the form of a straight leaf spring.
Z-springs add a significant amount of weight to trailing arm air
suspensions. The Z-springs typically weigh around 60 lbs. each. Additionally, the
relatively large amount of material that goes into manufacturing the Z-springs
is costly and the size of the Z-springs take up a substantial amount of space underneath
Use of Z-springs may also require the use of additional associated components which
adds even more weight.
Disclosures in the prior art include US-A-2300844 where the rear
ends of the chassis side members curve upwardly in front of the suspension mounting.
Upper and lower links between chassis and axle converge forwardly (in a vertical
plane) to provide a rocking axis which is inclined downwardly and forwardly. In
one embodiment two lower links extend horizontally, from brackets adjacent the
lower level of the chassis side members, back to brackets on the axle casing. Springs
extend up from the middles of the lower links to the higher-level rear extremities
of the chassis side members. Upper control links extend rearwardly in a convergent
'V' (in plan) from a chassis cross member, and incline upwardly to a pivot connection
at an upper part of a central axle mount. In a second embodiment the lower links
extend back from pivots on the chassis members, at the lower level, and slope
slightly upwardly back to pivot connections on the axle casing. The upper links
slope more steeply upwardly, from respective pivots on the chassis side members
back to pivots on the central axle mounts. Springs are connected between perches
on the axle casing and corner pieces at the upper (rear) level of the chassis
In US-A-2903256, on which the two-part form of claim 16 is based,
upper and lower trailing links are inclined slightly downwardly to the rear, being
pivotally connected at upper and lower parts of the axle mount components. The
upper link is a single longitudinal rod trailing from the centre of a chassis cross
member; the lower links trail from hanger brackets on the frame side members.
The suspension, frequency of a suspension system has an impact upon
the ride quality of the truck. A suspension with a high suspension frequency is
by its nature more rigid and thus transmits to the frame inputs such as road irregularities.
The high rigidity of such a suspension also means that the motion of the suspension
componehts in response to inputs is minimal. Movement of the suspension components
isolates the energy resulting from the road inputs. The more the suspension components
move in reaction to an input, the more energy is isolated or dissipated. The excess
energy that the high frequency suspension doesn't isolate or dissipate is transmitted
to the truck body and shows up as vibration and a rough ride quality. In contrast,
a lower frequency suspension has components that move more freely when subjected
to inputs. This isolates or dissipates more energy and thus produces less vibration
and a smoother ride.
Trailing arm suspensions, such as the one shown in FIG. 1, are torque
reactive. Due to the uses of higher horsepower engines and advances in engine technology,
there have been increases in the torque output of heavy duty truck engines. Such
increases have exacerbated the problems of driveline vibration and wheel hop associated
with the torque reactive trailing arm suspensions. When increased torque is applied
to the drive train of a truck equipped with such a torque reactive suspension,
such as during acceleration, the frame of the truck rises up and away from the
drive axle. This condition is known in the art as "frame rise" and results in the
driveline vibration and wheel hop.
Trailing arm suspensions clamped rigidly to the axle tend to twist
the axle housing in reaction to road surface irregularities encountered on one
side of the vehicle during operation. This axle twist tends to lift the tires
on the opposite side of the vehicle off of the ground, sometimes to the point where
traction is lost.
Axle twist is also detrimental to the fatigue life of the axle. As
a result, several truck and trailer manufacturers require heavier axle wall housings
for use with trailing arm air suspensions which increases the axle weight.
It is therefore an object of the present invention to provide an
air or hydraulic suspension system that saves weight and space and reduces cost
through the elimination of Z-springs and similar trailing arms and associated
Another object of the present invention is to provide an air or hydraulic
suspension that has a low suspension frequency.
Yet another object of the invention is to provide a suspension that
maintains greater tire traction when road surface irregularities are encountered.
Yet another object of the invention is to improve the axle connection
and thus enhance axle fatigue life.
The present invention is set out in two aspects in claims 1 and 15,
and is directed to a suspension system for supporting a vehicle chassis on an
axle. In some embodiments, each side of the vehicle suspension features the following.
A hanger is attached to a chassis side frame member. An axle seat is attached
to the axle. A lower control rod is pivotally connected at its forward end to the
hanger and at its rearward end to the axle seat so that the lower control rod is
inclined with its forward end appreciably above its rearward end. A bracket for
attaching the upper control rod to the frame is also attached to the chassis side
frame member. An axle mount is attached to the top of the axle midway between
the ends of the axle. An upper control rod is pivotally connected at its forward
end to the bracket and at its rearward end to the axle mount, and may lie in an
approximately horizontal plane. The lower control rod and upper control rod are
vertically appreciably closer together at their forward ends than at their rearward
ends. Spring means, such as an air spring, a hydraulic cylinder with accumulator,
an elastomeric spring or a mechanical spring, is mounted between the axle seat
and the chassis frame member.
In alternative embodiments, the pair of upper control rods are replaced
by a single longitudinal upper control rod combined with either a single transverse
upper control rod or a transverse Watt linkage. In both embodiments, the longitudinal
upper control rods may lay in an approximately horizontal plane so that they and
the lower control rods are vertically appreciably closer together at their forward
ends than at their rearward ends.
For a more complete understanding of the nature and scope of the
invention, reference may now be had to the following detailed description of embodiments
thereof taken in conjunction with the appended claims and accompanying drawings.
Brief Description of the Drawings
Description of the Preferred Embodiments
- FIG. 1 is a side elevational view of a prior art trailing arm torque reactive
heavy duty truck suspension;
- FIG. 2 is an isometric view of an embodiment of the suspension of the present
invention utilizing air springs and a bolt and bushing assembly upper axle mount;
- FIG. 3 is a top plan view of the suspension of FIG. 2;
- FIG. 4 is a side elevational view of the suspension of FIG. 2;
- FIG. 5 is an isometric view of an embodiment of the suspension of the present
invention utilizing air springs, a ball and socket upper axle mount and a cross
- FIG. 6 is a side elevational view of the suspension of FIG. 5;
- FIG. 7 is an isometric view of an embodiment of the suspension of the present
invention utilizing hydraulic cylinders;
- FIG. 8 is a side elevational view of the suspension of FIG. 7;
- FIG. 9 is an isometric view of an embodiment of the invention where the upper
control rods in the suspension of FIG. 2 have been replaced with a longitudinal
upper control rod and a transverse upper control rod;
- FIG. 10 is an isometric view of an embodiment of the invention where the upper
control rods in the suspension of FIG. 2 have been replaced with a longitudinal
upper control rod and a transverse Watt linkage.
Referring to FIG. 1, a typical trailing arm torque reactive suspension
is indicated generally at 5 which supports the rear of a vehicle, such as a heavy
duty truck on ground wheels indicated generally at 6 mounted on opposite ends
of a drive axle indicated generally at 7. As used herein "drive axle" designates
both the drive axle proper and the drive axle housing. The components of the suspension
5 on opposite sides of the vehicle are the same. The frame or chassis of the vehicle
is represented by the fore-and-aft side frame members 8.
Mounting bracket 10 is suitably mounted on the outer side of the
side frame member 8 so as to receive and support the front end of the Z-spring
11 so that Z-spring 11 generally pivots about point 13. The Z-spring 11 is mounted
to the drive axle by means of a conventional axle attachment assembly indicated
generally at 15. An air spring 17 is bolted at its bottom end to the cross channel
18 and that to the trailing end of Z-spring 11 and at its top end to side frame
member 8. Shock absorber 19 is similarly connected between the Z-spring trailing
end and the side frame member 8. Vertical line a-a intersects pivot point 13 while
vertical lines b-b and c-c intersect the axle 7 and air spring 21, respectively.
The vehicle chassis, as represented by side frame member 8 is resiliently supported
on drive axle 7 and the ground wheel 6 by the Z-spring 11 coacting with the bracket
10, air spring 17 and shock absorber 21.
The suspension frequency of a trailing arm air suspension is calculated
Suspension Frequency = sqrt(Linkage Ratio) X Air Spring
In this equation, the Linkage Ratio = A/B, where, referring to FIG. 1:
Note that the same equation could be used for a suspension that utilized alternative
spring members in place of the air springs.
- A = the horizontal distance between the suspension pivot point 13 and the air
spring 17, that is, the horizontal distance between line a-a and line c-c, and
- B = the horizontal distance between the suspension pivot point 13 and the axle
7, that is, the horizontal distance between line a-a and line b-b.
A typical value for the air spring frequency is 1.2 cycles/second
(Hz), while a typical value for the linkage ratio is 1.76. It follows, given the
equation above, that a lower linkage ratio would result in a lower suspension
frequency. A general practice in the automotive industry has been to strive for
a suspension frequency of about 1.0 Hz. Previous suspension geometries, such as
the one shown in FIG. 1, were inhibited from approaching this goal by their linkage
ratio. Additionally, with such suspensions, the flexibility of the Z-springs further
increases suspension frequency.
To achieve a linkage ratio closer to 1.0 with the suspension of FIG.
1, it would be necessary to shift pivot point 13 a horizontal distance away from
axle 7 and air spring 21. This would require increasing the length of Z-spring
11 which would increase its weight and cost. Additionally, the extended Z-spring
would take up more space and the length of its extension would be limited by other
undercarriage components such as the front suspension and fuel tank mounting.
Referring now to FIG. 2, an embodiment of the suspension of the present
invention is indicated generally at 21. The suspension supports a vehicle, such
as a heavy duty truck, on ground wheels indicated generally at 23 mounted on the
ends of a drive axle indicated generally at 25. The components of the suspension
21 on opposite sides of the vehicle are the same. The frame of the vehicle is
represented by the fore-and-aft side frame members 27. Note that the suspension
of FIG. 2 features upper and lower pivot points at the axle. In addition to providing
cost and weight savings by allowing elimination of the Z-spring, this arrangement
makes the suspension of FIG. 2 not reactive to torque. The arrangement also allows
the suspension displacement caused by the encounter of a surface bump by one tire
to be more independent of the opposite side of the suspension. This reduces the
amount of axle twist which improves traction of the tire on the opposite side
of the suspension.
Hangers 29 are suitably mounted on the outer sides of the side frame
members 27 so as to pivotally connect with the forward ends of lower control rods
31. The rearward ends of the control rods 31 are pivotally connected to axle seats
33 so that control rods 31 are in an inclined orientation as shown in FIG. 4. The
ideal orientation of lower control rods 31 is such that their rearward ends travel
through arcs that, if extended, would pass through a horizontal line running through
connection point 34 and perpendicular to side frame member 27. This orientation
minimizes the effect that the suspension has on drive axle pinion change during
articulation. The pivotal connections are such that lower control rods 31 pivot
in a vertical plane parallel to side frame members 27.
As FIG. 4 shows, axle 25 is attached to axle seats 33 by means of
axle attachment assemblies indicated generally at 35. The assemblies 35 comprise
bolts 37 which fit through top plates 39 and axle seats 33. Axle 25 is sandwiched
between top plates 39 and axle seats 33. Axle 25 passes between bolts 37. Lock
nuts 41 hold the assemblies together. This attachment is more robust than the
ones illustrated in the prior art because the bolts 37 are parallel and closer
to the vertical walls of the drive axle thus providing a more secure axle clamp.
Another advantage of assemblies 35 are that the bolts 37 are of the same length
despite the pinion angle.
On each side of the suspension 21 an air spring 43 of known type
is bolted at its base 45 to axle seat 33. The top of the air spring 43 is attached
to the adjacent side frame member 27 by air spring bracket 47. The bottom of shock
absorber 49 is pivotally mounted to axle seat 33. The top of shock absorber 49
is pivotally connected to side frame member 27 by shock absorber bracket 51.
Upper control rods 53 are each pivotally connected at their rearward
ends to the center of axle 25 by axle mount 55 so that each upper control rod 53
moves independently of the other. Each upper control rod moves in its own vertical
plane, each vertical plane making an angle with side frame members 27. The forward
ends of upper control rods 53 are each attached to brackets 57. Brackets 57 are
fastened to the inner sides of side frame members 27 and are supported in part
by frame cross member 59 as shown in FIGS. 2 and 3.
Referring now to FIG. 4, generally horizontal line d-d is drawn extending
longitudinally through the pivot centers 60 of upper control rods 53. Similarly,
line e-e is drawn extending longitudinally through lower control rods 31. Lines
d-d and e-e intersect at effective pivot point 61. Effective pivot point 61 is
analogous to pivot point 13 of FIG. 1. Unlike the suspension in FIG. 1, the suspension
in FIG. 4 has no contiguous Z-spring from the effective pivot point 61 to the axle
25 or air spring 43. Similar to FIG. 1, vertical line f-f passes through effective
pivot point 61 while vertical lines g-g and h-h pass through axle 25 and air spring
43 respectively. Distances A and B can then be used to calculate the linkage ratio.
A comparison between lengths A and B of FIG. 1 and lengths A and
B of FIG. 4 show that the latter are significantly longer. This is especially true
when one considers that FIG. 4 is drawn to smaller scale than FIG. 1. The greater
length of A and B allows the linkage ratio of the suspension of FIG. 4 to more
closely approximate a value of 1.0. Referring to the suspension frequency equation
above, this allows a lower frequency to be achieved for the suspension of FIG.
4 than for the suspension of FIG. 1. This results in a smoother ride and less
vibration for the suspension of FIG. 4.
The inclination of the lower control rod 31, as shown in FIG. 4,
offers numerous advantages over one that is positioned horizontally. For example,
it has been found that an inclined orientation induces less load in the lower
control rod 31. This allows for a lighter lower control rod 31 to be used which
also saves material cost. Additionally, less expensive bushings, due to the lower
loads, may be used at the lower control rod pivotal connections with the hanger
29 and the axle seat 33. Furthermore, the use of a horizontally oriented lower
control rod requires the use of a longer hanger 29 which again increases weight
and material cost. Finally, the longer hanger and horizontal lower control rod
would take up more undercarriage space and reduce ground clearance. The latter
would restrict the height of a road surface bump that the suspension could successfully
Referring now to FIG. 5, one side of an alternative embodiment of
the suspension of the invention is shown. This embodiment substitutes a ball and
socket axle mount 63 for the bolt and bushing axle mount 55 of FIG. 2. Also, a
different axle mount assembly, indicated generally at 65 is utilized in the embodiment
of FIG. 5 as is a cross channel 66. Note that either the ball and socket mount
63, the axle mount assembly 65 or the cross channel 66 of FIG. 5 may be used independent
of one another in other embodiments of the invention.
The rearward ends of upper control rods 67 of FIG. 5 enter ball and
socket axle mount 63 at a fixed angle α with respect to one another so that
upper control arms 67 may not move independently of one another. The forward ends
of the upper control rods 67 are attached to side frame members 69, only one of
which is shown in FIG. 5, in the same manner as illustrated in FIG. 2.
Axle mount assembly 65 comprises the usual inverted U or shackle
bolts 71, bottom spacer seat 73, top spacer seat 74 and spacer block 75. Lock nuts,
not shown, are attached to the threaded ends of U bolts 71 and hold the assembly,
including axle 76, to axle seat 77. A side elevational view of the embodiment of
FIG. 5 is shown in FIG. 6.
Referring now to FIG. 7, one side of another embodiment of the present
invention is indicated generally at 79. This embodiment utilizes hydraulic cylinders
81, with accumulators, in place of the air springs and shock absorbers of the
previous embodiments. As FIG. 7 shows, the top of hydraulic cylinder 81 is pivotally
connected to side frame member 83 by hydraulic cylinder bracket 85. Hydraulic
cylinder bracket 85 allows hydraulic cylinder 81 to pivot in a vertical plane perpendicular
to side frame member 83. The bottom of hydraulic cylinder 81 is pivotally connected
to axle seat 87 so that hydraulic cylinder 81 is able to also pivot in a vertical
plane parallel to side frame member 83.
Axle seat 87 is fastened to axle 89 by the axle assembly indicated
generally at 91. Bifurcated plates 93 are welded to the leading and trailing faces
of axle 89. Bolts 95 fit through spacers 97, bifurcated plates 93, spacer seat
98 and axle seat 87. Lock nuts, not shown, attach to the threaded ends of bolts
95 so as to anchor the dog bone tabs 93, and thus axle 89 to axle seat 87. Note
that the hydraulic cylinders 81, with accumulators, may be substituted for the
air springs in any of the foregoing embodiments. Similarly, the axle mount assembly
91 may also be substituted for the axle mount assembly in any embodiment previously
Referring now to FIG. 9, another embodiment of the suspension of
the present invention is indicated generally at 101. This embodiment utilizes a
longitudinal upper control rod 103 and a transverse upper control rod 105 in place
of the V-rod configuration of the upper control rods of the previous embodiments.
As FIG. 9 shows, the leading end of longitudinal upper control rod 103 is pivotally
connected to frame cross member 107 by upper leading bracket 109. The trailing
end of longitudinal upper control rod 103 is pivotally connected to axle mount
111 attached to axle 113. Upper leading bracket 109 and axle mount 111 allow longitudinal
upper control rod 103 to lay in an approximately horizontal plane and to pivot
in a vertical plane perpendicular to frame cross member 107.
Transverse upper control rod 105 is pivotally connected at its outer
end to side frame member 115 by frame side bracket 117. The opposite end of the
transverse upper control rod 105 is pivotally connected to transverse axle bracket
119. Transverse axle bracket 119 is attached to axle 113. Side frame bracket 117
and transverse axle bracket 119 allow transverse upper control rod 105 to lay
in an approximately horizontal plane and to pivot in a vertical plane parallel
to frame cross member 107.
In FIG. 10, an alternative embodiment of the suspension of the FIG.
9 is indicated generally at 121. In this embodiment, the transverse upper control
rod 103 of FIG. 9 is replaced by a transverse Watt linkage, indicated generally
at 123 in FIG. 10. The transverse Watt linkage is composed of Watt link 125, upper
link arm 127 and lower link arm 129. Watt link 125 is pivotally connected at its
center to axle combination bracket 131. Axle combination bracket 131, which is
attached to axle 132, is also pivotally connected to the trailing end of longitudinal
upper control rod 133.
The outward ends of lower link arm 129 and upper link arm 127 are
pivotally connected to frame side brackets 135, which are secured to side frame
members 137. Lower link arm 129 is pivotally connected at its inward end to the
bottom end of Watt link 125, while the inward end of upper link arm 127 is similarly
connected to the top end of Watt link 125. During articulation of the suspension
121, such as when the vehicle negotiates a bump or a curve, the components of transverse
Watt linkage all move in a vertical plane perpendicular to side frame members
137. Furthermore, during articulation, Watt link 125 remains in its initial, nearly