Note: Descriptions are shown in the official language in which they were submitted.
COMPOSITE LEAF SPRING CONSTRUCTION
HAVING DIFFERENT SPRING RATE FOR THE
FRONT AND REAR PORTIONS OF THE SPRING
~ackground of the Invention
Recently there has been a trend to reduce the ;~
profile of vans and trucks to provide a more aero~
dynamic appearance. However, it is important when
downsizing the profile of the vehicle that the ground
clearance not be reduced and the axle travel be retain~
ed. The "axle travel" is the vertical distance that `
the frame can move downwardly under load before bottom~
ing out on the axle. Under downsized conditions,
severe restraints are put on the size and movement of
the vehicle suspension and its components.
In a Hotchkiss leaf spring suspension, as the
stiffness ratio of the front half of the spring to the
rear half of the spring increases, there is a tendency ? ;''"'''``' ""'"'
to rotate the differential housing and increase the ~ :
pinion control angle as a load is applied to the sus-
pension, the pinion control angle being the degrees of
rotation of the pinion axis, per inch of axle travel.
On the other hand, as the stiffness ratio of the front
half of the spring to the rear half approaches unity,
the pinion control angle is decreased and under heavy
load conditions, the differential housing may rotate in
a manner to cause the housing to engage and possibly
dent the floor of a low profile vehicle. In the past,
attempts have been made to overcome this problem b~
mounting protective cross bars beneath the floor in
position to be engaged by the differential housing,
thus intending to prevent damage to the vehicle floor.
. . .
Summarv of the Invention
The invention is directed to a composite leaf
spring construction for a vehicle, in which the front
and rear sections of the spring have different spring
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rates to control rotation of the differential housing
and thus prevent the housing from engaging the vehicle
floor. `~
In accordance with the invention, the leaf
spring is composed of fiber reinforced resin and has a
constant cross sectional area throughout its length. ;~
The spring includes a front section having a greater
thickness and lesser width than the rear section, thus
providing the front section with a substantially higher
spring rate. The vehicle axle is preferably mounted to
the front section of the spring, forwardly of the
transition zone between the front and rear sections. -~
With this construction in which the front
section of the composite spring has a substantially ;-
greater spring rate than the rear section, rotation of ~ i
the differential housing is controlled under heavy load ~-~
conditions to thereby prevent the housing from engaging
the floor of the vehicle and possibly damaging the ~ -
floor. - ~ -
The spring construction of the invention is a ~ ~
compact unit which can be incorporated in vehicles ~ ~-
having restrict~d space for the suspension system.
As the construction of the invention incor~
porates a fiber reinforced resin leaf spring, it is ~ -
lighter in weight than suspension systems utilizing -
steel leaf springs. ` ~ "
The suspension system of the invention can be ~ -
used with various types of vehicles and has particular
application to light trucks and vans which can encount-
er heavy loads during use.
Other objects and advantages will appear in
the course of the following description.
Description of the Drawings -
The drawings illustrate the best mode ~-
presently contemplated of carrying out the invention.
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In the drawings~
Fig. 1 is a side elevation of the spring
construction of the invention: and
Fig. 2 is a top plan view of the spring
construction.
Description of the Illustrated Embodiment
The drawings illustrate a leaf spring con~
struction for a vehicle that has particular application
to vehicles that encounter heavy loads during use, such
as light trucks or vans. The construction includes a
fiber reinforced resin leaf spring 1 that is preferably --
composed of substantially continuous fibers bonded by a
thermosetting resin, such as an epoxy or polyester
resin. The fiber reinforcement may take the form of
glass fibers, graphite fibers, or the like.
An eye 2 is connected to the front end of
spring 1 and provides an attachment to the vehicle
frame, wh-le a standard shackle 3 is connected to the -
opposite or rear end of the spring for attachment to
the frame. -
An axle 4 is mounted on the spring 1 through ~ -~
an axle mount unit 5, which can be similar to that ~-
described in copending U.S. Patent Application Serial
No. 07/226,460, filed August 1, 1988. The axle mount
unit 5 provides a firm connection between axle 4 and
spring 1 without the necessity of forming holes in the
spring 1 which wouId sever the reinforcement and
detract from the mechanical properties of the spring.
In accordance with the invention, spring 1 -~
has a constant cross section area throughout its length
and includes a front section 6 and a rear section 7.
Front section 6 has a substantially greater thickness
than the rear section, as seen in Fig. 1, and has a
substantially lesser width than the rear section, as
shown in Fig. 2. Sections 6 and 7 are joined by a
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tapered transition zone indicated by 8. As shown in
Fig. 1, the upper and lower surfaces of section 6 con-
verge and merge into the upper and lower surfaces of
rear section 7. As seen in Fig, 2, the side edges of
front section 6 diverge and merge into the side edges - ~;
of rear section 7. `
Axle 4 is mounted on the front thicker sec- ;~
tion 6 and is located immediately forward of the :--
transition zone 8.
Front section 6 has a substantially higher -
spring rate than rear section 7 and the specific ratio -
between the spring rates is determined by the particul-
ar requirements of the vehicle suspension. In general,
the ratio of spring rates between front section 6 and
rear section 7 will be in the range of 1:1 to 25:1. As
a load is applied to the vehicle, the front section 6
of the spring, having a higher or stiffer spring rate,
will be deflected to a lesser degree than the rear `~ -~
section 7, and this will reduce the amount of rotation
of the differential housing to prevent the housing from -
contacting the floor of the vehicle under maximum load
conditions.
As an example, with a stiffness ratio of 8
(the stiffness of front section 6 being eight times `~
that of rear section 7), and a rear to front length
ratio of l.S8:1, a pinion control angle of 1.8 per
inch of axle travel is obtained. As the stiffness
ratio is increased to a value of 25 the pinion control
angle will also increase to a value of 2.5 per inch of
axle travel, but this increase comes at a diminishing
rate. The increased pinion control angle and corres~
ponding downward rotation of the differential housing
will act to prevent contact between the differential
housing and ~he floor of a low profile vehicle under
load conditions. -
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The suspension system of the invention is a
compact construction that can be incorporated with
vehicles having a restricted space for the suspension.
The differential spring rate between the front and rear
sections of the spring is designed to control rotation
of the differential housing and thus prevent the hous-
ing from engaging and possibly damaging the floor of `-
the vehicle. ~- ;
As the construction of the invention incor-
porates a fiber reinforced resin leaf spring it has a ~ `
considerably lesser weight than suspension systems
utilizing steel leaf springs.
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