Cylindrical vibration damping bushing

A cylindrical vibration damping bushing is provided which has an outer cylinder, an inner cylinder coaxially disposed within the outer cylinder, and having a radially outwardly expanded portion in its axially central portion, a pair of vibration damping rubber members press-fitted between the outer cylinder and the inner cylinder from both ends of the outer cylinder, and a pair of inserts, each being made of a resin material having good slidability and embedded in an inside end portion of each vibration damping rubber member so that an inside end surface thereof abut on each other. Each insert has a concave surface having a configuration conforming to that of the spherical outer surface of the expanded portion of the inner cylinder to enable the inserts to be slid on the spherical outer surface of the expanded portion. Each vibration damping rubber member has a seal portion in an outside end portion thereof, which is in air tight contact with the inner cylinder for retaining a lubricant between the concave surface of each insert and the spherical outer surface of the inner cylinder whereby the outer cylinder can be freely rotated about and twistingly rocked on the spherical outer surface of the inner cylinder with a simple construction and reduced production costs.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a cylindrical vibration damping bushing, 
and more particularly to a simply-structured vibration damping bushing 
which is preferably used in a coupling portion of a vehicle part such as a 
suspension arm. 
2. Description of the Prior Art 
Conventional cylindrical vibration damping bushing are provided with a 
vibration damping rubber body between coaxially disposed inner and outer 
cylinders, and are frequently used in portions of a vehicle which require 
vibration isolation. 
In the cylindrical vibration damping bushing used in the coupling portion 
of the suspension arm, the inner cylinder and the outer cylinder are 
ordinarly rotatable relative to each other. 
Recently, in order to improve the ride of a vehicle, vibration damping 
bushing have been developed which enable the twistable rocking of the 
suspension arm without any resistance. Several examples of such vibration 
damping bushings are disclosed in Japanese unexamined utility model 
publications Nos. Sho 61-49143, 62-110617, 62-110619 and 62-110644, and 
Japanese examined utility model publication No. Sho 63-44572. These 
vibration damping bushings are characterized in that an axially central 
portion of the inner cylinder has a spherical expanded portion, and that a 
vibration damping rubber body and an outer cylinder are disposed in that 
order around the spherical expanded portion through a resin member. 
However, the above-described conventional vibration damping bushings have a 
relatively complex construction. They require race metal fittings for 
retaining the resin member, and seal members for retaining lubricant 
between the expanded portion and the resin member. This result in 
difficult assembly and maintenance of these members and accordingly the 
production costs are increased. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a cylindrical vibration 
damping bushing which is simple in construction, allows the free twistable 
rocking of a suspension arm or the like, and can be produced at low cost. 
Another object of the present invention is to provide a cylindrical 
vibration damping bushing which prevents the generation of play in sliding 
and rotating parts, and maintains good sealing performance while allowing 
the free twistable rocking of the suspension arm or the like. 
The cylindrical vibration damping bushing in accordance with the present 
invention has an outer cylinder, an inner cylinder coaxially disposed 
within the outer cylinder, a pair of vibration damping rubber members 
press-fitted between the outer cylinder and the inner cylinder from both 
ends of the outer cylinder, and a pair of inserts, each made of a resin 
material having good slidability, embedded in an inside end portion of a 
respective vibration damping rubber member. 
The axially central portion of the inner cylinder is expanded radially 
outwardly to form an expanded portion having a spherical outer surface. 
Each of the inserts is provided with a concave surface for sliding on the 
spherical outer surface of the expanded portion. 
Each of the vibration damping rubber members is integrally provided with a 
seal portion extending from an outside end portion thereof towards an 
outer surface of each end portion of the inner cylinder. A projecting end 
of the seal portion is in airtight contact with the outer surface of the 
inner cylinder. 
To assemble the cylindrical vibration damping bushing having the 
above-described construction, first, each insert is embedded in each of 
the vibration damping rubber members, and the seal portion is formed 
therein. Then, the thus prepared vibration damping members are 
press-fitted between the outer cylinder and the inner cylinder from both 
end openings of the outer cylinder. The concave surface of each insert 
comes into sliding contact with the spherical outer surface of the 
expanded portion while the seal portion of each of the vibration damping 
rubber members comes into airtight contact with the outer surface of the 
inner cylinder. 
Upon fitting the outer cylinder in an eye of a suspension arm or the like, 
the suspension arm can rotate about the inner cylinder, and twistingly 
rock freely by virtue of the inserts sliding on the spherical outer 
surface of the expanded portion. 
As described above, the cylindrical vibration damping bushing in accordance 
with the present invention enables the free twistable rocking of a 
suspension arm or a like vibrating arm with a simple construction so that 
time and labour for the maintenance and assembling of vehicle parts, as 
well as production costs can be greatly reduced.

DETAILED DESCRIPTION OF THE EMBODIMENTS 
FIGS. 1 and 2 illustrate a first embodiment of a vibration damping bushing 
according to the present invention. 
In FIG. 1, an inner cylinder 1 having a ring-shaped cross section is 
coaxially disposed within an outer cylinder 3 having a ring-shaped 
cross-section. The axially central portion of the inner cylinder 1 is 
thick to provide an expanded portion 11 which expands radially outwardly 
so as to have a sperical outer surface. A pair of vibration damping rubber 
members 2A, 2B are respectively press-fitted between the inner cylinder 1 
and the outer cylinder 3 from both end openings of the outer cylinder 3. 
The vibration damping rubber members 2A and 2B are the same shape and 
symmetrically positioned with respect to one another. The details of the 
vibration damping rubber member will be explained with reference to FIG. 
2. The vibration damping rubber member 2A has a cylindrical shape, and the 
external diameter l.sub.1 thereof is greater than the internal diameter of 
the outer cylinder 3. A cylindrical resin insert 4 having a concave 
surface 4a having a configuration conforming to that of half of the 
spherical outer surface of the expanded portion 11 is embedded in an 
inside half portion of the vibration damping rubber member 2A. The inserts 
4 are made of a resin material having good slidability, such as high 
molecular weight polyethylene and a polyacetal. 
A thin-walled cylindrical seal portion 21 is integrally formed in an 
outside half portion of the vibration damping rubber member 2A so as to 
extend radially inwardly, and the internal diameter l.sub.2 thereof is 
less than the external diameter of the inner cylinder 1. An outside end 
portion of the vibration damping rubber member 2A projects radially 
outwardly like a step to provide a stopper portion 22. 
A pair of vibration damping rubber members, each having the above-described 
construction are press fitted between the outer cylinder 3 and the inner 
cylinder 1 coated with lubricant from both openings of the outer cylinder 
3 until inside end surfaces of the vibration damping rubber members 2A, 2B 
abut each other at the the expanded portion 11, and each of the stopper 
portions 22 abuts each of the longitudinal ends of the outer cylinder 3. 
In this state, the concave surfaces 4a of the inserts 4 come into sliding 
contact with the spherical outer surface of the expanded portion 11 via 
the lubricant, and projecting ends of the seal portions 21 come into 
elastic contact with the outer surface of the inner cylinder 1 to prevent 
the lubricant from leaking out from the interior of the bushing, and also 
prevent muddy water, dust or the like from entering there. 
In using the cylindrical vibration damping bushing of the present 
embodiment in a coupling portion of a suspension arm of a vehicle, the 
outer cylinder 3 is fitted in an eye (not shown) of the suspension arm 
while a bolt (not shown) provided in a suspension member (not shown) is 
fitted in the inner cylinder 1. The slide of the inserts 4 on the 
spherical outer surface of the expanded portion 11 enables the suspension 
arm to rotate freely about the bolt of the suspension member, and to 
twistingly rock freely thereon in the directions shown by the arrows in 
FIG. 1. 
FIG. 3 illustrates a second embodiment of a vibration damping bushing 
according to the present invention. In order to press fit the vibration 
damping rubber members 2A, 2B more securely, in the second embodiment an 
engageable convex portion 41 is provided in an inside end surface of one 
of the inserts 4 while an engageable concave portion 42 to be engaged with 
the engageable convex portion 41 is provided in the inside end surface of 
the other insert 4. 
In accordance with the second embodiment, upon the abutting of the inside 
end surfaces of the vibration damping rubber members 2A, 2B on each other, 
the engageable convex portion 41 and the engageable concave portion 42 are 
engaged with each other so that the vibration damping rubber members 2A, 
2B are more fixedly secured between the inner cylinder 1 and the outer 
cylinder 3. 
FIG. 4 illustrates a third embodiment of the present invention wherein the 
vibration damping bushing is used in a coupling portion of a suspension 
arm of a vehicle. In FIG. 4, reference numeral 5 designates an eye 
provided in an end of a suspension arm (not shown). The inner cylinder 1 
is coaxially inserted into the eye 5, and is secured to a bracket 62 
provided in a vehicle frame (not shown) by means of an axis member 61 
inserted into the inner cylinder 1. An expanded portion 11 having a 
spherical outer surface is provided in the axially central portion of the 
inner cylinder 1. The vibration damping rubber members 2A, 2B are 
respectively press-fitted between the inner cylinder 1 and the eye 5 from 
both end openings of the eye 5. 
The details of the vibration damping rubber members of the third embodiment 
will be explained with reference to FIG. 5. Vibration damping rubber 
member 2B has a cylindrical shape. The outer cylinder 3 which has an 
L-shaped cross-section, is joined to the outer surface of the vibration 
damping rubber member 2B, and is provided with a flange portion 31 in its 
outside end. A resin insert 4 which is made of a resin material having 
good slidability is embedded in the vibration damping rubber member 2B. 
The inside end portion of the insert 4 protrudes from the inside end of 
the outer cylinder 3 by a predetermined amount l.sub.3. The inside half 
portion of the insert 4 has a concave surface 4a having a configuration 
conforming to that of the spherical outer surface of the expanded portion 
11. 
A thin-walled cylindrical seal portion 21 extends radially inwardly from 
the outside portion of the vibration damping rubber member 2B, and 
inwardly projecting seal lips 211 and 212 are formed in the seal portion 
21 in parallel with each other. Another seal lip 213 is also formed in the 
seal portion 21 so as to project sidewardly. 
The vibration damping rubber member 2B is further provided with a shock 
absorbing rubber layer 22 extending along the flange portion 31 of the 
outer cylinder 3. 
The vibration damping rubber members 2A, 2B having the above-described 
construction are press-fitted between the eye 5 and the inner cylinder 1 
coated with lubricant from both ends of the eye 5 until the concave 
surface 4a of each insert 4 protrudes from the inside end of the outer 
cylinder 3 comes into contact with the outer surface of the expanded 
portion 11. Then, the vibration damping rubber members 2A, 2B are further 
press-fitted until the flange portions 31 of the outer cylinder 3 abut on 
the opening end of the eye 5. This results in the vibration damping rubber 
members 2A, 2B being compressed and deformed in an axial direction, and 
each insert 4 relatively moving backwards until the inside end surface of 
each insert 4 becomes substantially flush with the inside end surface of 
each of the vibration damping rubber members 2A, 2B as shown in FIG. 4. An 
elastic force of each of the vibration damping rubber members 2A, 2B is 
applied to each insert 4 with the result that the insert 4 is brought into 
close contact with the outer surface of the expanded portion 11. 
Accordingly, the concave surface 4a of each insert 4 comes into contact 
with the outer surface of the expanded portion 11 via the lubricant 
without generating play therebetween so as to smoothly slide thereon. As a 
result, the suspension arm can smoothly rotate about the inner cylinder 1, 
and also twistingly rock freely in the directions shown by the arrows in 
FIG. 4. 
At this time, the seal portions 21 are forcibly deformed outwardly by the 
inner cylinder 1 so that the seal lips 211, 212 come into pressure contact 
with the outer surface of the inner cylinder 1 to prevent the lubricant 
from leaking out from the interior of the vibration damping bushing. 
Moreover, when the brackets 62 are attached to the inner cylinder 1, the 
end of each seal lip 213 comes into elastic contact with the inside 
surface of each bracket 62 to prevent dirt or the like from entering the 
interior of the vibration damping bushing. 
The shock absorbing rubber layers 22 serve to prevent the generation of 
noise or the like when the flange portions 31 of the outer cylinder 3 abut 
on the inside surfaces of the brackets 62. 
FIG. 6 illustrates a fourth embodiment of the present invention. 
In FIG. 6, the seal portion 21 in the free state is of the same shape as it 
is when deformed due to the penetration of the inner cylinder 1, and the 
internal diameter thereof is less than the external diameter of the inner 
cylinder 1. The construction of the fourth embodiment of the remainder of 
the vibration damping bushing is substantially the same as that of the 
third embodiment. In accordance with the fourth embodiment, substantially 
the same operation effect as that of the third embodiment can be obtained. 
FIG. 7 illustrates a fifth embodiment of the present invention. In FIG. 7, 
each insert 4 is provided with an annular groove 43 having a rectangular 
cross section in an inside end portion thereof so as to face the expanded 
portion 11. Groove 43 which serves as a grease groove for retaining 
lubricant around the inner cylinder 1. The construction of the remainder 
of the vibration damping bushing of the fifth embodiment is substantially 
the same as that of the third embodiment. In accordance with the fifth 
embodiment, the grease groove enables the smoother rotation of the 
suspension arm about the inner cylinder 1. 
FIG. 8 illustrates a sixth embodiment of the present invention. In FIG. 8, 
the spherical expanded portion 11 is provided with a flat top surface 11a. 
A space serving as the grease groove is formed between the flat top 
surface 11a and the concave surfaces 4a of the inserts 4. This 
construction also achieves an operational effect similar to that of the 
fifth embodiment. 
FIG. 9 illustrates a seventh embodiment of the present invention. In FIG. 
9, the concave surface 4a of each insert 4 has a configuration which does 
not conform to that of the top surface 11a of the expanded portion 11 so 
as to generate a space between the top surface 11a and the opposed concave 
surfaces 4a. This space serves as the grease groove. The seventh 
embodiment also achieves an operational effect similar to that of the 
fifth embodiment.