Vehicular powertrain mount assembly

A vehicular powertrain mount assembly comprising two metal bracket members and a volume of a resilient elastomeric material sandwiched between and adhesively bonded to the two brackets. An epoxy adhesive is used in bonding the metal to the elastomer producing a bond having a minimum tensile rupture strength of 3,000 Newtons when tested by ASTM D-429.

FIELD OF THE INVENTION 
The present invention generally relates to a vehicular powertrain mount 
assembly comprising two bracket members and a volume of a resilient 
material sandwiched therein and, more particularly, is concerned with a 
vehicular powertrain mount assembly comprising two bracket members and a 
volume of a resilient material sandwiched between and adhesively bonded to 
the two brackets. 
BACKGROUND OF THE INVENTION 
A vehicular powertrain mount assembly is usually known as an engine mount, 
a transmission mount, or the like. When an internal combustion engine 
powers a motor vehicle, there are numerous vibrations set up such as 
jounce vibrations, fore and aft vibrations, and torque and torque reaction 
vibrations. It is a customary practice to isolate these vibrations from 
the passenger compartment by using resilient powertrain mounts. Powertrain 
mount assemblies are also used to support a powertrain member on a 
vehicular frame to provide for jounce and roll control of the powertrain 
member relative to the frame. In a conventional powertrain mount assembly, 
two or more bracket members are bonded to a volume of a resilient material 
by adhesive means. The bracket members are normally stamped cold-rolled 
steel parts which can be attached by mechanical means to either the 
powertrain member or the frame member of a vehicle. A typical resilient 
material used in a powertrain mount assembly as a rubber material capable 
of absorbing most of the vibration from the powertrain member and the 
jounce from the frame member such that they are sufficiently isolated from 
each other. The type of rubber materials normally used are natural rubber, 
styrene-butadiene rubber, ethylene-propylene-diene-monomer rubber, and any 
other suitable elastomeric materials. 
The bonding of the rubber material to the metal bracket is ordinarily 
accomplished with a solvent-based adhesive that is applied to the metal 
prior to the rubber molding process and then co-vulcanized with the rubber 
during the cure cycle. This is frequently called an in-mold bonding 
process. Numerous problems are associated with the in-mold bonding process 
and its resulting product. A first problem is the costly rubber-removal 
operation. In a contemporary mount design with complicated rubber block 
shapes and interlocking structures, it is impossible to seal rubber from 
certain forbidden areas. Subsequent operations to remove the unwanted 
rubber are labor intensive. Moreover, a secondary phosphating operation is 
required to replace the phosphate coating removed with the rubber flash. 
Secondly, in an in-mold bonding process, metal brackets must first be 
placed in a mold cavity prior to the rubber vulcanization process. This 
greatly reduces the number of cavities allowed in a given mold size. The 
mold is frequently damaged from improperly positioned metal brackets. 
Furthermore, the mold cycle time of the mount assembly is increased 
because cold brackets must first be heated in the mold. 
Thirdly, there is a significant amount of solvent emissions from the 
in-mold bonding process due to the solvent-based adhesive used. In most 
cases, the use of expensive recovery equipment is necessary to meet air 
pollution regulations. 
It is therefore an object of the present invention to provide a powertrain 
mount assembly that can be bonded together after the rubber block is first 
vulcanized. 
It is another object of the present invention to provide a 
post-vulcanization bonded powertrain mount assembly that can be bonded 
together by an inexpensive process suitable for use in a production 
environment. 
It is yet another object of the present invention to provide a 
post-vulcanization bonded powertrain mount assembly comprising two bracket 
members and a volume of a rubber material sandwiched between and bonded to 
the two brackets by an epoxy adhesive. 
SUMMARY OF THE INVENTION 
My novel invention is a powertrain mount assembly comprising two bracket 
members and a volume of a rubber material sandwiched therein and bonded to 
the brackets by an epoxy adhesive. The rubber material is vulcanized prior 
to the bonding process. The epoxy adhesive can be cured slowly at room 
temperature or can be cured quickly at elevated temperatures. The epoxy 
adhesive allows the use of a very low bonding pressure applied on the 
metal brackets during the adhesive cure cycle. This is a great process 
advantage in that no bulky fixtures are required for the bonding process 
and furthermore, deformation of the rubber material can be avoided. My 
novel post-vulcanization bonded powertrain mount assembly can be cured at 
a lower temperature and in a shorter time than the conventional 
solvent-based adhesive bonded mount assembly. My post-vulcanization bonded 
powertrain mount assembly can be manufactured with essentially no 
formation in the rubber block resulting in a more consistent product. More 
design freedom in the rubber block shapes in my post-vulcanization bonded 
mount assembly is achieved since more complicated shapes of rubber blocks 
can now be used. 
I have further discovered that the use of an epoxy adhesive between rubber 
and metal in a powertrain assembly, i.e. a dynamic loading application, 
taught by the present invention produces a greatly unexpected result. I 
use the words "dynamic loading application" to describe applications in 
which the loading on the part is of a dynamic or a consistently changing 
nature instead of a static load which does not change. All powertrain 
mounts previously have been bonded with solvent based rubber adhesives. 
To someone skilled in the art in making powertrain mounts it would have 
been obvious that, in order to survive a dynamic loading condition, the 
adhesive joint itself must remain flexible and thus producing an impact 
resistant joint interface between rubber and metal. The adhesive joint 
produced by an epoxy adhesive is by no means flexible; instead, it is a 
very rigid joint. It is, therefore, entirely unexpected to the inventor 
that a rigid adhesive joint produced by an epoxy adhesive could survive in 
a dynamic loading application. 
This greatly unexpected result is further supported by Anderson, U.S. Pat. 
No. 4,198,037 in that, in his dynamic loading application, he concluded 
that no commercially available adhesive system could produce an acceptable 
adhesive bond in his elastomer compression spring. The only method 
Anderson found possible for bonding polyester elastomer to metal plates 
was to cause the elastomer to flow into the apertures in the plates 
forming a mechanical lock.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
My novel invention is a vehicular powertrain mount assembly comprising two 
bracket members and a volume of a rubber material sandwiched therein and 
bonded to the brackets by an epoxy adhesive. I have discovered that by 
bonding a vulcanized rubber block to metal brackets using an epoxy 
adhesive resulted in a powertrain mount assembly having superior 
properties and processing advantages. 
Referring initially to FIG. 1, where a typical engine mount assembly 10 is 
shown. A first metal bracket member 20 and a second metal bracket member 
40 are bonded to a volume of rubber material 30 by adhesive means. The 
adhesive used in our preferred embodiment is a two-part epoxy adhesive 
shown in FIG. 2 at joint interface 26 and 46. Mechanical means for 
securing engine mount assembly 10 to an engine (not shown) and a vehicular 
frame member (not shown) are shown at 22 and 42 in FIG. 1. 
In our assembly process, a volume of a rubber material (commonly known as a 
rubber block) is first compression molded in a press. A mold release is 
used which does not leave any residue on the rubber surface. I have 
successfully used rubber material such as natural rubber and 
ethylene-propylene-diene-monomer rubber for my powertrain mount 
assemblies. Other suitable rubber materials such as styrene-butadiene 
rubber, nitrile rubber, or the like, words equally well in my mount 
assemblies. I have used a silicone type mold release material which can be 
sprayed and curved on the mold surface. The rubber block surface to be 
bonded is normally primed with a material that makes it compatible with 
epoxy adhesives. For natural rubber, I have found a primer under the 
tradename of Chemlok.RTM. 7701 supplied by the Lord Corporation worked 
very well. Chemlok.RTM. 7701 is a solution of an organic acid which can be 
sprayed or brushed on the rubber surface and then dried at room 
temperature for five minutes. 
The epoxy adhesive I used is a two-part structural grade epoxy adhesive 
supplied by the Lord Corporation under the tradename of Fusor.RTM. 320 
resin and Fusor.RTM. 310B hardener. A structural grade adhesive is one 
that can be used in application where there are high stress loading 
conditions. The mix ratio I have used is ten parts resin to five parts 
hardener which resulted in a higher softening temperature than that 
specified by the manufacturer after cure. Fusor.RTM. 320 resin is a 
bisphenol-A type epoxy resin having a viscosity between 250,000 to 
1,000,000 CPS as determined by a Brookfield viscometer at 25.degree. C. 
with T-Bar-C at 5 RPM. It has a density (weight per gallon) between 11.7 
to 12.7 oz. The Fusor.RTM. 310B hardener is a mixture of a polyamide resin 
(60 to 70%), an aliphatic amine (2-7%), and aluminum powder (15-20%). It 
has a viscosity between 200,000 to 450,000 CPS as determined by the 
Brookfield viscometer at 25.degree. C. with T-Bar-C at 5 RPM. It has a 
density (weight per gallon) between 10.1 to 10.5 oz. 
I have used other types of structural adhesives that worked equally well in 
my novel invention. These include Epoxy Patch.RTM. 9340 supplied by the 
Hysol Division of Dexter Corporation, Epon.RTM. 828 resin supplied by the 
Shell Corporation cured by Versamid.RTM. 140 supplied by the General Mills 
Corporation. Other non-epoxy type structural adhesives such as 
polyurethane base adhesives may work equally well. One of such adhesives I 
have used successfully is Tyrite.RTM. 7500A and Tyrite.RTM. 7510B supplied 
by the Lord Corporation. 
After Fusor.RTM. 320 and Fusor.RTM. 310B are mixed together, it has a shelf 
life between 20 to 30 minutes. Within this time, the adhesive is applied 
to either the rubber surface or the metal bracket surface. After the 
rubber block and the metal brackets are put together, a low pressure (less 
than 5 PSI) is applied to the assembly normal to the bond planes. The 
pressure should be sufficient to spread the adhesive in the joint 
interface and extrude a small amount from the edges. The powertrain 
assembly under pressure is then subjected to a heating medium such as hot 
air or infrared such that the bondline temperature reaches 250.degree. F. 
for one minute. It can also be cured at room temperature in approximately 
24 hours. After the adhesive is cured, the bonded powertrain assembly is 
removed from the fixture and ready for packaging and shipment. 
My novel powertrain mount assembly bonded by an epoxy adhesive can be 
assembled easily and can be used at continuous service temperature as high 
as 220.degree. F. It has passed a vehicular service test at 220.degree. F. 
for six days under maximum engine load conditions. 
My post-vulcanization bonding process produces powertrain mount assembly 
having superior tensile rupture strength when compared to those bonded by 
the conventional in-mold bonding technique. I have conducted laboratory 
adhesion tests performed in accordance with the American Society of 
Testing and Materials (ASTM) test D-429 (method A). In this test, rubber 
is bonded between two parallel metal discs that are one inch in diameter. 
The two metal discs are then pulled apart in a tensile testing machine to 
determine the tensile rupture strength of the bond. 
For comparison, I have tested several commercial adhesives used in both the 
conventional in-mold bonding method and my novel post-vulcanization 
bonding method. 
TABLE 1 
______________________________________ 
TENSILE RUPTURE STRENGTH, NEWTONS 
POST- 
IN-MOLD VULCANIZATION 
SAMPLE BONDING BONDING 
______________________________________ 
Chemlok .RTM. 236 
1,378 1,150 
Chemlok .RTM. 238 
1,356 -- 
Thixon .RTM. OSN-2 
1,751 -- 
Chemlok .RTM. TS3604-72 
3,370 -- 
Fusor .RTM. 320/310B 3,846 
______________________________________ 
Chemlok.RTM. adhesives are supplied by the Lord Corporation. Thixon.RTM. 
adhesives are supplied by the Dayton Chemical Company. In Thixon.RTM. 
OSN-2 bonded samples, the bond strength or the tensile rupture strength of 
the bond is lower than usual since the samples tested were prepared with 
metal discs that were not phosphated. 
It is seen from Table 1 that epoxy post-vulcanization bonded samples 
(Fusor.RTM. 320/310B) showed higher bond strengths than all the other 
samples bonded with solvent-based rubber adhesives. It pulled 
approximately 15% higher than the best of the four adhesives tested with 
conventional in-mold bonded techniques, and also showed about 300% better 
strength than the samples post-vulcanization bonded by the conventional 
solvent-based rubber adhesive. 
I have found that with epoxy post-vulcanization bonded samples, the tensile 
rupture strength obtained in ASTM D-429 test was consistently over 3,000 
Newtons. Even though in-mold bonded Chemlok.RTM. TS3604-72 test samples 
also show an average tensile rupture strength of over 3,000 Newtons, many 
individual test samples were tested at strength values of under 3,000 
Newtons. It is therefore my conclusion that only epoxy post-vulcanization 
bonded samples consistently show an improved bond strength in powertrain 
mounts. 
While my invention has been described in terms of a preferred embodiment 
thereof, it is to be appreciated that those skilled in the art will 
readily apply these teachings to other possible variations of the 
invention.