Introduction:
Urethane jounce bumpers are a primary component in an automobile’s suspension
system and are often subjected to static and dynamic loading. Fatigue caused by these every
day are desirable in analysis in order improve noise, vibration, and roughness performance for
the overall vehicle. Test engineers research the effects of impact energy on these bumpers to
improve safety, and durability in harsh road condition.
Design engineers are often tasked with designing a test system to determine bumper
deformation associated with these real-life environmental forces. The purpose of this study is
to design an impact energy test system to deflect a jounce bumper 0.0031mm as way to
validate jounce bumper strength. It is known that a force of 9 kilonewtons will deflect a
urethane jounce bumper 0.0031mm, hence the aim of the machine tester is to deflect new
bumpers to a known a displacement. This will serve as a basis for destructive impact testing and
help improve strength and durability for such critical automotive components.
Design Considerations:
Considerations were made in the designing of the chain drive such as velocity
fluctuation under the excessively stretched chain conditions, and corresponding drive gear
strength requirements. The design of a drive chain was developed in a way that maximizes
torque while converging the most energy by the motor, thus production maximum power
transmission. A drive chain provides many advantages, such as less load on the shafts (due to
the dual chains), in can be used in both short and long-distance power transmission, as well as
providing more power than belt and rope drives. The metal chains also occupy less area than
the drive belts due to having higher tensile strength per square cm. Since the component is a
chain, lubrication can reduce frictional loss, be operated under adverse thermal and
atmospheric conditions. The lubrication can allow of the operation under wet conditions. The
chain drive will need careful maintenance, lubrication, as it’s in constant tensile stress.
The disadvantages of the drive were also considered but are far outweighed by its
advantages. The three most common ways that a chain may fail are tensile, fatigue and wear. In
a tensile failure, the chain is overloaded in tension until it is stretched so badly it will not
function properly, or it is literally pulled apart. In a wear failure, the chain is loaded repeatedly
in tension, at a load below the yield strength (the chain is not stretched), until microscopic
cracks develop in the link plates or sidebars. In a wear failure, material is removed by sliding, or
sliding combined with abrasion or corrosion, until the chain will not function properly (will not
fit the sprockets) or the remaining material is so thin that it lets the chain break.
To counter the failure, frequent and proper lubrication of the chain is necessary
for the chain to avoid accelerated wear. The majority of chain drives and conveyors will
perform better and last longer when timely and adequate lubrication is provided. Even if overall
chain life is acceptable, lack of proper lubrication can cause other problems. When a chain is
starved for lubrication, wear from one joint to another can vary greatly, causing erratic action.
Rapid joint wear can cause early loss of timing in a conveyor. Lack of lubrication can increase
friction and power consumption and cause a harmful temperature rise. Chain lubrication is
needed mainly to slow the wear between the pins and bushings in the chain joints, to flush out
wear debris and foreign materials, and to smooth the chain’s engagement with the sprocket.
Additionally, lubrication may be needed to inhibit rust and corrosion, to carry away heat, and to
cushion impact forces.
Since chain lubricant should have low enough viscosity to penetrate critical internal
surfaces and high enough viscosity, or necessary additives, to maintain an effective film at the
prevailing temperature and pressure; the lubrication of choice is SAE Engine 20 for the chain.
This oil is ideal for due to the low shear rate (<9.3 mm^2/s) on the chains and conditions not
exceeding 150 degrees Celsius which is a perfect limit for the machine system. The preferred
oil for the rotating gears is SAE Gear Oil 80W. This is the ideal multipurpose gear lubricant for
shifting transmissions and protects against rust, corrosion, and has outstanding thermal
stability for long gear life.
Materials and Parts
The base (specimen cup) of the system tester is welded to four aluminum shafts (7075
Aluminum Alloy). The base plate is comprised of 1045 Medium Carbon Steel to stabilize the
machine in an upright position and by providing a low center of gravity. It’s high bulk modulus
allows the base to be resistant to compression, ideal in mounting the jounce bumper and
absorbing impact from the hammer. This carbon steel alloy was also chosen for the material of
the drive chain and gears. Since the belt will be in constant tension while raising the hammer as
well as absorbing vibrations from the impact, it’ll require considerable strength. The gears
would also be subjected to varying torsion from the motor, hence requiring high strength. The
creep must be considered for the chain for proper maintenance and lubrication also must be
practice. AISI 1045 is widely used for all industrial applications requiring more wear-resistance
and strength.
1045 Medium Carbon Steel
Shaft 7075 Aluminum Alloy, commonly known as “structural aluminum” was the
chosen material for the vertical rails, and base of the machine designed. The most important
benefit of 7075 aluminum is its high strength. While it does not have the same level of
corrosion resistance or weldability that other common alloys due, its resistance to stress and
strain makes it highly useful in impact applications where it allows for weight savings over steel.
7075 Aluminum Alloy
The composition of the hammer is 1060 high carbon steel. 1060 Carbon Steel is a
great compromise between hardness (edge holding ability) and pliability (strength) making it a
versatile carbon engineering steel for used for high impact machining. The fixed displacement
height of the hammer is 0.75 meters above jounce bumper which will be held in place by the
specimen cup of similar diameter to the bumper sample.
1060 High Carbon Steel
Conclusion
Designing impact force testers is a proven way to analyze that jounce bumpers
being tested meets proper specifications. By fixing the deflection size for the bumpers,
engineers can use Newton’s Laws along with Strain Energy Theories to approximate the
required force to produce damage. The objective of developing a machine to meet the 9
kilonewton load that the jounce bumper can withstand before and after deflection was met.
Having a system tester capable of consistently producing impact force is useful in bumper
design, and essential in prolonging its durability.
Bibliography
1. “Automotive Component Durability Testing using Quartz Piezoelectric Force Sensors,”
Metz, R, Automotive Testing Expo, 205
2. Department of Mechanical and Manufacturing Engineering, Faculty of Engineering,
University of Malaysia, 8 Jan. 2011, http://cdn.intechopen.com/pdfs/13358/InTechFatigue_characteristics_of_automotive_jounce_bumper.pdf. Accessed 22 Nov 2019.
3. Aidy All, R.S. Sidu and M.S.A. Samad (2011). Fatigue Characteristics of Automotive
Jounce Bumper, New Trends and Developments in Automotive System Engineering,
Prof. Marcello Chiaberge (Ed.).,ISBN: 978-953-307-517-4.