Car Jack Preliminary Analysis
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This plot shows the change in height of the top plate with a linear change in distance between the left and right pivot. This demonstrates the non-linearity of the system under usage. From a usage standpoint this non-linearity would require the user to apply a larger torque in the early stages of the lift. As the car is lifted higher the amount of torque needed to cause upward motion will decrease. | This plot shows the change in height of the top plate with a linear change in distance between the left and right pivot. This demonstrates the non-linearity of the system under usage. From a usage standpoint this non-linearity would require the user to apply a larger torque in the early stages of the lift. As the car is lifted higher the amount of torque needed to cause upward motion will decrease. | ||
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Revision as of 23:15, 1 March 2007
Contents |
Mechanics Of The Car Jack
This plot shows the change in height of the top plate with a linear change in distance between the left and right pivot. This demonstrates the non-linearity of the system under usage. From a usage standpoint this non-linearity would require the user to apply a larger torque in the early stages of the lift. As the car is lifted higher the amount of torque needed to cause upward motion will decrease.
This plot shows the force between the left and right pin that would be applied to the threaded rod under 1000lbs of downward loading. It can be seen that when the jack is in its mostly closed state a much larger force must be applied to the thread to raise the 1000lb load. Under normal conditions the pinch weld of a car is approximately 4 inches off the ground. By this point the system has reached a linear portion of its travel and becomes easier for a person to operate.
Input forces required to lift a car
A relationship between torque applied to a thread and the resulting tension or compression force generated can be determined as follows:
T = Torque required (inch pounds)
F = Bolt tension desired (Axial Load) (pounds)
D = Nominal bolt diameter (major dia)
Equation: T = .2 * D * F
Looking at the case where a 1000lb compression load must be applied to the threaded rod
T = .2 * .546in * 1000lb
Torque required will be 109.2 in*lbs
Since the lever arm included with the jack is 6 inches long. The force required by the user will be
F = 109.2 in*lbs / 6in
F = 18.2lbs
Buckling of a upper arm
A simplified model of the upper arm has been modeled in Ansys and analyzed to find its capacity before buckling. The 1st buckling mode was seen at approximately 22,000lbs. A video of this mode shape can be seen here.
Loading Conditions
Shown here is the model of the upper arm with visible loading conditions. The Bearing load of 1lb is used to simulate the force transfered to the upper arm from either the right or left pin. This number will be multiplied by the a factor until the system has become unstable and buckling has occurred. Cylindrical Support 1 simulates the radial and axial constraints applied to this member by the upper pin. Cylindrical Support 2 simulates the tangential constraint applied by the gear profile that mates with the other upper arm.
References
http://www.engineersedge.com/torque.htm
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