• Abstract
  • Reason for the Design.
  • Introduction.
  • Design analysis of power screw
  • Design criteria
  • The calculations and analysis

The work in this study is in general described, an electrically operated car jack, automatically operated by switch buttons .The prototype includes motor powered from the car drive shaft. The motor with gearing system will be the lifting mechanism. When the car needed to be lifted, just press the button and release the button at a desired height level. The common problem faced by the current available car jacks in the market is it is manually operated and needed physical effort to lift the vehicle.

  • Available jacks that's uses for left the car are difficult to use and need to some strength while lifting the car, so it’s difficult to use especially for the elderly and women.
  • Furthermore, available jacks are typically large, heavy and also difficult to store, transport, carry or move into the proper position under an automobile.
  • There also reports on car jacks which lead to a serious number of accidents.
  • Therefore, our project will solve this problem radically; where we are going in our project to design a built in automatic car jack will lift the entire car or sides of it by pushing a button next to the driving seat.
  • Our jack is self-locking, which make it safer than other jack technologies like hydraulic jacks which require continual pressure to remain in a locked position.
  • So in use of our jack we will save effort, time and don’t need to storage area like traditional jacks.
  • Our jack will be designed as four power screw jacks. And will be connected to four positions in the car beside every wheel.
  • These four jacks connected to one power source which internal car power source (the car drive shaft) with another shafts and controllers as bellow in the figure below.

  • Each jack will have a single button to control it from the driving seat, so there is four buttons for the four wheels.
  • Our jack will be designed to lift a car with an average weight of 1.5 tons with factor of safety to be 3.
  • our design is safe, reliable and able to raise and lower the height level by control system.
  • So as a result in our project we will make astudy,analysis,design andselection to a power screw jack and its components (screw, gears and bearings …), the shafts, the power source and the electrical connections …..

See the figure below which show the component of the power screw jack which we

will going to analysis and design.

  • The total average weight of the car is to beas following

( 1500 kg * 9.81 = 14715 N = 3306.742 Ibf );

then this weight will be distributing to the four jacks and we will take the

maximum load to be applied (1000 Ibf ) for each.

  • Our design steps will be according to satisfying the design factor of safety that’s we chosen to be at …. then we will make a trials with changing the major diameter for the power screw from table ( 8 – 3 ) and when we achieve or exceed our design factor of safety we will stop the trials and deciding to chose that’s parameter in the last trial .

Design criteria

The power screw material is chosen to be steel , machine oil (to minimizing friction )

with nut material “ the gear “ of steel then the coefficient of friction ( ƒ ) for thread

pairs from table ( 8 - 5 ) is to be ( 0.17 ) “ starting friction “ .

The power screw is to be a single thread then the lead is the same as the pitch.

The power screw is an Acme thread with thread angle equal to 29 ْ= 2α.

The calculations and analysis …

Firstly we find the mean and root diameters then the lead …

Then substitute it in the raising and lowering torque equations …

Check power screw for self locking condition by make sure that’s the following relation is satisfying ( where tan λ = l/ π dm ) then for self locking …

To find the efficiency during lifting the load we use …

Then get the stresses by using these equations …

Then the three-dimensional stresses according to the following figure …

And sub it in the von Mises stress equation …

Finally check out for the factor of safety to be equal or more than 3

( we chose from table ( A – 18 ) a steel G10060 (HR) with yield strength = 24 kpsi ) then

And get the factor of safety ( n ) .

Trial / F / d / P / dr / dm / L / π / f / sec α / λ / self locking
1 / 1000 / 0.25 / 0.0625 / 0.1875 / 0.21875 / 0.0625 / 3.141593 / 0.17 / 1.0329 / 0.0909457 / yes
2 / 1000 / 0.3125 / 0.071429 / 0.241071 / 0.276786 / 0.071429 / 3.141593 / 0.17 / 1.0329 / 0.0821445 / yes
3 / 1000 / 0.375 / 0.083333 / 0.291667 / 0.333333 / 0.083333 / 3.141593 / 0.17 / 1.0329 / 0.0795775 / yes
4 / 1000 / 0.5 / 0.1 / 0.4 / 0.45 / 0.1 / 3.141593 / 0.17 / 1.0329 / 0.0707355 / yes
5 / 1000 / 0.625 / 0.166667 / 0.458333 / 0.541667 / 0.166667 / 3.141593 / 0.17 / 1.0329 / 0.0979415 / yes
6 / 1000 / 0.75 / 0.166667 / 0.583333 / 0.666667 / 0.166667 / 3.141593 / 0.17 / 1.0329 / 0.0795775 / yes
7 / 1000 / 0.875 / 0.2 / 0.675 / 0.775 / 0.2 / 3.141593 / 0.17 / 1.0329 / 0.0821445 / yes
Trial / TL / TR / e / τ / σ / σB / σb / σ' / Sy / n
1 / 9.112774 / 29.62578 / 0.335761 / 22889.49 / -36216.6 / -17694.4 / 61930.37 / 94666.28 / 24000 / 0.253522
2 / 12.74872 / 36.19105 / 0.314117 / 13156.31 / -21908.8 / -12236.2 / 42147.06 / 60819.63 / 24000 / 0.394609
3 / 15.78206 / 43.13109 / 0.307502 / 8853.198 / -14967.1 / -8708.96 / 29859.29 / 42398.5 / 24000 / 0.566058
4 / 23.30349 / 56.12098 / 0.283593 / 4465.966 / -7957.75 / -5375.9 / 18143.66 / 24428.17 / 24000 / 0.982472
5 / 20.67506 / 75.3786 / 0.351901 / 3987.252 / -6061.04 / -2679.68 / 9500.685 / 15240.66 / 24000 / 1.574735
6 / 31.56412 / 86.26219 / 0.307502 / 2213.3 / -3741.77 / -2177.24 / 7464.822 / 10599.63 / 24000 / 2.264231
7 / 35.69641 / 101.3349 / 0.314117 / 1678.101 / -2794.49 / -1560.75 / 5375.9 / 7757.606 / 24000 / 3.093738

The position of installing the jack