# Homework Help: Engine - Drive Shaft Coupling Torque

1. Dec 26, 2011

### 123321

1. The problem statement, all variables and given/known data

A solid drive shaft is connected to an engine by a coupling, which has drive pins located on a pitch circle diameter of 80 mm (Note: the diameter of the pitch circle is greater than the diameter of the drive shaft). If the maximum power output of the engine is 90kW at 5000 rev/min, the shear stress in drive pins is not to exceed 60 MN/m2, and the shear stress in drive shaft is not to exceed 70 MN/m2, determine:

(i) The minimum acceptable diameter of the shaft
(ii) If the minimum number of solid drive pins that are required is 5 determine the diameter of each pin

2. Relevant equations

T/J=$\tau$/r

P=Tω

3. The attempt at a solution

I worked out the torque of the engine to be 47.12 MNm by using P=Tω but can I just put this value into T/J=$\tau$/r to find the answer to (i)?

2. Dec 26, 2011

### nvn

123321: Your value for torque, T, currently looks incorrect. Try again, paying attention to units and correct unit conversions. After you obtain T, yes, you can use T in your first relevant equation.

By the way, MN/m^2 is called MPa. Always use the correct, special name for a unit. E.g., 60 MPa, not 60 MN/m^2.

3. Dec 26, 2011

### 123321

Thanks for answering this question too nvn, I think I'm going to skip the I beam question. I've got no clue. Haha!

To convert rpm to rad/sec you times by 2$\Pi$/60 right? Which give me 523.6 rad/sec. Then multiplying this by the power to give me T, which gives me the same answer.

4. Dec 26, 2011

### nvn

123321: Should you not divide this into power? Check your algebra, and try again.

5. Dec 26, 2011

### 123321

Haha! That was embarassing...

6. Dec 27, 2011

### 123321

I worked out the torque of the engine to be 171.89 and then I was going to put it into T/J=τ/r the problem is that J = 2I = Πd^4/32 so do I use 40 mm as the radius or am I supposed to have two unknowns?