Design

 

Design Considerations

 

We at Car Tech System have to consider the following when designing a piston… but that’s why we’re here so that you don’t have to.

Before a piston is designed Car Tech System need to get a list of specifications from the customer. These are known as the terms of reference.’ This is basically an outline of the conditions that the engine designer expects the piston to operate in and include: maximum rpm, maximum torque, bore length, type of fuel, the expected lifespan (in hours) and the ring material specifications. As well as that the designer needs to have combustion chamber shape and size information, and valve intrusion specifications.

From these details the piston manufacturer produces the lightest possible design that’s capable of meeting the customer’s lifespan requirements. It sounds fairly straightforward until you realize how many variables the designer needs to cope with. The shape of a piston in an internal combustion engine, for example, is far more complex than a simple cylinder. The shape needs to take into account gas flow, compression ratios, unequal expansion, valve-intrusion and port timing.

On top of that it needs to be light and it needs to, cope with massive temperatures (380°C) and huge pressures (187 Bar). To put this in perspective, bike tires are set around 2-3 bar. On top of that pistons are placed under enormous loads; having to travel from up to 35 m/s to zero and back to 35 m/s as much as 36000 times a minute. Now 35 m/s works out at 78 mph which does not sound a lot until you realize that it has to slow down and stop, then accelerate back up to speed at a rate of two million one hundred and sixty thousand times an hour. That’s not all. On top of that a piston is required to seal gas, have minimal wear rates, and be reliable. 

One of the most interesting things about piston design is that they are not cylindrical in shape at all. In fact when cold they are oval and barrel shaped. The reason for this is because the thickness of the material of the piston varies considerably, and this, coupled with the fact that there’s a temperature gradient running all the way down from the crown to the skirt of a piston (and because the expansion of metal is directly proportional to the temperature), complicates matters so much that they have to be machined in such a way when cold to be perfectly cylindrical when hot. Add to this the basic requirement of minimal weight and maximum strength and suddenly the designer has a fair bit on his plate. 

Car Tech System’s knowledge and experience in this area has enabled the company to meet the demands of high performance automotive parts.

 

 

 

 

 

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