Structural engineers are key players powering Perkins performance.

Mention structural engineering and many people immediately picture teams designing bridges and skyscrapers. That amuses Graham Hill because the focus of his work as a structural engineer is on components that often are small enough to be held in his hands.

Graham is the engineering manager for structural simulation at Perkins. His team is responsible for making sure that every part that goes into a new Perkins engine is structurally sound and will deliver the durability and performance customers expect.

The process begins long before the first prototype engine is built and continues long after it is released for serial production. It usually starts with the crankshaft which is the heart of the engine.
 

First, get the crankshaft right.

“If you get the fundamental dimensions of the crankshaft right,” Graham explained, “you’ve determined the physical size of the engine and its robustness and efficiency. But, that’s not as simple as it sounds.

“The industry is demanding more power density, meaning engines that are physically smaller but still deliver the power we used to get from a larger engine. Customers also want better fuel efficiency and longer maintenance intervals. And, of course, today’s engines have to meet global emissions standards. Balancing those requirements can be tricky.”

A smaller crankshaft, for example, needs to be stronger if it’s going to deliver the same power as its larger predecessor. That usually means it will need larger bearings to handle the increased load.

But, larger bearings generate more drag as they rotate and that consumes energy which isn’t available to do work outside the engine. That, in turn, impacts fuel economy. Making the bearings smaller may impact durability, though, so it’s a very delicate balancing act to get everything optimised.
 

Build the right tools.

“You can do some of the basic calculations with simple pencil-and-paper mathematics,” Graham continued, “but that quickly becomes inadequate for something as complex as an engine. Then you need the power of computing and specialised software to get the answers you’re looking for and soon you’re in the realm of simulation and modelling.”

The sophisticated simulation and modelling tools available today didn’t exist when Graham and his team began to utilise computers in their work. So, they wrote their own software. Today, they use the best available commercial software but enhance its capabilities with their in-house developed proprietary code.

“We’re convinced that our in-house code gives us an advantage over our competitors,” Graham said. “It lets us build in an extra degree of durability, or compactness, or performance as appropriate for the particular engine we’re designing. That’s a step beyond what we can do with commercial code and it gives us an edge in the marketplace.”
 

Model the whole system.

Graham notes that the models allow the team to analyse not only the behaviour of individual components, but also of the interactions of multiple parts and even the entire engine. Going back to the crankshaft example, the model allows them to examine how the load generated by the piston and connecting rod is transferred to the crankshaft and subsequently to the engine block and everything attached to it.

“We can look at how all the components attached to the engine respond to the excitation to make sure they really are durable. But, that’s only one example of how modelling and simulation allow us to optimise an engine design.”

Graham explains that noise is an issue in many engine applications, and that simulation tools can be used to reduce it. By observing how the load that each cylinder applies to the engine as it fires is transmitted throughout the assembly, it’s possible to identify the source of the subsequent noise. Adding a rib to a section of the block that is vibrating like a loud speaker, for example, can eliminate the noise it produces. The same analytical tools can also be used to make sure the stresses produced in the crankshaft aren’t high enough to damage it over the life of the engine.
 

Measure things you can’t see.

“Simulations can even let you measure things in an engine that you can’t actually see or measure while it’s running,” Graham noted. “Cylinder bores change shape as they heat and cool, but you can only physically measure the shape when the engine is cold.

“You start by measuring the cold bore and comparing it to the simulation. Then you adjust the model until it agrees with the physical measurement. Now you can run the model to simulate the changes as the bore heats up with high confidence in the result.

“We really can tell what’s going on inside an engine well beyond what can be physically measured.”
 

Reduce OEM new product introduction time.

The value of simulation and modelling doesn’t end with a prototype or production engine. Many customer applications have unique parts or configurations that need to be investigated before they are released. A simulation can shorten the process.

“Once you’ve simulated the configuration and are confident it will work, you only have to do one physical test to confirm the result,” Graham said. “Then you can quickly move to production and start delivering reliable engines to the customer with high confidence.”
 

Use the power wisely.

Building an engine in “cyber space” before building a physical prototype or moving to serial production can shorten the development cycle, but the technology needs to be applied carefully.

“A good engineer always wants more data and more accurate data, but that comes at a price,” Graham said. “The more physics one puts into the system the longer it takes to compute the answer.

“There are times when a pencil-and-paper calculation is probably adequate, and it can get you an answer quickly. And there are times when a detailed model is the only solution, and you just have to wait for the answer.

“The trick is knowing which method to use for a particular issue, and that comes from experience. Using the right tool, in the right way, at the right time is the key to our success.”

Graham also recently caught up with industry journalist Peter Haddock for his Discovering the Power of Perkins video series. Check out the video below.