“Too many moving parts” has gone from something gearheads and engineers would say to a common expression. Whenever something is complex and difficult to keep going, people describe it that way. Recent developments in internal combustion engines are continuing the trend of using less fuel to get more power while making lower emissions, but this progress comes at a cost. More and more parts are needed, which drives up costs to build and maintain them.
Adding more and more complexity, more moving parts, cannot go on forever. If current trends hold, simpler electric drivetrains will become cheaper to build, maintain and charge. Few consumers would pick internal combustion in this scenario.
Before we talk about the current developments, we need to take a quick look at the history of engine complexity and give a quick look at the technology for the unfamiliar.
Some of the internal combustion engine’s parts have been around since ancient times. Combustion and expansion, when done repeatedly, creates a reciprocating, or “back and forth” motion that needs to be converted into circular motion to be useful. Cranks (pictured above) have done this since at least 200 BC, if not earlier, for the back-and-forth motion from human muscles to drive a machine with our hands. Over centuries, inventors around the world came up with the idea of using multiple cranks on one shaft in various machinery, and invented the first crankshafts. This way, circular motion could be converted into multiple reciprocating motions, or, multiple sources of reciprocating motion could join together to make a stronger circular motion than one source alone.
By the 17-18th century, inventors were playing with using combustion to push pistons, which were then connected by connecting rods to a crankshaft, like shown above. Early experiments relied on gunpowder, but were not mass produced. Later, in the 19th century, inventors were using the burning of flammable gases to push the pistons. The first modern example of this was in the 1860s, when Lenoir and Otto built a complete engine that resembled the above animation, including a flywheel to smooth out the circular motion (part is black), which was borrowed from external combustion engines like steam engines.
The rest of the 19th century saw a wide variety of approaches to the rest of the puzzle: putting in air and fuel and getting the burnt exhaust out. the simplest designs only had an intake and compression stroke, and an exhaust stroke like pictured at right. The movement of the piston inside the engine opened and closed the holes at the right time. Cooling is done with fins on the side for air cooling. The only extra moving parts are the fuel pump and the magneto, to make electricity for the spark plug.
This simple design is still in use today for many off-road applications. Tightening emissions standards during the 20th century first pushed two-stroke engines into smaller vehicles like motorcycles, and then off the road entirely. Later regulations in some places have pushed many manufacturers to move to more complex designs, once again to reduce emissions.
Four-stroke engines gave more control over the flows of gases, but at the cost of increased complexity. A mechanism for controlling when the valves were to be open and when they were to be closed had to be developed.
The above example uses the Otto Cycle, with an intake stroke, compression stroke, power stroke and exhaust stroke. While the exact placement varied, most four stroke engines use a camshaft (a shaft with lobes that push the valves open) and spring mechanisms to open and close the valves. This set of mechanisms is known as the valvetrain. The above animation uses a single cam over the top of the pistons, known as an overhead cam.
The simplest designs have only one camshaft, and control the valves in all cylinders, no matter the number. This requires one timing belt or chain to turn the camshaft, and doesn’t have a great number of moving parts. But to get greater control, manufacturers moved to using as many as four camshafts with four or more valves per cylinder. This meant valvetrains grew to be more complex than the rest of the engine. Some manufacturers struggled to come up with good, reliable designs as they became more and more complex, but with experience, these problems have become less common.
During the 20th century, many other moving parts became more common. Air cooled engines are becoming more and more rare, so most engines have a water pump, thermostat, and radiator. Hand cranks were used to start the earliest gasoline vehicles, but electric starter motors were added to make starting the car much easier. Oil pumps were added to increase lubrication. Magnetos were replaced by generators and then alternators, which attach to the engine to use rotational energy to make electricity. Carburetors were replaced with fuel injection systems that have as many as 2 injectors per cylinder.
Complex computer control systems proliferated. Emissions components were added. The end result was the complexity you see in the Youtube video above, and it has only become more complex from there. I can’t cover it all here, but variable valve timing, direct injection, and a host of other technologies all added moving parts that could cripple the whole system if they malfunction.
Current Trends In Gasoline Engines
This trend toward increased complexity is not over yet. The big challenge they’re working on right now is that you need far less power to move a car at cruising speed than you need to accelerate to that speed. If you build an engine big enough to accelerate, you are wasting that extra size when cruising. Build an engine just big enough to cruise, and you get slow acceleration that most buyers won’t put up with.
One solution has been forced induction. By adding a turbo or supercharger to a smaller engine, you stuff in more air and fuel, so it makes more power. By having bypass valves, you can effectively “turn off” the turbo for cruising, but have that extra power available only when the driver needs it. However, this does come at a cost of complexity.
The turbo or supercharger requires several additional parts, including the turbine or supercharger itself, control valves, sensors, the intercooler and cooling.
Another approach is to make a gas-electric hybrid. A relatively weak engine that most customers wouldn’t tolerate is enough for cruising speeds, but gets help from an electric motor during acceleration. At cruising speeds, the engine makes just a bit more power to recharge the battery, and during deceleration, regenerative braking charges the battery. The end result is that the engine usually only runs when it can be at its most efficient, and can be a lot smaller.
This has proven to be more reliable than normal cars, but batteries do need replaced and recycled eventually. It’s still a cost effective option, because refurbished batteries are well under $1000 for most models, including installation, if you shop around.
Some manufacturers are combining these approaches, with both forced induction and hybridization. One model even has both a turbo and a supercharger, plus an electric motor. That’s a hell of a lot more moving parts.
Yet another approach is the one Mazda is taking with their Skyactiv-X engine. By making the engine run more like a diesel engine, they can run a much leaner air-fuel ratio, meaning less fuel is needed. They can get away with this because, like a diesel engine, they use compression to ignite and combust the fuel rather than relying on the sparkplug alone. The downside is that this requires much tougher components and a moving baffle in the intake to introduce a swirl at the right time.
Nissan is taking another approach that’s similar chemically, but even more complicated mechanically.
They’re adding a linkage between the piston and the crankshaft, along with an actuator and its own arm, to change the compression ratio on the fly. For greater power, they lower the compression and burn more fuel. For efficiency when cruising, they increase compression and run a leaner mixture of fuel and air. As you can see, this engine has several more parts, but it’s worth noting that it also has a turbo. It’s significantly more complex than a regular, non-turbo gasoline engine.
Along with all of the changes being made to engines, transmissions are getting more and more complex. By spacing the gears closer together in ratio, it’s easier to keep the engine in its most efficient range of RPM.
Here’s a 5-speed manual transmission. It’s relatively simple. Most cars used to have a transmission similar to this, with 4 or even 3 gears in the older ones.
Now, compare this to the GM/Ford 10-speed automatic:
As you can see, there are a whole lot more moving parts than there used to be. Plus, with more gear changes going on, the moving parts are moving a lot more than they used to.
The Electric Competition
Now, let’s compare the complexity above to this:
The electric motor has one moving part: the rotor. The single-speed gear reducer (like a single speed transmission) only has a handful of moving parts. That’s it. Some batteries are air-cooled, but the ones that are water cooled require an electric water pump that only runs part-time.
Electric vehicles aren’t under pressure to add complexity to get better efficiency. When you aren’t pressing the accelerator, they can coast without using any electricity. When you stop at a light, they don’t use electricity. They can use a lot of power when you’re taking off, but once you’re cruising, they use less power with no mechanical gimmicks required.
Gasoline engines, on the other hand, are going to need to keep adding more and more parts to get better efficiency. Rising fuel economy mandates, a savvier customer base, and competition from electric vehicles all will push this trend for the foreseeable future.
Meanwhile, electric vehicles are getting cheaper. For one, they’re being produced in greater numbers, which makes the per-unit price go down. Battery chemistries are improving, meaning longer service lives and lower initial costs. With prices of gas vehicles on the rise and prices of electric vehicles coming down, the day will soon come that electric vehicles are cheaper to buy.
On top of this, the reduced complexity has another benefit: less maintenance. For example, the Chevy Bolt EV requires nothing but tire rotations and cabin filter replacements for the first 150,000 miles. Service lives of up to 1 million miles are entirely possible because the manufacturers are making better and better batteries that don’t degrade like older hybrid batteries did. Gas motors? Not so much. Adding parts means adding to the chance of failure, adding required maintenance, and eventually shorter lifespans.
All of this points to an unsustainable future for gasoline vehicles. The sooner the industry realizes this, the sooner we can fix it.