How a Eaton G80 locker works

A GM C Sierra with an Eaton G80 locking differential traverses the ditch simulation. Click image to enlarge

With the locking axle, the vehicle was driven slowly on the roller and the wheel spun freely. By accelerating slightly so the spinning wheel is turning about 100 rpm or about 13 km/h, centrifugal weights in the differential latch to a locking mechanism that forces the differential gears to spread apart and engage clutches in the sides of the differential. Within one turn of the wheel, the clutches lock both sides together and the truck drives over the obstacle with ease. I have pulled out of icy parking spots with a GM vehicle equipped with an Eaton locking axle many times when I would have been stuck without one.

Another demonstration simulated driving the trucks over a ditch at an angle. When the truck was in the middle of the transition, one rear wheel and one front wheel had almost no load on them. With the four-wheel drive vehicles, both the one front and one rear wheel without load would spin and the truck would move no further. It was stuck. Even with four-wheel traction control, the vehicle remained stuck because the computer would reduce power at the same time it braked the spinning wheels. There still wasn’t enough torque transfer to the wheels with traction to get the truck moving.

As the two-wheel drive truck with the Eaton locking axle reached the transition, the unloaded rear wheel began to spin but within one turn of the spinning wheel the axle had locked and the truck drove through. It demonstrated that a locking axle in a two-wheel drive vehicle can perform better than four-wheel drive.





Eaton G80 locking differential. Click image to enlarge

Eaton’s locking differential is used for low speed traction. At speeds above about 30 km/h, a centrifugal weight disables the locking mechanism so that the wheels can turn independently. Unlike limited slip or Positrac differentials which have spring loaded clutches that are engaged at all speeds, the locking differential now allows one wheel to spin. This ensures vehicle stability if you encounter black ice on the highway. If both wheels were locked, they would both spin and the rear of the vehicle would have no stability. Without being locked, only one wheel spins and the other maintains some traction.

Traction at low speeds with the stability of an open differential at higher speeds: Eaton offers this for only about $300 as an option on GM trucks. It’s definitely worth the money.

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automobile Journalists Association of Canada (AJAC).
Technology

Sparks Fly

Sparks Fly

You can understand a two-stroke engine by watching each part of the cycle. Start with the point where the spark plug fires. Fuel and air in the cylinder have been compressed, and when the spark plug fires the mixture ignites. The resulting explosion drives the piston downward. Note that as the piston moves downward, it is compressing the air/fuel mixture in the crankcase. As the piston approaches the bottom of its stroke, the exhaust port is uncovered. The pressure in the cylinder drives most of the exhaust gases out of cylinder, as shown here:

Fuel Intake

As the piston finally bottoms out, the intake port is uncovered. The piston's movement has pressurized the mixture in the crankcase, so it rushes into the cylinder, displacing the remaining exhaust gases and filling the cylinder with a fresh charge of fuel, as shown here: Note that in many two-stroke engines that use a cross-flow design, the piston is shaped so that the incoming fuel mixture doesn't simply flow right over the top of the piston and out the exhaust port.

The Compression Stroke

Now the momentum in the crankshaft starts driving the piston back toward the spark plug for the compression stroke. As the air/fuel mixture in the piston is compressed, a vacuum is created in the crankcase. This vacuum opens the reed valve and sucks air/fuel/oil in from the carburetor. Once the piston makes it to the end of the compression stroke, the spark plug fires again to repeat the cycle. It's called a two-stoke engine because there is a compression stroke and then a combustion stroke. In a four-stroke engine, there are separate intake, compression, combustion and exhaust strokes. You can see that the piston is really doing three different things in a two-stroke engine: On one side of the piston is the combustion chamber, where the piston is compressing the air/fuel mixture and capturing the energy released by the ignition of the fuel. On the other side of the piston is the crankcase, where the piston is creating a vacuum to suck in air/fuel from the carburetor through the reed valve and then pressurizing the crankcase so that air/fuel is forced into the combustion chamber. Meanwhile, the sides of the piston are acting like valves, covering and uncovering the intake and exhaust ports drilled into the side of the cylinder wall. It's really pretty neat to see the piston doing so many different things! That's what makes two-stroke engines so simple and lightweight. If you have ever used a two-stroke engine, you know that you have to mix special two-stroke oil in with the gasoline. Now that you understand the two-stroke cycle you can see why. In a four-stroke engine, the crankcase is completely separate from the combustion chamber, so you can fill the crankcase with heavy oil to lubricate the crankshaft bearings, the bearings on either end of the piston's connecting rod and the cylinder wall. In a two-stroke engine, on the other hand, the crankcase is serving as a pressurization chamber to force air/fuel into the cylinder, so it can't hold a thick oil. Instead, you mix oil in with the gas to lubricate the crankshaft, connecting rod and cylinder walls. If you forget to mix in the oil, the engine isn't going to last very long!

Disadvantages of the Two-stroke

You can now see that two-stroke engines have two important advantages over four-stroke engines: They are simpler and lighter, and they produce about twice as much power. So why do cars and trucks use four-stroke engines? There are four main reasons: Two-stroke engines don't last nearly as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear a lot faster. Two-stroke oil is expensive, and you need about 4 ounces of it per gallon of gas. You would burn about a gallon of oil every 1,000 miles if you used a two-stroke engine in a car. Two-stroke engines do not use fuel efficiently, so you would get fewer miles per gallon. Two-stroke engines produce a lot of pollution -- so much, in fact, that it is likely that you won't see them around too much longer. The pollution comes from two sources. The first is the combustion of the oil. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit huge clouds of oily smoke. The second reason is less obvious but can be seen in the following figure: Each time a new charge of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port. That's why you see a sheen of oil around any two-stroke boat motor. The leaking hydrocarbons from the fresh fuel combined with the leaking oil is a real mess for the environment. These disadvantages mean that two-stroke engines are used only in applications where the motor is not used very often and a fantastic power-to-weight ratio is important. In the meantime, manufacturers have been working to shrink and lighten four-stroke engines, and you can see that research coming to market in a variety of new marine and lawn-care products. http://www.chooseindia.com

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