In tracing the air starter and related devices, I found several cars that made broader use of the compressor, to inflate tires or push the fuel up into the engine. A dozen cars had air systems in 1912, and another dozen had acetylene starters. Most cars already had an acetylene tank for the lights, so this made sense.
Something was missing. The air starters and acetylene starters had a distributor running in parallel with the spark distributor. The acetylene systems were already full-fledged fuel injection, but used only for starting. The air systems could have become fuel injection with a metering jet on each cylinder’s air pipe.
Did anyone see this potential at the time? Yes.
One invention took the idea all the way into the future. The Church Pneumatic Transmission was installed in a car for demo purposes, but the company clearly didn’t want to make cars. They wanted to make the system as a component. (The amazing 1905 Sturtevant full-automatic was similar.)
Church is best described in Horseless Age. All the articles call it radical and for once they were right.
Like the other systems, Church supplied air for starting and tire-filling and jacking the car.
It was also:
all at once.
The key to the system was three air pistons facing forward, seen in the picture below.
Flywheel on the left, output shaft to differential on the right. The cylinders containing these pistons were solidly mounted on the flywheel, which isn’t entirely clear in the pic. Only one of the pistons is shown. When the engine is turning and the wheels are stopped, each piston is driven by a bevel gear. This action is sort of relativistic. In an ordinary compressor the bevel gear on the right would be turned by a motor while the cylinders are still.
In the stopped situation the pistons develop strong pressure, which is vented to the housing around the flywheel, and from there to an external tank.
After you release the brakes, the compression of the pistons starts to push back against the crank, which then starts to turn the driveshaft and move the car.
Now the difference between flywheel and output shaft is less, so the pistons are producing less pressure. The difference will never go to zero, because there will always be some compression to ‘block’ the pistons and direct the motion toward the driveshaft. In other words there will always be some slippage, as in a torque converter.
Where does the pressure in the housing go? It goes to the air inlets in the engine’s cylinders, timed by the air distributor.
In other air starter systems, this forced flow only happens during startup, and the engine is always sucking through a regular intake manifold and carburetor. After the regular intake starts firing the engine, the driver releases the starter pedal and the airflow halts.
In the Church setup, the compressed air is the ONLY air going to the engine, and each inlet has a vaporizing jet to create the air-fuel mix. Thus the system is a supercharger and fuel injector.
Control comes from two sources: (1) The throttle pedal simply varies air intake to the compressor cylinders, and thus indirectly controls the overall flow. (2) The elegant part of the system is the feedback loop. The flywheel turns much faster than the output shaft when the driver is trying to accelerate, AND when the wheels are loaded by hills or brakes or headwinds. The increased DIFFERENCE between flywheel and driveshaft creates MORE pressure in the supercharger, thus feeding more air-fuel mix to the engine.
= = = = =
In modern terms this was a feedback-controlled fuel injection system plus supercharger.
It wasn’t really a transmission; more like a fluid coupling. In 1913 this would have been adequate, because cars rarely had a chance to go faster than 20 mph. For faster speeds an extra ratio, like Ford’s planetary, would need to be tacked onto the back, and again it could be controlled by the air pressure. More load or more desired acceleration shifts down to low. The system would also need a true neutral, with a separate control channel to keep the air flowing at idle.