30 May 2008

Modification - the vacuum pump

A relatively long time ago, manufacturers started putting an assist on the brakes to make it easier to stop the heavier and heavier cars they were making. Now it is a standard "feature". Usually they use the vacuum generated by the engine. EVs don't have anything that naturally creates a vacuum so converters add some kind of pump. The converters of this car found a nice little box that contains a small pump, a vacuum switch, a muffler, and lots of sound killing foam. One thing with EVs is noise. With no engine roaring all the time you can hear everything your car does. So adding a pump that turns on and off randomly (mostly when you use the brakes) adds annoying noise. Thats why this pump is wrapped in foam.

There was no vacuum reservoir on the car, and I think I will need to add one. The pump is fairly small displacement and pressing the brake pedal it takes an extra second for the pump to catch up. Adding one will reduce the number of on-off cycles the pump makes. Not all cars need a vacuum assist either. It's possible to replace the master cylinder with one designed for no assist and still get the same performance. For now I'll keep the pump, mostly because it involves the least amount of work!

It took me quite some time to figure out where to put the pump. I trial fit it all over the motor bay thinking about how it will fit with the rest of the parts to go in there. Eventually I found a corner where it would fit perfectly, and the hose would have a clean path to the brake booster. So I bent some mild steel into a bracket and welded it together to hang the pump off of. This location really keeps it out of the way of everything, leaving me lots of room for other components. I added a plastic cable sheath to the wires and put a connector on the other end that plugs into a connector on the right side of the motor compartment. The plug connects to ground and through an existing fuse slot in the main fuse box which becomes hot when the key is switched to run.

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