The brake booster used to get its needed vacuum from the manifold of the original gasoline engine. Now that it is removed vacuum needs to be generated using electricity as it is the only energy source that will be used. I bought a dismantled electric vacuum pump from some model of VW Golf MK4. The pump was measured to reach a vacuum of 0.8 bar while drawing a current of 8 amps.
A simple vacuum switch is used to control the pump so that it will only be turned on when more vacuum is needed. The vacuum switch was made many years ago by my father who used a vacuum advance unit of a ignition distributor and a microswitch. The working principle of the vacuum switch is very simple. The vacuum advance unit pulls a lever according to the vacuum applied to it. Once enough vacuum is applied the lever operates the microswitch. The operating point of the vacuum switch can be easily adjusted just by positioning the microswitch to be operated on a desired level of vacuum. Using the vacuum gauge shown in the picture a vacuum level of 0.57 bar was adjusted as the operating point of the vacuum switch. Once it is reached the microswitch cuts the power off from the vacuum pump. A power diode was placed parallel to the vacuum pump motor to increase the lifetime of the microswitch.
When the vacuum pump motor is stopped it leaks vacuum through it so a check valve is needed between the brake booster and the vacuum pump. The vacuum level to be adjusted by the vacuum switch needs to be taken from the brake booster side of the check valve. In this case the original Corolla's check valve was able to be used as it was working well without any leak and it was easy to mount an additional pipe to connect the vacuum switch between the check valve and the brake booster.
The test setup worked well. Pressing the brake pedal all the way down caused the vacuum to drop to a level of ~0.44bar and it took one second for the pump to reach the 0.57bar vacuum again. As the tests looked ok, this setup will be assembled to boost Corolla's brakes. Further braking experiences will have to wait for the first road test drives.
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