[mizlplix]

Greetings: Although I am new to this forum, I am far from a Noob at automobile theory.

Engine braking in class A diesel engines employ a hydraulic device in the rocker arm box to open the exhaust valve at the moment of TDC compression to release the energy into the atmosphere.

Engine braking on a Medium duty diesel engine uses an exhaust pipe valve to prevent the exhaust gas flow thereby slowing the engine until released.

Both of these systems shut off the fuel during the braking event.

A gasoline engine is a little more difficult. It uses it's inherent operational friction, but it still pulls fuel from the idle circuits in the carb, or the engine idle function in the ECU, unless it was mapped differently.

It is a myth that automatic transmissions "free wheel" when engine braking. They are always coupled to the engine, albeit less than a manual transmission would be.

Most latter day automatics use a lock-up type converter to prevent the converter turbine from overheating when in an over drive ratio. They usually lock up in mid-third gear.

With the use of an aftermarket shift modifier, the shift points and lock-up can be controlled. Some even resort to a manual switch to lock the converter early to squeeze out better fuel economy.

My EV uses Regenerative motor braking to stop the vehicle. It is so impressive that I rarely use the hydraulic brakes at all. The side benefit is that I recapture about 10% of the energy I used to accelerate.

An early form of this was used in heavy haul trucks in the form of a "retarder". That was a field winding built into the flywheel area of the engine that slowed the truck by electric generation of current, but it was wasted by turning into heat and radiated into the atmosphere.

Miz