Re: (Off Topic): Diesel compression, (on topic) EV brakes

At 02:34 AM 16/05/08 +0000, robert harder wrote:
G'day All

Funnily enough, as I said off-list to Peter, the absolute answer is "it
depends". For my sample of vehicles, most have throttle bodies and do
produce vacuum. Definately, absolutely certainly do have them. Large
vehicle diesels are out of context as conversion candidates, and so what
they do or do not have is not relevant. Other diesel engines in potential
conversion candidate sized vehicles may or may not have them and would be
very unlikely to have exhaust brakes. My parent's Toyota Land Cruiser (long
since sold) was non-turbo diesel and had a throttle body, and I believe the
turbo variants of that vehicle also had throttle bodies. My most recent
vehicles (Fiat Ducato trucks) are the first diesels that I have had that
are EFI turbo-diesels and I don't know if they have throttle bodies or not,
but I suspect not.

Also, *in my experience* the worst compression braking is from the variant
of anything with an automatic transmission (regardless of diesel or
petrol). Your results may vary, as there are a great variety of vehicles
out there. However, *from my experience* I would expect to find the biggest
brakes of a particular variety of passenger vehicle on a turbocharged [or
whatever is the most powerful] automatic transmission (weakest effective
compression braking) variant. Diesels tend to be heavier than petrol
engines, so despite the increased compression braking would be unlikely to
have smaller brakes.

My first employer had two Holden Gemini (Isuzu) diesel sedans. On several
occasions (until I got used to them) I spun them in the wet by lifting off
the accelerator and hitting the brakes without de-clutching. The effect of
compression braking plus mechanical brakes would break rear traction to
cause the spin. The solution was to de-clutch when breaking in the wet.

Diesel engine variants may be better candidates for DC motor conversions,
as *the ones in my experience* have had different gear ratios due to
revving to lower maximum RPMs [your results may vary]. For a DC conversion
this may provide motor speeds that are in better ranges for the typical
use. Again, that would depend on the needs of the user.

I live in a hilly town, so really notice the difference in compression
braking levels between the different vehicles I drive (between my business
and family that is currently seven vehicles that cover the scope of the
discussion). Because of this I want to do something to gain some
regenerative braking in my EV-in-progress to make up for the loss of
compression braking. I can't afford AC at this time, plus have a good
collection of things suitable for a series DC conversion. Consequently the
regen braking will be from some kind of 'add on', which as a bonus will
give me something else to tinker with :^)

Hopefully this ends the discussion on diesel engines and returns focus to EVs.

Regards

[Technik] James

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