Saturday, June 9, 2018

What's that noise?

I have received many enquiries bout the repetitive "grinding" noise one can here in the post;  Sunday, January 4, 2015.

Well, glad you ask, and now take a seat and get prepared to be bored to tears.......

The Hydropneumatic (no it's not air) suspension that Citroen developed in the 40's and that saw it's full deployment in all its glory in 1955 on the Citroen DS (like the one in this Blog), was a true marvel of engineering; that it also powered the brakes, power-steering (yes, in 1955)  and c-matic (manual-clutchless transmission) adds to its awe.

It is a constant flow system, that is, the pump is constantly turning, with oil flowing through the system and with a valve that opens at the required pressure to re-pressurise the accumulator; off-which the system relies to maintain pressurisation. This 7 piston pump is driven by the camshaft. So, in other words, the pump is constantly turning, most of the time under no pressure.

Being electric, we needed to save as much battery power as possible, so a constantly powered second motor (not the main propulsion motor), but a small high-torque unit, was not ideal. We re-engineered the system to include a high-pressure (around 1000psi) pressure-switch that at the right pressure, turned-off the electric motor and restarted it as the pressure fell to the lower-limit of pressure required.

So that "grinding" noise is a little, low-rev, high-torque motor that cuts-in at the right moment to repressurise the accumulator, maintaining the system at optimal pressure, under any condition. 

And yes, the magnificent 1974 Citroen DSev is still running great (not without ongoing enhancements) and is now being prepared to travel overseas for European touring.


  1. Hi Aldo, I've been reading your blog of your Citroen conversion with great interest. I think I will soon be getting the Citroen EV that you referenced back when you started this project. I believe it may be the only one in N. America. I'm wondering if you would be open to seeking your advice as I attempt to put it back on the road again? I'm guessing it will be a long process. It will be my first EV and I'm not a Citroen guy so I really am jumping in the deep end.

    1. Hey Kevin, Apologies for my delayed response. Unfortunately the blog does not alert me when I get messages. More than happy to share my learnings with you. This was my first EV conversion but I did have some amatuer experience on Citroens having owned them in the past. COntact me on, if you prefer. Aldo.

  2. Had a '68 DS19, with auto clutch - same as pedal clutch, without the pedal. The main pump was constantly belt-driven, but only "worked" when building pressure. The noise sounded like "jingle, jingle, slosh, slosh".The "water" pump/fan and alternator were belt-driven off the camshaft There was a separate"little" pump to power the gear shift.

    1. Hey Omar, Just saw your message. Apologies for my tardy response. How can I help? Aldo.