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Throttle Linkage Ratio Change


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A minor bug bear of mine on the Zero was the throttle travel. Running the standard jenvey linkage on the throttle bodies, and the GBS pedal, it's not really possible to get a nice range of actuation - the pedal needs to be longer than is possible in the footwell in order to get full (wide open) throttle. This meant that as a temporary measure I was driving around with the pedal about 2 inches further up than the brake pedal, which was pretty horrible to live with. The jenvey linkage was already at the maximum extent of it's adjustment so it really was a case of having to change the fundamental geometry of the throttle linkage at one end - either at the throttle bodies or the pedal.

 

Changing at the pedal box end wasn't going to be easy simply because of space. You'd need to extend the top part above the pedal, but there was no room, or else you'd need to shorten the lower half of the pedal, but that would move the pedal itself or else I'd have to manufacture some sort of new pivot point and re-route the cable. To cut a long story short, it's just easier to change it at the throttle body end. This is the linkage setup we're talking about - the lever/quadrant removed here and the linkage just temporarily sitting on the TB studs to get an idea of measurements...

 

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I've made up a spreadsheet that helps work out the ratios of the various components, given some measurements from the car... in particular how much linkage travel I need for Wide Open Throttle (WOT), versus how much pedal travel I have at the footwell end. If it's any use to you, it's here to download and re-use.

 

I worked out that I needed to reduce the effective input lever ratio on the quadrant (the bend around which the cable wraps) from the existing 30mm to a smaller 26mm radius. Using the spreadsheet, this gave me an increased ratio on the throttle linkage that worked out to roughly the amount of pedal travel I desired. So I set about designing the part using Onshape - again, the 3D model is available on my open account here if you want to re-use it.

 

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Set the mill off on some 2.5mm aluminium. I needed to make it in 3 parts because of the cable guides that need to go on either side of the quadrant, to keep the throttle cable in place. Much the same as the original Jenvey quadrant really; wasn't re-inventing the wheel here. A few M3 socket-head screws later...

 

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Was dubious about whether my calculations would work out right... :) fitted it into place and blow me down with an induction backfire if it wasn't just about spot on :D....

 

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...and now a nice pedal position, slightly proud of the brake pedal but certainly not 2 inches worth!

 

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Thats a neat idea Peter.....I use it on throttle linkages on my toy planes,

but it seems not many people use it nowadays.

 

Just an afterthought....we constructed a snail cam throttle quadrant for the vette.

we needed a de-sensitised throttle for the road ie low throttle openings, but

a far higher ratio for higher throttle openings.

I cant find a picture at the mo'

Edited by Bob Tucker
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