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Strain Gauge on H pattern shifter assembly

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Good day to all.

I am currently working on a G4+ Xtreme install for a GC8 street car with a few upgrades. One of the features the owner would like to explore was the gear dependent strategies with gear detection via a strain gauge. From what I am have seen, the implementation of the strain gauge for gear detection is a lot more common a sequential (push-pull) shifter unit and all too uncommon on conventional H pattern shifter assemblies.

I am still quite busy with the install of the G4+ as there's myriad of sensor feedback strategies to implement with full dash integration. I would be especially grateful if anyone could share their practical work experiences of using a strain gauge of a H pattern shifter assembly please.

Many thank in advance for your time, cheers!

Hi Damien,

There are a couple of quite separate technologies involved here. First of all you have the actual gear detection which is what tells the ECU which gear is currently selected. In purpose built sequential race boxes this is usually measured directly from the shift barrel and an analogue voltage is output to the ECU and consequently calibrated against the current gear.

Without the benefit of a direct gear position sensor, your only other option is to estimate the current gear based on driven wheel speed and engine rpm. This can be done inside the G4/G4+ by configuring the gear ratio table which is effectively a frequency of rpm to ground speed. This works exceptionally well though and allows you to produce gear-based control of events such as boost control for instance. It does require at least one functional speed sensor on the drive shaft to work correctly.

Now to move on to the strain gauge. A strain gauge gear lever is designed to provide an analogue signal to the ECU that tells it when the driver is attempting to change gear (pulling or pushing on the lever). Unlike a digital lever which only provides a signal when the force exceeds a certain threshold, the strain gauge can also define if the lever is being pulled back or pushed forward.

Before I move on, is the gearbox a synchro mesh or dog engagement type? Usually these sort of gear levers are implemented to allow gear cut control for flat shifting without using the clutch. This is only feasible with a dog engagement box though. If you want to use gear cut control with an H pattern box, the strain gauge will need to be configured to provide a cut signal in either direction of travel.

Let me know if you have further questions.

Gents,

I'm shortly taking delivery of a GForce GF-5R transmission with an H-Patern shifter, and would like to utilize a shift cut strategy with my Motec M1 ECU.

Any recommendations of a strain gauge for this application, and vendor?

Thanks,

Adam

Really not worth the aggro on an H-pattern.

Although I've only seen one implemented it didn't look to work any better that just lifting (for upshift) and blipping (for downshift) manually. Bear in mind however that unless you have a very low inertia engine, flywheel and clutch, clutchless shifting puts immense shock loads on things. I've snapped the input shaft of a dog box this way.

With a sequential (especially with paddle shift) you have far better control of the whole strategy but bear in mind you still have rotating assy inertia to deal with.

Unless you have very low inertia, using the clutch just makes a lot more sense if you want things to last.

I also wouldn't do clutchless shifting on gravel (rally car)...

Chris,

Thanks for the advice.

I'm running a triple plate carbon clutch at 3.44 kg, and a 3.58 kg flywheel. I figured the inertia shock wouldn't be that critical?

If it's 5.5" (140mm) the inertia is reduced but I'm still not convinced it's a worthwhile move to put a shift cut on an H-Pattern.

Here's a video demonstration I did a few years of clutch-less up and down shifting with a gpN Impreza with dog-box. https://www.youtube.com/watch?v=d9t_41t0Sog Like I said, I wouldn't routinely do it again (especially on a gpN car with a heavy flywheel) but it is entirely possible.

Here is someone else's https://www.youtube.com/watch?v=H98vSNz6vrw

[edit] for clarity, my video is using H-pattern the second video is using sequential without any torque reduction (ignition cut) device. The technique though is the same. It's also usual to use the clutch for 1st-2nd because of the larger drop in revs between those ratios.

If you're convinced that clutchless shifting and left foot braking are going to make you faster and you have low inertia rotating assembly then of course try it. The technique is not difficult so down't in my opinion warrant any electronic control/intervention.

I will be going paddle shift sequential in my new car but I have an SQ6M to control that (if I ever get time to figure it all out)!

Good day to you Chris

Many thanks for sharing such a practical perspective, a lot of what you've noted is exactly correct but not always well understood.

In my humble opinion, the definition of what will quantify as a technical advantage within an uncompromising competition scenario can be blurry for want of a better word; the yard stick doesn't confirm to the same rational.

Thanks again, cheers!