VSS help please

[Bernard Fife]

Addicted,

Yes, but unless I know what frequency your scope shot was taken at (and any other frequencies you have tested at) I will have a hard time interpreting your reported results. For example, if the scope shot is suggesting that the input period is 40 milliseconds (or perhaps 40msec/div, I couldn't say), then the frequency is just 25 Hertz, and that is a very low speed for most configurations. It could even be below the minimum speed setting, in which case you wouldn't expect to see any reading on the speedo (the dash speedo surely isn't more credible than a direct frequency measurement, especially since the introduction of additional measuring circuits can cause unforeseen resonances, etc.).

Of course I can try it myself, of course, but I am trying to understand why yours isn't working, not why mine does; so more info is always helpful.

Also, did you try feeding the symmetric top signal into the VR circuit? You said you were going to try that.

Lance.

[Addicted]

Sorry Lance, I see your point, as usual.

Maybe this photo will answer more questions..



Ignore the noise, I've quickly replaced the opto with a voltage devider circuit and haven't fitted any caps yet.. (100k and 66k)

OK, Lance, take a look at the attached datalog... it IS working... its just that its reporting very slow..

[Bernard Fife]

Addicted,

It appears from your scope shot that your input frequency is 19.44 Hertz. With your settings loaded, on my bench I see:

194 Hz = 22.8 mph
40 Hz = 4.4 mph

So we would expect that 19.4 Hz would be ~2.3 mph (22.8*19.4/194). However you have your 'Min. Vehicle Speed' set to 3.0 mph (http://www.msgpio.com/manuals/mshift/V41tune.html#gv) so any speed under 3.0 mph is set to zero. That could be why your speedo isn't registering anything.

You should also read the note in bold the link about setting the VSS input masking to either 0 (= disable masking) or between 50 and 100 (yours appears to be set to 5).

Lance.

[Addicted]

Hello again and thanks for sticking with me, this is turning into more of a blog than a forum post...

On paper (old school) I get a speed of 10mph for 19.44 hertz

23" diameter wheel. Circumference = 23 x 3.142 = 72.26"

Number of VSS teeth = 8

19.44 hertz = 19.44 pulses per second, 1166.4 pulses per minute.
8 pulses per revolution of output shaft, therefore 1166.4/8 = 145 rpm

145 rpm x 72.26" = 10477.7" per minute = 628662" per hour

628662" / 63360" (1 mile) = 9.922mph

Edit:
Your calculations are based on the VSS being on the output shaft of the gearbox BEFORE the final drive. With a transaxle the VSS is AFTER the final drive!

[Bernard Fife]

Addicted,

Ah, okay! In that case, try setting the axle ratio to 1.000. Then the drive ratio will match the number of teeth per revolution.

On my bench, setting the axle ratio to 1.000 gives 9.2 mph at 19 Hz.

I will need to think about how to better incorporate your VSS setup into the code.

Lance.

[Addicted]

Lance,

What are the Gear Ratios used for? Do I need to alter them to incorporate the final drive ratio? Although I see that the max value is 7:1 and first would be 11.64:1...

Martin

[Bernard Fife]

Martin,

The gear ratios are potentially used for a few purposes:

- they are used to determine if the rpm after a shift would be too high or low. In this case, the calculation is always a ratio of two gear ratios, so the gear value does not need to be adjusted.

- they are used to estimate engine rpm IF the CANbus is not enabled AND PT5/VR3 is not used as a tach input.

- they are used to estimate the input shaft speed (IF PT5/VR3 is not used for ISS input).

The last two cases will probably need some adjustments in the code.

The axle ratio is used to determine the speed from the VSS, as we have seen. It currently assumes that the VSS signal rate is multiplied by the axle ratio. That's often true for RWD, and often untrue for FWD. The code ought to have an option to specify the location of the VSS (i.e. before or after the final drive) so that the setting don't need to be fudged, and I will work on this.

But for you, for now, just set the axle ratio to 1.000 and then you shouldn't have to change anything else (unless I am overlooking something).

Lance.

[Addicted]

Cheers Lance,

I'll try and test today and get back to you..

Thanks,

Martin

[Addicted]

Lance,

It works!

See later part of attached log.. even shifts into second..

[Bernard Fife]

Martin,

That's great!

I will attached some test code that has the new VSS Location parameter. This is under 'General Setting -> VSS Setup'. The options are:

1. Between Transmission and Final Drive (typ. RWD)
2. Between Final Drive and Wheel (typ. FWD)

In general, if the vehicle's speed sensor is mounted on the transmission's output shaft , i.e. between the transmission and the final drive (typically rear wheel drive rear axle), then select 'Between trans. and Final Drive (typ. RWD)'. If the sensor is mounted so that its ring turns as the same speed as the wheel (and half-shaft), as it does for you, then choose 'Between Final Drive and wheel (typ. FWD)'.

This seems to work well on my bench, but may need some further tweaks.

Monitor_5095t8.abs.s19

(78.78 KiB) Downloaded 632 times

GPIO_MShift_5095.ini

(261.51 KiB) Downloaded 642 times

Lance.