Unfortunately engines usually cannot rev as high as we’d love them to, so we have to protect them from over-revving.
Downshift is “risky” scenario for engine especially in high RPM shift zone, that’s why it’s very important to setup Over-rev protection.
Over-rev protection table uses Gear at (X) axis. Output (Z) of the table is RPM above which downshift REQUEST is denied resulting in downshift schedule not happening.
How to set it up properly:
- Determine Your engine max RPM
- Determine gear ratios of Your transmission
- Calculate what RPM engine has right after UPSHIFT at certain gear.
- Enter calculated RPM as Z of origination gear.
Hint #1 : You’re mostly hitting downshift rev limiter when fully braking usually meaning that RPM drop over time (deceleration). Taking into consideration that shift takes time You may set RPM limit a bit higher than calculated (or just calculate for a bit higher RPM rev-limiter). Use this practice ONLY if You’re sure that in such case engine won’t get damaged.
Example #1 : Let’s say our engine has rev-limiter at 7500RPM, and our gear ratios are as follows (GS7D36SG DCT long ratio):
It means that if shift happens at 7500 RPM, the revs will drop to :
1-2: 5227 RPM
2-3: 5181 RPM
3-4: 5245 RPM
4-5: 5325 RPM
5-6: 6021 RPM
6-7: 6316 RPM
Then over-rev table should be setup like this:
If I’m at gear (X) 7, then disable downshift above (Z) 6316 RPM
If I’m at gear (X) 6, then disable downshift above (Z) 6021 RPM
If I’m at gear (X) 3, then disable downshift above (Z) 5181 RPM
Hint #2: A bit special case is 2 to 1 downshift as is something You’d probably like to disable after take-up, then setup over-rev protection at 2nd gear to lower value if You don’t want to allow to downshift to 1st gear at high RPM.