Injector staging:
Only the number of primary injectors can be set, the number of secondaries is automatic. So possible primary + secondary combinations (when staging, max primary nr is 6):
- 4 + 4
- 5 + 2
- 6 + 2
- 1 + 1
- 2 + 2
- 3 + 3
The top N (say 7 for a 5+2) "injgroup" entries are used (see Injector outputs). Will be reflected in [VT help]
This text is a direct result of the discussions between Dave Brul and Jörgen Karlsson held during the 2006 VEMS tour that visited Sweden, Denmark, Germany, Holland, Belgium and France.
There are primarily two ways and reasons to stage injectors.
- One reason is that you might want to switch to another fuel at a certain time, or that you just want to switch to an injector in a secondary location as it provides better atomization or some other advantage. The switch case is best controlled with load and rpm. We call this way to control the injectors SWITCH.
- The most common is that two smaller sets of injectors is used to get a larger dynamic range and that only one set is used up to a certain point. We call this way to control the injectors STAGE. The stage case is best controlled with the primary sets injector duty cycle as an input. For example turn the secondary set on if the primary set is used at >90% duty and turn the secondary set off if the primary set can fuel the engine with <80% duty.
STAGE operation mode.
The STAGE operation mode has two sub modes, one where the primaries and the secondary set is injecting at the same duty cycle and one where you have a bias toward the primary set.
- In the bias operation mode the primaries will just be held at a set maximum duty and the secondary set will complement them by injecting a small amount of fuel. This mode has to be used when for example a single secondary injector is used to help fuel the engine. It can also be useful when different fuels are used in the two injector sets.
- In the balanced mode the two injector sets are driven at the same duty, this is useful when two sets of similar injectors in similar locations are used.
SWITCH operation mode.
The SWITCH operation mode can be combined with the STAGE-BIAS and the STAGE-BALANCED modes. The combination of the SWITCH and STAGE-BIAS modes are more likely to be useful. This can happen when a set of small primaries is used near the valve and a large set of secondary injectors is used near the mouth of the intake runner. In a case like this you might want to switch to the secondary set at a certain load and rpm, if for example the switch from the small set to the large set is not set to occur soon enough the ECU may need to fill in with some fuel from the secondary set. Or it could be that after the ECU has switched to the secondary set it finds that it will still not be able to provide enough fuel with that set alone, in that case it can start to fill in with some fuel from the primary set.
Injector properties.
Each injector set will need it’s own openingtime and peak time. The PWM duty will have to be common for both injector sets of both are low-z. This is not a problem. The peak time is used to disable the PWM mode for a set of high-z injectors if it is paired with a set of low-z injectors.
Injector timing.
One injector timing table will be sufficient even if the timing of the primary and secondary set in SWITCH mode may very well be very different. As the switch mode is rpm-load based a single three dimensional injector timing table is enough to tune the optimal timing.
Fuel calculation
This type of advanced staging may be simpler if we change the fuel calculations a bit. After discussions it seems better to input the engine size and the injector sizes. This will of course be a problem with the current injector outputs as the standard output has very bad physical injector control. But very good physical control of the injector is necessary for this type of injector staging and switching in any case. We absolutely need to be able to predict the exact amount of fuel injected regardless of if it’s a 1000cc injector or a 150cc injector. Otherwise we will not be able to make a smooth transition between the two sets.
The ideal fuel calculation would output a number that is proportional to the amount of fuel needed by the engine. The simplified enginesize X VE X Lambda X multiplicative corrections + additive corrections will give a number like this.
This would then be passed on to the injection part of the calculation that decides which set will be injected and for how long it will have to inject to provide the commanded fuel amount.