9.2
In this section, we are implementing a 4-inline engine control unit which can implement variable
valve timing on both the intake and exhaust. It can also implement spark advance/retard. Similarly,
we can also advance/retard fuel injection; it means that we can fuel at any point during the intake
stroke or compression stroke.
The details of the integrated engine control unit (IECU), is shown in Figure 9.2. At the top of the
Figure is the valve advance calculator (VAC). This section has been extensively discussed in
Chapter 8. The VAC basically creates virtual angles (in steps of 10) on the trigger wheel. The
RPM-LUT contains advance angles corresponding to each RPM. For example, suppose we want
to implement VVT advance of 150 and retard of 100. These angles are with reference to TDC.
Using the 10 clock, we can operate a 3600 down counter, starting at BDC. For and advance of 150,
the counter will have down counted to 3600-1800+150 = 1850 (i.e., 185 10-clock pulses). 100 retard
means 10 10-clock pulses after TDC, which is 3600 – (1800-100) = 1700. These values of 185 and
170 will be stored in the RPM LUT against the appropriate values of RPM, which acts as the LUT
address. At BDC, the advance value corresponding to a specific RPM will be downloaded to IVO
counter, which after down counting to zero, will operate a valve solenoid for a time period
determined by VRTT. Thereafter, power to the valve will be cut off, waiting for the next change
of state. The IVC counter determines how long the valve stays in the open position. This is
analogous to lift duration in the conventional cam system. Note that after triggering the IVC, IVO
can be preset at BDC with the IVC continuing with its down count, unaffected by this action. The
Injector Timing, IT counter determines the time when the injector starts firing. This could be in
intake stroke or compression stroke, the position on the chosen stroke can be programmed. The
Injector Pulse Width, IPW counter stores number of pulses the injector should stay on. Note that
IPW and IVC counters are fed with throttle position data. A higher throttle data position will make
the engine rev higher. All the variables IVO, IVC, EVO, EVC, IT, IPW, ST are obtained from
their respective RPM LUTs and loaded to their respective counters. The advance/retard ECU
generates these variables in the first place, [57], [126].
Figure 9.2b shows the Otto cycle for a 4-inline engine with firing order 1-3-4-2. In Figure 9.2a, it
is the advance/retard ECU which generates the signals IVO, EVO, Spark, Fuel. It is similar to
Figure 6.12, but with the addition of valve events equations for the 4 cylinders. The Otto cycle
states are labled as P1, P2, P3 and P4. In P1, only piston number 1 is in the power stroke. Using
the indicated firing order, piston 3 will be in the compression stroke, waiting to go to power stroke.
Pistons 4 and 2 will be in the intake and exhaust strokes respectively, [11], [33].
To implement advance, the action to be done in the next state, must start at the current state. For
example, in state P1, piston 2 will be in the exhaust stroke. Since piston 2 will go to intake stroke
next, to implement IVO advance, we assert and output trigger, IVO2, to initiate a down counter so
that it reaches the desired down count value before TDC, as corresponding to the advance angle.