Twin-rotor Wankel Cycles :

The picture below shows how the different strokes operate in each rotor for a 1080° of Crank (in fact eccentric shaft) Angle (CA) cycle. As there are3 working faces in each rotor, the 4 strokes happen on each face with an angular delay of 360°CA (or 120° rotor angle, due to the 3:1 ratio between e-shaft and rotor rotational speeds). Also, there is a 180°CA delay between front and rear cycles (due to a physical 60° angle between the 2 rotors, and the 3:1 ratio).
In term of combustion inititation, such a Wankel engine needs a spark every 360°CA per rotor, with a 180°CA difference between front and rear rotor. In term of engine management, it is similar to a 4-cylinder engine working in semi-sequential mode (wasted spark). That would be totally true if there wasn't a second spark plug per rotor, firing with a slight delay (up to 20°CA for the Renesis in Run mode). But the ECU requirements will be discussed below.
The injection pattern follows the semi-sequential 4-cyl pattern too. But the High Power Renesis has 3 levels of injectors, for better fuel distribution apparently.

In order to manage a Renesis engine, the following specifications are needed for the Engine Management System, assuming the following simplifications for a racing application : original fuel system replaced, Electronic Throttle Body replaced by cable throttle, no emission related features, no Mass Air Flow Sensor and no VFAD.

Hardware :
- 1 Variable Reluctance Sensor input
- 4 independent logic ignition drivers
- 6 independent high impedance injection drivers
- 1 Throttle Position Sensor Input
- 1 DC Motor driver (for the APV)
- 2 switch drivers (SSV, VDI)
- 1 wide band UEGO sensor input - the original wide band sensor needs to be replaced by a NTK UEGO or a Bosch LSU.
- 1 switch input (SSV feedback)
- 1 Rotary Position Sensor (APV feedback)
- 1 Knock Sensor input
- 1 stepper motor driver (for Metering Oil Pump)
- 2 Temperature sensor inputs (for Engine Coolant Temp and Intake Air Temp)

Software :
- Injection : 1 injection every 180°CA (i.e. semi-sequential 4-cylinder), and 3 levels of injections. Strategy similar to any other engine.
- Ignition : Special strategy allowing the firing of 2 ignition drivers at every firing TDC. It can be implemented with 2 separate 2-dim (LOAD,N) base maps (one for Leading, and teh other for Trailing plugs), or with a main 2-dim base map for Leading plugs, and a 2-dim offset table for the Trailing plugs (giving the offset in °CA from the Leading ignition advance angle). All the other offset funtions (for ECT, IAT, MAP,...) are common and similar to any other engine
- Metering Oil Pump (MOP) : oil injection strategy with 1 2-dim (LOAD,N) table giving an output in steps from 0 to 60. Some zeroing function of the stepper motor should also be provided. The original strategy is more complex but for racing purposes, it can be simplified. In fact, as most of the running is at full load, the MOP table could be a 1-dim vector as a function of N (engine speed).
- APV : the strategy for this function can be very simple (on or off) and related to engine speed only. Some position verification can be programmed using the feedback sensor.
- SSV, VDI : a simple On/Off actuation related to 1 engine speed for each is sufficient
- The software must be adapted to the mutli-teeth synchronisation trigger pattern.

Further simplification of the system :

We made the following modifications in order to further simplify the system, and to use a non-specific engine management :
- Modification of the original Mazda trigger disk to give the EFI Technology Euro-1 default trigger pattern : 4+1 teeth
- De-activation of the APV (we actually took off the rotary ports) as we do not have a DC motor driver.
- SSV always opened.
- All the MOP hardware has been taken off, and replaced by fuel/oil pre-mix
- We kept the 6 injectors, but the Primary and Secondary injectors fire together (Low Level injectors) and the Auxiliaries are the High Level injectors.
- No knock sensing
- No feedback of the APV and SSV position

These changes did not cost too much power. The open SSV has actually no impact as we always run at speeds well over 4000 RPM on track. The APV costs us some torque in the 5500 - 6300 RPM range. Moreover, these changes enabled the use of Euro-1 ECUs to drive the Renesis. In fact, 2 ECUs are used, working in semi-sequential 4-cyl mode, and sharing the following functions :
- ECU No 1, is the main ECU, and drives the Low Level injectors, the Leading spark plugs and the VDI.
- ECU No 2, is the secondary ECU, and drives the High Level injectors and the Trailing spark plugs.
They both are synchronised on the same trigger disk (4+1 teeth), and on the same VRS sensor (sine voltage output). We had to duplicate the temperature sensors (ECT and IAT) as they actually are resistors (thermistors). The UEGO sensor is connected to the main ECU only as it covers most of the fuelling. It allows us to use closed loop fuelling without any unwanted interaction between the 2 ECUs.

Potential future improvements :

Potential future improvements :
- APV : we could control the APV by using an external driver consisting of relays. Some mid-range torque is to be gained here.
- Diagnostics : make full use of the diagnostic fetaures of the ECUs
- Fault-proving : there must be a way to allow the engine to "limp home" on ECU No 2 if ECU No 1 fails. The engine can already run only from ECU No 1 if necessary.
- Engine loom : replace the modified OEM loom by a bespoke full autosport loom.