ISSUE 012 Winter 2021 Sigma Powertrain EMAX transmission dossier l In conversation: David Hudson l 48 V systems focus l 2021 Battery Show North America and Cenex-LCV reports l Everrati Porsche 911 digest l Switching insight l Motor laminations focus

is split) from the inverters to the two e-motors to achieve the road speed or acceleration requested from the driver’s pedal. “The safety MPU is enabling and disabling H-bridges almost all the time,” Knieper adds. “For instance, if the driver wants to shift from first to second gear, the ECU needs to shut off the first gear clutch, and control motors A and B to synchronise with the second gear before allowing it to fire.” Also, since the solenoids and linear actuators are current-controlled, the main MPU calculates the correct duty cycle percentage in order to complete the shift without consuming too much or too little current. “The EMAX’s subsystems communicate over two CAN networks, one of which is a powertrain CAN bus running between the inverters for control of the traction motors; the other is a vehicle interface bus,” Knieper says. “That provides the human-machine interface, carrying commands from the EV’s pedals and shift lever through to the powertrain, and sends back status updates to the vehicle to tell the driver which gear they’re in, the position of the accelerator pedal, whether they are ISO 26262 is not a commercial vehicle standard, both the control hardware and software have been developed with its specifications in mind in case SPT ever has to obtain that level of certification. Before cutting any metal for the EMAX prototypes, Knieper and his team custom-built a GUI for simulating the physics of the transmission, initially using input parameters from the Raptor EVolved test vehicle. It was in this simulator that the control algorithms for smooth gear shifting, safety, Hill Hold, motor control and so on (as well as propulsion mappings such as accelerator pedal to output torque) were developed. “The GUI consists of four major components,” Knieper says. “The first is the simulator, which displays a powertrain lever diagram to show us everything that’s going on, with an output rate of 10 ms steps to enable precise diagnostics and debugging. It allows us to confirm the control logic long before we have a transmission in hand. “Second, we have a dynamometer control interface, as we wanted to use that same GUI for operating our 450 kW load motor simulator – which we can also use to simulate inclines, hard braking and other things on EMAX systems that are key for programming challenging shifts such as going from Park to Drive. “The interface in this mode also provides driver inputs to the powertrain, such as accelerator pedal position and the desired drive mode.” The GUI’s third mode is as a data collector, and the fourth is a data analysis tool for graphing and studying the flows of inputs, processes and outputs step by step, against time and the locations of simulated events across the powertrain. With these tools, SPT’s software engineers spent several months writing the algorithms in C#, all the while following a number of core braking, regeneration, or the status of Park brake or Hill Hold modes. Really, anything the driver wants to be aware of can be delivered over that second CAN.” The MPUs are integrated into both networks via independent transceivers in the ECU, in order to manage the inverters as well as the electrical actuators. Information on the performance of the motors and inverters is delivered to the MPUs via the powertrain CAN. “We also have an extended bank of capacitors, as our actuators are high- current devices, running at 48 V and up to 30 A at their peak,” Knieper says. “The peaks last only for up to 150 ms when we’re firing the clutches, and at all other times we’re using little more than what is needed for running the MPUs, but the peaks are still enough to merit having those caps there to store the excess power and avoid stressing the electrical system.” The software and algorithms are currently proprietary, although SPT has filed for patents on them, including protections for additional algorithms written with safety countermeasures covering NVH and functional safety. While ;Oe .<0 siTulator sOo^s a t^o Totor E4(? set to first Near with forward torque from motor A and reverse torque from motor B Winter 2021 | E-Mobility Engineering 29 Dossier | Sigma Powertrain EMAX transmission