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

For Park, both brakes are activated, grounding all moveable transmission components and preventing the EV from moving. In Hill Hold, as the EV is parked on a hill, one side of the second gear clutch is engaged and the other is inactive. Which one engages depends on which gear the vehicle is in, to ensure the correct direction of holding. Hill Hold thereby prevents rolling backwards while in first gear and forward while in reverse, regardless of slope. ECU Management of the powertrain comes from a patented ECU that consists primarily of two microcontrollers: a main microprocessor unit (MPU) and a safety MPU, connected for redundancy and hence functional safety. Both MPUs are produced by STMicroelectronics: the main MPU is an STM32F413ZHTx, and the safety MPU is an STM32F413RHTx. Each system is built around a 100 MHz ARM Cortex-M4 core, with 320 kbytes of RAM and 1 Mbyte of ROM. The main MPU primarily monitors the different speeds of parts across the entire transmission, to ensure shifting and traction are being executed normally, without parts slipping or becoming unsynchronised, even if a driver mistakenly switches back and forth between modes in rapid succession. Six independently controllable H-bridge circuits run to the clutch actuators and are actively managed by the safety MPU. One or two of them can be configured for controlling additional components – for example, SPT is considering adding an oil pump for some future applications that might need further lubrication and cooling at the bearings. SPT’s software manager Dan Knieper explains, “Every clutch has an embedded speed sensor that monitors the differential speed across the races. When a threshold speed differential is realised – 50 rpm for static clutches, say, or 100 rpm for dynamic clutches – the safety MPU turns off the H-bridge to the actuator controlling that clutch. This ensures that no clutch is set to ‘on’ in a potentially damaging, non-synchronised state. “There are also position sensors on each static rocker clutch rocker that report back the state of the rockers in the clutch [as mechanically ‘on’ or ‘off’]. This data is used in our Park, Hill Hold and gearshifting algorithms.” Kimes notes here that the position sensors, from Magnetic Sensing Solutions, are highly desensitised to magnetic field interference – a critical capability for ensuring they are safe for high-power commercial EVs. When the driver requests a particular gearshift or mode change, the main MPU receives the command input (from the EV’s VCU, for example) and decides when the time is right to fire or release the relevant clutches based on measurement inputs from the position and speed sensors. It also determines the ideal power delivery (and how it Some key suppliers Microcontrollers: STMicroelectronics Sensor chips: Allegro Powertrain control modules: Powertrain Control Solutions Motors: Cascadia Motion/BorgWarner Motors: Dana TM4 Electromechanical actuators: McCleer Power Electromechanical actuators: Applinetics Bearings: Koyo Inverters: Cascadia Motion/BorgWarner Inverters: Dana TM4 Gearsets: Delta Research Powderedmetal components: GKN Powder Metallurgy Powderedmetal components: Keystone Powdered Metal Prototyping: TNT EDM Solenoids: Husco Position sensors: Magnetic Sensing Solutions Bidirectional rocker clutches (visible protruding inwards on the inner circumference of this clutch assembly) enable hill-holding and parking functions for EVs on slopes 28 Winter 2021 | E-Mobility Engineering