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

or three rockers respectively run radially in each direction to hold torque.” For its dynamic clutches used in third gear, the EMAX uses a second type of electromechanical device: linear servo-actuators. When one of these actuator’s motor is powered, it pushes forward on a ring of plunger-like cams, which feature an arrow-head shape on their front ends. The cams are inserted under the locking element to push the rockers into their ‘on’ positions, acting in a similar way to the cam on a parking pawl rod. “Generally we’ll use the linear servo- actuated banks of plungers in clutches that have just two states – that is, the 11/00 type,” Kimes says. “But the 11/10/01/00 function can also be achieved by using two sets of linear motors and cams, where one motor controls a bank of plungers that lock the clutch in the power-on direction and the other motor locks it in the regeneration direction.” The linear motor clutch consists of a stator ring which is grounded and an actuator ring which is hard-connected to one of the clutch races. The race can be permanently grounded, or it can rotate. The interface between the stator and actuator is rotation-agnostic, which notably makes the system agnostic to whether the clutch is dynamic or static, with a constant air gap between stator and actuator in either case. “The function of our linear motor clutches is analogous to dog clutches using a shift fork, but in our case there is no mechanical linkage, only an electromagnetic linkage,” Kimes says. “With our actuator configuration, there are no extraneous linkages from a shift fork going to an external electric motor or worm screw; we are packaged completely inside the case. “Equally important, these magnetically latching clutches also have extremely low parasitic losses. The only power consumed with them is the <200 ms electric pulse that turns the clutch ‘on’ or ‘off’. Once in state, the clutch is kept there by a very strong permanent magnet latch in both the on and off states. Gearshift transmissions Each of the EMAX powertrain’s modes uses a different transmission sequence (the key parts of which are laid out in the EMAX Anatomy sidebar on page 25) and combination of clutch activations in order to yield the desired re-optimisation of output torque and speed. What follows is a description of each gearshift (the diagram above can be used as a reference layout to differentiate between the clutches). In first gear (A1B1), clutches B3 and C234 are disengaged, and B12 and C14 are activated. As a result, motor B is coupled to (and therefore driving) the first sun gear. The B12 clutch is used to ground the first carrier and the second ring gear to the housing (through the notch plate), while B3 is left open to ensure that the first sun gear can move freely. Motor A directly supplies torque to the second sun gear while motor B supplies an equal torque in the reverse direction of rotation to the first sun gear. Cumulatively, this results in an output torque ratio of about 6.2:1. The output torque = TA(RA) + TB(RB), so assuming equal torques in both motors’ yields, output torque = motor torque x (3.63 + 2.64) or 6.12 x motor torque. In second gear (A1B2), the B12 clutch is engaged and the B3 clutch is deactivated (the brake clutches remain as in first gear), Motor B is directed to the output shaft via clutch C234 being activated and C14 being deactivated. Motor B changes direction and at a 1:1 ratio, while motor A remains at a 3.63 ratio. That means an output torque ratio of 4.63:1. For third gear (A2B2), brake clutch B12 disengages and brake clutch B3 locks, while the two main clutches continue as in second gear, for a 2.72:1 torque output. Shifting to fourth gear (A3B2) engages both dynamic clutches C234 and C14 and disengages both brakes. In this state, motor B applies torque to the first sun gear and to the output shaft via the first ring gear and the second carrier; none of the rotating parts are grounded to the housing. Motor A is also locked in a 1:1 state. That means an output torque ratio of 2:1 – the output torque is the exact sum of both motors’ input torque values. In addition to the four driving gear modes, further shifting is performed to achieve the Reverse, Park, and Hill Hold gears. For reverse gear, the clutches and brakes work identically to first gear, but the motors deliver torque in their reversed directions, giving 6.2:1 torque with the output shaft spinning in the opposite direction to first. A cutaway diagram of the key clutches and inputs for the EMAX’s gearshifts 26 Winter 2021 | E-Mobility Engineering Dossier | Sigma Powertrain EMAX transmission