This white paper covers the future development trends in electric and hybrid vehicle drivetrain. In particular, the integration of the powertrain electrical and electronic systems. This white paper deliberately ignores the battery pack and talks about everything else in the powertrain system.
As more EV’s come onto the market there are some clear trends emerging in the development of powertrain systems. Due to the higher volumes, the passenger car industry is leading this drive, but we are also seeing signs of these trends in the commercial vehicle sector as OEM’s start to seriously look at higher volume programs and critically how to drive out costs from their electric vehicle offerings. We also have some OEM’s onto their 2nd and even 3rd generation electric vehicles now so they have learned a lot from the initial volume production and are taking design improvements forwards. It is helpful to look at this evolution to learn more about what can be done to optimise the powertrain design.
Clearly, OEM’s are looking hard at how to drive out material Bill of Materials (BOM) costs from the vehicles in order to reduce the selling price and also improve their margins. They are also looking at how to aid the production line assembly through simplification of the vehicle design. Whilst there is a lot of activity around the battery pack and cell costs, the rest of the powertrain should also not be forgotten. There are significant materials costs in the main powertrain subsystems such as the traction inverter, DC/DC converter, on-board charger and also the high voltage (HV) wiring harness and interconnection systems.
In one word this major design trend is integration. More specialised platform specific componentry which is highly integrated. A couple of good examples of this can be found in the Tesla Model 3. For the Model 3, Tesla has designed a highly integrated power distribution module which is sometimes referred to as the battery penthouse, this sits to the rear of the battery module under the back seats of the car.
The fact that this is a fully integrated module that includes the master Battery Management System (BMS) controller, DC/DC converter, onboard battery charger and high voltage junction box fully integrated into a single module is in itself showing a good level of integration, putting all of these devices into a single box saves on a lot of external HV wiring harness and interconnects. Busbars are used throughout the module that are protected with plastic insulation guards. This will save a huge amount of weight and cost compared to a more traditional approach with separate units. Any HV component integration that can delete HV wiring harness and interconnects is a good thing as it helps to save cost, weight, manufacturing complexity and also improves safety.
But looking a little more closely also shows us that the DCDC and onboard charger are a single integrated liquid cooled unit. This makes a lot of sense, not least because when the demand on the charger is at its highest the demand on the DC/DC converter which is used to step the HV from the battery down to 12V for the other onboard systems like the HVAC and infotainment is at its lowest, so even if there was no other component commonality than shared cooling this would be a smart move. In the Tesla, the motor and inverters were already highly integrated on the model S and this has been followed through to the 3, with the inverter, motor, and gearbox packaged into a single drive unit. High-performance versions having an integrated motor drive unit at the front of the car and another at the rear, also giving 4-wheel drive. There are also some other benefits to this approach that we will go in to in the future.
The new Hyundai Kona, also features a highly integrated drive unit, this time it is mounted up front in the vehicle more like a traditional engine would be. A similar approach is also used in the Nissan Leaf. The Kona has a module which stacks the motor inverter, high voltage junction box, and onboard charger together at the front of the car. These are effectively separate units that are very close coupled so not quite as integrated as on the Tesla. The Tesla’s positioning of mounting the power distribution, OBC and DCDC directly on the battery also helps them to reduce HV cabling over the Kona and Leaf. The primary constraint of the Kona and Leaf is their adaption of the electric drivetrain to a vehicle bodyshell that was designed for an internal combustion engine.
The highly acclaimed Jaguar I-Pace features somewhat less integration on the subsystems than the competitors, probably due to this being their first pure electric vehicle effort. The difference can really be seen when looking at the amount of orange cabling in the I-Pace compared to the Tesla Model 3 which has had a lot of the orange cabling eliminated, which is ideal.
In the commercial vehicle world the new trucks from Daimler with the eActros, Tesla and Nikola with their artic tractor units all feature interesting and similar powertrain layouts that are changing the norms. All these new trucks are using integrated motor/transmissions with individual motors for each driven wheel. This is instead of the more traditional single large motor driving the wheels through a differential. This drivetrain configuration eliminates the vehicle differential and allows the power to be split between multiple electric motors. This has some other benefits which we will look at in a future white paper. The power electronics are also closely coupled to the motors but not yet as highly integrated as something like the model 3.
More of this integration is expected, and the recent purchase of commercial vehicle motor and power electronics firm TM4 by Dana which is a leader in truck axle manufacture would indicate a move towards more highly integrated truck drive lines in the future. Whilst the volumes may be lower and packaging challenges are different on a truck compared to a car the challenge is still to optimise the powertrain cost, simplifying assembly and improving overall vehicle efficiency.