Electric Powertrain for HEV and BEV with GKN 2-speed Torqueshift Transmission
Dipl. Ing. Theodor Gassmann, VP Advanced Engineering, GKN Driveline
- Torqueshift technology concept
- ePowertrain and demonstrator vehicle
- Model based design and automatic code generation
- iECO – Intelligent Energy Control Algorithm
In this paper the development of a new electric powertrain for Hybrid (HEV) and battery electric vehicles (BEV) using GKN’s torque shift technology is presented.
The electric powertrain has been developed with the purpose of obtaining a highly compact and ready to install mechatronic product, to be easily used in Battery Electric (BEV) or Plug-in Hybrid Electric (PHEV) vehicles with minor structural and electronic modifications. The proposed electronic architecture allows the system to be integrated in any vehicle as main powertrain (by substituting the original one as is presented on this paper) or as an extra powertrain located in the secondary driven axle.
The main components of the developed powertrain are 1) a two-speed automatic gearbox hydraulically controlled, 2) an axial flux electric motor, 3) an inverter to control the traction motor and, finally, 4) an ECU for controlling the whole system. In addition, the torque shift technology concept combines a two-speed gearbox with an automatic shifting with a minimum shifting time and a smooth torque transition. By using the two-speed gearbox, the torque transmitted to the wheels is best fitted and the efficiency map of the motor can be managed in a proper way to supply the desired torque while using minimum energy or to recover the maximum energy while braking. Compared to a single-ratio transmission, energy savings up to 10% can be achieved while keeping the driver sensations while driving. With the additional gear ratios, not only can higher running speeds be attained, balanced with exciting acceleration and improved range, at the same time associated systems such as the motor and power electronics can be downsized, reducing final manufacturing cost and system weight.
The ECU, exclusively developed for this project, can directly drive the different electro-hydraulic devices of the powertrain, such as hydraulic BLDC pump, the clutch control valves and the park-lock motor, manage the inverter through CAN bus and therefore vehicle whole traction system and incorporate the communication interface with the rest of the vehicle ECUs and HMI.
Two different driving modes have been developed for gear shifting strategy. 1) The I-ECO (intelligent ECO Mode) tries to select the right gear according to driving style and driving condition, which are identified while the vehicle is being driven, in order to save energy. This novel algorithm minimizes the energy consumption by selecting the most suitable vehicle speed for gear shifting while applying the requested torque by the driver. 2) The SPORT mode selects the gear which can supply the highest torque to the wheels according to the vehicle speed so the maximum torque is available for the driver. This mode can be selected by the driver or it’s automatically activated when the system detects a high acceleration demanded by the driver.
In order to achieve successful results in a complex project like this, model based design methodology and automatic code generation have been used for the software development in order to complain with best practices for automotive embedded code generation, such as ISO26262. Several iterations across the V model methodology were needed for testing the different software components by using different backward and forward models.
During the last testing stage, previous to be mounted in the vehicle, the complete powertrain was integrated in a mechatronic testbench specially developed for this project.
VOLVO C30 Electric Vehicle was selected as project technology demonstrator. The new powertrain was integrated in this vehicle by substituting its original powertrain for the one developed in this project.
Finally, the vehicle was tested in two real circuits, in normal and extremely weather conditions, where several functional tests were performed in order to verify that the technology developed fulfilled the project objectives.
The obtained results clearly verify that the electric powertrains based on multi-ratio gearbox can optimize the power transmitted to the vehicle and the global energy efficiency, and this open the possibility to downsize rest of components of the powertrain, especially the motor and inverter set.
Dipl. Ing. Theodor Gassmann
VP Advanced Engineering