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Abstract— This paper reports the intensive study performed at Punch Powertrain that compared the PRE-configuration (electric motor 1 in front of the variator) and POST- configuration (electric motor behind the variator) for a CVT based hybrid powertrain. This study led to the decision to further develop the POST-configuration into the current hybrid powertrain. The main deciding factor in the decision is the possible fuel saving that can be realized with either of both configurations. The other factors also taken into account in the decision are also treated. For both configurations a hybrid strategy was elaborated in depth. After optimizing the strategy for both configurations simulations were run on different type approval as well as real world drive cycles. The POST configuration yields a better fuel consumption reduction over the NEDC cycle as well as real traffic cycles. Additionally, the optimized strategy for the PRE- configuration is a lot more complex than for the POST- configuration. This may require more powerful controller hardware both in processor power and memory capacity. Additionally, the EV-range for the POST configuration is substantially longer than for the PRE-configuration. This longer EV-range of the POST-configuration is attributed to the fact that the electric power to the wheels while driving and from the wheels while braking does not incur the variator losses. Moreover, the braking torque that can be transferred by the CVT belt is not completely clear. Prior experience has shown that the allowable torque transfer is a lot lower than the permissible driving torque. Next to the fuel consumption the distinct advantages of one of the configurations over the other were studied. I. INTRODUCTION When Punch Powertrain started the development of its hybrid powertrain two configuration options were available. The decision of which configuration to develop needed to match in the ambitious development targets set forward. The first option is to link the electric motor/generator with the powertrain in front of the CVT variator. This configuration is applied in mild hybrids like the Honda Insight/Civic and Hyundai Accent (aka Kia Rio). Hyundai applied the VT2 CVT from Punch Powertrain in its hybrid. Patrick Debal is project leader of the hybrid powertrain development at Punch Powertrain in Sint-Truiden, Belgium (phone: +32 11 679 266; fax: +32 11 679 230; e-mail: [email protected]). Saphir Faid is project leader of the switched reluctance motor development at Punch Powertrain in Sint-Truiden, Belgium (phone: +32 11 679 193; fax: +32 11 679 230; e-mail: [email protected]). Steven Bervoets is project engineer for the development of the switched reluctance motor development at Punch Powertrain in Sint-Truiden, Belgium (phone: +32 11 679 215; fax: +32 11 679 230; e-mail: [email protected]). 1 When electric motor is used in this paper, it is a subsystem that can operate as motor as well as generator. In figures it may be abbreviated to EMG which stands for electric motor/generator. Lotus in the UK developed the EVE, a full hybrid demonstrator based on a Proton passenger car also using the VT2 CVT from Punch Powertrain. These examples use a thin, sandwiched flywheel motor. Another possibility is to link an electric motor with a more standard form factor with gears or a chain to the input shaft of the transmission. At Punch Powertrain the configuration with the motor before the CVT is called the “PRE”-configuration. EMG Bat CVT + PowEl ICE PRE-Configuration EMG Bat CVT + PowEl ICE ICE PRE-Configuration Figure 1: PRE-Configuration Schematic The other configuration, hence called the “POST”- configuration, links the electric motor/generator behind the variator. This configuration was not yet seen on the market, neither with CVT or stepped transmissions. It offers a direct connection of the electric motor to the wheels. EMG ICE Bat CVT + PowEl POST-Configuration EMG ICE ICE Bat CVT + CVT + PowEl POST-Configuration Figure 2: POST-Configuration Schematic Punch Powertrain investigated next to the fuel consumption reduction different other aspects of both configurations. This resulted in the clear decision to go for the best one. II. POTENTIAL EFFICIENCY IMPROVEMENT The major reason for vehicle constructors to develop hybrid vehicles is fuel saving. The hybrid passenger cars on the market have a low fuel consumption that is partially attributed to the hybrid powertrain and partially to additional measures like highly efficient engines, streamlining, mass Configuration Selection for Hybrid CVT Patrick Debal, Saphir Faid and Steven Bervoets, Punch Powertrain
