75 Vehicle Architectures and Design Adequate spaces under the vehicle must be available for routing the fuel lines and the exhaust pip- ing. A high-voltage electrical circuit diagram has to be developed alongside fuel line and exhaust system drawing. While analyzing the packaging and mounting of the hybrid components, front-to- rear weight ratios must be maintained at 60:40 or less for acceptable drivability, ride performance and dynamic braking. In conclusion, the mass savings in engine and fuel system downsizing in a hybrid vehicle will more or less be consumed by the additional components added; and the packaging issues are much more complicated for re-engineered vehicles.
It would always be advantageous to design a hybrid from ground up rather than retrofit and re-engineer an existing IC engine vehicle. 3.7 MISSION-BASED DESIGN WITH VEHICLE SIMULATION The vehicle design is driven by the customer which in turn sets the mission profile for the vehicle system and its powertrain. Vehicle acceleration, maximum speed, all-electric range, fuel economy and passenger and loading capacity are the choice factors that a customer cares about either in part or fully in selecting a passenger vehicle, which is essential to be considered during the vehicle design process.
The considerations for the critical parameters resulting from the choice factors are widely different when designing a delivery truck as compared to that of designing a passenger sedan. In recent years, there has been an uptake in the interest and sales in EVs where the custom- ers are willing to pay comparatively more than an equivalent IC engine vehicle due to a variety of reasons including high-acceleration performance, environmental consciousness, new technology appeal, quiet operation and convenience of fueling/charging at home and at work. The mission is set by the customer which necessitates simulation and analysis tools that incorporate the customer requirements.
A simplified approach of incorporating the customer requirements in vehicle design and component sizing is to use the various standardized drive cycles used for evaluating vehicle performance in different driving scenarios. The various drive cycles available reflect the customer driving preferences and mission of the vehicle [9]. In this section, we will evaluate the vehicle system requirements and then utilize the one- dimensional vehicle system model developed earlier in Chapter 2 to build a system simulation model for the analysis, simulation and design of a vehicle using the standardized drive cycles.
Although more complex design and analysis tools are used in the automotive industry, fast and easy-to-use design and simulation tool helps us develop an understanding of vehicle system and its components, evaluate different design topologies and identify the important system interactions. 3.7.1 V ehicle s imulaTion m odel The simulation model of a vehicle system is an essential tool for the design and performance evaluation of the vehicle. With numerous choices available for electric and hybrid architectures, and on powertrain component technologies, simulation saves time and cost in predicting tank- to-wheel energy usage as well as in-depth vehicle performance outputs.
The simulation models can be developed with varying degrees of sophistication as required by the user. At the vehicle level, a simulation model can predict fuel economy, emissions or wheel torque for a regulated drive cycle; at the subsystem level, component parameters such as electric machine or IC engine torque are available. The objectives of a simulation analysis are varied which can be summa- rized as follows: • Vehicle performance prediction – Various vehicle-level performance parameters such as fuel economy, vehicle range and acceleration and load carrying capacities can be predicted for a given vehicle with specified powertrain components under different driving scenar- ios.
The simulation model can be used to optimize and tune the supervisory control system of an electric or hybrid vehicle.