Search Results

The standard vehicle propulsion system and its controls are compared with a flywheel propulsion system. Different concepts of control and various system configurations are explored. Some considerations for the design of a general purpose automatic flywheel transmission vehicle are presented and discussed. Specifications required for a flywheel transmission system which can achieve substantial mileage improvements and provide high performance are presented. The resulting vehicle would have performance of 0–60 mph in less than 10 seconds and achieve 50 miles per gallon on the Federal Urban Driving Cycle (FUDC) at an inertia weight of 3,000 lb. Higher mileages are possible for lighter vehicles. Fuel economy is achieved by (1) engine operation only at minimum BSFC, (2) elimination of engine idle, (3) recovery of energy from braking and (4) minimizing transmission losses.

A flywheel to manage energy between a prime mover and a load has been used in many engineering applications. Automotive applications, however, pose a number of difficult problems which can be overcome only with proper design. Substantial mileage and performance improvements while meeting emission constraints can then be accomplished with the concept. An experimental flywheel car has been designed and built at the University of Wisconsin that has demonstrated a mileage improvement of about 50% over a corresponding production vehicle on the EPA/FUDC. With continued research and development gains of 100% appear feasible.

The flywheel energy-storage unit is examined as a tool for engine load management. The control decision to store or retrieve energy is formulated and discussed. Vehicle dynamics are simulated on a digital computer in combination with dynamic programming techniques to obtain optimal operation policy. The simplified algorithm is explained, as well as the cost-function criteria and optimization constraints. The sensitivity of the optimal path and the vehicle gas-mileage improvements are elaborated. The study of losses indicates that the transmission is the largest energy sink in the power train. The result of this study provides an indication of the appropriate real-time control policy.

The electric car has many features that make it attractive for urban use. Currently, its principal shortcomings are its short range and poor efficiency for a realistic driving cycle. An electric hybrid car of advanced design, such as the University of Wisconsin model described here, can overcome the limitations of the all-electric car, while retaining most of its advantages, but only at the expense of greater complexity. More research and development is required before either version can be an adequate replacement for our present internal combustion engine cars.

Four hybrid powertrain designs are compared for a refuse collection truck driven over approach, loading and return segments of a representative route. Appropriate matching of component characteristics, drivetrain design and control strategy is shown to reduce fuel consumption by 39% to 56% compared to a conventional vehicle. Concurrently, brake usage is reduced 54% to 85% and the number of engine revolutions is reduced 66% to 84%. The four hybrid powertrains consist of “Integrated” and “Add-On” designs using flywheel or accumulator energy storage to recover braking energy and optimize engine efficiency. The average engine efficiency for each design is comparable and the vehicle fuel economy depends on the ability of each design and control strategy to minimize parasitic losses and use of the service brakes.