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A control strategy has been designed for a city bus equipped with a pneumatic hybrid propulsion system. The control system design is based on the precise management of energy flows during both energy storage and regeneration. Energy recovered from the braking process is stored in the form of compressed air that is redeployed for engine start and to supplement the engine air supply during vehicle acceleration. Operation modes are changed dynamically and the energy distribution is controlled to realize three principal functions: Stop-Start, Boost and Regenerative Braking. A forward facing simulation model facilitates an analysis of the vehicle dynamic performance, engine transient response, fuel economy and energy usage.

A Range-Extended Electric Vehicle (REEV) usually has an auxiliary power source that can provide additional range when the main Rechargeable Energy Storage System (RESS) runs out. The range extender can be a fuel cell, a gas turbine, or an Internal Combustion Engine (ICE) bolted to a generator. Sizing the powertrain for a REEV is primarily to investigate the relationship between the capacity of the main RESS and the power rating of the range extender. Worldwide harmonized Light vehicles Test Procedures (WLTP) introduced a Utility Factor (UF) which is a curve used to calculate the weighted test results for the Off-Vehicle Charging-Hybrid Electric Vehicle (OVC-HEV) from the measured Charge Depleting (CD) mode range result, and the Charge Sustaining (CS) mode Fuel Consumption (FC). Therefore, the RESS capacity, the range extender power rating, the control strategy, and the UF are the key factors affecting the weighted FC of a REEV on the test cycle.

For the vehicles with frequent stop-start operations, fuel consumption can be reduced significantly by implementing stop-start operation. As one way to realize this goal, the pneumatic hybrid technology converts kinetic energy to pneumatic energy by compressing air into air tanks installed on the vehicle. The compressed air can then be reused to drive an air starter to realize a regenerative stop-start function. Furthermore, the pneumatic hybrid can eliminate turbo-lag by injecting compressed air into manifold and a correspondingly larger amount of fuel into the cylinder to build-up full-load torque almost immediately. This paper takes the pneumatic hybrid engine as the research object, focusing on evaluating the improvement of fuel economy of multiple air tanks in different test cycles. Also theoretical analysis the benefits of extra boost on reducing turbo-lag to achieve better performance.

Recovering as much braking energy as possible, and then fully reusing it, can significantly improve the vehicle powertrain efficiency, hence reducing the CO2 emissions and fuel consumption. A 48 V mild hybrid system recovers less braking kinetic energy than a HV (High Voltage) hybrid system due to the reduced peak power/current rating. However, the cost of the 48 V mild hybrid system is significantly less than the HV hybrid system which gives the 48 V mild hybrid system a much better cost-benefit ratio. The 48 V mild hybrid system can have several different system layouts (e- machines at different positions, or have numerous e-machines at different position combinations). The aim of this study is to investigate and explain how the system layout affects the powertrain system efficiency and CO2 benefit. Simulation models are used to predict the CO2 of three such configurations.

The objective of the work reported in this paper was to identify how turbocharger response time (“turbo-lag”) is best managed using pneumatic hybrid technology. Initially methods to improve response time have been analysed and compared. Then the evaluation of the performance improvement is conducted using two techniques: engine brake torque response and vehicle acceleration, using the engine simulation code, GT-SUITE [1]. Three pneumatic hybrid boost systems have been considered: Intake Boost System (I), Intake Port Boost System (IP) and Exhaust Boost System (E). The three systems respectively integrated in a six-cylinder 7.25 l heavy-duty diesel engine for a city bus application have been modelled. When the engine load is increased from no load to full load at 1600 rpm, the development of brake torque has been compared and analysed. The findings show that all three systems significantly reduce the engine response time, with System I giving the fastest engine response.

Recovering the braking energy and reusing it can significantly improve the fuel economy of a vehicle which is subject to frequent braking events such as a city bus. As one way to achieve this goal, pneumatic hybrid technology converts kinetic energy to pneumatic energy by compressing air into tanks during braking, and then reuses the compressed air to power an air starter to realize a regenerative Stop-Start function. Unlike the pure electric or hybrid electric passenger car, the pneumatic hybrid city bus uses the rear axle to achieve regenerative braking function. In this paper we discuss research into the blending of pneumatic regenerative braking and mechanical frictional braking at the rear axle. The aim of the braking function is to recover as much energy as possible and at the same time distribute the total braking effort between the front and rear axles to achieve stable braking performance.