Technical Background

Introduction

There are approximately 20,000 full sized city buses currently operating in the UK. According to the DfT, city buses emit approximately 3 million tonnes of CO2 per annum.   If the gearboxes in the UK bus fleet were replaced by the Mechanical Regenerative Braking System proposed in this Kestrel Project, it is predicted that CO2 emissions would be reduced by 30% in general mixed operations, and up to 50% during inner city operations. This would reduce CO2 emissions by 1 million tonnes per year.  Furthermore, because the Torotrak transmission can dramatically change the engine duty cycle, it may be practicable to make CNG a viable alternative to diesel, thereby further reducing CO2 emissions.

Strategic Focus

The Kyoto targets for emissions and energy usage represent a substantial technological and political challenge.  A requirement for zero emissions capability is evident.  This proposal focuses on making a significant contribution towards achieving the Kyoto targets by:-

• reducing the energy consumption of a typical city bus by approximately 30% overall

• reducing the CO2 emissions from such a bus by approximately 35% including zero emission capability via an Integrated Starter/Alternator (ISA)

• improving urban bus operation by reducing noise, in many cases increasing passenger carrying capacity and making journeys smoother.

The increased cost of the driveline would be recouped within a two-year period by lower energy and maintenance costs alone.  The driveline could be retro-fitted to almost all existing city buses in the UK and Continental Europe, and could be maintained within the existing infrastructures.  Certain urban delivery vehicles could also benefit from this technology.

This technology is replicable throughout the motor industry world-wide, with similar benefits being achievable in each application with a similar number of traffic stops. 

Objective of this proposal

The objective of this project is to build and test two midi-buses (8 tonne Gross Vehicle Mass similar to the bus shown below), each fitted with a mechanical regenerative braking system (MRBS). 

The buses will then be used to demonstrate the substantial reductions in fuel consumed and exhaust gases emitted made possible by this particular technology.

Bus operations will be improved by:-

• carrying passengers more smoothly, with less noise, and less vehicle maintenance

• reducing the quantities of fuel used and pollutants emitted by 50 - 60% in city centre use.

This technology could then be applied to full sized buses in a subsequent programme.

Costs and timing

The proposal has been structured in 3 phases, each with specific tasks to achieve within a specific time and budget.  At the end of each phase, there is planned a “Gateway Review” to ensure that all the objectives have been met and risk levels assessed before the recommendation to proceed to the next phase.  This ensures that the financial commitment for each phase is well justified beforehand. 

The attached outline timing plan details the 3 phases for the project:-

Expected Result

The anticipated outcome of the expenditure will be two midi buses each equipped with a Mechanical Regenerative Braking System, which can be demonstrated in real bus fleets to prove out the claims of this technology. 

Pending successful trials, the driveline could then be replicated across the UK and Continental Europe.  Buses in other world-wide markets could equally be modified to gain the benefits of MRBS.   Furthermore, urban delivery trucks in certain operations would benefit from MRBS.

Background

During the early 1980's, Leyland Vehicles developed a Continuously Variable Transmission (CVT) for city buses.  The units were successfully developed and demonstrated in a 16 tonne Leyland National bus, improving fuel consumption over a standard bus by approximately 10% for a typical “6 stops per mile” duty cycle.  A transmission went on to complete over 25,000 miles of accelerated durability running, after which the variator unit at the heart of the transmission was found to be in satisfactory condition.  Production plans were formulated, but were cancelled due to the demise of Leyland Bus following de-regulation of the bus industry. 

Another casualty of the Leyland Bus demise was a second Leyland National bus fitted with a mechanical regenerative braking system consisting of a composite high speed energy storage flywheel made by BP, a smaller diesel engine, and the Leyland CVT as the main transmission.  Tests to validate well founded predictions of 40 - 55% reductions in fuel consumption were, regrettably cancelled when the CVT production plans were abandoned.  The bus was, however, successfully demonstrated to the UK DTI, and to BP and Leyland Vehicles management. The EC approved a project under the Thermie initiative in 1984 to build 4 similar vehicles to demonstrate the very significant energy saving potential across the EC. The Leyland Bus demise caused cancellation of the project. 

In 1988, the British Technology Group, who had funded much of the development that led to the Leyland CVT successes, pooled all the technology relating to the CVT into a venture called Torotrak.  For understandable commercial reasons, design and development work focussed on passenger cars, and this work has led via some European front wheel drive transmissions to a  Sport Utility Vehicle (Light Truck) transmission for the US market that gives 17% fuel saving.  

Given sufficient resources, a bus transmission using the latest developments of the Torotrak technology could be designed and built starting almost immediately.  However, the commercial realities for Torotrak mean that priority effort will continue to be concentrated on passenger car transmissions which have the most potential for licence income. 

However, from the perspective of energy savings across Europe, an effective Regenerative Braking driveline for city vehicles remains hugely attractive.  It could be packaged to be retro-fitted to most existing full sized UK city buses and the majority of mainland European city buses too, thus halving the energy required for the operation of this huge bus fleet. 

Current proposal

A schematic of the proposed driveline is shown in the illustration below

The transmission that Torotrak has now developed for the Sport Utility Vehicle (SUV) market could readily be modified to build some demonstration Regenerative Braking "midi" buses with diesel engines so that interested parties could evaluate the technology in a real environment with real fare paying passengers, and real operators giving their feed back. 

The lessons learned could then be incorporated into a full scale design, test and demonstration programme.