Consortium develops low-cost, add-on hybrid drive system

  • 19-Dec-2008 05:41 EST
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Professor Nick Vaughan of Cranfield University is with the ADDZEV twin electric motor drive unit mounted in a test cradle.

A consortium to develop a retrofit hybrid-electric drive system for light commercial vehicles has been formed in the U.K. between Cranfield University and the European Advanced Lead Acid Battery Consortium, with assistance from Provector, Oxford University, and Millbrook Proving Ground. The consortium, named ADDZEV for Affordable Add-On Zero Emissions Vehicle, is receiving funding from the U.K. Department for Transport through the U.K. Energy Savings Trust’s (EST) Low Carbon research and development program.

The project aims to demonstrate a low-cost electric drive system using an advanced valve regulated lead-acid battery (VRLAB), which can switch between hybrid drive and electric-only operation. The consortium is also developing the drive control strategies and battery management system needed for the vehicle. A prototype is under development, based on a Vauxhall Combo light cargo van fitted with a 1.3-L common-rail diesel engine.

“The call under which ADDZEV is funded was an energy storage call,” Andy Eastlake, Head of Laboratories at Millbrook, told Automotive Engineering International (AEI). “So it was really focused on initially trying to get lead acid to perform in that hybrid environment. One of the key benefits from the lead-acid side is cost, relative to some of the other battery technologies that are around.”

Recycling is a second consideration, and lead acid is expected to offer greater recycling potential than other advanced battery types. “Where you get things like end-of-life requirements, it’s relatively straightforward. There’s already an established recycling industry around lead acid,” continued Eastlake.

“The project is trying to focus on this light van but also look at what size of components would be required by other applications. The low-cost element drove the consortium toward a low-cost retrofit to focus on the existing vehicle fleet,” said Eastlake. “Then we can actually generate real carbon savings more quickly than just relying on a replacement strategy. That then presents quite a few problems when you start to try and integrate a new piece of technology onto an existing vehicle.”

Oxford University supplies the drive motors, similar to those used in the Morgan Life Car project, codeveloped with Cranfield University. Provector is handling the battery management and software systems. Millbrook has been involved with integrating the various technologies into an existing vehicle. The demonstrator should be running by early 2009.

The EST laid down fairly tight parameters for the project. The vehicle had to offer a 20-km (12-mi) range under electric power, for instance. The project is based around a front-wheel-drive vehicle. Electric drive is then added to the rear wheels, replacing the rear axle with an electric drive module. Two axial flux motors are mounted in-board. The system also includes an onboard plug-in recharge facility so short-range, low-speed operations such as mail delivery can operate mostly under electric power.

“The key to make it a retrofit solution is minimizing the complexity of the integration into the existing vehicle. The simpler you can make that, the more potential there is to bolt it on and make it a retrofit,” said Eastlake. “The control strategy is really where the skill is in terms of, for example, getting the maximum regeneration braking, without upsetting the stability of the vehicle and understanding how to interface that with the existing braking system.

“What we’re looking at the moment is a manually switchable electric or ICE [internal-combustion engine] drive operation. That would hopefully give us a very simple interface to the vehicle, rather than try to come up with a very sophisticated control strategy that gives you electrical assist, whilst using standard ICE drive. At the moment, we’re leaving the ICE idling whilst we’re running in electric mode, so you don’t get zero emissions; you potentially get a very low emission concept. As a demonstrator, that’s where we’re at.”

With the range requirement, the vehicle needs significant battery capacity, and at present the additional batteries and drive system add around 200 kg (440 lb) to the basic vehicle weight. “The weight penalty is more significant than we would hope for if we took it forward to fleet demonstration level,” admitted Eastlake.

Using lead-acid batteries is part of the reason for the comparatively high weight at this stage. The batteries are also likely to take up some space in the load area. Since cargo vans of this size rarely use the full weight capacity or body volume, this should not present a significant compromise for a demonstration vehicle. “The vast majority of vans in the light to medium sector are front-wheel-drive diesel vehicles, so if we can come up with a module that will bolt in and retrofit into that, you’ve got a very broad market,” said Eastlake.

The project plans to be able to scale up the motors and energy storage system to suit a range of applications. “In my view, I think what we will see is hybrids being developed on a modular basis,” said Eastlake. “It might well be, for example, that in a bus application you have the same architecture but you have a different battery size for two different cities where the duty demands are different.”

The project includes work on duty-cycle simulation, undertaken by Cranfield University. Vehicle operators will provide information about typical usage patterns. “Based on that information, we will undertake simulations of the applicability to as many areas as possible,” Professor Nick Vaughan, Head of Automotive Engineering at Cranfield, told AEI. “One of the aspects of that we were particularly interested in was the effect of road gradient. We were interested in extending the ideas to determine where you could apply this sort of design and how it might have to be modified for various application areas.”

“Taking it to the next level,” said Eastlake, “we are going to simulate how it would look with a mild hybrid front end to give an extended-range capability. That would also potentially provide the electrical systems that would allow you to switch off the engine. Rather than try and do too much at once, we thought we’ll focus on the retrofit electric module and then desktop-simulate a mild hybridization of the existing ICE.”

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