1.2m Stop-Starts For A New Generation Of Micro-Mild Hybrid Vehicles

No issues were identified with the technology in any of the recorded test data throughout this extended period of unrelenting stop-start testing followed by a successful teardown and forensic examination of CPT's award winning motor-generator system.

We have tested the unit as painstakingly as possible to confirm its capability of frequent stopping and re-starting of an engine way beyond the 150,000 to 300,000 stop-starts currently mandated by vehicle OEMs, but consistent with the continuing trend towards increasing levels of hybridisation and more opportunities for stop events, says Nick Pascoe chief executive of CPT.

A stop-start system has to be specified for near-future requirements including extending vehicle life and increasingly demanding hybridisation strategies, and a typical modern car moreover can easily last 250,000 miles over 15 years, says CPT hybrid product group manager Peter Scanes. More critically, fuel economy targets require reduced stop-inhibits, not just stopping the engine when the driver places the transmission in neutral. Latest implementations allow frequent stop-start events in crawling traffic and future coast-down strategies. Switching off the engine, but preparing for immediate re-starts if the driver demands acceleration, will further increase the frequency of stop-starts. We needed therefore to demonstrate as convincingly as possible the near-zero probability of failure during the lifespan of a vehicle as well as the ability to achieve the maximum number of re-starts, because one of the most cost effective solutions for low fuel consumption is simply stopping the engine at every single opportunity - even if it's only for a few seconds every stop counts.

Al Muncey senior engineer for SpeedStart mechanical and electrical systems at CPT and lead engineer on the project, commenting on the durability and maintenance free attributes of the innovative SpeedStart solution, added: The sealed unit with its integrated control and power electronics avoids any ingress of dirt and its thermal management is of a high order with the liquid cooled unit plumbed into an engine's coolant system.

The first engine stop-start test began on 15 October 2010 and continued around the clock for 24 hours a day seven days a week until 1.2 million restarts had been achieved almost a year later on 30 September 2011. The unremitting test schedule demanded a restart on average every 12 seconds, with the actual time between starts varying between 5 and 25 seconds, which is equivalent to 300 an hour or 7,200 re-starts every single day for a total duration of 350 days of continuous testing.

Before this initial validation programme had been completed, another test was commissioned on 2 June 2011 with a second SpeedStart unit, which from September 2011 onwards was tested 24 hours a day for five days a week until another 1.2 million restarts had been achieved almost two years later on 15 February 2013. Testing of this second unit will now continue, ad infinitum or until it does ultimately fail, to establish just how many restarts can be achieved and the likely maximum service life.

In addition to its start-stop capability, the SpeedStart technology has been designed from the outset to provide significant brake energy recuperation and is an efficient motor-generator. Despite the frequency at which the engine was continuously stopped followed by immediate re-starts, and with a regularity which the average motorist is unlikely to experience even in the most heavily congested urban traffic, the SpeedStart units still had sufficient time to generate more than three times the amount of electrical energy required to restart the engine following each stop event.

Such was the rate of generation that over the two-and-a-half year test period the two SpeedStart units regenerated 35 Gigajoules of electrical energy, which is approximately 10MWh and enough to supply a typical UK household for six months and a typical US home for almost five months. In terms of chemical energy it's the equivalent of combusting six barrels of oil.

For a vehicle to recover that much energy it requires an efficient electrical machine, which is almost as important as exceeding the industry's durability requirements, says Pascoe. And when you do eventually reach the end of life of the vehicle it's equally important that all the material can be easily recovered and recycled. And this is where switched reluctance machines have another major advantage, because they eliminate the need for permanent magnets made from expensive rare earth materials - leaving only steel, copper and aluminium and small amounts of plastic and silicon in the electronic components to be recovered. Consequently, the recyclability of our machines is virtually 100 per cent.

Multiple SpeedStart units are also undergoing accelerated testing to represent a lifetime of generation in the hostile under-hood environment, cycling between -25 and +125⁰C air temperature, between -25 and +110⁰C engine coolant temperature and between zero and full electrical loads.

Developed from the outset for 12, 24 and 48 volt applications, CPT's powerful SpeedStart system is the world's first liquid-cooled switched-reluctance motor-generator developed for automotive stop-start. Even at 12 volts the CO2 and fuel economy benefits of this highly efficient starter-generator combined with high current electrical energy regeneration can be as much as 20 per cent. The driver benefits also include its high torque and rapid response, leading to a desirable and virtually unnoticeable stop-start experience with a unique 'Driver Change of Mind' capability to ensure that its operation is not intrusive to normal driving styles.

Already at a high level of technology and manufacturing readiness the powerful SpeedStart motor-generator has been demonstrated to major vehicle OEMs and incorporated into the company's latest LC Super Hybrid technology demonstrators. The availability of this production ready technology is expected to appear in a new generation of micro-mild hybrid vehicles reaching dealer showrooms from 2015 onwards.