What is stop-start technology?

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Can a system which switches a car engine off and back on again in busy traffic help a driver save fuel? Will it be reliable enough to cope with constant switching on and off? We take a look at the growth of stop-start systems in new cars on the road today.

What is stop-start?

Stop-start goes by many different names (see below) but they all essentially do the same thing. A stop-start system will automatically switch off the engine when a car is stationary.

This is usually after a short period of time (e.g. 1.5 seconds), meaning the engine automatically switches off in traffic jams and at red lights.

As the name suggests, the system then automatically switches the engine back on when the driver is ready to move off.

Why is stop-start being used?

Car makers are getting greener. There are two reasons for this, the first being necessity. European laws have led to certain levels of emissions being given numbers (Euro 3, Euro 4, Euro 5 etc) and over the years the level new cars have to comply with has increased.

From 2012 all new cars sold in Europe must be Euro 5 compliant and this means car makers need to reduce emissions on their new cars.

The other reason is choice. As the industry becomes more competitive and in tough economic times, car makers have realised customers are looking for the lowest driving costs possible.

Rising fuel prices mean improvements to fuel economy is vital for many buyers and the lower a car's CO2 emissions, the less road tax a driver will have to pay.

This has necessitated the introduction of stop-start, once the domain of premium cars, into everything from small family cars to more budget city cars in recent years.

How does stop-start save me money?

The theory behind stop-start is simple. In busy traffic the short bursts of engine inactivity will add up to a saving of fuel that would usually be wasted because the engine would be on and the car would not be moving.

By switching off the engine the car saves a few seconds' worth of fuel and this all adds up over the days and weeks to a relatively big fuel saving.

In fact, Bosch predicted stop-start could help improve fuel economy by up to 15 per cent in particularly busy traffic. At the pumps, this will certainly save drivers money over the course of a year.

It also have benefits in terms of CO2 emissions. Stop-start reduces the CO2 figure and as a result CO2-based payments such as Vehicle Excise Duty (what is VED?) could be reduced as a result.

How much money can stop-start save me?

According to research by Continental Tyres, the average UK driver spends a full year in traffic jams in their lifetime.

A full year of fuel is a huge amount and indicates just how much money can be saved in the long run by saving small amounts each time the car is driven.

What are the problems with stop-start?

The obvious problem with stop-start is the fact an engine restarting means a short delay in the driver actually being able to move off from stationary when the traffic clears or the light turns to green.

Fortunately, stop-start technology is advanced enough to ensure this is not a problem. Stop-start systems generally take less than a second to restart and most drivers will notice very little difference than that of a car without stop-start.

Another problem is the cost of the stop-start technology as highlighted by Citroen recently when it rejected stop-start for the C1.

A typical stop-start system, says Citroen, costs around £400 on the price of a new car. If the system does not save that much at the pumps it is pointless to install the technology.

Again, this should not be a problem in future. Advances in technology mean it is sure to drop in price and on larger cars than the Citroen C1 the savings will be larger.

Plus, if the stop-start system shaves a few grams per kilometre off the CO2 emissions figure it could lead to the car falling into a lower band of VED and as a result be eligible for lower yearly payments, which could easily add up to a few hundred pounds depending on the car.

How can stop-start be improved?

Not only is stop-start now being used in more cars than ever, from small cars to the largest family models, but it is now becoming more efficient.

At the forefront lies Peugeot and Citroen's e-HDi technology which adds some clever technological advances to the stop-start system to improve efficiency.

What is e-HDi?

The e-HDi system has been described as 'micro-hybrid' technology because it uses a small 'e-booster' to improve the efficiency of the stop-start system.

The e-booster stores energy from when the car brakes - known as regenerative braking - and uses it to increase the speed and efficiency of the stop-start system when it turns the engine back on.

This technology is being introduced into Peugeot cars such as the 3008 crossover and the 508 saloon and Citroen models such as the Citroen DS5 and promises to improve stop-start and as a result, boost efficiency even further on new cars.

What else is stop-start called?

Manufacturers tend to have different names for stop-start which is usually some variation of the two words with differing punctuation. For example:

Alfa Romeo: Start & Stop

Chevrolet, Vauxhall: Start/Stop

Citroen: Stop & Start

Fiat: Start&Stop

Ford: Auto-Start-Stop

Jaguar: Intelligent Stop/Start

Peugeot: Stop & Start

Renault: Stop and Start

Seat: Start/Stop

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Author Stephen Hurrell Published 17th January 2012 Comments (0)