Debunking myths surrounding stop-start systems
On the 20th anniversary of Valeo’s first rotating stop-start system, Stephen Knight takes the opportunity to debunk and dispel some of the common myths surrounding stop-start systems, which still prevail after all this time.
The automotive industry is continuously evolving, with a strong focus on developing technologies that enhance fuel efficiency and reduce environmental impact. Stop-start systems are one such development but they still, even after 20 years of existence, attract distrust and even scepticism. Questions like – does it use more fuel? or does it cause more wear to other components? are commonly asked. Here’s a few answers.
What is stop-start?
Firstly, let’s clarify what the main function of the stop-start system is. When driving in cities and towns, vehicles are stationary for nearly 35% of the time (traffic jams, red lights etc), with their engines idling needlessly. The stop-start system automatically switches off the engine when the vehicle is at a standstill and restarts the engine immediately, as soon as the driver lifts his foot off the brake or disengages the clutch, leading to a significant reduction in CO2 emissions and fuel consumption and helping to keep our air cleaner and environment safer.
Myth 1
Vehicles equipped with stop-start use more fuel
There is an older belief that it takes more fuel to restart the engine than to leave it idling. However, this is a myth left over from the days of carburettors. Modern fuel injection systems use a precise amount of fuel injected into the engine for start up, as well as normal operation. There is no longer a significant amount of excess that’s left over like on previous carburettor-equipped engines. Engine management is also constantly evolving. Today’s advanced engine technologies allow the fuel injection process to speed up the cranking phase and start our engine faster. Studies by Valeo, as well as other independent research companies such as the American Automobile Association, have found that stop-start technology resulted in a 5% to 7% improvement in fuel economy.
Myth 2
Vehicles equipped with stop-start cause more pollution
Regardless of how we drive there will always be moments when our van is stationary. As a result, a journey using a vehicle equipped with stop-start that cuts off the engine when stationary will give off fewer emissions than the same journey without one.
A study from the Polytechnic University of Madrid measured the CO2 emissions of two four-wheel drive vehicles. A reduction of more than 20% was recorded for the vehicle equipped with the stop-start system. Researchers concluded that despite variability in driving style, grade and type of streets, traffic congestion and engine operating temperature: “the vehicle equipped with the stop/start system has intrinsically a lower CO2 emission factor.”
It’s important to note that the EU has a regulation that sets CO2 emission performance standards for new passenger cars and vans (Regulation (EU) 2019/631). The EU fleet-wide CO2 emission targets set in the Regulation for vehicle manufacturers state that for the period of 2020 to 2024 each new van produced cannot exceed 147g of CO2 per km. If the average CO2 emissions of a vehicle manufacturer’s fleet exceed its specific emission target in a given year, the manufacturer must pay – for each of its new vehicles registered in that year – an excess emissions premium of €95 per g/km of target exceedance. Because of this, stop-start systems have played a huge role in helping vehicle manufacturers reduce CO2 emission output.
Myth 3
Stop-start systems wear out your battery
Not many people realise vehicles equipped with a stop-start system have specifically designed batteries which utilise different technologies to standard lead acid batteries commonly found in vehicles without stop-start. The batteries used within stop-start systems are typically either EFB (enhanced flooded battery) or AGM (absorbent glass mat), and these technologies are more suited to multiple start ups.
Not only does the technology inside the battery change on stop-start systems but live data from the battery is constantly communicated to the ECU via the SpyBat sensor. This sensor communicates information such as battery state of charge, battery state of health and battery temperature. This live feed of information allows the vehicle to ensure the battery is kept at an optimal condition as well as having all the information it requires with regards to ensuring enough power is available for the restart phase. This ensures the battery is kept healthy for the duration of its life.
Myth 4
Stop-start systems damage your engine
It is commonly perceived that starting the vehicle multiple times will cause damage to the engine, this perception is based on the principle of starting the engine from cold.
When the engine is started for the first time, the engine oil has settled within the oil sump. It therefore takes time for the oil to circulate throughout the engine and lubricate the necessary components. When starting from cold the oil also needs time to increase its temperature and reduce its viscosity in order for it to circulate with ease.
With stop-start systems after the initial start up the time that the vehicle would shut down for during a stop/start phase is minimal and certainly not enough time for the engine oil to dramatically reduce the temperature or drain into the sump. The oil temperature and engine temperature are also monitored by the ECU and should there be any reduction in temperature to the point where it may cause an issue, the system will not allow the vehicle to stop, or should it be in the stopped phase, will activate the start up procedure.
The system constantly monitors various signals through the engine management system and will only allow the stop-start function to operate when all of the parameters which are pre-set by the manufacturer are met.
Myth 5
The constant stopping and starting wears the starter motor faster
On stop-start systems that still require a starter motor it is first important to understand that conventional starter motors do not comply with stop-start cycling features. Technology such as the Valeo ReStarter (reinforced starter) have been developed to support extended life cycles and be reinforced to interface with the engine’s flywheel.
Conventional starters are designed to withstand on average 50,000 cranking cycles in their lifetime. By comparison, the Valeo ReStarter is mechanically reinforced to achieve 300,000+ cycles. In addition to pure cycling resistance, the ReStarter has improved internal electronics that gives it a higher power efficiency. This allows for a quicker, more efficient start which improves driver comfort and limits battery voltage drop during the cranking phase.
Stop-start systems – conclusion
There’s no doubt that stop-start technology reduces CO2 emissions and help protect the environment. In the pursuit of eco-friendly and fuel-efficient solutions, stop-start technologies such as Valeo’s StARS have emerged as pivotal innovations. With advancements in stop-start technology now making impacts on mild hybrids (48v systems), vehicle manufacturers are using the technology more and more as we enter the realms of electric vehicles to produce more environmentally friendly vehicles. For the foreseeable stop-start is here to stay!
