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What is the automatic start-stop system and how does it work?

The automatic start-stop system: a technical innovation that benefits the environment

The idea behind the start-stop system is simple: if the vehicle's engine is switched off during short waiting times, for example at a traffic light, fuel consumption and emissions decrease. The automatic start-stop system helps save fuel and protect the climate. With the technology, the CO2- Reduce emissions by 3 - 8%. The benefits for the environment and the improved economy ensure that the automatic start-stop system will spread rapidly across all vehicle classes. In view of the more stringent EU regulations on pollutant emissions from motor vehicles, car manufacturers are starting to implement intelligent start-stop systems in their fleets.


This is how the start-stop system works

The start-stop system registers when the car is stationary and uses sensors to determine a number of other factors relating to the vehicle's operating condition. If the driver stops at a red light and puts it into neutral, the start-stop system switches off the engine. In some newer models, the motor even switches off when the speed drops below a certain value. Although the engine, and thus the primary energy source for all systems, is switched off, all connected electrical consumers and assistants are still supplied with power. The vehicle battery takes care of that. As soon as the clutch is actuated, the automatic start-stop system starts the engine again. In vehicles with an automatic or dual clutch transmission, the start-stop system only reacts to the actuation of the brake. If the vehicle is braked to a standstill and the driver's foot remains on the brake, the automatic start-stop system switches off the engine. If the brake is released, the automatic starts the motor again.


Sensors control the automatic start-stop system

An automatic start-stop system obtains its information on the driving status from various sensors. The neutral gear sensor, wheel speed sensor and crankshaft sensor provide information on whether the car is stationary or moving. The engine control unit coordinates the start and stop processes and harmonizes them with the energy management. The electronic battery sensor EBS transmits data on the state of charge, voltage and battery temperature. Since the voltage in the vehicle electrical system drops briefly every time the engine is started, compensation is necessary to ensure that important devices and electronic assistants function properly. . In order for the starter to withstand the stresses and strains associated with the increased starting processes and not wear out prematurely, components of the starter unit that are particularly stressed are reinforced and designed for long service lives. This applies to bearings, gears and the starter gear mechanism.


Recuperation and automatic start-stop: New generations of batteries for innovative technologies

While conventional starter batteries already reach their limits when used in vehicles with an automatic start-stop system, batteries with AGM technology have been specially designed for vehicles that, in addition to a start-stop system, have braking energy recovery (recuperation) and other fuel-saving systems feature. A battery with AGM technology is able to absorb the energy fed in via recuperation with a high degree of efficiency. Batteries with EFB technology, on the other hand, are designed exclusively for entry-level cars with automatic start-stop systems.

You might also be interested in: When is it worth upgrading to AGM?


Recuperation - this is how electricity is generated from braking energy

With recuperation or braking energy recovery, electrical energy is generated as soon as the vehicle brakes and the engine goes into overrun mode. The generator in cars with recuperation feeds the recovered energy back into the battery instead of wasting it and using it in the subsequent stop phase to operate the convenience functions. By using this efficient technology and a high-performance AGM battery, higher fuel savings can be achieved than with simple start-stop systems and emissions can be reduced. In order to further increase the overall efficiency, the alternator, which normally runs continuously (and requires engine power) in some vehicles, is decoupled when accelerating. This means that the entire engine power is available for the acceleration process and the engine can work particularly efficiently. In this phase, all electrical functions are supplied by the battery - this shows once again how important a high-performance battery that is tailored to the vehicle's energy management is in modern on-board networks.