Integrated Starter Alternator, Basic Function - GF15.40-P-1000A

Model All (CAR) 

Overview 

This document contains information on:

• General 
• Function 
  • Engine start/Automatic engine start/stop 
  • Alternator 
  • Boost effect 
  • Recuperation 
  • Gliding 

General 

The integrated starter alternator (ISA) combines the functions of the starter and the alternator into one system, thereby replacing the individual components used up till now. The more compact design enables a higher output density compared to the belt-driven starter alternator. The start time of the combustion engine is shortened and the typical starting noises are reduced. The ISA also has additional functions such as the additional energy recovery through recuperation and output boost when accelerating.

While the generation 1 integrated starter alternator is located on the engine side, the generation 2 integrated starter alternator is located on the transmission side. Concept changes from Generation 1 to Generation 2 have enabled modularization to be further developed, whilst greater use of standardized interfaces for the starter-alternator technology facilitates installation on a range of combustion engines. With the generation change, the generation 2 integrated starter alternator is redesigned and consists of the rotor and stator.

Example illustration of generation 1 integrated starter alternator 

Courtesy of MERCEDES-BENZ USA

Courtesy of MERCEDES-BENZ USA

Exploded view of generation 1 integrated starter alternator 

Courtesy of MERCEDES-BENZ USA

Example illustration of generation 2 integrated starter alternator 

Courtesy of MERCEDES-BENZ USA

Exploded view of generation 2 integrated starter alternator 

Function 

Engine start/Automatic engine start/stop 

The integrated starter alternator replaces the conventional starter. It is connected directly to the crankshaft, meaning that a pinion gear can be dispensed with. As a result, the entire combustion engine starting procedure is further optimized and more uniform. Starting occurs more rapidly and smoothly at idle speed with significantly reduced starting noise.

Alternator 

The integrated starter alternator supplies the 48 V battery with energy via the alternator. The belt drive is no longer required due to the integrated starter alternator being connected directly to the crankshaft.

Boost effect 

The boost effect improves the vehicle's response/acceleration characteristics with comparatively low fuel consumption.

The integrated starter alternator supports the combustion engine in terms of output and torque as required. The support is achieved by overlaying the torque of the combustion engine with that of the integrated starter alternator.

For example, when accelerating, an additional output of approx. 10 - 15 kW or a torque of 180 Nm for spark-ignition engines (200 Nm for diesel engines) is generated. When starting off at low combustion engine speeds, the integrated starter alternator supports the combustion engine due to its better rpm/torque characteristics and thus increases agility.

Recuperation 

During braking, the integrated starter alternator can recover energy and supply the 48 V battery with energy.

Brake intentions are detected in combination with an electromechanical brake booster. Depending on the required brake force, either regenerative braking alone, or hydraulic braking can be used.

Gliding 

When coasting at higher speeds, the direct connection of the integrated starter alternator enables the combustion engine to be switched off as soon as the driver releases the accelerator pedal, thereby saving fuel.