Starter generator

from Wikipedia, the free encyclopedia

A starter generator combines the functions of the starter and alternator in a single electrical machine . It can both accelerate the internal combustion engine of a motor vehicle (start mode) and generate electricity when the engine is running (generator mode). Starter generators are currently mainly used in mild hybrid vehicles with a 48-volt electrical system.

Modern, powerful starter generators can save energy in hybrid electric vehicles by feeding electrical energy back into the vehicle battery when the vehicle is braked and using this energy later to support the combustion engine when a particularly large amount of energy is required, for example when accelerating. The electric drive machines of many plug-in hybrids can also start the internal combustion engine, but since starting is only a secondary function for them, the term starter generator is not used.

Since starter generators are constantly connected to the internal combustion engine, there is no loud noise that is common with conventional starters, which occurs when the starter pinion engages and when the pinion in the internal combustion engine's flywheel is turned.

Historic starter generators

Dynastart direct current starter generators

Starter generators based on DC motors were mass-produced by Siba from 1935 under the brand name Dynastart and after 1959 (after Siba was taken over by Bosch) by Bosch. At that time, starter generators were also known as light starters (from the alternator and starter). The Dynastart machines sat directly on the crankshaft of the engines without any additional gears. Dynastart machines were initially available at DKW and later in the BMW 700 , BMW 600 , the BMW Isetta , Heinkel Cab , NSU Prinz , Goggomobil , Messerschmitt Kabinenroller , AWZ P70 , Steyr-Puch 500 and 650, Steyr-Puch Haflinger and since 1969 in the Vespa 50 Elestart.
The two-stroke engines that are often installed in small vehicles can also run in reverse if they are started in the corresponding direction of rotation. By simply reversing the polarity of the starter generator, it was possible to save the reverse gear on the transmission.

Today the brand name DynaStart is used by ZF Friedrichshafen for modern crankshaft starter generators based on the principle of the permanent magnet synchronous machine .

Modern starter generators

In modern hybrid electric vehicles, a distinction is made between two types of starter generators, belt-driven starter generators and integrated starter generators . Usually they are synchronous or asynchronous machines that work with three-phase current and are connected to the on -board DC voltage system and the battery via a converter .

Belt-driven starter generators

Belt-driven starter generators or belt starter generators ( RSG , Belt-Driven Starter Generator ( BSG ), or Belt-Driven Integrated Starter Generator ( B-ISG )) are coupled to the internal combustion engine via a belt drive , like a conventional alternator . For this, small mechanical changes to the tensioning system of the belt drive are required, since the idle and load strand alternate during operation . Air or water-cooled synchronous machines , asynchronous machines or switched reluctance machines can be used as electrical machines . However, the power that can be transmitted by a belt with reasonable costs and mechanical losses is low, so that belt-driven starter generators can only be used for micro and mild hybrids.

Examples of vehicles with a belt starter generator in the 12-volt electrical system are vehicles from the PSA group with e-HDi engines (from 2010, for example Citroën C4 , Citroën C5 or Peugeot 308 ). These vehicles have starter generators from the French supplier Valeo with a nominal output of 2.2 kW. The mhd models of the Smart (451 series) also have a 12-volt belt starter generator from Valeo.

Vehicles with belt starter generators with 48 volts operating voltage ( mild hybrid ) have been built in series since 2016 . The higher voltage means that electrical outputs of up to 10 or 15 kW can be achieved. Such systems, in conjunction with a small lithium-ion battery, can help to reduce fuel consumption by longer stop-start phases, sailing on the motorway and more recuperation on the test bench by 13 percent and in city traffic by more than 20 percent.

Below is a selection of the 48 volt RSGs available on the market in 2018.

supplier Max. Power (electrical, recuperation) Max. Power (mechanical, boost)
Robert Bosch GMBH 11.5 kW 9.7 kW
Continental AG 16 kW 14 kW
Valeo 12 kW -

Integrated starter generators

Integrated starter generators ( ISG , also crankshaft starter generator ( KSG ), English Crankshaft-Mounted Integrated Starter Generator ( C-ISG )) are used in more powerful mild hybrid vehicles . These sit directly on the crankshaft between the combustion engine and transmission. The power that can be transmitted is therefore essentially only limited by the performance of the starter generator or the converter. The disadvantage is that considerable mechanical changes to existing systems are required and the installation on the crankshaft (coaxial) results in an extension of the drive train . To maintain the overall length, the ISG can also be mounted axially parallel next to the motor at the expense of the width and integrated via a reduction stage. Because of the reduction, the electric motor can be designed for a higher speed and thus lighter.

If the combustion engine is decoupled via an additional clutch, there are no losses due to the engine drag torque. Therefore, an integrated starter generator can recuperate higher electrical power than a belt-driven starter generator. Electric driving is also possible.

The first vehicle with a 48-volt ISG in 2017 was the Mercedes-Benz S-Class (maximum mechanical boost power: 16 kW)

Advantages of starter generators

Starter generators, which today are usually built as permanent magnet synchronous machines, have a much higher degree of efficiency than alternators and have a high power density.

Startup process

When starting, starter generators have many advantages over conventional systems with starters. A conventional starter accelerates the crankshaft to a certain speed (around 250 rpm) after meshing. Then it is injected for the first time and the combustion engine accelerates independently to over 1000 rpm. On the one hand, this process takes a relatively long time and is accompanied by a lot of annoying vibrations and noises. A 48-volt starter generator, due to the higher output and the permanent connection with the crankshaft, can accelerate the crankshaft directly to 500 / min or 1000 / min (ISG), only then is the fuel injected (high-speed start). Starting with a starter generator is therefore hardly noticeable for the driver, which improves the acceptance of start-stop systems .

The start also takes significantly less time. While a conventional starter needs around 0.8 s, 48-volt starter generators currently in series do this in around 0.5 s. Due to the meshing process, a starter can only start the engine when the crankshaft is at a standstill. Starting the engine while driving is therefore problematic and particularly slow in change-of-mind situations. For this reason, start / stop is only activated at very low speeds. This is different with starter-generators, these are permanently connected to the crankshaft and can therefore also start an engine that is revving. Production vehicles with starter generators therefore activate the start / stop function at speeds of 20 km / h, which has a positive effect on fuel consumption. The engine can also be switched off in certain driving situations if it is not required for propulsion ( sailing ).

Additional advantages

In addition to starting the engine, starter generators also offer the following options:

  • Boost function ; improved starting and acceleration thanks to additional torque.
  • Recuperation ; increased energy recovery and better efficiency compared to conventional alternators.
  • Vibration dampening in the drive train.
  • Accelerator start / stop ; The combustion engine can be started when accelerating and switched off when the accelerator is removed.
  • Load point optimization ; The internal combustion engine is operated close to the best efficiency point, in which the starter generator generates energy as an additional engine load and feeds it into the battery or takes it as an engine support.
  • Exhaust gas optimization ; The cold blowing of exhaust gas aftertreatment through relatively cool idle exhaust gases can be avoided by switching off the internal combustion engine frequently.

Starter generators, especially as 48-volt systems, can cost-effectively close the gap between simple start-stop systems and full hybrids.

literature

  • Karl-Heinz Dietsche, Thomas Jäger: Kraftfahrtechnisches Taschenbuch. 25th edition. Friedr. Vieweg & Sohn Verlag, Wiesbaden 2003, ISBN 3-528-23876-3 .
  • Hans-Hermann Braess, Ulrich Seiffert: Vieweg manual automotive technology. 2nd Edition. Friedrich Vieweg & Sohn Verlagsgesellschaft, Braunschweig / Wiesbaden, 2001, ISBN 3-528-13114-4 .
  • Kurt-Jürgen Berger, Michael Braunheim, Eckhard Brennecke: Technology automotive engineering. 1st edition. Verlag Gehlen, Bad Homburg vor der Höhe 2000, ISBN 3-441-92250-6 .
  • M. Timmann, M. Renz: 48V at Mercedes-Benz - options for further applications. In: M. Bargende, HC Reuss, J. Wiedemann (Eds.): 14th International Stuttgart Symposium. Automotive and engine technology. (= Proceedings ). Springer Vieweg, Wiesbaden 2014, ISBN 978-3-658-05130-3 . doi : 10.1007 / 978-3-658-05130-3_45
  • M. Timmann, M. Renz, O. Vollrath: Challenges and potentials of 48-V starting systems. In: ATZ Automobiltechnische Zeitschrift. Volume 115, No. 3, March 2013, pp. 216-220. doi : 10.1007 / s35148-013-0059-6

Individual evidence

  1. ↑ Second start-stop generation with e-HDI technology. In: www.focus.de. June 9, 2010, accessed October 20, 2015 .
  2. ↑ Chris: Peugeot e-HDi: Micro-hybrid technology ensures low consumption in 27 models. In: www.grueneautos.com. August 2, 2011, accessed October 20, 2015 .
  3. ↑ H. Hakvoort, T. Olbrich: Series application of a 48-V hybrid drive. In: MTZ Motortechnische Zeitschrift. Volume 78, No. 9, 2017, pp. 28-37. doi: 10.1007 / s35146-017-0087-y
  4. ↑ Tom Grünweg: New fuel- saving technology : Hybrid for everyone! In: Spiegel online. June 19, 2015, accessed October 31, 2016 .
  5. ↑ Robert Bosch GmbH: The Boost Recuperation System: accelerate faster with more comfort and less consumption. (PDF, 1.58 MB) Retrieved September 3, 2018 .
  6. ↑ Continental AG: 48 volt belt starter generator. Retrieved September 3, 2018 .
  7. ↑ J. Schaub, C. Frenken, B. Holderbaum, P. Griefnow, R. Savelsberg, O. Coppin: FEV ECObrid - a 48V mild hybrid concept for passenger car diesel engines. In: J. Liebl, C. Beidl (ed.): Internationaler Motorenkongress 2017. (= Proceedings ). Springer Vieweg, Wiesbaden 2017, ISBN 978-3-658-17109-4 .