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Siemens VDO’s Full Hybrid Demonstration Vehicle

27 November 2006

C230
The C230.

The hybrid development team at Siemens VDO has built a full hybrid vehicle as a demonstration of its Hybrid Tool Box—a portfolio of hybrid components including high- and low-voltage motor inverters, electric motors and vehicle control algorithms and integration capabilities.

Simulations on the prototype—based on a Mercedes C230 K Sport Coupé—in FTP driving modes show improvements in fuel economy of 30% to 38%, depending on driving strategy. The hybrid functionality includes stop/start, regenerative braking, pure electric drive, gear shifting optimized to electric drive and regeneration and operating mode shift.

The non-hybrid base vehicle—a C230 K Sport Coupé—features a 1.8-liter 4-cylinder gasoline engine with 141 kW (189 hp) of power and maximum torque of 260 Nm (192 lb-ft). Acceleration from 0 to 100 kph takes 8.1 seconds, fuel consumption is 9.2 liters/100 km (25.6 mpg US), and CO2 emissions are 219 g/km. The engine is mated with a 5-speed automatic transmission.

Fhsc1
The electric motors and the clutch. Click to enlarge.

For the hybrid drivetrain, the Siemens team used a parallel architecture, with a primary motor, a clutch, and a second, smaller motor (Side-Mounted Starter Generator—SSG). The main motor connects directly to the input shaft of the automatic transmission and replaces the torque converter. The second electric machine is located in the belt drive, and is responsible for engine starts. Once the engine is synchronized to gearbox speed, the interconnecting clutch is closed.

The primary traction motor delivers peak power of 75 kW, with continuous torque of 97 Nm (71.5 lb-ft) over a wide speed range and peak torque of 276 Nm (203.6 lb-ft) for 30 seconds from 0 to 2,700 rpm.

The secondary motor also contributes to the operation of the hybrid vehicle when the battery is low and with high vehicle load at steep grades—conditions in which the electric clutch needs a lot of electric energy. The SSG can deliver 5 kW of power continuously.

The inverter electronics are one of the main focus points of the toolbox, according to the Siemens team. The prototype inverter in the Sport Coupé offers a voltage range of up to 450V, continuous phase current of 75°C. The inverter also houses the control board with the microcontroller. Monitoring, diagnostics and basic safety concept is included.

Fhsc2
Photograph of the battery pack. Click to enlarge.

The Siemens team chose a nickel-cobalt-based lithium-ion battery with an average power density of 1.3kW/kg at the cell level. The cells have 6.8 Ah capacity, and a peak recharge power of 200A for 10 seconds.

The battery pack consists of 100 cells connected in series, and is 80 liters in size.

Siemens VDO terms its driving strategy for hybrids IPM (Integrated Powertrain Management). IPM comprises two main parts: Traction Energy Management (TREM) and Torque Management.

Fhsc3
Siemens VDO IPM.

TREM receives the current battery status regarding state-of-charge (SOC) and state-of-health (SOH) from the battery management system. Depending on these characteristics the different driving modes are released or limited. TREM can deactivate the Boost function, for example, to prevent the battery from further discharge.

TREM sets charge and discharge limits depending on the current battery status. Those limits are specific for the type of energy storage.

Torque Management includes a driver and situation detection function, which includes a driver pedal interpretation for the accelerator and the braking pedal. The Operating State Control determines the different driving states: Launch, Pure Electric Driving, Boost, Regenerative Braking and several more.

A special challenge for the system is the transient behavior between different driving states. Dynamic transients must not cause shocks in the drivetrain and must not be recognized by the driver.

A typical driving cycle for the Siemens system is as follows:

  • After the power up the driver engages gearlever-position D and steps on the accelerator pedal. The Sport Coupé launches immediately in pure electric mode with the combustion engine declutched from the drivetrain.

  • During further acceleration the combustion engine is started by the Side-Mounted Starter Generator and synchronized to the transmission input speed. If the speed difference is minimized the interclutch is closed and the driving torque can be transferred from the combustion engine.

  • The electric machine is now either operated in generator mode to charge the battery or in motor-mode to support the acceleration. During braking phases the interclutch remains either closed or the clutch is opened and the combustion engine is shut off to optimize the potential for regenerative braking.

  • In cold-start situations, IPM can request gear neutral although gearlever-position D is selected by the driver. The interclutch is closed and the combustion engine is started by the motor. With the engine idling the interclutch is opened again, the gear is engaged and the vehicle is launched electrically.

  • If the high voltage battery is deeply discharged the drivetrain is operated as serial hybrid.

This powertrain configuration supports a high potential for fuel consumption reduction as well spontaneous and crisp driving behavior. One of the challenges is to design an electric drive system that performs in extreme situations like steep grades with multiple stop start sequences.

For the Sport Coupé Prototype we found a solution that promises to work well. The potential in fuel savings of 38% (simulated) is great and benefits from omitting the T/Q and the high efficiency of the electric drive including the battery.

The system can thus be transferred to other vehicle platforms like transversal engine, small, mid-size, or large sedans. Even SUVs are possible, the weight to torque ratio has to finely balanced and the serial hybrid mode needs to be adapted to cooling and battery capacity.

—Mathias Deiml, et. al.

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November 27, 2006 in Hybrids | Permalink | Comments (7) | TrackBack (0)

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Comments

In Germany, it's quite normal these days for this type of complex systems integration to be marketed and executed by specialized vendors in the automotive supply chain. Siemens VDO competes with Robert Bosch GmbH in many areas, though it can arguably draw on a vast pool of electric drive and power electronics expertise in its parent company. For example, they figured out how to implement field weakening in a synchronous PM motor by changing the magnet remanence on-the-fly.

Using a separate starter-alternator sounds superfluous, but evidently it simplifies a number of operations such as cold cranking. Li-ion batteries still tend to perform poorly in cold weather, so I expect the regular lead-acid battery is used for that. The secondary motor may also be used to match the engine speed to that of the gearbox so the clutch can be engaged more rapidly and transparently.

Note that the serial (usually referred to as series) hybrid mode invoked when the battery suffers a deep discharge is probably intended to maximize recharge speed by operating the engine at high power. The 75kW motor-generator pair in the electric torque converter is powerful enough for normal operation, provided the driver demands only moderate acceleration (especially at autobahn speeds). Of course, fuel economy suffers in this mode compared to parallel hybrid operation in which the clutch is engaged. Deep discharge states would be common in PHEV applications, though I suspect Siemens VDO was thinking primarily of an emergency fallback mode.

The Tier 1 suppliers have the hybrid components in place (Johnson Controls etc too).

Which manufacturer is going to bite first?

what is the cost of this hybrid sytem compared to using a turbo diesel engine to replace the gasoline fueled engine for better mpg?

I think it's pretty cool that they can just pick these components "of their shelves" and fit them in an existing vehicle with such an impressive result. That bodes well for actual implementation within reasonable time.

I'd like to see a similar exercise with a weaker powered engine though, like say 120-130 hp. With electrically boosted acceleration that should be more than enough, at least to Europeans. It'll still allow you to travel at 130 mph on the German autobahn, if that's your desire...

It looks to me like Siemens may be showing German auto makers what they can do. An expensive application demonstation, with the purpose of generating some potential future business. I have not heard a lot from Europeans about upcoming hybrid cars being planned. Maybe they are trying to jump start the process.

I'd like to see aftermarket hybrid systems that can be retrofitted to any number of vehicles - FWD economy cars, pickups, classic cars, etc.

I completely agree. The system used on the Sprinter Hybrid van was relatively simple to implement as it installed between the engine/transmission. Fine for rear drive but not easy to implement on front drive vehicles.

One thought is a motor/generator/clutch that shares the same form factor as a torque converter. The clutch can disengage the engine as needed. This would be easier to retrofit with minimal changes to the drivetrain form factor. It would require some modification to the transmission (to feed power to the motor and coordinate operations) but could be easily deployed across model lines.

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