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Hybrid drive at Daimler AG
Stuttgart. First motor vehicle propulsion systems with hybrid solutions existed in the history of Daimler AG as long as some 100 years ago. After early attempts at alternative drive systems by Wilhelm Maybach, in 1907 the Austrian affiliate of Daimler-Motoren-Gesellschaft introduced the Mercedes Mixte with electric motor and internal combustion engine, developed by Ferdinand Porsche. This drive system was successfully used in passenger cars, buses and fire-fighting vehicles – and even in a racing car. In 1969, the OE 302 hybrid bus marked a new beginning of research in this field. Since then, the corporate Research unit has set up more than 20 concept and research vehicles with hybrid drive systems in all vehicle categories, from the smart HyPer via the Mercedes-Benz S-Class BLUETEC HYBRID to the Atego.
The automotive drive system of the future
The company is following a five-stage roadmap on the way to the automotive drive system of the future. Content of this roadmap: the consistent advancement of conventional gasoline and diesel engines through the use of new, environmentally compatible fuels and the development of alternative drive system concepts ready for series production. Hybrid technology plays a central part in this effort. Daimler AG sees hybrid drive technology as a bridge on the road to vehicle propulsion by a zero-emission fuel cell. Today, hybrid drives in concept and research vehicles already achieve fuel savings of between 15 and 25 percent in the NEDC (New European Driving Cycle).
Numerous other alternative drive solutions have been studied over the past years in corporate research labs. Some already have resulted in production vehicles like electric vans or natural-gas-powered cars.
Hybrid technology – an overview of “mixed drive” solutions
Hybrid drive derives its name from Latin “hybrida” for crossbreed. In the motor industry, hybrid vehicles feature two energy converters. One of them is usually an internal combustion engine, the second one a complementary electric motor. However, a hybrid system may also consist of a single electric motor which is fed from two sources from energy (for instance battery and overhead wires).
Whether 100 years ago or 35 years ago – the aim of the engineers in developing hybrid drive systems always was to perfect existing configurations. The idea was to build upon existing drive systems instead of completely replacing them. So most hybrids combined an internal combustion engine with alternative types of drives, usually an electric motor.
However, the various designs varied greatly in their approach to optimization. In the case of early hybrid vehicles like the Mercedes Mixte, the main purpose was to reduce the mechanical stresses in an internal combustion engine with manual transmission, whereas the overriding objective pursued with the hybrid buses of the 1970s was to avoid local emissions of exhaust gases and noise, for example in sensitive downtown areas.
Current designs, by contrast, aim at reducing both the vehicles’ fuel consumption and environmental pollution. Advanced hybrid studies by Daimler AG have achieved this by expending large technical effort to combine two types of drive system to utilize the synergies of the two different units.
Serial or parallel? Different hybrid concepts
Basically, hybrid drives can be classified as serial or parallel. In the serial hybrid the individual drive systems are connected in series – the internal combustion engine drives a generator, for example, which in turn supplies energy to the electric traction motor. In the case of parallel hybrids, both drive units can be used either singly or together. In such solutions the electric motor provides a boost to the internal combustion engine, for example during acceleration.
The parallel hybrid has established itself as preferred solution for concept cars and prototypes mainly of passenger cars, SUVs and light-duty commercial vehicles. Compared to serial solutions, the parallel hybrid affords a bigger opportunity to utilize synergies between the two different types of drive system. Thus, as sole drive the electric motor can bring its stronger torque to bear for moving off; while on the go it then assists the internal combustion engine when needed so that the latter usually can operate in its optimum range.
Parallel hybrids are subdivided into “micro hybrids”, “mild hybrids” and “full hybrids”. The difference lies in the ratio of the two drive systems’ use. Full hybrids can run on the electric motor alone, for instance at low speed and when starting off from standstill. “Mild hybrids” by contrast use the electric motor only for boosting the internal combustion engine’s performance and efficiency under high loads, especially during acceleration. “Full hybrids” also offer this booster function, though with clearly higher additional output contributed by the electric motor. “Micro-hybrids” feature an automatic start/stop function as well as brake energy recuperation for charging the battery.
The so-called powersplit hybrid concept is an intelligent synthesis of serial and parallel hybrid. Unlike previous single-mode systems, the patented two-mode hybrid uses a significantly smaller electric motor. The system is thus more compact while on the other hand, the two-mode hybrid covers two operating ranges with maximum power output and reduced fuel consumption. The electric motor serves as a starter and as a start-off booster; it can also be used as a generator for converting kinetic into electric energy.
Early experiments by Wilhelm Maybach
A step towards the modern hybrid drive system were the early experiments of Wilhelm Maybach in engine development, which sought to optimize the existing gasoline engine by combining it with alternative drive technologies. In 1902 he patented a two-cylinder engine which was supposed to combine the functions of the internal combustion engine and the steam engine. But especially his “vehicle drive system consisting of an internal combustion engine and a pneumatic engine,” patented on January 29, 1905, was intended to eliminate design drawbacks of the internal combustion engine.
It provided for a compressor driven by a gasoline engine. The compressed air thus obtained was additionally heated by the exhaust gas to raise the compression level. Two pneumatic engines, horizontally opposed units arranged beneath the body, converted the pressure into kinetic energy to drive the wheels. With this unconventional engine, Maybach wished to get higher torque for starting off (among other things). Above all, however, the system, a serial hybrid drive system, was intended to eliminate heavy engine parts: as an advantage of his engine, the design engineer emphasized the “elimination of the toothed wheel drive, the differential, the clutch and the brakes on the gearbox, i.e., the elimination of parts which previously gave rise to complaints.” Also, the drive system was said to be very easy to operate. However, high cost and poor efficiency spoke against putting the patent into practice.
1907 - The first hybrid from Daimler: The Mercedes Mixte
The first hybrid vehicle of the Mercedes brand originated in Vienna. As early as in 1906, the Viennese edition of Allgemeine Automobil-Zeitung (AAZ) announced the launch of the Mercedes Mixte for the next year. In 1907 the car drew an even bigger response from the trade press: “The >Mixte< is the Mercedes company’s special new product of the season,” AAZ wrote, recommending it for the “mature motorist who looks forward to new sensations in motoring with the mixed car.”
The Austrian affiliate of Daimler-Motoren-Gesellschaft, which built the electric and hybrid vehicles of the Mercedes brand, originated in 1899 as “Österreichische Daimler Motoren Commanditgesellschaft Bierenz Fischer & Co.” Initially, Paul Daimler, Gottlieb Daimler’s eldest son, took over as Chief Engineer. On July 19, 1906, the Austrian engineer Ferdinand Porsche was appointed Chief Engineer. Porsche already had designed an electric motor for wheel hub installation in 1897. This system was fitted for the first time in the Lohner-Porsche of 1900. This car was created in the workshops of the “imperial and royal car factory” of Jacob Lohner & Co. in Vienna, for which Porsche started working in 1898. In 1900 the new car made a big splash at the Paris World Exposition.
The engineering of the Mixte vehicle relied on the Lohner-Porsche system. Ferdinand Porsche, Chief Engineer of Daimler-Motoren-Gesellschaft since 1906, had further improved a development of his own and combined it with an internal combustion engine for the Mercedes Mixte. AAZ had already described a Porsche-built forerunner of the Mercedes Mixte in 1902. The “Mercedes-Lohner-Porsche” was manufactured by Lohner with different outputs for the Mercedes engine. The racing car built in 1902 using a 28-hp (21-kW) engine from the Mercedes Simplex could make do entirely without a battery as buffer unit owing to the high output of the gasoline engine.
A contemporary report described the design of the serial hybrid drive system of the Mercedes Mixte: “The motive power is supplied by a gasoline engine, which entirely corresponds to the engines used in the gasoline car. Coupled with the gasoline engine is a dynamo that converts the energy of the gasoline engine into electric energy to supply power to two traction motors which, like the electric motors, are designed as wheel motors.”
The gasoline engines used were mainly the 45 and 70 hp (33 - 52 kW) units. The model designations of the Mercedes Mixte referred to the internal combustion engines, not the output of the electric drive. A six-pole dynamo was permanently coupled to the engine by means of a drive shaft and took over the function of the flywheel. The magnet cluster around which the armature of the dynamo rotated was not rigidly installed, but could be moved 20 millimeters. This permitted regulating the current when the tractive power had to be changed. The dynamo took over the function of the flywheel – quite similar to several modern-day hybrid drive systems. In some cars it served as a starter motor for the internal combustion engine. The electric energy produced by the generator was transmitted to two wheel hub motors. The spokes were attached to the armature housing of the wheel hub motor – motor and wheel formed a unit, reducing energy losses which the friction of mechanical power transmission would have caused.
In the Mercedes Mixte the motors were positioned on the rear axle. A few fire-fighting vehicles were delivered with front-wheel drive, as was standard on the Lohner-Porsche. Although Ferdinand Porsche made the motors, which ran on two ball bearings, appreciably narrower than the traction motors of his first electric automobiles, the Mercedes Mixte and Mercedes Electrique easily could be recognized by their unusual hubs. Reporters at the Vienna motor show in 1907 pondered over the aesthetics: on the one hand, they expressed their admiration for the established “mature beauty of the Mercedes cars,” but now there was this “dumpling”, the wheel hub motors on the rear wheels.
The combination of internal combustion engine as source of power and electric motor as drive proper particularly proved itself in buses. The gentle acceleration of the vehicles and the lack of heavily stressed components like clutch and transmission recalled the advantages of electric cars. In continuous operation, however, the Mixte was superior to the electric car owing to the large range lent to it by the gasoline engine coupled with a generator. To demonstrate the performance of the series, Porsche developed a Mixte racecar before the end of 1907. The car’s generator was powered by a 30/55-hp gasoline engine; wheel hub motors with enhanced power input transferred the electric energy to the road. The hybrid racer was supposed to start in the Taunus Race, but skidded off the track during tests and was severely damaged.
In 1912 the Austrian Daimler-Motoren-Gesellschaft dissolved its ties with the parent company in Germany. The company, located in Vienna’s Neustadt district, was renamed “Austro-Daimler Motoren AG,” and Ferdinand Porsche remained its Chief Engineer until 1923. Owing to the rapid succession of innovations in automobiles with gasoline engines, the interest in hybrid vehicles quickly subsided in the first quarter of the last century. For several decades this technology ceased to play a prominent role in the development of the automobile.
The more recent hybrid history at Daimler AG
Modern times in hybrid research began in 1969. At the Frankfurt International Motor Show in that year, Daimler-Benz introduced the first prototype of the OE 302 hybrid-electric bus. The project sought to optimize the drive system of line-service buses mainly for the purpose of reducing exhaust emissions in downtown areas. While in these sensitive zones the buses traveled on current from batteries, in less densely populated areas the serial hybrid drive system switched to a diesel engine that supplied energy to the electric traction motor by means of a dynamo.
The successor to the OE 302 was presented in 1978 at the “transport ‘78” trade fair. The OE 305 hybrid-electric bus again featured an electric traction motor driven by a diesel engine via the generator. The drive system capacity was designed so that the bus attained the performance of a comparable diesel-powered O 305 urban bus model, the heavy batteries notwithstanding. Despite the heavy load on the batteries, they survived an average of 800 recharges.
In the course of 1979, thirteen hybrid-electric buses, model OE 305, commenced operation in the local public transport systems of Stuttgart and Wesel. By 1983, the buses had done 1.3 million kilometers of service. Again in 1979, Daimler-Benz introduced a second hybrid bus: In addition to the standard diesel engine, the duo bus, or dual-powered bus, was equipped with an electric motor supplied with current from an overhead (trolley) wire. While the electric motor was used in the city, in rural areas the bus ran on the diesel. Still in 1979, three of the vehicles took up trial operation in Esslingen in scheduled service. Over the next few years, more than 50 of these vehicles were used in regular service internationally. A second variant of the duo bus only had an electric traction motor which got its energy either from the trolley wire or from batteries. Hybrid buses were steadily improved during the following years.
1982 - Hybrid as alternative to the electric car
Again and again, tests with pure electric drives for passenger cars showed that the operating range simply was too small due to the low energy density of the batteries. So in 1982, a first concept car featuring a serial hybrid drive system and direct front-wheel drive via two magneto-electrically excited motors was brought out by Mercedes-Benz. Hybrid drive systems in sedans of the C-Class in the 1990s represented further steps in development. To these cars the engineers applied both the principle of the parallel hybrid drive (55 kW/75 hp diesel engine and 20 kW/27 hp electric motor) and the serial hybrid drive.
1996 - Return of the wheel hub motor
To power the low-floor O 405 NÜH interurban hybrid bus of 1996, Daimler-Benz decided in favor of three-phase AC wheel hub motors. A diesel engine powered the generator of the hybrid bus, which supplied current to the traction motors and recharged the battery on interurban routes. In urban areas the bus ran on electricity from the battery. Four of these low-emission low-floor buses were used in urban and interurban service in Bavaria.
The trials were intended to show a way in which especially environmentally compatible vehicles could be operated in local public transport. The progress achieved in the development of hybrid buses since the OE 302 was demonstrated among other things by the battery of this vehicle. The accumulator, which weighed 3.5 tons in the early hybrid buses, now only weighed 800 kilograms, but developed a similar output. The weight savings were made possible by the use of sodium nickel-chloride batteries as energy storage units.
1998 - Mercedes-Benz E-Class Hymatic
A marketable hybrid system must be capable of installation in an existing vehicle if the cost is not to be too high versus automobiles with conventional drive systems. “Minimum design changes, maximum added benefits” were already achieved by Daimler-Benz Research in developing the Mercedes-Benz E-Class Hymatic, a passenger car equipped with a hybrid drive system in 1998. The Hymatic was based on an E-Class with 4MATIC automatically engaging four-wheel drive and gasoline engine (150 kW/204 hp). The power of the internal combustion engine was transferred to the rear axle. The front wheels were driven by an electric motor (26 kW/35 hp). Following the “through-the-road” (TTR) principle, the outputs of both units first came together on the road.
Consumption and emissions of the Hymatic were improved by as much as 15 percent over the sister model. But it was the combination of the drives that mainly proved promising. Depending on power requirements, either the electric motor was engaged to supplement the internal combustion engine (for overtaking and in four-wheel-drive operation), or the gasoline engine alone powered the vehicle (standard mode), or the Hymatic moved only by means of the electric motor (for short distances at low speeds).
1999 - A-Class HyPer
The A-Class HyPer study of 1999 focused on the performance of the alternative drive system. This is obvious from the name of the vehicle, a combination of “hybrid” and “performance.” Unlike the 1998 Mercedes-Benz E-Class Hymatic, in this design the transversely installed internal combustion engine (1.7 liter CDI diesel, 66 kW/90 hp) drives the front axle, while the electric motor (26 kW/35 hp) acts upon the rear axle. The developers dispensed with downsizing the internal combustion engine from the basic model. The result was a very sporty hybrid car with four-wheel drive as an option. The HyPer sprinted from 0 to 100 km/h in only eight seconds with a boost from the electric motor, whereas the standard version of the A 170 CDI took 13 seconds to reach the same speed. The HyPer owed this additional zip to the good torque of the electric motor. Overall, despite its nimbleness the HyPer consumed less diesel fuel than the production model’s 4.9 liters.
2000 - Vario and Atego with hybrid drive system
In 2000, Mercedes-Benz also presented the Vario van and the Atego truck with hybrid drive systems. Instead of a “through-the-road” system, the power of both drive units was transmitted to a common drivetrain in these parallel hybrid concepts. The diesel engine of the Vario 814 D Hybrid had an output of 100 kW (136 hp); that of the Atego 1217 Hybrid, 125 kW (180 hp). The diesel engines were assisted by electric motors with outputs of 55 kW (75 hp) and 60 kW (82 hp), respectively. Depending on requirements, the maintenance-free lead-gel batteries of the vehicles were charged either by the vehicle’s diesel engine or with mains electricity (by means of an onboard charger).
On the other hand, the two hybrid commercial vehicles were not equipped with the hybrid drive system merely to optimize consumption and emissions. The possibility of operating both vehicles in purely electric mode particularly recommended them for noiseless, zero-emission operation in pedestrian zones, health resorts, or on the grounds of hospitals, clinics and trade fairs. In contrast to purely electric vehicles with their limited range, the hybrid commercial vehicles Vario and Atego also were convincing performers in intercity service. Owing to the interaction of the engine and the electric motor, the mixed drive ensured dynamic performance and low fuel consumption.
2001 - smart city coupe HyPer
More driving pleasure, more comfort: When the smart city coupe HyPer was introduced in 2001, the company’s smallest hybrid concept car set new standards. The prototype had an electric motor (20 kW/27 hp) that was combined into a single unit with the three-cylinder diesel engine (30 kW/41 hp) because of the restricted space. The little hybrid car accelerated more briskly than the production model from a standing start and while on the move. Despite 85 kilograms added weight, it also consumed less than three liters of diesel fuel (getting in excess of 78 mpg, about 13 percent better than the production car). An automatic start-stop function and a regenerative braking system contributed to the result.
2002 - Mercedes-Benz M-Class HyPer
A road test report on the M-Class HyPer in 2002 described it in the words, “Put adrenaline in your tank.” A start from standstill clearly demonstrated the perfect combination of the two drives in the hybrid car. Up to a speed of 15 km/h, the 45-kW (61-hp) electric motor, fitted between engine and transmission, propelled the vehicle forward with its high torque. Then the five-cylinder common rail diesel of the ML 270 CDI (120 kW/163 hp) cut in, and the combined accelerating power of both units termed “booster” pushed the offroad vehicle ahead with full force.
The electric motor in the M-Class HyPer was a “disc motor,” so called because of its short overall length. The shape of the powerful disc made it easier to integrate this additional unit in the drivetrain of existing vehicle configurations. This aspect became all the more important the closer the prototypes with hybrid drive system came to series production. For this reason, in the hybrid ML 270 CDI the engineers accommodated the water-cooled nickel metal-hydride battery and the battery management system in the spare wheel recess so as not to compromise interior space.
But the disc motor was more than a space-saver. The motor, which engineers distinguish from the conventional, long stretched-out electric motor (called “sausage motor”) also served the hybrid vehicle as starter and generator. So the M-Class HyPer could do without an alternator and starter motor, which made the car lighter and simplified drivetrain design. The innovative motor and its controls also permitted particularly good utilization of the braking energy to obtain electricity. The regenerative performance (i.e. the electric energy recuperated from the kinetic energy per unit of time) of the ML 270 CDI HyPer was about twice as good as that of earlier hybrid studies. In total, measured according to the “New European Driving Cycle” (NEDC), the M-Class HyPer saved up to 20 percent diesel fuel compared with the production ML 270 CDI. And the car’s driving dynamics, thanks to the support of the electric motor, put it on a par with the next larger
The M-Class HyPer owed its sporty, cultivated driving feel also to the electronically controlled clutch, which ensured continuous, harmonious interaction of the two drive units with the six-speed manual transmission. The clutch particularly balanced the speed and torque of the two units, gently engaging (“tow-starting”) the diesel engine after the electric drive had accelerated the car to 25 km/h from full stop, or providing a powerful boost for overtaking on the motorway. The clutch also connected the two when the battery was being recharged by the diesel engine during constant-speed travel. In this case the electric unit worked as a generator.
2002 - Unimog E-Drive
For the Unimog, a commercial vehicle legend, the researchers developed a serial hybrid variant in 2002. The 130-kW (177-hp) diesel engine of the Unimog E-Drive drove a generator of 100 kW (136 hp) capacity which supplied the electric traction motor and the drives of the implements with energy. A particularly fascinating aspect of this solution was the possibility of driving without a transmission: by means of the electric motor the speed of the advanced Universal-Motor-Gerät, or universal working machine, could be continuously varied from a slow walking pace to 85 km/h. The great versatility of the Unimog was fully retained in the E-Drive variant: electric equipment as well power takeoffs for hydraulic tools could be used with the hybrid vehicle.
2003 - F 500 Mind
When Mercedes-Benz introduced the F 500 Mind research car at the Tokyo Motor Show, the laboratory on wheels caused quite a stir. More than a dozen innovations had been embodied in the car. The developments included new assist systems like a night vision system and multi-vision display, a new interior concept, and the novel door technology featuring a B-pillar that could be unlatched to open the rear doors toward the back.
But the most important development, as far as the research car’s consumption and drivability was concerned, was to be found under the hood. The most powerful hybrid drive system to date in a research car developed 234 kW (318 hp) and 860 Newton meters of torque.
The combination of the two drive units – the designers termed this solution “P2 configuration” – assured the F 500 Mind the excellent performance figures of a powerful hybrid automobile. For the hybrid drive system, the V8 diesel engine from the S-Class (displacement of four liters, 184 kW/250 hp, maximum torque of 560 Newton meters) and a 50-kW (68-hp) electric motor were used. The electric motor was fed by a lithium-ion battery with two kilowatt-hours storage capacity and an electric potential of 300 volts. The battery was charged during braking by having the electric motor function as a dynamo driven by the wheels through the five-speed automatic transmission. If necessary, the battery could also be recharged while the vehicle was traveling at a constant speed. During acceleration, however, the electric motor functioned as a booster to give the research car its dynamic performance.
Extensive practical tests with the F 500 Mind have provided valuable knowledge about the everyday practicality of the hybrid drive system. Operational tests showed that in the city the hybrid drive system conspicuously reduced consumption compared with the internal combustion engine. The results clearly reflected the benefits of the engine cutoff function at traffic lights (the electric motor then handled the subsequent start-off) and the recuperation of braking energy.
In test series based on the NEDC cycle, the F 500 Mind achieved a 20 percent reduction in consumption. Ten percent of this was due solely to the utilizing of synergies between the two drives: During start-off, or moving at a walking pace, or while parking, the engine management system shut off the diesel engine, and the F 500 Mind rolled over the road as a pure electric car. The recuperation of electric energy during braking reduced consumption by another five to seven percent. Finally, the load point shift of the diesel engine, which the hybrid drive system allowed to operate under optimum conditions, saved another four percent fuel.
2004 - Vision GST 2
The Vision GST 2 presented in January 2004 at the North American International Auto Show in Detroit was not simply the successor to the Vision GST of 2002, because the new study of a Grand Sports Tourer no longer was powered by a gasoline engine, but by the forward-looking hybrid V8 diesel plus electric motor, used in similar form also in the F 500 Mind. The study car with four-wheel drive and six-speed automatic transmission couples the 184-kW (250-hp) four-liter diesel engine to a 50-kW (68-hp) electric motor. The nickel-metal-hydride battery was placed in the rear of the car.
The Vision GST 2 afforded very dynamic driving pleasure; its fuel consumption was lower and its emissions were improved compared with the V8 diesel without electric motor. The two drive units accelerated the study from standstill to 100 km/h in 6.6 seconds with 860 Newton meters of torque; the top speed was limited electronically to 250 km/h. The decision when diesel engine and electric motor would work together was made by the computer controls taking into account the best possible utilization of the hybrid drive system for low-consumption, low-emission operation. At the same time, the driver experienced impressive accelerating performance owing to the intelligent combination of the two drives.
2005 - Near-launch road trials of Hybrid Sprinter with CDI and electric motor
The Mercedes-Benz Sprinter introduced in 2004 was to be built both as a “plug-in” hybrid and with a conventional hybrid drive system. “Plug-in” means that the vehicle’s batteries can be charged via the mains network. This suggests itself mainly for vehicles which frequently operate with purely electric drive. They can “refuel” mains electricity in between uses or at night.
The Hybrid Sprinters of both designs have an electric motor between automatic transmission and clutch, which is supplied by a nickel-metal-hydride battery. In emission-sensitive areas in town centers or in buildings, the Sprinter can run exclusively on the electric drive for noiseless, zero-emission operation. Depending on the proportion of electric operation, the consumption of diesel fuel is reduced by ten to fifty percent versus the base model. But, of course, if the electric mode is used to a great extent, the batteries have to be recharged from the mains network. It takes around six hours to charge a completely empty accumulator.
The 70-kW (95-hp) electric motor of the Sprinter with “plug-in” technology also serves as a generator which develops 40 kW (54 hp) to operate tools and other equipment. The Sprinter with hybrid drive system without charging socket combines its diesel with a smaller electric motor (30 kW/41 hp) and a smaller battery. The drive nonetheless suffices for noiseless, zero-emission operation in pedestrian precincts and similar areas; the range is three or four kilometers.
2005 - S-Class Hybrid
The next generation of hybrid drive system was presented in January 2005 at the North American International Auto Show (NAIAS) in Detroit. The Mercedes-Benz S-Class Hybrid is powered by a V8 diesel engine and two electric motors. Together these units develop as much as 241 kW (328 hp). This was a new high for hybrid vehicles. With the concept of a hybrid S-Class, in Detroit the company introduced the basis for the further development of hybrid technology, which according to a Memorandum of Understanding dating from 2004 was to be pursued jointly with General Motors. In this alliance of equal partners, DaimlerChrysler mainly intended to concentrate on the development of luxury-class rear-wheel-drive automobiles with hybrid drives. Dr. Thomas Weber, member of the Board of Management and responsible for Research and Technology as well as for Development in the Mercedes Car Group, declared: “Our solution brings its advantages to bear mainly for powerful engines. So we simultaneously ensure high driving dynamics and comfort along with appreciably reduced fuel consumption.”
The hybrid power plant of the S-Class presented in Detroit pointed in this direction. The power of the mixed drive comes from an eight-cylinder CDI diesel engine (191 kW/260 hp) and two electric motors with a joint output of 50 kW (68 hp). With the second electric motor, the diesel can be engaged almost imperceptibly when the car is on the move. The ride comfort of the hybrid vehicle is just as convincing as its acceleration: from standstill to 100 km/h in 7.6 seconds. The combination of electric drive and 7G-Tronic automatic transmission makes it possible to operate the S-Class Hybrid to a large extent in the diesel engine’s optimum range while enjoying high comfort.
The new hybrid drive system thus enables favorable consumption figures also on longer journeys at constant speeds. The mixed drive’s advantages for starting off, parking, stop-and-go traffic and moving at low speeds through traffic-reduced zones, can be taken for granted. The fuel consumption in various test cycles is between 15 and 25 percent less than that of the standard diesel engine.
2005 – S-Class DIRECT HYBRID and BLUETEC HYBRID
At the 2005 Frankfurt International Motor Show, two concept cars based on the new S-Class (W 221) were displayed: The DIRECT HYBRID with gasoline engine and electric motor, and the BLUETEC HYBRID combining a BLUETEC diesel engine with an electric motor. In both concept cars, the electric motor develops six kW (8.2 hp), serves as starter and start-off booster and can also be used as a generator for converting kinetic into electric energy. In the development of the latest hybrid generation, Mercedes-Benz focused on creating a powerful and compact drive system. The result is a so-called powersplit hybrid concept, an intelligent synthesis of serial and parallel hybrid. Unlike previous single-mode systems, the patented two-mode hybrid uses a significantly smaller electric motor. The system is thus more compact while on the other hand, the two-mode hybrid covers two operating ranges with maximum power output and reduced fuel consumption.
This two-mode hybrid was developed within the framework of a cooperative venture with General Motors, which has meanwhile also been joined by BMW with the signing of a Memorandum of Understanding. The. In this consortium named Global Hybrid Cooperation, Mercedes-Benz focuses on the development of premium-class hybrid cars with rear-wheel and four-wheel drive.
2005 – 500 hybrid city buses for New York
In October 2005, DaimlerChrysler Commercial Buses North America received an order for 500 Orion VII hybrid city buses for the local public transport operations of New York. At the time, it was the largest order for hybrid buses on a global scale. New York City Transit took delivery of 216 units, Metropolitan Transportation Authority (MTA Bus) of 284 units. Deliveries began in the second quarter of 2006. It was the third hybrid bus order placed by the city of New York with Orion after orders of 200 and 125 units, respectively, at an earlier stage. Orion started operating the first hybrid buses in the early 1990s and is the world market leader in this field with some 1,500 vehicles sold.
Prior to the RAI Commercial Vehicle Show in Amsterdam in October 2005, the company presented hybrid technology in the
Mercedes-Benz Sprinter, the Mitsubishi Fuso Canter and the Freightliner/Eaton distribution vehicle – all of which were about to be launched into the market.
2006 – Canter Eco Hybrid from Mitsubishi Fuso
In early July 2006, the Mitsubishi Fuso affiliate presented the Canter Eco Hybrid for immediate availability in the Japanese market. At the time, it was the world’s most environment-friendly light-duty truck from large-scale production, with a payload of two to three tons depending on the version. It was also the first light-duty truck which complied with the Japanese emission legislation which came into force in August 2007 – one of the world’s most stringent emission norms, specifying emission limits which the Canter Eco Hybrid undercuts by 41 percent where nitrogen oxides are concerned and by 46 percent where particulates are concerned. Over and beyond this, the vehicle is the most fuel-efficient of all Japanese hybrid commercial vehicles, with reductions in fuel consumption being as high as 20 percent compared to models with conventional engines and being in part attributable to brake energy recuperation. The reduction in fuel consumption is particularly great in stop-and-go traffic and in distribution transport.
The key element of the parallel hybrid system is a newly developed, small-volume turbocharged diesel engine with a displacement of three liters (92 kW/125 hp). It works together with an extremely narrow electric motor (35 kW/48 hp) which doubles as a generator. The energy storage unit is an advanced lithium-ion battery. Power is transferred to the wheels by an automated transmission named Inomat-II which operates without gearshift lever and clutch pedal having to be operated.
As the Group’s Center of Competence for hybrid commercial vehicles, Mitsubishi Fuso is responsible for the development of progressive hybrid technologies which can be incorporated in commercial vehicles in different markets. The new Canter complements Mitsubishi Fuso’s range of hybrid vehicles and underlines the company’s position as technology leader in this segment.
Large-scale production of a hybrid city bus, the Mitsubishi Fuso Aero, also commenced in 2006. Prototypes were tested during the 2002 World Cup, and the production bus was launched in 2004.
2006 – Hybrid Sprinter in near-launch trial operation
A modified version of the Mercedes-Benz Sprinter with hybrid drive started near-launch trial operation in September 2006 – a European premiere. The European branch of logistics service provider FedEx Express took delivery of a vehicle for use in day-to-day distribution in and around Paris. The Sprinter 316 CDI is powered by a 115-kW
(156-hp) diesel engine and a 70-kW (95-hp) electric motor. The latter is installed between internal combustion engine and automatic transmission. It derives its energy from a lithium-ion battery which it recharges in its capacity as generator on the move, during braking and on downhill stretches. In addition, the batteries can also be recharged when the vehicle is not in operation, for instance at a socket overnight – which is known as the plug-in option. In purely electric operation, the hybrid vehicle with a permissible gross vehicle weight of 3.5 tons has a range of up to 30 kilometers. In this mode, the Sprinter moves along extremely quietly and with zero emissions – a significant advantage in sensitive areas such as pedestrian precincts or halls. The lithium-ion battery with a capacity of 15 kilowatt hours is installed under the floor and therefore does not reduce the load capacity. Thanks to the intelligent combination of two drive systems, the Sprinter can be operated in the optimal range in any given situation. When full power is required and the driver puts his foot down, engine and motor operate jointly.
2007 – Extended cooperation with BMW
In March 2007, the company extended its cooperation with BMW in the field of hybrid drive systems. The two equal partners develop a hybrid module for rear-wheel-drive passenger cars in the premium segment. It is planned to market the system from 2010. Thomas Weber: “Cooperation in the field of innovative drive systems makes sense – not only technically but also economically – because the two partners make similar demands on the premium segment and are thus able to strengthen their competitive position. The idea is to launch propulsion technologies which are convincing in terms of efficiency, performance and comfort – especially in this category of cars.”
The hybrid module, which in engineering terms ranks among the “mild hybrids”, is to be developed at the two partners’ engine and drive system development locations in Germany. The development teams of both manufacturers work closely together in this field. The module will be adapted to the specific brand to ensure the individuality of the different models concerned.
2007 – New hybrid bus based on the Citaro
A new hybrid bus was announced in May 2007. Trial operation of the Mercedes-Benz Citaro versions is planned to commence in 2008; the production launch is scheduled for 2009. The diesel-electric propulsion system promises to reduce fuel consumption and carbon dioxide emissions by 20 – 30 percent. It is a serial hybrid which permits zero-emission operation in battery mode only over short distances. This drive system will be installed in the Citaro G articulated bus and in this configuration will be unique on a global scale.
In the Citaro Hybrid, the diesel engine drives the generator to produce electricity as required. Maintenance-free lithium-ion batteries accommodated on the roof of the Citaro store this electricity as well as the current generated by means of recuperation. The bus wheels are driven by four electric wheel hub motors on the central and rear axles of the vehicle. At 320 kW (435 hp), the total output of the wheel hub motors is generously high even for an articulated bus operated under harsh conditions.
2007 – smart fortwo hybrid drive
In July 2007, smart introduced its fortwo hybrid drive. The combination of electric motor and internal combustion engine makes the car even more economical and environment-friendly than the conventional fortwo. Measured according to the New European Driving Cycle, the fuel consumption of the smart fortwo hybrid drive powered by a diesel engine improves from 3.3 to 2.8 liters/100 km (from 71 to 84 mpg), and carbon dioxide emissions decline from 88 to 77 grams per kilometer. The carbon dioxide champion is thus setting new standards for the so-called three-liter car (meaning fuel consumption of three liters or less per 100 km / 78 mpg or more).
The smart fortwo hybrid drive has a 33-kW (45-hp) diesel engine and a 20-kW (27-hp) electric motor which is powered by a nickel-metal-hydride battery with a capacity of one kilowatt hour. The battery is accommodated underneath the driver’s seat; it is recharged by the electric motor and by means of brake energy recuperation. Engine and motor can operate jointly or separately. In combined operating mode, the smart is a power-pack with output of 53 kW (72 hp) and torque of 160 Newton meters. The interruption in torque flow during gearshifts, especially when changing from first into second gear, is compensated by the simultaneous operation of both drive systems. As a result, the smart fortwo hybrid drive completes the sprint from standstill to 100 km/h some four seconds earlier than the smart fortwo cdi. The hybrid concept is thus a unique combination of motoring pleasure, economic efficiency and environmental compatibility.
In July 2007, the company made another announcement which may appear to be somewhat less spectacular at first glance but is no less momentous. In the course of efforts revolving around climate protection, all vehicles are developed with the option of hybridization from now on.
2007 – smart fortwo micro hybrid
Since October 2007, a 52-kW version of the smart fortwo with economy-enhancing start/stop function has been coming off the assembly line in Hambach: the smart fortwo micro hybrid drive. From the end of this year, it will be available as coupe and convertible in all three lines – pure, pulse und passion. The propulsion system uses idle periods to switch off the engine and temporarily prevent fuel consumption, pollutant and noise emissions from occurring in the first place. The key element of this system is a special belt-driven starter-generator (rSG) which supplies the onboard network with electricity and doubles as a starter motor. It is capable of starting off the gasoline engine comfortably and in fractions of a second as soon as the driver takes his or her foot off the brake pedal. The conventional starter motor, acting on the flywheel of the crank assembly, can therefore be dispensed with. In combination with slightly modified transmission ratios, this strategy leads to reductions in fuel consumption in the range of some eight percent in the NEDC. Consumption thus drops from 4.7 liters of gasoline per 100 kilometers (50 mpg) by some 0.4 liters to approx. 4.3 liters per 100 kilometers (55 mpg). Depending on traffic conditions (slow-moving traffic), reductions in the range of 13 percent are conceivable. The carbon dioxide emissions correspondingly decline from 112 to some 103 grams per kilometer.
The high-performance electronic system ensures that the internal combustion engine is switched off in idle, for instance at traffic lights, level crossings or in stop-and-go traffic. In the interest of fuel economy and comfort, the electronic system switches off the engine at a speed below eight km/h (five mph) provided the driver actuates the brake pedal and thus signalizes that he or she intends to stop. As soon as the driver takes his or her foot off the brake pedal, the engine is restarted. In this way, starting off without delays is ensured. A switch in the center console, in front of the gearshift lever, can be operated to deactivate the start/stop function as required – until the next time the engine is switched off and on by means of the ignition key.
Further information from Daimler is available on the internet at: www.media.daimler.com
Daimler Communications, 70546 Stuttgart/Germany