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Producing the Mercedes-Benz GLC F-CELL fuel-cell SUV

Daimler is currently systematically preparing for series production of the Mercedes-Benz GLC F-CELL; the company had shown preproduction models of the hydrogen fuel cell SUV at the IAA International Motor Show in Frankfurt last September (Earlier post.)

The plug-in hybrid SUV will be produced at the Mercedes-Benz plant in Bremen. Mercedes’ partner EDAG supports the plant with respect to integration of the drive system, and is located in the immediate vicinity of the plant. The first GLC F-CELL cars will go to selected customers before the year is out.

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The PEM fuel cell is structured like a sandwich. In the center is a thin plastic film, the Proton Exchange Membrane (PEM). This membrane is coated on both sides with a thin catalyst layer and a gas-permeable electrode made of graphite paper. The membrane is surrounded by two bipolar plates into which gas ducts have been milled. Through these gas ducts flows hydrogen on the one side, and oxygen on the other. Individual fuel cells are stacked one behind the other to create a the full fuel cell stack to power the vehicle. Click to enlarge.

Daimler subsidiary NuCellSys GmbH, based in Kirchheim/Nabern in the Stuttgart metropolitan area, developed the complete fuel cell unit and hydrogen storage system for the GLC F‑CELL. This is also where the first prototype vehicles were built, the pre-series models then being produced at the Mercedes-Benz Tech Centre in Sindelfingen.

Compared with the B-Class F-CELL, on the market since 2010 (fuel consumption: 0.97 kg H₂/100 km, combined CO₂ emissions: 0 g/km), the overall drive system of the GLC F-CELL offers around 40% more output. The fuel-cell system is around 30% more compact than before, can for the first time be housed entirely in the engine compartment and is installed on the usual mounting points like a conventional engine. Also, the use of platinum in the fuel cell has been reduced by 90%.

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Further development work is particularly necessary to reduce material costs: Factors in this include the further reduction of sizes and components, and also of the proportion of expensive materials. If we compare our present system with that of the B-Class F-CELL, we have already achieved a great deal—alone by reducing the platinum content by 90%. But we need to go further. Process optimizations in production will also help to lower costs – but this is more a matter of economies of scale.

—Prof. Dr. Christian Mohrdieck, head of Fuel Cell Drive Development and General Manager of NuCellSys

The Daimler home plant in Untertürkheim is responsible for production of the complete fuel cell system. The centerpiece of the fuel cell system, the fuel cell stack consisting of around 400 fuel cells, is created at Mercedes-Benz Fuel Cell (MBFC), which operates the world’s first plant dedicated entirely to the production and assembly of fuel cell stacks in British Columbia.

The drive unit consists of 250 components including the fuel cell stack and the cooling, fuel and exhaust systems plus the electronics. The production process uses a suspended conveyor system which is also used for engine assembly at the Untertürkheim plant. The fuel cell systems are assembled in the Kirchheim-Nabern location, an annex of the Mercedes-Benz plant in Untertürkheim, which has been producing the drive systems for the pre-series vehicles since 2017. The conveyor system only needed minor modifications for the alternative drive unit, mainly involving an adapter to hold the assembly in place.

The assembly worker is able to rotate the drive unit in the conveyor system so that the respective assembly points are ergonomically accessible. The worker receives digital, visual instructions for every working stage via a screen at the relevant workstation. This is updated in real time, as tools linked by WLAN are used in the assembly process. For example, when a bolted connection has been made to the prescribed torque, the on-screen marking of this bolt changes to green. At the same time the assembly stage is documented and archived.

The same applies to the quality checks integrated into the assembly process. These include leak-testing of the hydrogen, air and coolant circuits. Here too, attention was paid to a test-friendly product design, e.g. eliminating unnecessary interfaces with integrated wiring and lines. Testing is carried out with a hydrogen mix, so that even leaks in the ppm (parts per million) range can be reliably detected.

The test procedure for the electrical insulation and resistances, designed for an operating voltage of 400 volts, is a high-voltage test with 2150 volts. To protect the personnel, the high voltage is only switched on after a laser scanner has definitely confirmed that no person is in the vicinity of the drive unit. To protect the components from electrostatic discharge (ESD), the entire working area in the assembly shop is shielded against electrostatic discharge by a floor coating.

At the end of the production process, a test run is carried out over the entire dynamic performance range of the drive unit. This too is precisely electronically documented—and the power generated is fed into the plant’s network (around 400 MWh to date). The fuel cell systems are then dispatched to Bremen by truck, where final vehicle assembly takes place with the batteries from Kamenz (Saxony) and the hydrogen tanks from Mannheim (Baden-Württemberg).

The test facilities in Nabern include five climatic chambers allowing temperatures of -40°C to +85°C. Some test rigs have an inclination feature which allows the drive unit to be inclined along both axes, and also diagonally, by 19 degrees. This, for example, verifies the absolute cold-starting ability of the fuel cell system.

The two carbon-fibre-encased tanks built into the vehicle floor hold around 4.4 kg of hydrogen. Due to globally standardized 700 bar tank technology, the supply of hydrogen can be replenished within just three minutes—about the same amount of time it takes to refuel a car with an internal combustion engine.

The lithium-ion battery comes from the wholly-owned Daimler subsidiary ACCUMOTIVE in Kamenz/Saxony, Germany. The lithium-ion battery in the pre-series vehicles has a gross capacity of 13.8 kWh (9.3 kWh net) and additionally serves as an energy source for the electric motor. Like the drive motor, the storage battery is installed in the rear of the SUV. By means of the 7.2 kW on-board charger, it can be conveniently charged from a standard, domestic power socket, a wallbox or a public charging station. The charging time is around 1.5 hours if the full capacity is used.

Non-mobile fuel cell systems. Convinced of the potential of fuel cell technology and of hydrogen as a storage medium in the context of the overall energy system, the company is taking a comprehensive approach and expanding its development activities into application areas beyond the automobile.

Together with the market leaders Hewlett Packard Enterprise (HPE) and Power Innovations (PI), a LiteOn company, Daimler AG with its subsidiary company NuCellSys GmbH and the support of MBRDNA and the Daimler innovation incubator Lab1886 will develop prototype systems for (emergency) power supply to computer centres and other stationary applications, and integrate automobile fuel cell systems to this end.

Comments

HarveyD

Which major (Toyota-Honda-Hyundai-Mercedes-WV-BMW) or one from other UE countries or from China or USA, will mass produce the next generation, much lighter lower cost FCs.

Toyota claims their FCs size and cost will be reduced by 75+% by 2020/2022. Can German, So-Korean, Chinese majors do as well or even better?

If so, we could see many new Hybrids with FCs and pure FCEVs by 2022 or so?

SJC

We need HTPEM, then we can use bio fuel reformers.

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