Driving the VW e-Golf; strategy, assembly in Wolfsburg, Braunschweig battery plant
21 July 2014
|The e-Golf. Click to enlarge.|
The e-Golf (“Das e-Auto” earlier post), the Volkswagen brand’s second series production battery-electric vehicle after the e-up!, is a key model, as it is the best and most current implementation of its strategic decision to begin providing e-mobility based on large-scale production models rather than special “small niche” cars. The Golf is core to Volkswagen; the company has sold more than 30 million units worldwide since the first introduction in 1974. The e-Golf is based on current 7th generation Golf, itself based on the strategic MQB toolkit.
Put another way, Volkswagen’s goal, based on its strategic approach, is for the e-Golf to deliver the performance and handling of a Golf which happens to have a battery-electric powertrain. Based on a second, and slightly longer, chance to drive the new e-Golf unsupervised, we think Volkswagen has succeeded splendidly in this goal; we find the e-Golf to be a nimble and quiet electric delight.
Series production of Volkswagen’s e-Golf began five months ago in March at Volkswagen’s plant in Wolfsburg, Germany. The e-Golf is currently on sale in Germany, and will be launched late this year or early next year in the US, initially in the ZEV (zero emission vehicle regulation) states (i.e., California, and those states which have signed on to the California ZEV requirements). As part of the run-up to that introduction, Volkswagen of America brought journalists (including GCC) out to Wolfsburg to have some seat time with the new BEV, as well as to take a look at the assembly of the MQB-based e-Golf in the massive Wolfsburg plant; to have a walk through the new battery pack assembly plant in Braunschweig; and to get a better sense of Volkswagen’s (brand and group) thinking on e-mobility.
Strategy. Volkswagen began working with electric vehicles back in the early 1970s, noted Dr. Harald Manzenrieder, head of e-Golf production at the Wolfsburg plant. These—including, for example, an electric version of the T2, the iconic VW van of the late 1960s and 1970s—were mostly test cars and prototype cars, but also small fleets for special purposes.
Now, however, given all the market drivers facing the auto industry (regulations, fossil fuel availability, societal changes, etc.), Volkswagen is positioning itself for a broad-scale strategic shift in the types of powertrains in its vehicles—a shift that, because of its size, mandates an approach that can deliver the types of numbers it requires.
We are working on changing our focus from fossil fuel to higher efficiency for cars and to different possibilities to drive our cars. We are starting with optimizing our conventional drive trains—the TDI diesel engines, the TSI engines, the DSG transmission, all of those technologies have helped us to lower our fuel consumption a lot. We have different alternative fuels in our program such as CNG and LPG, we are working on some synthetic fuel. We have hybrids in our program to lower fuel consumption, mild hybrids, full hybrids, plug in hybrids coming out this year and of course we are working on the pure electric drive.
We are thinking that the right way [to do this] is large scale production, not special small niche cars and we think that a broad product range is necessary to bring this to the markets.—Dr. Soeren Hinze, Volkswagen Electric-Traction (EL) Technical Development
(Dr. Hinze is the engineer in charge of the rollout of the e-Golf and e-up!)
As the number two OEM in the automobile business in the world, it only makes sense for us if we see a certain volume behind it. So we won’t just jump into any technology only to be the first. We are coming with a solution that we think is a fit for the market.
We believe that the right way to bring electric vehicles is to implement them into the models that the customers like the most. For us that is the Golf, the best selling car in Europe and one of the most successful cars in the world, but also in other vehicles.—Christian Buhlmann, Volkswagen Product Communications
This approach requires not just the design engineering of the vehicle, but also the development of the integrated assembly process (enabled by the MQB), plus training of personnel in the plant. (More on this below.)
With the MQB-based designs and processes in the place, Volkswagen is confident that is can respond appropriately with whichever powertrain technologies become in demand.
If you look at the MQB cars, we started out with Golf now, and the successors of current PQ35 cars, which is Passat, Jetta and so on, will all be based on MQB, and are receiving MQB components at this time already, if you think of combustion engines like the 1.8 TSI, the 2.0 TDI latest generation. Those are all components that we are implementing from the MQB into existing models. Once the new generations are coming out, if we see a reasonable market share for EVs and PHEVs, we can deliver [those] without having to redevelop.—Christian Buhlmann
The e-Golf. The e-Golf is powered by a 24.2 kWh, 323V Li-ion battery pack—318 kg (701 lbs), or 21% of the e-Golf’s DIN unladen body weight—with the component 25 Ah cells and modules (6-cell and 12-cell) provided by Panasonic. The pack is located between the front and read axles. The front end of the battery is equipped with the Battery Management Controller (BMC) which performs safety, diagnostic and monitoring functions and also regulates the battery’s temperature in the Battery Junction Controller (interface to energy supply for the motor).
The pack itself is assembled in Braunschweig, and incorporates Volkswagen’s energy and battery management control logic. The production configuration of the pack was a bit challenging, noted Dr. Holger Manz, the head of the battery development department in Braunschweig, because of the need to fit in the space made available by the standardized MQB approach.
The e-drive unit consists of a 85 kW (114 hp), 270 N·m (199 lb-ft) synchronous electric motor (EEM 85) and single-speed transmission (EQ 270) with integrated differential and mechanical parking brake. Both motor and gearbox, which form a compact, modular unit, were developed in-house at Volkswagen. The e-drive unit is made at the Volkswagen components plant in Kassel, Germany.
The power electronics module controls the high-voltage energy flow between the e-motor and the lithium-ion battery (between 250 and 430 V depending on the battery voltage). The power electronics converts the direct current (DC) stored in the battery to alternating current (AC). The primary interfaces of the power electronics are its traction network connection to the battery; 3-phase connection to the electric motor; connector from the DC/DC converter to the 12-V electrical system; and a connection for the high-voltage power distributor.
Volkswagen developed a special electromechanical brake servo for its electric cars. This optimizes the driver’s braking force in the same way that brake servos do in conventional cars. However, with the electromechanical brake servo this happens by what is known as brake blending—a process in which low levels of deceleration are produced solely through the e-motor’s braking torque. Stronger deceleration, meanwhile, is achieved by combining the braking torques of the electric motor and the hydraulic brake system.
A newly developed heat pump—which will be applied in the US e-Golf—enables better driving range in colder temperatures. An add-on module to the electric heating (high-voltage heater) and electric air conditioning compressor, the heat pump recovers heat from the ambient air and the heat given off by the drive system components. This significantly reduces the high-voltage heater’s electric power consumption to keep the passenger cabin comfortable. When the heat pump is used, this increases the driving range in cold weather of the e-Golf by more than 30% compared to a conventional heating system.
Volkswagen was able to lower the air drag of the Golf by developing very specific measures such as reducing the volume of cooling air (via a radiator shutter and partially closed-off radiator grille), new underbody panelling, rear body modifications with a rear spoiler and C-pillar air guides, and by developing new aerodynamic wheels (essentially closing off gaps, making the wheels flush with the car’s exterior).
Whereas on the standard Golf (1.6 TDI with 77 kW) air drag is 0.686 m2, air drag was reduced to 0.615 m2 on the e-Golf, which represents a 10% improvement. Correspondingly, the cD value was lowered to 0.281.
Volkswagen was able to achieve another positive effect on energy consumption and range by optimizing the tires (205/55 R16 91 Q). Reducing the rolling resistance coefficient from 7.2 per 1,000 (Golf BlueMotion) to 6.5 per 1,000 for the e-Golf (likewise an improvement of 10%) also improves the range.
The Golf offers the CCS charging system, enabling both AC and DC fast charging. A 3.6 kW charge to 100% SOC will take about 8 hours; a DC fast charge to 80% SOC will take about 30 minutes.
Driving. We had the opportunity to drive the e-Golf from Wolfsburg to Braunschweig—a drive of about 36 km (22 miles) that offers some higher speed highway driving as well as in-city conditions.
The e-Golf reaches a speed of 60 km/h (37 mph) within 4.2 seconds, and 100 km/h (62 mph) in 10.4 seconds, with top speed limited to 140 km/h (87 mph. Range is estimated, on the NEDC cycle, to be up to 190 km (118 miles); Volkswagen suggests a realistic real-world range of 130 km (81 miles) to 190 km, depending upon temperature, driving style, etc.
As we noted earlier, the e-Golf is essentially a Golf: comfortable, quick and with good handling. The weight of the battery pack helps keep the car anchored to the road, but there is no wallowing sensation in quick cornering maneuvers, even at higher speeds.
With its limited top speed, the e-Golf is not designed for scorching down the Autobahn, but it is more than capable of delivering an enjoyable driving experience in standard city and suburban conditions. We had no problems at all with high speed merging onto the highway, and, as with electric drives in general, the immediate torque after starting up from a stop was most satisfying.
The e-Golf offers two technologies to balance optimal utilization of the vehicle’s energy against the driver’s wishes. One is the five different levels of regenerative brake settings, described above. Higher levels of regen allow the driver to slow the vehicle almost to a stop (with “B”), while recharging the battery. Levels “D2”, “D3” and “B” decelerate the car sufficiently that the brake lights come on.
Switching levels of regen easily with a tap of the shifter allow the driver to customize the vehicle’s performance in response to terrain and driving styles. In combination with the recuperation monitor (again, above), this also gives drivers the chance to learn how best to drive their e-Golf.
The other driver-focused optimizing technology is the three driving profiles: “Normal”, “Eco”, and “Eco+”. The Volkswagen automatically starts in “Normal” mode. In “Eco” mode, the electric motor’s maximum power is reduced to 70 kW, and drive-off torque is limited to 220 N·m (162 lb-ft). In parallel, the electronics reduce the output of the air conditioning system and modify the response curve of the accelerator pedal. In this mode, the e-Golf can reach speeds of up to 115 km/h (71 mph) and accelerate to 100 km/h in 13.1 seconds.
In “Eco+” mode, the electronics limit power output to 55 kW and drive-off torque to 175 N·m (129 lb-ft). At the same time, the accelerator pedal response curve is made flatter, and the air conditioning is switched off. The e-Golf now reaches a top speed of 90 km/h (56 mph) and accelerates at a slower rate. Nonetheless, drivers can still obtain full power, maximum torque and a top speed of 140 km/h in “Eco” and “Eco+” mode by kick-down.
(Our favorite combination in general was “Normal” with “B”.)
|e-Golf driving modes|
|Air conditioning||Normal||Reduced||Ventilation only|
|Acceleration (0-100 km/h)||10.4 s||13.4 s||20.9 s (to 90 km/h only)|
|Power||85 kW||70 kW||55 kW|
|Top speed||140 km/h||115 km/h||90 km/h|
Under the NEDC, the e-Golf is rated with energy consumption of 12.7 kWh/100km. Based on our short “real world” drive (with a bit of a heavy foot on the accelerator), we appeared to achieve between about 11-16 kWh/100 km, based on different conditions; sometimes much lower, sometimes a bit higher. (The touchscreen monitor will show you exactly how much you are consuming, adding to the driver-training aspect over time.)
Volkswagen implemented an acoustic concept for the e-Golf that is specifically tailored to the characteristics of an electric vehicle, greatly enhancing its already quiet attributes.
As one example, the motor’s suspension system was switched to a pendulum mount with modified response characteristics, which greatly enhances the acoustics despite the e-motor’s high torque build-up when accelerating. In designing the motor housing unit, Volkswagen was also able to achieve an extremely low level of noise emissions.
Furthermore, the highly sound-absorbent and yet very lightweight materials used in the interior produce a luxury-class level of acoustic comfort. It is indeed quite quiet.
Owners of e-Golfs can order nearly all the optional features and assistance systems of the full Golf model series.
Production overview. One of the mantras of the Volkswagen Group surrounding the benefits of its modular assembly toolkits is that they enable the streamlined production of a variety of vehicles using common components on the same line. The MQB-based e-Golf is certainly a case in point—with the exception of a detached loop added, for the time being, for high voltage (HV) component assembly. This includes the battery pack, power electronics and all the connections, and first pack power to the vehicle.
Aside from the detached assembly for the high voltage components, the e-Golf is just another Golf moving through the assembly process; the electric powertrain and drivetrain components are assembled in an area on a floor beneath the main assembly line, along with conventional powertrain and drivetrain elements. These assembled powertrain and drivetrain elements—with a significant gap in the middle in the case of the e-Golf to accommodate the battery pack—are automatically “married” to their appropriate bodies, rising up from the floor underneath in a tightly controlled process.
|Audi A3 e-tron production|
|Audi, one of the Volkswagen brand’s Group siblings, is not using a detached high voltage assembly loop for the production of its A3 e-tron plug-in hybrid.|
|With the exception of an added station where the battery pack is installed, the A3 e-tron is moving along the line like every other A3, says John Schilling, Manager of Product Communications for Audi of America.|
There were a number of reasons driving the decision to implement a detached high voltage assembly, said Dr. Manzenrieder. These include:
The possibility of an unbalanced work load for each operator due to different bill of materials;
The restricted workshop area ensures optimal safety control;
Flexible production equipment enables optimized process design. This is a learning laboratory as well as a production loop;
The opportunity to establish specific high-voltage component expertise. All operators are HV-experts and ensure best process and quality control; and
The possibility for technical reviews at the car without disrupting the assembly process.
By running this production line, I have the opportunity to focus and to gain expertise on high voltage components, their characteristics and, which is very important, the interaction between components. If it was produced on a stepped production line in one minute steps, I can see only very limited steps. Here I can see all the parts together.
The operators we use in this area are all experts, not only mechanically, but they also know the components. We have optimized this way to control the process and the product. We have the possibility to call other experts from R&D, from the quality department to take a look at each stage within the assembly. Our equipment is flexible so that we can do any other model or generation.—Dr. Manzenrieder
The operators work in teams of two, each team handling the entire final high-voltage assembly process from start to finish.
|Top. The high-voltage components addressed in the detached final assembly loop. Bottom left. Installing the battery pack. Bottom right. Connecting the power electronics. Click to enlarge.|
Braunschweig battery plant. Volkswagen’s facility in Braunschweig is one of the larger producers of running gear in the world—and the oldest plant in the Volkswagen Group. Since 2007, it has also been the site for the development and production of battery systems for electric vehicles. Beginning in 2012, the pre-series center for the e-Golf was situated there.
Braunschweig is now responsible for the development and production of the battery packs for the e-Golf and the e-up!, and features a new, discrete automated facility dedicated to battery production.
In the run-up to series production, the Braunschweig team had evaluated using prismatic 25 Ah cells from Panasonic, or 18650 cells (i.e., similar to Tesla), said Dr. Manz. Volkswagen opted for the 25 Ah prismatic cells from Panasonic.
We tested several cells and several manufacturers of the cells and Panasonic was the best we could use for this project.—Dr. Manz
I myself don’t want to be a battery system, because I know what is done with such systems. Before we get the release of a battery system we make a test of about 12 weeks with shocks, vibrations and we do a temperature test. At the end we dip it 20 times into water; we heat it before and then dip it into cold water. And after the 20 dips, there should be no leakage. These are the heaviest tests I’ve ever seen for such a system.—Dr. Manz
Currently, the e-up! battery pack production line is producing 40 packs per day. The e-Golf line is producing 44 packs per day; by the end of the year it will produce 100 packs per day. The new Braunschweig facility has plenty of room for adding additional lines.
Battery futures. The great advantage of Volkswagen doing its own development on the battery system—especially in areas of packaging and management, is that it is now “relatively free to change from one cell supplier to another,” said Dr. Manz. “It’s a great advantage that we have.”
Volkswagen is pursuing a number of advanced chemistry options through its different organizations, including its Palo Alto, California-based research organization.
|“We are thinking about 28 [Ah] to 34 [Ah] and more. Never have so many people surged and developed on new technologies and new chemsitry and new cells like today.”|
—Dr. Soeren Hinze
In a presentation at the Barclays Future Powertrain Symposium in London earlier in July, the Volkswagen Group’s Prof. Dr. Wolfgang Steiger suggested that the Group has identified a short term roadmap that will increase battery energy density to about 220 Wh/kg (compared to the 170 Wh/kg in the cells in the e-Golf.) Beyond that, the Group is looking to Li-sulfur (500 Wh/kg) and Li-air (1,000 Wh/kg) as future solutions.
Put another way, he noted that the group sees a pathway from the 25 Ah cells currently used in the e-Golf and e-up! to 28 Ah, 34 Ah, and 36 Ah cells in the future. Combined with other refinements in energy consumption, weight, aerodynamics and rolling efficiency, the Group expects to be able to deliver significant increases in battery-electric range.
Think of diesel in the early 1990s where it had tiny single digit market shares, and now it’s up to 50%. The market for this [e-mobility] must develop. We have a new technology here that is coming into the market that will also start with single digit market shares but it will grow eventually. We can already see it in some of the markets.—Christian Buhlmann
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