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Researchers from Hyundai Motor have found that the use of a new sulfone-based electrolyte greatly improved the capacity and reversible capacity retention of a Li-sulfur battery compared to the performance of ether-based electrolytes. In a paper presented at the SAE 2104 World Congress in Detroit, they reported that use of the sulfone-based electrolyte increased capacity by 52.1% to 715 mAh/g and capacity retention by 63.1% to 72.6%.
Lithium-sulfur systems are of great interest as a “beyond Li-ion” solution with increased energy densities that would enable much greater electric vehicle range. The Li/S system has a high theoretical specific energy of 2600 Wh kg-1; however, rapid fading of charge capacity is a well-known issue (e.g., earlier post). The poor long-term performance has been associated with both the shuttling of polysulfides dissolved into the electrolyte, in addition to irreversible deposition of solid lithium sulfide (Li2S) and other mixtures of insoluble discharge products on the cathode.
Chemical processes in Li/S battery include Li ion dissolution from Li metal anode and sulfur reduction to Li polysulfides (PS, the series of sulfur reduction intermediates) on the sulfur cathode while discharging (S8→Li2S8→Li2S6→Li2S4→Li2S), and reversible chemical reactions occur during charging. Among the PS formed in this mechanism, Li2S6 and Li2S4 are soluble in electrolytes. PS solubility plays an important role to improve cyclability as increasing the sulfur utilization.
Ether type solvent has been considered as a suitable electrolyte for Li/S battery because it has good PS solubility and chemical stability. Meanwhile, dissolved PS causes redox shuttle resulting in a low COlumbic efficiency, poor cycle life and self-discharge. Therefore, this work aimed at developing a new electrolyte in order to prevent redox shuttle and improve cyclability.—Shin et al.
In their study, the Hyundai researchers compared the performance of 5 single component ether-based systems (DME, DEGDME, Triglyme, TEGDME and DIOX); one binary system (TEGDME:DIOX); and three versions of a ternary system with sulfone (TEGDME:DIOX:Sulfolane at ratios of 1:1:1, 1:1:2, and 1:1:3).
They assembled coin cells for electrochemical testing using a sulfur cathode and Li metal foil as an anode, with a polyethylene separator between them. Cycling test were performed between 1.5V and 2.65V and room temperature at C/20 rate.
Among the single component ether systems, use of DME resulted in the highest capacity of 878 mAh g-1, with DEGDME a close second at 857 mAh g-1. However, the cells with these electrolytes showed drastic capacity fade after 6 and 2 cycles, respectively.
While cyclic ether, DIOX, showed 1,040 mAh g-1 at first cycle, this dropped to 640 mAh g-1 at 12 cycles. The high initial discharge capacity showed that DIOX appeared to be effective on developing high capacity; however, after 13 cycles it evidenced a drastic capacity decrease.
TEGDME showed a low initial capacity of 200 mAh g-1, but it did not show drastic capacity fade.
The researchers combined TEGDME and DIOX into a 1:1 binary system to investigate the synergy of the good cyclability of TEGDME and the high capacity of DIOX.
The cell with the binary ether electrolyte showed first discharge capacity of 1057 mAh g-1 and 470 mAh g-1 after 20 cycles. Compared to the single component results, this cell showed good cyclability. However, the issues large drop in capacity after the first cycle and the low reversible capacity retention of 44.5% after 20 cycles remained.
The researchers then inserted a glass filter between the electrodes to restrain the high resistance around the electrodes in the cell with the binary electrolyte. (The glass filter absorbs electrolyte, thereby preventing a deficiency of electrolyte next to the electrode.) This served to increase overall capacity to 605 mAh g-1 after 20 cycles, lowered the capacity decrease after first cycle, and improved capacity retention.
Chemical analysis suggested that sulfone solvent could form a protective layer on the anode surface, and prevent the PS shuttle by blocking the reaction between the Li anodes and PS. In addition, the protective layer can mitigate the crack formation on the surface observed with the other electrolyte systems, the researchers determined.
The Hyundai team used Sulfolane (a sulfone-based solvent), as it is already known as a suitable Li battery electrolyte. They prepared three ternary compositions of electrolyte, adding different amounts of sulfolane to the binary TEGDME : DIOX mixture.
They found that the 1:1:2 (TEGDME:DIOX:Sulfolane) mixture (TDS2) showed the best cyclability, as noted above with capacity of 715 mAh g-1. TDS1 also showed improved capacity and retention: 674 mAh g-1 and 68%. Cycle performance worsened in TDS3.
The researchers also found that cracks on the anode surface diminished significantly.
Shin, N., Ryu, K., Kim, Y., and Lee, H. (2014) “Improved Cyclic Performances of Li-Sulfur Batteries with Sulfone-Based Electrolyte,” SAE Technical Paper 2014-01-1844 doi: 10.4271/2014-01-1844
In an effort to improve future data management and access, DOE’s Water Power Program is establishing a Marine and Hydrokinetics (MHK) Data Repository to manage the receipt, protection, and dissemination of scientific and technical data generated by DOE-funded awards.
Capabilities of the proposed MHK Data Repository include:
Custom metadata schema;
Secure storage of sensitive data;
DOE says that the MHK Data Repository will reduce duplication of effort and accelerate MHK innovation by allowing fewer resources to be spent on data discovery, freeing up resources for analysis, innovation, and implementation.
DOE’s MHK Technology Database moves to the Open Energy Information (OpenEI) website where the MHK community now has an interactive database to help showcase project and technology development around the world. In addition, users can learn about Hydrodynamic Testing Facilities capabilities across the US. The MHK community can share their facilities latest capabilities by creating a profile through OpenEI.
The Water Power Program has also collaborated with the International Energy Agency’s Ocean Energy Systems group to create the Tethys database, which catalogues, shares, and maps environmental research from around the world to enable sustainable development and expansion of clean, renewable ocean power.
Researchers at Stanford University have developed a nanocrystalline copper material that produces multi-carbon oxygenates (ethanol, acetate and n-propanol) with up to 57% Faraday efficiency at modest potentials (–0.25 volts to –0.5 volts versus the reversible hydrogen electrode) in CO-saturated alkaline water.
The material’s selectivity for oxygenates, with ethanol as the major product, demonstrates the feasibility of a two-step conversion of CO2 to liquid fuel that could be powered by renewable electricity, the team suggests in their paper published in the journal Nature. Ultimately, this might enable a closed-loop, emissions free CO2-to-fuel process.
We have discovered the first metal catalyst that can produce appreciable amounts of ethanol from carbon monoxide at room temperature and pressure—a notoriously difficult electrochemical reaction.—Matthew Kanan, an assistant professor of chemistry at Stanford and coauthor of the Nature study
Two years ago, Kanan and Stanford graduate student Christina Li created a novel oxide-derived copper electrode material. While conventional copper electrodes consist of individual nanoparticles that just sit on top of each other, oxide-derived copper, is made of copper nanocrystals that are all linked together in a continuous network with well-defined grain boundaries. The process of transforming copper oxide into metallic copper creates the network of nanocrystals, Kanan explained.
For the Nature study, Kanan and Li built an electrochemical cell: two electrodes placed in water saturated with carbon monoxide gas. When a voltage is applied across the electrodes of a conventional cell, a current flows and water is converted to oxygen gas at one electrode (the anode) and hydrogen gas at the other electrode (the cathode). The challenge was to find a cathode that would reduce carbon monoxide to ethanol instead of reducing water to hydrogen.
The electrochemical conversion of CO2 and H2O into liquid fuel is ideal for high-density renewable energy storage and could provide an incentive for CO2 capture. However, efficient electrocatalysts for reducing CO2 and its derivatives into a desirable fuel are not available at present. Although many catalysts can reduce CO2 to carbon monoxide (CO), liquid fuel synthesis requires that CO is reduced further, using H2O as a H+ source. Copper (Cu) is the only known material with an appreciable CO electroreduction activity, but in bulk form its efficiency and selectivity for liquid fuel are far too low for practical use. In particular, H2O reduction to H2 outcompetes CO reduction on Cu electrodes unless extreme overpotentials are applied, at which point gaseous hydrocarbons are the major CO reduction products.—Li et al.
In the Nature experiment, Kanan and Li used a cathode made of oxide-derived copper, with the resulting high yield of ethanol and acetate at 57% Faradaic efficiency (i.e., 57% of the electric current went into producing these two compounds from carbon monoxide). By comparison, conventional Cu nanoparticles with an average crystallite size similar to that of oxide-derived copper produced nearly exclusive H2 (96% Faraday efficiency) under identical conditions.
The researchers attributed the ability to change the intrinsic catalytic properties of Cu for this notoriously difficult reaction to the growth of the interconnected nanocrystallites from the constrained environment of the oxide lattice.
The Stanford team has begun looking for ways to create other fuels and improve the overall efficiency of the process.
In this experiment, ethanol was the major product. Propanol would actually be a higher energy-density fuel than ethanol, but right now there is no efficient way to produce it.—Matthew Kanan
In the experiment, Kanan and Li found that a slightly altered oxide-derived copper catalyst produced propanol with 10% efficiency. The team is working to improve the yield for propanol by further tuning the catalyst’s structure. Ultimately, Kanan would like to see a scaled-up version of the catalytic cell powered by electricity from the sun, wind or other renewable resource.
For the process to be carbon neutral, scientists will have to find a new way to make carbon monoxide from renewable energy instead of fossil fuel, the primary source today. Kanan envisions taking carbon dioxide (CO2) from the atmosphere to produce carbon monoxide, which, in turn, would be fed to a copper catalyst to make liquid fuel. The CO2 that is released into the atmosphere during fuel combustion would be re-used to make more carbon monoxide and more fuel—a closed-loop, emissions-free process.
Technology already exists for converting CO2 to carbon monoxide, but the missing piece was the efficient conversion of carbon monoxide to a useful fuel that's liquid, easy to store and nontoxic. Prior to our study, there was a sense that no catalyst could efficiently reduce carbon monoxide to a liquid. We have a solution to this problem that’s made of copper, which is cheap and abundant. We hope our results inspire other people to work on our system or develop a new catalyst that converts carbon monoxide to fuel.—Matthew Kanan
The Nature study was coauthored by Jim Ciston, a senior staff scientist with the National Center for Electron Microscopy at Lawrence Berkeley National Laboratory.
The research was supported by Stanford University, the National Science Foundation and the US Department of Energy.
Christina W. Li, Jim Ciston & Matthew W. Kanan (2014) “Electroreduction of carbon monoxide to liquid fuel on oxide-derived nanocrystalline copper,” Nature doi: 10.1038/nature13249
The four partners in the European research project ”MotorBrain”—Infineon Technologies, Siemens, the Institute of Lightweight Engineering and Polymer Technology at the Technische Universität (Technical University) Dresden and ZF Friedrichshafen—are presenting their first prototype of a lightweight electric motor system that requires no rare earth metals.
The €36-million (US$50-million) MotorBrain effort is one of the largest single European research projects in the area of electromobility. The MotorBrain prototype integrates the motor, gear drive and inverter. The prototype is three-quarters the size of models from 2011, the year when MotorBrain began; the prototype now being presented could fit in a conventional-sized laptop or notebook backpack.
The motor is also lighter than before. The integration of motor, gear drive and inverter enabled an approximate 15% reduction in weight of the powertrain from 90 kg (198 lbs) to less than 77 kg (170 lbs). A medium-sized vehicle with MotorBrain electric motor and performance of 60 kW (equal to about 80 hp) would be able to drive about 30 to 40 kilometers (19 to 25 miles) farther than today’s electric vehicles with their average range of approximately 150 kilometers per battery charge.
Rare earth metals are currently a fundamental cost driver in hybrid and electric vehicles. Today rare earth metals are an important component in the permanent magnet of any electric motor, generating a particularly strong, constant magnetic field. The stronger the magnetic field, the higher the performance capabilities of the motor.
However, obtaining rare earth metals is complicated and environmentally harmful. Also, rare earth metal prices are high and fluctuate widely. The MotorBrain electric motor therefore utilizes readily available and less expensive ferrite magnets. The lower performance level of ferrite magnets compared to those with rare earth metals is compensated for by the specially developed high-RPM (revolutions per minute) rotor of the MotorBrain electric motor.
The project. Led by Infineon, a total of 30 partners from nine European countries are conducting research in MotorBrain with the goal of increasing the range and safety of electric vehicles while at the same time reducing dependency on rare earth metals.
The team includes universities, non-university research facilities, semiconductor manufacturers, electric motor builders, automobile component suppliers and automobile manufacturers.
The MotorBrain project began in the fall of 2011, and will conclude in October 2014. The time beween now and October will be spent validating and proving the research results.
Chemists at Ludwig Maximilians Universität München report that 20% of the gases produced by the combustion of R1234yf—the approved low global warming potential refrigerant for mobile air conditioning (MAC) systems, the adoption of which has met with resistance from German automakers (earlier post)—consist of the highly toxic chemical carbonyl fluoride.
Carbonyl fluoride is structurally related to phosgene (which contains chlorine in place of fluorine), which was used as a chemical weapon during the First World War. Kornath and his co-workers have just published the results of their investigation in the journal Zeitschrift für Naturforschung B.
It has been known for some time now that combustion of R1234yf results in production of the toxic hydrogen fluoride. Our analysis has now shown that 20% of the gases produced by combustion of the compound consist of the even more poisonous chemical carbonyl fluoride.—Andreas Kornath, Professor of Inorganic Chemistry at LMU
The simplest fluoride, hydrogen fluoride (or hydrofluoric acid, HF) is also highly corrosive and so toxic that burns about as big as the palm of one’s hand can be lethal. The agent binds avidly to calcium in body fluids, and this can result in heart failure unless an antidote is rapidly administered.
Carbonyl fluoride is even more dangerous, because it penetrates the skin more easily, and causes severe irritation of the eyes, the skin and the airways. If inhaled, it can damage the alveoli in the lungs, allowing it to reach the circulation and shut down vital functions.
According to guidelines issued by the European Union, automobile manufacturers are legally obligated to use a low global warming potential refrigerant in the air-conditioning systems installed in their cars. Use of the previously approved refrigerant R134a in new models has been forbidden in the EU since 2011, as the agent had been shown to contribute to the global warming in the atmosphere.
However, R1234yf, the recommended replacement (earlier post), has already been the subject of much heated debate in Germany. Studies carried out by various institutions and by German auto manufacturers had pointed to the compound’s flammability, and shown that, in the event of accidents in which vehicles catch fire, combustion of R1234yf leads to the release of hydrogen fluoride.
An interim report in 2013 based on independent testing by Germany’s Kraftfahrt-Bundesamt (Federal Motor Transport Authority) found that there is “no sufficient evidence of a serious risk” as defined by the Product Safety Act (ProdSG) related to the use of the low global warming potential (GWP) refrigerant R-1234yf. (Earlier post.)
KBA found that in the most severe crashes (level 3), one of the four models ignited and emitted toxic hydrogen fluoride (HF) gas; “non-negligible amounts” of HF were also found in two other test crashes. However, the level 3 crash testing was outside of the bounds of the statutory scope of product safety regulations—i.e., the level 3 tests could not be associated with the necessary concrete probability of occurrence, but served as a general appraisal of the risk.
More recently, a scientific review of research regarding the safety aspects of the use of refrigerant R1234yf in Mobile Air Conditioning (MAC) systems, published by the European Commission, also shared the conclusion that there is no evidence of a serious risk in the use of this refrigerant in MAC systems under normal and foreseeable conditions of use under product safety guidelines. (Earlier post.)
That review, carried out by Europe’s Joint Research Centre, provided an in-depth analysis of testing and a subsequent report on the refrigerant’s safety by KBA in order to ascertain whether the results stemming from the tests were well founded and supported by a rigorous and scientific methodology.
Based on the LMU results, however, Professor Kornath is urging a re-assessment.
The risk analyses carried out by the manufacturers of the refrigerant so far have not taken carbonyl fluoride into account. In light of our results, we advise that the risks associated with R1234yf should be urgently reassessed.—Andreas Kornath
Michael Feller, Karin Lux, Christian Hohenstein, and Andreas Kornath (2014) “Structure and Properties of 2,3,3,3-Tetrafluoropropene (HFO-1234yf),” Z. Naturforsch. 69b, 379–387 doi: 10.5560/ZNB.2014-4017
A comprehensive survey of major power management control algorithms for hybrid-electric (HEVs) and plug-in hybrid electric vehicles (PHEVs) proposes that future work will need to consider the vehicle as part of a larger system which can be optimized at an even larger scale.
This type of large-scale optimization will require the acquisition and processing of additional information from the driver and conditions outside the vehicle itself, suggests Dr. Andreas Malikopoulos, Deputy Director of the Urban Dynamics Institute and an Alvin M. Weinberg Fellow in the Energy and Transportation Science Division with Oak Ridge National Laboratory (ORNL).
The research reported in the literature to date has aimed at enhancing our understanding of power management control optimization in HEVs and PHEVs. While much progress has been made, some improvements have been incremental, and there has been considerable repetition of a limited number of basic concepts. It appears that the current state of the art is now at a point where new and significantly different approaches are needed.
… There is a solid body of research now available that has aimed at enhancing our understanding of power control optimization in HEVs and PHEVs. … The biggest remaining uncertainties are related to external factors, including the driver’s driving style, the surrounding traffic environment, and the driving terrain. It appears that future research studies need to be devoted to considering the vehicle as part of a larger system, which can be optimized at an even larger scale. Such large-scale optimization will require the acquisition and processing of additional information from the driver and conditions outside the vehicle itself.
This is likely to require addition of new sensors and/or better utilization of information generated by existing sensors. However, the processing of such multiscale information will require significantly new approaches in order to overcome the curse of dimensionality. One particular area where new sensors will be needed is in vehicle-to-vehicle communication.
… we can assume that these technologies will be available in a few years. The question is whether we could take advantage of these technologies and optimize the power management control in HEVs and PHEVs. What if we would consider the problem of optimizing fuel economy and emissions for a fleet of vehicles rather than a single vehicle, thus eliminating the uncertainty related to traffic? What would be the appropriate conceptual approaches for modeling and optimization?—Malikopoulos (2014)
Malikopoulos starts his paper by reviewing the power management control problem and presenting control algorithms that can be used to derive the optimal control policy—e.g., dynamic programming (DP); equivalent fuel consumption minimization strategy (ECMS); and model predictive control (MPC).
Dynamic programming has been widely used as the principal method for analysis of sequential decision-making problems such as deterministic and stochastic optimization and control problems, Markov decision problems, minimax problems, and sequential games, Malikopoulos notes. DP relies on the principle of optimality—i.e., regardless of the initial state of the system and initial decision, the remaining decisions must constitute an optimal policy with regard to the state resulting from the first decision.
Although DP can yield a global optimal solution in closed form, the associated computational requirements are often overwhelming, and for many problems, a complete solution by DP is impossible, Malikopoulos says.
Model predictive control uses prediction models to obtain a control action by solving an online optimization problem; it is often used in constrained regulatory related control problems of large-scale multivariable systems, where the objective is to operate the system in a certain desired way.
The instantaneous equivalent fuel consumption minimization strategy (ECMS) allows the battery SOC to be taken into account.
Malikopoulos then enters into his survey of the applications of major power management control algorithms reported in the literature to date within four discrete categories: parallel HEVs; series HEVs; power-split HEVs; and PHEVs, with subcategories of parallel, series and power-split architectures.
In the parallel HEV, both the engine and the motor are connected to the transmission, and can power the vehicle either separately or in combination. Parallel HEVs can use a smaller battery pack as they rely more on regenerative braking and the engine can also act as a generator for supplemental recharging; thus, they are more efficient for highway driving than in urban stop-and-go conditions or city driving, he notes.
Parallel HEVs offer two architectures: pre-transmission and post-transmission. In a pre-transmission architecture, the electric machine can start the engine; thus, a starter/alternator is not necessary, and there are some savings associated with the reduced weight. In the post-transmission architecture, the regenerative braking efficiency is maximized due to the physical location of the motor. There are also fewer to no spinning losses through the transmission.
In a series HEV, the electric motor is the only means of providing the power to the wheels; the motor draws electric power in combination from the battery and from a generator run by the engine. The engine is typically smaller in series HEVs as it only has to meet on average the driver’s power demand, and the battery pack is generally more powerful than the one in parallel HEVs to provide remaining peak driving power needs.
The larger battery and motor, which are required by series HEVs, along with the generator, add to the cost, making series HEVs more expensive than parallel HEVs. While the engine in a conventional vehicle may inefficiently operate to satisfy the driver’s power demand, e.g., stop-and-go driving, in a series HEV, the engine operates only at its most efficient speeds and loads as it is not coupled to the wheels.
Since series HEVs are superior in stop-and-go driving, they are primarily being considered for buses and other utility vehicles.
The power split HEV combines the advantages of both series and parallel configurations; series HEVs are more efficient at lower vehicle speeds, whereas parallel HEVs are more efficient at high speeds. The power split HEV costs more than a parallel HEV as it needs two electric machines acting as both a motor and a generator and a larger battery pack.
The “power split” name comes from the power split device (PSD), which is a planetary gear set that replaces the traditional gearbox and acts as a continuously variable transmission with a fixed gear ratio. The PSD allows the smaller of the two electric machines to act as a starter for the engine, thereby eliminating another component of a traditional gasoline engine.
The engine can both power the vehicle directly, as in the parallel drivetrain, and be effectively disconnected from the wheels so that only one of the electric machines acting as a motor propels the vehicle, resembling a series HEV.
PHEVs are hybrid vehicles with rechargeable batteries that can be restored to full charge by connecting a plug to an external electric wall socket. A PHEV shares the characteristics of both an HEV, i.e., having a battery, an electric motor, and an engine, and an all-electric vehicle, i.e., having a plug to connect to the electrical grid.
The numerous control algorithms described cover the period from 1998 to the present, and they are distinguished by the HEV or the PHEV architecture in which they were implemented and their approximate chronological order.
Investigating a new optimization framework that considers a fleet of vehicles could aim to compute the most efficient vehicle speed in centralized locations and communicate this with driver information systems to the driver to avoid congestion, thus improving overall efficiency and reducing emissions in conventional vehicles.
In HEVs and PHEVs, the power management controller would have to account for limited uncertainty about surrounding traffic and commute and be able to optimize fuel economy, pollutant emissions, as well as battery lifetime and range. The detailed investigation of these issues could provide policymakers with unique new tools to assess the implications in promoting the development of technologies and infrastructure in new directions.—Malikopoulos (2014)
Malikopoulos, A.A. (2014) “Supervisory Power Management Control for Hybrid Electric Vehicles: A Survey,” IEEE Transactions on Intelligent Transportation Systems doi: 10.1109/TITS.2014.2309674
Volkswagen of America, Inc. will debut a concept version of the latest SportWagen model featuring a 4MOTION all-wheel drive system and the new EA288 TDI Clean Diesel engine (earlier post) at the New York Auto Show. The concept previews the new Golf SportWagen that will go on sale in early 2015.
Based on the new MQB (modular transverse matrix) architecture, the Golf SportWagen will continue the trend introduced by the seventh generation Golf whereby it is lighter, bigger, roomier, more fuel efficient and more powerful than the outgoing SportWagen model. The new SportWagen will be offered with two powertrains:
A 170 hp (127 kW), 1.8-liter turbocharged and direct-injection four-cylinder TSI engine, mated to five-speed manual or six-speed automatic transmissions. These powertrains offer manufacturer highway fuel economy that’s improved by as much as 17% compared to the 2.5-liter Jetta SportWagen.
The new EA288 2.0-liter common-rail, turbocharged and direct-injection diesel engine that makes 150 hp (112 kW), an improvement of 10 hp over the current SportWagen model. The TDI model will have a choice of six-speed manual or DSG dual-clutch automatic transmissions.
Through the extensive use of high and ultra-high strength steels, the new SportWagen bodyshell is lighter than the current Jetta SportWagen and offers an enhanced crash structure. Throughout the car, optimized components—such as the seats, air conditioning unit, and electrical architecture—help to save weight.
The Golf SportWagen is 1.1 inches longer and 0.7 inches wider than the current SportWagen model. It is also 0.9 inches lower, which benefits both aerodynamic performance and the car’s proportions: the CdA number has been reduced by almost 10% compared with the previous generation.
The interior package has been optimized to give more rear-seat leg- and shoulder-room. Although the new SportWagen’s overall height was lowered by nearly an inch, front and rear headroom has been improved by 0.4 inches.
The new SportWagen also offers nearly 10% more cargo room with the rear seats folded than the outgoing model. Essentially, VW suggests, the Golf SportWagen provides a sportier alternative to compact SUVs.
Because it is based on the MQB architecture—which dictates a fixed relationship between the front wheel centerline and the pedals—the car’s proportions have changed. The front wheels, for example, are now 1.7 inches further forward than on the current SportWagen design. This has created what Klaus Bischoff (VW Brand Design) calls a cab-backward impression. “That’s what we call the proportions of premium-class vehicles, where the hood is long and the passenger compartment is a long way towards the back.”
The new SportWagen features a new standard driver assistance system called the Automatic Post-Collision Braking System. This system automatically engages the vehicle’s brakes after it is involved in a collision in order to help reduce secondary collisions and to help bring the vehicle to a stop. The system is triggered when the airbag sensors detect a primary collision and it is limited to a maximum retardation rate of 0.6g by the Electronic Stability Control (ESC) unit.
The driver can effectively override the system at any time; for example, it is disabled if it recognizes that the driver is accelerating. The system is also deactivated if the driver initiates braking at a higher rate than 0.6g.