Incremental improvements deliver major reductions in vehicle emissions

Paul Boughton
Europe is maintaining its squeeze on the automotive industry. On one hand manufacturers are facing more stringent legislation to cap the levels of carbon dioxide (CO2) that vehicles produce, while drivers and vehicle operators are under pressure from the European Commission's proposed Europe-wide carbon tax on road fuel.

Automotive manufacturers and their suppliers therefore need to develop and implement innovative technologies to reduce emissions and, by implication, fuel consumption. Interestingly, EC Regulation 443/2009, which proposes more stringent emissions performance standards for new passenger cars, suggests that the measure will play a key role in helping to stimulate innovation.

Leaving aside what might be considered 'long-term' measures such as hydrogen fuel cell cars and all-electric vehicles, the main areas for development are likely to include everything from vehicle weight reduction to improved engine efficiency, wider adoption of start/stop technologies, and more effective, lower-cost hybrid vehicles. There is also potential to use related technologies such as self-driving cars where more efficient speeds can be sustained on motorways, resulting in a reduction in fuel consumption for each convoy of vehicles.

Boosting engine efficiency is an important focus for automotive manufacturers as they strive to cut fuel consumption and reduce emissions. One innovation with much promise is a fully variable hydraulic valve control system that the developers hope will cut CO2 emissions by 25 per cent. UniAir, which is a joint development between the Schaeffler Group and Fiat Powertrain, will make its debut on Fiat's new Alfa MiTo 1.4 MultiAir. The UniAir technology provides improvements in start-up, partial load and acceleration behaviour of the vehicle. During the engine warm-up phase, for example, hydrocarbon (HC) emissions can be 40 per cent lower, and nitrogen oxide (NOx) emissions are down by as much as 60 per cent. In addition, UniAir is said to offer a greatly improved driving experience through greater power, higher torque and better engine response.

UniAir is a cam-actuated, electro-hydraulic valve train system. For petrol engines, the UniAir systems enables throttle-free, continuously variable, software-based load control across the entire engine map. With diesel engines, regulation of the temperature of the combustion chamber is achieved via the precise control of exhaust gas recirculation rates. At the same time, the effective compression ratio in the cylinder can be varied and homogeneous combustion ensured.

According to Schaeffler and Fiat, UniAir allows, for the first time, not only variations in the valve stroke, but also in the opening and closing of valves several times during one cycle, at different points in time. Importantly, UniAir enables car engines to be downsized. Fiat uses UniAir in its four-cylinder Fire series of engines and in its small two-cylinder engines that are currently being developed.

Low friction engine components

Schaeffler has also been working with Porsche in a project to reduce friction in engine components and throughout the powertrain. Visitors to the recent ATZ/MTZ Congress in Esslingen, Germany, saw the CO2ncept-10% concept vehicle, which is based on the V8-engined Porsche Cayenne. In the joint development, Schaeffler was responsible for the design and testing of components, while Porsche managed system co-ordination and validation for the entire vehicle.

In the CO2ncept-10% concept vehicle the engine accounts for 5.8 per cent of the optimised fuel consumption and associated CO2 emissions. Most of this (4.1 per cent) comes from modification of the VarioCam Plus valve control system, by replacing hydraulic cam timers with electromechanical equivalents, as well as the use of optimised switching tappets on the intake side. An extra 1.7 per cent reduction is achieved through minimising frictional losses and by cross-system optimisation of the valve train, belt drive and chain drive components.

Schaeffler's double-row angular contact ball bearings, which are installed in the front and rear axle differentials, account for a further 1.1 per cent in fuel savings. Additional savings have been made via the chassis: by replacing the hydraulic roll stabiliser with an electromechanically controlled equivalent, and by using lower-friction wheel bearings to deliver a 3.2 per cent reduction in fuel consumption.

As a further example of friction-reduction technologies, NSK recently announced a low-torque bearing that offers a 50-60 per cent improvement in frictional losses compared to conventional bearings, thereby helping to improve fuel efficiency. It might have been assumed that it would be difficult to achieve further reductions in the torque loss of ball bearings beyond the current state of the art, yet NSK has achieved this by dramatically reducing the number of balls and by optimising the ball diameters, race dimensions and clearances. Losses have also been reduced by using specially shaped resin cages to agitate the lubricating oil during operation. This bearing technology will be adopted first by Toyota for its latest Prius, but NSK expects to see further sales to manufacturers of hybrid vehicles outside Japan.

Improving the efficiency of a vehicle when it is moving is clearly important but, when being driven in towns and cities, vehicles spend a considerable amount of time not moving. Start/stop technology has become available on standard production vehicles from a number of manufacturers, with typical start/stop systems delivering fuel consumption improvements in the range five to ten per cent, depending on the driving conditions. Nevertheless, the technology has not yet matured, which leaves research and development teams with plenty of scope for introducing enhancements.

An innovation from Valeo is the StARS (Starter Alternator Reversible System) micro-hybrid system that is said to offer emissions reductions of up 25 per cent in heavy urban traffic, with the benefit for automotive manufacturers of no radical changes being required to the engine architecture. In the latest development, SKF has supplied a new magnetic sensor bearing for StARS; this provides a powerful magnetic field that enables the bearing to function effectively under severe running conditions, including high temperatures and speeds. Furthermore, the accurate and repeatable magnetic field makes it possible to gather data on the speed and positioning of the shaft. Valeo's StARS technology is used in a number of vehicles, including Citroen's C2 and C3 Stop&Start models, the Smart Micro Hybrid Drive model, and the Mercedes-Benz A Class and B Class Blue Efficiency Models.

Further start-stop system innovations

Further stop/start innovations have recently been announced by Controlled Power Technologies (CPT). Following the launch of its earlier stop/start technology, the company has now developed a second-generation system that it says is more efficient and usable than the first-generation systems. This latest evolution integrates all of the power and control electronics into a single electric motor assembly and, by maximising the number of stop/start events, the system aims to reduce fuel consumption and CO2 emissions significantly. The fully developed system also meets manufacturers' requirements for a service life of 10 years or 250,000km (160,000miles), which is in line with automotive industry standards for major powertrain components.

To demonstrate the technology, CPT has installed its SpeedStart system in a Volvo S40 equipped with a 2.0-litre common rail diesel. Not only was the SpeedStart system more than capable of coping with this high-compression diesel engine, but restarts took around half the time taken by a conventional starter motor (0-750rpm in less than 0.4seconds against a typical time of 0.75seconds).

Operating with up to 86 per cent efficiency, which is significantly better than state-of-the-art conventional alternators, the SpeedStart system employs switched reluctance motor technology, thereby offering the advantages of simple construction, accurate control and very high power density and efficiency. The breakthrough, according to CPT, results in a system with the torque and power necessary to restart quickly, smoothly and more frequently, whether the engine in question is diesel or petrol. CPT senior manager Mike Dowsett comments: "Unlike existing systems SpeedStart allows the vehicle to remain in gear when the engine is stopped, which is more natural for the driver and facilitates a faster restart."

Fast-acting electric supercharger

SpeedStart also forms one element of CPT's power regeneration and engine-boosting concept (RegEnBoost). This concept integrates a Variable Torque Enhancement System (VTES) - which is a fast-acting electric supercharger - and an advanced Turbo-generator Integrated Gas Energy Recovery System known as Tigers. The three technologies are integrated within a powertrain electrical power network (PEPN) that also includes a dc-to-dc converter and an enhanced lead-acid battery that is optimised for fast energy storage and release. The combination of electronics, advanced battery technology and charging techniques ensures the system can deliver the required rapid charge and discharge performance while maintaining a stable 12volts for the vehicle's main electrical system.

The overall concept ensures long-term energy storage for delivering short bursts of power to the VTES supercharger during acceleration and to the SpeedStart stop-start device during engine restarts. Conversely, short bursts of power can be absorbed by the SpeedStart generator for recharging the battery during vehicle deceleration. Power for the battery and VTES electric supercharger is not only supplied by the SpeedStart integrated starter/generator (ISG) but also by the Tigers exhaust-driven turbo-generator. The electronic controls supervise the optimal switching between the SpeedStart and Tigers electrical generators according to the driving conditions and regenerative power availability.

CPT says the RegEnBoost system enables a typical family-sized car to achieve CO2 emissions of less than 100g/km with a 1-litre gasoline engine but, when required, the system can deliver the same performance and in-gear acceleration of a 2-litre naturally aspirated powertrain. This CO2 level is comparable to that of equivalent-sized full hybrid vehicles, yet it avoids the need for high voltages and the significant impact that a hybrid's large batteries and traction motors have on overall vehicle cost, mass and packaging.

Kinetic energy storage system

The cost and size implications of the battery pack is certainly one of the factors holding back hybridisation of vehicles, but a new technology developed by Ricardo could help. The company has devised Kinergy, a high-speed, hermetically-sealed flywheel kinetic energy storage system with an innovative and patented magnetic gearing and coupling mechanism. According to Ricardo, the high power density and long-life potential of its Kinergy technology combine both simplicity and effectiveness, avoiding the need for vacuum pumps and seals typically associated with high-speed flywheel systems based on carbon fibre. The lack of any mechanical coupling or other mechanical linkage through the system's casing makes the Kinergy system a highly robust, compact and lightweight package that is suitable both for incorporation in new designs and retrofitting to existing vehicle fleets.

The range of potential Kinergy applications is significant, not least due to its projected comparatively low production costs. The technology is therefore highly suitable for use in road vehicles where regenerative braking and torque assistance is employed as a means of improving efficiency - and hence reducing fuel consumption and CO2 emissions. Ricardo group technology director Neville Jackson comments: "Mechanical hybridisation using Kinergy-based systems offers the prospect of enabling a wide range of energy management solutions, including low-carbon vehicle powertrains for applications where electric hybridisation is not considered to be cost-effective."

Another technology offering potential benefits for hybrid vehicles is the Range Extender developed by Lotus Engineering. In a series hybrid vehicle, the Range Extender engine is attached to a generator and provides a highly efficient energy source to power the electric motor directly or charge the vehicle's battery. The battery can also power the electric motor, which enables the design of a drivetrain that has low emissions, optimised performance and acceptable range.

The Lotus Range Extender engine was developed as part of the Limo-Green project funded by the UK's Technology Strategy Board, which is a collaboration between Lotus Engineering, Jaguar Cars, MIRA and Caparo Vehicle Technologies, demonstrating a large, lightweight, prestigious executive saloon with less than 120g/km CO2 emissions. The Range Extender features an innovative aluminium monoblock construction that integrates the cylinder block, cylinder head and exhaust manifold in one casting. This results in reduced engine mass (56kg), assembly costs, package size and improved emissions and engine durability. With these characteristics, the engine certainly offers advantages for series hybrid drivetrain configurations.

The three-cylinder, 1.2-litre Range Extender's performance is optimised between two power generation points, giving 15kW of electrical power at 1500rpm and 35kW at 3500rpm via the integrated electrical generator. The engine uses an optimised two-valve port-fuel injection combustion system to reduce cost and mass and, in line with Lotus Engineering's extensive research into renewable fuels, can be operated on alcohol-based fuels or gasoline.

Simon Wood, technical director of Lotus Engineering, states: "Most series hybrid vehicles that are currently being developed will use adaptations of existing, conventional engines, which are therefore compromised in the efficiency that they can achieve, designed as they are for a wide range of operating conditions. Designing the Lotus Range Extender purely for use in series hybrids has allowed us instead to develop an optimised engine that has high thermal efficiency, low fuel consumption, multi-fuel capability and a 35kW peak output from a 1.2-litre, low-cost architecture over the precise operating range required by a series hybrid drivetrain."

Road trains: improving traffic flow?

Even highly efficient hybrid vehicles suffer losses when subjected to acceleration/deceleration cycles; the ideal would be to drive at a constant (preferably optimised) speed. As long as humans remain in control of individual vehicles there will be acceleration/deceleration cycles that could otherwise be avoided. One answer, therefore, is to use technology to take control of vehicles under certain favourable conditions. A new EU project Sartre (Safe Road Trains for the Environment) aims to develop and test technologies for vehicles that can drive themselves in road trains on motorways. As well as reducing fuel consumption and emissions, this has the potential to improve traffic flow and journey times, offer greater comfort to drivers and reduce accidents.

Test cars equipped with this technology are due to be driven on test tracks as early as 2011. These vehicles will be equipped with a navigation system and a transmitter/receiver unit that communicates with a lead vehicle. Since the system is built into the cars, there is no need for infrastructure along the road network. The idea is that each road train (or convoy or platoon) will have a lead vehicle that drives exactly as normal, with the driver retaining full control. This lead vehicle is driven by an experienced driver who is thoroughly familiar with the route - for instance, a taxi, bus or truck driver. Each road train will have six to eight vehicles.

A driver approaching his destination takes control of his own vehicle, leaves the convoy by exiting to the side and then continues alone to his destination. The other vehicles in the road train close the gap and continue on their way until the road train splits up.

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