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The GM Silverado/Sierra hybrid is a full-sized pickup truck. Unlike the Toyota Crown, it doesn’t use an electric motor as a traction motor or for mechanically powering accessories when the engine is not running. Instead, it uses a conventional 5.3-litre V8 and 4-speed automatic transmission with a 14kW, 3-phase induction AC starter/ generator sandwiched between the transmission and the engine. Energy storage is by a 36V lead-acid battery. [GM] The New Era in Car Electrical Systems The first cars using the new 42V standard are now being released. So why the move from 12V and what are the implications for the design of higher voltage car electrical systems? By JULIAN EDGAR B ACK IN OUR JULY 2000 issue, we briefly looked at the way in which vehicle electrical systems are changing. The use of high-output alternators and 42V electrical systems were being mooted as technical solutions to the ever-increasing electrical power demands in cars. What’s happened since? Well, in a few words – a lot! Toyota in Japan currently sells a car with a 42V electrical system, while GM in the US is this year releasing a 42V pickup truck – and some organisations are already using pre-delivery vehicles. New technical standards are being developed to cover everything from 42V battery terminal and fuse 20  Silicon Chip design to the colour-coding of 42V wiring. Automotive component suppliers have developed 42V alternators, starter motors, circuit breakers and other components. Some are predicting that by 2010 as many as half of all vehicles will use 42V electrical systems. In 20 years, the forecasts suggest that all cars will use this voltage. Even more interesting is the relationship developing between “mild” petrol/electric hybrids and 42V electrical systems. Throw in the increasing availability of mains power in cars (yes, that’s right – in the USA you can now have a factory-fitted mains power socket in your car!) and the whole area of car electrical systems is undergoing a change of a magnitude never seen before. Power-hungry cars The trends in automotive technology can be summarised as: • Better fuel economy • Reduced exhaust emissions • Improved safety • Better comfort and convenienc Each of these has implications for the load placed on car electrical systems. For example, improvements in fuel economy can be gained by applying systems such as automatic engine stop/start capabilities, electricallyassisted acceleration from a standstill, electric engine cooling pumps and fans, and electric power steering and air-conditioning. Also being thoroughly investigated is the electromechanical operation of engine valves. While it could bring about significant increases in engine power and efficiency, this approach looks likely to be electrically power hungry, with estimates of up to 2.4kW peak loads on a six-cylinder engine. siliconchip.com.au Table 1 • • • • • Daimler Chrysler Renault/Nissan General Motors Peugeot/Citroen Ford • • • • • Fiat BMW Toyota VW/Audi Honda Car manufacturers in North America, Europe and Japan currently developing 42V cars Reductions in emissions can come from electrically heated catalytic converters (some cars already have these), while dynamic safety can be improved by the use of active electric power steering, active suspension and high-powered electric de-icing of glass. Finally, increasing comfort and convenience can lead to the use of electrically heated and cooled seats, electrically heated steering wheels, high-end sound systems, in-car computers, navigation systems and the provision of mains-power sockets. Even without including electrical propulsion, components supplier Delphi expects the growth in electrical loads in cars to be 5% per year over the next 20 years. If electric propulsion is included, that estimate rises to 8% per year. Fig.1 shows the past and estimated future increases in car power demands. The consumer acceptance of the latest model Toyota Prius – this year Toyota expects to sell 50,000 in the USA alone – has given car manufacturers the confidence to start thinking seriously about incorporating electricassist into otherwise conventional designs. These so-called “mild hybrids” use electric assistance only in certain conditions. For example, in a mild hybrid, the petrol engine is turned off whenever the vehicle is stationary. The electric motor then helps the car accelerate as the petrol engine re-starts. The gains in fuel economy are not as great as in high-voltage full hybrids but the manufacturing and development costs are much lower. This acceptance of mild hybrids makes the rate of growth in electrical power demand likely to be close to Delphi’s 8% per year estimate. 42V systems Prior to 1955, vehicles used 6V elecsiliconchip.com.au Fig.1: past and estimated future increases in car power demands (note the logarithmic vertical axis). The massive increase in electrical power loads is seeing a move to 42V systems. [Delphi] ACCESSORIES BELT STARTER (INITIAL START) PULLEY MAGNETIC CLUTCH ENGINE GEAR MOTOR/GENERATOR (MG) INVERTER 36V BATTERY DC/DC CONVERTER DRIVE WHEELS 12V BATTERY ECU CONTROL UNIT Fig.2: the mild hybrid Toyota Crown is the first car in the world to feature the new 42V standard. It uses a 3kW 3-phase AC synchronous motor/ generator in conjunction with a 147kW petrol engine. The transmission is a conventional 5-speed automatic. The motor/generator, which is larger than a conventional starter motor but not as large as the traction motor used in a full hybrid, charges a 20Ah 36V battery via a water-cooled inverter. [Toyota] trical systems. However, recognition in the US that higher ignition energy would be required for the high compression V8s then being introduced prompted the adoption of a higher voltage system. In addition, the introduction of higher power headlights, radios and higher-powered starter motors were all showing the limitations of the 6V system. 12V systems – using 13.8V regulation – were then introduced, with most manufacturers achieving the transition within two years. November 2004  21 STARTER MOTOR/ GENERATOR CONTROL UNIT 12V BATTERY OIL PUMP 36V BATTERY Fig.3: in the Toyota Crown, the 12V battery is charged via a DC/DC converter and the 36V battery from the generator inverter. Both batteries are mounted over the rear axle of the car in the forward section of the boot. [Toyota] 36V VALVE REGULATED LEAD ACID BATTERY INVERTER, ECU DC-DC CONVERTER MG AT OIL PUMP ELECTROMAGNETIC CLUTCH Fig.4: the use of an electromagnetic clutch allows the Toyota’s motor/generator (MG) to drive the accessory belt even when the engine is off. By engaging the clutch, the motor generator can start the engine and even help propel the car. [Toyota] The increasing power demand of current cars has now caused a similar situation to develop – a higher voltage is needed. However, the situation isn’t quite the same – there are far more devices of vastly greater sophistication working on the current 12V standard than there were working on 22  Silicon Chip 6V in 1955. The new standard is termed a 42V system. That is, battery voltage is 36V with the bus regulated at 42V. Basing the standard on the 42V running-car voltage, rather than the 36V lead-acid battery voltage, was done to cater for future developments that might displace lead-acid batteries and traditional charging systems. One benefit of increasing the voltage to 42V is a reduction in wiring gauges. A current mid-size car has a wiring loom that weighs 35kg or more and contains 2km of wire, 1000 cut leads and 300 connectors. With the potential for loads of many kilowatts (the catalytic converter heating in the BMW 750iL requires a short-term power of 17kW!), the current flow required at 13.8V becomes very high indeed. As a result, conductor sizes are large, adding cost and weight. Increasing the voltage reduces the current flow and so smaller conductors can be used. In addition to reducing conductor size, adopting a 42V standard allows the development of powerful combined starter/generators, more compact and powerful electric motors, and other actuators that are smaller, have a lower mass and improved performance. Table 3 shows some of the benefits of adopting 42V systems. Another advantage of the higher voltage is in the field of semiconductors. The cost of semiconductor switches, which are expected to be used very widely in cars, depends on the current and voltage ratings of the device. The current-handling capability is related to the semiconductor’s area, while the voltage rating is tied to the device’s thickness and doping profile. A reduction in required current capability results in a smaller chip area, decreasing costs. For example, an electric powersteering controller may need to handle a power of 600W. At 14V with an assumed electronic efficiency of 85%, the switch is required to handle 50A. However, at 42V the required current handling drops to less than 17A, reducing the cost of the powerdependent components by 60%. But why just 42V? If reductions in conductor and electric motor size are the criteria, why not use 500V, say, as does the current model Toyota Prius? There was widespread consensus that the new voltage standard should be sufficiently low to ensure the personal safety of those that come in contact with it. During the development of the new standard, the Society of Automotive Engineers performed an in-depth study of the research that had been carried out on human tolerance to electrical shocks. The society concluded that protection against direct contact siliconchip.com.au Toyota Crown Running Modes The petrol engine switches off whenever the car is stationary. On restart, the electric motor/generator drives the car and starts the engine. In normal driving the petrol engine propels the vehicle. If battery charge is low, the electric motor/generator is used to charge the battery. During braking or any other time that the fuel supply to the engine is cut, the electric motor/generator regeneratively brakes and so charges the battery. When the vehicle is stopped, the engine is turned off and the electric motor/generator powers the accessories such as the air-conditioning compressor. [Toyota] was not required if the voltage did not exceed 65V DC, including ripple. Subsequently, the German standards body VDE reduced this to 60V. The specification of 42V systems suggests that a maximum bus voltage of 55V is permitted during dynamic overvoltage conditions. Table 1 shows car manufacturers in North America, Europe and Japan currently developing 42V cars, while Table 2 lists the automotive component suppliers currently developing 42V components. The first 42V cars The first two cars featuring 42V technology are mild hybrids that run dual 12/42V electrical systems. The Toyota Crown mild hybrid has been produced in small numbers in Japan siliconchip.com.au since 2001 and initial deliveries of the General Motors Silverado/Sierra hybrid twins are occurring now, with full sales to begin later this year. (1). The Toyota Crown Mild Hybrid: the Crown uses what Toyota dubs a “Toyota Hybrid System – Mild”, or THS-M. Fig.2 shows its layout. A belt-driven motor/generator comprising a 3kW 3-phase AC synchronous motor is used in conjunction with a 147kW 3-litre in-line 6-cylinder petrol engine. The transmission is a conventional 5-speed automatic. The motor/generator, which is larger than a conventional starter motor but not as large as the traction motor used in a full hybrid, charges a 20Ah 36V battery via a water-cooled inverter. The motor/generator is used to: • restart the stopped engine (initial starting is by a conventional 12V starter motor). • help drive the vehicle when moving away from a standstill. • generate all electrical power. • provide regenerative braking on deceleration. • drive engine auxiliaries when the engine is stopped. The 12V battery is charged via a DC/DC converter. Both batteries are mounted over the rear axle of the car in the forward section of the boot (Fig.3). The motor/generator, which is located where a conventional belt-driven alternator normally would be, is able to drive the accessories with the petrol engine stopped because in this mode a magnetic clutch is used to decouple the accessory belt drive system from the engine. November 2004  23 Just some of the parts developed for the mild hybrid Toyota Crown (clockwise from top left): the engine; 36V battery; inverter & electronic control unit; and electric motor/generator. Fig.4 shows an overview of the engine bay. In stop/start urban conditions, fuel consumption is improved by about 15%. (2). GM Silverado/Sierra hybrid the GM Silverado/Sierra hybrid is a full-sized pick-up truck. Unlike the Toyota Crown, the GM mild hybrid does not use the electric motor as a traction motor or for mechanically powering accessories when the engine is not running. It uses a conventional 5.3-litre V8 and 4-speed automatic transmission – the design criteria required that an existing GM engine be used and that the transmission had only minor modifications for its new hybrid vehicle role. Overall driveline length also needed to remain the same as non-hybrid versions. In order that these criteria could be met, the starter/generator (GM call it simply the ‘electric machine’ - EM) is inserted between the engine and the transmission, with the torque converter being reduced in diameter to create the space. To overcome problems of excessive heat resulting from a smaller torque converter, the transmission control strategy is revised to allow Table 2 • • • • • • • • • Bosch Motoral SPS Aisin Motoral AIEG Continental Teves Siemens VDO Delco Remy America Infineon Delphi Table 1 •• Daimler • Yazaki Chrysler •• Renault/Nissan • Denso •• General Motors • Valeo •• Peugeot/Citroen JCI (Johnson Controls)• •• Ford • Visteon Fiat BMW Toyota VW/Audi Honda • Lear Car manufacturers in North America, Europe and Japan currently developing • Varta 42V cars • Magneti Marelli Some of the automotive component suppliers currently developing 42V components. Delphi, for example, state that they can now provide a complete 42V generation, conversion, storage, distribution and usage system. 24  Silicon Chip earlier-lock-up of the torque converter clutch. The EM is then used to reduce poor driveability resulting from this early lock-up. The EM is a 14kW, 3-phase induction motor. The rotor is bolted to the engine’s crankshaft and surrounds the torque converter. This approach allows the crankshaft’s bearings to support the rotor. The stator is located around the rotor and is supported by an assembly positioned by existing dowels projecting from the rear of the engine block. It is clamped between the transmission and the engine. The stator is watercooled via a thermostat-controlled feed from the engine coolant system. Changes made to the transmission included the use of a unique bellhousing and flex-plate and an alteration to the hydraulic valve body that allows the transmission to drive the engine (and so the EM) on over-run in second and third gears. In addition, a small electric pump is used to provide hydraulic pressure within the transmission until the transmission pump is rotating quickly enough to provide normal working pressures. The GM mild hybrid uses these strategies to reduce fuel consumption: • deceleration fuel cut-off much more frequently used, with the EM smoothing the resulting torque fluctuations. • automatic engine stop during stationary and very low speed vehicle operations. • lower speed torque converter lockup clutch engagement. • regenerative braking. A 42V electro-hydraulic power steering pump replaces the traditional engine-driven unit, while air conditioning requirements with the engine stopped are met by “careful management of refrigerant capacity already in the system prior to the stop”. The traditional starter motor is deleted. 42V challenges The change in such a universal and long-standing car standard as 12V has some major challenges – technical and financial. Taking the latter first, why should customers feel any urge to pay more for a car that has a 42V electrical system? General Motors puts it like this: “A 42V system is only an enabler. It is not something that consumers will be willing to pay for directly – so it absolutely must deliver the capabilisiliconchip.com.au MAINS OUTLETS General Motors see the inclusion of 110VAC power sockets in their mild hybrid pick-up truck as a major selling point of hybrid technology. The circuits are protected by ground fault detection and up to 14kW is available. ties and features that customers desire and value.” The company suggests examples of such customer-desirable features are mains-power outlets, new entertainment systems, electrically heated windscreens, fast heating and cooling systems and “by-wire” chassis and engine controls. They also suggest the thinner wiring looms and smaller components will provide space for more features likely to appeal to the consumer. The fuel economy achieved by 42V combined starter/generator systems will also have immediate consumer appeal. It’s for customer justification reasons that GM has highlighted the availability of mains power (there are four outlets!) in its promotion of the Silverado/Sierra hybrid. General Motors delivered its first hybrid pick-up truck on May 3, 2004. The mild hybrid uses a combined electric motor/generator and boasts 10-12% improved fuel economy. The car is only the second to use the new 42V standard. [GM] 12V/42V possibilities What about cars where a 42V electrical system is introduced in conventional engine form? As with the two hybrid cars that we’ve looked at, it’s very likely that cars will continue to have both 42V and 12V systems for some time to come. In fact, it is suggested that incandescent lighting will stay at 12V because of bulb durability issues associated with the automotive use of higher voltages. Three 12V/42V architectures are likely to be used: • Single voltage generation and single voltage energy storage – a 42V alternator charges a 36V battery which services 36V loads, with a DC/DC converter used to charge a 12V battery siliconchip.com.au The GM mild hybrid control system incorporates an inverter to generate 110VAC mains power (four mains power outlets are provided on the truck), a DC/DC converter to operate the 12V loads and an inverter that operates the starter/generator. [GM] that services 12V loads; • Dual voltage generation and single voltage energy storage – a dual 14V/42V alternator charges two separate systems, one 12V and the other 36V; • Dual voltage generation and dual voltage energy storage – a dual 14V/42V alternator charges a dual 12/36V battery. In all cases the inclusion of 42V car systems poses challenges in controlNovember 2004  25 Table 3 Current Technology Benefits of 42V Architecture Electric power steering More power, improved fuel economy Electric brakes Redundant power supplies Power windows, power seats, power hatchback lifts Reduced size and mass of motors; more efficient operation Heated catalytic converter Lower emissions; quicker light-off time Heating, ventilation, air-conditioning blower motors and cooling fans Greater efficiency; smaller/lighter units; flexible packaging Mobile multimedia More power available for video, mobile phones, navigation systems, audio amplifiers, fax machines Water pumps Improved efficiency; longer service life Selected engine management system components (eg, exhaust gas recirculation valves, ignition systems, control actuators) Reduced size and mass; increased performance Fuel pumps Reduced size and mass Heated seats Faster heating, more efficient operation; increased power The benefits to current automotive electrical technology of adopting a 42V system. [Delphi] ling arcing and corrosion, especially in the presence of contaminants like salt water. (An example? – consider a boat trailer’s electrical system that can be under water quite frequently!) Another “real-world” problem is the use of jumper leads. To prevent people with 42V cars attempting to jump-start 12V vehicles, 42V vehicles will have non-accessible batteries and use a dedicated jump-starting connection with a unique, fused connector. 42V jumper leads will be specific to the application and incorporate microprocessor control. One proposal sees the use of 42V jumper-leads occurring in the following manner: • Connect terminations to each car or car and boost pack. • Units activates (wakes up) and checks polarity – both LEDs flash. • LED flashes red if either or both batteries are reversed. • Low current circuit is activated and checks for conductivity. • If all is OK then green LED flashes. • Switch is pushed and internal relay is activated – green LED on. • Relay is opened if either battery is disconnected – green LED flashes. • If both batteries are below 36V or either battery is below 18V, relay will Super-Capacitors For 42V Systems Super-capacitors suitable for 42V automotive systems are being developed. These capacitors can be used to meet peak loads and then be recharged over a period from an existing battery or at a fast rate through regenerative braking. A 10kJ, 42V super-capacitor has sufficient energy to operate the combined starter/generator of the 5.7-litre V8 GM Silverado/Sierra hybrid for two consecutive engine starts (the engine starts in 0.3–0.5 seconds). Compared with a lead-acid battery, a combined super-capacitor-battery prolongs battery service life with its ability to handle high recharge/discharge events typical of a mild hybrid car. However, at this stage super-capacitor costs remain high when compared with traditional battery technology. 26  Silicon Chip Suppliers have already developed a complete range of 42V automotive components. Here are two 42V compatible bimetallic circuit breakers, available in 5 - 30 amp ratings. [First Technology] not activate – red LED on. Fuses also need redesigning. Testing was carried out of normal 12V blade-type fuses on 42V and it was discovered that when subjected to overload, terminals could melt away (probably through arcing) and the plastic fuse housing was subjected to intense heat, resulting in carbonisation and melting. New 42V fuses use polyamide housings and feature a slightly different shape to 12V fuses, preventing 12V/42V fuse inter-changeability. Circuit breakers suitable for 42V operation are already available. Wiring standards also need to be upgraded. The current proposal is that all 42V wiring is coloured amber. Because of the potential problems of arcing, all 42V terminal connections will need to be correctly seated and locked. More sealed connectors will be used. Note that not all wiring will be reduced in conductor size – in many cases those wires that are 0.35mm2 will remain that size even when working on 42V, as this is the minimum size for mechanical durability. Conclusion While it was initially thought that the first 42V cars would be luxury cars with very high electrical power loads, mild hybrids have beaten them to the punch. In addition, a report that Daimler Chrysler has put 42V system development on hold appears to be a temporary setback for that company. However, over the next few years a wide range of cars will appear with 12V/42V systems and as they become common, it won’t be long before dediSC cated 42V cars appear. siliconchip.com.au