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Is there a HYBRID in your future? By Ross Tester 6  Silicon Chip www.siliconchip.com.au With petrol prices approaching a dollar per litre in many areas of Australia, motorists are starting to think “alternative”. Immediately “electric” springs to mind but electric vehicles, especially cars, have yet to prove commercially viable. Now though, there is another alternative: the hybrid – a passenger car driven by both internal combustion (petrol) AND electric engines. Hybrids made quite a splash at October’s Sydney International Motor Show. T here were two (or was it three?) hybrid vehicles on display at the Sydney Exhibition Centre. We went there specifically to look at the hybrids. Toyota’s Prius was launched with much fanfare. Honda had their Insight there – but being a year old, it wasn’t given star treatment (in fact, it was almost undersold – I had to ask if it was actually there!). And since the show, I’ve discovered that there was a Toyota Tarago hybrid also on display – at least according to the Toyota PR people. OK, so what exactly is a hybrid vehicle? To be more accurate with the answer, we should say there are two different types of hybrids – series and parallel. Both are based on the same theme: motive power is provided by both hydrocarbon fuel (usually petrol) and electric engines. In a series hybrid, the whole of the fuel engine output is devoted to driving a generator, which in turn supplies the electric motor which turns the wheels. It’s a similar arrangement to a diesel-electric locomotive. The main difference is that in most series hybrid vehicles, there is also some form of battery storage which can power the vehicle independently of the fuel engine – to some degree, anyway. In a parallel hybrid, the fuel engine AND the electric motor can both drive the wheels. They share the load (pun intended!) according to the way the vehicle is being driven, ranging from 100% fuel engine and zero electric through to 100% electric and zero fuel. For a lot of the time, the proportions vary all over the place, under the management of one or several computers. Why not all-electric? As we mentioned before, while immense development has taken place around the world on 100% electric vehicles (ie, no fuel engine at all), there have been very few vehicles actually make it into production – and even fewer which have been commercial triumphs. In fact, the score to date hovers marginally above the zero mark! Why is this? Quite simply, it is very difficult – if not impossible – to cram enough battery capacity into a vehicle to come even close to the energy Above is the Honda Insight, while opposite is the Toyota Prius. Both are now available in Australia; both use a combination of petrol engine and electric motor. www.siliconchip.com.au December 2001  7 available from an equivalent volume, and especially weight, of hydrocarbon fuels – petrol, diesel, gas, etc. Then there is the matter of energy replenishment. Electric vehicles need their discharged batteries recharged (or swapped over) at even shorter intervals than you would normally fill your petrol tank. Usually, this means charging overnight. It also means you cannot wander too far away from a charger or source of power. While a jerry-can and funnel can get your petrol vehicle out of trouble out in the sticks within a few minutes, you’d need several hours and one mighty long extension cord for an electric vehicle! Range is also a problem: 250-300km is often quoted as the best that the very best electric vehicles can achieve (and then only under ideal conditions); most petrol/diesel cars can achieve double or even triple this. While huge advances have been made in batteries (and more recently fuel cells) they still simply cannot replace the easily-filled tank of fuel feeding an internal combustion engine. That’s not to say it won’t happen – somewhere down the track it (or another development) most certainly will. In fact, major manufacturers (including Toyota) are currently working on electric and fuel cell electric hybrid vehicles. The Honda’s engine looks much like other modern engines – until you get inside it! It’s actually two engines in one. But don’t hold your breath for something this year or even next. Toyota are talking “sometime in the next ten years . . .” Back to the hybrids . . . Honda and Toyota have taken quite different approaches to achieve quite similar results. We’ll look at the Honda Insight first, mainly because it has been around for the best part of a year. The Insight is based on the Honda Integrated Motor Assist (IMA) system. This combines a highly efficient one litre 3-cylinder lean-burn VTEC ULEV (ultra low emission vehicle) engine and ultrathin electric motor to produce 56kW of power. When we say “combines” we really mean it: an ultra-thin (60mm thick!) permanent-magnet electric motor is built into the engine, residing between the flywheel and the gearbox. Electricity for the motor is stored in a 144V, 6.5Ah nickel-metal hydride battery pack controlled by an advanced electronic Power Control Unit (PCU). You read that correctly: At left is a cutaway of the Honda hybrid engine – the blue parts are the petrol driven while the red are the electric. Above is a drawing of the 60mm wide 10kW electric motor. 8  Silicon Chip www.siliconchip.com.au It’s a very “conventional” looking dash and control layout, belieing the technology elsewhere in the car. The Honda has a 5-speed manual transmission. the battery pack is rated at only 6.5Ah and is in fact made up of 120 “D” cells! Power for the system is primarily sourced from regenerative braking, eliminating the need for an external power source for recharging. The battery pack, PCU and electronics package are hidden under a panel under the rear cargo area. The PCU ensures the battery can be neither overcharged nor overdischarged, resulting in much longer life than you’d normally expect from a NiMH unit. Design features combustion, low-emission engines, variable valve timing, high-efficiency electric motors, regenerative braking, nickel-metal hydride battery technology and microproccessor control help-ed engineers develop an efficient, lightweight and compact hybrid drive system. The Insight’s primary power source is a 1-litre, 12-valve, 3-cylinder VTEC-E petrol engine. Although the engine alone provides sufficient driving performance – even in sustained uphill driving – a permanent-magnet electric motor mounted between the engine and transmission provides additional power assistance under certain conditions, such as initial acceleration from a stop. The electric motor’s role as power assistance allows it to be made smaller and lighter compared with the fullsized traction motors in other hybrid systems. As the IMA petrol engine enters its mid-to-high-rpm operating range, the electric motor assist ceases and power is supplied solely by the engine, which is operating in its high-rpm 4-valve mode. Power for the electric motor comes mainly by recapturing energy from the forward momentum and braking of the vehicle, rather than from the petrol engine. When the Insight is coasting or the brakes are applied while the vehicle is in gear, its electric-assist motor becomes a generator, converting forward momentum into electrical energy. When a normal vehicle brakes, this energy is wasted as heat. But in the Insight, on light “braking” the brakes are not actually applied. Instead, regeneration slows the vehicle. Only on harder pressure do the brake pads actually contact the discs in the conventional way. IMA electric motor assist The ultra-thin 10kW DC brushless motor is highly efficient, light and compact. The IMA electric motor is capable of There are many innovations in the Insight design, not the least of which is its aluminium body, weighing 40% less than a comparable steel car but having 13% greater rigidity. The vehicle also has a very low coefficient of drag – 0.25 – which means it cuts through the air with minimal friction. Even the side mirrors and the skirts around the rear wheels have been designed for minimal drag and wind turbulence. The Insight features specially designed 165/65 R14 low-rolling resistance tyres, mounted on 14 X 5.5 JJ aluminium-alloy wheels, improving fuel efficiency by 6%. The tyres have 40% less rolling resistance and a 5% reduction in weight, compared with conventional tyres. The power plant Technologies such as lean-burn www.siliconchip.com.au The battery pack – consisting of 120 “D” cells – and the control unit hide under a panel roughly below the golf clubs. (The clubs are not standard equipment!). December 2001  9 providing high torque at low speeds, and assists the one-litre engine during low-rpm acceleration for increased efficiency during normal driving. The IMA’s central rotor is manufactured using the “lost wax” casting method to give a precise shape and high strength for a 20 per cent weight reduction. For the rotor magnet, Honda enhanced the neodymium magnet originally used in the Honda EV Plus for an improvement in magnetic flux density or torque ratio by 8%. This also improved heat resistance, eradicating any need for a cooling system. To create a thin motor, Honda used a simple structure including a split stator with compact salient-pole field winding and centralised bus ring, allowing a width of 60mm – 40% thinner than if conventional technologies were used. The motor also doubles as a generator for the IMA system and a high-rpm starter, quickly spinning the engine to its ideal speed. If the IMA system battery charge is low or in the case of extreme temperatures, a separate (conventional) 12V battery and starter motor will start the engine. The Honda Insight is not a cheap vehicle. At $52995 plus on-road costs it would take a lot of savings in petrol to make up the difference. And the recommended fuel for the Insight is the more expensive 95RON premium Toyota wanted to get in on the golf-bag act, too. . . but it does show just how roomy (and how “normal”) the Prius is. The little vents you can see behind the rear doors are battery/controller excess heat vents. unleaded. Fuel economy, by the way, is 3.6l/100km city cycle and 2.8l/100km highway cycle – very good in anyone’s language. Toyota Prius Again and again, the staff at the Motor Show kept emphasising just how “normal” the Prius was. Normal to look at, normal to get into and out of, normal to drive, normal in “just about” every way. And that’s how Toyota have marketed their new five-seat “baby”. Admittedly, they believe a significant proportion of their sales will be to new technology junkies and more than half will be sold to government and fleet buyers wanting to reduce running costs. But the rest, they believe, will buy the Prius because it is so normal. Like the Honda Insight, it has a very low drag coefficient (0.29) to help it slip through the air. Standard equipment includes dual SRS airbags, ABS brakes, front seatbelt pretensioners with force-limiters, power windows Under the lid of the Toyota things do look a little different to a conventional car engine bay. The petrol power plant is on the left while one of the Prius’ two electric motors can be seen on the right. Notice the heavy (red) power cables in the rear of the pic – they go off to the batteries and controller in the rear of the car. 10  Silicon Chip www.siliconchip.com.au and power mirrors, electric power steering and climate control air conditioning with an economy mode. There is only one “option” available for the Prius: an integral satellite navigation system, based on DVDs. Everything else (and the list is extensive) is built in. Oh, one other option – it comes in various colours! If it is so normal, what is different? Well, for a start, the Prius has not two engines but three. Petrol engine Main power is provided by an advanced 1.5-litre Atkinson Cycle, VVTi-equipped petrol engine which delivers 53kW of power at 4500rpm and 115Nm of torque at 4200rpm. An Atkinson Cycle engine, by the way, has smaller combustion chambers and a higher compression ratio than a conventional (or “Otto cycle”) engine. Compression ratio on the Prius powerplant is a whopping (for a petrol engine!) 13.5 – approaching that of diesel engines. The Atkinson cycle was proposed in the 1880s by English engineer James Atkinson, to enable the compression stroke and expansion stroke to be mechanically set independently of each other. The Atkinson cycle design makes better use of combustion energy by keeping the exhaust valves closed until the end of the expansion stroke. The expansion stroke is extended until the expansion pressure has virtually dissipated, converting more of the combustion energy into torque on the crankshaft. Toyota has combined the Atkinson cycle with a long-stroke engine design, offset crankshaft, direct ignition and variable valve timing with intelligence (VVTi), to further improve efficiency. The Hybrid System in Prius seam-lessly combines the power of this engine and a 33kW electric motor. In addition, the motor is part of the regenerative braking system. It converts the kinetic energy of the decelerating vehicle into electricity, for storage in the battery. Permanent-magnet generator The Toyota Hybrid System (THS) also has a high-efficiency AC permanent magnet synchronous generator, to run the electric motor and charge the battery. The generator also serves www.siliconchip.com.au Toyota have chosen a slightly different dash layout for the Prius. Of partic-ular interest is the centre console, shown enlarged at right, which contains the engine management touch screen showing the status and operation of the fuel and electric sections. This doubles as the screen for the only Prius option: a DVD-based satellite navigation system. Below this is a totally integrated entertainment system (including CD stacker). as a starter motor for the petrol engine. In addition, the THS system uses the generator to control the ratio of power distribution from the power-split device. Inverter/Converter Energy that is not required to propel the car is stored in a sealed 274V battery, for use when required. The inverter turns direct current from the battery into alternating current for the drive motor, and the converter takes alternating current from the generator and motor (in regenerative braking mode) into direct current for storage in the battery. Environmentally friendly The Prius uses up to 50% less petrol than an equivalent-sized conventional car and emits about half the carbon dioxide on a typical city drive cycle. The petrol engine automatically switches off when the car is stationary and going downhill. When moving off, initial power is provided by the electric motor but the petrol engine also starts automatically with a virtually seamless transition. Emissions of carbon monoxide, NOx and hydrocarbons are only one thirteenth of legislated maximum permissible levels and one fifth those of an equivalent sized conventional car. Actual consumption figures for the Prius are 4.6 l/100km city cycle and 4.2l/100km highway cycle – obviously not as good as the Honda Insight but the car is a lot cheaper! Continuously variable transmission Prius’ Toyota Hybrid System acts as an electronically controlled CVT, which can freely vary the engine speed. It achieves this by controlling the generator’s revolutions. Therefore, the vehicle does not need a conventional transmission. The power-split device operates December 2001  11 via a planetary gear system, in which the engine output shaft drives the planetary gear carrier and uses a set of pinion gears to simultaneously transmit power to the outer ring gear and the inner sun gear. The shaft of the outer ring gear connects directly to the electric motor and (through the drive shaft) to the reduction gears and hence the front wheels. The shaft of the sun gear drives the generator. The use of one set of planetary gears to achieve two roles provides a significant saving in weight and space under the bonnet, compared with either a traditional automatic transmission or a belt and pulley type CVT. There is no torque converter and hence no loss of energy through slippage in the driveline. The Toyota Prius is significantly cheaper than the Honda Insight at $39,990 plus on-road costs. It is fully imported and numbers available for Australia are quite limited: we were told each dealer can have a maximum of one Prius per month. Toyota Prius Vs Honda Insight Quick Comparison TOYOTA PRIUS HONDA INSIGHT Main Engine In-line 4 cylinder DOHC 4V In-line 3cyl SOHC VTEC Capacity 1497cc 995cc Maximum Power 53kW<at>4500rpm 56kw<at>5700rpm Maximum Torque 115nm<at>4200rpm 113nm<at>1500rpm Compression ratio 13.0:1 10.8:1 91 RON (unleaded) 95RON (PULP) 4.6l/100km 3.6l/100km Fuel Consumption - City cycle 2.8l/100km Permanent Magnet 33kW 10kW 274V 6.5Ah NiMH 144V 6.5Ah NiMH Electronic Continuously Variable 5 speed manual Electric Power Assisted Electric Power Steering 9.4m 10.2m 4315 x 1695 x 1485mm 3955 x 1695 x 1355mm 1250kg 827kg Steel Aluminium Output power Battery Transmission Steering Turning Circle Vehicle Size Weight Body Yes Yes ULEV standard ULEV standard Regenerative Braking Emissions Going for a drive . . . Auto engine shutoff on idle We didn’t get the opportunity to drive the Honda but we did drive the Toyota Prius, thanks to Bill Buckle Toyota who, as luck would have it, are just around the corner from the SILICON CHIP office. It takes a few minutes to get used to the Prius because it behaves differently to other cars. That’s not to say it behaves badly – far from it. It’s just “different”. One of the main differences is due to the continuously variable transmission. There is no change from one gear to the next. Similarly, there is no push-in-theseat acceleration, either. You plant your foot and you think it’s taking off rather sedately – until you glance at the speedo and you’re doing 80 in a 50 zone. Woops! Sorry, officer. But the major difference is in noise or, to be more correct, lack of it. Sitting at a set of lights you think “it’s stalled” which in truth it has – but deliberately so. Accelerate a little and you still hear virtually nothing. You are still hardpressed to hear anything even when the petrol engine starts. You certainly don’t feel anything except, perhaps, you are aware that you have more power available. The main reason you know that the engine has cut in is that the LCD touch- Price 12  Silicon Chip 4.2l/100km 2x high efficiency AC Consumption - Highway cycle Electric Motor(s) Warranty Yes Yes $39990 + ORC $52990 + ORC 3 years/100,000km 3 years/100,000km screen on the dashboard tells you so. We’ll look at little more closely at that LCD in a moment. Another thing that the LCD tells you is that power is being taken from, or supplied to, the batteries. Driving along, you are completely unaware what is powering what unless you look at that screen. Regenerative braking, where the electric motor becomes a generator and starts recharging the battery, occurs whenever you lift your foot off the accelerator or when you apply the brakes. Braking is quite normal, except for one thing. Most of the time the brake pads make no contact with the discs! All of the braking effort (and you can feel it) is courtesy of regenerative braking. Only in an emergency stop, or when you apply very hard pressure to the brake pedal, will the mechanical brakes actually come into play. If you’re travelling down a long hill, you can move the gear lever to “B” and the engine forcibly brakes the vehicle all the way down, supplying electricity (and cutting off the fuel engine) as it does, without you touching the brake pedal. Toyota maintain that brake pad wear will be a tiny fraction of a normal vehicle and tyre wear should also be way down. It is virtually impossible to “chuck a wheelie.” We mentioned before the touchscreen LCD panel. As well as giving a huge range of information about the vehicle and being the input device for a lot of user settings (eg, radio, air con, etc), it also doubles as the display for the optional $3800 satellite navigation system. I have to confess, techno junkie that I am, this was the thing that tickled my fancy most of all (forget the impressive range of technology I was driving . . .). It tells you exactly where you are, where you are going, how to get there, even how to un-stuff a stuff-up (like when it tells you to turn left and you turn right instead!). It could even direct me right to my door (and those who know where my home is hidden will be mightily surprised at that!). Just in case you couldn’t tell, I’m impressed with the Prius. SC www.siliconchip.com.au