The most frequent hybrid cars are petrol-electric, like the Prius. In addition, there are actually one or two high-torque electric motor-generators, although petrol-electric hybrid cars work with a normal petrol engine, just like you’d discover in any other car. The motor-generator(s) draw power from a bunch of car batteries stored either in the floorpan of your car (for a low centre of gravity) or in the rear (for convenience). With power supplied to the motor-generator, it behaves just like an electric motor. When no power is supplied but the shaft is turning, it becomes a generator to create power. In this mode, you get regenerative braking, the location where the energy expected to slow the car down is perhaps all taken up in the motor-generator to re-charge the battery packs. Both the petrol engine and also the motor-generator(s) are associated with an onboard computer system which has been programmed by men in white coats to work as efficiently as you possibly can. There are three mainstream technologies in the hybrid market during the time of writing, each championed from a different company or band of companies. Note: Hybrid drives can be the standard drivetrains from front wheel only to 4-wheel drive, although the diagrams below all show rear wheel drive for comfort of explanation.
IMA – integrated motor assist (Honda)
honda hybridHonda Integrated motor assist hybrid drivetrain
The motor-generator (electric motor and regenerative generator) is in-line with all the petrol engine, typically built in the bell-housing in front of the gearbox. The motor-generator is used to support the petrol engine, thus reducing the load on it and allowing it to be smaller than it might otherwise be for a vehicle of the same weight. For example the Civic hybrid uses a 1.3l engine in which the non-hybrid utilizes a 1.8l engine. The motor-generator cannot turn without turning the petrol engine too. First, generation systems didn’t have enough power to be able to run the car on electric alone. Current generation ones do through higher powered motors and the cabability to shutoff the petrol engine when coasting. The regenerative braking works very simply – while you start to brake, the motor becomes the generator, because the motor-generator is within-line. Conversely additionally it is used as being the primary starter motor for spinning the petrol engine up quickly after it has been switched off, for example at traffic lights. There is also a backup ‘regular’ starter motor for cold-starts and emergencies. From the three mainstream hybrid technologies, IMA is undoubtedly the simplest to implement, maintain and repair. In the following images, red is the battery pack, green is motor-generator 1 and blue or purple is motor-generator 2.
Hybrid Synergy Drive (Toyota)
toyota hybridToyota Hybrid Synergy Drive
Toyota’s take on hybrid drive has a pair of motor-generators, one in-line much like the Honda IMA design, one not. The important thing to its success is the compound planetary gearset in the transmission. In the Toyota system, the petrol engine and one motor-generator are connected to one of the inputs, the second motor-generator to the second input as well as the wheels for the third. Via a clever consumption of electronics, the planetary gearbox can be locked and unlocked in various configurations dependent on what is required. As an example under modest acceleration, the petrol engine drives the planetary gearbox as well as the first motor-generator. The output from that is fed to the second motor-generator combined with the output from your gearbox to get the wheels. In pure electric mode, the first motor-generator freewheels, the petrol engine is switched off and all the electrical power is fed on the second motor-generator. Under regenerative braking the 2nd motor-generator becomes the generator as it does in the IMA system above. The difference is when the battery pack is full, the energy derived from the second motor-generator is redirected to the first motor-generator which uses it to induce drag from the petrol engine to slow the vehicle down. Consequently, the actual brakes in a Toyota Hybrid car do not wear very quickly at all because most of the braking is supplied by the motor-generators. Only in severe cases perform the brake pads actually engage the brake rotors. This can be all made possible by the central engine computer and throttle-by-wire / brake-by-wire system.
Dual-mode or 2-mode Hybrid (GM).
2 mode hybridGM 2-mode Hybrid drivetrain
The third hybrid system originates from GM and has two operating modes as oppose on the single mode of IMA or HSD. It again uses two motor-generators. In second and first gears, the first motor-generator sends capacity to the second motor-generator, and that coupled with the petrol engine supply the power to the wheels. In higher gears or under heavier loads, the petrol engine always runs (as oppose to the IMA and HSD systems where it may be turned off or have cylinders deactivated). The main difference is in exactly how the motor-generators function in cooperation from it. The first motor-generator gets to the point where it’s providing no useable input towards the drivetrain, as speed increases. At this point it begins to freewheel as well as the second motor-generator begins to act as a generator. The initial motor-generator starts to act as a generator again and at this stage its power is once more fed towards the second motor-generator which now becomes a motor, as speed increases further. Coupled with variable intake timing, direct common-rail injection and a host of other technologies, all of these come together to offer GM’s take on hybrid technology.
toyota prius energy display
Most hybrids have an energy display screen mounted either in the instrument cluster or in the centre console. This is a small LCD which supplies you, the motorist, information about what mode you’re driving in, and in which the power goes. Again, by far the most recognisable and famous of such displays currently is that from your Toyota Prius (see right). The only real issue with these displays is the fascination they provide to the novice hybrid driver. Watching the animations spin around and the energy arrows scroll here and there as you drive is unquestionably informative yet not really conducive to safe driving. One benefit however is the constantly-updated gas-mileage chart. Many Prius owners are convinced that this spurs them to try to get videogame-like high scores in their cars, driving them in such a fashion as to get the highest recorded mpg from their cars. If nothing else, the vitality display affects most drivers in terms of educating them concerning how their driving style directly impacts their gas-mileage.
The battery question
The estimated lifespan for your batteries within a hybrid car is about seven years before they need to be swapped out, at the time of writing. The expense of doing this for that Toyota hybrids is now about US$3,000 which is a sizeable chunk of change (although a lot less than it was originally). The first theory was that you would have driven enough distance to recoup the extra cost via fuel savings but with the cost of petrol where it is now, that is becoming harder and harder to obtain. So, far there hasn’t been a large recall for batteries for any one of the hybrid manufacturers and I’ve not yet heard about anyone kicking up a stink concerning the cost. It means one of three things. (1) The batteries are lasting longer than expected, so people haven’t had to swap them out yet. (2) They’re paying the money but nobody has complained in the press. (3) The manufacturers are doing it free once and for all publicity.