August 2020 marked the first time Australia’s new-car market was dominated by a hybrid vehicle.
The popularity of the Toyota RAV4 hybrid has almost single-handedly driven curiosity in the burgeoning technology, with almost every major manufacturer exploring hybrid technology in some capacity.
But while 'hybrid' might be a catch-all phrase to describe a combination of two types of propulsion system (typically an internal-combustion engine and an electric motor with battery) hybrid cars themselves can take many forms. By the same measure, the term 'electrification' is also on the rise – not just to describe electric cars, but also hybrid systems.
Below, we break down the three main kinds of hybrid cars and how they vary from one another.
A plug-in hybrid car, or plug-in hybrid electric vehicle (PHEV) uses a combination of petrol engine and battery power, but benefits from an external source to be fully recharged.
PHEV cars have the benefit of being able to be driven exclusively on electric power, or with a mix of petrol and electric power, depending on the amount of charge you have left and the type of driving you’re doing.
“For many commuters, PHEV models can be the ideal solution for locally emission-free driving, because many daily routes can be covered in fully electric mode and thus with zero local emissions,” Audi explains of its own PHEV models.
“In addition, PHEV models are suitable for long-distance driving thanks to their petrol engines. Due to evolutionary leaps in battery capacities and powertrain management, electrical range has clearly increased in recent years.”
Very generally speaking, batteries in PHEV cars tend to range in size between 13kWh and 18kWh, offering around 40-60km of electric-only range. Once electric range is depleted, a PHEV will operate much like a regular hybrid.
Charging times vary greatly depending on battery size, vehicle and charging outlet but, as a guide, Audi's PHEVs (with 14.1kWh batteries) take two-and-a-half hours to fully charge on a 7.4kW AC charger, or six-and-a-half hours on a regular home wall socket.
Most will have some capacity to charge the battery using the combustion engine as an on-board generator, though doing so isn't the most efficient way to replenish the EV range.
BENEFITS: Able to be driven only on electric power, presence of petrol engine removes the risk of range anxiety, fuel consumption and CO2 emissions can be reduced.
DOWNSIDES: Must be charged externally for best results, pure-electric range isn't usually enough to carry you through a full week of driving, fuel economy can be higher than full hybrids when battery isn't charged.
Sometimes referred to as a self-charging hybrid or closed-loop hybrid, this configuration sees the electric motor and petrol engine work in tandem to power the car, without the need for external charging.
As a Toyota spokesperson explains: “In simple terms, hybrids use a combination of energy from a petrol engine and from a battery to move the vehicle.
"At low speeds the battery is generally used to power an electric motor which drives the wheels. When more power is required (that the battery can’t supply), the petrol engine seamlessly starts and supports.
“The engine is also able to drive the wheels of the car, but also charge the hybrid battery simultaneously so that when needed, the car can switch to EV mode and only use the batteries to move.”
The engine, plus the friction from something called ‘regenerative braking’, ensures you’ll never get a flat drive-system battery.
“In addition to the engine, a hybrid is able to capture energy that would otherwise be wasted in slowing down using regenerative braking to recharge the hybrid battery,” the Toyota spokesperson says.
“In this case of a self-charging hybrid, external 'plug-in power' is not required as the battery charges whilst being driven, either from the petrol engine or using captured energy from the car’s movement.”
However, this also means that full hybrids don’t offer a significant electric-only range of more than a kilometre or two, when driven sedately, and can typically only be driven solely on electric power up to a certain speed (usually 30km/h or less) – depending on the hybrid implementation, which may vary by brand.
This allows for various levels of operation: a combination of petrol and electric propulsion, electric propulsion only, or petrol propulsion only – full hybrids can shift between all three without driver intervention.
BENEFITS: Lower overall fuel economy, no need for external charging, no range anxiety.
DOWNSIDES: Can only be driven on purely electric power at very low speeds.
Currently less common in Australia but rising in popularity, particularly among premium brands, is the use of a ‘mild hybrid’ system.
This typically sees a small motor (typically 48-volt, but can be 12-volt or 24-volt) added to the powertrain to provide assistance to the internal combustion engine. Often this will be in the form of an integrated starter-generator, or ISG.
The key word here is ‘assistance’, as the electric motor in a mild hybrid can’t accelerate the car by itself and instead works to improve performance and efficiency.
It does this by acting much like an idle-stop system would at lower speeds – kicking in to cut off the ignition when the car is at a standstill or coasting and turning it back on when required.
At higher speeds, the motor is also able to assist by providing a boost to acceleration, and reducing the load that might otherwise be fully shouldered by the combustion energy.
Some mild-hybrids also utilise regenerative braking (the generator part of an ISG) to recoup some lost power as the vehicle slows down.
In a nutshell: “When compared with mild hybrids, the main difference [with a full hybrid] is that the two power sources within full hybrid cars operate entirely independently of each other,” a Toyota spokesperson explains.
BENEFITS: Can improve performance and fuel economy, smaller in scale and lower in cost than full hybrid.
DOWNSIDES: No pure-electric driving mode available.