Demand for plug-in hybrid vehicles (PHEVs) has surged over the past few years, and there are now more than 40,000 such vehicles on the roads. PHEVs offer excellent flexibility – featuring the benefits of a battery electric vehicle’s motor combined with the range of a petrol or diesel engine.
And the numbers are only set to increase. In 2020, PHEVs are expected to hit the one million mark, led by increasingly stringent carbon dioxide emissions deadlines set by governments, as well as a rise in customer demand for efficiency. Consumers are now beginning to rely on hybrids for day-to-day use. As well as using them to meet their efficiency needs, they also want them to provide the performance and driving pleasure of a regular combustion-engine car.
However, only 35% of the owners of hybrids then go on to buy another hybrid, a recent study by Michigan research firm Polk has discovered. Removing the most popular hybrid, the Toyota Prius, from the mix, consumer commitment to hybrids drops to 25%, so 75% of non-Prius hybrid customers choose to ditch the hybrid after their first hybrid purchase.
Part of the reason for this, claims Ray Kuczera, vice-president of global product technology at GKN Driveline, is that the performance of hybrid vehicles is just not up to scratch. “One of the interesting trends we have seen is the emergence of a fuel economy war where the industry is trying to meet the requirements for fuel economy and CO2 emissions, but there is also a horsepower war,” he says.
Because hybrid cars have twin-powered engines, the petrol engine that is the primary source of power is much smaller than that in a single-engine powered car, and the electric motor is low-power. “The combined power of both is often less than that of a gas [petrol]-powered engine, which just doesn’t meet consumer needs for car performance,” says Kuczera.
Performance focus
GKN is experiencing demand from OEMs to make their vehicles more exciting to drive as well as being more efficient, says Andreas Mair, the supplier’s senior director for electric drive (eDrive) product technology. However, the company cannot achieve this through just the internal combustion engine, so it has to do it using hybridisation and electric engines, he says. “More and more, we are seeing OEMs that are really using the performance aspect of this, too. In the past, when you thought of a hybrid vehicle, you thought of a Toyota Prius. While it is a great vehicle, it is not something you’d consider fun to drive or exciting. Now they’re trying to use the power from electric motors to make the vehicle more efficient, consume less fuel and emit less CO2, but also exciting to drive,” says Mair.
Axle energy
To tackle this problem, the company has been working on eDrive technologies for automotive OEMs that are seeking to fit their hybrids with new driveline concepts. Current mass-production vehicle platforms can draw only around 30% of their energy from a battery. But on future vehicles, GKN expects small, powerful, torque-vectoring electric axles will deliver 60-70% of the power. It recently produced what it says is the industry’s first two-speed electric drive axle (eAxle), which can deliver electric power throughout a vehicle’s entire speed range.
The technology is an evolution of the system the company designed for the Porsche 918 Spyder. The single-speed system minimises weight to 20.9kg while optimising efficiency, installation space and costs for mass-market vehicle applications. A two-staged gear train with a gear ratio of 12.5 provides up to 2,000Nm torque and 65kW power in pure-electric mode, and balanced wheel torque in all-wheel drive mode. The technology can also improve 0-100km/h acceleration times by several seconds, provide a usable pure-electric range, and reduce a vehicle’s CO2 emission rating to less than 50g/km.
The eAxle technology is being launched on the new Volvo XC90 T8 twin-engine plug-in hybrid SUV, and is the world’s first disconnecting eAxle on a premium SUV.
“The technology allows the vehicle to be transformed into an all-wheel drive from front-wheel drive, as well as being a hybrid,” says Mair. “This allows for much more horsepower, driving excitement, and low-end power for taking off in traction. If you compare the overall power from the hybrid version to the Volvo XC90, it’s much more than the conventional drivetrain. This means the car can take advantage of the fuel efficiency and the great-to-drive factor, meaning OEMs can leap ahead of their competitors in the horsepower war but also remain competitive in the CO2 reduction war.”
Another recent GKN eDrive development is an electric drive system that aims to make hybrid vehicles more efficient and dynamic. The plug-in hybrid module, eTwinster, makes it simpler for vehicle platforms to offer electric all-wheel drive and torque vectoring.
The driveline combines the eAxle technologies – proven in the Volvo XC90 T8 twin-engine, Porsche 918 Spyder and BMW i8 plug-in hybrids – and the twin-clutch torque-vectoring technology that features in the Ford Focus RS and Range Rover Evoque.
“Our eTwinster is part of our range of eDrive technologies that GKN is developing to help shift the balance of power from engines to batteries in the next decade,” says Kuczera.
Petrol power
OEMs are also using driveline technologies to enhance the performance of their hybrid models for customers. Mitsubishi’s Outlander PHEV leads the UK market as the most popular plug-in. Its petrol engine operates as a generator, supplying electricity to the battery, which in turn powers the motors. This is a highly efficient use of fuel and occurs when the battery charge falls below a predetermined level or when more powerful performance is required, such as when overtaking, or climbing a hill.
Another OEM working on bringing performance hybrid technology to market is Infiniti, which has released several performance-enhancing technologies –Direct Adaptive Steering, Dynamic Digital Suspension and Drive Mode Selector – on its new Q50 PHEV. “We have made the Q50 even better by offering new and stand-out technologies,” says Francois Bancon, Infiniti’s vice-president of
product strategy.
The model incorporates an advanced twin-turbo system, which contributes to smooth and immediate power delivery while promoting gains in efficiency. A new turbine speed sensor and an optimised turbine blade design combine to provide greater performance with a more immediate response. The turbine speed sensor allows a 10% increase in turbine speeds, enabling the turbocharger to revolve at up to 220,000rpm. With greater capacity for faster revolutions, the twin turbochargers enable the engine to deliver greater power and torque.
“Advanced valve timing control, incorporating a new electric motor mounted to the valve timing system, delivers quicker reactions to driver inputs” says Bancon.
“Along with improved response, more immediate valve timing also helps the engine operate more efficiently, precisely controlling fuel and air quantities entering the combustion chamber.”
Motor evolution
By 2025, GKN expects that 40% of vehicles will have some form of electrification, so companies will have to react accordingly. “This means that eAxles will have to adapt to meet the requirements of the electric motor, which will evolve to become more powerful,” says Mair.
“Drivers are environmentally conscious, and they like technology to offer clear benefits. The challenge is introducing eco-friendly technologies that add real value for them. We believe that plug-in hybrids with all-wheel drive make sense. The public’s positive response to vehicle programmes that offer this combination – such as the Volvo XC90 T8 twin-engine, BMW i8 and Porsche 918 Spyder – can only continue to grow.”
However, GKN predicts that this increase in electrification will involve PHEVs and electric engines co-existing rather than EVs completely taking over. “It will be a mix at the end,” says Kuczera. “The electrical vehicle will always be more popular in the urban areas, and will not necessarily have the range to work in rural environments without hybridisation. Maybe in 25 years a split will go towards pure EVs, but for the next 20 we predict a mixed situation.”
However, in the future, the company expects that PHEVs will become more attractive and practical than conventional hybrids. A recent survey commissioned by GKN revealed that more than one-third (37%) of drivers still believe that petrol engines provide the best driving experience. Hybrids came second in the poll with
13.5%, just beating diesels with 12.8%.
“OEMs want eAxles that can handle more powerful electric motors and have the capacity to transmit greater levels of torque to the wheels,” says Kuczera. “We are reaching a ‘tipping-point’ in the delivery of power from a vehicle, with the majority of the power soon to be delivered by the electric motor, and the combustion engine used to supplement that. For customers, we will continue to develop plug-in hybrid systems that will make personal mobility more sustainable and enjoyable for decades to come.”
This predicted trend will enable OEMs to downsize engines, making their vehicles cleaner – a process that is already happening to a certain degree, according to Mair. He cites the example of the BMW i8 supercar. “It only has a 1.6-litre engine – not normally the engine you’d expect from a supercar. But combined with the electric motor, you have fantastic performance,” he says.
Voltage increase
Future hybrid cars will see voltage increasing to deliver more power, Mair believes. “That is the big advantage of our eAxles – they can work with electric motors of varying power. What’s key here is the systems-integration element, making sure that our technology is properly integrated into the mechanical and electrical fabric of the car to produce optimum performance,” he says.
“We are focused on developing technologies that can achieve this tipping-point for electric drives in mass production. More powerful, dynamic electric drives will help put batteries in the driving seat and create new electric driving experiences for customers. Our eDrive technologies demonstrate how the right kind of hybridisation creates value propositions for the driver.”
Overall, it looks as though in the future hybrids will gradually become more enjoyable to drive, so that eventually they will provide not only the efficiency but also the pleasure that today’s consumers are demanding from their vehicles.