FT-Bh - a concept bringing efficiency to a new level
03/06/2012
Toyota
Making its World Premiere at the 2012 Geneva Motor Show, the FT-Bh concept is an ultra-light, sub-800 kg, full hybrid vehicle designed to lower fuel consumption and minimise emissions for an affordable B-segment family car.
Clearly expressing the Under Priority design language and Keen Look styling of Toyota's next generation vehicles, the FT-Bh has the dimensions of a B-segment vehicle. It is 3,985 mm long, 1,695 mm wide and 1,400 mm high, with a long wheelbase of 2,570 mm.
The new concept's design is driven by 5 key pillars targeting optimum fuel efficiency and minimised emissions: Mass Reduction; Driving Resistance in the form of aerodynamics and tyre rolling resistance; Powertrain Efficiency; Thermal Energy Management and Electricity Saving.
Combining a highly significant reduction in weight for a car of this class with painstaking aerodynamics, a rigorous reduction in driving resistance and a frugal yet highly efficient full hybrid powertrain, the FT-Bh concept is projected to deliver an average fuel consumption of just 2.1 l/100 km and CO2 emissions of only 49 g/km.
The FT-Bh targets CO2 emissions which are less than half those of the current 1.0 litre Yaris. But only through the mass-production of an affordable ultra-low emissions vehicle can sales volumes be large enough to make a genuine contribution to the real world reduction of total vehicle CO2 emissions on a global scale.
Aimed, therefore, at maximum affordability, the techniques and thought processes demonstrated in the concept's design do not involve the use of exotic, expensive materials or complex procedures, but only those already commonplace to the automotive industry.
Moreover, the goals of light vehicle weight, a low centre of gravity and maximum powertrain efficiency are beneficial not only in terms of low fuel consumption and emissions, but also in offering a more responsive, agile and engaging driving experience.
Design
Styled under the 'Ecomotion' theme, the FT-Bh concept's exterior design combines emotive shapes with an extremely high level of aerodynamic performance to achieve ultra-low fuel consumption.
Its form inspired almost entirely by the natural flow of air over the exterior surfaces, the concept represents a new approach to bodywork design. Key panels such as the roof are formed to represent fabric stretched taut between fastening points, reflecting their ultra-lightweight composition.
Inheriting elements of Toyota's Under Priority design language and Keen Look styling, the front of the vehicle is dominated by a large undergrille, a powerfully sculpted bonnet and vertical headlamps integrated into the front wings.
The stretched fabric styling of the roof panels adds a feeling of lightness to the vehicle. This is further emphasised by ultra-slim A- and C-pillars which maximise the glazed area of the cockpit for improved visibility and perceived cabin spaciousness.
The FT-Bh's arch-shaped rear creates a stable stance with low centre of gravity. With the cabin merging seamlessly into the rear of the vehicle, an uplifted rear bumper and crisp, chevron-shaped corner elements, the styling optimises aerodynamic performance, contributing to a low drag coefficient of only 0.235 Cd.
The stretched fabric panel design theme is continued throughout the car's interior styling, and is readily apparent in the form of the centre console, dashboard, seats and steering wheel. The concave form of the centre console creates a driver-focused cockpit whilst maintaining a feeling of both lightness and spaciousness.
Reduced Overall Mass
Fabricated in a combination of high-tensile steel, aluminium and magnesium, the FT-Bh concept targets an overall mass reduction of some 25% over the 1,030 kg 1.0 litre Yaris, bringing its total weight down to just 786 kg.
Because the hybrid powertrain is marginally heavier than a conventional 1.0 litre engine, the overall mass reduction required of the bodyshell, interior trim, chassis and electronics is actually some 340 kg, or 33% of the Yaris' weight.
Conversely, the FT-Bh's full hybrid powertrain adds some 60 kg in weight to the concept.
Toyota engineers have identified reduction targets of 33% for the body and chassis -with no detriment to safety performance- and 27% for the powertrain and electronics. With a body-in-white mass reduction of 20-25%, key to achieving a total mass reduction of over 30% is a reduction in the weight of interior parts and trim by approximately 50%.
This is reflected in the minimalist interior design of the FT-Bh concept, which features the minimum of structure and lightweight components of high torsional stiffness to combine superior ergonomics and functionality with the lowest possible weight.
Such a large saving in the weight of cabin parts has a highly significant 'ripple effect' in weight reduction throughout the rest of the vehicle. For instance, it reduces the applied load on both the body structure and the suspension, allowing for a commensurate downsizing of components. It also leads to a reduction in the required engine displacement, saving both weight and thermal energy losses.
Further benefits of such a substantial reduction in vehicle mass include a lower centre of gravity -just 541 mm- for more responsive, agile handling and powerful braking, and a reduction in production costs, making the vehicle more readily affordable to a larger cross-section of customers.
Lowered Driving Resistance
Measures to save fuel by reducing the road load of the FT-Bh concept are focused on aerodynamics and a tyre rolling resistance coefficient reduction. Minimisation of the aerodynamic coefficient of drag and the vehicle's particularly small frontal area target a resistance reduction of 25%. And the use of low rolling resistance tyres accounts for a significant improvement in fuel efficiency.
The concept is a comprehensive study in next generation aerodynamic techniques. It features air curtain intakes to the frontal extremities, air-stream alloy wheels, airflow-disrupting door mirrors replaced by cameras, handle-less electric latch doors, a pagoda roof with a dropped rear section, and a sharply cut rear end section incorporating an air outlet slit and an underfloor spoiler to smooth the flow of air away from the rear of the vehicle.
In combination, these measures lower the FT-Bh's coefficient of drag from a B-segment average of about 0.29 Cd to just 0.235.
The new Toyota concept highlights several cyclical 'efficiency benefit sequences' made possible by the synergy between aerodynamics and fuel efficiency.
For example, if fuel efficiency is improved, then the powertrain generates less heat, and the cooling system can be downsized. This allows for a reduction in the amount of cooling air necessary, allowing the front of the vehicle to be changed. This change lowers the coefficient of drag, in turn leading to a further improvement in fuel efficiency.
The fuel tank provides a further example: if fuel efficiency improves, the fuel tank can be downsized. Downsizing the fuel tank allows the amount of air that flows under the rear of the car to increase, which decreases resistance. Aerodynamic drag is reduced, leading to an additional improvement in fuel efficiency.
The concept rides on narrow, large diameter, 145/55R18 low rolling resistance tyres, which make a further significant contribution to lowering the FT-Bh's road load and driving resistance with no loss of grip or traction.
High Efficiency Powertrain
The FT-Bh's full hybrid drive system is a masterpiece of powertrain downsizing. Almost 90 kg lighter than the Prius' HSD system, it features substantial weight savings to every component of the drive-line.
The petrol engine is 38 kg lighter than that of the Prius. And the lithium-ion battery pack weight is almost half that of the Prius' nickel-metalhydride battery.
The lightweight, 2-cylinder, 1.0 litre Atkinson cycle petrol engine combines high efficiency with a low thermal capacity. Combustion efficiency has been maximised through the adoption of a long stroke, a high, 13:1 compression ratio, a next generation D4 injection system with a high fuel-injection pressure, a larger Exhaust Gas Recirculation (EGR) system with cooling and a high tumble port design.
Ultra-low friction measures have been applied to the axis receivers, timing belt and electric water pump, and painstaking thermal energy management involves the use of a low heat capacity, reduced cold friction and the careful control of heat flow to regulate engine oil and water temperatures.
As a result, this remarkable powertrain achieves an average fuel consumption of only 2.1 l/100 km, and CO2 emissions of just 49 g/km.
A combination of light vehicle weight and hybrid power offers FT-Bh drivers a return to the fundamental pleasures of city driving. The concept's light, 786 kg kerb weight maximises responsiveness to both throttle and brake inputs, while the hybrid powertrain's electric motor produces maximum torque from a standstill to provide nimble drivability in traffic.
Reinforcing the adaptability of Toyota's Hybrid Synergy Drive(R) technology to alternative energy sources, the FT-Bh also serves as a study for even greater fuel efficiency in the mid-term future through the potential installation of two alternative powertrains: a compressed natural gas hybrid (CNG-HV) version with CO2 emissions of only 38 g/km, and a Plug-in hybrid (PHEV) version emitting just 19 g/km of CO2.
Thermal Energy Management and 50% Electricity Saving
The FT-Bh targets improvements in the recovery of thermal energy and a 50% reduction in electricity consumption.
Using the twin strategies of a reduction in demand for heat and a reduction in heat loss, further stringent measures are applied within the interior. The FT-Bh uses lighter cabin components that have a smaller thermal capacity or a high degree of thermal insulation. Carefully zoned air-conditioning targets only occupied areas of the cabin, and any remaining waste heat -already minimised due to the ultra-high-efficiency hybrid powertrain- is effectively used.
The current draw from the FT-Bh's LED headlamps, interior lighting and other electrical components has been drastically reduced, lowering power consumption to 50% of that of conventional cars. The glazing construction has been designed for maximum thermal efficiency, and even the concept's pearl white, matte-finish heat-reflecting paint possesses excellent thermal insulation characteristics.