10
July
2012
|
18:00
Europe/Amsterdam

Prius+ 2012 dpl: optimised full hybrid powertrain featuring a new lithium-ion battery

&bull First non-plug-in Toyota full hybrid equipped with a lithium-ion battery

&bull Only MPV to combine 7 seats with a full hybrid powertrain

&bull Compact, high output lithium-ion battery located within the centre console

&bull Optimised Hybrid Synergy Drive® powertrain for improved efficiency

&bull Improved Exhaust Heat Recirculation system, electric motor cooling changed from air to liquid

&bull Final drive gear ratio lowered to match standard Prius acceleration

The Prius+'s full hybrid system features a 1.8 litre VVT-i petrol engine, a powerful electric motor, a generator, a high performance lithium-ion battery, a power control unit, and a power split device.

The HSD system uses power from both the petrol engine and electric motor in tandem, as well as alone, maximising the efficiencies of both units to achieve the optimum balance of driving performance and fuel efficiency.

During deceleration and under braking, the electric motor acts as a high-output generator to effect regenerative braking. Normally wasted as heat, kinetic energy is recovered as electrical energy for storage in the high performance battery.

The system's seamless, E-CVT electric continuously variable transmission is controlled by Shift-by-Wire technology, using an electronic shift lever system.

As in the standard Prius, the Prius+ features three 'on-demand' drive modes to increase the capabilities of the full hybrid powertrain, including a full hybrid-unique, EV mode which allows for ultra-quiet running on electric motor power alone, resulting in zero fuel consumption and CO2, NOx and PM emissions.

Compact, High Output Lithium-ion Battery

The Prius+'s lithium-ion battery replaces nickel-metal hydride technology within a non-plug-in Toyota full hybrid for the first time. Located within the vehicle centre console between the front seats, the new battery is significantly lighter and more compact than that of the Prius.

A new cell structure design equips the lithium-ion battery with just 56 cells arranged in a vertically double stacked structure. This occupies significantly less volume than a Prius battery and, at 34 kg, is 8 kg lighter.

Despite these reductions in both size and weight, the Prius+ battery has the same rated voltage of 202 V, and has an identical maximum output.

1.8 Litre Atkinson Cycle Engine with Improved Exhaust Heat Recirculation

The lightweight, highly compact, 4-cylinder 1,798 cc Atkinson cycle petrol engine develops 98 DIN hp/73 kW at 5,200 rpm and 142 Nm of torque at 4,000 rpm. Combined with a cooled Exhaust Gas Recirculation system, the adoption of the Atkinson cycle offers significant gains in fuel efficiency and the reduction of emissions.

Because the intake valves close late in an Atkinson Cycle engine, compression is delayed. This creates a high expansion ratio for less compression, reducing intake and exhaust energy losses and converting combustion energy to engine power more effectively. As a result, the exhaust temperature is lower than that of conventional engines. Cooled Exhaust Gas Recirculation reintroduces cooled exhaust gas into the intake system, further reducing engine operating temperatures.

Together, these technologies minimise situations when the cooling effect of 'fuel enrichment' is necessary to protect the catalytic converter from overheating damage, thereby improving fuel economy and lowering emissions.

Improving cold weather fuel economy and cabin comfort, an engine heat management system combines an improved Exhaust Heat Recirculation system with an electric water pump. To reduce mechanical losses, an electric system replaces the conventional water pump drive belt. As a result the coolant flow rate can be controlled with greater precision, contributing to greater fuel efficiency.

Via a valve built into the exhaust assembly, the revised Exhaust Heat Recirculation system redirects exhaust gases to heat up the engine coolant at start up.

The new system is 33% lighter and 27% more efficient than that of the standard Prius engine. Specifically, a greater amount of heat can now pass from the exhaust to the coolant in the heat exchange system. This significantly reduces engine warm up times, particularly in cold weather. It allows a more rapid delivery of effective cabin heating, and improves hybrid system efficiency and fuel economy.

E-CVT Hybrid Transaxle

Housing the electric motor, generator, power split device and double-motor reduction mechanism in one lightweight, highly compact transmission casing directly comparable in size to that of a conventional gearbox, the transaxle lies at the heart of the Hybrid Synergy Drive® system.

The transaxle features a multi-function gear train integrating four types of gears including a double-motor reduction mechanism, making it lightweight and highly compact.

Compensating for the Prius+'s weight increase over the Prius, the final drive gear ratio has been lowered from 3.498 to 3.704, maintaining similar acceleration performance to that of the standard Prius.

60 kW Electric Motor/Generator

The high performance, permanent magnet, synchronous 60 kW electric motor/generator works in tandem with the petrol engine to boost acceleration and power the driven wheels alone when the Prius+ is operating in EV mode.

In order to maintain optimum efficiency despite a vehicle weight increase over Prius, the motor cooling system has been changed from air to liquid.

The motor generates instant power from 0 rpm and a maximum 207 Nm of torque. A maximum drive voltage of 650 V DC allows for a lower operating current and, hence, a reduction in heat, improving HSD system efficiency.

Power Control Unit

Similar in size to a 12 volt battery, the Hybrid Synergy Drive® power control unit consists of a voltage boost converter, an inverter and a DC/DC converter.

Controlled by the motor control ECU from the Power Management ECU, the Power Control Unit boosts the DC voltage level from the hybrid battery and converts it to AC electricity to drive the electric motor.

A conventional, non-hybrid vehicle is equipped with an alternator to charge the auxiliary battery. However, because an alternator cannot operate during engine cut-off driving mode, a full hybrid vehicle requires an alternative system. Hybrid Synergy Drive® incorporates a DC/DC converter to reduce the high voltage of the 202V system battery pack to 14V, supplying power to the accessory systems and charging the auxiliary battery.

Performance

The Prius+'s Hybrid Synergy Drive® powertrain combines the 99 DIN hp/73 kW output of the 1.8 litre petrol engine with the 60 kW output of the electric motor for a maximum system power output of 136 DIN hp. The Prius+ will accelerate seamlessly from 0-100 km/h in 11.3 seconds and has a top speed of 165 km/h.

Its environmental performance enhanced by the Prius+'s class-leading aerodynamic performance and low weight, the full hybrid drive system returns both class-leading fuel economy and CO2 emissions of 4.1 l/100 km and 96 g/km[1] respectively.

Hybrid Synergy Drive® in Operation

Over the course of any journey, Toyota's Hybrid Synergy Drive® system operates in several different modes to maximise the Prius+'s overall efficiency.

At rest, the engine stops automatically to conserve fuel. Under operating conditions of low engine efficiency such as start up and low to mid-range speeds, the vehicle automatically runs in EV mode, on the electric motor alone, thus eradicating CO2 and NOx emissions.

Under normal driving conditions, power allocation is constantly adjusted between engine and electric motor to combine optimum performance with maximum fuel efficiency.

Via an Electronically Controlled Brake system (ECB), the electric motor acts as high-output generator during deceleration and under braking to effect regenerative braking, optimising energy management in the Hybrid Synergy Drive® system by recovering kinetic energy (normally wasted as heat under braking and deceleration) as electrical energy for storage in the high performance battery.

Battery power level is constantly managed via an engine driven generator to obviate any requirement to recharge the system from an external source.

Three 'On-Demand' Driving Modes - A Unique Eco Driving Experience

Supplementing the NORMAL drive mode of the new Prius+'s seamless, E-CVT electric continuously variable transmission, three alternative, 'on-demand' drive modes —EV, ECO and POWER- may be selected to further increase driving efficiency, performance and fuel economy.

These drive modes also incorporate comprehensive Eco driving support for those who wish to adopt more environmentally-friendly driving techniques.

From start with the NORMAL drive mode selected, the new Prius+ automatically operates in EV mode, driving under electric motor power alone to give instant power and an extraordinarily smooth, quiet ride with minimal NVH. This driving experience is unique to full hybrid technology and is not available to drivers of mild hybrid vehicles.

In NORMAL mode, the full hybrid system can operate on electric motor power alone at vehicle speeds up to 70 km/h, the petrol engine smoothly starting in higher speed ranges when its output is required.

The driver may also select EV mode manually. Though the petrol engine will still start if the system judges that its output is necessary, this switchable EV mode allows for significantly greater throttle inputs without engine start up. Hence, with vehicle range dictated by battery charge, the EV drive mode allows for urban driving with minimal noise and zero CO2, NOx and PM emissions as often as possible.

Its full hybrid powertrain helps Prius+ deliver significant levels of zero-emissions operation. The powertrain is optimised to operate in the most efficient mode, eliminating the need for the petrol engine as often as possible.

Toyota's own evaluations illustrate this potential. Data from several urban and extra urban trips show that the cumulative effect of the full hybrid powertrain leads to high proportions of zero-emissions operation, averaging up to 61% of journey time and 50% of total distance travelled.

Because the use of only light to medium throttle inputs keeps the petrol engine switched off throughout its operation, the EV drive mode contributes to a significant reduction in the new Prius+'s overall fuel consumption.

In ECO mode, throttle response to aggressive accelerator pedal inputs is reduced and air-conditioning control optimised for improved fuel economy. Depending on driving conditions, the ECO mode can help drivers achieve around a 10% reduction in fuel consumption.

A POWER mode also modifies the response of the Prius+ to throttle inputs, here boosting power to improve acceleration and enhance driving pleasure. The POWER mode provides a 25% higher throttle response to accelerator pedal input.

Complimenting these three on-demand drive modes, an Eco Drive Monitor helps drivers maximise the fuel efficiency of Toyota's full hybrid powertrain. Via the Toyota Touch multi-information screen, drivers may monitor the flow of energy within the Hybrid Synergy Drive® system for each driving mode. This helps them develop relaxed, fuel efficient driving techniques and maximise system efficiency.

[1] Equipped with 16" wheels