While the first competitors to bring their very first models with full hybrid drive on the road, sending the Lexus RX 450h already the second generation into the race.
Like its predecessor, the new RX 450h combines the power split full hybrid with an electric motor on the rear axle and realized as a (limited) four-wheel drive ("E-Four").
The hybrid drive of the RX 450h is a further development of the Lexus RX 400h represents the new model, the engineers achieved but through a comprehensive development of all the details of the hybrid drive components a significant increase in efficiency: With ten percent higher system performance uses the RX 450h 23 percent less fuel. In addition, the SUV unlike his predecessor also be driven on electric power.
With a system output of 220 kW (299 hp), the RX 450h to factory specifications in requirement 200 km / h. The 100-km/h-Marke to the "Recreational Crossover" ("RX") break through in 7.8 seconds. Lexus postulated with a consumption of 6.3 liters per 100 kilometers - equivalent to CO2 emissions of 148 g / km - the lowest fuel consumption of all crossovers in this segment.
Configuration of the hybrid drive
The hybrid drive system includes two separate drive systems for front and rear axle. The front wheels are driven by a power-split hybrid system, which distributes the flow of force between the V6 petrol engine, the front electric motor and the generator according to the respective operating conditions.
Electric motor, generator, planetary gears and the reduction gear for the electric motor are housed together in a compact housing. This integration reduces the size to the size of a conventional gearbox and loud Lexus is a crucial prerequisite for the deployment of the hybrid system in a crossover platform with front engine. The hybrid control unit is also located in the engine compartment, the high-performance battery is installed on the other hand under the rear seats.
A second electric motor on the rear axle, the front wheel drive system added to a four-wheel drive. From the hybrid control unit in conjunction with the integrated vehicle dynamics management VDIM (Vehicle Dynamics Integrated Management) variable rear drive unit operates without mechanical connection to the front-wheel drive. Whose seamless and imperceptible interaction ensures the hybrid controller.
New V6 petrol engine
The 3.5-liter DOHC V6 based on the engine of the RX 350th The Lexus engineers have him but optimized for use in hybrid vehicles. The power of the engine increases to 183 kW (249 hp) at 6,000 rpm, with maximum torque of 317 Nm at 4800 rpm.
In addition, records from the motor through three innovations: the Atkinson cycle, the cooled EGR (Cooled Exhaust Gas Recirculation) and the exhaust heat EHR (Exhaust Heat Recovery), which all lead to a reduction in fuel consumption.
When Atkinson cycle, the intake valves close later in the compression stroke than with a conventional gasoline engine, whereby the force required for compression is reduced. In the working cycle on the other hand, the exhaust valves remain closed for longer than in conventional four-stroke engines, so that the full combustion pressure may be longer acting on the pistons. This more combustion energy is converted into motion.
The EGR supplied via a separate conduit system a precisely regulated amount of exhaust gas again into the combustion chambers. Before it is cooled by up to 880 ° C maximum temperature to below 150 ° C. The motor can be operated unthrottled, which reduces fuel consumption, especially in high-load range.
The exhaust heat EHR uses the heat of the exhaust gases to rapidly warm up the engine and allows to switch off the petrol engine and the earlier purely electric driving mode to move. As a result of the consumption of the RX 450h is reduced compared to the previous model at low ambient temperatures by more than 30 percent.
Hybrid transmission
The new RX 450h is equipped as the first hybrid vehicle with intelligent shift control AI-SHIFT. This system determined from a comparison of the speed with the accelerator pedal position, whether the route is uphill or downhill. The transmission automatically selects the optimum gear and keep it constant, in order to keep the engine speed within the optimum range for the acceleration uphill or downhill exploit the engine braking effect.
Additionally, the transmission offers now in the driving position "S" a sequential shift mode. In this mode, the driver can select six fixed gear ratios for intermediate sprints or higher engine braking. Nevertheless, the transmission is the subjective weakness in the drive train, because everyone acceleration process is accompanied by clearly audible yelp.
The electric motors were taken from the RX 400h. The front comes to a power of 123 kW / 167 hp, the rear provide 50 kW / 68 PS. Thanks to optimized cooling and power electronics increases the yield strength: The front electric motor is now ready from the first rotation, 335 Nm, the rear contributes further 139 Nm. The speed range at which the maximum torque is applied, has been at the front electric motor extends to 15km / h, at the rear, even by 35 to 45km / h A value that represents just the best discipline of full hybrids, the regenerative braking (regenerative braking), a significant improvement. The more kinetic energy can be stored in the battery, the lower the fuel consumption.
Hybrid control unit
The RX 450 also underwent fine-tuning the details. So the power consumption of the hybrid control unit decreases by ten percent. The control unit is responsible for many important functions, such as the implementation of the battery voltage of 288 volts DC to 650 volts AC to operate the electric motors for the power control of electric motors and gasoline engines as well as for the conversion of the hybrid battery voltage in board voltage to supply the usual Consumers and the 12-volt battery.
The new hybrid controller falls with a volume of 18.2 instead of around 30 liters of significantly more compact and weighs only 22 instead of 30 kg. His new, multi-level inverter now allows cooling of both sides. Thus, the energy density increases by 40 percent, and the electrical losses are reduced by more than ten percent.
High Performance Battery
The 288 volt battery consists of three equal-sized blocks, each with ten modules of eight cells. The common sheet steel per block its own cooling fan, the common control unit, the relay for the positive and negative line and the safety plugs are housed.
The Lexus Hybrid Drive in practice
In coasting and braking, the Nitro is turned off. Both electric motors operate as a generator. Three new driving modes - "ECO", "EV" and "SNOW" - will also reduce fuel consumption and improve vehicle performance. In "ECO" mode, the performance of the automatic climate control and reduced the characteristic of the electronic accelerator pedal modified to support a particularly fuel-efficient driving style.
During soft start, the RX 450h runs up to a speed of about 40 km / h, the "EV" mode and so on electric power. Via a switch built into the steering wheel allows the "EV" mode (Electric Vehicle) also manually activate a function of speed.
New suspension
The new RX 450h has a longer wheelbase and wider track than its predecessor. The newly designed double-wishbone rear suspension ensures significantly reduced rolling and pitching movements of the body. The front suspension now performs under a revised geometry, new shock absorbers, coil springs and new stabilizers optimized their service.
Optionally available are electrically controlled roll bars. They reduce the lateral inclination of the vehicle body during cornering with 0.5 g lateral acceleration in comparison with a conventional suspension of almost 40 percent.
The system consists of centrally positioned in the stabilizers of the front and rear axle actuators consisting of direct current motors with an integrated reduction gear. You need to take control of two stabilizer parts torque: When driving straight ahead, they remain inactive in contrast to traditional, hydraulically-operated active stabilizers to save energy. Only when cornering they are activated. It calculates a control device based on the steering angle and vehicle speed, the required torque. The front and rear independently be controlled moments minimize the body roll of the car body and to thereby provide greater stability and responsive handling.
Optionally, also an electronically controlled air suspension on board. It varies the body height adjustment in four stages over a range of 60 millimeters.
Newly designed rear, advanced front
At the rear, a newly developed rear suspension with trailing arms and double wishbone suspension is used. To create more space in the cargo area, the engineers moved the coil springs under the floor and chose a low, angled mounting position for the shock absorbers so that the chassis components barely intrude into the luggage compartment.
The front suspension was newly developed shock absorbers. The two front coil springs are wound mirror images of each other, twist during compression so opposite. Thus the resulting rotational forces cancel each other out, which benefits the agility, driving stability and ride comfort to the good. In addition, a stronger front stabilizer bar for enhanced cornering stability.
Electric power steering
Compared to a conventional hydraulic system causes the electric power steering (Electric Power Steering), a fuel saving of around three percent because they Unlike hydraulic assisted steering when driving straight ahead does not consume energy. Even in situations with low steering angles, the energy consumption is considerably lower. Despite the wider track and longer wheelbase, the new RX is waiting on the same turning radius as its predecessor (12.20 m).
On vehicles with conventional drive kinetic energy during coasting and braking goes wasted. The RX 450 h in the electronically controlled brake system (Electronically Controlled Braking) ensures that a portion of this kinetic energy is converted into electrical energy each wheel and stored in the high performance battery. The electronic switch while the hydraulic brake system to the rice only when the recuperation of the electric motors is not sufficient to apply the desired delay. The input signal for providing the way, such as the brake pedal is actuated.
To reduce the operating noise of the brake control, it relies on three plunger and a separate power supply. The brake system is networked with the dynamic driving dynamics management VDIM to ensure a linear braking force profile and optimum braking force distribution to each individual wheel, and to maximize the braking energy recovery.
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