Lexus Hybrid Drive Evolution Includes Worlds First Full V8 Hybrid and All-Wheel Drive
August 29, 2007
August 29, 2007 - With the launch of the 2008 LS 600h L, the continued evolution of the Lexus Hybrid Drive system has achieved an unparalleled combination of acceleration performance and superior quietness. Featuring the world's first full hybrid V8 powertrain and full-time all-wheel drive (AWD), this latest Lexus Hybrid Drive was created to smoothly transmit its exceptional torque with instantaneous power and minimal noise, vibration and harshness (NVH).
Lexus' ongoing commitment to hybrid technology has its roots in an expanding hybrid lineup. The first Lexus Hybrid Drive system arrived in April 2005 with the launch of the RX 400h, the world's first gas-electric hybrid-powered luxury utility vehicle. It commenced with an electric four-wheel-drive system, and later added a front-wheel-drive hybrid powertrain, with a 3.3-liter V6 engine and two high-capacity motor-generators (MG1 and MG2).
The RX 400h AWD also included a rear motor-generator (MGR) that drives the rear wheels when traction demands, such as during acceleration or tire slip. The RX's hybrid drive features an Electronically controlled Continuously Variable Transmission (ECVT) with a reduction device, providing smooth yet powerful acceleration on par with 4.0-liter V8 gas engines. It comes with fuel-efficiency ratings comparable to compact sedans while attaining Super Ultra Low Emission Vehicle (SULEV) certification, producing nearly 70-percent fewer smog-forming emissions than the average new car.
In April 2006, the GS 450h debuted as the world's first hybrid-powered performance luxury sport sedan. With an innovative new longitudinal hybrid transmission and V6 engine, the GS 450h offers 4.5-liter V8-like performance, fuel efficiency ratings nearly 30 percent better than some V8 models, and carries a SULEV certification.
In the GS 450h, the Lexus Hybrid Drive powertrain evolved to combine a new 3.5-liter V6 engine with a compact, permanent magnet electric motor within the transmission, all driving the rear wheels. The hybrid powertrain collectively produces 340 horsepower and effortlessly accelerates the GS 450h from zero-to-60 mph in just 5.2 seconds. Just as impressive is how quickly and powerfully torque is delivered during mid-range acceleration. The hybrid system's electric-drive motor delivers maximum torque immediately upon demand, a unique power-delivery characteristic most noticeable and most useful during 30-to-50 mph passing and in traffic-merging maneuvers.
Power from the gas engine and electric drive motor (MG2) is distributed to the rear drive wheels via a planetary gear-type Electronically controlled Continuously Variable Transmission (ECVT). This unique transmission, which eliminates specific gear ratios, features a dual-range torque-multiplication device that allows drivers to select from among three driving modes: power, normal and snow.
The arrival of the LS 600h L brings with it 10 years of hybrid technological progression dating back to the launch of the first Prius in Japan. This new luxury hybrid sedan has the world's most advanced gas-electric hybrid system and is one of the most highly developed automobiles to date. Through an all-new V8 engine, high-output electric motors and a newly designed, large-capacity battery pack, this latest Lexus Hybrid Drive system brings with it superior acceleration, quietness, fuel efficiency and emissions.
The LS hybrid's iteration of Lexus Hybrid Drive carries with it some impressive new feats. The coupling of the LS 600h L's potent all-new V8 to a high-output electric motor and dual-range motor speed-reduction device that utilizes the overall power at a wide range of speeds and AWD, achieves acceleration performance on par with V12 engines. The combined gas engine and kW capacity of the hybrid-battery output produces a total of 438 overall system horsepower. Fuel efficiency ratings for the LS hybrid are on par with many AWD 3.0-liter V6 luxury sedan engines and is certified with an SULEV emissions rating while the luxury sedan renders a tranquility that is apparent whether at idle or high speeds.
The LS hybrid's 389-horsepower, 5.0-liter V8 engine (2UR) was part of a unique development process new to Lexus with performance, fuel efficiency and emissions targets establishing the displacement. The V8 is a part of the UR engine family, along with the LS 460's 4.6-liter V8 (1UR), and has a 6.5-mm stroke increase. During its development, emphasis was placed on reducing NVH and weight, while still increasing power.
In order to achieve its performance goals, the new V8, in comparison to the 1UR, required changes to the pistons, crankshaft, connecting rods, damper pulley, VVT-iE, exhaust manifold, oil pan and mounting bracket areas. For example, the crankshaft was made of forged steel and polished to a mirror finish with oil-hole smoothing in order to reduce friction and improve quietness.
An innovative Variable Valve Timing with intelligence and Electronically controlled intake cam system (VVT-iE), with an electric-motor-controlled intake cam, improves engine output and start-up performance, increases power output, improves fuel efficiency and reduces emissions. The VVT-iE delays the intake valve timing to lower compression, which reduces engine vibration to create an extremely quiet and smooth engine restart when the vehicle is at rest or being powered by the electric motor-generator.
NVH was also minimized by placing sound-isolating material around the head cover, using a dual-mass-type pulley with a torsion and bending damper, and by utilizing a dynamic damper-engine mount.
The 5.0-liter V8 features a hollow camshaft with forged lobes for higher strength and lighter weight to improve power and fuel efficiency. Camshafts, piston pins and the crankshaft are polished to a mirror finish to reduce friction areas and power loss. In addition, a unique cylinder honing was performed at a 30-degree crosshatching for reduced friction and mechanical loss. An electric relief valve on the fuel-delivery line better regulates fuel pressure to assist in delivering lower emissions and better fuel efficiency, while a dual-pipe air intake allows for a lower-profile hood design and reduces high- and low-frequency noise.
A new Hydrocarbon Adsorber and Catalyst (HCAC) system acts as a storage system in the exhaust system for hydrocarbons produced immediately following a cold start. HCAC adsorbs hydrocarbons during and following cold starts and holds them until the engine and catalytic converter reach operating temperature, contributing to fewer emissions and better fuel efficiency.
The LS 600h L's Lexus Hybrid Drive system contains the world's first all-wheel-drive Electronically controlled Continuously Variable Transmission (ECVT). It is an evolution of the world's first longitudinal hybrid transmission on the GS 450h and consists of two planetary gear sets with a dual-range reduction device that controls high and low ranges for optimum torque output.
The LS' hybrid powertrain includes two motor generators, MG1 and MG2, which are water-cooled and have a maximum system output of 650V DC. Like the GS 450h, MG1 starts the gas engine when needed and acts as a generator to recharge the hybrid battery. MG2 features a three-magnet structure, as opposed to the two-magnet layout of the GS 450h's MG2, which optimizes the magnet position and enables a smoothing out of the changes in magnetic force during rotation to help suppress vibration and reduce associated noise.
The LS 600h L's MG2 turns the transfer-input shaft connected to the Torsen center-differential transfer case where the power is split between the front and rear wheels. When acting as a generator, it converts kinetic energy to electricity to recharge the hybrid battery when coasting or braking. MG2 has a maximum output of 165 kW (221 hp) as compared to the GS 450h's 147 kW (197 hp).
To reduce NVH as much as possible, the transmission's gear teeth and areas where the gears engage were finished in the micron range, with the teeth being polished as well. Gear noise is also minimized by controlling the drive gears' rotation speed at the transition moment. An acoustic analysis of the hybrid transmission was conducted and as a result, unique acoustic covers were created in targeted areas to shield the passenger compartment from as much NVH as possible.
The LS 600h L's hybrid drive creates full-time mechanical all-wheel drive via a new compact Torsen limited slip differential (LSD) that is integrated with the rear-output shaft. It operates when a wheel-speed difference occurs between the front and rear wheels to optimally distribute the motive force from the hybrid ECVT. This gives the LS 600h L excellent traction during acceleration, at high speeds and when cornering. It has a 40/60 power split during normal driving conditions and is capable of a near 30/70 power split.
As demanded by this ultra quiet hybrid luxury sedan, further NVH reduction was engineered in a number of areas. In addition to smoothing the gear teeth, the integration of the Torsen LSD provides rigidity and reduced noise creation. Overall, the LS 600h L's all-wheel-drive system is lighter, more compact, and quieter than the GS 350 AWD and the competition while providing superior capabilities. It has a 30-percent reduction in size and is 11 pounds lighter as compared to the GS 350 AWD, while lending 50 percent more capacity. A gear-driven LSD, as opposed to the chain-driven GS 350 AWD, reduces weight and NVH.
The LS 600h L's AWD system is smaller and more compact than the Mercedes-Benz 4matic and the Audi Quattro. While gear-teeth smoothing helps make it quieter than the Mercedes-Benz 4matic system, the Torsen LSD displays advanced traction and corner-tracing capabilities versus both the Mercedes-Benz 4matic and the Audi Quattro.
This new Lexus Hybrid Drive system provides three modes: hybrid for everyday driving, power for improved acceleration and response, and snow for enhanced control on slippery surfaces. An eight-speed sequential engine braking system allows greater control on downhill grades.
The LS 600h L features a new 240-cell, 288V, nickel-metal hydride (Ni-MH) hybrid battery. The package includes two DC/DC converters for the auxiliary equipment and Electric Power Steering battery, and for the optional Active Stabilizer Power Suspension System battery. The converters are built on the side of the hybrid battery for a more compact layout. While the surrounding cabin air cooled the hybrid battery on previously models, for the first time the hybrid battery can also be cooled via the rear air conditioning unit, with a dedicated fan circulating cool air. Speed sensors enable the fan to slow or stop as the LS 600h L slows down, helping to ensure maximum cabin quietness.
A new smaller and lighter inverter, which converts the current from AC to DC and back depending on whether the vehicle is accelerating or in a braking/recharge mode, has been made more efficient with lower NVH. By utilizing the same dedicated cooling system as MG1 and MG2, the inverter's output has increased by 13 percent. Its structure has also been reinforced to minimize the noise and vibration normally created by high-frequency vibrations associated with inverters or transformers.
A new Electric Vehicle (EV) mode has been created for the LS 600h L. The EV mode, which can be engaged under certain conditions via a dedicated button, will keep the vehicle in electric-only mode at speeds below 25 mph for up to six-tenths of a mile. This will help emissions and efficiency in low-speed circumstances, such as when driving in residential areas or in parking garages.
The LS 600h L also has a new power meter located on the IP displaying total system output in three ranges: Power, Eco and Charge. The Power reading will indicate acceleration, the Charge reading will register during regenerative braking or charging, and the Eco reading will indicate an efficient normal cruising rate. In addition to the new power meter, for the first time the Lexus Hybrid Drive provides a dedicated tachometer for the gas engine's rpm output.
The LS 600h L's newest evolution of the Lexus Hybrid Drive system achieves a new level of innovation and sophistication not found in its competitors. It is a seemingly contradictory combination of engine performance, fuel efficiency and clean emissions not often found on the road today.