18/11/11

Overview: Lexus GS 450h

Click here for our earlier article about the GS 450h.

Lexus unveiled its fourth generation GS models in the U.S. during the summer. Engineering priorities, according to Lexus, were more engaging road-manners and better accommodation. The new model will reach Britain early in 2012, in the form of the conventional GS 250 and the hybrid GS 450h. Lexus promises more GS models in the near future, though we don’t know which variants will be offered in Britain.

The bodyshell is appreciably new — wider and stiffer than previously, the latter thanks to an increased number of spot-welds and the use of laser welding on some seams. A 15mm increase in the height of the roofline allows for more rear passenger accommodation. The drag coefficient is a very respectable Cd 0.26. The wheelbase is unchanged.

Lexus GS.

The track is wider by 40mm at the front and 50mm at the rear. Suspension is revised at both ends; at the front, aluminium upper and lower control arms employ larger bushings, while the rear subframe has been completely redesigned to accommodate an all-new multi-link suspension set-up. The dampers use lighter-viscosity oil than previously: it is interesting that Lexus persists with oil-filled items.

The 10 airbags fitted to the GS include knee bags for both driver and front passenger; the rear seat occupants have seat-mounted side airbags, and side curtain airbags are fitted. New Whiplash Injury Lessening (WIL) front seats are fitted: these are designed to increase the likelihood that occupants will be in the best (or least worst) position at the moment of impact, enhancing the protective effect of the seatbelt and airbag system. Pretensioners with force limiters are fitted to the seatbelts in the front and outboard rear seating positions.

Optional driver assistance systems include a pre-collision system, which uses the dynamic cruise control system’s radar to provide early warning of objects ahead that might present a risk of a collision. The system also uses an infrared camera to monitor the driver’s eyes: if the driver is not looking forward when a collision appears imminent, the system will sound a warning sooner than otherwise. If the driver still does not respond and make the appropriate manoeuvre, the system will initiate braking up to two seconds prior to impact.

Other assistance systems that are available for the GS include a night vision system, a head-up display, a blind spot monitor, and Lane Keeping Assist (LKA) with Lane Departure Warning (LDW). The Lane Keeping Assist delivers active steering torque to provide a small degree of assistance in maintaining course, while the LDW feature alerts drivers if they begin to drift out of their lane.

The multimedia package in the GS provides Bluetooth with automatic phonebook download and streaming audio. DVD audio and video compatibility, MP3 sound enhancement, Surround Sound, and a high-resolution 20cm central control display are standard. Cars fitted with the navigation system (and the hybrid) will have an enormous 31cm high-resolution multi-media screen, large enough to support simultaneous, split-screen viewing of a map display, plus audio, climate or other vehicle information in a wide 24:9 format.

The dashboard is divided into two zones: an upper ‘display zone’, which includes the giant LCD multi-display screen, and a lower ‘operation zone’, with system controls such as the second generation of Lexus’s computer mouse-style Remote Touch Interface (RTI).

A new front seat has a lower hip point, placing the driver closer to the car’s centre of gravity. The seats have multiple adjustments, including butterfly-style head-restraints, shoulder supports, side supports, four-way lumbar support and an adjustable cushion length.

The steering wheel has been given an extra 50mm of reach adjustment and has been set at a low angle to make it easier for the driver to make larger steering inputs without having to over-reach.

The instrument binnacle incorporates large-diameter Optitron dials. The new head-up display relays information such as gear shift position, tachometer and navigation instructions, projected onto the base of the windscreen. Forward visibility has been increased by means of slimmer A-pillars and a taller windscreen.

The rear seats have a revised seat-back angle and redesigned cushion shape. The thin front seat design improves knee-room by 10mm, and headroom has been increased by 20mm.

The new GS has a more practical boot, thanks to a more compact rear suspension layout. It also has a wider opening, increased deck length and lower deck height. Additionally, the hybrid battery has been repackaged in a stacked layout to provide more luggage space.

In what Lexus claims (plausibly) to be a world first, customers can choose a real bamboo finish for the steering wheel.

An all-white LED interior lighting system features ‘sequenced illumination’: this begins as occupants approach the car, even before it is unlocked, and continues through the vehicle start procedure.

The new GS comes with an air-conditioning unit that is allegedly 10 times more powerful than before and uses ‘S-flow’ technology to maintain cabin comfort while reducing power consumption. Using sensors to determine which seats are occupied, it automatically closes all vents serving unoccupied seats to reduce ventilation losses. Additionally, the system automatically shifts to an ‘eco’ mode when the Eco drive mode is selected, switching on the seat heaters in order to reduce the amount of power needed to bring the cabin up to a comfortable temperature. (We don’t like to be nay-sayers, but most drivers we know rank their feet pretty highly in the thermal comfort stakes, and seat heaters put a fair load on the alternator.)

The air-conditioning incorporates a new system called Nano-e. This is an air-cleaning technology that operates automatically when the system is turned on. It releases 20nm-50nm diameter ‘Nano-e’ particles — anions (negative ions) ‘wrapped’ in water molecules — into the cabin through the air vent on the driver’s side of the dashboard. By attaching themselves to airborne particles and molecules, these Nano-e ions can have an air purifying and deodorising effect. They can also remove smells from the upholstery and rooflining to create a cleaner cabin environment. Toyota claims that, in addition, there can be a moisturising effect on skin and hair.

Drive-train

The new GS 450h uses the second generation of hybrid drive-train to emerge from Lexus. At its heart is a new 289PS 3.5-litre V6 petrol engine running on a pseudo-Atkinson cycle — in which the gas expansion ratio is greater than the mechanical compression ratio — with cooled exhaust gas recirculation and exhaust heat recovery. The V6 works in tandem with a water-cooled, permanent-magnet electric motor. An 18 per cent. improvement in overall fuel consumption is claimed, with an NEDC return of 44.8mpg; CO2 emissions are now below 145g/km.

Significant reductions in NOx and particulate emissions are claimed, with no loss of performance compared with the previous model.

The total power output of the hybrid drive-train is 342PS and 345Nm — though not for sustained periods, because the battery-pack can sustain high loads only for short spells. Standing-start acceleration to 100km/h is achieved in a claimed 5.9s, while the maximum speed is limited to 155mph.

Like every Lexus hybrid, the new GS is a ‘series-parallel’ hybrid: it can be powered by its petrol engine, its electric motor, or both together. All drive goes to the rear wheels.

Other components in the drive system include a generator; a nickel hydride battery-pack; a power split device which, using planetary reduction gears, combines and allocates power from the engine and electric motor, or delivers torque from the wheels or the engine to the generator, according to driving conditions; and a compact power control unit to govern the interaction of the other system components.

With conventional four-stroke petrol engines, there are times when fuel enrichment is required to cool the exhaust gases and prevent degradation or destruction of the catalytic converters. Because the intake valves close late in an Atkinson cycle engine, compression is delayed. This creates a high expansion ratio for less compression. As a result, the exhaust temperature is lower than that of conventional engines.

The EGR system reintroduces metered quantities of exhaust gases into the intake system, using a bespoke delivery manifold. This further reduces engine operating temperatures, while also reducing engine pumping losses through a decrease in intake vacuum pressure.

Together, the adoption of the pseudo-Atkinson cycle and cooled EGR reduce the situations where the cooling effect of fuel enrichment is necessary to protect the catalytic converter from overheating damage. As an aside, albeit a significant one, a new specification of catalyst has been adopted that uses a smaller mass of precious metals than previously.

The exhaust heat recovery system uses exhaust gas heat to warm the engine coolant at start-up. This obviously shortens the engine’s warm-up time. One effect of this is that the V6 can be shut off by the hybrid controller — if circumstances allow — earlier in a journey, particularly in winter. As a result, the new GS 450h manages a marked increase in cold weather efficiency compared to its predecessor.

Further reductions in fuel consumption have been achieved through a high mechanical compression ratio of 13.0:1 — beaten only by Mazda’s extraordinary Sky Activ engine — a new, mid-port intake tumble generator, and the adoption of new direct injection technology dubbed D-4S. This is the latest evolution of Lexus’s stoichio­metric direct injection technology. With one injector in the combustion chamber and a second mounted in the intake port, it combines the functions of both direct and port injection. The system features new slit-type injector nozzles with a modified port shape, a higher fuel pressure, and idle port injection for improved NVH.

Engine NVH and friction have been lowered by adopting a lightweight chain drive, changing the piston pin offset, and reducing the number of drive belt reinforcement ribs.

The Power Control Unit’s cooling performance has been improved by the adoption of dual cooling paths and a single-piece, integrated AC/DC converter. System control has also been improved: the PCU boosts motor drive voltage to a maximum of 650V in Sport mode, and limits it to a maximum 500V in Eco mode.

The electric motor has lighter mounts, and friction has been reduced. The range of the system’s regenerative braking operation has been increased. Additionally, the battery layout has been redesigned, the new stacked configuration helping increase the amount of luggage space in the boot.

Dynamics

As we have mentioned, Lexus placed dynamic improvements high on its shopping-list for the new GS. And so it is that the new car has a stiffer bodyshell; it also features Active Variable Suspension, and it is available with a four-wheel steering system as part of a package called Lexus Dynamic Handling.

As you would expect, the driver has a choice of driving modes — four in this case: Eco, Normal, Sport S and Sport S+.

So far as bodyshell rigidity is concerned, the new car features a new rear underbody, rear suspension member and front-end module components. Increased spot and laser welding has improved the rigidity of the door apertures, the rear under-body and rear partition. Additional reinforcements, or sheet metal with a thicker gauge, have been used in the cowl panel, the front and rear underbody and the rear partition, and the designs of the front suspension member, front side member, rocker inner and dash panel have been made stronger. Together, these improvements have increased bodyshell torsional rigidity by 14 per cent.

In ‘designing’ the car’s aerodynamics, Lexus has taken an approach it describes as ‘aerodynamic damping’. This involves bringing the airflow closer to the vehicle body and using it to help control vehicle movement and, says Lexus, improve handling stability. This is interesting, and counter-intuitive: if the car has been deliberately made sensitive to airflow, then it will be sensitive to unhelpful airflow, such as crosswinds. One would normally aim to isolate the car as much as possible from external influences that cannot be controlled.

Lexus paid particular attention to managing the airflow along the sides of the car to provide body movement damping. The smoothing of the airflow in and around the wheelarches, and the reduction of air pressure within the wheel arches themselves, contribute (we are told) to better steering response, a flatter ride and better roadholding.

The new GS has double wishbone front suspension with a multi-link arrangement at the rear. The front, high-mount double wishbone set-up incorporates a new design of unequal length upper and lower aluminium control arms. The caster trail has been lengthened to improve straight line stability and steering feel, and larger lower bushings reduce the transmission of vibrations. Also, revising the suspension geometry by positioning the toe control arm further aft allows for greater cornering force.

At the rear is a multi-link set-up with toe control bars and an aluminium rear axle carrier. Though unchanged in essence, it has been completely redesigned. The spring and damper have been separated to create a more compact design, which intrudes less into the boot space. Rear stability has been improved by adding a rebound spring, replacing suspension ball joints with bush joints, positioning the toe control arm at the rear, and minimising toe change during the suspension stroke. As mentioned, the dampers now use oil of lower viscosity than previously — though they do still use oil.

The power of the brake servo booster has been increased and, on a more subjective level, the brake pedal shape, angle and operating ratio have been changed. Brake cooling performance has been improved by increasing the volume of ducted cooling air. The Electronically Controlled Braking system’s characteristics have been modified to give better responsiveness.

The GS’s Adaptive Variable Suspension lets the driver choose between two damper settings: Normal and Sport. AVS automatically adjusts damping at each corner in response to driver inputs, vehicle body motion and road surface conditions.

Selecting Sport mode automatically increases the difference between inner and outer damping rates through corners to reduce body roll. At the same time, the VGRS (variable gear ratio steering) automatically reduces the steering gear ratio by around 10 per cent., and the EPS increases steering assist torque by about four per cent.

Drive Mode Select, as we have seen, lets the driver choose between Eco, Normal Sport S and Sport S+ driving modes. In Eco mode, engine output, throttle opening and gear selection are modulated to gain the best fuel efficiency in all driving conditions. The air conditioning system temperature, airflow volume and seat heater operation are co-ordinated to help reduce fuel consumption. In Sport S mode, engine speed and throttle responses are adjusted to deliver a more engaging driving experience. On models equipped with adaptive variable suspension, Sport S+ mode combines the performance of Sport mode with co-ordinated control of the adaptive suspension, EPS (electric power steering) and VDIM (Vehicle Dynamics Integrated Management).

Although hybrid’s the transmission is a CVT, it offers a manual mode with six pre-defined ratios and shift paddles mounted on the steering wheel. The transmission’s control system blips the throttle on down-shifts.

In Eco mode, the ambient instrument illumination is blue; this changes to red when Sport S or Sport S+ is selected. More usefully, the system power indicator automatically changes into a tachometer.

Lexus Dynamic Handling (LDH) integrates Adaptive Variable Suspension (AVS), Dynamic Rear Steering (DRS), Variable Gear Ratio Steering (VGRS) and Vehicle Dynamics Integrated Management Step 5 (VDIM), giving co-ordination of all aspects of front and rear wheel control.

Monitoring vehicle speed, steering direction and driver inputs, the system calculates the optimum angle for all four wheels: using the variable ratio electric power steering for the front wheels alongside the rear-wheel steering system, it can independently control front and rear wheel steering angles. The DRS system measures vehicle speed and yaw rate, steering angle and rate of change, and lateral G-force to determine the necessary rear wheel steering input, up to a maximum 1.5 degrees.

At speeds below 50mph, the front and rear wheels turn in opposite directions; above this speed they turn in the same direction.

The dynamic handling system will automatically adjust the adaptive suspension and active safety systems to suit road conditions, vehicle speed and driving style.

Driver assistance

Hradline driver assistance systems fitted to the GS 450h are...

  • Pre-crash safety system (PCS) with driver monitor camera;
  • Adaptive cruise control (ACC); this now works at all speeds down to 0mph;
  • Step 5 Vehicle Dynamics Integrated Management (VDIM), working with Dynamic Rear Steering (DRS);
  • Lane-Keep Assist (LKA) and Blind Spot Monitor (BSM);
  • Lexus night view system;
  • Head-up display (HUD), with expanded content menu, including tachometer information.

The pre-crash safety system primes the front seatbelts and braking systems to help reduce damage and injury in the event of a collision. The adaptive cruise control, which uses the same radar technology as the PCS, now functions at all speeds.

Additional active safety features include Lane-Keep Assist (LKA), a blind spot monitor, the Lexus Night View system and a head-up display with an expanded content menu.

The PCS uses a millimetre-wave radar that operates across a 20-degree scanning radius to detect obstacles in the vehicle’s path, even when cornering. The pre-collision system monitors vehicle speed, steering angle and yaw rate inputs to help determine in advance whether a collision is unavoidable. If it calculates a high probability of a collision, PCS will alert the driver by sounding a buzzer and triggering a warning on the multi-information display. At the same time it will activate the pre-crash seatbelt pretensioners, retracting all the slack in the front seatbelts, and, as soon as the driver begins to brake, implement pre-crash brake assist. PCS also initiates interaction between the car’s variable gear ratio steering (VGRS), rear steering, adaptive variable suspension (AVS) and the Vehicle Dynamics Integrated Management system (VDIM), improving response to the driver’s emergency steering inputs.

If the driver does not brake and a collision becomes inevitable, the pre-crash brake will automatically apply the brakes to reduce impact speed.

PCS has been revised for the new car: both the timing and magnitude of brake intervention have been changed, with the intention of reducing the collision speed.

The driver monitor camera uses two near-infra-red LEDs and a CCD camera built into the top of the steering column. The system monitors various aspects of the driver’s face, including the degree of eye opening; if there is a danger of collision, the timing of the pre-crash warning sequence is brought forward. There is no apparent attempt to use sound or steering vibration to wake up a dozing driver, though.

The all-speed adaptive cruise control operates in two modes: constant speed control, and vehicle-to-vehicle distance control. The constant speed control operates at speeds over 31mph, in the same way as a conventional cruise control system. The vehicle-to-vehicle distance control system can differentiate between vehicles directly ahead and those in adjacent lanes. It uses the millimetre-wave radar, together with constant speed, decelerator, follow-up and accelerator controls to slow the car to match the speed of the vehicle in front. Once the road ahead is clear, it will accelerate back to the pre-set cruising speed. If the ACC brings the car to a complete stop, and the vehicle in front pulls away again, the driver needs to press the accelerator briefly to reactivate the system.

Vehicle Dynamics Integrated Management (VDIM) Step 5 is Lexus’s snappy way of referring to the central controller that coordinates the chassis-based driver assistance systems. Sensors around the vehicle provide status data to enable VDIM to integrate the electronically controlled brakes (ECB) — which feature four-wheel independent braking, ABS and electronic brake-force distribution — with the traction control, vehicle stability control, the electromechanical power steering with its variable gear ratio rack, adaptive variable suspension and Dynamic Rear Steering systems.

The previous GS’s VDIM could help limit vehicle yaw and roll motion by controlling the AVS and VGRS, but the new Step 5 system goes further, incorporating the rear-wheel steering to control the steering angle of all four wheels to increase control over the car’s lateral motion.

Lexus stresses that the GS’s safety systems begin to operate before the car reaches its dynamic limits, which is not the case with the majority of others, which wait for a loss of traction or a severe yaw or roll value to be registered.

Lane-Keep Assist uses an on-board camera to detect road lane markings. It helps to keep the driver from drifting off-course by generating steering torque.

The blind spot monitor uses radar devices mounted on the corners of the rear bumper to detect overtaking vehicles in adjacent lanes. The system works at speeds above 25mph where the relative speed of the two vehicles is less than about 17mph, warning the driver by lighting up the indicator lamp in the offside door mirror. If the turn indicator is operating at the time, the warning will flash at a faster frequency. What the passing driver will make of the right turn indicator is an interesting question: we cannot help feeling that a different method of warning the driver might have been worth investigating.

The Lexus Night View system combines an infra-red camera mounted at the top of the windscreen and infra-red LED lamps within the headlight clusters with a Night View ECU to display an image of the road ahead on the car’s multi-information display screen. The system works at speeds between 9mph and 50mph, displaying an area up to 200m in front of the vehicle.

The head-up display projects key driving data in white graphics in the driver’s sight-line at the base of the windscreen. The information includes vehicle speed, turn-by-turn navigation, and a rev-counter display. It also includes information from the audio system — does this really count as essential information?

High-intensity LEDs are used for the read-outs. The system is easy to use: pressing HUD switch turns it on or off. The position of the display can be adjusted, and its brightness can be automatically adjusted to suit the ambient light conditions.

Lexus GS 450h
Cylinders 6V
Bore/stroke 94.0/83.0
Swept volume 3456cc
Compression
ratio *
13.0:1
Engine PS 289
System PS 342
System Nm 345
Maximum speed 155
0-100km/h 5.9
Combined MPG
(l/100km)
44.8
(6.3)
CO2 g/km 145
Transmission CVT
Driven wheels Rear
Battery type Ni-H
Nominal voltage 288V
Length 4850
Width 1840
Height 1455
Wheelbase 2850
* Mechanical compression ratio. Actual compression ratio ca. 9.5:1.
All figures are preliminary and for guidance, subject to vehicle homologation.
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