With the introduction of the world’s first hybrid-only luxury car, the 2010 HS 250h, Lexus brings the promise of sustainable luxury to the forefront of the auto industry. In the process, the brand also elevates luxury transportation with innovative engineering and intelligent, driver-inspired design that offers excellent roominess and nimble maneuverability.
Each new generation of Lexus hybrids brings with it new gains in efficiency. With the HS 250h, designers and engineers took the opportunity to create a truly unique luxury car that maximizes fuel economy while further shrinking its impact on the planet by using ecologically advanced materials, clever packaging of people and components and eradicating waste wherever possible. They also found fresh ways to make driving easier and more efficient, with the premium quality and luxury expected from a Lexus.
Engine and Hybrid System
Hybrid efficiency is at the core of the HS 250h and Lexus’ first four-cylinder gas engine and latest hybrid system take advantage of the company’s continuous engineering advances to maximize fuel economy, minimize emissions and deliver driving pleasure. A highly efficient engine design, an exhaust heat recovery system, major efforts to reduce parasitic losses, a new evaporative emissions system and driver-selectable driving modes all make notable contributions. Significant efforts were also made to minimize engine noise.
An Atkinson-cycle engine design was chosen for its high efficiency and compatibility with hybrid operation in the new HS. The twin-cam engine uses four valves per cylinder and Variable Valve Timing with Intelligence (VVT-i) on the intake side. The engine is undersquare, with an 88.5-mm bore diameter and 96 mm stroke and has a relatively high compression ratio of 12.5:1. Peak output equals 147 horsepower and in combination with the hybrid drive motor, the HS generates 187 total system horsepower. It also meets the California SULEV and federal Tier 2 Bin 3 exhaust emission standards, emitting 70 percent fewer smog-forming emissions than conventional vehicles; it is also augmented by a new system that reduces evaporative emissions to near zero.
Careful design of the intake system reduces engine pumping losses and its twin resonators minimize intake noise. The cooling system uses a modular construction that combines an aluminum engine radiator, hybrid system radiator, AC condenser and fan into a single assembly for minimal weight. Plus, the electric fan speed is controlled via Pulse Width Modulation to reduce energy consumption and noise. Careful ducting of the cooling system prevents hot engine air recirculation that tends to occur at low speeds and while idling, further enhancing efficiency.
One of the keys to lower fuel consumption involves heat. Similar to the Lexus RX 450h, the HS employs an Exhaust Heat Recovery System that captures the heat of spent exhaust gases to speed engine coolant warm-up and allow the hybrid system to stop the engine earlier and more often in the driving cycle when it’s not needed, for example in low power demand conditions in city driving. Overall, the system can improve fuel efficiency by as much as seven percent in low ambient temperatures.
Using a two-motor hybrid system, the HS 250h uses a 141 hp drive motor that combines with the 147 hp gas engine (Note that the sum of the engine and motor power are not equal to the total system power as the operation of the engine and motor cannot be maximized in the same operation range). A second motor in the hybrid system serves as both engine starter and generator to charge the hybrid battery pack.
The efficient two-motor system also uses an electronically-controlled continuously variable transmission (CVT) that is a model of efficiency, simplicity and compact size with extremely smooth and quiet operation. A motor speed-reduction planetary gear unit helps provide high power output in this small package. The HS250h also uses an easy-to-operate shift-by-wire system that eliminates the need for bulky shift cables, saving space and weight while allowing much more design freedom in placing the shift lever in the interior.
An electric transmission oil pump eliminates another source of parasitic loss to further increase efficiency. Electronic operation allows a control strategy that invokes the oil pump only when needed, and since the oil also flows over the drive motor, overall efficiency of the motor and transmission are improved.
The HS 250h also incorporates a drive-mode switch, an important element in improving efficiency that involves driver and car interaction. The driver can select among four modes: Power, Normal, Eco and EV. Each switch position changes the rate of throttle opening for a given throttle-pedal angle. Normal mode has an essentially linear throttle action that gives naturally progressive power. In Eco mode, the throttle actuation on the engine and drive motor is reduced relative to the pedal angle to emphasize fuel economy. While Eco mode assists the driver in achieving improved fuel efficiency, overall the automatic A/C and hybrid battery coolant control helps achieve maximum fuel efficiency. Power mode can be selected for a more responsive feel when desired. Under certain circumstances, a new driver-selectable EV mode can allow the vehicle to be driven short distances using only the electric motors.
Aerodynamics
The HS 250h body design received considerable attention to aerodynamics. Ambitious goals were set requiring designers to work closely with aerodynamicists from the outset to create a low-drag form in an attractive, spacious, yet compact package. Their work yielded a top-in-class 0.27 coefficient of drag (Cd), which makes a considerable contribution to fuel economy, especially at highway speeds.
The low nose encourages airflow while also helping enhance vehicle dynamics. Smooth transitions along the front fender and A-pillars avoid disturbance of the airflow. Subtle front- and rear-bumper spoilers and a rear-lip spoiler contribute to low drag and minimize lift. The body sides taper from the center pillar to the rear where they meet the slightly kicked-out tail lamps, helping reduce drag-inducing wake turbulence. Also, a gull wing-shaped roof panel enabled designers to lower its profile to reduce air resistance and with a shape that is naturally stiffer than a conventional curved roof, engineers were able to reduce its thickness for further weight reduction.
Several measures were also taken under the car to promote airflow and reduce drag. Airflow resistance in the engine compartment was improved by optimizing the duct profiles around the radiator. Careful positioning of numerous underfloor covers plus added diffuser fins on the rear covers further reduce drag while enhancing straight-line control.
Acceleration and Fuel Economy
All of this focus on efficiency means that performance benefits as well, not only from gains in the engine and hybrid powertrain, but also from the HS 250h’s excellent aerodynamics (a product of frontal area, body drag and airflow management) and weight reduction efforts throughout the car. Outstanding fuel economy with confident, responsive acceleration is the inevitable result.
The HS 250 is expected to achieve an EPA-estimated 35 mpg city and 34 mpg on the highway for a combined 35 mpg. Careful drivers can use the Eco mode in conjunction with a new hybrid system monitor plus eco-driving indicator to improve on these numbers in certain conditions. The expected fuel efficiency is more than 20-percent better than the most fuel-efficient model currently in the Lexus lineup, while earning a SULEV emissions rating utilizing regular 87-octane gasoline.
Acceleration from 0-to-60 mph is rated at 8.4 seconds. Responsive passing acceleration that benefits from the instant torque of the electric motor and the CVT’s ability to quickly find the optimal gear ratio enhance the driving experience.
Sustainability
Underlying the HS 250h’s forward-thinking interior design is one of the most extensive implementations of bioplastic material in an automobile to date. Known more formally as Ecological Plastic, the material uses plant sources as raw material and its use for parts of the interior upholstery in the HS 250h is a world first.
Ecological Plastics is also used in a number of injection-molded, foam and board components throughout the car, including trunk compartment trim, cowl side trim, door scuff plates, seat cushions and the package tray. Overall, approximately 30 percent of the interior and trunk are covered in Ecological Plastic, resulting in a reduction of carbon emissions by approx. 20 percent over the estimated life of the vehicle.
Driver-Inspired Technology
From the driver’s perspective, several important developments inside the HS 250h transform the driving experience, making it easier and more enjoyable while also helping to enhance the driver’s attention to the road ahead.
A new standard multi-media package offers a comprehensive suite that includes voice recognition, Bluetooth® technology, integrated satellite radio (subscription required – first three months free) and USB iPod connectivity operated via steering wheel controls or from the display screen. A multi-information display situated in the instrument cluster keeps the driver informed of the numerous actions controlled by the steering wheel-mounted switches.
The HS 250h’s next generation navigation system is optional and, as noted earlier, features Lexus’ exclusive Remote Touch controller with user-adjustable haptic feedback. The innovative controller, similar to a computer mouse, eliminates the need for touch screen controls, allowing the pop-up navigation system screen to be mounted further up the center stack and away from the driver. The driver benefits with a clear, high-resolution screen, improved site lines and reduced eye movement. These advances combined with the physical feedback provided by the controller make the system extremely easy to use.
A new casual-language voice recognition feature, Voice Command, is standard on navigation-equipped vehicles. This new technology, previously only available on the 2010 Lexus RX350 and RX450h, allows the driver to give more flexible, conversational commands for easier access to audio and climate, as well as navigation system functions. Voice Command users avoid having to speak commands in a specific order (e.g., “Phone > Dial by Name > Dial Bob”). This same task can now be completed simply by saying, “Call Bob at home.” The Voice Command system also works to control many functions of the audio system, heating and air conditioning, and the navigation system. Commands such as, “Make it cooler,” “Let’s find XM channel 46,” “Show me Japanese restaurants,” and “I need a gas station,” make tasks easier to accomplish, in fewer steps, and help allow drivers to focus more on the road ahead.
As part of the all-new Lexus EnformTM navigation platform, the HS 250h also features XM NavTraffic® and XM NavWeatherTM services. These XM services will offer 3-month trials, after which subscriptions will be required. XM NavTraffic informs the driver of current traffic conditions with real-time traffic displays. When traffic problems are detected, in order to avoid them, the navigation system alerts the driver so that the route can be adjusted. XM NavWeather will provide near real-time weather conditions as well as spoken and nav-screen forecasts, both based on official National Weather Service data.
Also standard on navigation-equipped HS vehicles is XM® Sports and Stocks, a new service that is included with an XM satellite radio subscription. XM Sports provides game results and schedules for up to five personally selected national league sports teams. Drivers can add their desired teams to the navigation system and receive available team information by Voice Command or by using the haptic mouse controller. XM Stocks provides data for up to 10 personally selected stocks. After inputting their chosen stock symbols, drivers can receive available data via the navigation system or by Voice Command. Another driver-inspired development is an optional Heads-Up Display (HUD). The system projects a miniature display on a small portion of the windshield in front of the driver, significantly reducing eye movement to see frequently viewed information such as vehicle speed. The display has been developed for maximum visibility, with crisp, high-contrast white lighting that makes it possible to see even in difficult lighting conditions such as driving on snow-covered roads. In addition to speed, the system also displays turn-by-turn navigation arrows and drive-assist warnings, as well as audio information and Touch Tracer (sensors on steering-wheel switches will show an image of switch layout in the HUD), both of which can be turned off separately from the rest of the display.
The high-visibility, electro-luminescent instrument cluster offers fresh methods of keeping track of the various systems in the car and helps the driver to conserve fuel. A hybrid system indicator displays the hybrid system output and regenerative charging status, simultaneously indicating the efficiency of the system related to driving style. An auxiliary eco driving indicator light further assists the driver in maintaining the most economical use of system power. In practice, the added driver awareness has been shown to improve fuel economy several percentage points.
A multi-information display resides in the center of the hybrid system indicator. It uses high-contrast organic light-emitting diode (OLED) technology for maximum visibility and indicates various conditions such as fuel consumption, ambient temperature and cruising range. Additionally, several vehicle functions can be customized through use of the display with the multi-information switch.
Like most Lexus products, the HS 250h comes equipped with a rear-view camera as part of the available navigation system. However, the new HS adds an available Wide-view Front Monitor to enhance the driver’s ability to see in the traditionally blind areas around the front of the vehicle. The front grille-mounted camera has a maximum 190-degree lateral field of view and allows the driver to see as close as approximately 23.5 inches in front of the car within an 83-degree vertical field of view.
Images from the two monitors feed into the available park assist ECU which process and sends them to the navigation system display at separate times depending on whether the vehicles is moving forward or backward. The front monitor operates in either of two modes: Normal mode allows the driver to manually operate the camera with a switch on the lower left dash area. In auto mode, images from the front monitor automatically display when the vehicle slows to about six mph or less and automatically shuts off when speed rises above approximately 7.5 mph. The driver can also toggle the front monitor on or off while in the auto mode.
Two more items related to visibility merit mention: Over the years, changes to body structural requirements for safety have made it difficult to keep A-pillars slender, affecting the driver’s field of vision. But HS 250h designers were able to create a relatively slim A-pillar structure that improves visibility without degrading structural integrity. Additionally, the HS uses side glass with a water-repellant coating that improves wet weather visibility and aids defrosting performance.
Safety
As it is with ride, handling, noise and vibration, the body structure plays a key role in the fundamental safety characteristics of the HS 250h. To help protect the driver and passengers, the body is designed to be extremely strong but strategically resilient to help absorb and distribute energy in the event of a crash. High tension steel components are carefully located in the body structure, doors and other areas to help ensure strength in key areas. This includes special rear side members that are specifically designed to conform to the latest safety regulations requiring compatibility with a high-speed rear impact.
The HS 250h incorporates a standard class-leading 10-airbag Supplemental Restraint system with dual-stage airbags and knee airbags for driver and front passenger, side curtain airbags, and both front and rear seat-mounted side airbags to help protect front and rear passengers in certain types of severe frontal or side collisions. The front passenger airbag is a twin-chamber type that further helps protect the front-passenger. Additionally, front and outer rear seatbelts incorporate pretensioners with force-limiters to help protect occupants in the event of a severe frontal collision. Also, active head restraints are provided for the front seats.
An optional Pre-Collision System (PCS) with Dynamic Radar Cruise Control and Driver Monitor uses millimeter-wave radar to measure and maintain a pre-set following distance from a vehicle traveling ahead. The radar sensor can detect certain obstacles in front of the car, and a PCS computer with vehicle speed, steering angle and yaw-rate inputs helps to determine whether a collision is highly possible. In such a situation, PCS alerts the driver with audible and visual warnings, preemptively retracts front seat belts and pre-initializes Brake Assist so that increased braking will be applied the instant the driver depresses the pedal.
Interior: Design for Innovation
The interior of the HS 250h was designed to communicate the high level of innovation inherent in the car with the craftsmanship expected from Lexus products. Because of the high frequency of interaction with it, Lexus’ exclusive Remote Touch navigation system controller is a focal point of the interior design.
The center stack sweeps rearward to the Remote Touch which naturally meets the driver’s hand atop a “floating” form over the center console. Switches and displays are neatly arranged for ease of operation and free of visual complexity, courtesy of Remote Touch.
Leather-trimmed seats are standard and special soft touch stitched details on the center stack and instrument hood provide an extra premium touch in the cabin. Interior trim colors include black leather, new light gray leather, parchment leather, and a distinctive black/light gray two-tone leather trim. All include standard high-finish trim or available brown walnut wood trim. Front door trim that mirrors the shape of the center stack and armrest provide a comfortable symmetry. And the steering wheel center pad appears to float on the wheel, surrounded by control switches that mimic the design and color of those on the center stack.
Body Design and Packaging
Efficiency was a priority in the HS 250h body design, with careful packaging of people and components to maximize space and special attention to aerodynamics to reduce drag. But the HS 250h is also a Lexus luxury car and its designers were very intent on creating a fresh, appealing design befitting the brand that is also hybrid-distinct.
Body designers looked to the Lexus L-Finesse design language to create a new shape for their first dedicated hybrid. The silhouette displays a smoothly flowing line from front to rear; the C-pillar has a unique arrowhead shape; the grille is set low in the front with no openings to facilitate smooth airflow over the hood; there is an air inlet directly below the grille to cool the hybrid system and a larger one lower in the fascia to cool the engine and radiator. The standard projector-beam headlamps provide a focused look, while innovative, efficient LED headlamps are available; and rear-combination lamps are clear with blue-accented frames that intentionally signal “hybrid.”
Striving to create a sleek and aerodynamic shape with a roomy cabin while containing the physical footprint of the car and packaging the hybrid system components, HS 250h designers had their work cut out for them. To accomplish their goals, they used a somewhat taller profile and more forward A-pillar location than used in conventional sedans. This allowed a higher seating position for both front and rear passengers, providing improved passenger vision and easier egress/ingress, while also creating a better location for the batteries. The battery components, including the high-voltage battery pack, auxiliary battery and battery-connected devices, were carefully packaged to take advantage of this layout, resulting in a spacious cabin and surprisingly large trunk space.
The HS250h will offer 10 premium Lexus exterior colors: Matador Red Mica, Tungsten Pearl, Smoky Granite Mica, Obsidian, Golden Almond Metallic, Black Sapphire Pearl, Starfire Pearl, and three hybrid exclusive colors – Black Opal Mica, Aurora White Pearl and Silver Opal Mica, which debuts on the HS.
Dynamics
Nimble handling, excellent body control, smooth ride and low noise in the HS 250h begin with a stiff body structure. The HS body is designed with superior stiffness overall with added focus in strategically-located areas that have the greatest effect on ride, handling and noise.
Designed to balance handling, ride and NVH at high levels, the HS uses a rigid and compact MacPherson strut front suspension. The system employs lateral force-reducing coil springs, a 24-mm diameter stabilizer bar plus large diameter pistons and rebound springs in the shock absorbers to help provide superior ride control. The steering rack is directly mounted (no rubber bushings) to create an unfiltered connection between it and the suspension members to help accurately communicate to the driver what is happening where the rubber meets the road.
The double-wishbone rear suspension used in the HS also balances performance and comfort and is important to its overall handling. Its compact design uses low-mount coil springs that help improve cargo space. As in the front suspension, rebound springs are used to aid both handling and ride, and all mountings and bushings are optimized to help provide an excellent combination of ride, handling and low noise.
Standard 17-inch aluminum alloy wheels on the HS 250h are shod with P215/55 R17 all-season tire. Available 18-inch aluminum alloy wheels are equipped with larger P225/45 R18 all-season tires. All wheels feature the direct-type Tire Pressure Monitoring System (TPMS).
As one of the leading users of electric power steering (EPS) in its vehicles, Lexus’ experience continues to improve the breed. For the HS 250h, a column mounted EPS system has been developed to work with both manual and available power tilt-telescoping steering columns. The vehicle-speed sensitive steering has been optimized to provide ideal steering feel at any speed. Inertia compensation control, friction feedback and recovery control assist in tailoring the steering feel and effort. The HS EPS system also improves fuel economy by eliminating the need for a belt driven-pump and its associated belts and fluid, further benefiting the environment.
Like all Lexus vehicles, the HS 250h braking system is comprehensive, and as a Lexus hybrid it is augmented by regenerative braking which also helps recharge the hybrid battery back and improve fuel economy.
The HS uses a newly developed electronic controlled brake (ECB) system actuator that is managed by the ECB computer and acts on the system’s hydraulic brake components. The ECB computer also controls the interaction between the four-wheel disc friction brakes and the regenerative brake system. The new ECB actuator is smaller, lighter and consumes less electrical current than previous systems, making additional contributions to fuel economy. Enhancements in the system design also help improve brake feel and controllability.
Comfort and Convenience
When more than one driver uses the HS 250h, an available new memory system allows individual driver settings to be recalled automatically by individual keys, saving the drivers the trouble of recalling their particular setting. The system memorizes the steering-wheel position, seat position, exterior mirror positions and air conditioning settings associated with each key, translating to shorter preparation time prior to driving.
Leather-trimmed seating is standard with a 10-way power-adjustable front seat, including power lumbar, for the driver. The passenger receives a standard eight-way power-adjustable seat, with a 10-way power-adjustable option. Heated or heated/ventilated front seats trimmed in semi- aniline leather are available in premium grade vehicles.
Climate control in the HS 250h is designed to provide comfort and clean air for all passengers. A dual temperature control system is used for front seat occupants and a dedicated rear blower mounted in the center console promotes quick cool down for the rear passengers. A plasma cluster ion generator, A/C clean air filter and a pollen removal mode help purify air inside the cabin. The interior get a little extra help from the windshield, which has infrared-ray reduction properties that help keep the interior cool, allowing a smaller size air conditioning system than would otherwise be required.
A 10-speaker, 137-watt Lexus premium audio system featuring a six-disc CD changer, a subwoofer and center speaker is standard. The system uses two-way woofer and tweeter systems in both front and rear for rich, clear sound quality.
Audiophiles will appreciate the HS 250h’s available Mark Levinson® 5.1-channel Premium Surround Sound system. Power is rated at 330 watts at only 0.1% total harmonic distortion from 20-20, 00 Hz, and the system uses 15 strategically placed speakers for outstanding audio performance and sound quality.
The HS250h accommodates a variety of music sources, providing standard auxiliary and USB inputs, Bluetooth® Audio wireless connectivity and standard XM® satellite radio capability (requires subscription after a three-month trial). Standard voice recognition and Bluetooth technology allow phone calls to be made and received while driving. When an iPod® is attached via the USB port, information such names for the artist, track and album is displayed on the available navigation or audio screen.
Noise and Vibration
As the newest member of the Lexus family and in keeping with its environmentally advanced design, aggressive noise and vibration targets were set for the HS 250h. A comprehensive and painstaking approach was taken with particular efforts directed at engine and booming noise as well as wind noise.
Component solutions on the HS include acoustic windshield glass and an extensive package of optimally positioned sound insulation materials. Measures such as dynamic dampers for the engine mounts, dual intake resonators and optimized muffler capacity were employed to achieve a smooth, linear sound quality without unnatural peaks and valleys.
Extensive aerodynamic work was conducted with both computational fluid dynamic (CFD) analysis and wind tunnel evaluation to identify noise sources, assist designers to create appropriate design elements and prove countermeasures. For example, a smoother transition between the windshield and roofline (backed by a sound-insulating inner layer) has improved air-flow and turbulence, reducing wind noise in the process.
Also, strategically placed seals, barriers and insulation material are used throughout the HS to eliminate noise paths and insulate passengers from noise sources.
Lexus EnformTM with Safety ConnectTM
The Lexus HS 250h is slated to be the first vehicle to offer the all-new telematics system Lexus EnformTM with Safety ConnectTM, available by subscription on the dedicated luxury hybrid sedan when it goes on sale in late summer. Safety Connect, the cornerstone of the services, is available on both non-navigation and navigation-equipped HS250h vehicles and offers four fundamental safety and security features: Automatic Collision Notification, Stolen Vehicle Location, Emergency Assistance Button (SOS), and enhanced Roadside Assistance, which adds GPS data to the already included warranty-based Lexus roadside service.
Lexus Enform services include all of the Safety Connect features and build upon them with the premium services of Destination Assist and eDestination. Destination Assist agents are available via the on-board cellular equipment and can help drivers find a specific address, a business by name, or a type of business (e.g., gas station, movie theater, etc.), and even Zagat-rated restaurants, and then send the coordinates to the navigation system for routing. With eDestination, drivers can go online via Lexus.com’s drivers’ site to save and sort destinations in up to 20 folders holding as many as 10 destinations each – all personalized by the driver. Then drivers can send the locations – up to 200 at a time – to their vehicle, where they will be available for download into the navigation system. Online, drivers can create personalized location names (e.g., “Favorite sushi,” “1 PM Appt,” “Kids’ doc,” etc.) and even list notes about their saved locations – all helping them see exactly the information they choose in the vehicle.
One-year trial subscriptions of Lexus Enform and Safety Connect are included with all new HS250h purchases. Renewal subscriptions will be available in a variety of terms. Drivers of navigation-equipped vehicles will have the option to subscribe to Safety Connect only or to Lexus Enform with Safety Connect. Both the Lexus Enform and the Safety Connect response center operate 24 hours a day, 7 days a week – every day of the year.
Launching with Lexus Enform is Lexus Insider, a complimentary, opt-in service available without a subscription on all navigation-equipped HS vehicles. Debuting in late summer, this feature offers in-vehicle audio casts that provide owners access to useful vehicle tips and event information, and insights into exclusive owners' benefits – all designed to further enhance the Lexus experience. Drivers who do not wish to receive the messages can easily opt out of the service. Those who do wish to receive them can elect whether or not to receive notification of new messages at vehicle start up.
Lexus Luxury
Lexus has developed another new system for the HS 250h called Lane Keep Assist (LKA) that is designed to help drivers stay within their chosen lane. To accomplish this, LKA combines two basic functions: The first is a lane-departure warning (LDW) function that eases the burden on the driver by smoothly increasing steering torque a small amount to assist in maintaining course. It does not steer the vehicle independently and it requires the driver to maintain active steering control. This function depends on the detection of lane markers by an on-board camera, so LKA is intended for use primarily on well-developed roads and highways.
The second function works in cooperation with the dynamic radar cruise control to alert the driver with an indicator in the multi-information display and gently counter-steers the car toward the center of the lane. The LKA must be turned on by the driver and the system shuts off automatically when it detects driver input through the steering, brake pedal or turn signal operation.
Warranty
All new Lexus vehicles come with a 48-month/50,000-mile basic limited warranty with roadside assistance for 48-months/unlimited miles. Powertrain and restraint system coverage is provided for 72 months/70,000 miles. Corrosion perforation protection is covered for 72 months, regardless of mileage. The hybrid-related components, including the HV battery, battery-control module, hybrid control module and inverter with converter, are covered for eight years/100,000 miles.
Source: Toyota/Lexus
