- EPA-Estimated Rating of 35 MPG Combined Using 87-Octane Fuel
- Innovative Driver-Inspired Cabin
- Ecological Plastics Illustrate Sustainable Luxury
Engine and Hybrid System
The HS 250h features the brand’s first four-cylinder gas engine paired with Lexus Hybrid Drive. Utilizing the most recent generation hybrid system, HS 250h takes 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, an 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 HS 250h. 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 a 3.48-in. bore diameter and 3.78-in. 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 250h generates 187 total system horsepower.
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, A/C 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 helps prevent 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 luxury utility vehicle, 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 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 (ECVT) 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 HS 250h also incorporates drive-mode buttons that allow the driver to select between four modes: Normal, Power, Eco and EV. Each mode changes the rate of throttle opening for a given throttle-pedal angle. Normal mode has an essentially linear throttle response that gives naturally progressive power. Power mode can be selected for a more responsive feel when desired. In Eco mode, air conditioning settings are adjusted and the throttle response is reduced relative to the pedal angle to emphasize fuel economy. Under certain circumstances, the EV mode can allow the vehicle to be driven short distances using only the electric motors.
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 ECVT’s ability to quickly find the optimal gear ratio enhance the driving experience.
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 strong but strategically resilient to help absorb and distribute energy in the event of a crash. High strength steel components are carefully located in the body structure, doors and other areas to help ensure strength in key areas.
Additionally, front and outer rear seatbelts incorporate pretensioners with force-limiters to help protect occupants in the event of certain severe frontal collisions. Active front headrests are also standard.
An optional Pre-Collision System (PCS) with Dynamic Radar Cruise Control and Driver Monitor can help reduce collision damage. Dynamic Radar Cruise Control uses millimeter-wave radar to measure and help maintain a pre-set following distance from a vehicle traveling ahead. The radar sensor is designed to 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 (BA) so that increased braking will be applied the instant the driver depresses the pedal.
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 Drive Indicator light further assists the driver in maintaining the most economical use of system power.
The HS 250h offers an optional Lane Keep Assist (LKA) feature that is designed to help drivers stay within their chosen lane and uses Dynamic Radar Cruise Control and the lane-departure warning (LDW) function. LKA and LDW depend on the detection of lane markers by an on-board camera, and are intended for use primarily on well-developed roads and highways.
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.
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 an available 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.
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.
The HS 250h interior was designed to communicate the high level of innovation inherent in the car with the craftsmanship expected from Lexus products. The center stack sweeps rearward to the available 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.
Ecological plastics are 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 combined interior and luggage areas covered in ecological plastic.
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.