2014 Acura RLX Sport Hybrid SH-AWD: Powertrain

2014 ACURA RLX: POWERTRAIN

The 2014 RLX Sport Hybrid's all-new three-motor hybrid powertrain combines the power of a conventional V-8 engine with 4-cylinder-like fuel efficiency and the performance-enhancing capabilities of torque-vectoring all-wheel drive.

The RLX Sport Hybrid shares it basic engine architecture with the two-wheel-drive RLX with P-AWS. The 3.5-liter, 310-horsepower, 24-valve direct-injected SOHC V-6 engine with i-VTEC® and VCM™ adds an idle-stop feature to further maximize fuel efficiency, and revised cam timing to smooth engine restart after idle stop. Peak torque to the front wheels is rated at 273 lb.-ft. at 4,700 rpm (versus 272 lb.-ft. at 4,500 rpm in the RLX with P-AWS). 

An all-new advanced 7-speed dual-clutch transmission (DCT) is standard on the Sport Hybrid—a first for Acura. Unlike a conventional automatic transmission, the DCT offers ultra-quick gear changes and eliminates the need for a torque converter, which significantly improves efficiency. It can operate in fully automatic mode, or can be shifted manually via steering wheel-mounted paddle shifters.

The RLX Sport Hybrid SH-AWD uses three electric motors: a single 35-kilowatt (47 hp) motor that is integrated with the 7-speed Dual Clutch Transmission supplements the V-6 engine in driving the front wheels, and a rear-mounted Twin Motor Unit (TMU) containing two 27-kilowatt (36 hp) motors that dynamically distribute electric-motor torque to the rear wheels. Both the front and rear motors capture kinetic energy during vehicle deceleration and braking and convert it to electricity to supply the Intelligent Power Unit's 72-cell, 1.3-kWh lithium-ion battery pack, located behind the rear seatback. Together, the 310-horsepower V-6 engine and three electric motors produce a total system output of 377 horsepower and 341 lb.-ft. of torque—the most ever in a production Acura.

The front motor is integrated with the 7-speed DCT and is connected to the driveshaft via a clutch.  The motor accomplishes three tasks: (1) It supplements the V-6 engine in driving the front wheels when additional power is required, such as in a passing situation; (2) provides regenerative braking to the front wheels; (3) converts engine power to electricity to supplement regenerative braking in recharging the lithium-ion batteries.

Acura's mechanically-based Super Handling All-Wheel Drive (SH-AWD) made its debut on the RL luxury sedan in 2005, and has since been used on a range of Acura models in several iterations. In the RLX Sport Hybrid, SH-AWD operates independent of the gasoline engine. Drawing power from the lithium-ion battery pack, the Twin Motor Unit's two electric motors deliver torque directly to the rear wheels, thereby eliminating the weight and energy losses associated with a conventional driveshaft and differential mechanism.

When cornering, the RLX Sport Hybrid delivers more torque to the outside rear wheel, much like mechanical SH-AWD, but with more available torque at low engine speeds. Sport Hybrid SH-AWD can also simultaneously apply brake torque to the inside rear wheel during cornering to further enhance cornering control. In addition, since it doesn't rely on engine torque, electric SH-AWD can create a larger torque difference between the left and right rear wheels, even during small throttle applications, at low engine speeds or even during deceleration (such as when lifting throttle mid-corner). This substantially magnifies the positive handling benefits of SH-AWD across a much wider range of driving conditions.

POWERTRAIN COMPARISON

 

2014 RLX (P-AWS)

2014 RLX Sport Hybrid SH-AWD

Gasoline Engine type

Aluminum-alloy V-6

Aluminum-alloy V-6

Displacement, liters

3.5

3.5

Fuel injection

Direct

Direct

Valvetrain

Belt drive, SOHC,
i-VTEC® 24-valve
with VCM

Belt drive, SOHC,
i-VTEC® 24-valve
with VCM and idle stop

Gasoline Engine Horsepower @ rpm (SAE net)

310 @ 6500

310 @ 6500

Gasoline Engine Torque @ rpm (lb-ft) (SAE net)

272 @ 4500

273 @ 4700

Total Combined Hybrid System Horsepower

NA

377

Compression ratio

11.5:1

11.5:1

Redline

6800 rpm

6800 rpm

Transmission

6-speed automatic transmission with Sequential SportShift paddle shifters, Sport Mode, Grade Logic and Shift Hold Control

7-speed dual-clutch transmission (DCT) with Sequential SportShift paddle shifters, automatic Drive Mode, Grade Logic and Shift Hold Control

Drive type

FWD

SH-AWD

EPA Fuel Economy Rating1 (city / highway/ combined)

20/31/24

28/32/30

Recommended fuel2

Premium unleaded
91 octane

Premium unleaded
91 octane

CARB emissions rating

ULEV-2

LEV Ⅲ SULEV30

Tune-up interval3

No scheduled tune-ups required for 100,000 +/- miles

No scheduled tune-ups required for 100,000 +/- miles

Powertrain at a Glance

Engine

  • 3.5-liter, SOHC, V-6 engine produces 310 horsepower at 6,500 rpm and 273 lb.-ft. of torque at 4,700 rpm
  • i-VTEC® (intelligent Variable Valve Timing and Lift Electronic Control) for intake valves with VCM (Variable Cylinder Management)
  • Computer-controlled Direct Injection (DI) with multi-hole fuel injectors
  • 11.5:1 compression ratio
  • High-strength steel crankshaft
  • X-shaped magnesium intake manifold
  • Drive-by-Wire™ throttle system
  • Direct ignition system
  • Detonation/knock control system
  • Variable flow exhaust system
  • Maintenance Minder™ system optimizes service intervals
  • 100,000 +/- miles tune-up interval

Emissions/Fuel Economy Ratings

  • High-flow, close-coupled next-generation precious-metal catalytic converters plus under floor catalytic converter
  • High capacity 32-bit RISC processor emissions control unit
  • LEV III/SULEV30 emissions compliant
  • EPA 28/32/301 mpg (city/highway/combined) fuel economy ratings

Noise & Vibration (NV)

  • 60-degree cylinder V-angle for smooth operation
  • Automatically tensioned, maintenance-free serpentine belt accessory drive
  • Active Control engine Mount (ACM)
  • Active sound control

7-speed dual clutch transmission

  • Electronic Gear Selector provides fully electronic push-button shift control with Sport mode button
  • Steering wheel mounted racing-inspired paddle shifters
  • Sport mode with remapped, more aggressive automatic shift points and more pronounced engine braking during deceleration
  • Advanced shift-hold control limits up shifts during spirited driving
  • Grade Logic Control System reduces gear "hunting" on steep hills

The RLX Sport Hybrid's key hybrid components are laid out for maximum packaging efficiency. One electric motor is integrated with the 7-speed DCT transmission, while two more electric motors are packaged inside the Twin Motor Unit (TMU) positioned between the rear wheels. The Power Drive Unit (PDU) is located longitudinally, low in the vehicle between the front seats, while the Intelligent Power control Unit (IPU) and its 72-cell lithium-ion battery pack is placed immediately behind the rear seatback.

Engine Architecture
The RLX Sport Hybrid 3.5-liter VTEC® V-6 has a smooth-firing 60-degree V-angle and compact overall dimensions. The V-6 has a die-cast lightweight aluminum alloy block with cast-in-place iron cylinder liners. The first ever application of direct injection in an Acura vehicle combines with i-VTEC and Variable Cylinder Management (VCM) to give the RLX a potent blend of power and fuel efficiency.

The aluminum-alloy 24-valve engine produces 310 horsepower at 6,500 and generates 273 lb.-ft. of torque at 4,700 rpm. Torque is markedly improved vs. RL in the lower ranges, where the engine typically operates. Along with the increased horsepower, the updated V-6 also contributes to increased fuel efficiency, due in part to internal friction reduction features, including an oil-ring ion-plating treatment, and plateau honing. A new tumble-type intake port design improves combustion efficiency.

Engine Block and Crankshaft
With its 60-degree V-angle, the V-6 engine is inherently smooth and has compact overall dimensions that allow efficient packaging within the vehicle. The V-6 has a die-cast lightweight aluminum alloy block with cast-in-place iron cylinder liners. Made with a centrifugal spin-casting process, the thin-wall liners are high in strength and low in porosity. The block incorporates a deep-skirt design with four bolts per bearing cap for rigid crankshaft support and minimized noise and vibration. The 3.5L V-6 uses a high-strength steel crankshaft for minimum weight.

A new cooling control spacer positioned in the water jacket surrounding the cylinders helps to maintain consistent operating temperature. Plateau honing of the cylinder lining further lowers the friction level between the pistons and the cylinders by creating an ultra-smooth surface. This two-stage machining process uses two grinding processes instead of the more conventional single honing process. Plateau honing also enhances the long-term wear characteristics of the engine.

Pistons/Connecting Rods
Designed with special "cavity-shaped" crowns, the pistons help maintain stable combustion and contribute to stratified-charge combustion. Ion-plated piston rings help reduce friction for greater operating efficiency. The compression ratio is 11.5:1. Heavy-duty steel connecting rods are forged in one piece and then the crankshaft connecting rods are "crack separated" to create a lighter and stronger rod with an optimally fitted bearing cap.  

Cylinder Heads/ Valvetrain
Like other Acura V-6 powerplants, the RLX Sport Hybrid engine's 4-valve cylinder heads are a single-overhead-camshaft design, with the cams driven by the crankshaft via an automatically tensioned toothed belt. Made of low-pressure cast, low-porosity aluminum, each cylinder head incorporates a new "tumble port" design that improves combustion efficiency by creating a more homogeneous fuel-air mixture. An integrated exhaust manifold cast into each cylinder head reduces parts count, saves weight, improves flow and optimizes the location of the close-coupled catalyst.

i-VTEC Valve Control System
The RLX Sport Hybrid V-6 engine combines Variable Cylinder Management (VCM) with Variable Valve Timing and Lift Electronic Control (VTEC), which changes the lift profile, timing and lift duration of the intake valves. A switching mechanism allows each cylinder to operate with low-rpm valve lift and duration or high-rpm lift and duration. The rear cylinder bank's valve gear can also leave all intake and exhaust valves closed to maximize fuel efficiency during cylinder deactivation.

The "intelligent" portion of the system is its ability to vary valve operation based on the driving situation and engine rpm. At low rpm, the VTEC intake valve timing and lift are optimized (low lift, short duration) for increased torque, which allows a wide range of 3-cylinder operation. As engine rpm builds past 5,000 rpm, the VTEC system transitions to a high-lift, long-duration intake cam profile for superior high-rpm engine power.

Variable Cylinder Management ™ (VCM™)
The RLX Sport Hybrid engine employs Acura's Variable Cylinder Management (VCM) cylinder deactivation technology. The VTEC system combines with Active Control engine Mounts (ACM) to allow the VCM system to operate with three cylinders in a wide range of situations to maximize fuel efficiency and lower emissions. When greater power is needed, the system switches seamlessly to 6-cylinder operation. With the strong power output of the Direct Injection RLX engine, a 4-cylinder operating mode (as used on the port fuel injected 2013 RDX) is not needed.

During startup, aggressive acceleration, or when climbing hills – any time high power output is required – the engine operates on all six cylinders. During moderate-speed cruising and at low or moderate engine loads, the system operates just the front bank of three cylinders.

The VCM system can tailor the working displacement of the engine to match the driving requirements from moment to moment. Since the system automatically closes both the intake and exhaust valves of the cylinders that are not used, pumping losses associated with intake and exhaust are eliminated and fuel efficiency gets a further boost. The system combines maximum performance and maximum fuel efficiency – two characteristics that don't typically coexist in conventional engines.

VCM deactivates specific cylinders by using the i-VTEC (intelligent Variable Valve-Timing and Lift Electronic Control) system to close the intake and exhaust valves while the Power Control Module (PCM) simultaneously cuts fuel to those cylinders. The spark plugs continue to fire in inactive cylinders to minimize plug temperature loss and prevent fouling induced from incomplete combustion during cylinder re-activation.

The system is electronically controlled, and uses special integrated spool valves in the cylinder heads. Based on commands from the system's electronic control unit, the spool valves selectively direct oil pressure to the rocker arms for specific cylinders. This oil pressure in turn drives synchronizing pistons that connect and disconnect the rocker arms.

The VCM system monitors throttle position, vehicle speed, engine speed, automatic-transmission gear selection and other factors to determine the correct cylinder activation scheme for the operating conditions. In addition, the system determines whether engine oil pressure is suitable for VCM switching and whether catalytic-converter temperature will remain in the proper range. Importantly, the drive by wire control is able to finely match torques in 6-cylinder and 3-cylinder combustion modes, making the transition between the two virtually unnoticeable.

Direct Injection System
Conventional engines using multi-port fuel injection mix fuel and air before they enter the combustion chamber. With direct injection, fuel is injected directly into each combustion chamber. This allows for better combustion and overall efficiency.

The RLX V-6 engine is the first application of direct injection for an Acura vehicle in the United States. The system features a compact, high-pressure, direct-injection pump that allows both high fuel flow and pulsation suppression, while variable pressure control optimizes injector operation. A multi-hole injector delivers fuel directly into each cylinder (not to the intake port, as in conventional port fuel injection designs).

The multi-hole injectors can create the ideal stoichiometric fuel/air mixture in the cylinders for good emissions control. Theoretically, a stoichiometric mixture has just enough air to completely burn the available fuel.

Based on the operating conditions, the direct-injection system alters its function for best performance. Upon cold engine startup, fuel is injected into the cylinders on the compression stroke. This creates a weak stratified charge effect that improves engine start-up and reduces exhaust emissions before normal operating temperature is reached.

Once the engine is fully warm for maximum power and fuel efficiency, fuel is injected during the intake stroke. This helps create a more homogeneous fuel/air mix in the cylinder that is aided by the high-tumble intake port design. This improves volumetric efficiency, and the cooling effect of the incoming fuel improves anti-knock performance.

Active Control Engine Mounts and Active Sound Control
A new, more powerful 28-volt Active Control Engine Mount system (ACM) is used to minimize the effects of engine vibration as the VCM system switches cylinders on and off. The 28-volt ACM is a key factor in the VCM's broad range of operation in the new RLX. Sensors alert the Electronic Control Unit (ECU) to direct ACM actuators positioned at the front and rear of the engine to cancel engine vibration. In the cabin of the RLX, an Active Sound Control system further reduces low frequency sound relating to the function of the VCM system. (See Interior section for more information.)

Vibration Reduction Technology
Since the RLX Sport Hybrid's gasoline engine can be shut down during certain driving conditions (idle stop), it incorporates measures to mitigate engine vibration during restarts. Compared to the two-wheel-drive RLX, the RLX Sport Hybrid has unique intake cam profiles that close the intake valves later, effectively lowering the compression ratio at startup to reduce vibration. To further reduce vibration, the electrically actuated hydraulic Active Control Mounts (see above) are synchronized with engine start-up. A dual-mass flywheel helps further reduce engine vibration when the gasoline engine is in operation.

Drive-by-Wire Throttle System
The RLX doesn't use a conventional throttle cable, but instead has smart electronics that "connect" the throttle pedal to a throttle valve inside the throttle-body. The result is less underhood clutter and lower weight, as well as quicker and more accurate throttle actuation. Plus, specially programmed "gain" between the throttle pedal and engine offers improved drivability and optimized engine response to suit specific driving conditions.

Acura's Drive-by-Wire throttle system establishes the current driving conditions by monitoring throttle pedal position, throttle valve position, engine rpm and road speed. This information is used to define the throttle control sensitivity that gives the RLX's throttle pedal a predictable and responsive feel that meets driver expectations. There are two different throttle profiles available in the RLX. When the transmission is in "D" (Drive) the drive-by-wire system uses the normal profile. When the Sport mode is engaged by pressing the Sport button located near the shift lever, the system changes the throttle map to enhance response feel.

Direct Ignition and Detonation/Knock Control
The RLX's Power Control Module (PCM) monitors engine functions to determine the best ignition spark timing. An engine block-mounted acoustic detonation/knock sensor "listens" to the engine, and based on this input, the PCM can retard the ignition timing to prevent potentially damaging detonation. The 3.5L V-6 has an ignition coil unit for each cylinder that is positioned above each spark plug's access bore.

Close-Coupled Catalysts and Variable Flow Exhaust System
The exhaust manifolds of the 3.5L V-6 are cast directly into the aluminum cylinder heads to reduce weight, decrease parts count, and create more underhood space. The result of this casting design is that the two primary catalytic converters are positioned much closer to the combustion chambers. High-efficiency next-generation precious metal catalytic converters are mounted directly to the exhaust port of each cylinder head to enable extremely rapid converter "light-off" after the engine starts. A significant weight savings is realized by eliminating traditional exhaust manifolds.

Downstream of the close-coupled catalytic converters, a hydroformed 2-into-1 collector pipe carries exhaust gases to a secondary catalytic converter located under the passenger cabin floorboard. This high-flow secondary catalytic converter has a large inlet and outlet to enhance exhaust flow. To balance the engine's need for quiet operation at low rpm and higher flow at high rpm, the RLX's dual exhaust system incorporates a variable flow rate feature. Pressure-operated exhaust valves in each silencer are closed in normal operation, reducing exhaust noise by as much as 8 dB. When the driver demands more performance from the RLX, rising exhaust gas pressure opens both valves. The additional exhaust flow ads five horsepower to the engine's peak output.

Emissions Control
The 2014 RLX Sport Hybrid utilizes a higher amount of precious metals in its under-floor catalyst to meet CARB LEV III SULEV 30 emissions standards.

A number of advanced technologies are factors in the emissions performance. The unique cylinder head-mounted close-coupled catalytic converters light off more quickly after engine start up, and a 32-bit RISC microprocessor within the powertrain control module (PCM) boosts computing power to improve the precision of spark and fuel delivery.

The RLX's V-6 engine features Programmed Fuel Injection (PGM-FI) that continually adjusts the fuel delivery to yield the best combination of power, low fuel consumption and low emissions. Multiple sensors constantly monitor critical engine operating parameters such as intake air temperature, ambient air pressure, throttle position, intake airflow volume, intake manifold pressure, coolant temperature, exhaust-to-air ratios, as well as the position of the crankshaft and the camshafts.

To further improve emissions compliance, the 3.5L V-6 makes use of an after-cat design exhaust gas recirculation (EGR) system that allows cleaner, cooler EGR gas to be fed back into the intake system. An EGR system, especially one that delivers a cleaner/cooler charge, reduces pumping loss for better fuel efficiency.

One-Touch Start System
To ensure consistent starting, the RLX has a one-touch start system that maintains starter engagement until the engine starts. Should the driver release the Start button before the engine starts, the system will start the vehicle. Simply push the Start button (with the fob in the vehicle) and the engine will automatically start up.

Noise & Vibration Control
With its 60-degree V-angle and compact, rigid and lightweight die-cast aluminum cylinder block assembly, the 3.5L V-6 powerplant is exceptionally smooth during operation. Other factors that help reduce engine noise and vibration are a rigid forged-steel crankshaft, die-cast accessory mounts, and a stiff cast-aluminum oil pan that reduces cylinder block flex.

Idle Stop Feature
Idle stop stops cylinder combustion and cylinder activation, eliminating fuel use when the vehicle is stopped, such as at traffic light or in heavy traffic conditions.  The engine is restarted by the 35-kilowatt front motor-generator using energy from the lithium ion hybrid battery pack.  Unlike some competing systems, the engine restart is extremely smooth and refined, practically undetectable to the vehicle's occupants. 

7-Speed Dual-Clutch Transmission (DCT)
To maximize performance and fuel efficiency, the RLX Sport Hybrid has a standard 7-Speed Dual-Clutch Transmission (DCT). In the 7-speed DCT, one clutch controls the odd gears while the other clutch controls the even gears. This arrangement allows gear changes with a much smaller interruption in power to the wheels, resulting in millisecond-quick shifts. Compared to a conventional manual transmission, the operation of the clutches and shifting mechanisms are electronically controlled, eliminating the need for a clutch pedal or shift lever. Compared to a conventional automatic, the torque converter and its mechanical inefficiencies are also eliminated. The DCT transmission in the RLX Sport Hybrid also features a 17-percent wider ratio range than the 6-speed automatic transmission in the RLX with P-AWS.

Gear Ratios

 

RLX with P-AWS
(6-speed AT)

RLX Sport Hybrid SH-AWD
(7-speed DCT)

Low

14.276

15.732

2nd

8.903

9.851

3rd

6.310

7.281

4th

4.527

5.534

5th

3.206

4.090

6th

2.361

3.014

7th

-

2.228

RVS

9.644

13.110

Final

4.25

3.579

Ratio Range

6.05

7.06

Electronic Gear Selector
In the RLX Sport Hybrid, a conventional console-mounted shift lever is replaced with an all-new Electronic Gear Selector fully electronic, shift-by-wire gear selector. Park, Neutral and Drive are selected with the push of a button. Reverse is selected by pulling back a dedicated switch. Indicator lights near the buttons indicate the mode selected. As an added safety feature, if the vehicle is brought to a stop in Drive, the system will automatically select Park if the driver's seatbelt is unbuckled and the driver's door is opened.

Transmission Modes
When in Drive mode, the 7-speed dual-clutch transmission can be controlled steering wheel-mounted paddle shifters. While traveling up or down hills, Grade Logic Control alters the transmission's shift schedule to reduce shift frequency and improve speed control. A shift map in the transmission computer continually measures throttle position, vehicle speed and acceleration/deceleration, and then determines when the vehicle is on a hill. The shift schedule is then adjusted to hold the transmission in lower gears to boost climbing power or to provide engine braking when traveling downhill.

Shift Hold Control keeps the transmission in its current (lower) gear ratio when aggressive driving is detected, as in the case of decelerating at a corner entry. Shift Hold Control leaves the chassis undisturbed by excess shifting and ensures that power will be immediately available (without a downshift) at the corner exit.

The RLX Sport Hybrid features Sport and Normal modes. A selector button located on the center console allows the driver to toggle between the two operating modes. Normal mode is aimed at overall energy efficiency. Sport mode, by contrast, puts greater emphasis on the driving experience, delivering a more responsive and direct feel. Sport mode offers more aggressive and sporty shift mapping, engine rpm "blips" on downshifts, while VCM and idle stop functions are cancelled. All of the transmission logic systems work together to automatically alter shift timing based on driving conditions.

Temporary Manual Operation in "Drive"
Whether in Drive or Sport mode, special transmission logic programming allows the use of the steering-wheel-mounted paddle shifters. When the driver operates the steering wheel-mounted paddle shifters while in Drive, the transmission responds to the driver's shift command and then returns to its normal fully automatic mode if further paddle shift inputs are not made within a given time. This special logic makes it easy for the driver to command a quick downshift without leaving the comfort of Drive mode. When in Sport mode, use of the paddle shifters puts the transmission into full manual mode that remains until another mode of operation is selected.

Manual Mode
By pressing the "Sport" button located near the gear selector button, Sport mode is engaged. This mode offers automatic operation with more aggressive shift mapping. A pull on the racing-inspired paddle shifters (mounted on the steering wheel) places the transmission in fully manual mode. A digital display in the instrument cluster indicates which gear the transmission is in. The system reverts to normal fully automatic mode if further paddle shift inputs are not made within a given time.

Sport Hybrid Super Handling All-Wheel Drive (SH-AWD)
The RLX Sport Hybrid is the first production vehicle to employ an electric version of Super Handling All-Wheel Drive (SH-AWD). Previous mechanical versions of SH-AWD had the ability to vary the amount of power sent to the rear axle, and to also vary rear power distribution between the left and right rear wheels via a longitudinally mounted drive shaft and rear differential with twin electronically controlled clutch packs.

In the RLX Sport Hybrid, the driveshaft and rear differential of a conventional all-wheel drive system is eliminated, replaced by twin 27-kilowatt (36 hp) electric motors that independently drive the left and right rear wheels. Each motor can also capture regenerative braking energy and apply negative (regenerative braking) torque to further enhance cornering capability.

Independent distribution of torque to all four wheels is a key feature of SH-AWD and its ability to enhance both dynamic handling and all-weather traction. When cornering, more positive (drive) torque is applied to the outside rear wheel, while negative (regenerative braking) torque can be applied to the inside rear wheel. This torque differential creates a yaw moment, producing sharper turn-in, more linear cornering, enhanced traceability and improved steering response with reduced understeer tendencies. In addition, since the system doesn't rely on the gasoline engine for torque, electric SH-AWD can create a larger torque difference between the left and right rear wheels, even during small throttle applications, at low engine speeds, or even during deceleration (such as lifting throttle mid-corner). This substantially magnifies the positive handling benefits of SH-AWD across a much wider range of driving conditions. 

Power Drive Unit (PDU)
The Power Drive Unit, packaged in the center of the vehicle beneath the center console, dictates the power management strategy of the Sport Hybrid SH-AWD system, including motor power and battery recharge.

Intelligent Power Unit (IPU)
The Intelligent Power Unit is positioned above the Twin Motor Unit, behind the rear seatback. The IPU contains the hybrid system's lithium-ion battery, 12-volt DC/DC converter, junction board, and Electronic Control Units (ECU) for the motors and the battery. The IPU is air-cooled via an integrated fan unit that draws air from inside the vehicle cabin via an intake duct located beneath the rear seats.

1.3-kWh Lithium-Ion Battery
The RLX Sport Hybrid's advanced 72-cell lithium-ion battery has 29 percent greater power density and 5 percent greater energy density compared to the lithium-ion battery in the ILX hybrid.

Front Electric Motor
A single 35-kilowatt (47 hp) electric motor is integrated with the 7-speed DCT. The motor's operating temperature is optimized by a temperature-controlled flow of Automatic Transmission Fluid (ATF) through the motor housing. By tightly controlling the motor temperature, the motor's torque output (both drive and regeneration) can be improved up to 100 percent.

Twin Motor Unit (TMU)
The RLX Sport Hybrid's Twin Motor Unit (TMU) is located in between the rear wheels, where a differential on an all-wheel-drive vehicle is typically mounted. Inside its die-cast aluminum housing are two electric motors positioned back-to-back. Each 27-kilowatt (36-horsepower) motor powers a single rear wheel and can also apply negative torque to the same wheel. A clutch allows each motor to be decoupled from its wheel in certain operating situations to improve efficiency.

Electrically Powered Air Conditioning Compressor
Since the RLX Sport Hybrid engine has an idle-stop feature, it is equipped with an electrically powered air conditioning compressor. This allows continuous air conditioning operation even when the gasoline engine is shut off.

Hybrid System Safety
To maximize passenger safety, the hybrid system components are positioned in well-protected areas of the vehicle. In the event of a collision that triggers the airbags, an automatic high-voltage circuit interrupt in the Intelligent Power Unit cuts power to the hybrid system.

100,000 Mile Tune-up Intervals
The RLX's 3.5L V-6 requires no scheduled maintenance for 100,000+/- miles or more, other than periodic inspections and normal fluid and filter replacements. The first tune-up includes water pump inspection, valve adjustment, replacement of the camshaft timing belt, and the installation of new spark plugs.

Maintenance Minder™ System
To eliminate unnecessary service stops while ensuring that the vehicle is properly maintained, the RLX Sport Hybrid has a Maintenance Minder™ system that continually monitors the vehicle's operating condition. When maintenance is required, the driver is alerted via a message on the Multi-Information Display (MID).

The Maintenance Minder™ system monitors operating conditions such as oil and coolant temperature along with engine speed to determine the proper service intervals. Depending on operating conditions, oil change intervals can be extended to a maximum of 10,000 miles, potentially sparing the owner considerable expenditures and inconvenience over the life of the vehicle. The owner-resettable system monitors all normal service parts and systems, including oil and filter, tire rotation, air-cleaner, automatic transmission fluid, spark plugs, timing belt, coolant and more. To avoid driver distraction while the vehicle is being operated, maintenance alerts are presented on the MID when the ignition is first turned on.

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