Acura Automobiles: 2014 Acura RLX Sport Hybrid SH-AWD: Chassis

The RLX Sport Hybrid is responsive and surefooted in a way that makes precision driving easy – delivering on Acura’s commitment to create “the synergy between man and machine”.

Key traits of the RLX Sport Hybrid chassis dynamics include:

  • Agile and accurate cornering with linear response
  • Tight, stable and nimble handling
  • Smooth and connected handling
  • Outstanding high-speed stability
  • Comfortable, flat and smooth ride
  • Confident braking performance
  • Outstanding steering feel
  • Low NVH properties

Chassis Concept
The goal behind the RLX Sport Hybrid chassis was to deliver “the synergy between man and machine” or dynamic handling that truly responds to “the will of the driver.” This refers to the way in which Acura engineers envisioned the entire package of the RLX responding instantaneously and precisely, with technology used to improve the driver’s capability and confidence. The result is a vehicle that, more than any Acura before it, creates a driving experience that performs at the will of the driver.

Sport Mode
A driver-selectable Sport mode further enhances driving dynamics across a wide range of driving situations. When the driver engages the Sport button on the center console, the system adopts more aggressive shift mapping and rear wheel torque-vectoring control. The system also deactivates Idle Stop, Variable Cylinder Management (no 3-cylinder mode) and the Reactive Force Pedal, plus the Active Sound Control system is modified to provide an even sportier driving experience.

Front Aluminum Subframe
The RLX Sport Hybrid has a lightweight and rigid front aluminum front subframe that is specifically designed to support the high performance of the double wishbone, lower double-joint front suspension with Amplitude Reactive Dampers and belt-type Electric Power Steering (EPS) system. Using die cast front corners, the RLX Sport Hybrid’s front subframe is also wider across the middle, features wider middle and rear rails, and a wider rear section vs. RL to accommodate the new EPS system. Rigidity is up 82 percent compared to RL.

With its lightweight and rigidity, the new aluminum front subframe contributes to agile and light handling, straight-line stability, higher fuel efficiency, flat cornering and pleasing ride comfort, and smooth and precise steering feel (with reduced torque steer tendencies).

The RLX Sport Hybrid subframe is matched to the Active Control Engine Mount (ACM) system that is engineered specifically for the RLX’s higher-output engine and Variable Cylinder Management (VCM) system. (See Powertrain section for more information.)

Lower Double-Joint Front Suspension
The RLX Sport Hybrid utilizes the same double-wishbone, lower double-joint front suspension as the RLX with P-AWS, which significantly improves intuitive handling agility, driver confidence and security, and ride sophistication. The system includes a lower double joint with a split lower control arm, optimized kingpin geometry, upper control arm, hydraulic compliance bushing, special dual-stage Amplitude Reactive Dampers made for Acura by ZF-Sachs, and a stabilizer bar that is heat treated for high strength.

Benefits include:

  • Agility – Improved steering feel characteristics including stability, linearity, response and tracing performance
  • Driver Confidence – Increased high speed linearity with reduced torque steer/pulling, shimmy and judder
  • Ride Sophistication – Flat ride with reduced harshness and steering vibration

Multi-Link Rear Suspension
Like the lower double-joint front suspension, the RLX Sport Hybrid’s multi-link rear suspension with Amplitude Reactive Dampers provides optimal handling agility, driver confidence and ride sophistication. The multi-link system geometry is optimized for a flat ride during cornering, confident turning capability, and a sophisticated ride in a variety of urban, highway and open road scenarios. The system includes multi-link control arms, control-arm bushings that are optimized for the best blend of NVH isolation and handling precision, Amplitude Reactive Dampers, and a rear stabilizer bar that is hardened with a special shot-peening process.

Amplitude Reactive Dampers
Amplitude Reactive Dampers provide superior ride comfort and handling in all driving conditions. The dampers have two separate damping mechanisms: one that is tuned for maximum efficiency on smoother roads with small inputs; and the other that is tuned to handle large inputs such as rough roads, potholes, and sudden steering and braking action. The result is a vehicle that remains composed and comfortable in a wide range of driving conditions.

The core technology contained within the Amplitude Reactive Dampers is their two separate damping pistons, including a main piston and a second piston. To improve overall ride comfort, when smaller inputs occur during normal driving conditions, only the main piston works to provide the ideal damping characteristics. To improve the RLX’s ride and handling during more severe conditions, the second piston operates to provide additional damping force.

The Amplitude Reactive Dampers are a purely mechanical system that does not require electronic controls. Altogether, they provide a much wider range of damping performance than the previous RL.

High-Output Electric Power Steering (EPS)
The RLX Sport Hybrid Electric Power Steering (EPS) system uses a high-power, belt-type electric steering assist. The system increases the torque available to assist the driver in steering the vehicle smoothly, with instantaneous response, direct feel, and improved low-speed agility and high-speed stability.

The variable gear ratio EPS uses a high-output electric assist motor with a belt-drive system. The system is designed and tuned to provide the two most essential characteristics in a high-performance luxury vehicle’s steering. These include a smooth initial response (shorter delay) at the start of steering input, and greater linearity response (steering force camber increase) as input is increased. As a result, the RLX’s high-output EPS provides agile performance in low-speed driving maneuvers such as at intersections, improved overall accuracy and road feel, and superb high-speed stability.

Rigid Steering Column
The RLX Sport Hybrid steering column is a highly rigid design with an aluminum bracket and resin angular bearing. The resulting stiffness gives maximum driver steering feedback along with minimizing vibration felt in the wheel.

The steering shaft is significantly larger in diameter than the shaft found in the previous RL, and together with the stiff but lightweight aluminum support bracket and angular bearing, yields maximum vibration-damping characteristics for a more luxurious driving experience.

Electrically actuated tilt and telescoping adjustment makes it easy to set the steering wheel to the ideal position for drivers of different sizes.

4-Wheel Disc Brakes with ABS and Brake Assist
RLX Sport Hybrid is equipped with 4-wheel disc brakes with a 4-channel anti-lock braking system (ABS) for confident stops. The front discs measure 12.99 inches in diameter, while the rear discs measure 12.2 inches in diameter.

ABS independently modulates braking power at each wheel to help the driver retain steering control during heavy braking, while Brake Assist recognizes emergency braking situations and almost instantly applies full braking force when appropriate.

The brake pads are a high-friction type for peak stopping performance even under strenuous conditions. The brake calipers are designed to reduce brake drag when not in use, reducing rolling resistance and improving fuel efficiency in the process.

Electric Servo Brakes
The RLX Sport Hybrid’s electric servo brake system maximizes regenerative braking capability for improved fuel efficiency. The braking system is fully hydraulic from the master cylinder all the way to the 4-wheel disc brakes, just like a traditional braking system. The key difference is that the braking function is electronically controlled rather than a purely mechanical activation, allowing regenerative braking from the front and rear electric motors to slow the vehicle, rather than the hydraulic friction brakes, under most circumstances. Besides its payoff in efficiency, the system offers excellent feel and feedback for the driver through the brake pedal.

When the driver applies the brake pedal, a signal is sent to the vehicle’s Electronic Control Unit (ECU), which determines the appropriate amount of braking force to assign to regenerative braking through the electric drive motor and to the hydraulic friction braking system. In many cases, friction braking is not needed until the vehicle speed drops below 9 mph, as the vehicle slows to a final stop. When the ECU determines that friction braking is needed, the dual hydraulic master cylinder pumps brake fluid through the system. Midway between the master cylinder and the calipers is a separate motorized electronic actuator. This actuator receives an electronic signal, generated in the master cylinder module that precisely defines how the driver has applied the brakes – soft or hard, slow or fast. The actuator then directly apportions hydraulic pressure to the brake calipers at each wheel.

While the RLX with P-AWS uses a 10-inch vacuum booster to assist the driver in applying needed brake pressure, the RLX Sport Hybrid uses an electric servo brake actuator.

Reactive Force Pedal
The RLX Sport Hybrid is the first model to apply the Acura-developed Reactive Force Pedal technology. In Normal mode, the system measures vehicle speed and dynamically varies pedal force to help the driver in applying the optimal amount of throttle for both spirited performance and good fuel economy.  In slippery conditions, the system can also help the driver apply the optimal amount of driving force while minimizing wheel slip, utilizing input from the Vehicle Stability Assist system.  Further, in the event that the Collision Mitigation Brake System (CMBS) detects that a frontal collision is imminent, the Reactive Force Pedal will push back on the driver’s foot even before the CMBS system activates its visual and auditory alerts.

Electric Parking Brake + Automatic Brake Hold
The combination of Electric Parking Brake (EPB) and Automatic Brake Hold are a first for the Acura division. Together, they meaningfully reduce the effort of driving the vehicle, thereby raising overall comfort to a true flagship level.

Electric Parking Brake

The Electric Parking Brake (EPB) on the RLX Sport Hybrid makes using the parking brake easier and more comfortable. Actuating the parking brake is now as simple as pulling a button on the center console. To release the parking brake, the driver simply   presses on the accelerator pedal. In addition to being simpler, more convenient and more comfortable to use than a traditional parking brake, the new Electric Parking Brake makes hill starts easier when the RLX is parked on a grade.

The ease of use also promotes the use of the parking brake. Further, since only a few competitive vehicles have an Electric Parking Brake (EPB) system, its inclusion in the RLX further defines the new Acura as a true flagship. As with a traditional manually activated parking brake, EPB functions on the rear wheels only.

Automatic Brake Hold
The RLX Sport Hybrid also features Automatic Brake Hold, which retains brake pressure when the vehicle is stopped, simplifying driving in heavy traffic or hills. This frees the driver from continually pressing the brake pedal to maintain the vehicle in a stopped position, a significant improvement in driving enjoyment in difficult conditions.

Operating the system requires two simple actions from the driver:

  • Activating/deactivating the system via a switch on the center console.
  • Pressing on the brake pedal when the vehicle comes to a stop.

Once these steps are taken, Automatic Brake Hold will indicate engagement and then maintain brake pressure when the vehicle has come to a stop, even if the driver releases the brake pedal. The RLX then remains stopped – even on a hill – until the driver presses the accelerator pedal. At this point Automatic Brake Hold releases the brakes and the vehicle resumes normal braking function.

Vehicle Stability Assist™ (VSA®)
The RLX Sport Hybrid’s high-efficiency Vehicle Stability Assist™ (VSA) works in conjunction with the ABS and the Drive-by-Wire throttle systems. This premium VSA system enhances vehicle stability when cornering. If vehicle understeer or oversteer is detected, the system selectively reduces power and/or applies braking force to individual wheels to help correct the condition and stabilize the vehicle.

Traction control monitors front-wheel slippage, such as when starting on slick surfaces or patches of ice. If it is detected, traction control activates one or more brake calipers and reduces engine torque to slow the spinning wheel so it can regain traction.

Agile Handling Assist
Agile Handling Assist works in near limit cornering by using the brakes to create a yaw moment, helping the driver smoothly and easily trace the desired line with smaller steering-wheel inputs. The result is improved dynamic performance in all driving conditions, helping the RLX Sport Hybrid perform at the will of the driver.

Tire Pressure Monitoring System (TPMS)
A standard Tire Pressure Monitoring System (TPMS) helps the driver maintain proper air pressure to improve driving safety and fuel efficiency, as well as reduce wear and tear on the vehicle’s tires. Located in the instrument panel, a TPMS icon illuminates to alert the driver whenever any of the tires has a significantly low-pressure reading that requires the driver’s attention.

Noise-Reducing Wheels
The RLX Sport Hybrid features model-exclusive10-spoke, 19x8J alloy wheels with a painted Glitter Silver Metallic finish.  The RLX Sport Hybrid’s wheels have a special noise-reducing design that lowers noise by as much as 7 dB in the mid-frequency range. The key elements of the noise-reducing four resin moldings fitted on the inside of the wheel rim. The result is reduced noise resonance in the air column inside the wheel.

All-Season Tires
The RLX Sport Hybrid is shod with 245/40R19 M+S tires. The RLX features an easy-to-use tire repair kit in lieu of a spare tire. This reduces weight and increases trunk volume, and simplifies temporary repairs in the event of a flat tire.

Capless Fueling System
The RLX’s capless fueling eliminates the fuel cap, meaning that fueling the vehicle now simply requires opening the fuel-tank lid, refueling, and then closing the lid. This reduces the possibility of damaging the vehicle’s paint with the fuel cap or tether, or forgetting the fuel cap at the gas station. The system also allows the use of a smaller fuel-cap door, which cleans up the lines of the vehicle.

The system consists of two integrated components, including an outer shutter mechanism that prevents the intrusion of dirt and dust, and a self-sealing fueling flap that is closed by a torsion spring. Both operate automatically.

At a gas station, the driver simply opens the fuel lid (which automatically locks with the doors) and then inserts the fuel nozzle. Inserting the nozzle automatically opens the outer shutter and fueling flap. When fueling is complete, removing the fuel nozzle automatically closes both the fueling flap and outer shutter.

15.1-Gallon Fuel Capacity
The RLX Sport Hybrid’s resin fuel tank capacity of 15.1 gallons gives the RLX an ample cruising range. Both the fuel tank and fuel pipe are made of high-impact resin for lightweight and durability. The fuel tank is located in a protected area in front of the rear suspension.