2011 Acura ZDX - Chassis
From the beginning, with the ZDX concept Acura designers committed to meeting and surpassing the vehicle dynamics and driving feel of its primary competitors— the BMW X6 and Infiniti FX35. The essential engineering targets included steering, suspension, braking and overall dynamic performance. In addition, superior control of noise, vibration and harshness (NVH) was paramount, as was the choice of dedicated Comfort and Sport modes made possible by an available Integrated Dynamics System (IDS).
To achieve a combination of ride comfort and a fun-to-drive character in most weather conditions, Acura used the famed Nürburgring Nördschleife circuit in Germany as an essential development tool. This 12.9-mile course contains more than 170 corners and is considered the toughest natural road course in the world. Engineers used the Nürburgring as a "weakness finder" because it clearly exposes problems with a vehicle's dynamics, making them easier to identify and fix. Engineers took the ZDX to the Nürburgring on two separate occasions— once during pre-prototype testing to develop what would become the production suspension systems, and a second time with a prototype.
With its standard 19x8.5-inch wheels and available Active Damper System, the ZDX offers an excellent blend of all-season handling capability. Focusing on a passionate European driving experience, while also providing sophisticated control of NVH, the ZDX is a supremely comfortable long-distance machine and an exhilarating partner on back roads.
The overall dynamic target for the Acura ZDX was to provide sports sedan-like ride and handling without compromising ground clearance and all-weather handling performance. Built for driving passion, the ZDX achieves these three main goals:
- Enjoyable and comfortable overall driving experience
- Exciting on-road, track-quality handling for driving enthusiasts
- Moderate off-highway capabilities
For general driving conditions, Acura simultaneously targeted a smooth ride with extremely accurate vehicle control— all while limiting NVH. In addition, the available Integrated Dynamics System (IDS), which includes Active Damping System (ADS), allows the driver to switch between Comfort and Sport modes, expanding the personality of the ZDX. The range between the two damper settings is significantly wider compared to the damper systems offered on the BMW X6 and Infiniti FX35. In addition, with IDS the steering performance is linked to ADS to better suit the performance desires of the driver.
Two typical scenarios where the Active Damper System (ADS) suspension shines:
- Cruising up the coast in the Comfort mode provides a comfortable, controlled and non-fatiguing driving experience
- Driving on a mountain road in the Sport mode delivers more precise, exceptionally responsive handling and steering
The ZDX's front chassis was tuned to provide the best balance of handling precision, road isolation and impact aftershake damping. MacPherson struts team with coil-over springs and lower control arms constructed of forged aluminum to reduce unsprung weight. The front subframe "floats" on rubber mounts to provide road and engine isolation, and the subframe assembly is affixed to the main body structure with heavy-duty braces. The front suspension also uses hydro-compliance bushings to provide superior ride isolation as well as chassis vibration control. Suspension and engine mounts are specifically tuned to provide minimum vibration transfer to the occupants, and the front struts employ internal rebound springs to improve ride and handling. Anti-dive properties were specially tuned to reduce impact harshness and improve ride comfort.
The ZDX's rear suspension is a multi-link design mounted on a separate steel subframe. Cast aluminum uprights reduce unsprung weight, while precise trailing-arm mounting points reduce body squat during hard acceleration. Constant rate coil springs, dampers and an anti-roll bar are tuned for the optimum combination of ride and handling. Rear subframe mounts and lateral control link bushing rates create a discrete level of lateral force steer at the rear axle. Since the SH-AWD™ system constantly varies drive torque at the rear axle, the longitudinal and lateral force steer properties were carefully developed for optimum response, stability and consistency.
ACTIVE DAMPER SYSTEM
Many luxury vehicles offer some type of body motion control system using air suspension, electronically controlled dampers or automatically adjustable stabilizer bars. Acura considered all of the available technologies before choosing electronically-controlled "semi active" Magneto-Rheological fluid-filled dampers as the ideal technology to maximize ride comfort and handling— all in one integrated system. Included within the available Advance Package, the Active Damper System gives the 2011 ZDX an elevated level of handling precision designed to satisfy the most discriminating drivers, while maintaining a smooth and controlled ride.
The overall goal of the Active Damper System is to achieve an outstanding level of handling response while maintaining a refined level of ride comfort. This allows the driver intuitive vehicle control in a relaxed environment— free from a jarring ride, neck straining head toss and other sudden vehicle motions. This is made possible by the quick response of the dampers as controlled by computer algorithms that keep the dampers a step ahead of actual body movements.
Advantages of the Active Damper System include:
- Flat cornering feel with a reduced body roll— even during spirited driving
- Responsive, precise and secure steering feel
- Elimination of unwanted under-damped body heave, roll and pitch motions
- Improved tire adhesion, vehicle stability and road isolation
Real Time Damper Control
The secret to the ZDX's Active Damper System is its fast-acting "semi active" Magneto-Rheological fluid-filled shock absorbers. These dampers are built and tuned specifically for the ZDX and offer the ability to individually adjust from minimum to maximum damping force in as little as five milliseconds (0.005 sec.). The ability to significantly change damping rate hinges on the principle of electromagnetic induction.
Each damper carries a field coil—a collar containing many windings of magnetic wire—that generates an electromagnetic field when current is passed through it. Special damper fluid contains microscopic (about 10 microns in diameter) ferric spheres that align when surrounded by an electromagnetic field, dramatically and instantly changing the effective fluid viscosity. Not only is the overall range of damping force significantly more than that of a conventional damper, but there are also hundreds of small steps available within that range.
An electronic control unit (ECU) determines the amount of electrical current that passes through the field coils via special algorithms which determine the best setting for the road conditions. The continually variable oil viscosity, combined with nearly instantaneous reaction time of the dampers, allows damping control to occur before the ZDX's tires or body experience any extraneous motion.
The Active Damper System will deliver low damping when the road is smooth and the vehicle is being driven at a constant speed. Less damping reduces the amount of vibration and harshness that passes from the suspension to the body, quieting and improving the overall vehicle ride quality.
Using the dampers' 5-millisecond response time, the Active Damper System reacts to sudden changes in driver or road inputs. A high damping force achieved in this short time allows the dampers to quickly aid the coil springs and stabilizer bars in roll and pitch control, greatly improving the handling of the ZDX.
The result of the improved transient handling, road isolation and body control afforded by the ZDX's Active Damper System is a noticeable reduction in the driver's workload. In short, the system is able to achieve the benefits of a sport-tuned suspension without the traditional ride comfort trade-off. The overall benefit is more driving enjoyment, better vehicle control and less passenger fatigue over a long drive.
The computer algorithms that control the Active Damper System were specially created for the ZDX and offer a substantial difference between Comfort and Sport modes. Thus, drivers whose primary interest is comfort will be coddled over most road conditions, while those interested in a sport-driving experience will find the ZDX ready to tackle challenging roads.
The Active Damper System does not require any special maintenance, has no scheduled replacement interval and maintains the same quality, durability and performance as all other Acura components.
POWER RACK & PINION STEERING
Of the luxury SUVs that Acura targeted in developing the ZDX, the BMW X6 offered the best steering quality. Acura set out to exceed the BMW's combination of linearity, precise feel and security at high speed by using torque-sensing, power-assist rack-and-pinion steering.
Acura engineers spent considerable time studying steering "on-center" feel in an effort to elevate the quality of steering feedback the driver receives. Beyond offering the correct steering effort level, the ZDX provides subtle transient steering feedback that is an integral part of its subjective handling quality.
WHEELS AND TIRES
The 2011 ZDX has standard 19x8.5-inch 7-spoke aluminum wheels finished in luxurious silver with a bright-machined face and a chromed Acura center cap. Standard are Michelin Latitude P255/50R19 103H all-season tires that were specially developed for the ZDX by Michelin engineers. The tires offer outstanding traction in dry and wet conditions, while maintaining highly useful level of snow/ice traction as well. Of particular interest, the specially-developed tires deliver a substantial improvement in wet and dry handling as well as a 5-percent reduction in rolling resistance— thus helping to improve fuel economy.
For the first time in Acura history, 20x9-inch wheels are available for the ZDX from Acura Genuine Accessories.
In the event of flat tire, a 17x4-inch wheel with T165/80D17 tire is mounted underneath the rear of the ZDX. Acura designed the spare-tire storage area to accept either a temporary or a full-size wheel, allowing the ZDX owner to carry a damaged full-size wheel and tire beneath the vehicle instead of in the rear cargo area.
4-WHEEL DISC BRAKES
The 4-wheel disc brakes on the 2011 ZDX are the largest brake system ever featured on a production Acura vehicle, an honor shared with the MDX. The brake system is engineered to provide best-in-class braking performance in dry conditions, as well as while driving in rain, snow or icy conditions.
Engineers benchmarked the Acura ZDX against top competitors including the Porsche Cayenne and BMW X6 for braking performance and overall pedal feel. As a result, the ZDX has minimal pedal travel and a firm pedal feel, in keeping with the sport-minded direct feel that enthusiast drivers desire. The ventilated front brake rotors measure 13.0-inches in diameter with a thickness of 1.1 inches, while the rear rotors are a 13.1-inch diameter solid design with a thickness of 0.43 inch. The front brake calipers are dual-piston design while single-piston calipers are used in the rear.
The ZDX has an anti-lock braking system (ABS) with Electronic Brake Distribution (EBD), Brake Assist and Hill Start Assist as standard equipment. In addition, a Collision Mitigating Braking System™ (CMBS™) is available as part of the Advance Package.
VEHICLE STABILITY ASSIST™ (VSA®) WITH TRACTION CONTROL
Vehicle Stability Assist™ (VSA®) is included as standard equipment on the ZDX. By continually monitoring the vehicle's operating parameters (such as road speed, throttle position, steering wheel angle, accelerating/braking/cornering loads), VSA® detects if the vehicle is experiencing oversteer or understeer. To help correct either of these situations, VSA® automatically reduces engine power output as needed, and applies one or more brakes individually to help stabilize the chassis. The VSA® response is so quick that the instability may be corrected even before the driver knows that it is occurring. Traction Control is integrated into VSA® and helps the ZDX accelerate smoothly on low traction surfaces. As described in detail within the SH-AWD™ section, VSA® works with SH-AWD™ to adjust engine torque distribution— thus allowing Direct Yaw Control of the ZDX to maximize stability under all driving conditions.
TIRE PRESSURE MONITORING SYSTEM (TPMS)
An onboard Tire Pressure Monitoring System (TPMS) warns the driver if the air pressure decreases significantly in any tire. The system helps reduce the chance of damaging a tire or losing control of the vehicle due to low air pressure. Such pressure monitoring is important because a slow leak (such as one that might be caused by a nail or road debris) might not be easily detectable— but over time could cause significant air loss, reduction of grip and potentially a blowout.
TPMS uses a small sensor mounted on each wheel that continually monitors tire pressure and sends a coded signal to the TPMS electronic control unit (ECU). The process begins with a signal initiator located inboard of each tire on the chassis that sends a unique signal for each TPMS sensor. The TPMS sensor then sends tire pressure data to the TPMS ECU, which compares the values for each tire's pressure against an acceptable range of pressures.
When a tire's pressure drops significantly below the proper level, a "CHECK TIRE PRESSURE" alert will appear on the Multi-Information Display (MID) screen. The TPMS system can display the air pressure in all four tires simultaneously via the MID, making it simple to locate a specific low-pressure tire. If there is a fault in the system, a "CHECK TPMS SYSTEM" alert appears.
At the driver's preference, the Multi-Information Display can continually show the air pressure in all four tires as the vehicle is driven. Regardless of whether the driver chooses to monitor the pressures, a warning will still occur if a tire drops a specified level.
Although the ZDX is not designed as a hardcore "go-anywhere" off-road vehicle, it is engineered to be capable and competent whether traveling just off the pavement or off the beaten path. Engineers mandated specific minimum performance criteria for the ZDX, including safe travel through standing water nearly eight inches deep, steep approach and departure angles (19.8-degrees front and 23.2-degrees rear, respectively, with a 16.9-degree break-over angle), off road and paved grades up to 60-percent incline. Moreover, components located underneath the ZDX are tucked away to help avoid damage during off-highway driving, a steel guard protects the fuel system's evaporative canister and there is a generous 8 inches of clearance.
The high-torque 3.7-liter V-6 engine and SH-AWD™ system with Grade Logic and computer-controlled traction capabilities all help the ZDX meet most off-road challenges without the need for a dedicated low-range transfer case or a driver-selected 4WD "lock" mode. Generous front approach, break-over and rear departure angles also help the ZDX meet the various needs of its target buyers.
SNOW AND ICE CAPABILITY
The same technologies that make the ZDX capable off-road also enhance its performance in snow and ice. The SH-AWD™ system with Grade Logic Control and computer-controlled traction monitoring capabilities work together with the all-season tires to maximize power delivered to the road surface, and thus driver control, in winter driving conditions.
NOISE, VIBRATION & HARSHNESS (NVH)
Elimination of undesirable wind or road noise, vibration and harshness (NVH) in the passenger cabin was among the highest and most essential priorities that engineers attacked for the ZDX. Acura began by focusing on vibration in the body during the engineering phase instead of simply adding materials to the body to damp it out later. Two examples of this process are the rear suspension mounting points, which have robust attachments to the unit-body for greater rigidity and reduced vibration, and stiff front and rear subframes, which allow the mounting bushings to be made softer.
Engineers paid strict attention to addressing two specific issues—concrete road noise and drumming—neither of which are acceptable to luxury customers. Thus, melt sheets are used in critical areas on the front bulkhead and floor, and light insulators are used on the bodysides, doors and roof. A hybrid carpet and padding system further reduces noise intrusion.
In addition to building a stiff unit body structure, Acura engineers installed three different types of body separators located in the A-, B- and C-pillars. These special separators close off the traditional hollow areas within the separator structures to help ensure that noise does not travel from the road into the passenger cabin. While other Acura vehicles also use pillar separators, the ZDX has the highest use of any Acura vehicle.
Additional sound-controlling mechanisms found in the ZDX include a windshield constructed of acoustic glass, 5mm thick side glass (compared to 3.5mm glass used by most manufacturers), 7-layer acoustic floor under covers (including the first Acura use of a rear-wheel inner fender insulator), front and rear sub-frame stiffeners, textile-covered inner fender liners and Active Noise Cancellation (ANC). In particular, the acoustic floor undercovers are especially effective.
With a towing capacity of 1,500 pounds, the 2011 ZDX can tow items such as a personal watercraft, motorcycles or a camping/utility trailer. A Towing Package is available as dealer-installed accessory that includes a Class I hitch, receiver, ball and wiring harness.