Acura unveiled the production model of the next-generation NSX at the North American International Auto Show (NAIAS) this past January (earlier post), and now has provided more technical detail on the high-performance hybrid sports car and its new Sport Hybrid-AWD power unit.
At the core of this new hybrid power unit is a bespoke, mid-mounted twin-turbocharged, 75-degree 3.5-liter DOHC V6 engine with dry sump lubrication, mated to an all-new 9-speed dual clutch transmission (9DCT) and Direct-Drive Motor. This is augmented by the front Twin Motor Unit (TMU) driving the front wheels. The NSX Sport Hybrid power unit offers exceptional horsepower and torque with a broad powerband for tremendous throttle response and acceleration. Total system peak output is estimated at 573 horsepower—500 horsepower from the gasoline engine and 73 horsepower from the front TMU.
Twin-Turbocharged V6 Engine. Featuring a wide V-angle of 75 degrees to help lower the center of gravity, the NSX’s twin-turbocharged V6 engine strives to achieve the best balance between power production, overall compactness and reduced mass. With a displacement of 3.5 liters, it combines both direct injection and port injection, along with Variable Timing Control (VTC) to deliver optimal camshaft phasing, for precision combustion control throughout the entire rpm band while simultaneously achieving high power output and performance at high engine speeds.
Making use of an electronic wastegate for each turbocharger for faster response as well as more precisely varying vane positioning, the single-scroll turbocharger design allows for the use of smaller turbos to reduce weight and improve packaging, while still meeting power and performance benchmarks. Furthermore, their single-scroll design allows for more efficient collection of exhaust as it escapes from within the cylinders.
To reduce the response delay that is associated with turbocharged powerplants, the rear Direct Drive Motor acts directly on the engine’s crankshaft and works in unison via a sophisticated algorithm to realize direct, high output, high torque acceleration performance. The enhanced efficiency of this design arrangement is particularly noticeable in normal everyday driving when accelerating from a low engine speed, Acura said. Additionally, the rear electric motor also acts as a generator to provide supplemental power to the vehicles lithium ion battery pack, which also powers the front-mounted TMU.
Other key engine design elements include a sand-cast engine block; lightweight and compact cylinder heads; FC thermal spray coating on the engine block cylinder sleeves (for higher thermal efficiency, weight and compactness); and a dry sump lubrication system that significantly reduces the engine’s center of gravity—allowing 61 mm reduction from the crank center to the engine bottom versus a conventional wet sump—while ensuring effective lubrication at high cornering speeds.
The NSX has a compact valve train utilizing swing arm-type valve actuators, helping to reduce the inertial weight of the valve train and allowing a more compact head structure. The structure is similar to those found in some Honda racing engines. Intake and exhaust variable cam timing (VTC) is deployed to provide an excellent balance of high power, torque, fuel economy, and emissions.
With the newly designed twin-turbocharged 3.5-liter V6 engine, special consideration was given to how the engine would be secured to the chassis in order to achieve the highest structural rigidity while producing the lowest levels of noise, vibration and harshness (NVH). The solution was to create an engine cradle system that combines hydro-engine mounts with a rigid aluminum sub-frame plate that simultaneously supports the engine while acting as a vibration and noise inhibitor. Engine mounts are ideally located to minimize pitch and roll movement of the powertrain mass. Testing and analysis demonstrated that this novel configuration provides notably improved vehicle handling performance while exceeding targeted NVH levels.
9-Speed Dual Clutch Transmission with Direct Drive Motor. The new 9-speed dual clutch transmission works in concert with the engine and Direct Drive Motor to make full use of the power unit’s broad power band, producing lightning quick gear changes that support the NSX’s zero-delay response. As a key component of the Advanced Sports Package, the 9DCT has been optimized for compact size, low mass and low CG.
The 9DCT has a very wide ratio range that allows for optimal gear selection in all driving conditions. First gear ratio is configured for maximum vehicle launch acceleration, while the close-ratio gears (2nd through 8th) are matched to make the most of the power unit’s power band. Conversely, high gear (9th) has been optimized for fuel efficiency during steady-state highway cruising.
In efforts toward compactness and reduction of mass, the clutch and the differential are uniquely situated side-by side in a common housing. By adopting this design, overhang from the rear axle is minimized while the center of mass is moved forward.
Other advanced technologies incorporated into the 9-speed DCT are:
Electronically-operated wet dual clutch, a high-rigidity shift fork, double-cone synchronizer, and an electronic shift actuator to more precisely synchronize power unit torque with shift timing for the quickest and smoothest shifts possible.
Precision surfaced high-efficiency hypoid bevel gear tooth shape for all gears for improved operation with reduced gear noise.
Addition of two oil “rooms” within the transmission housing for more efficient and higher-capacity cooling.
Clutch case and differential carrier integrated into the transmission for a more lightweight and compact structure.
Lightweight high-strength gearbox case.
Multiple-plate limited slip differential (LSD) provides increased traction when accelerating and cornering at the limits of adhesion.
Twin Motor Unit (TMU). The exceptional direct and linear acceleration and dynamic response of the new NSX is enabled in part by its front-mounted Twin Motor Unit (TMU). It is a major driving force in creating the vehicle’s zero-delay acceleration and can directly generate a yaw moment to support turning, and also recovers braking energy during deceleration.
The TMU provides instant torque as well as AWD traction, allowing direct and stress free launches from start. In addition to improving 0-to-60 mph and quarter-mile times, this zero-delay acceleration response allows the driver to experience a heightened sense of G-loading. Most importantly, the Sport Hybrid SH-AWD works in harmony with the poised chassis and brake system to provide intuitive brake pedal and steering feel so the driver always feels completely in control.
The TMU is geared to support acceleration up to 200 km/h (124 mph), but continues to support Direct Yaw Control at all vehicle speeds. It is also a key enabling technology for driving in the Quiet mode setting of the IDS, allowing for hushed vehicle operation by operating the NSX as an electric vehicle.
Intelligent Power Unit (IPU)/Power Drive Unit (PDU). The IPU integrates the lithium-ion battery pack and a high-voltage distribution bus bar, with voltage distribution controlled by the PDU. The newly developed lithium-ion battery pack allows for increased energy density and improved electrical output when compared to similar systems in existing vehicle models.
The Power Drive Unit (PDU) is centralized in a low position within the vehicle, hidden below the center console. The high-voltage lithium-ion battery is mounted within the Integrated Power Unit (IPU), which is in turn mounted behind the driver and passenger, forward of the firewall.
With the Sport Hybrid SH-AWD, zero delay performance is ensured in virtually any driving scenario:
When accelerating, the system provides instantaneous torque via its three electric motors—the rear direct drive motor and front Twin Motor Unit—that is maximized at all four tires when accelerating or powering out of corners.
When trail-braking into a corner, the system utilizes the front TMU for enhanced deceleration—the advanced braking system works in concert with the vehicle’s mechanical brakes to precisely decelerate, and the Direct Yaw Control delivers precise and immediate turn-in performance while allowing drivers to point their eyes toward the corner apexes.
When exiting a corner, the driver can pick up the throttle earlier and with more confidence and accelerate with added precision and as well as reduced workload.
Using Honda’s original beta method to consider overall handling performance, we’ve been exploring direct yaw control torque vectoring for over two decades. With the development of the Sport Hybrid Super-Handling All Wheel Drive System, we can take advantage of the superior responsiveness of the electric motor characteristics within the system powered by an independent battery to significantly expand the benefits of direct yaw control.—Ted Klaus, Acura NSX Global Development Leader
Driving modes. The NSX hybrid features four driving modes:
Quiet. Quiet mode prioritizes electric-only driving at lower speeds, maximizing energy efficiency and minimizing cabin sound. The vehicle uses the TMU for initial launch from a standstill. When power demand requires the engine, it starts more quietly than in other modes and maximum engine speed is limited to 4,000 rpm, while the Active Exhaust and Intake Sound Control valves are closed for a more hushed operation. The transmission shift map also prioritizes lower engine speeds. The Driver Interface (tachometer and center console information display screen) features a cool and quiet blue color.
Sport. Sport mode takes advantage of the Sport Hybrid system to offer the driver a direct responsive vehicle or a more relaxed vehicle according to their driving inputs. Compared to Quiet Mode, it eliminates the 4,000 rpm limit on the engine and provides a more aggressive throttle map for quicker response. A more aggressive transmission shift map holds gears longer and allows higher rpm shift points. The Intake Sound Control system and the Active Exhaust Valve are activated, allowing exhaust and intake sound to permeate the cabin for a more emotional driving experience. Like the Quiet mode, sport mode provides idle stop function. The Sport setting is the default setting in normal vehicle operation.
Sport+. Sport+ prioritizes maximum drivetrain response and dynamic performance with faster up- and down-shifts of the 9 DCT and still more aggressive throttle mapping. Maximum use of the electric motor torque provides more explosive acceleration. Increased agility is achieved by harmonizing a more aggressive Direct Yaw Control setting that works in concert with the magneto-rheological dampers, Agile Handling Assist, and the Electric Power Steering System—perfect for a spirited drive on a winding road. It also offers the driver a higher degree of steering feedback, while intake and exhaust note sounds via Active Sound Control are further increased for an even more exhilarating and emotional driving experience. The TFT Meter sports an aggressive yellow “con-trail” along the tachometer needle supporting easy recognition of engine RPM. Red highlights for the center console information display also reinforce that the driver is in now in Sport+ mode.
Track. Optimized for circuit driving, Track mode invokes the most aggressive settings and parameters to deliver the fastest and most consistent lap times possible, along with maximum acceleration from a standstill when utilizing launch control mode). The braking system offers enhanced performance-oriented pedal feel. Up/down gearshift execution of the DCT and performance of the Super Hybrid SH-AWD and active driver aids (VSA, AHA) are programmed to support circuit limit driving, and an even greater amount of engine intake sound permeates the cabin for a more heightened and emotional driving experience offering enhanced driver feedback even when wearing a helmet.
This setting also prioritizes the lithium-ion battery state-of-charge to maintain a consistent level of torque delivery and direct yaw moment from the three electric motors to ensure consistent dynamic response and lap times.
Of note, the VSA operation is progressively “loosened” from the IDS Quiet mode up to Track mode, enabling a progressively higher degree of freedom for the driver in exploring the dynamic capabilities of the NSX. In "Track" mode, the VSA system can also be completely disabled by the driver. The NSX IDS system has the world's first custom setting menu that allows the driver to configure the vehicle's mode during startup. For example, drivers can program the car to always start in Quiet or Sport mode, along with the ability to schedule the NSX to operate exclusively in Quiet mode during any specified time period such as the early morning to avoid waking the neighborhood.
To support new concepts in vehicle dynamics—in particular the direct yaw control effected by the torque vectoring capabilities of the front-mounted TMU and the direct, zero-delay response of the chassis to driver inputs—the NSX engineering team was challenged to create a new concept for body design that delivered ultimate rigidity while minimizing weight and meeting other critical targets such as visibility, crash safety performance and durability/quality/reliability (DQR).
The final result of this engineering challenge is the NSX multi-material space-frame which achieves structural rigidity far superior to its top-in-class competitors. The aluminum-intensive space frame utilizes extruded and cast parts to provide exceptional rigidity and light weight.
In order to directly translate the direct yaw moment generated by the TMU, and to precisely deliver feedback to the driver with zero delay, individual aluminum castings have been utilized at each and every attachment point for the suspension. These castings are supported in all three dimensions (x, y, z) by optimized extrusions.
Utilizing Global and local optimization routines, each casting and extrusion was analyzed for potential weight savings. The result is that most extrusions have custom wall thickness and many have a different wall thickness for each of their sides.
Steel stampings have also been added to the architecture in certain areas where energy absorption is required, with supplemental aluminum stampings used where low weight is a key consideration. The front floor panels are constructed of carbon fiber core.
Ablation Cast Nodes. One of the most difficult design challenges in the development of the all-new Acura NSX was to minimize the front and rear overhangs of the vehicle while managing energy absorption in key areas for crash safety performance and to maintain desired structural rigidity. To solve the issues of crashworthiness and occupant protection, a particular challenge in mid-engine vehicles, traditional aluminum castings were rejected due to their brittle characteristics. Instead, engineers have applied an innovative new technology called “ablation” casting, an all-new material application and a world-first in the automobile industry.
Jointly developed with Alotech, ablation casting technology is being utilized in the creation of six joining members, or nodes—two upper and two lower nodes in the front frame and two rear nodes. The front upper and rear nodes also serve as ultra-rigid suspension mounting points. The ablation casting process allows for the fine-tuning of both the cast part’s shape, as well as the material properties of the castings in the energy-absorbing areas of the vehicle, while minimizing weight in the form of a hollow part with optimized wall thickness.
Unlike traditional castings, the high-strength and ductile properties of the aluminum ablation cast members allow these sections of the space-frame to progressively crush and are designed to withstand tremendous loads of up to 210 kN without breaking.
3-Dimensional Bent and Quenched Ultra-High-Strength A-Pillar. For the A-pillars, new advancements in ultra-high-strength steel parts forming provided a solution that met the engineering team’s goals for safety performance while maximizing forward visibility for the driver by reducing the A-pillar width. The original NSX was known for its outstanding forward visibility, giving drivers a feeling of being connected to the road, and this design attribute was considered essential to preserving a core characteristic of the NSX driving experience.
The NSX A-pillars have been precisely crafted using an all-new, three-dimensional forming and tempering process that allows for a complex parts shape with ultra-high tensile strength of 1,500 megapascals. This “3D bent and quenched” component is heated and then robotically bent. During the bending process the part is cooled and tempered (quenched) using water jets. This process enables a very small section A-pillar with precise shape specification and tolerances, yet meets the increased structural rigidity for roof-crush performance requirements.
The design and construction of the A-pillars in the new NSX represent the world’s first application of a three-dimensionally formed, ultra-high-strength steel system to be used in this manner within the automotive industry.
Carbon Fiber Core Floor. When evaluating material composition and placement throughout the body, the design team determined that carbon fiber core would serve as the ideal material for the floor section forward of the seats. In addition to its light weight, this material is strong enough to handle the loads of driver and passenger placed upon it for vehicle ingress/egress. If aluminum had been used, the aluminum sheeting would have required additional cross-member frame support beneath it; this would have added additional weight.
Construction Techniques. A number of innovative construction techniques are used in the manufacture and assembly of the all-new Acura NSX at the company’s new Performance Manufacturing Center in Marysville, Ohio.
100% of the aluminum space frame components are joined by Robotic Metal Inert Gas (MIG) welding, the first time to be applied in a mass-produced automobile on this scale. To aid the accuracy of the robotic weld process, the PMC utilizes an innovative rotating trunnion, or rotisserie-type, jig that rotates the part into the optimal position for the robotic weld arms, another first for automobile body construction.
Exceptionally high-quality and precise space-frame construction is accomplished via this innovative methodology which combines highly precise robotic control of the weld process with the advanced skills of PMC weld technicians. A robust in-line quality confirmation process, for both the quality of the weld and conformity of part to established specs, involves confirmation by both robotic measuring equipment and by highly skilled weld technicians at every stage of the construction process.
The NSX’s team of aerodynamicists utilized a new total airflow management approach to give the NSX the superlative airflow management one expects of a next-generation supercar, while simultaneously providing the effective and highly efficient thermal management required for its hybrid power unit. There are seven different heat sources in the hybrid-based powertrain—the 3.5-liter V6 engine, twin turbochargers, the 9-speed DCT, Dual Clutch system, Power Distribution Unit, Twin Motor Unit. To provide efficient cooling, airflow is managed through 10 different heat exchangers.
Through the use of computational fluid dynamic (CFD) simulations as well as testing of 40% scale models in the company’s advanced wind tunnel facility in Ohio, the NSX development team fine-tuned the various body shapes, intake and exhaust vents and vehicle strakes to reduce aerodynamic drag, create downforce, maximize cooling and efficiently exhaust unwanted heat.
The highly innovative total airflow management developments that were discovered and implemented into the new NSX by the Ohio team were later confirmed at the company’s full-scale/moving ground plane wind tunnel in Japan.
Total airflow management design highlights:
Efficient cooling openings at the front of the vehicle to maximize cooling airflow across the key heat exchangers located within the front section (front engine radiators, twin motor unit cooler, condenser, the transmission gear cooler, hybrid Power Distribution Unit).
Optimized front exit flow paths considering total flow, maximum downforce, low coefficient of drag, and achieving downstream flow structure to feed the mid-engine air inlets.
Wheel wake management vents work in conjunction with fender vents to stabilize airflow down the side of the vehicle, allowing the air to enter the signature side intakes for efficient cooling. The air that enters the side intakes is distributed to three areas: engine intake, engine room cooling, and turbo intercoolers.
Air flowing over the roof and down the rear hatch glass is captured to feed the transmission clutch cooler and introduce engine room cooling flow.
A rear diffuser works together with the rear spoiler and taillight slots to generate significant downforce and effectively manage the air wake generated behind the vehicle.
Optimization of front/rear downforce distribution for improved handling and stability.