multitronic
Multitronic is a continuously variable transmission (CVT) developed by Audi AG in collaboration with LuK, introduced in late 1999 as a stepless automatic gearbox for front-wheel-drive models equipped with longitudinal engines.[1][2] The system utilizes a variator consisting of two variable-diameter conical pulleys connected by a narrow, oil-bathed link chain comprising over 1,000 individual links, enabling seamless gear ratio adjustments without discrete steps to optimize engine efficiency and ride comfort.[2] It incorporates an electronically controlled hydraulic multi-plate clutch for smooth stationary decoupling and features low internal friction alongside a wide gear-ratio spread for high overall efficiency.[2] Designed for dynamic performance, multitronic includes a sport program with tighter ratios for responsive acceleration and a manual mode simulating eight fixed gears, while its compatibility with start-stop systems further enhances fuel economy.[2] Initially launched in models such as the Audi A4 (B6) and A6 (C5) with torque capacities up to 330 Nm, subsequent variants like the VL380 (2004–2009) and VL381 (2007–2014) supported higher torques of 380 Nm and 400 Nm, respectively, extending its application to vehicles including the A5 and later A4/A6 generations.[1] Production of multitronic transmissions ceased in 2014, after which Audi transitioned to dual-clutch S tronic systems for improved reliability and performance in similar applications.[1]Introduction
Overview
Multitronic is a continuously variable transmission (CVT) developed by Audi AG for front-wheel-drive vehicles with longitudinally mounted engines, employing a steel chain drive system and adaptive electronic control to enable seamless and infinite gear ratio adjustments.[3][4] This design replaces traditional fixed-gear mechanisms with a variator consisting of two variable-diameter conical pulleys connected by the chain, allowing the transmission ratio to change continuously without discrete shifts.[3] The primary purpose of Multitronic is to optimize engine performance by maintaining the powerplant at its most efficient operating point, delivering smooth acceleration, enhanced fuel efficiency, and responsive driving dynamics.[4][3] By providing an infinite number of ratios within a spread from 2.4:1 to 0.4:1, it minimizes engine RPM fluctuations during acceleration and cruising, offering advantages over conventional stepped automatic transmissions in terms of reduced jerkiness and improved overall comfort.[3] Introduced in late 1999 on the Audi A6 (C5) model, Multitronic marked Audi's entry into advanced CVT technology, initially paired with engines up to 310 Nm of torque.[1] Despite its innovative benefits, early versions faced reliability challenges, and production was discontinued in 2014 in favor of dual-clutch systems.[5]History and Development
The development of Multitronic originated in the early 1990s as an in-house project at Audi, later partnering with LuK (now part of the Schaeffler Group) to engineer a continuously variable transmission (CVT) suited for premium sedans, driven by the need to enhance fuel efficiency amid rising European market demands.[6][5] This initiative responded to stricter EU emissions standards, such as the progressive CO2 limits introduced in the late 1990s, and aimed to compete with efficient CVTs from Japanese manufacturers like Honda and Nissan, which were gaining traction in global markets for their seamless power delivery and reduced consumption.[7][8] Key milestones included prototype development leading to initial production in 1999, with the transmission debuting in the Audi A6 (C5) that October, marking the first application of Schaeffler's innovative chain technology capable of handling up to 310 Nm of torque.[9][10] The system expanded to the Audi A4 (B6) in 2001 for European models, followed by broader adoption in the A6 lineup, and later to the Audi TT (8N) in 2006, reflecting Audi's strategy to integrate it across front-wheel-drive premium vehicles for improved drivability.[5][11] The first generation (1999–2007), designated as the 01J or VL300 variant, featured basic adaptive logic using a chain-driven variator for ratio changes, but encountered early challenges like chain slippage under high loads.[12] To address these, Audi implemented software updates in 2005–2006 for the transmission control unit, enhancing shift logic and pressure management to mitigate slippage issues.[13] This evolved into the second generation (2006–2013), which introduced dynamic torque control, upgraded chain durability, and refined adaptive programming for better performance in varying conditions, extending its use until eventual phase-out in favor of dual-clutch systems.[1][12]Technical Design
Operating Principle
The Multitronic continuously variable transmission (CVT) operates on the principle of a chain drive variator, enabling stepless adjustment of the transmission ratio to optimize engine performance across driving conditions. At its core, the system employs two pairs of variable-diameter pulleys—a primary (input) set connected to the engine and a secondary (output) set linked to the drivetrain—connected by a specialized steel push-chain. The effective diameters of these conical pulleys are altered hydraulically: as the pulley halves on the primary side move closer together under oil pressure from dual-piston cylinders, the chain is forced outward to ride higher on the pulley, increasing its effective radius and reducing the ratio for higher speeds; conversely, widening the primary pulleys decreases the radius, raising the ratio for low-speed torque. This adjustment occurs continuously without discrete steps, providing infinite ratio variations within the system's range.[3] The variator's ratio range spans continuously from approximately 2.4:1 (underdrive for maximum torque multiplication at low speeds) to 0.4:1 (overdrive for efficient cruising at high speeds), yielding an overall spread of 6 when combined with a fixed auxiliary reduction gear ratio of 1.109:1. To enhance driver feedback and mimic traditional automatics, the electronic control simulates discrete gear shifts: early models (1999–2003) in a 6-speed mode, increased to 7 speeds in 2004, and 8 speeds in later variants, briefly holding ratios at predefined points during acceleration or deceleration for a stepped sensation, though the underlying mechanism remains fully variable.[3] The transmission's operation is governed by an adaptive electro-hydraulic control system managed by the integrated gearbox control unit (ECU J217), which processes inputs from sensors monitoring throttle position, vehicle speed, engine load, and accelerator pedal angle to dynamically adjust pulley positions and ratio in real time. This ECU employs a dynamic control program that optimizes shift patterns for efficiency and responsiveness, such as holding higher ratios during steady-state driving or quickly downshifting under load; it also coordinates the engagement of oil-cooled multi-plate wet clutches (one for forward, one for reverse) to enable smooth low-speed creep, launch, and direction changes.[3][10] Power transmission efficiency in the Multitronic variator is fundamentally tied to minimizing chain slippage between the pulleys, approximated as \eta \approx 1 - s, where s is the slippage factor (typically under 2% in optimized conditions). Slippage is controlled by maintaining precise belt tension, derived from the equilibrium of forces on the chain: the required tension force F balances the torque T transmitted across the effective pulley radius r and chain width w, given by F = \frac{T \cdot r}{w} (with adjustments for friction and hydraulic clamping force to prevent slip under peak loads up to 310 Nm in early variants). This tension is actively regulated by the ECU via solenoid valves modulating oil pressure (10-80 bar range), ensuring high efficiency (up to 95%) by keeping the chain in near-frictionless wedging contact with the pulley sheaves.[3][14][15]Key Components and Innovations
The core of the multitronic continuously variable transmission (CVT) lies in its variator, which consists of primary and secondary pulley sets. Each set comprises two tapered discs mounted on axles, with the primary pulleys connected to the engine input and the secondary pulleys to the output shaft. These pulleys are adjusted axially by hydraulic actuators employing a dual-piston principle, where one piston maintains constant pressure and the other varies displacement to achieve precise control over the effective pulley diameters, enabling seamless ratio changes from 2.4:1 underdrive to 0.4:1 overdrive.[3] Power transmission between the pulley sets is handled by a multi-link steel chain, often referred to as the Link chain, manufactured by LuK GmbH. This chain features interlocking steel links with cradle-type pressure pieces that distribute load evenly, providing superior torque capacity compared to traditional rubber or steel belts used in other CVTs—up to 310 Nm in initial 01J/VL300 variants—while minimizing energy losses through high efficiency and low friction. The chain's design, with varying link plate lengths to reduce noise and vibration, marks a key Audi-specific advancement for longitudinal engine applications in premium vehicles. Later variants like VL380 (2004–2009, 380 Nm) and VL381 (2007–2014, 400 Nm) used reinforced chains with widths increased from 34 mm to 38 mm for higher load distribution.[3][16][17][18] Notable innovations include Audi's Dynamic Control System (DCS), which integrates a dynamic regulation program for real-time ratio adaptation based on throttle input, vehicle speed, and load conditions to optimize performance and fuel economy. The transmission incorporates multi-plate wet clutches for forward and reverse gears. Adaptive pressure valves, utilizing a hydraulic torque sensor, dynamically modulate chain clamping force to match input torque precisely, preventing slip under high loads while conserving hydraulic energy.[3][19] Component evolution focused on enhancing durability and capacity. Pre-2006 versions relied on chain designs more susceptible to fatigue under sustained high torque, whereas post-2006 iterations shifted to reinforced chains offering higher tensile strength through improved metallurgy and link configuration. This progression supported torque capacity increases from 310 Nm in the initial 1999 application to 400 Nm in later models like the 2008 Audi A6, achieved partly by widening the chain for better load distribution.[3][19][1]Applications
Vehicle Models Equipped
Multitronic was initially introduced in the Audi A6 (C5 platform, 1999–2004) with 2.0-liter inline-four, 2.5-liter V6 TDI diesel, and 3.0-liter V6 gasoline engines, limited to front-wheel-drive configurations.[20] It was subsequently adopted in the Audi A4 (B5 platform, 2000–2001 facelift models) paired with the 2.0-liter inline-four engine in front-wheel-drive setups.[1] These early applications marked Multitronic's debut in Audi's mid-size sedan and wagon lineup, with a torque capacity capped at approximately 330 Nm to suit lower-output engines.[5] During its expansion phase, Multitronic saw broader integration across updated models, including the Audi A4 (B6/B7 platforms, 2004–2008) with 2.0-liter TFSI gasoline and 2.0-liter TDI diesel engines.[1] It was extended to the Audi A6 (C6 platform, 2004–2011) paired with 2.0-liter TFSI/TDI and 3.2-liter V6 engines, as well as the Audi A8 (D3 platform, 2003–2005) with the 3.0-liter V6 gasoline engine in front-wheel-drive.[21] Further applications included the Audi A5 (8T platform, 2007–2014) and Audi TT (8J platform, 2006–2014), both primarily with 2.0-liter TFSI engines, and the Audi A7 (C7 platform, 2010–2014) with 2.0-liter TFSI/TDI engines.[5] The A5, A6 (C7, 2011–2014), A7, and TT represented Multitronic's final major applications, with production ending in 2014. High-performance S- and RS-line variants were excluded due to the transmission's torque limitations.[1] Multitronic was designed exclusively for front-wheel-drive vehicles with longitudinally mounted engines, emphasizing smooth operation in premium compact and mid-size Audis.[10]| Model | Platform | Production Years | Key Engine Pairings |
|---|---|---|---|
| A6 | C5 | 1999–2004 | 2.0L I4, 2.5L V6 TDI, 3.0L V6 |
| A4 | B5 | 2000–2001 | 2.0L I4 |
| A8 | D3 | 2003–2005 | 3.0L V6 |
| A4 | B6/B7 | 2004–2008 | 2.0L TFSI, 2.0L TDI |
| A6 | C6 | 2004–2011 | 2.0L TFSI/TDI, 3.2L V6 |
| TT | 8J | 2006–2014 | 2.0L TFSI |
| A5 | 8T | 2007–2014 | 2.0L TFSI |
| A7 | C7 | 2010–2014 | 2.0L TFSI/TDI |
| A6 | C7 | 2011–2014 | 2.0L TFSI/TDI |