VVT-i

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Cutaway view of Variable Valve Timing with intelligence on a ZR engine in Techniquest Glyndwr Toyota ZR engine cutaways valve gear.jpg
Cutaway view of Variable Valve Timing with intelligence on a ZR engine in Techniquest Glyndŵr

VVT-i, or Variable Valve Timing with intelligence, is an automobile variable valve timing petrol engine technology manufactured by Toyota Group and used by brands Groupe PSA (Peugeot and Citroen), Toyota, Lexus, Scion, Daihatsu, Subaru, Aston Martin, Pontiac and Lotus Cars. It was introduced in 1995 with the 2JZ-GE engine found in the JZS155 Toyota Crown and Crown Majesta.

Contents

The VVT-i system replaces the previous Toyota VVT system introduced in 1991 with the five-valve per cylinder 4A-GE "Silver Top" engine found in the AE101 Corolla Levin and Sprinter Trueno. The VVT system is a 2-stage hydraulically controlled cam phasing system.

VVT-i varies the timing of the intake valves by adjusting the relationship between the camshaft drive (belt or chain) and intake camshaft. Engine oil pressure is applied to an actuator to adjust the camshaft position. Adjustments in the overlap time between the exhaust valve closing and intake valve opening result in improved engine efficiency.

Variants of the system, including VVTL-i, Dual VVT-i, VVT-iE, VVT-iW and Valvematic have followed. Direct injection systems such as the D-4 (VVT-i D-4), D-4S and D-4ST are also used in conjunction with VVT-i.

VVTL-i

The 2ZZ-GE engine, the first and only engine to feature VVTL-i Toyota 2ZZ-GE.JPG
The 2ZZ-GE engine, the first and only engine to feature VVTL-i

VVTL-i (Variable Valve Timing and Lift intelligent system) (also sometimes denoted as VVT-iL or Variable Valve Timing and Intelligence with Lift) is an enhanced version of VVT-i that can alter valve lift (and duration) as well as valve timing. It was introduced with the 16-valve 2ZZ-GE engine found in the 1999 Toyota Celica. The engine head resembles a typical DOHC design, featuring separate cams for intake and exhaust with two intake and two exhaust valves (four total) per cylinder, but unlike a conventional design, each camshaft has two lobes per cylinder, one optimized for lower rpm operation and one optimized for high rpm operation, with higher lift and longer duration. Each valve pair is controlled by one rocker arm, which is operated by the camshaft. Each rocker arm has a slipper follower mounted to the rocker arm with a spring, allowing the slipper-follower to freely move up and down with the high lobe without affecting the rocker arm. When the engine is operating below 6,000–7,000 rpm (dependent on year, car, and ECU installed), the lower lobe is operating the rocker arm and thus the valves, and the slipper-follower is freewheeling next to the rocker arm. When the engine is operating above the lift engagement point, the ECU activates an oil pressure switch which pushes a sliding pin under the slipper-follower on each rocker arm. The rocker arm is now locked into the slipper-follower's movements and thus follows the movement of the high rpm cam lobe and will operate with the high rpm cam profile until the pin is disengaged by the ECU. The lift system is similar in principle to Honda's VTEC operation. Toyota has since ceased production of its VVTL-i engines in most markets because it does not meet Euro IV specifications for emissions regulations. This includes the Corolla T-Sport (Europe), Corolla Sportivo (Australia), Celica, Corolla XRS, Matrix XRS, and the Pontiac Vibe GT, all of which had the 2ZZ-GE engine fitted. On the other hand, the Lotus Elise and Exige continued to offer the 2ZZ-GE engine until 2011, with the Exige also offering the engine with a supercharger.

Dual VVT-i

The BEAMS 3S-GE 5th-generation engine ("Black Top"), the first to feature Dual VVT-i BEAMS 3S-GE Black Top.JPG
The BEAMS 3S-GE 5th-generation engine ("Black Top"), the first to feature Dual VVT-i

The Dual VVT-i system adjusts timing on both the intake and exhaust camshafts. It was introduced with the Altezza RS200's 3S-GE engine in 1998. Dual VVT-i was later used in Toyota's 3.5-litre 2GR-FE V6 engine, first appearing on the 2005 Avalon. This engine can be found on numerous Toyota and Lexus models. By adjusting the valve timing, engine start and stop occurs almost unnoticeably at minimum compression. Fast heating of the catalytic converter to its light-off temperature is possible, thereby reducing hydrocarbon emissions considerably. Most Toyota engines including the 1LR-GUE (V10, used in the Lexus LFA), UR engines (V8), GR engines (V6), AR engines (large I4), ZR engines (medium I4), and NR engines (small I4) use this technology.

VVT-iE

The 1UR-FSE engine, the first to feature VVT-iE Lexus 1UR-FSE.jpg
The 1UR-FSE engine, the first to feature VVT-iE

VVT-iE (Variable Valve Timing - intelligent by Electric motor) is a version of Dual VVT-i that uses an electrically operated actuator to adjust and maintain intake camshaft timing. [1] The exhaust camshaft timing is still controlled using a hydraulic actuator. This form of variable valve timing technology was developed initially for Lexus vehicles. This system was introduced on the 1UR-FSE engine in the 2007 Lexus LS 460. The electric motor in the actuator spins together with the intake camshaft as the engine runs. To maintain camshaft timing, the actuator motor will operate at the same speed as the camshaft. To advance the camshaft timing, the actuator motor will rotate slightly faster than the camshaft speed. To retard camshaft timing, the actuator motor will rotate slightly slower than camshaft speed. The speed difference between the actuator motor and camshaft timing is used to operate a mechanism that varies the camshaft timing. The benefit of the electric actuation is enhanced response and accuracy at low engine speeds and at lower temperatures as well as a greater total range of adjustment. The combination of these factors allows more precise control, resulting in an improvement of both fuel economy, engine output and emissions performance.

VVT-iW

The 8AR-FTS engine, the first to feature VVT-iW 2018 Toyota Crown 8AR-FTS.jpg
The 8AR-FTS engine, the first to feature VVT-iW

VVT-iW (Variable Valve Timing - intelligent Wide) was introduced with the 2.0L turbocharged direct-injected 8AR-FTS fitted to the Lexus NX 200t. VVT-iW uses VVT-iW on the intake valves and VVT-i on the exhaust valves. The intake cam has mid-position cam lock mechanism that retards the continuously variable timing. It offers expanded valve opening angles (Wide) which enables the engine to operate in a modified-Atkinson cycle at low rpm for improved economy and lower emissions and in the Otto cycle at high rpm for better performance, while also delivering high torque throughout the entire rpm band. [2]

Valvematic

The 3ZR-FAE engine, the first to feature the Valvematic system 2020 Toyota Voxy 2.0 ZRR80R 3ZR-FAE engine (20201113).jpg
The 3ZR-FAE engine, the first to feature the Valvematic system

The Valvematic system offers continuous adjustment to valve lift and timing and improves fuel efficiency by controlling the fuel/air intake using valve control rather than conventional throttle plate control. [3] The technology made its first appearance in 2007 with the 3ZR-FAE engine in the Noah [4] and later in early-2009 in the Avensis. This system is simpler in design compared to Valvetronic and VVEL, allowing the cylinder head to remain at the same height.

Direct injection systems

VVT-i has also been used in conjunction with Toyota's gasoline direct injection (GDI) systems, which includes the D-4, D-4S and D-4ST.

D-4

D-4 (Direct injection - Four) is a direct injection system used in a number of Toyota engines, sometimes referred to as VVT-i D-4. It appeared on the 1JZ-FSE and 2JZ-FSE engines found in some models of the Toyota Crown and Toyota Crown Majesta. It can also be found in several engines in the Toyota Avensis and Toyota RAV4. The D-4 system aims to reduce fuel consumption and emissions without compromising performance.

D-4S

The 2GR-FSE engine, the first to feature D-4S 2GR-FSE.jpg
The 2GR-FSE engine, the first to feature D-4S

D-4S (Direct injection - Four Stroke) is a twin injection fuel system combining both indirect and direct injection, working in conjunction with VVT-i. It debuted in the 2GR-FSE engine used in the Toyota Crown Athlete and the Lexus IS 350, which was also the first engine overall to combine both traditional fuel injection with direct injection. This system was also used in the 4U-GSE ( FA20 ) engine found in the 2012–2021 Toyota 86 and Subaru BRZ as well as the FA24D engine used in the 2022–present Toyota GR86 and Subaru BRZ, both working in conjunction with Subaru's AVCS system instead of VVT-i. Using a traditional manifold fuel injector on one end for low pressure and a direct injector on the other for high pressure, the D-4S system helps with providing more peak power at high rpms while also reducing emissions at the same time.

Despite some unverified claims, the "S" in D-4S does not signify a supercharged engine. Engines using the D-4S system such as the 4U-GSE and the 2GR-FSE do not have superchargers. Typically, supercharged engines are denoted as "Z" in Toyota's engine naming scheme, such as the 4A-GZE , 1G-GZE and 2TZ-FZE .

D-4ST

The 8AR-FTS engine, the first to feature D-4ST 2018 Toyota Crown 8AR-FTS.jpg
The 8AR-FTS engine, the first to feature D-4ST

D-4ST (Direct injection - Four Stroke with Turbocharger) is a variation of the D-4S twin injection system which is used in some Toyota engines with turbochargers. It works similarly to D-4S, but is optimized for use with a turbocharger. Like D-4S, it works in conjunction with VVT-i. It was introduced with the 8AR-FTS engine used in the Lexus NX 200t, working in conjunction with its VVT-iW system. The V35A-FTS and T24A-FTS engines (as part of Toyota's Dynamic Force line of engines) are also other engines to use the D-4ST system, working in conjunction with the integrated VVT-iE system.

VVT-i oil supply hose issues

In 2010, Toyota USA announced a Limited Service Campaign (LSC 90K) to replace the rubber portion of the oil supply hose for the VVT-i actuator on the 2GR-FE (V6) engine, which were found to be defective. In all, approximately 1.6 million vehicles manufactured prior to 2008 were affected. The defective oil supply hoses were prone to degradation and eventual rupture, causing oil to rapidly leak and resulting in permanent engine damage. In 2014, the LSC 90K Campaign was extended to 31 December 2021 [5] on 117,500 Toyota brand vehicles that were "missed" during the initial campaign.

See also

Related Research Articles

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References

  1. ↑ "Lexus LS engine page". Archived from the original on 2009-05-03. Retrieved 2009-09-29.
  2. ↑ "Camry in Europe features new 2.0L engine with VVT-iW." Green Car Congress. 2014-09-05. Retrieved 2016-06-27.
  3. ↑ "Toyota Develops Next-generation Engine Valve Mechanism — 'Valvematic' Achieves High Fuel Efficiency and Dynamic Performance —". TOYOTA. 2007-06-12. Archived from the original on 2010-01-21. Retrieved 2009-06-29.
  4. ↑ Nunez, Alex (2011-07-01). "Toyota Noah / Voxy: Valvematic for the people (movers)". Autoblog.com. Retrieved 2009-06-29.
  5. ↑ "Extension of Limited Service Campaign (LSC) 90K" (PDF). US: Toyota. Retrieved 2016-10-08.
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