Интересная информация по вариатору:
особенно понравилось, что CVT имеет на 45% меньше деталей, чем конвенциональная АКПП.
VT25-E/VT25-E AWD (M75/M16) Transaxle
2004 Model Year Summary
● Additional Application Mid-2003 In Saturn ION Coupe
● Bearing Upgrades On Output Axis
FULL DESCRIPTIONS OF NEW OR CHANGED FEATURES
ADDITIONAL APPLICATION MID-2003 IN SATURN ION COUPE
The VT25-E was added to the Saturn ION Coupe in March 2003 and received a slight modification to the torque converter housing to fit the ION mounting location.
BEARING UPGRADES ON OUTPUT AXIS
Two bearings that support the secondary or driven axis are more durable. A higher strength steel is used for one bearing, and the second bearing, a needle bearing, was made longer. These improvements are to increase high-mileage durability.
LOW MAINTENANCE
The VT25-E and VT25-E AWD use specially formulated oil called DEX CVT. This fluid is validated for the life of the transmission, however, an additive to prolong the life of the fluid is recommended but not required to be added through the breather/fill cap at 50,000 miles.
OVERVIEW
The VT25-E (M75) and VT25-E AWD (M16) use a special steel belt developed by supplier Van Doorne, of Tilburg, Holland, that is squeezed between two conical pulleys whose diameters can be varied to create an infinite number of effective ratios. The all-wheel-drive application uses a case modified for a bolt-on Power Takeoff unit (PTU). Both applications are used in the Saturn VUE, which went into production in the fall of 2001. The VT25-E also in used with the Saturn ION although the converter housing mounts are modified to fit the ION platform. The VT25-E and VT25-E AWD are virtually identical internally and are manufactured and assembled in Szentgotthard, Hungary.
In the Saturn SUV application, acceleration is described as a very linear one-speed transmission. When maximum performance is requested by driver through an electronic throttle control, the engine accelerates quickly to its peak power output speed and will remain at that speed while the transmission continuously changes ratios toward overdrive as the vehicle accelerates. As the vehicle gains speed, the engine will then slow. Combined with electronic throttle control, sometimes called “drive-by-wire,” VTi is programmable for a wide range of drivability characteristic s.
The size of the VT25-E is about the same as a current 5-speed manual transaxle of similar torque-handling capacity. It is a 4-axis design, with the added feature of a very competitive on-engine axis length. Because of its short length, a power takeoff unit could be packaged to route torque to the rear axle for all-wheel-drive versions of the vehicle. The VTi is one of the most compact automatic transmissions for its torque handling capability. Reducing the pumping losses of an engine is the VTi’s primary contribution to improved fuel economy. The variable ratioing allows the engine to run with the throttle blade in a more open position at relatively lower engine speeds.
The number of parts in the VT25-E is about 45 percent less than in a conventional four-speed automatic transaxle such as the 4T45-E. There is a single planetary gearset to effect forward and reverse drives, and all ratios in forward and reverse come from the two conical forged steel pulleys, which are connected by the steel belt. A clutch disconnects the engine from the transaxle’s drive pulleys when the gear selector is moved to “neutral” or “park” positions. The steel belt itself is 710mm long, and contains 472 bow-tie-shaped plates called elements that are 24mm wide. The elements are held together by two sets of 12 steel bands. The belt elements work in compression, pushing each other around the pulleys. Even though the belts are composed entirely of steel elements in contact with each other, testing has shown no apparent increase in noise from the Van Doorne belt compared to conventional transmissions.
A torque converter allows the engine to smoothly engage with the transaxle pulleys when the vehicle is started, and provides additional torque multiplication to the full underdrive ratio of the pulleys. The full underdrive ratio is 2.61:1, while full overdrive is 0.437:1. The torque converter can multiply these ratios by 1.7:1 at full stall speed. The effective final drive for the Saturn SUV application is 4.98:1, and ION application is 4.36:1. The torque converter applies with ECCC technology, GM’s proprietary driveline damping system. The torque converter is a unique squashed shape developed by supplier LuK, with a cross section shape more pear-like than circular. The torque converter clutch friction surface is made of carbon fiber for durability and consistent lockup smoothness over the life of the transmission.
A Delphi-Saginaw high-pressure hydraulic pump is chain-driven on the input side of the transaxle, and supplies approximately 700 psi of pressure to squeeze the pulleys into the steel belt. Solenoids drop some of that pressure as low as 140 psi to hydraulically vary the distance between pulley halves, and therefore change their diameters relative to the belt.
There are intermediate (I) and low (L) ratio positions on the gear selector (PRNDIL), and these serve to provide engine braking such as needed when coasting downhill with a heavy load or trailer. The effect feels very similar to manually downshifting a conventional automatic transmission. During normal driving with the gear selector in “drive” position the engine braking effect feels similar to closing the throttle on a manual transmission vehicle that is in top gear.
Because a vehicle equipped with the VTi can run at a broad range of speeds at any engine rpm, it can be tuned to run at ranges where the engine is most efficient or most powerful. This tuning is done electronically . VTi also has a wider range of drive ratios than are offered by most manual or automatic step-gear transmissions. That allows more performance out of an engine with the same output. The ratios allowed by the pulleys is a range of 5.9:1 from full underdrive to full overdrive, compared to a wide-ratio manual transmission, which reaches a maximum ratio range of about 5.0:1. Automatic transmissions generally have smaller ranges, and compensate through the multiplication effects of the torque converter. The VTi can likewise use the ratio multiplication of its torque converter. The low effective ratioing combined with the low final drive allows the Ecotec L61 four-cylinder to provide impressive acceleration upon takeoff for the mid-size Saturn VUE and compact ION coupe.
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