PROBLEM #177
Wrong Niva
Nikolai shares a concern with his teammates. They lifted a Niva onto the service elevator and claimed the machine is new and in good condition. Yet when he tried to turn the front wheel and then the rear wheel, he immediately noticed the front axle turning with more resistance. The vehicle is said to use symmetric four wheel drive. Could there be a fault worth checking for
Guidance for drivers and readers
Brief answers will not be enough. This is a challenge for the contributor who offers the most solid explanations and multiple supporting reasons.
Submit the answer marked Competition before February 1, 2023 to the postal address 107045, Moscow, Seliverstov per., 10, building 1. Include a contact number or another reliable way to reach you. Credit for the response will be shared with the best contributors.
Summary of the expert competition results published on October 1, 2022
The readers were asked to explain why an even number of gear steps is common in automatic transmissions
The winner, Sergey Rybkin from Moscow, provided a detailed explanation
Until recently automatic transmissions were seen as rare or extraordinary. Today they are common, and discussions continue about transmission structures and the practicality of various solutions
The basic question is how an automatic transmission creates different gear ratios
Planetary gear sets are used in hydromechanical gearboxes for passenger cars, with rare exceptions. These sets consist of a ring gear, a sun gear, and a carrier that holds satellites. A simple planetary gear has two degrees of freedom and requires one element of the set to be held still. The input shaft drives another element that becomes the leading element while the remaining element becomes the driven element
In the planetary arrangement, the components are labeled as follows: 1 ring gear, 2 satellite, 3 carrier, 4 sun gear
Without extra restrictions, one planetary gear can produce seven gear states: two reverse gears and five forward gears. If all parts are rigidly connected, a direct gear is included, otherwise the transmission can be in neutral
Theoretically a five speed automatic with a single planetary gear set is possible, but it is not used in practice. To simplify the design, keep the output element the same size for all gears. This approach yields two forward gears and one reverse. More gears require combining several gear sets in stages
Adding a second stage raises the count to four gears. The input at each stage can be fed by the previous stage’s output, effectively doubling the options while maintaining two gears and a reverse
This is why four speed automatics became popular: simple, proven, and reliable with a gear count considered sufficient for many years. Adding a third planetary gear set can double the gear count again to eight, which is a common limit for a three stage design found in premium cars
The six gear configurations are also common because they simplify braking and clutches, reducing manufacturing complexity while offering a broad range. Placing three planetary gear sets makes it impractical to build a traditional five speed while an eight speed is powerful but not always needed. For those seeking simplicity and cost efficiency, six gears are often seen as an ideal middle ground
Historically automatic transmissions started with pure hydraulic control. Gears engaged slowly and without precision. The arrival of electronic controls made multitier gearboxes affordable and reliable enough to fit into budget cars. There is a big gap between theoretical gear possibilities and practical implementation
The topic also touches on ten speed and other advanced designs. These use four planetary gear sets and can push efficiency higher, but their practicality remains debated. Top trims may showcase such gearboxes to highlight a company’s capability or simply to impress
Congratulations to Sergei Rybkin for his achievement
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