astronomy

Lepelletier planetary gearset

Lepelletier planetary gearset is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lepelletier planetary gearset rather than just read about it. In short: The Lepelletier planetary gearset or Lepelletier gear mechanisms is an epicyclic gear system with seven forward gears, six of which are usable. It has three degrees of freedom and is based on a concept by Pierre A.

Key takeaways

Lepelletier planetary gearset belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lepelletier planetary gearset to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lepelletier planetary gearset from memory before moving on to harder problems.

Reference excerpt

The Lepelletier planetary gearset or Lepelletier gear mechanisms is an epicyclic gear system with seven forward gears, six of which are usable. It has three degrees of freedom and is based on a concept by Pierre A. G. Lepelletier from 1992. It is a combination of a planetary gearset and a compound Ravigneaux gearset.

History The combination of serial and parallel power flow offers additional gear ratios without increasing the complexity of the design. This transmission is the first of its kind to take advantage of this benefit. Due to these advantages, this gearset concept became widely used in automatic vehicle transmissions. ZF was the first to start series production in 2000. Aisin/Toyota, Ford, and GM followed in 2005. For the first time, the construction costs could be reduced compared to the respective predecessor models.

Planetary gearset concept

Improved fuel economy The main objective in replacing the predecessor model was to improve vehicle fuel economy with extra speeds and a wider gear span to allow the engine speed level to be lowered (downspeeding), which is a decisive factor in improving energy efficiency and thus reducing fuel consumption. In addition, the lower engine speed level improves the noise-vibration-harshness comfort and the exterior noise is reduced. It has a torque converter lock-up for all 6 forward gears, which can be fully disengage when stationary, largely closing the fuel efficiency gap between vehicles with automatic and manual transmissions.

Reduced manufacturing complexity In order to avoid a further increase in manufacturing complexity while expanding the number of gear ratios, all major manufacturers switched from the conventional design method—in which the planetary gearset concept was limited to a purely serial or in-line power flow—to a more modern design method that utilizes a planetary gearset concept with combined parallel and serial power flow. This was only possible thanks to computer-aided design and has resulted in a globally patented gearset concept. The resulting progress is reflected in a better ratio of the number of gears to the number of components used compared to existing layouts.

No use of 5th (direct) gear from the original concept The Lepelletier gearset concept actually provides 7 forward gears. However, the 5th gear, which is configured as a direct gear (ratio 1.00) in this configuration, requires a releaseable brake for S1 (sun gear of the first gearset, which is the simple one) and thus a 6th shifting element without any corresponding benefit: with ratios of approximately 1.15 and 0.85, the 4th and 6th gears are so close together that the 5th gear can easily be dispensed with. This means that all manufacturers can manage with 5 shifting elements and all transmissions built have 6 gear ratios instead of the possible 7.

Quality The ratios of the 6 gears are nicely evenly distributed in all versions. Exceptions are the large step from 1st to 2nd gear and the almost geometric steps from 3rd to 4th to 5th gear. They cannot be eliminated without affecting all other gears. As the large step is shifted due to the large span to a lower speed range than with conventional gearboxes, it is less significant. As the gear steps are smaller overall due to the additional gear(s), the geometric gear steps are still smaller than the corresponding gear steps of conventional gearboxes. Overall, therefore, the weaknesses are not overly significant. As the selected gearset concept saves up to 2 components compared to 5-speed transmissions, the advantages clearly outweigh the disadvantages. The layout brings the ability to shift in a non-sequential manner – going from gear 6 to gear 2 in extreme situations simply by changing one shift element (actuating clutch E and releasing brake A).

Illustration In the illustrations, the Ravigneaux gearset is shown vertically mirrored, contrary to actual practice, for the sake of clarity.

Limitations The limitations of the Lepelletier gearset mechanism lie in the number of gear ratios provided and in the efficiency issues that Ravigneaux gearsets always contend with. Therefore, starting in 2008 with the ZF 8HP, the Lepelletier gearset mechanism was replaced by gearset concepts with even more gears and largely dispensing with the use of Ravigneaux gearsets. This was followed later by the GM 8L, Aisin-Toyota 8-speed transmission, and the Ford-GM 10-speed transmission, for example.

Applications

The gearset was used in a wide range of automatic vehicle transmissions.

See also ZF 6HP transmission Ford 6R transmission GM 6L transmission Aisin AWTF-80 SC

References

Illustrations

Worked examples

Example 1 — a first encounter with Lepelletier planetary gearset

Start with the simplest possible case. Write down what Lepelletier planetary gearset claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lepelletier planetary gearset before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lepelletier planetary gearset ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lepelletier planetary gearset

In research: Lepelletier planetary gearset appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lepelletier planetary gearset in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lepelletier planetary gearset is common in secondary-school and first-year university syllabi. It links to neighbouring topics Epicyclical gearing, Gears, so understanding it makes those chapters shorter.
In everyday life: Look for Lepelletier planetary gearset outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Lepelletier planetary gearset in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lepelletier planetary gearset means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lepelletier planetary gearset out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lepelletier planetary gearset in simple terms?

Why does Lepelletier planetary gearset matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lepelletier planetary gearset?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lepelletier planetary gearset.