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.P. A. G. Lepelletier, Multispeed automatic transmission for automobile vehicles, (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.

+ Planetary gearset concept: manufacturing complexity WithAssessment Output:GearRatios InnovationElasticityΔ Output : Δ Input Input: Main Components Total Gearsets Brakes Clutches 6HPRef. Object Topic Δ Number Relative Δ Δ Output · Δ Input 6HP5HP 24/30 65 Progress 89 33 23 33 Δ Number 1 -1 0 -1 0 Relative Δ · 6HP5HP 18/19 65 Progress 810 33 23 34 Δ Number 1 -2 0 -1 -1 Relative Δ · 6HP3-Speed 63 Market Position 87 32 23 32 Δ Number 3 1 1 -1 1 Relative Δ ·

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).

+ Planetary gearset concept: gear ratio quality In-Depth AnalysisWith AssessmentAnd Torque RatioAnd Efficiency Calculation Planetary Gearset: TeethLepelletier Gear MechanismCount Nomi-nalEffec-tive Cen-ter Simple Ravigneaux Avg. MakeModel VersionFirst Delivery S1R1 S2R2 S3R3 BrakesClutches RatioSpan GearStep Gear R 1 2 3 4 5 6 GearRatio Step Δ Step ShaftSpeed Δ ShaftSpeed TorqueRatio Efficiency 2000: first manufacturer to use the Lepelletier gearset mechanism: ZF 6HP 1st generation ZF 6HP 26ZF 6HP 19ZF 6HP 32 2000 (all) 3771 3138 3885 23 Gear R 1 2 3 4 5 6 GearRatio Step 1.0000 1.5382 1.3178 1.2549 Δ Step 1.1589 1.1559 1.0502 Speed 1.0000 1.7826 2.7419 4.8096 6.0354 Δ Speed 1.0000 0.7826 0.9593 1.1599 1.2258 TorqueRatio –3.3116–3.2665 4.01863.9436 2.28372.2559 1.51071.5055 1.13591.1325 0.86330.8613 0.68670.6845 Efficiency 0.97330.9600 0.96350.9455 0.97610.9642 0.99310.9897 0.99390.9910 0.99550.9932 0.99370.9905 2007: ZF 6HP 2nd generation ZF 6HP 28ZF 6HP 21ZF 6HP 34 2007 (all) 3771 3138 3885 23 Gear R 1 2 3 4 5 6 GearRatio Other manufacturer using the Lepelletier gear mechanism AisinAWTF-80 SC 2005 5090 3644 4496 23 Gear R 1 2 3 4 5 6 GearRatio Step 1.0000 1.5238 1.3436 1.2532 Δ Step 1.1484 1.1311 1.0722 Speed 1.0000 1.7500 2.6667 3.5926 4.8272 Δ Speed 1.0000 0.7500 0.9167 0.9259 1.2346 TorqueRatio –3.3023–3.2568 3.99563.9204 2.31272.2841 1.54441.5389 1.14711.1434 0.85530.8532 0.68130.6791 Efficiency 0.97300.9596 0.96320.9451 0.97570.9636 0.99290.9893 0.99350.9903 0.99530.9928 0.99360.9904 Ford6R 606R 80 2005 (all) 3771 3138 3885 23 Gear R 1 2 3 4 5 6 GearRatio Ford6R 140 2005 4995 3747 4797 23 Gear R 1 2 3 4 5 6 GearRatio Step 1.0000 1.5293 1.3389 1.2744 Δ Step 1.1594 1.0504 Speed 1.0000 1.7143 2.6216 4.6290 5.8993 Δ Speed 1.0000 0.7143 0.9073 1.1710 1.2703 TorqueRatio –3.0449–3.0035 3.82903.7576 2.26152.2333 1.50551.5003 1.14191.1383 0.85430.8522 0.66920.6669 Efficiency 0.97330.9601 0.96350.9456 0.97560.9635 0.99320.9898 0.99370.9906 0.99520.9927 0.99340.9900 GM6L 456L 50 2006 4989 3747 4797 23 Gear R 1 2 3 4 5 6 GearRatio Step 1.0000 1.5293 1.3557 1.2662 Δ Step 1.1408 1.0703 Speed 1.0000 1.7143 2.6216 4.7643 6.0346 Δ Speed 1.0000 0.7143 0.9073 1.2499 1.2703 TorqueRatio –3.1138–3.0710 3.91563.8421 2.31272.2826 1.53961.5340 1.14901.1453 0.84900.8468 0.66920.6692 Efficiency 0.97300.9597 0.96330.9452 0.97530.9630 0.99290.9893 0.99340.9902 0.99510.9925 0.99340.9900 GM6L 806L 90 2005 5094 3546 4692 23 Gear R 1 2 3 4 5 6 GearRatio Step 1.0000 1.5429 1.3522 1.2781 Δ Step 1.1604 1.0580 Speed 1.0000 1.7037 2.6286 4.7258 6.0401 Δ Speed 1.0000 0.7037 0.9249 1.2310 1.3143 TorqueRatio –2.9817–2.9410 3.87943.8068 2.30482.2756 1.52131.5160 1.14481.1412 0.84780.8456 0.66220.6599 Efficiency 0.97320.9599 0.96340.9454 0.97510.9628 0.99310.9896 0.99360.9904 0.99500.9924 0.99320.9898 Actuated Shift Elements Brake A ❶ ❶ ❶ ❶ Brake B ❶ ❶ ❶ Clutch C ❶ ❶ Clutch D ❶ ❶ Clutch E ❶ ❶ ❶ Geometric Ratios: Speed Conversion GearRatioR & 3 & 6OrdinaryElementaryNoted GearRatio1 & 2OrdinaryElementaryNoted GearRatio4 & 5OrdinaryElementaryNoted Kinetic Ratios: Torque Conversion TorqueRatioR & 3 & 6 TorqueRatio1 & 2 TorqueRatio4 & 5

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