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Ari Holopainen / light_truck | |
| O. Medium & Light Truck Transmissions: Mainly progressive gear steps Like personal car transmissions most of these medium and light truck transmissions have only main gearbox without splitter or range-change unit. So you can use progressive gear steps, which means the higher gear the smaller gear step between gears. Although 12-speed transmission has splitter unit and 8-speed transmissions have range-change unit also those main gearboxes have some progression in gear steps. Major difference between personal car and light truck transmissions is that light trucks have larger gear steps and overall gear ratio. In real world light truck transmissions are also stronger and heavier while they have to handle more torque. Note that here medium truck means mid range lorry or commercial truck, not pickup truck. And light truck means pickup, van or small lorry. O.1. 5-speed version V, overall gear ratio 6,00: Inspirer: ZF S5-42
This transmission is 1st light truck transmission but 5th 5-speed transmission. First four 5-speed gearboxes are later shown personal car gearboxes.
This transmission is also big brother of later shown 4-speed version I personal car transmission. Only difference is added slow gear, ratios of other gears are straight from 4-speed gearbox. New 1st gear and large gear steps of 4-speed gearbox make this transmission perfect to light truck use. You may notice that this gearbox has actually 6 gears. Problem is that gear step between 1st gear and slow extra gear doesn’t suit to this gearbox’s gear step progression. That why slow extra gear is abandoned. If you build this gearbox you have to make shift pattern that doesn’t allow to switch to that extra gear (check Building example). O.2. 5-speed version VI, overall gear ratio 5,71: Inspirer: ZF S5-42 This 5-speed light truck transmission is based on later shown 4-speed version II personal car transmission. New feature is added slow gear, other gears’ ratios are taken from 4-speed gearbox. This version much simpler than previous light truck transmission but price is that gear step progression is not so good.
While input axle is supported by two technic brick 1x2 with 2 holes you may have difficulties to attach studded lego motor to the input axle. If you need hints to solve this problem check 4-speed version II in personal car transmissions. O.3. 6-speed version II, overall gear ratio 8,00: Inspirer: Eaton Fuller FS-6406B
Here is 6-speed version of medium & light truck transmissions. Gear steps are only partly progressive and progression is not very strong. This means that largest gear step 1-2 is only 1,67 so this transmission works also with larger low speed diesel engine in which performance speed range (engine speeds from maximum torque to maximum power) is more narrow than in light trucks with smaller engines.
This design is remake with more compact and simpler design but price is that ratio set is not so optimized. But ratio set is still quite realistic, check gear step comparison in picture Ratio comparison (lego version is overdrive but Fuller direct drive). Original version has better ratio set but otherwise design is not very good. But it’s still available on page Junkyard if you want to check it. So, here is quite simple and usable universal lego 6-speed transmission with realistic ratio set for light truck, lighter medium duty truck, heavier van and pickup truck. O.4. 6-speed version IV, overall gear ratio 8,57: Inspirer: ZF S6-66
Here is another 6-speed light truck transmission. Structure before synchro axles is simpler than in previous 6-speed version but after synchro axles structure is more complicated. All in all this transmission is quite small for 6 speeder that has progressive gear steps.
This lego design is remake. Original design has XS(8)-M(24) gear pair after synchro parts. So there are significant overdrive situations in some gear wheels in some gears which can lead to bad efficiency. So original design is moved to page Junkyard if you want to check it. While input axle is supported by two technic brick 1x2 with 2 holes you may have difficulties to attach studded lego motor to the input axle. If you need hints to solve this problem check 4-speed version II in personal car transmissions. O.5. 6-speed version VI A & B, overall gear ratio 7,50: Inspirer: ZF Ecolite
Here is very simple version of 6-speed transmission that has progressive gear steps. But problem was that its overall gear ratio is too high for personal cars and slightly too small for light trucks. With some web search I found that lighter version of current ZF Ecolite has overall gear ratio 7,62 so this lego version VI became as light truck transmission that also suits for wide ratio personal cars that are usually diesel powered in real world. All in all lego design has good progressive gear steps and there are no significant overdrive situations in any gear wheel in any gear so gearbox’s efficiency should be good.
Available is two brick frame setups plus studless version B. In brick frames old school original setup uses 14 teeth thin bevel gears and modernized alternative setup has 20 teeth clutch gear. These setups have different design in 2nd and 5th gear but only ratio change is in 2nd gear. Gear wheel changes also makes alternative setup slightly more narrow. Version B with studless frame uses same gear wheels and ratios as alternative brick frame setup. So, if you are looking for 6-speed lego transmission for light truck, van, pickup or wide ratio personal car I recommend to build one of these choices. And if you abandon 1st gear in lego version you get 5-speed personal car transmission with typical overall gear ratio 4,29 (original) or 4,00 (alternative & version B). So this lego version is quite versatile. O.6. 7-speed, 1 reverse gear, overall gear ratio 11,67: Inspirer: Eaton Fuller 7-speed B ratio (like T-14607B in Eaton Transmission Specifications Catalog)
Wide ratio version of 7-speed transmission with progressive gear steps can be used in buses & coaches (city buses with automatic transmissions excluded) and light & medium duty trucks. It can offer quite good performance in high speeds (top gear step 6-7 only 1,25 in lego version) with mid-range move off and climbing capability (overall gear ratio now 11,67) in same single gearbox without auxiliaries. But engine’s torque peak must be wide enough that it can handle large gear step 1-2 (now 1,80), so 7-speeder doesn’t suit to largest truck engines.
This lego version is remake with several improvements: design is simpler and two studs shorter, and reverse gear is added. Design is also modernized while it uses new 28 teeth gear (ML) and 20 teeth clutch gear (Mu’) instead of old 14 teeth thin bevel gears. Original design is still available on page Junkyard if you want to check it. Modernization causes that lego version’s reverse gear is slower than in real 7-speed transmissions. But if you have old 14 teeth thin bevel gears you can do simple reality upgrade: just change reverse gear’s Su(12)-Su(12)-Su(12)-Mu(20) gear train to Th(14)-Su(12)-Su(12)-Mu(20), it changes reverse ratio to -10,00. In my opinion 7+R-speed is largest manual transmission you can handle with single shift lever and H shift pattern. 6 forward gears keep things simple when shift lever centers itself to 3-4 line, movement to right gives 5-6 line and movement to left gives 1-2 line. And if reverse gear is behind lock or extra spring load 6+R-speed can be shifted without risk of wrong gear. In 7+R-speed lines R-1 and 6-7 need some extra spring resistance or other methods that you don’t accidentally shift to those gears while shifting to gears 2-5. This is when neutral is between lines 2-3 and 4-5. If neutral is in line 4-5 only line R-1 needs extra spring resistance. O.7. 7-speed version IV, 1 reverse gear, overall gear ratio 13,13 REMAKE: Inspirer: Eaton Fuller 7-speed B ratio (like T-14607B in Eaton Transmission Specifications Catalog)
This 7-speed transmission version IV is wide ratio design with strongly progressive gear steps. Like previous 7-speed it can be used in buses & coaches (city buses with automatic transmissions excluded) and in light & medium duty trucks. So it combines good performance in high speeds (top gear step 6-7 only 1,25 in lego version) and good move off and climbing capability (overall gear ratio now 13,13) for light and medium duties. But price is that engine needs wide torque peak to handle large gear steps in lower gears (step 1-2 now 1,84), so strong progression is not usable with largest truck engines.
This lego version is remake with two improvements: design is smaller and reverse gear is added. Original design is still available on page Junkyard if you want to check it. This 7-speed mixes old and new technic while it has old 14 teeth thin bevel gears (Th) and new 20 teeth clutch gears (Mu’). This mix gives some reality advantages like slightly faster reverse gear than 1st gear. If you don’t have old 14 teeth gears previous 7-speed version I is modern version for you. O.8. 6-speed & 12-speed, overall gear ratios 8,33 & 10,71: Inspirer: ZF S6-66 & ZF S6-66 + GV66
These gearboxes are inspired by ZF’s transmission S6-66 and its additional splitter unit GV66. Splitter means that main gearbox’s front mounted constant gear pair is replaced with 2 constant gear pairs. New constant gear ratios mean that main gearbox’s gear step 5-6 becomes larger to be suitable for splitting, but other main gearbox’s gear steps stay unchanged. Of course all ratios are different except direct gear. While S6-66 is only main gearbox it has progressive gear steps. When splitter GV66 is added gear steps in higher gears become geometrical. Also splitter’s gear steps (1-2, 3-4, 5-6 etc.) are geometrical (constant value). But in compound shifts (2-3, 4-5, 6-7 etc.) and when only main gearbox is used gear steps are progressive except 2 highest gear steps. So gearbox S6-66 + GV66 has partly progressive gear steps.
Redesigned lego versions (6-speed version V & 12-speed version III) follow quite closely ZF’s modular design. 6-speed transmission needs only two modifications to get 12-speed version: ratio of top gear is changed from 0,75 to 0,70 (gear step changed from 1,33 to 1,43) and splitter is added. This means some minor changes in gear wheels and bricks but 6-speeder and main gearbox of 12-speeder are very close to each other. If you want compare these lego designs check YouTube clip in which transmissions are built simultaneously. O.9. 8-speed, 2 reverse gears, overall gear ratio 9,80: Inspirer: Scania GR875 & Volvo R52 This 8-speed transmission has 4-speed main gearbox with a reverse gear and range-change unit. Although there is range-change unit main gearbox has some progression in gear steps. This feature is taken from those Scania’s and Volvo’s gearboxes.
Progressive gear steps and range-change unit is a little bit problematic combination while gear step 3-4 is significantly smaller than next range change 4-5 and gear step 5-6. If you have to use all the gears (for example heavy loaded) low range is just continuous upshifting until you come to range shift. But in high range progression is good thing while you can take advantage of decreasing gear steps in high speeds. And if you can skip gears upshifting sequence 2-4-5-6-7-8 gives fully progressive gear steps. More info about progressive gear steps and why they are not often used with auxiliary gearboxes is in page Gearbox theories. Note that lego version has 2 reverse gears but high range reverse is not advertised in Scania’s and Volvo’s gearboxes. Reason for this is that high range reverse is too fast for move off so you need to start with low range and make large gear step range change to get high reverse. And for many situations high reverse is just too fast while you need to look both mirrors to see where you are going. O.10. 8-speed version II, 2 reverse gears, overall gear ratio 10,88: Inspirer: Volvo R62
Here is another 8-speed transmission that has 4-speed main gearbox and range-change unit. Also this version II has some progression in gear steps but not so much as version I. Structure in this version II is more compact and simpler than in version I while length is reduced from 19 studs to 15 studs and axles and gear wheels are packed in 2 layers instead of 3. If you have low speed motor and 8 gears are enough here is your choice.
Available is also alternative setup in which main gearbox and range-change unit are located parallel. So this setup is shorter but wider. For main gearbox’s shift lever use 8 studs long axle with longitudinal bricks at the both ends. Put bush to the right side of the left brick to prevent axle’s movement to the left. For range shift lever use axle pin and 3rd longitudinal brick on the right side. While range lever is between bricks it’s well supported. Range lever also prevents main lever’s axle to slide to the right. While input axle is supported by two technic brick 1x2 with 2 holes you may have difficulties to attach studded lego motor to the input axle. If you need hints to solve this problem check 4-speed version II in personal car transmissions. One interesting fact is that gear steps are very close to each other in lego version and Volvo R62 transmission. But ratios are all different while lego version is overdrive and Volvo’s transmission direct drive. Check picture called Ratio comparison. Note in Volvo’s transmission that 2 decimal accuracy in ratios causes calculation error between gear steps 2-3 and 6-7, they should have same value. One notable thing is that gear step 7-8 (also 3-4 due to range-change unit) is smaller than the others. In real trucks engine rpm is often matched to be in economic zone when you drive in top gear at highest allowed speed limit. In Europe this speed limit is usually 80 km/h. If gear step 7-8 is for example as high as 1,40 speed in 7th gear is only about 57 km/h when you drive in same engine rpm as in top gear at speed 80 km/h. So speed limit 70 km/h means trouble because in top gear engine rpm is too low (not enough power for uphill situations) but too high in 7th gear (increases fuel consumption). Other problem is in acceleration to 80 km/h while you need to rev engine out of economic zone in 7th gear before upshift to top gear if you want to get faster acceleration. Early upshift to top gear means slower acceleration because in lower engine rpm you have less power and in high speeds you need most power. These are the reasons why they often make gear step 7-8 smaller in 8- or 9-speed transmissions. O.11. 8-speed version III, 2 reverse gears, overall gear ratio 9,12: Inspirer: Scania GR875
Here is one more 8-speed transmission that has 4-speed main gearbox and range-change unit. This time main gearbox has strong progression in gear steps to be used with auxiliary gearbox. Ratios of lego version are copied from Scania’s 8-speed transmission and you can check picture Ratio comparison to see how close ratios are to each other. Progression in main gearbox means that all gear steps in low range are too small. But from range change and in high range you can take advantage of decreasing gear steps. And if you can skip 1st and 3rd gear you get six gears with good progressive gear steps.
There are two setups available in lego version. In original setup main gearbox and range-change unit are located parallel so transmission is short but wide. For shift lever axles you need 3rd longitudinal brick to be placed between gearboxes. When you put both axles only half studs inside this middle brick shift levers are well supported. In alternative setup range-change unit is in front of main gearbox so this setup is longer but more narrow. There are some gear pair changes in alternative setup but they don’t affect to ratios and gear steps. Progressive gear steps in main gearbox make lego structure a little bit complicated but it was difficult to get gear step 1,46 with lego gears. Gear step 1,43 would have been much easier to get but then overall gear ratio would have become too small and it is already small in this transmission. One notable thing in Scania’s transmission is that reverse gear is significantly slower than 1st gear while in lego transmission they have same ratio. If you want slower reverse gears for lego version there is a simple conversion you can do in alternative setup: replace gears XS(8)-XS(8)-XS(8) with Su(12)-Su(12)-Th(14). Next pictures and YouTube video show you more info.
You can also convert original parallel setup but you need to move gears wheels of reverse from front to rear.
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Primary content in this document is © Ari Holopainen. All other text, images, or trademarks in this document are the intellectual property of their respective owners. |
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