Võistlusmootorratta käigukasti analüüs

Lõputöö eesmärgiks oli teada saada millist materjali on kasutatud hammasrataste valmistamiseks. Milliseid termotöötlus protsesse on kasutatud. Mõista miks hammasrattad purunevad. Mida peaks hammasrataste juures muutma et neid edaspidi usaldada saaks ning need ei puruneks nii tihedalt. Kõik need küsimused leidsid vastused. Materjaliks on 18 CrNiMo 7-6. See leiti tänu materjali keemilise koostise määramisele. Sealt saadud andmete põhjal otsiti sobivaim materjal. Teades et seda materjali kasutatakse tihedalt Saksamaal hammasrataste valmistamiseks ning uuritavad hammasrattad on valmistatud samuti Saksamaal võib kindlalt väita et materjal on õigesti leitud. Teiseks eesmärgiks oli teada saada millist termotöötlus protsessi on kasutatud. Tehase toe puudumisele tuli see leida töö käigus. Madala süsiniku sisalduse tõttu ei ole materjal karastatav. Sellepärast on tehtud sellele tsementiitimine. Selle käigus on pind rikastatud süsinikuga ning seejärel tehtud pind karastamine. Sellele viitavad ka materjali kõvadused pinnalt ning seest. Hammasrataste sisu on pehme ning väliselt kõvad. Sisemine kõvadus on 39 HRCd ning pinnalt 55 HRCd. Kolmandaks eesmärgiks oli teada saada miks hammasrattad purunevad. Sellele vastuseks on liiga kõvad kõvadused hammasratta pinnale. Soovituslik maksimaalne kõvadus pindkarastusel on 50 HRCd aga mõõdetud tulemused näitavad keskmiseks tulemuseks 55 HRCd. Maksimaalne kõvadus mõõtmisel tuli 57 HRCd. See on seitse ühikut üle soovitatud normi. Materjali kõrgemal kõvadusel on materjal hapram ning murdub lihtsamini. Samuti tekitas probleeme hammasratastele rakenduv jõud. Hammasrattad ei pidanud sellele jõule vastu. Seda kinnitas hammasratastele tehtud analüüs Solid Edges. Sellele leiti kaks lahendust. Esimese variandina muudeti hammasrattaid 8 mm laiemaks. Selle muutuse tulemusena peavad hammasrattad sellele pingele vastu. Teise variandina muudeti hammasratta materjali. Kasutati 18 CrNiMo 7-6, aga pakutav materjal mis arvutuste kohaselt peab vastu on Uddeholm Bure. Kokkuvõtteks võib öelda et kõik eesmärgid, mis püstitati ka lahendati. Töö arendas autori nägemust kuidas hammasrattad ning käigukast toimib.

The topic of this research is "Analysis of the Gearbox of a Competition Motorcycle." The thesis became the author's problem while using the Zabel engine. During the period 2015-2021, the author was engaged in motocross, more precisely in a motorcycle with a sidecar. During this period, the gears of the gearbox broke very often. During the season, which lasted from May to September, the gearwheels had to be changed five to six times. There are 18 to 22 races per season plus pre-season and in-season training. During that duration, you get 80 to 100 hours of driving. The main concern was the third gear. This gear is the most used and because of that, it broke the most. The gears do not wear out, do not overrun, or anything like that. The whole tooth breaks off from the gearwheel. 99% of the time the broken tooth comes from the third gear. There have been instances where other gears have broken, but these are very rare. The service life of gears varies greatly. The author has managed to drive half of the season with one pair of gears. It's about 10 races or 20 hours. The least used gear was used for one race, which lasted 20 minutes plus two laps. Thus, it is not possible to predict how long a pair of gears can be used. As a result, breakage cannot be prevented. Usually, it is not possible to finish the race with broken gear. This means you do not finish the race and won't score any points. The cost of one third gear pair is 300 €. It takes 1500 to 1800 € per season. This is a bargain for a budget. The author's strong driving style or gear changes are not the cause of the breakage. Also, the frequency of breakage is not changed by changing the gearbox oil brand. In an interview, four-time world champion Etienne Bax said he changes third gear gears after each race. In the World Championship stage, one race lasts 30 minutes plus two laps. So he exchanges them more than the author. Without the support of the factory, I would like to know more about the materials, processing, and required quality of the gears. The thesis aims to find out what material has been used to make the gears. What heat treatment processes have been used. Understand why gears break. What should be changed about the gears so that they can be trusted in the future and they will not break so easily. Suggest solutions for changes. During the research, all these questions were answered. The material is 18 CrNiMo 7-6. This was due to the chemical composition of the material. Based on the data obtained there, the most suitable material was searched. Knowing that this material is widely used in Germany for the production of 32 gears and that the gears under investigation are also manufactured in Germany, it can be stated with certainty that the material has been correctly found. The second goal was to find out what heat treatment process was used. The lack of factory support meant that this had to be found during the work. Due to its low carbon content, the material is not hardenable. That is why it has been cemented. In the process, the surface is enriched with carbon and then the case is hardened. This is also indicated by the hardness of the material on the surface and inside. The gears are softer inside and hard on the outside. The internal hardness is 39 HRC and the surface is 55 HRC. The third goal was to find out why the gears break. The answer is too hard hardness on the surface of the gear. The recommended maximum hardness for case hardening is 50 HRCd, but the measured results show an average result of 55 HRC. The maximum hardness measured was 57 HRC. This is seven units above the recommended standard. With higher material hardness, the material is more fragile and breaks more easily. The force applied to the gears also caused problems. The gears could not withstand this force. This was confirmed by the analysis of the gears in Solid Edge. To this problem, two solutions were found. The first solution was found to make the gears 8 mm wider to withstand this tension. The second solution is to change the material. Originally they are made of 18 CrNiMo 7-6 but the author thinks that Uddeholm Bure would be a much more better choice. In conclusion, all the goals that were set were solved. The work developed the author's vision of how gears and gearboxes work.