Designing a two-speed gearbox requires a systematic approach to achieve reliable torque and speed conversion between input and output shafts. This article outlines key engineering considerations for constructing a spur-gear-based manual transmission with a sliding dog clutch mechanism.
(how to make a 2 speed gearbox)
Gear Ratio Definition: Begin by defining required gear ratios (e.g., 3:1 for low gear, 1.5:1 for high gear). These ratios dictate torque multiplication and output speed ranges. Calculate teeth counts to satisfy ratios while ensuring constant center distances between shafts. For example:
– Low gear: 50-tooth driven gear / 25-tooth drive gear = 2:1 ratio
– High gear: 30-tooth driven gear / 20-tooth drive gear = 1.5:1 ratio
Verify center distance consistency: (25+50)/module = (20+30)/module.
Shaft Configuration: Utilize three shafts:
1. Input Shaft: Hosts fixed drive gear (G1) engaging countershaft.
2. Countershaft: Fixed gears (G2, G3) mesh with output shaft gears.
3. Output Shaft: Contains free-rotating gears (G4, G5) and spline-mounted sliding dog clutch.
Gear Meshing: G1 permanently engages G2 on countershaft. G3 (countershaft) meshes with G4 (output shaft) for low gear. G2 simultaneously engages G5 for high gear. All gears must share identical module/pitch for correct meshing.
Shifting Mechanism: A fork-controlled dog clutch slides axially on output shaft splines. When engaged:
– Low gear: Clutch locks G4 to output shaft.
– High gear: Clutch locks G5 to output shaft.
– Neutral: Clutch disengaged from both gears.
Component Sizing:
– Gear Materials: Case-hardened steel (e.g., AISI 8620) for durability.
– Shafts: Size for maximum torsional stress. Use ASME code: \(d = \sqrt[3]{\frac{16T}{\pi S_{allow}}}\).
– Bearings: Select deep-groove ball bearings based on dynamic load rating exceeding gear separation forces.
Lubrication & Housing:
– Immerse gears in ISO VG 220 oil bath for cooling and wear reduction.
– Design rigid cast aluminum housing with breather, drain plug, and sealing gaskets.
Manufacturing Tolerances:
– Gear teeth: AGMA Class 8 accuracy.
– Shaft alignment: ±0.05mm concentricity.
– Clutch dogs: Hardened and ground for impact resistance.
Validation: Perform bench testing under incremental load to verify:
– Shift engagement smoothness.
– Temperature rise (<70°C).
- Noise levels (<85 dB(A)).
(how to make a 2 speed gearbox)
This design ensures efficient power transmission and user-controlled ratio selection. Proper material selection, precise manufacturing, and rigorous validation are critical for longevity and performance.