The double countershaft transmission is a crucial component in the heavy-duty vehicle industry, thanks to its superior transmission performance and high load capacity. Due to its complex structure, the gears on the intermediate shaft must be precisely machined, and the alignment of the internal and external teeth directly impacts the assembly quality of the transmission, which in turn affects the overall performance of the system. To meet the processing requirements for our new product, this paper introduces a simple yet effective tooth alignment device that ensures the symmetry of internal and external teeth. The device is not only easy to use but also highly efficient, making it well-received by users.
**Process Flow**
*Figure 1: Intermediate shaft second gear*
The second gear of the intermediate shaft in a certain type of our company uses an internal spline with an outer ring gear structure, requiring a symmetry tolerance of within 0.06mm (as shown in Figure 1). To meet these design specifications, we implemented the following process:
1. Due to the small diameter of the internal spline, the pinion cutter used has a smaller size and fewer teeth, resulting in poor surface quality and shorter tool life. To address this, we opted for a broaching process, which offers higher efficiency and better precision.
2. For the outer ring gear, we selected a shaving process after rough cutting to ensure accuracy. This required designing a dedicated gear-tooth clamp to hold the outer ring gear securely during machining.
**2. Analysis of the Tooth Problem**
According to the product design requirements, the internal spline’s tooth groove must be symmetrical with the outer ring gear’s tooth groove. We selected one internal spline tooth groove as the reference point and adjusted the cutting edge of the pinion cutter so that it would cut exactly opposite the internal spline’s groove on the outer ring gear (see Figure 2).
*Figure 2: Gear shaping*
**3. Solving the Tooth Alignment Issue**
To meet the tooth alignment requirements of the product, we designed a specialized gear-tooth fixture (as shown in Figure 3). The fixture uses a spline groove positioning method. A ball is mounted on a sliding block, which is spring-loaded. When in use, the operator manually pushes the handle, places the workpiece, releases the handle, and slightly rotates the workpiece by hand until the ball locks into the internal spline groove. This ensures accurate circumferential positioning, and then the sleeve is tightened to secure the workpiece in place.
*Figure 3: Pinion to tooth fixture*
During the first trial production run, 50 workpieces were processed. After the machine tool and the gear-tooth fixture were properly adjusted, 45 consecutive pieces were produced. Each was measured for symmetry, and all maintained a stable tolerance within 0.06mm, meeting the on-site production standards.
**4. Conclusion**
Through field testing, we found that after applying the machining process and using the gear shaping jig, the symmetry of the outer ring gear could be consistently controlled within 0.06mm. This solution fully satisfies the demands of mass production and ensures reliable performance in the final product.
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Lachoi Scientific Instrument (Shaoxing) Co., Ltd. , https://www.lachoinst.com