The double countershaft transmission plays a crucial role in the heavy-duty vehicle industry due to its excellent power transmission performance and high load capacity. Because of its complex structure, the gears on the intermediate shaft must be precisely machined to ensure proper meshing. The alignment between internal and external teeth directly affects the overall assembly quality of the transmission, which in turn influences the performance and reliability of the entire system. In response to the processing needs of our new product, this paper presents the design of a simple yet effective tooth-matching device. This tool ensures stable internal and external tooth symmetry, features a straightforward structure, and is easy to operate—making it highly appreciated by users.
**Process Flow**
*Figure 1: Intermediate shaft second gear*
The second gear of the intermediate shaft in a specific type of our company's transmission 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 requirements, we implemented the following process:
1. Due to the small hole diameter of the internal spline, the shape of the pinion cutter is limited, resulting in fewer teeth and lower machining quality. This leads to poor spline quality, shorter tool life, and reduced efficiency. To address this, we opted for a broaching process using a broach, which offers higher precision and better efficiency.
2. For the outer ring gear, we selected a shaving process after rough cutting to ensure high machining accuracy. This required designing a dedicated gear-tooth clamp to hold the outer ring gear during the process.
**2. Analysis of the Tooth Problem**
According to the product design specifications, after machining, one groove of the internal spline must be symmetrical with one groove of the outer ring gear. We selected a specific groove on the internal spline as a reference point and adjusted the cutting edge of the pinion cutter to precisely cut the corresponding position on the outer ring gear (see Figure 2).
*Figure 2: Gear shaping*
**3. Solving the Tooth Alignment Problem**
To meet the gear alignment requirements of the product, we designed a specialized tooth clamp as shown in Figure 3. The device uses a spline groove positioning method. A ball is fixed on a slider, which is spring-loaded. When in use, the handle is pushed manually, the workpiece is loaded, the handle is released, and the workpiece is slightly rotated by hand to lock the ball into the internal spline groove. This ensures accurate circumferential positioning, after which the sleeve is tightened to secure the workpiece.
*Figure 3: Pinion to tooth fixture*
During the first trial run, 50 workpieces were produced. After the machine tool and the tooth clamp were properly adjusted, 45 units were continuously processed. All of them were measured for symmetry, and the results showed a consistent deviation of less than 0.06 mm, meeting the production requirements on-site.
**4. Conclusion**
Through practical application, the machining process combined with the gear shaping jig effectively controlled the symmetry within 0.06 mm, fully satisfying the demands of mass production. This solution not only improves the quality of the intermediate shaft but also enhances the overall performance of the double countershaft transmission.
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Lachoi Scientific Instrument (Shaoxing) Co., Ltd. , https://www.lachoinst.com