1.The high-speed rotation requirement of gears
▶ present situation
High-speed gears have been widely adopted in new energy vehicles, primarily for their ability to transmit power stably at high speeds. Their application involves multiple aspects including material selection, design, manufacturing, and lubrication. The gear speed in new energy vehicles has evolved from 12,000 rpm to over 20,000 rpm, and is now trending toward 30,000 rpm and beyond.
The development of high-speed gears has raised higher requirements for gear design, material selection, and manufacturing, especially in terms of controlling gear lifespan, lubrication, heat dissipation, and NVH (Noise, Vibration, and Harshness).
▶ throw down the gauntlet
Reliability: High-speed operation accelerates tooth surface contact fatigue, fretting fatigue, and stress concentration, leading to premature gear failure. Currently, materials such as 20MnCr5 are selected for gears, which offer higher strength, better toughness, and superior heat treatment and processability.
Lubrication & Heat Dissipation: At high rotational speeds, gears experience higher linear velocities, resulting in increased heat generation during meshing and hindering oil film formation, thereby elevating the risk of gear failure. This also poses greater challenges in gear design, requiring stricter specifications for anti-caking properties, slip rates, and linear velocities. A well-designed tooth profile is particularly critical, while the selection of lubricants and proactive lubrication of gears are equally vital.
Dynamic balancing: As the rotational speed increases, the impact of dynamic balancing factors on the NVH of electric drives gradually intensifies, and the dynamic balancing requirements for shaft-to-tooth components become more stringent. Currently, all shaft-to-tooth components now include dynamic balancing inspection requirements.
Gear NVH: The expanded torque, speed, and rotational frequency ranges at high gear speeds significantly increase NVH control complexity. This raises challenges in managing gear excitation and vehicle transmission paths, requiring coordinated design of both electric drive sound packages and vehicle sound packages, along with vibration and noise isolation for structural pathways. At higher speeds, the torque and speed ranges broaden considerably, while the corresponding rotational frequency range nearly doubles, substantially complicating NVH control. As a result, acoustic packages have become a standard feature in electric drive systems.
Gear manufacturing: The precision requirements for gears are becoming increasingly stringent. Currently, the industry is transitioning from the national standard grades 5-6 to grades 5 and above, making the manufacturing process more challenging.
The requirement for high gear ratios
▶ present situation
With the development of motor performance, the peak speed of motor is gradually increased, the limit of the maximum speed is gradually improved, and the limit of the gear ratio is gradually released.
Considering the vehicle acceleration and electric drive economy, increasing the speed ratio can quickly improve the wheel-end torque of the vehicle, and reduce the volume of the motor to achieve the economic index.
As the peak speed of the motor approaches 20,000+, the gear ratio is also showing a gradual increasing trend. For example, Huichuan has mass production projects with a gear ratio> 12, and Huawei has mass production projects with a gear ratio> 13. Designs with gear ratios above 13 are gradually becoming the norm.
▶ throw down the gauntlet
The application of high-speed ratio gears has increased the difficulty in both gear performance and manufacturing.
NVH performance: High-speed ratio gears typically generate more noise and vibration, and their design, material selection, and manufacturing pose greater technical challenges.
In terms of reliability, high speed ratio gear needs to bear larger torque and speed, and the linear speed of gear meshing is also larger, which puts forward more strict requirements on the reliability index of bending and contact.
Material: With the increase of the speed and torque, the performance of the gear material is also required to be higher, which needs to consider the strength and wear resistance.
In the manufacturing, the high speed ratio gear is more sensitive to the gear meshing excitation, which makes the gear require higher precision and consistency.
High NVH requirements for gears
▶ present situation
Unlike internal combustion engines, new energy vehicles are more sensitive to gear NVH performance, requiring higher NVH standards for gear systems, particularly in terms of transmission smoothness and noise reduction.
Gears are a key power source in electric drive systems. Given their lengthy manufacturing processes and high control complexity, NVH (Noise, Vibration, and Harshness) issues in gears pose a significant challenge for the industry. Industry statistics indicate that 70-80% of aftermarket NVH problems stem from bearings and gears, with gear-related issues accounting for 50-60%. Gear NVH is a major contributor to overall vehicle NVH performance. As high-speed and high-ratio gears become increasingly prevalent, addressing NVH challenges in gears has emerged as the industry’s top priority.
▶ throw down the gauntlet
Gear NVH involves multiple aspects such as gears, electric drive, chassis, and the whole vehicle. It is a systematic control index with a wide range and great difficulty in control. At the beginning of the design, risks should be identified and controlled in advance from the dimensions of gear design & manufacturing and path.
In gear design, NVH of shaft gear involves many fields, such as gear design, machining, assembly, shell support stiffness, bearing stiffness, shaft gear mode, shell mode, electric drive mode, motor mode, transmission path, acoustic radiation, etc.
Figure 2: Axis-tooth squeal control points Source: Compiled from public data
In gear manufacturing, precision requirements are escalating. While the industry currently adheres to national standard grades 5-6, rising NVH (Noise, Vibration, and Harshness) demands now require specific gear precision metrics to exceed grade 4, posing significant challenges for both accuracy and consistency assurance. Given the lengthy processing cycle and multiple critical stages, stringent controls are essential across all phases—from material selection and blank production to heat treatment, finishing, and gear grinding. Each process requires precise parameter optimization, further complicating manufacturing. Comprehensive monitoring is imperative for NVH-critical parameters including tooth profile orientation, cumulative runout, surface roughness, Fourier analysis, tooth surface waviness, three-dimensional profile, dynamic balance, and grinding patterns.
