Electric Camshaft Phaser Spring Biasing for Backlash and NVH
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Solution Overview
Problem
Variable camshaft timing (VCT) phasers in internal combustion engines face challenges with backlash, noise, vibration, and harshness (NVH) due to compliance between planet gears and ring gears, which existing designs fail to adequately address.
Innovation Solution
The electrically-actuated VCT phaser assembly incorporates a planetary gear set with a spring biasing mechanism that prevents relative rotation between planet gear pins and the planetary gear set, minimizing wear and NVH by isolating the spring from direct contact with the planet gear, and utilizing carrier plates with apertures and spring slots to facilitate radial movement and engagement with ring gears.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If planet gears engage directly with ring gears in a planetary gear set, then the structure is simple and compact, but backlash and NVH increase due to compliance between gears
Solution Approach 1:
A spring mechanism is introduced as an intermediary element between the planet gears and ring gears. The spring applies a biasing force that maintains consistent contact pressure between the gear teeth, eliminating backlash while accommodating thermal expansion and manufacturing tolerances. This mediator resolves the compliance issue without requiring a completely different gear engagement structure.
Solution Approach 2:
The patent modifies the engagement parameters by introducing a controllable spring force that adjusts the contact pressure between planet gears and ring gears. By changing the force parameter through the spring mechanism, the system achieves zero-backlash engagement while maintaining the simplicity of the planetary gear structure. The spring constant and preload can be optimized to balance NVH reduction with structural simplicity.
2Device complexity
If springs directly contact planet gears to provide biasing force, then the biasing mechanism is simple, but wear increases due to direct contact between spring and rotating gear
Solution Approach 1:
A planet gear pin is introduced as an intermediary component between the spring and the planet gear. The spring contacts the pin instead of the rotating planet gear, while the pin transfers the biasing force to the gear through its mounting structure. This mediator eliminates direct contact between the spring and the rotating gear surface, preventing wear on the gear teeth while maintaining the simplicity of the spring-based biasing mechanism.
Solution Approach 2:
The biasing mechanism is segmented into separate functional components: the spring provides the biasing force, the planet gear pin serves as a non-rotating mounting element, and the planet gear receives the force without direct spring contact. This segmentation allows each component to perform its specific function optimally—the spring for force generation and the pin for force transmission without wear.
3Manufacturing precision
If planet gear pins are fixed to prevent rotation relative to the planetary gear set, then engagement precision improves, but the system loses adaptability to accommodate thermal expansion and manufacturing tolerances
Solution Approach 1:
The planet gear pin is designed with selective fixation: it is constrained from rotating relative to the planetary gear set to maintain engagement precision, but it is allowed to move radially or axially within controlled degrees of freedom. This dynamic design enables the pin to accommodate thermal expansion and manufacturing tolerances by adjusting its position while maintaining the precise rotational engagement required for zero-backlash operation. The spring mechanism further enhances this adaptability by providing continuous force adjustment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively minimizes backlash and reduces NVH, enhancing the reliability and performance of VCT phasers by ensuring precise engagement and reduced wear, thereby improving the dynamic adjustment of camshaft rotation for better engine efficiency and emissions control.
Implementation Method 1
one or more springs that bias the planet gear pin(s) and the planetary gear(s) toward the first ring gear and the second ring gear
Data Source
AI summary
An electrically-actuated variable camshaft timing (VCT) phaser assembly, comprises a sun gear configured to receive input from an electric motor and one or more planet gears having radially-outwardly-extending gear teeth that engage the sun gear; a first ring gear, having radially-inwardly extending gear teeth that engage the radially-outwardly-extending gear teeth of the sun gear, configured to receive rotational output provided by a crankshaft; a second ring gear, having radially-inwardly extending gear teeth that engage the radially-outwardly-extending gear teeth of the sun gear, configured to couple to a camshaft; one or more planet gear pins that carry the planet gear(s) and engage a planetary gear set to prevent the relative rotation of the planet gear pin(s) relative to the planetary gear set; and one or more springs that bias the planet gear pin(s) and the planetary gear(s) toward the first ring gear and the second ring gear.