NVH Development of Digital Hydraulics System for Off-Highway Vehicle Applications 2015-01-2856

Fuel economy of both highway and off-highway vehicles is a major driver for new technology development. One of the technologies to meet this driver is a digital valve based hydraulic system. Digital Hydraulics technology employs high speed on/off valves to achieve the same functionality with no throttling loss. Furthermore, by forming various architecture by using digital valves, it provides the system level capability and flexibility for energy saving and productivity improvement.

There are many challenges in fully realizing the full efficiency benefits of the system in an actual application. These challenges include packaging, durability, a change in the operator's perception of the vehicle as well as hydraulic system performances during operation. One significant issue is the noise, vibration and harshness (NVH) of the system. Due to the nature of the digital valve operation, there are severe transient dynamics in the fluid system. The fluid dynamics not only generate fluid-born noise, but also causes structure-born noise through the transmission of the high frequency and impact forces to the rest of the vehicle structures, thus causing unfamiliar noise to bystanders and the operator in a vehicle cab.

This paper provides an overview of systematic NVH mitigation methodology and corresponding measures taken during the hydraulic and vehicle integration process. A source-path-receiver approach is adopted during the development. Physics-based analytical models have been developed for the hydraulics components and system. Extensive tests are conducted to correlate the simulation results for high confidence of the models. These models help to understand the noise generation and transmission mechanisms. The analysis is used to identify the critical design parameters of the system for better performances.

Besides reducing the noise generation and transmission, significant efforts are also taken to understand the impact noise perception of the operator. An array of sound quality metrics were selected to investigate the most critical characteristics of the noise. These metrics are sound loudness, sound impulsiveness, and etc. Extensive noise data were collected and jury tests were conducted to correlate the sound quality metrics. The noise and vibration tests and sound quality results demonstrate the significant improvement of digital valve hydraulic system in an excavator.