REDUCED NOISE, INCREASED POWER.
Operator comfort can be improved with more powerful steering, however the gear pumps needed can be noisy. We developed a technology to solve this problem, and IVT (Industrial Vehicle Technology magazine, Chinese edition) has just featured an article that’s all about our innovative Quiet-Technology.
Value can be added to a vehicle in the off-highway industry today by increasing operator comfort. Two key ways in which machine designers can work to achieve this are by working on cab noise (by reducing sound quantity and improving sound quality) and by enhancing steering comfort.
At the Danfoss Application Development Center (ADC) in Nordborg, Denmark, a tractor from one of the market leaders was used to investigate ways to improve steering performance and cabin comfort, where a low-noise gear pump (double-contact flank technology) was used for steering function.
Eventually, the tractor steering unit was replaced with a Danfoss OSPE electro-hydraulic steering unit, and the steering pump with Turolla’s innovative, patented, low-noise gear-pump technology, shhark®. The end result saw an improvement of both cabin and steering comfort.
The theory behind the solution
Assuming two pumps produce the same sound level, the human perception of the sound heard in the cab of the machine can vary a lot between using one or the other pump. Moreover, when evaluating the noise in the cab it is important to refer to sound level as well as sound quality.
From the operator’s point of view the cab with the minimum sound level and maximum steering comfort in all the different working conditions would be the preferred choice over the other machines.
In order to evaluate how to reach that optimum condition the tractor at the Danfoss ADC was tested with different configurations.
Initially a double-contact flank gear pump was installed for steering function. Next, a shhark® pump with a higher displacement was installed to improve the steering comfort, and to verify if it was able to maintain at least the same noise emission in the cab or even better. The test was successful. Below are the results in detail.
When driving in a field, farmers like good controllability when driving straight (avoiding constant corrections to the steering), in particular when putting seeds or fertilizer in the earth. Then, when they reach the end of the row and perform a headland turn, they would like to turn aggressively without having to use a lot of energy turning the steering wheel.
The tractor in this test was therefore equipped with a Danfoss electrohydraulic steering unit called OSPE that facilitates quick steering. This system required a larger displacement pump – changing from a dual flank gear pump 11 cc to a shhark® 14 cc – yielding a higher potential steering ow, requiring fewer turns of the steering wheel for the headland turn.
Noise: sound quantity
The sound level in the cab is a key factor for the final end-user. To reduce the sound level, a low noise gear pump (dual flank technology) was already installed on the test tractor.
As discussed above to improve the steering comfort a higher displacement pump was then installed. Because the noise produced by a gear pump is proportional to its displacement, Turolla decided to next install a shhark® pump to further reduce noise levels.
The dual flank technology is a very well-known method to reduce the noise produced by a gear pump, which achieves this by reducing the backlash between the gears to zero, causing a double frequency of noise emission, but at the same time a reduction of pressure pulsation by 75%.
Turolla shhark® technology utilizes a totally new concept. In this case the non-working side of the gear is removed, allowing the addition of more teeth – consequently increasing the frequency of noise emission, at the same time reducing pressure pulsation by 78%.
Noise: sound quality
The human perception of noise is highly sensitive to the frequency at which the noise is emitted. For low noise gear pumps in off-highway application it is possible to define the sound quality as the level of sound emission of the second harmonic, the reason is that typically the frequencies at which the second harmonic is emitted are those that interact with the cabin frame frequencies, having high impact on the noise perceived by the operator in the cab. In ADC Nordborg, Turolla and Danfoss equipped the machine in order to be able to measure the second harmonic emitted by the dual flank technology and by shhark®. The sound pressure level during operation was measured by a sound meter in the cab, then a Fourier transform was applied to the signal obtaining the main harmonics. As Fig.1 shows, extracting the second harmonic it is possible to see that in all operating conditions with shhark® the value is about 10 dB (A) lower than with the dual flank technology, resulting in a better comfort for the operator.
In the range of 20 to 10,000 Hz, a noise emitted at higher frequency is more annoying for the human ear than a noise emitted at lower frequency – even if at the same or lower overall intensity. Therefore, the sound emitted by the second harmonic can be the reason why some operators speak about “an annoying whistle” heard in the cab, even if all components are working properly and the overall sound pressure in the cab is low. That phenomenon is an indicator of bad sound quality.
Since shhark® produces less noise at the second harmonic than the dual flank technology, it is the best choice in terms of sound quality.
Noise: sound consistency
Dual flank technology has long been the most common design to reduce noise. It is based on the concept of zero backlash, which means ‘zero’ clearance between one tooth and its mating tooth. A pump may be ‘zero clearance’ when it is new, but due to normal operating conditions (e.g. oil contamination, wear, etc.) in time the pump loses this feature and starts to operate as a standard (noisy) pump.
The shhark® LoNoise pump instead, is based on a new patented technology that has the advantage against other technologies to maintain its top performances throughout the machine life, representing a cost saving for the machine designer.
Machine designers can improve operator comfort, driven by clear market requirements, adopting an improved steering unit (e.g. Danfoss OSPE) along with a shhark® gear pump. The advantages of this solution are a good controllability when driving straight, an easier headland turn, and an improved sound quality and sound quantity in the cab.
In a nutshell, the advantages of shhark® technology over the existing dual flank technology are: lower sound quantity, better sound quality, better sound consistency.
Further tests in Danfoss ADCs (Nordborg, Ames, Haiyan) and in Turolla are planned to evaluate shhark® performance on other machines.