This month we are taking an in-depth look at the MDS mount, designed to provide superior isolation and achieve the standard of comfort and quietness in a cab that is demanded by today’s operators.
In today’s world of ever tighter restrictions, the operator compartments of off-highway vehicles are held to almost the same NVH (noise, vibration and harshness) standards as automobiles. To address this, we developed a proven solution to meet these new demands and withstand the harsh environment of off-highway vehicles.
The MDS (multi-directional snubbing) cab mounts are a passive solution to a complex problem, achieving a higher level of sophistication in isolation, noise attenuation and motion control.
The passive MDS mount succeeds because of its design that enables a softer spring rate, with a defined linear-operating range, and then a nonlinear compression plus bulk modulus snubbing region that sets maximum deflection limits for the mount. This means the soft rate will give superior isolation while the snubbing will control excessive motion under high g-loads.
Combine these two features with our extensive selection of elastomers with associated dynamic performance, and the mounts can also become a very effective barrier to structure-borne noise. There are a number of applications in production where the MDS mounts have reduced cab noise by over 4dB, bringing some operator compartments into the mid 60dB level and maintaining high levels of ride quality.
It is perhaps best to consider the effectiveness of a cab mount system by its ability to achieve three prime goals. Firstly, the NVH has to be considered. This is where the cab mount will have to support the cab properly and isolate structure-borne noise and vibrations. This is also the stage where maximum cab-travel limits and ROPS loads can be evaluated, based on supplied customer information.
Engineering analysis will usually cover this aspect of the design and how it will perform in the system. The MDS mount has the soft rate needed for isolation and sufficient snubbing to control motion and survive the largest loads. In contrast, other comparable mounts have a soft rate for isolation, but uses high damping to control motion. This is not as effective because the damping is only reduced over a narrow ‘notch’ frequency band, in which any noise and vibration falling outside that range is not as adequately accommodated. Under high gloads and ROPS loads, secondary snubbing systems, or overload protection, may also need to be employed with fluid mounts.
Secondly, there is ride evaluation. Here, installed cab mounts are tested by vehicle operators and a subjective survey is taken. This part of the qualification testing is the most critical because if the operators do not like the ride and feel of a cab, all the other work goes unnoticed. There also has to be plenty of support from the vehicle builder at this level. The potential knock-on effect created when a cab becomes much smoother and quieter is that operators tend to notice issues that were muffled before. MDS mounts are suited to meet subjective operator testing and have tunable features to dial in the ride without sacrificing isolation.
Last but not least, the cab mount has to be cost-effective. This not only means it has to be an economical design/product, but it must also be easy and inexpensive to install, both initially and in the field. The MDS mount is a simple two-piece design that fits into a socket with no chamfer required, and is a single bolt installation. Compare that to a more complex mount which requires multiple bolts to install and, in most cases, also requires additional ROPS containment systems.
There are a number of considerations when selecting cab-mount solutions. Good levels of isolation from the many different sources of noise and vibration have to be balanced with the practicality of the mounting system in environments where ruggedness and maintainability must also be taken into account.
Typical installation of the MDS mount: