MDS Improvements Over Standard Overload Protected Cab Mounts

 

Written by Don Farbotnik 2/15/09

When competing against a standard cab mount where an overload ring or cup is used the following general characteristics and claims can be made to justify a switch to MDS mounts. Terms: Standard Cab Mounts:

  • Mushroom style similar to the Novibra EH mount
  • Mushroom style with fold over tail section for rebound snubber
  • Conical design similar to the Metacone
  • Tubeform design with cylindrical compression head, integral tube body and rebound washer
  • "Marc Mount" Compression head separate inner tube and unbounded ring snubber

Overload ring:

  • Metal tube cut to length and welded to the frame or cab that fits over the mount to limit travel

Overload Cup

  • Metal cup the is either stamped or fabricated that fits over mount on through bolt to limit travel

Evaluation of potential cab for MDS solution.

First determine the current cab set up or previous cab set up. If it meets the description of the Standard Mount with Overload Ring or Cup then proceed with past performance questions.

  1. How has the mount system been performing on the cab? Answers of acceptable or not acceptable are fine, but measured levels are better.
    1. Ask about vibration levels.
    2. Ask about noise levels.
    3. Ask about ride comfort and gross motion.
  2. Inquire about why they have the overload ring or cup?
    1. Was it for motion control?
    2. Was it to improve life of the mount?
    3. Was it because the last cab had it on it too?
  3. Ask if they have cab performance variations from machine to machine?
    1. Do machines all have the same performance off the line?
    2. Do some machines cabs have to be reworked or adjusted?
    3. Is there an aligning process for cab mounts on the line?

Why use the MDS style mount?

  1. Ease of installation is a good starting point since MDS is the best in class.
    1. MDS is a single bolt installation reducing complexity over the Conical three bolt installation.
    2. MDS does not require a machined socket with a chamfer or radius such as the mushroom mounts where machining is required and critical to their life.
    3. MDS has the metal cup skirt which goes into the socket hole protecting it from damage and extending life since it has the perfect radius built in.
    4. MDS mounts are designed to handle full bolt torques of Grade 10.9 (Grade 8 English) hardware. Conical mounts have reduced torques with thin inner tubes.
    5. MDS mounts have inner tubes that have a large abutment contact area which means hardened washers are not required under full bolt torques. Tubes can be tightened directly against castings, forgings, or fabrication steel without compromising the integrity of the bolted joint. This saves a washer in the assembly if there is enough contact area above the mount to cover the full diameter of the mount.
    6. MDS mounts are very tolerant of misalignments and thickness variations. This means hole to hole tolerance at the customer which are not exact will not always result in a machines with degraded performance. Also if the plate thickness or angle of the frame to cab vary the mount performance will not vary. This is a statement where a study can show how much variation MDS can take in each application. It will be more than all standard desigs.
  2. Performance benefits can follow these points.
    1. MDS mounts have a linear operating range which is soft and provides great isolation and good structure borne noise attenuation.
    2. MDS mounts have a non-linear compression rate that comes in after a preset deflection which helps control motion and buffers the snubbing region of the mount.
    3. MDS mounts use a molded in cup to capture the bulge of the elastomer and by restricting the bulge area the mount basically becomes hydraulically snubbed. This means we know the max deflection of the mount and how far all points move under any load. The overload protection of the MDS mount is at a set deflection and is not load dependant. It is also a restricted bulge area method of snubbing with no harsh metal to metal interface driving up G loads like in overload ring and cup designs.
    4. The overload protection keeps the MDS mount working is a safe operating which gives it exceptional life. High spike G loads do not damage this mount as they would a standard cab mount.
    5. MDS mounts use symmetrical top and bottom sections. This allows the rebound side of the mount to perform just the loaded side improving ride comfort and can be adjusted using MDS rings.
    6. Parts are completely covered in elastomer for corrosion protection.
    7. MDS overload cups are molded in so concentricity is held very tight which leads to consistent performance. Welded on rings are not perfectly centered over parts so alignments of these can easily change performance of the covered mount. Separate cups which go on the bolt have tolerance issues as well as sometimes needing to be hardened based on bolt clamp loads. Also there is no wearing of the MDS elastomer interface surfaces unlike that seen in the cup and ring design.
    8. Very good motion control which can be tuned to the manufacturers' specification using MDS rings.
    9. Low profile design to fit into tight spaces.
  3. Cost benefits of the MDS mounts.
    1. MDS mounts should be very comparable in price to all the standard designs.
    2. MDS mounts are more cost effective to install than other designs. No machining required as on mushroom designs and two to four bolts less than conical designs.
    3. Some conical mounts require an extra stiffening ring around the flange to prevent rebound loads from tearing the bolt flange.
    4. MDS mounts don't require hardened washers because of low abutment stresses.
    5. Possible to remove top washer because of low abutment stresses if load area is sufficient.
    6. Reduced cab to frame tolerances, eliminate cab alignments on the line or eliminate rework loops for problem cabs due to mount alignment.
    7. No extra cost for overload cup which add to the number of assembled parts.
    8. No extra cost to manufacture overload rings and weld them to cab or frame.
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