Volvo Engine Mountings for Mobile Installation
The engine and transmission are connected in the flywheel housing and have a common mounting in the chassis, i.e. engine mounting. It is important for engine function that the engine mounting and its characteristics be configured. Configuration also has great significance for vehicle stability and driver's cab noise levels. Volvo Penta has four mounts for its engines. The type of transmission installed on the engine has great significance regarding the internal forces on the flywheel housing and the forces on the engine mounts. In order to avoid the installation causing damage, consideration must be given to the following:
• The mounting system may not allow stress to the engine due to frame deflection of vibrational
• There must be sufficient play all around the engine. Bear in mind that radiated heat may
cause adjacent equipment to expand.
• If the engine moves due to shocks, torque absorption or other forces, it must not come into
contact with the chassis or other components.
• Consideration must be given to factors that have great influence on inner forces and mounts:
vehicle specifications (axle arrangement, wheel base).
• Install vibration insulation so that requirements for correct noise levels are fulfilled.
Dynamic forces that affect engine mounts Forces that are transferred from the road causing parts to oscillate: drive train, front axle, rear axle, cab and frame. The level of these forces depends on:
?component masses and their suspension stiffness.
?longitudinal forces from the drive shaft depend on friction in the spline couplings.
?transverse forces that affect the U-joint. Most drive shaft installations have joint angles that give asymmetrical rotation speeds, which create rotational forces.
Static forces that affect engine mounts
• Drive shaft torque
• The weight of affected components.
Proven experience expressed as rules of thumb
• Forces increase with chassis suspension stiffness.
• The weaker the frame the more forces increase on semi-rigid designs.
• The lighter drive train mass is the more dynamic forces decrease.
Volvo engines are designed for two flywheel housing supports and two front engine mounts. (TAD1650VE has three-point mounting)
• The rear mounts must absorb almost all the front and rear forces created when connecting a
trailer, or exposed to shocks from loading docks. Practically no front or rear shock forces are
absorbed by the front mount. The front mount must therefore be designed such that it is relatively free from shear in all horizontal directions, but stiff vertically.
• Concerning mounting system resonance, its natural frequency is the frequency at which the
engine vibrates when it is struck by an external force. It is important to separate the natural frequency for front and rear axle installations compared to the engine.
• When selecting vibration insulation it should be understood that satisfactory insulation from
existing resonance vibrations is not achieved until the natural resonance frequency is exceeded by > 1.41. In order to achieve good comfort at idle (frequencies from combustion, shaft forces) these forces should also be above this resonance frequency. Special consideration must also be given to resonance frequencies from forces that are transferred via the suspension system such as roll, pitch and yaw forces.
It is important to protect the engine from torsional forces emanating from the frame.
The following applies to systems with two front engine mounts:
• The centerline of the insulator must be located as close to the cylinder block as possible to minimize bending stress.
The selection of the rear support is crucial in that it must support the larger part of engine weight and absorb most of the inertial load in all axes. Torque absorption, the absorption of imbalances and angular forces in the drive train must in the first instance be through the rear mounts. In the longitudinal axis a location immediately outside the flywheel housing is recommended. If the engine mounts are supplied by the customer, the distance between the center of the attachment to the SAE housing may not exceed the distance for the equivalent engine mounts from Volvo Penta accessories; refer to the illustration A. Where this is not possible in individual cases, contact Volvo Penta, Sales Engineering Industrial.
In combination with four engine mounting points On certain large or heavy transmissions, end support is installed on the transmission. The end support does not need to be stiff or limit movement when it is exposed to frame bending. Support strength must be changed for very low suspension speeds. Vertical and transverse stiffness of approximately 15 % of the rear engine mounts is recommended.
Engine Mounting and Engine Room Layout
Correct mountings and couplings to the load are essential for good results in all engine installations. The type of mount depends on the type of installation the engine is to be used for and the final transmission device. It is therefore important to note that when the engine is installed to the driven unit/equipment the dynamic behavior will be the sum of the entire installation's components. It is important to ensure that critical engine rpm (the range within which the chosen engine has its intended operations) for all installations are within limits.
Volvo Penta industrial engines are installed in three fundamental application categories:
Installations in this category move while they are in use. Examples of such installations are terrain-going trucks, heavy construction equipment and many specialist machines. The installed engine usually drives the machine as well as its auxiliary functions electrically, mechanically or hydraulically. In this category it is extremely important that alignment is maintained and that mobility rules are followed.
Where fixed installations can be used they have several advantages. Some examples of this type of installation are stand-by power systems, ventilation fans and pumps etc. Fixed installations are advantageous thanks to the fact that they entail fewer mounting and structural problems than other categories. Conditions may however require noise and vibration insulation, which make engine mounting more complicated.
In these installations the machine is moved occasionally, but the engine is not usually used as a source of motive power for the machine, and nor is the engine usually run when the machine is being moved. Examples of semi-mobile installations are stone crushers, cement mixers, mobile air compressors and mobile irrigation devices etc. There are several examples of machines within this category that move while the engine is running, but only at low speed, such as certain cranes, concrete layers or surface laying machines etc. Despite this category being similar to fixed installations, a semi-mobile installation requires consideration to be taken to other factors concerning power transfer. Mounting is a deciding factor in minimizing machinery stress and the preservation of correct alignment.
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