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News Release from: Freudenberg Simrit LP | Subject: Vibration-control components
Edited by the Engineeringtalk Editorial
Team on 24 August 2005
Holistic approach aids tractor vibration
control
Vibration-control benchmarking has enabled Freudenberg Simrit to develop a system for quick and targeted modelling of damping, bearing and spring suspension components for tractors.
The legal requirements for vibration control and noise reduction in tractors are becoming ever more stringent At the same time, comfort is a key competitive issue for manufacturers of agricultural machinery
This article was originally published on Engineeringtalk on 18 Feb 2003 at 8.00am (UK)
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By conducting vibration-control benchmarking on four tractors in the 100kW class, Freudenberg Simrit has established a basis for the quick and targeted modelling of damping, bearing, and spring suspension components.
Viewing the tractors as an entire vibration-control system plays a central role in this process.
If this system competence is employed at an early stage of development, development times are reduced, and tractors with different comfort levels can be realised on standardised platforms for different markets in an economical manner.
Today, two main factors determine how tractors are developed: EU Directives (2002/44/EC, 2003/10/EC) require that vibrations and noise be reduced to defined threshold values.
In addition, comfort has become an increasingly important decision-making factor for farmers when buying tractors.
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Vibro-acoustic fine-tuning for heavy machinery
Optimising heavy machinery in terms of vibration control and acoustics is a particularly difficult technical challenge.
In order to comply with threshold values and ensure a higher degree of comfort, modern spring suspension systems are necessary for axles and cabs, whereby it is not enough to take only individual components into consideration in isolation.
Rather, all possible interactions with other components must be taken into account.
In order to generate a reliable database for this purpose and to estimate in advance what developments will be needed and what the requirements of machinery manufacturers are, Freudenberg Simrit conducted a neutral benchmark of the comfort of the vehicles produced by leading tractor manufacturers.
This benchmarking study makes it possible to standardise vehicle tests and to define achievable threshold or target values.
It also provides a reliable basis for comparing new developments.
At the same time, current trends become clear and the developmental philosophies of various manufacturers can be compared.
Above all, however, the results of the benchmarking study serve to create a database for simulation models.
The data acquired in this manner help to make future simulations and calculations even more precise and support predictions about defined system properties at a very early stage of development.
A tractor is a complex system in terms of vibration control.
In order to implement the improvements in comfort (noise and vibration) necessary for observing the legal threshold values as quickly and as economically as possible, and to use the competitive edge offered by sophisticated comfort concepts, it is necessary to view these complex structures as an entire system.
Chassis, engine, drive trains, tools, cross members, grapplers, or elevators mutually affect each other in their transmission of noise and vibrations.
Uneven surfaces cause wheels and/or axles or chassis to transmit vibrations and affect the agricultural machinery as outside forces.
The interconnected components - mounting elements of all kinds - along the transmission path and in the frame design, the body structure, as well as their transfer function and coupling, determine system performance.
It is necessary to differentiate between vibrations that apply to the entire vehicle and those that apply to the cab's mounting alone.
Vehicle vibrations occur primarily as lifting and pitching movements, whereas the cab's natural vibrations can be far more complex, eg lifting, pitching, lengthwise, rolling etc.
In addition to these primary movements, longitudinal and lateral forces resulting uneven surfaces induce the vehicle to transmit longitudinal and transverse vibrations.
Furthermore, the oscillating parts of the reciprocating engine and its combustion processes produce internal excitations, which cause any existing frame and all addon pieces to vibrate via the engine bearings, thereby reducing comfort.
The vibrations of the engine as a rigid body influence the transmission of vibrations to the cab and must be taken into account when tuning.
A comprehensive measurement programme that simulates daily stresses as realistically as possible is therefore necessary for in-depth analysis.
The measurement programme includes road tests and test rig measurements.
The road tests involve: smooth track measurements according to ISO5008 at 8, 12, 16, 20, 24 and 28km/h; driving over an obstacle - a beam 26cm wide by 4cm deep - at 6 and 8km/h; and driving at maximum speed on a level surface.
The following is conducted on the test rig: a sine excitation at frequencies of 1 to 40Hz and an amplitude of +/-2mm on the front and/or rear axle.
In all cases, accelerations are measured at selected positions on the vehicle, eg front axle, block, cab mounting.
In addition, acceleration at the seat anchorage point is recorded, thus serving as a measure of comfort.
The test rig measurements provide insights into the natural vibrations of different components, eg the cab's natural frequencies as a rigid body in its mounting.
They also reveal comfort-reducing interactions between different components.
For example, the lateral resonance of the cab can create an unwanted increase in vibrations if the oscillation of the front axle is causing the vehicle to vibrate.
The test rig studies clearly show the effects of the four tractors' different front axle suspensions and cab mountings.
This not only paves the way for considerable improvements, but also illustrates the comfort-reducing interaction between tyres and the engine in individual cases - eg regarding frame construction.
When driving over a beam at 8km/h, the measured acceleration values at the seat anchorage point showed an up to 40% lower acceleration level for one of the four tractors.
The reason for this striking difference is that the front axle suspension in some models is deactivated when the tractor is traveling at low speeds, thereby greatly reducing the tractor's comfort level.
In the road test, accelerations at the seat anchorage point and the noise level in the cab are measured.
The benchmarking study highlights the dominating influence of vehicle movements on comfort.
Here also, however, the analysis reveals significant differences - up to a factor of 3 - regarding the acceleration values at the seat anchorage.
The interior noise level was at best around 73dB(A) and at worst around 78dB(A).
Accelerations at the seat anchorage point are measured in the tests conducted on the standardised smooth track.
The benchmark measurements show that although vertical accelerations are very similar for all vehicles, there are great differences in pitching accelerations.
The reason for this can be found in the different isolation performance of the cab mounting.
The mobile measurements on the smooth track also demonstrate the (at times) distinct differences in vibrational comfort, thus clearly revealing the strengths and weaknesses of the various suspension concepts for both the front axle and cab.
In addition to comparing the comfort of the tested tractors, different cab suspension concepts can also be compared with one another.
The main criterion in this case is the isolation of the vehicle's pitching movement.
In this way, different mounting concepts - such as pure elastomer mountings and hydroelastic mountings - can now be compared with mechanical, hydropneumatic and pneumatic suspension systems.
All measurements are weighted according to relevance in order to derive comparative values in terms of comfort and service life.
The load distribution used for this purpose defines a share of 40% each for driving over a beam and the smooth track test, both of which simulate fieldwork, 15% for driving at maximum speed, and 5% for idle operation.
While taking this frequency distribution into account, a comfort index can be calculated which makes it possible to compare the tested tractors objectively.
This comfort index shows that the vibration load exerted on the driver is 35% lower in the most comfortable tractor than in the least comfortable tractor.
The test data acquired in this manner form the basis on which a multibody simulation model for a tractor can be improved.
This model will in future help to design suspension systems in a targeted manner in order to achieve rapid and economical improvements in vibrational comfort.
Based on this, vibration-control components that have been optimised in this way will be specified and manufactured, and their properties verified in tests.
These components can, for example, take the form of individually optimised rubber-to-metal mounts, torsional vibration dampers, or vibration absorbers.
Alternatively, destructive forces - whether caused by the engine or the operating conditions - can be compensated for by an optimised combination of vibration damper, mount and decoupling in a single component: the innovative hydro mount, which was designed specially for agricultural and construction machinery.
In this way, the influence of vibration-control components on system characteristics can be specified at a very early stage of development, thereby allowing tractor manufacturers to be supplied with optimised components and engine bearings as early as the testing phase.
Freudenberg Simrit is the only provider worldwide that simultaneously develops and produces suspension systems as well as decoupling elements for vibrations.
Simrit not only provides the manufacturers of vehicles and agricultural and construction machinery with a complete range of vibration control products and hydropneumatic suspension systems, it also puts the company's research and development expertise, which has been gathered in the company's technical development centre down through the years, at their disposal.
With the help of mobile and stationary measurement technology, data about the condition of machinery can be registered anywhere and at any time.
In other words, tests are not restricted to test rigs; they can also be conducted in the field.
Special tools are then used to analyse deficiencies.
The benchmarking described above makes it possible to gauge optimisation possibilities very quickly and precisely for other tractors and innovations.
However, the holistic system approach also makes it possible to show suitable mounting and suspension systems in order to strategically implement different levels of comfort.
These comfort levels are available in different price ranges and with different technical features, thereby allowing customers to choose exactly the right solution for their needs.
The targeted implementation of different comfort levels in a series of tractors makes it easier for manufacturers to adapt their tractors individually to different market requirements.
In this way, manufacturers acquire a decisive and global competitive advantage by being able to offer both a high level of comfort through the use of a hydropneumatic suspension, for example, as well as a lower and more cost-efficient level of comfort through the use, for example, of an optimised rubber-to-metal component for a tractor of the same construction.
As a result, tractor and machinery manufacturers can implement market-satisfactory solutions on a standardised platform.
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