Road structure – process – or apparatus – Apparatus – Tamper
Reexamination Certificate
1999-11-02
2001-04-10
Lillis, Eileen D. (Department: 3673)
Road structure, process, or apparatus
Apparatus
Tamper
C404S102000, C404S084100, C404S084050, C405S271000, C074S088000, C366S116000
Reexamination Certificate
active
06213681
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a soil compacting device.
2. Description of the Related Art
Vibratory tampers, vibrating plates or vibrating rollers are generally used for soil compaction. Whereas tampers are displacement-excited vibratory systems with a large amplitude, vibrations in the case of vibrating plates are produced by means of force excitation. For reasons connected with the excitation of vibrations in the soil particles, guideability and to protect the operator against unwanted body vibrations, vibrating plates are often designed in such a way that they have a relatively high frequency (40 to 80 Hz) and a small amplitude of the vibrating base plate. From the category of vibrating rollers, trench rollers are generally used for soil compaction, in which vibrations are produced by rotating unbalanced weights within the facings or on the chassis forming a lower mass.
When using vibrating plates, in particular, on moist soils (what are referred to as cohesive soils with a high water content or saturated soils), such as silts and clays, that is to say fine-particle soils with little tendency toward water permeability, there is the problem that the soils can only be compacted to a limited extent by the action of vibrations. This is due to the fact that the cohesion which is often typical of cohesive soils affects the adhesion of the individual particles to one another and hence prevents repositioning of the particles. In the case of vibrating plates, the small amplitude of the vibrating base plate in conjunction with the high frequency leads to a further supersaturation of the soil with water, making the latter softer and more plastic in terms of vibration and causing its adhesive effect on the vibrating plate to increase. As a result, the vibrating plate may sink into the soft earth and no longer be capable of being moved along. In practice, this has led to vibrating plates not being used in damp weather or on saturated cohesive soils even though the soil compaction and surface quality that can be achieved by means of vibrating plates are highly regarded.
In practice, however, there is frequently the problem that, although the vibrating plates are used primarily only on non-cohesive soils, it is necessary for them at certain points to cross supersaturated cohesive soils which are likewise situated in the area to be compacted. In this case, the vibrating plates run the risk of sinking in or digging themselves in due to their natural vibration as they cross these points.
DE-B 11 68 350 has disclosed a vibration device for compacting the construction site with a vibratory plate. The vibratory plate is attached by springs to a road roller, between the front roller drum and the rear wheels. To increase the contact pressure of the vibratory plate on the ground, hydraulic cylinders are provided, these hydraulic cylinders pressing the springs and the vibratory plate against the ground and thereby increasing the spring preload. The problem described of self-propelled vibrating plates on cohesive soils does not arise with this device since the roller ensures sufficient propulsion.
Similar vehicles with attached soil compacting devices are known from DE 43 40 699 A1 and DE-A 20 46 840, where a plurality of vibratory plates or tampers are attached to a heavy travel drive.
U.S. Pat. No. 5,387,370 has disclosed an electroviscous fluid for dampers with variable damping properties, the change in damping being brought about by subjecting the electroviscous fluid to a suitable electric voltage.
U.S. Pat. No. 5,547,049 describes a construction with a magnetorheological fluid in which the damping properties of the fluid can be adjusted by varying an applied magnetic field.
OBJECTS AND SUMMARY OF THE INVENTION
The object on which the invention is based is to specify a soil compacting device in which the abovementioned problem of the device sinking in when temporarily crossing cohesive soils is avoided.
A soil compacting device according to the invention with an upper mass, a lower mass for soil compaction, a spring system coupling the upper mass and the lower mass, and with a damper system, which is arranged between the upper mass and the lower mass and interacts with the spring system, is distinguished by the fact that the damping properties of the damper system can be varied during the operation of the device. This makes it possible to vary the vibration properties and vibration behavior of the device and, for example, to adjust them in such a way that the amplitude of vibration is increased in such a way when crossing cohesive soil, for example, that the upper mass is induced to perform a resonance-type vibratory movement in order thereby to exert larger amplitudes and forces on the lower mass. The lower mass in this context is generally the actual base plate including the exciter by means of which the soil is compacted, while the upper mass is formed by the drive and the control system for the device.
By virtue of the fact that the vibration behavior can be varied during the operation of the device by means of the damping properties of a damper system provided for the partial or complete coupling of springs, the operator can cross the cohesive soil without interrupting his work. The damping properties can be adjusted manually or automatically, as defined in a number of the subsequent subclaims.
The forces on the lower mass generated by appropriate variation of the vibration properties (frequency, amplitude, direction of vibration) of the lower and the upper mass make it possible to overcome the increased sticking at the base plate caused by moist soils and associated with vibration and adhesion. The large amplitudes with an appropriately forward-directed force vector allow the device to execute a jumping movement, even on soils which are of low elasticity and are predominantly plastic.
In a particularly preferred embodiment of the invention, at least one damper of the damper system has a damping material composed of an electroviscous fluid. In the case of electroviscous fluids, the viscosity of the fluid can be varied under the action of electric voltage. This means that, depending on how the fluid is acted upon by an electric voltage, almost any viscosities and hence damping constants can be set at the damper. Dampers incorporating an electroviscous fluid are therefore particularly suitable for enabling the damping properties of the damper to be changed quickly during its operation. The response time of typical electroviscous fluids is around 3 milliseconds.
The damping properties of the damper system provided for intermittent or continuous coupling of spring systems can therefore advantageously be adjusted by subjecting the electroviscous fluid to a suitable electric voltage.
It can be particularly expedient if the electric voltage is clocked. This is particularly recommended when the vibration properties are adjusted by means of an automatic control system.
The electric voltage can additionally be adjusted to different levels.
However, it is also possible to vary the clocking, i.e. to change the lengths of time for applying voltage.
In a preferred embodiment of the invention, the electric voltage or clocking can be adjusted by means of an automatic control system. It is advantageous if the automatic control system has at least one sensor system.
It is particularly preferred if the sensor system has at least one acceleration sensor. If, namely, the base plate of the vibrating plate sinks into a soft soil or comes into contact with a soft soil, the reaction forces exerted by the soil on the plate change relative to the forces exerted by a firm underlying surface. In addition, there is a change in the frequency, amplitude and length of the jump of the lower mass and this can be detected by the acceleration sensor. When presettable limiting values are undershot, the sensor can give the signal that the contact area of the plate with soft soil is increasing at this moment or that it is already moving on said soil. This knowledge will then caus
Maurer Thomas
Reiter Thomas
Riedl Franz
Sick Georg
Steffen Michael
Boyle Fredrickson Newholm Stein & Gratz S.C.
Lillis Eileen D.
Pechhold Alexandra K.
Wacker-Werke GmbH & Co. KG
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