Piston cylinder unit with a movement determination device

Details Piston cylinder unit with a movement determination device Piston cylinder unit with a movement determination device

1999-01-14

2001-11-20

Oberleitner, Robert J. (Department: 3613)

Brakes

Internal-resistance motion retarder

Position of thrust member relative to chamber

C092S00500L, C091S001000

Reexamination Certificate

active

06318524

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a movement determination device for determining movement between two movable parts in a piston-cylinder unit.
2. Description of the Related Art
German reference DE 40 41 407 C2 describes a device for detecting the relative speeds of a piston and cylinder of a vibration damper. The device discloses a sound generator and a sound pickup arranged in the working space of the cylinder remote from the piston rod of the vibration damper. The bottom of the cylinder, specifically the bottom valve, serves as the reflection surface for reflecting the transmitted sound. Although this device is purported to be suitable for so-called single-tube vibration dampers, this assertion is difficult to confirm because single-tube vibration dampers have a separating piston that separates a compensation space from the working space remote from the piston rod. This compensation space—and thus the separating piston—must compensate for the volume of the in-and-out moving piston rod. The separating piston is movable in the axial direction of the vibration damper and therefore cannot be used as a reference mark. Furthermore, the separating piston is completely reflective, so that the cylinder bottom can supply no reflections or only too few reflections.
Another prior art device is disclosed in German reference DE 40 41 407 C2 in which a transmitter is located at the end of the piston rod. In this device, it is absolutely necessary to employ a hollow piston rod, so that the connection cable can be run to the sound generator and pickup. This creates additional design problems, because the piston rod must be hydraulically tight at its end. In addition, the contacts are also easy to assemble.
Yet another prior art device is disclosed by German reference DE 36 20 957 A1, which describes a suspension system with a fluid compression spring strut having a hollow housing supported by two end elements that are movable toward or away from each other in the axial direction of the spring. A device is provided on one end element to measure the axial distance between the end elements by the transmission of ultrasound pulses in the axial direction. The pulses are sent back by the other end element, for example, so as to measure the travel time of the pulses in the housing and thus determine the distance between the two end parts inside the housing at any time. Preferably, a transmitter-receiver is arranged on one end element and a reflector is arranged on the other end element, while a stationary reflector attached to the end element carrying the transmitter-receiver provides a reference value.
The ultrasound waves are propagated in the cushion of the spring. The gas inside the spring has practically no damping effect on the vibrating body, so that many signals are reflected from the surfaces in the spring, and the signal that represents the correct distance between the two end elements must be filtered out.
For physical reasons, this type of ultrasound transmission and reception in a gaseous environment is only able to correctly measure distances of at least 0.3 m between the end elements. Shorter distances can be detected only by separately operating transmitter and receiver parts. However, these entail considerable apparatus-related expense.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a measurement device for a piston-cylinder unit which overcomes the problems known from the prior art.
The object of the invention is attained in one embodiment by arranging the transmitter and receiver inside the piston rod guide. In this embodiment, a wave reflected by the piston-piston rod component group is analyzed to determine the movement of this component group. The piston rod guide is an advantageous location for the transmitter and the receiver because no modifications to the piston rod are required and also because the accessibility for electrical connections is not problematic. Furthermore, any damping effect of a fluid in the working space may be used, firstly, to obtain the clearest possible reflection signal and, secondly, to employ higher frequencies, so that a more precise measurement of the movement of the piston rod-piston component may be effected.
To create the preconditions for the most precise reflection signal possible, the piston rod guide includes a focusing channel that bundles the waves emitted by the transmitter. To the extent allowed by the axial and radial extensions of the piston rod guide, the focussing channel is designed with a funnel-shape to enhance the bundling effect.
A basic problem in analyzing the reflection is that the reflection body must be attached in stationary fashion to the body in question. Therefore, the piston-piston rod component has a reflection body that is independent of the movable parts on the piston. The movable parts could include valve disks or an axially movable piston ring, for example. Experience shows that the movement of these parts is very slight. Nonetheless, in some circumstances, the desired measurement precision is so high that these possible movements have an effect on the measurement result.
In an alternative embodiment for a piston-cylinder unit according to the invention which includes a first part including a cylinder with a piston rod guide and a second part including a piston rod with a piston run in an axially movable fashion inside the piston rod guide. A movement determination device including a transmitter in one of the first and second parts and a receiver in the other of the first and second parts for determining the movement of the first and second parts relative to each other from the travel time of waves generated by the transmitter which transmits sound waves along the surface of the one of the first and second parts associated with the transmitter. The sound waves are reflected by the other of the first and second parts. The advantage of this variant of the invention is that the vibration frequency in the solid body parts of the piston-cylinder unit are very high, which benefits measurement accuracy. This advantage is particularly significant in the case of units that have no fluid filling.
In a further embodiment, the transmitter is mounted in an especially protected position, for example, when the piston-cylinder unit is used in a motor vehicle. The transmitter is attached to a section of the piston rod that remains outside the cylinder even during the maximum inward travel of the piston rod. The front face of the cylinder thereby forms a reflection surface in the area of the piston rod guide. A further advantage is that the cylinder and the piston rod guide need no access opening for the transmitter and receiver or for a combined transmitter-receiver. A sealing point is thus unnecessary. The area on or in the attachment element of the piston rod can serve as an especially protected location for the receiver.
The transmitter, as desired, can be a shear converter or a transversal converter in connection with a wedged or tapered seating.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.


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patent: 40 41 407 (1997-07-01), None
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