FIELD OF THE INVENTION

The invention relates to a filter assembly, in particular used as a portable service unit for hydraulic applications, at least comprising a motor-pump unit. One outlet of the motor-pump unit is connected to a filter element in the main flow. The other outlet of the motor-pump unit is connected to a device for measuring particles in the fluid in the bypass flow, which device has a particle sensor. As a component of the device for measuring particles, a fluid line of predeterminable length as a stilling section on the inflow side of the particle sensor in such a way that gases carried along in the fluid re-dissolve in the fluid.

BACKGROUND OF THE INVENTION

A filter assembly of this type having the product designation OF7CM is known from the applicant's brochure D7.940.5/02.15. Such filter assemblies can be used in filling hydraulic systems, in flushing small hydraulic systems and in cleaning them in bypass applications. The portable design also permits the use for temporary bypass filtration of hydraulic systems. At the same time, the particle measurement device permits the fluid to be monitored for contamination by solids. State of the art particle counters are used for this purpose, which operate based on the opacity method. As disclosed in document EP 0 427 908 B1, the counting of opaque particles in a fluid flow is performed by a light barrier whose light beam passes through a measuring channel for the fluid. Evaluation electronics are installed downstream of the receiver of the light barrier. The accuracy of the counting result is impaired if there are undissolved gas components carried along in the fluid. The bubbles of those gas components cause the optical particle counter erroneously to detect those bubbles as contamination of the fluid owing to the different refractive indices of gases (air) and medium. Therefore, as stated in document DE 103 43 457 C5, it is state of the art to provide a fluid line in the flow path upstream of the particle sensor having a length sufficient to act as a stilling section. Within the stilling section, gases carried along in the fluid, such as air, are re-dissolved. This re-dissolving means that any gas or air input is no longer detected as contamination of the fluid, avoiding misinterpretations regarding the quality of the fluid.

SUMMARY OF THE INVENTION

Based on this state of the art, the invention addresses the problem of providing a filter assembly of the type mentioned at the outset, which is characterized by a particularly compact design.

According to the invention, this object is basically achieved by a filter assembly having, as an essential feature of the invention, the fluid line of a pre-determinable length being accommodated in a housing part of the assembly, combined to form at least one winding. In comparison to the aforementioned known filter assembly, in which the fluid line forming the stilling section is attached to the outside of the assembly in the form of a hose line having a length of 2.5 m, a line coil can be used to implement a stilling section of a corresponding length in a particularly compact design. If the line is wound into a coil, it can be integrated into the assembly itself, eliminating the surrounding space required for an external hose section.

Advantageously the respective winding is formed by a helix inside the housing part.

In particularly advantageous exemplary embodiments, there are two helices in the housing part, which are separated by a housing wall in a sealing manner except for a common fluid connection point. The flow is routed through both helices in sequence. For helices adjacent to each other along one housing wall, a long pipe length in a particularly flat design can be achieved.

It may be advantageous to arrange the helices in such a way that, when accommodated in the housing part, one helix faces the particle sensor and the other helix faces away, and that the particle sensor is mounted on the housing part.

Advantageously the flow is routed through the helix facing away from the particle sensor from the outside to the inside towards one end of the helix. At a point of passage in the sealing housing wall, this end merges into one end of the other helix facing the particle sensor. The flow through the other helix is routed from the inside to the outside, and passes the fluid from the stilling section to the particle sensor.

In advantageous exemplary embodiments, a further filter element is installed between the output of the stilling section and the input of the particle sensor. After the coarse contamination has been removed, the particle sensor detects the fine contamination of the fluid.

For pressurizing the stilling section, a counterbalance valve can be installed downstream of the particle sensor, for example in the form of a spring-loaded non-return valve.

In advantageous exemplary embodiments, the motor-pump unit has two hydraulic pumps ensuring the fluid supply in the main flow and in the bypass flow.

A pressure relief valve can be installed in a bypass branch downstream of the outlet of the bypass hydraulic pump, which pressure relief valve secures the stilling section located in the bypass and in that way the particle sensor.

The output of the main hydraulic pump can be protected by a counterbalance valve in the branch, which, like the counterbalance valve of the bypass flow, can be a spring-loaded non-return valve.

Viewed in the direction of the fluid flow, a fluid connection is downstream of the filter element located in the main flow. The fluid connection preferably is provided with a throttle or orifice, and can be routed to the inlet side of the main hydraulic pump, serving as dry-run protection. The provision of the dry-run protection prevents the assembly from being damaged if there is no fluid in the pump. In this way, the containers can be emptied without risk. This arrangement also renders the assembly suitable for extracting leakage oil.

Advantageously the main flow and the bypass hydraulic pump can be implemented using a single vane pump, which can be designed as a dual pump.

Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the drawings, discloses a preferred embodiment of the present invention.

