EP1613844A2

EP1613844A2 - Hydraulic filter and device comprising a by-pass hydraulic filter

Info

Publication number: EP1613844A2
Application number: EP03758415A
Authority: EP
Inventors: Pierre Gerard Willem Nieuwland; W. P. M. NTZ Nederland BV SCHAERLAECKENS
Original assignee: NTZ Nederland BV
Current assignee: NTZ Nederland BV
Priority date: 2002-10-24
Filing date: 2003-10-24
Publication date: 2006-01-11
Also published as: AU2003274436A1; AU2003274436A8; WO2004038190A2; WO2004038190A3

Abstract

Mechanical device such as an engine or a transmission for a personal vehicle, requiring the use of hydraulic means therein, comprising a by-pass filter (7) arranged in a by pass filter arrangement showing a supply line (1) to a mechanical device part (2) to be by-passed, e.g. a cooler device, a discharge line (3) discharging hydraulic means passed through said device part, and the by-pass filter being incorporated in parallel to said device part in connection with said supply line and said discharge line, in which the device comprises a hydraulic flow restriction means (9), incorporated in said connection from the supply line to the by-pass filter.

Description

HYDRAULIC FILTER AND DEVICE COMPRISING A BY-PASS HYDRAULIC FILTER

The present invention relates to a device comprising a by-pass hydraulic filter configuration as defined in the preamble of claim 1.

Such devices are generally known, e.g. in the form of combustion engines and of transmissions for automotive vehicles. The lifetime and quality of operation of such a device is considerably enhanced by the presence and use of a by-pass configuration filter. Such type of filters, due to their nature, operate at a filtering level that is considerably more refined than standard so called in-line filters, but also have a relatively slow pace of flow through it. Reason for this is that standard alternatively denoted full flow filters mainly function on the basis of a surface based filtering principle, while by-pass filters, very often also micro-filters, function on the basis of an in-depth filtering principle, at which the oil is filtered within a thick and relatively dense layer of filter material. Due to the latter nature, the pass through of oil is much slower than as compared to standard or surface based filters. In contrast herewith however, both the degree of filtering refinement and the degree of efficiency of the filtering of passing oil at such filters may be considerably higher as e.g. may be known from the SAE-paper 2001-01-0867 "Automatic transmission hydraulic system cleanliness - the effects of operating conditions, measurement techniques and high efficiency filters, which article promotes the cellulose fibre based micro-filter, and which is regarded included here.

The feature of relatively low flow of fluid per minute, in many cases directs the micro-filters towards application in a said by-pass configuration. The by-pass configuration may be made as a separate hydraulic circuit having a separate pump for providing a pressure required for the oil to pass through the micro-filter. However, such additional pump is saved in case such by pass is favourably made over a part of such hydraulic means using mechanical device. Such part could e.g. be a cooler part of such mechanical device and could be used as a suitable location for a by-pass configuration at which a separate pump and extensive amounts of connections are saved. Relevant criteria in this respect are the presence of a supply and a discharge line, and a pressure difference caused by the part that is by-passed.

Very often the filter applied in such by-passing configuration is to be adapted to and restricted by the nature of such mechanical device part to be by passed. E.g. in case the part is formed by a cooler, the filter should not be designed or chosen to allow a pass through of too large a flow, i.e. not over a predefined value determined for the specific configuration. Passing such predefined maximum allowed amount of flow would in such by-pass configuration draw away fluid from the device that is by-passed, and would set it at the risk of ceasing to function properly.

Yet it is an object of the current invention to promote the functional quality of such by-pass configurations, in particular to maximise the amount of flow passed through the by-pass filter, and thereby to improve the lifetime and functional quality of the mechanical device it is serving. According to the invention such may at hindsight in a surprisingly simple manner be realised by applying the measure according to the invention as defined in the characterising portion of the following claim 1. In such novel configuration, an improved by-pass filter, i.e. a by-pass filter allowing a considerably larger flow that the predefined maximum for the configuration, may be applied. This is done in combination with a hydraulic flow restricting means incorporated in a connection line connecting the supply line and the by-pass filter, i.e. including the entry opening of the by-pass filter. In this novel configuration the restriction is configured to bring down the flow through of the improved flow filter to said allowed maximum under the most favourable conditions i.e. at maximum operating temperatures and at maximum value of occurring flow within the relevant part of the device.

Further ideas underlying and combined within the present invention are related to the fact that the resistance of a restriction means is related non-linear to the amount of flow. It was conceived by the invention that such may be used to relatively increase the flow through the "improved" by pass filter at operating conditions where the amount of flow is less that the pre-defined allowed maximum. Such effect is additionally also recognised to be present in the difference of temperature effect on the filter element and the restriction respectively, as is in detail further explained in the description.

Thus it is an important effect of the invention that the use of a restriction means in the defined manner, allows the inclusion of a large flow by-pass filter. Using this possibility considerably improves the overall efficiency of the by-pass filter under all operating conditions within the boundaries set by the two maximum values for operating temperature and maximum flow respectively. It may be evident that by the inclusion of this relatively simple restriction means, in the manner as defined, the functional quality of both the filter configuration and thereby of the mechanical device using it may consequently considerably be improved. The invention will be further explained by way of example be elucidated further along a drawing in which:

Figure 1 is a schematic example of a typical prior art by-pass filtering configuration for a mechanical device using hydraulic fluid at operation; Figure 2, is a scheme according to figure 1 in which the structural part of the improvement according to the invention is represented;

Figure 3 in a graphical representation represents the functional part of the improvement according to the invention at a common operational temperature of 90 degrees Celsius. Figure 4 is a representation according to figure 3 at a temperature of 40 degrees

Celsius.

In the figures, identical reference numbers relate to identical or at least comparable technical features.

Figure 1 represents a portion of a mechanical device using hydraulic fluid to be filtered for the benefit of the operation and lifetime of the device. The device part includes a supply line 1, supplying hydraulic means from another part, e.g. a transmission casing to a device part 2, in this example a fluid cooler, and a hydraulics return line 5 returning the fluid passed through the device part to the mechanical device. The passage of oil through part 2 may be for use or for treatment thereby. In casu, the part being a cooler, the fluid is merely treated. Supply and discharge lines 3 and 4 respectively represent the lines for coolant medium for heat exchange with the hydraulic fluid for the mechanical device. A pressure difference Pd over the part 2 allows the hydraulic fluid to pass through the part 2. This pressure difference is provided by another part of the device, not depicted in the drawing, e.g. by a pump. The existing pressure difference and the existing hydraulic supply and return lines are favourable used in this example to create a by pass filter configuration using these existing means. In this respect, a micro filter 7 is connected in parallel to the device part 2 via a supply line 6 connected to the supply line 1 and a return line 8 connected to the return line 5. The whole of the represented structure may be provided as an integrated unit.

In the configuration according to figure 1 , the filter is designed to allow a predefined maximum amount of flow of oil to pass through it, so as not to take too much oil away from the part 2 of the mechanical device, and thereby so as not to jeopardise the operation said part 2 and/or the mechanical device. It is therefor believed that the depicted configuration, though economically and spatially favourable by its design, is functionally limited in filtering capacity. This condition may therefor in practice hamper the inclusion of a by pass filter in certain applications. It is however an object of the invention to increase the functional quality of the current configuration without undue effort, thereby increasing the chances for apply a micro filter or thereby increasing the performance of an existing by-pass configuration, all while maintaining the existing advantages and safeguards within the configuration.

In accordance with the invention the above aim is, at hindsight in a surprisingly simple manner achieved by applying a restriction means in the manner as provided by figure 2, i.e. in the supply line 6 connecting the supply line 1 of the configuration with the by-pass filter 7. The restriction may alternatively also favourably be included in the the filter device itself, i.e. at the entrance thereof.

For such hydraulic system applying an oil cooler with a micro high efficiency filter in by-pass the following can further be stated by way of elucidation. At the maximum pressure difference over the oil cooler, e.g. 50 psi = approx. 3,5 bar, under warm oil conditions, e.g. temperature oil = 90 degrees, the maximum allowed oil flow over the filter element is 3,5 litre/min. This is to ensure that not too much oil flow is taken away through the by-pass circuit through the filter element. With a flow improved filter element this starting position should still be valid. To ensure this, a restriction is added before the flow improved filter element is applied. At doing so, the following principles are used. The flow performance of a micro high efficiency filter is characterised by a linear relation with the applied pressure difference and is further showing a direct dependence of the oil viscosity. This means that the oil flow through the oil filter is characterised by the following formula:

Pressure difference Pd = factor F1 * oil dynamic viscosity / oil flow (1) The micro high efficiency filter can be optimised regarding flow performance by which for example a relation is obtained for an "improved flow element". A normal restriction, for example a small hole, can be characterised by:

Pressure difference Pd = factor F2 * density * oil flow^Λ2 (2)

Beneficially, since the maximum allowed oil flow at a certain pressure difference and under warm oil conditions must remain similar, the added restriction is applied in series with a flow improved micro high efficiency filter. When the oil flow through the by-pass circuit - thus through the filter element 7 and through the restriction 9 when incoφorated - would decrease, e.g. because of a lowered total pressure difference Pd or because of a higher oil viscosity, the combination of restriction and flow improved micro high efficiency filter will result in a higher oil flow through the filter element 7 and thus better filtration performance, as when compared to the common prior art configuration reflected by figure 1. Thus a main benefit of the novel configuration is improved filter performance at lower pressure differences and lower oil temperatures - related to a reference maximum pressure difference and corresponding maximum oil flow through the filter element at a reference oil temperature.

By further way of example the following typifying data will be used in an implementation configuration designed by applicant 90 degrees O: vise. = 5,7 cP density = 0,797 kg/ltr 40 degrees C: vise. = 23,8 cP density = 0,829 kg/ltr at which data the combination of improved filter element and restriction realised a 3 times higher oil flow for a certain pressure difference at a certain oil temperature in comparison to the standard filter element. At 90 degrees oil temperature, the standard by-pass filter element, at Pd = 3,5 bar (50 psi) realised a flow Fo of 3,5 Itr/min. In the novel configuration the restriction is tuned such that the combination with an improved flow element by requirement at Pd = 3,5 bar (50 psi) also realises Fo = 3,5 Itr/min. At Pd = 2,1 bar (30 psi), however, the standard configuration realises Fo = 2,1 Itr/min through the by-pass filter, while the combination of improved filter with restriction realises a comparatively significantly increased flow of 2,55 Itr/min through the filter 7; At a low temperature of 40 degrees these figures improve even more, however now for both pressure levels. In the prior art configuration, at 40 degrees Celsius and at 2,5 Bar a flow of 0,83 Itr/min. is realised, increasing to 1,98 Itr/min in the novel configuration. At Pd = 2,1 Bar, the flows Fo are 0,5 and 1 ,28 Itr/min, respectively.

Figure 3 and 4 illustrate the above numerical example, and the improvement gained by inclusion of the restriction means, in a graphical manner for temperatures at 90 degrees and 40 degrees Celsius. Along the X-axis the oil flow Fo is plotted in liter per minute (l/min), while along the Y-axis the pressure difference Pd over the by-pass configuration filter is provided in units of Bar. The uppermost line 10 in the graphs represents the characteristic of a standard filter element within the present configuration. The line 11 , represents the flow characteristic of the improved flow filter element, which allows a larger flow at lower pressure differences. Line 12 represents the flow characteristic of the restriction, while line 13 represents the characteristic of the combined effect of restriction and improved flow filter in the present configuration. It may be seen that at oil pressure differences lower than the maximum of 3.5 Bar, the restriction including configuration, when combined with an improved flow filter element, perfores better than the prior art by-pass filter configuration, in which the maximum flow of the filter was chosen to be equal to that of the maximum flow allowed in the bypass branch of the configuration.

The invention, apart from the following claims, also relates to the preceding description and all details and aspects in the drawing which are directly and unambiguously derivable there from, at least by a man skilled in the art.

Claims

1. Mechanical device such as an engine or a transmission for a personal vehicle, requiring the use of hydraulic means therein, comprising a by-pass filter (7) arranged in a by pass filter arrangement showing a supply line (1) to a mechanical device part (2) to be by-passed, e.g. a cooler device, a discharge line (3) discharging hydraulic means passed through said device part (2), and the by-pass filter (7) being incorporated in parallel to said device part (2) in connection with said supply line (1) and said discharge line (3), characterised in that the device comprises a hydraulic flow restriction means (9), incorporated in one of said connection from the supply line (1) to the by-pass filter (7) and an entry opening of said by-pass filter (7).

2. Device according to claim 1 , in which the maximum possible flow through the by-pass filter (7) at a given pressure difference Pd, e.g. a maximum occurring pressure difference in said configuration (1-3), is higher than the maximum flow allowed to pass through the by-pass branch (6-9) including said filter (7) in said by-pass configuration.

3. Filter, in particular for use in a by-pass configuration fitted with a flow restriction means (9) at an entry opening for hydraulic means to be filtered.

4. Integrated cooler and filter unit (1-9) provided with a hydraulic flow restriction means (9).

5. Integrated cooler and filter unit according to the preceding claim, characterised in that the restriction means (9) is incorporated in a connection line from a supply or entry port of said unit to the by-pass filter (7).