DE102008044148B4 - Expansion tank for hydraulic power steering - Google Patents

Abstract

Expansion tank which is integrated in a medium circuit, wherein the expansion tank has a bottom inlet (4) and a bottom outlet, characterized in that in its axial extension below a minimal expected medium level arranged rotation generating element (6) is fixedly disposed within the expansion tank which extends in the axial direction from the bottom inlet (4) towards an opposite end of the container, and at its end opposite the inlet (4) has an end element (7) designed as a baffle plate, the rotation-generating element (6) and the end member (7) each having an outer periphery which is spaced with respect to an inner wall (3) of the expansion tank, so that a rotation space (9) is formed for the medium.

Description

The invention relates to a surge tank having the features of the preamble of claim 1, wherein the surge tank is integrated in a medium circuit, and wherein the surge tank having an inlet and an outlet.

Such expansion tanks are known, for example, as storage tanks for the hydraulic fluid (servo oil tank) of a hydraulic power steering system of a motor vehicle. Currently known, hydraulic power steering systems are used by way of example in passenger cars, trucks or the like motor vehicles, and have a medium pump z. B. on a hydraulic pump. The hydraulic pump causes a, independent of a speed of an internal combustion engine, constant fluid or medium flow. The medium pump is connected to the outlet of the expansion tank. The medium pump causes a transport of the medium z. B. to a steering gear, from where the medium is transported back to the expansion tank. The exemplary servo oil tank serves primarily to compensate for level fluctuations caused for example by thermal expansion, dissolved gas in the fluid and to a lesser extent system leakage.

The constant fluid flow is ensured by an internal control valve (flow control valve), which controls the discharge of the medium from the surge tank into the medium circuit. However, these control valves are very susceptible to contamination which may be in the medium or fluid. Small particles, especially hard oxides such as silicon and / or aluminum oxides (SiO ₂ , AlO ₂ ) get into the gap between the control valve piston and its bore, and so can destroy the respective material or component and thus the entire control valve. Contamination causes the flow-limiting valve to become blocked or locked. As a result, the flow rate is pump speed dependent, resulting in different power assistance (depending on the engine speed).

Of course, the medium pump itself can be destroyed by the particles. Due to the high sensitivity of the pump against contamination of the fluid, in particular against entrained in the fluid or medium flow particles (eg., SiO ₂ , AlO ₂ ) filter elements are provided, which are arranged in connecting lines or hoses or the expansion tank itself , The filter elements filter out the contaminants from the fluid stream, thus preventing the contamination from entering the pump or control valve, for example.

One of the main drawbacks of such filter elements is that they negatively influence the medium flow or disrupt the flow, since the free flow cross-section is considerably restricted. In addition, the filter element increasingly clogged after a certain period of operation, so that further amplify the aforementioned disadvantages, which can even result in a pressure drop. Another disadvantage is the fact that the filter elements are very expensive.

The DE 100 02 118 A1 discloses a surge tank of a hydraulic system having an inlet and an outlet, which are respectively arranged on the bottom side. In the expansion tank, a filter element is arranged.

The DE 1 042 359 B deals with a centrifugal separator for gas, air or steam. The centrifugal separator is supplied to the top side gas, which flows through flow channels. In this respect, the inlet is probably arranged on the head. Opposite, ie foot side, the outlet is arranged.

The US 6,286,545 B1 discloses a medium container, in particular for a steering fluid of a power steering. The medium container has an input line and an output line, which are arranged parallel to each other in such a way that the liquid in the container is set in rotation. In this case, the liquid rotates in an annular channel around a filter carrier occupied by a mesh filter, so that the liquid can pass through the mesh filter to the pump outlet. The liquid should have a particularly long residence time in the medium container, so as to achieve effective cooling, whereby cool liquid can mix with heated liquid.

The US 5,879,545 A deals with a cyclone filter in which unwanted solids are separated from a liquid by exploiting centrifugal forces. The cyclone filter has a vertically oriented cylindrical tube in which the laden with the heavy fluid is introduced tangentially. Via openings in an upper closure element, the liquid passes in a conically tapered region of a drop tube, which widens conically at the other end and opens into an opening of a lower closure element. In the drop tube, a central tube is arranged, which is spaced with its lower opening to the conically widening area. The central tube pierces the upper closure element in the conically tapered region of the downpipe, and, with its upper end opposite the lower end, laterally spaced apart passes through the upper closure element and opens into here a filter chamber. On the inner wall of the cyclone filter, a filter element is arranged. The liquid is set in rotation on its way in the downpipe in the direction of the conically widening region, so that the heavy materials are transported by centrifugal force to the inner wall of the downpipe or of the conically widening region. In the region of the central tube then only solids-free liquid should be, which is transported via the central tube into the filter chamber. The solids pass through the lower opening into a collection area. With the US 5,879,545 A should be used on the one hand, the centrifugal force for the elimination of unwanted heavies from the liquid, but at the same time the filter element to serve as a cleaning filter and the other at the same time as a collection for the heavy materials in the lower part of the cyclone filter.

The invention is based on the prior art, the object to improve a surge tank of the type mentioned with simple means so that a separation of heavy materials, or undesirable solids from the liquid without use of a filter element can be achieved.

According to the invention the object is achieved by a surge tank with the features of claim 1, wherein in the surge tank, a rotation generating element is arranged, which extends in the axial direction from the inlet towards a container end opposite thereto, and at its opposite end to the inlet a closing element, wherein the rotation-generating element and the closing element each having an outer periphery which is spaced in each case with respect to an inner wall of the medium container, so that a rotation space for the medium is formed.

According to the invention, the rotation-generating element is fixedly arranged in the expansion tank, which means that the rotation-generating element in the expansion tank itself does not rotate about its central axis.

Expediently, the rotation-generating element has deflection elements which are arranged on a middle element. The central element is preferably congruent with the central axis of the surge tank when the rotation generating element is mounted in the surge tank. The deflecting elements are designed in the manner of turbine blades, ie have a curved course from the central element to the opposite end of the deflecting elements.

Advantageously, the deflection elements end at their opposite end to the central element spaced from the inner wall of the surge tank, so that the rotational space is formed, in which the medium rotates about the central element.

The rotation-generating element is preferably spaced apart from the inlet in the axial direction, but may also be placed directly on the container end associated with the inlet. The inlet is arranged on the bottom side, so that the rotation-generating element rests on the ground or is spaced therefrom with its bottom end.

The inlet can now be arranged with its central axis congruent to the central axis of the rotation generating element, or laterally offset with this with its middle ash to this. Preferably, the inlet has a clear diameter which is smaller than the diameter of the central element, wherein the clear diameter may also be larger, so that the inlet projects beyond the middle element in the radial direction. Of course, the clear diameter may also have the same amount as the diameter of the middle element. In this way, medium entering the expansion tank can flow past the inlet at the middle element.

The closing element is designed according to the invention as a baffle plate, which is arranged at the opposite end to the inlet of the rotation-generating element. The closing element can have the same extent as the deflecting elements viewed in the radial direction. The closing element can be seen in the radial direction but also be made smaller or larger than the deflecting elements. If the deflecting element is larger than the deflecting elements when viewed in the radial direction, so that the terminating element projects beyond the deflecting elements in the direction of the inner wall, the outer circumference of the terminating element is preferably dimensioned such that it is spaced from the inner wall of the medium container, so that the rotational space is also in the region of End element is preserved.

The expansion tank can have a minimum and maximum medium level. Appropriately, the rotation-generating element is designed in its axial extent so that it is covered even with minimal media level in the reservoir from the medium, so that the rotation generating element or its terminating element below the predetermined, minimum medium level (liquid level) is.

Through the inlet, the medium flows axially to the central axis of the surge tank or to the central element in the surge tank. In this respect, the incoming medium has a linear flow. Due to the rotation generating element, the linear flow is converted into a rotational flow. In this case, the closing element is advantageously provided, which forces the incoming medium past the deflecting elements, so that a swirl or vortex of the medium is generated. In this respect, a linear flow is converted into a rotational flow. The twist or rotation of the medium acts on the entrained particles or solids which are transported to the inner wall of the surge tank. On the inner wall of the expansion tank, the rotational speed of the medium is so low that the particles fall due to gravity.

Usually, the particles fall due to gravity to the bottom of the expansion tank, which is why bottom side, preferably in the region of its inner wall expediently recesses, ie collection pockets are provided, in which reach the sinking particles or are absorbed and accumulated. The depressions are provided in a preferred embodiment with partitions, and form "dead water zones", ie zones in which no or at least such a low flow prevails that particles remain in the wells or collection pockets. In this respect, the depressions prevent a re-feeding of separated or sedimented particles into the medium circuit. Of course, it can also be provided to arrange a single continuous recess without a partition wall, seen in the circumferential direction, at the bottom of the expansion tank or at the edge region thereof, so as to form a circumferentially continuous collecting pocket, ie "dead water zone".

Conveniently, it is provided that the outlet is arranged with its mouth within the rotation space, can be sucked in the particle-free medium. It is envisaged that the outlet is arranged on the same container end as the inlet, ie on the bottom side. In this respect, the medium passes axially into the expansion tank and is sucked out axially out of this (pump), since at least the resulting center axes of both (inlet, outlet) may preferably be arranged parallel to each other.

Characterized in that the particles or solids are transported in the medium due to the rotation of the medium to the inner wall of the surge tank, and there fall due to gravity, and the rotational space is thus particle-free, can be dispensed with a filter element for collecting the particles. In this respect, the outlet to the medium pump is not impaired in its passage, it being ensured that the particles or interfering solids can not get back into the medium circuit, as they are safely collected in the collection pockets at the bottom of the surge tank. Compared with filter elements used in expansion tanks, the expansion tank according to the invention has no negative effects on the effectiveness of the medium circuit, and can be made much cheaper available, since it can be dispensed with a filter element. This is advantageous at low and / or very low outside temperatures (no noise, low oil foaming). Since a filter element is omitted, this also can not clog, so that therefore no negative effects on the effectiveness of the medium circuit can be expected. Of course, the wells will be filled after a certain period of operation of the medium container so that a cleaning is required. However, the depressions or collecting pockets can advantageously be dimensioned such that even a cleaning interval can be considerably increased compared to filter elements. Of course, it is entirely within the meaning of the invention that the recesses are designed or dimensioned so that they do not need to be cleaned during the entire life of the vehicle. However, the expansion tank according to the invention may only need to be cleaned, ie the collecting pockets have to be emptied, whereas a blocked filter element generally has to be replaced by a new one, so that the original effectiveness of the medium circuit impaired by the filter element can be achieved again.

The middle element is closed in a preferred embodiment at its inlet-oriented end, so that the medium flows past outside of the central element. The central element can be designed as a solid body or as a hollow body. However, it is also conceivable embodiment in which the central element is open at its inlet-oriented end, wherein the central element is designed as a tube which may be closed at its opposite end to the inlet. The closing element can here have the diameter of the tube, or as previously, as seen in the radial direction be equal to or greater than the radial extension of the deflection executed. The middle element or the tube can have outlet openings in its wall, through which medium which enters the central element can escape and thus impinge directly on the deflecting elements. Thus, the same effect can be achieved as before, namely to convert a linear flow into a rotary flow. Of course, the openings should be sized so that they are not added by the particles or solids become. Appropriately, however, the entire incoming medium flow should enter the central element, wherein the medium flow can then escape through the outlet openings spaced in the vertical direction and / or in the radial direction, and strikes the deflection elements so as to achieve a rotational movement of the medium.

Further advantageous embodiments of the invention are disclosed in the subclaims and in the following description of the figures. Show it

1 a plan view of a rotation generating element according to the invention as a section,

2 a representation of the forces acting on particles, and

3 a velocity profile of the medium in an expansion tank according to the invention by a deflection element.

1 shows a plan view of a surge tank, which as a section by means of its wall 1 is shown in cross section. The wall has an outside 2 and an inside 3 on. The inside 3 is hereinafter referred to as inner wall 3 designated. The surge tank is in the illustrated embodiment with its wall 1 executed around.

The surge tank further has a bottom, not shown, and an opposite thereto, also not shown head area.

Bottom side is an inlet 4 arranged. Not shown is an outlet.

In the surge tank is a rotation generating element 6 arranged, viewed in the axial direction of the inlet 4 in the direction of an opposite end of the container, that extends from the bottom region in the direction of the head region. At his to the inlet 4 opposite end has the rotation generating element 6 a conclusion element 7 on, which by means of the circle line 8th shown as a phantom line. The rotation generating element 6 and the final element 7 each have an outer periphery, which in each case based on the inner wall 3 the expansion tank is spaced, so that a rotation space 9 is formed for the medium.

The rotation room 9 is seen in the radial direction between the circular line 8th and the inner wall 3 arranged.

The rotation generating element 6 is fixedly arranged in the surge tank, which means that the rotation generating element 6 in the expansion tank itself does not rotate about its central axis.

Conveniently, the rotation generating element has 6 deflecting 11 on which at a middle element 12 are arranged. The middle element 12 is with its central axis preferably way congruent to the central axis of the expansion tank. The deflecting elements 11 are designed in the manner of turbine blades, so have a curved course from the central element 12 to the opposite end 13 the deflecting elements 11 on.

Advantageously, the deflection ends 11 with her to the middle element 12 opposite end 13 spaced to the inner wall 3 of the expansion tank, so that the rotation space 9 is formed, in which the medium around the rotation-generating element 6 rotates.

The rotation generating element 6 is an example of the inlet 4 spaced in the axial direction. The inlet 4 is arranged on the bottom side.

In the illustrated embodiment, the inlet 4 with its central axis congruent to the central axis of the rotation-generating element 6 , In the preferred embodiment, the inlet 4 a clear diameter which is smaller than the diameter of the central element 12 , Of course, the clear diameter of the inlet 4 also be designed larger, so that the inlet 4 the middle element 12 Seen in the radial direction, wherein also in its clear diameter equal to the inlet 4 can be provided. This can be in the expansion tank entering medium from the inlet 4 at the middle element 12 flow past.

The final element 7 is designed as a baffle plate, which at the inlet 4 opposite end of the rotation generating element 6 is arranged. The final element 7 has in the radial direction, for example, the same extent as the deflecting elements 11 ,

The expansion tank is designed as an expansion tank of a hydraulic circuit. The inlet 4 is exemplified with a steering gear. The outlet is connected to a medium pump. The medium pump causes a transport of the medium from the expansion tank to the steering gear and from there back into the expansion tank.

The rotation generating element 6 with his graduation element 7 extends from the floor towards the head area but ends below a predetermined minimum level of medium within the container, so it is always located below the liquid level in the surge tank.

Through the inlet 4 the medium or liquid flows into the expansion tank linear and at the central element 12 past. Through the final element 7 , which is arranged below the liquid level, the medium is forced to the deflection elements 11 to pass, so that the linear flow is converted into a rotational flow. With the medium particles or solids are transported, which so to the inner wall 3 be transported.

In 3 is shown a velocity profile of the medium, which by the deflection 11 is effected. Visible is that on the Innwand 3 such a low velocity prevails that particles or solids can sink.

Therefore, the bottom side in the area of the inner wall 3 advantageous depressions 14 or collection bags 14 arranged in the medium container in which the sinking particles or heavy materials are deposited. The wells 14 or collection bags have example of partitions 16 on.

The following formulas are intended to describe the behavior of the heavy substances or particles in the medium, wherein the symbols in the 1 to 3 are shown.

The total velocity of the heavy materials or particles is:

The radial velocity of the particles is calculated with:

h = Höhe (Länge) des Umlenkelementes v_aa = tanβ*B ⌢*f/b ⌢²*h The vertical velocity of the particles is calculated with:

h = height (length) of the deflection element v _aa = tanβ * B ⌢ * f / b ⌢ ² * h

To Fig. 2: Resulting centrifugal force

• F _Zres = F _ZC + F _ZF F _Zres = v ² _a / r (m _C - m _F ) F _Zres = v ² _a / r (v _c / ρ _C - v _F / ρ _F F _Zres = v2 _a v _C (1 / ρ _C - 1 / ρ _F ) With F _Z = m * v ² _a / r F _ZC = m _c * V ² _a F _ZF = m _F * v ² _a m _c = v _c / ρ _c m _F = v _F / ρ _F v _c = v _F

The weight is calculated assuming a spherical particle (spherical particles) with: F _Gres = _mc * a a = g * (1 -ρ _F / ρ _C -F _RV / F _G ) F _Gres = m _c * g (1 -ρ _F / ρ _C -F _RV / F _G ) With F _G = m * g F _RV = c _ω / ρ _c / 2 * v ² _h * A _st A _st = D ² _c * π / 4 c _{ω sphere} ≈ 0.4 so that F _Gres = m _c * g (1 - ρ _F / ρ _C - c _ω * ρ _C * v ² _h * A _st / 2 * m * g F _Gres = m _c * g (1 - ρ _F / ρ _C - c _ω * ρ _C * v ² _h * D ² _C * π / 8 * m * g

The resistance is calculated with: F _RH = c _ω * ρ / 2 * v ² _r * A _st F _RV = c _ω * ρ / 2 * v ² _h * A _st

It has been found that, if the density of the heavy substance ρ _C or the particle is greater than the density of the medium ρ _F , that the centrifugal force F _ZC which acts on the particle, greater than the centrifugal force F _ZF , which on the medium acts. Due to this power imbalance, particles are transported more strongly to the outside than the surrounding medium. ρ _C > ρ _F => F _ZC > F _ZF

In this respect, particles will always sediment near the inner wall, ie sinking, when the centrifugal force F _ZC acting on the particle is equal to the centrifugal force F _ZF acting on the medium and when the density of the heavy material ρ _C or of the particle is greater than the density of the medium ρ _F.

This is the case in areas where there is no or very little speed, since the centrifugal force is a function of the speed: F _ZC = F _ZF and ρ _C > ρ _F then F _ZC = F _IF if v = 0 because F _ZX = f (vx).

It follows that particles with a higher density than the density of the medium (ρ _C > ρ _F ) accumulate in areas where no velocity or very low velocity prevails. This is the case, for example, when r = R (see 3 ). Because of the high shear forces within the medium or within the liquid, the velocity is in the area of the inner wall 3 equal to zero (see 3 ). The bottom-side depressions cause a "dead water zone" in which there is virtually no flow velocity and thus the sedimented particles are not returned to the flow circuit.

The expansion tank or servo oil tank serves primarily to compensate for fluctuations in filling height.

Claims (10)

Expansion tank which is integrated in a medium circuit, wherein the expansion tank has a bottom side inlet ( 4 ) and a bottom outlet, characterized in that in its axial extension below a minimal expected medium level arranged rotation generating element ( 6 ) is arranged fixed within the surge tank, which viewed in the axial direction of the bottom-side inlet ( 4 ) extends towards an opposite end of the container, and at its inlet ( 4 ) opposite end designed as a baffle closure element ( 7 ), wherein the rotation-generating element ( 6 ) and the final element ( 7 ) each having an outer periphery, which relative to an inner wall ( 3 ) of the expansion tank is spaced, so that a rotation space ( 9 ) is formed for the medium. Expansion tank according to claim 1, characterized in that the rotation-generating element ( 6 ) Deflecting elements ( 11 ), which on a central element ( 12 ) are arranged. Expansion tank according to claim 1 or 2; characterized in that the rotation generating element ( 6 ) with bent deflection elements ( 11 ) is executed. A compensator tank according to one of the preceding claims, characterized in that the rotation (generating element 6 ) to the inlet ( 4 ) is spaced in the axial direction. Expansion tank according to one of the preceding claims, characterized in that the inlet ( 4 ) with its central axis congruent to the central axis of the rotation-generating element ( 6 ) is arranged. Expansion tank according to one of the preceding claims, characterized in that the inlet ( 4 ) has a clear diameter which is smaller than a diameter of a central element ( 12 ) of the rotation generating element ( 6 ). Expansion tank according to one of the preceding claims, characterized by bottom-side depressions ( 14 ). Expansion tank according to one of the preceding claims, characterized in that the outlet with its mouth in the region of the rotational space ( 9 ) is arranged. Expansion tank according to one of the preceding claims, characterized by recesses ( 14 ) for receiving sedimented solids, wherein the depressions ( 14 ) in the region of the inner wall ( 3 ) are arranged. Expansion tank according to one of the preceding claims, characterized by recesses ( 14 ) which form dead water zones.

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