EP1627216A2

EP1627216A2 - Method and arrangement for the quantitative determination of leakage of hydraulic components

Info

Publication number: EP1627216A2
Application number: EP04724977A
Authority: EP
Inventors: Walter Steeb; Siegfried Markus
Original assignee: Rausch and Pausch GmbH
Current assignee: Rausch and Pausch GmbH
Priority date: 2003-04-07
Filing date: 2004-04-01
Publication date: 2006-02-22
Also published as: DE112004001063D2; WO2004092701A3; WO2004092701A2

Abstract

The invention relates to a method and an arrangement for the quantitative determination of leakage of hydraulic components which are part of a measuring and testing segment in a fluid line. The method is carried out in a simple and automatic manner. A closed volume is thus completely filled with a fluid, said closed volume containing a hydraulic component which is to be measured. A specific amount of said volume is modified by means of a compression component in a relatively short space of time. First pressure modification occurring through the specific volume alteration is measured and a second pressure modification occurring in the closed volume is measured after a relatively long period of time, whereupon leakage is determined from the alterations in the measured pressure.

Description

Method and arrangement for the quantitative determination of the leakage of hydraulic components'

The invention relates to methods and an arrangement for the quantitative determination of the leakage of hydraulic components according to the preamble of the claims. It is preferably used for the short-term measurement of small leakage limit values of control components in automotive hydraulics.

A variety of leak measurement methods for measuring small and very small leakage quantities are known. Most of these leak measurement methods are based on measurements with compressed air or special test gases as media. The disadvantage of these methods for leak measurement on hydraulic components is that they work with a test pressure that is significantly lower than the operating pressure. When the test pressure is raised, the methods mentioned can no longer be used, are too time-consuming or are of concern with regard to occupational safety. In addition, there is no clear connection between a leakage quantity with gas and a leakage quantity with liquid, since a specific connection only applies to a specific geometric shape of a leak, but this is always unknown and inconsistent. Likewise, the significantly higher operating pressure in a hydraulic system can cause a leak that would not occur with a lower test pressure and would remain undetected. Extraction methods with liquids are also known, in which a test specimen is filled with liquid to a predetermined operating pressure and either examined for moist areas or an existing leak is concluded on the basis of a temporary pressure drop. However, the quantification of a leakage determined in this way is hardly possible or only very roughly, since the elasticity of the test medium or the air in the test medium or the measuring arrangement is not known or is not constant.

In the case of leakage measurements of valves, pipette measurement methods are also known which measure the leakage of a valve seat at the outlet virtually without pressure. A measurement under operating pressure and with the operating medium at the valve inlet is also possible. However, this method can only be used in laboratory operations and does not permit leak measurements outside and cannot be automated even with economically justifiable effort.

The present invention is intended to remedy the shortcomings indicated above and to show a method and an arrangement for measuring, in particular, small leaks in hydraulic systems, which is basically carried out in online operation and can be automated.

According to the invention, this object is achieved by the characterizing features of the first and fifth patent claims and supplemented by advantageous configurations according to the associated subclaims. The elasticity of the entire test section can also be recorded by integrating a compressibility determination and a test object into the test section, which is itself part of a fluid line. The short period in which the volume of the test track is changed by a defined, as small as possible amount, usually reduced, is in the millisecond range, which is small enough to avoid changing the other conditions of the test track. This results in a defined pressure change, usually pressure increase, which is related to the volume change rank. This means that it is known exactly which volume change belongs to which pressure difference. Then the pressure development, usually the reduction in pressure over a long period of time, which is in the range of seconds or minutes, is observed and the associated leakage volume is determined. It is assumed that only the test object shows unknown leakage losses and that the temperature is at least almost constant during the entire process and over the entire test section. Changes in temperature during the test process are recorded by means of temperature sensors and must be taken into account in the calculation. The leakage volume determined in this way determines the usability or uselessness of the respective test object. Before the test, the test track is first filled with the pressure medium provided in the test object. This can happen, for example, by the pressure medium flowing through the test section until all foreign media are expelled or the entire test section is evacuated and only then is the pressure medium flowed into the test section until a specified pressure is reached. In general, the method according to the invention for determining the leakage of hydraulic components is as follows: After the test section has been set up, a pressure pi is measured immediately before the membrane movement. Thereafter, by introducing a force F onto the membrane, the volume of the test section is reduced, for example by ΔV, and an increased pressure p _{2 is} generated and measured in the test section. The mathematical relationship ΔV / p ₂ - pι for the compressibility factor k _P [mm ³ bar] can be formed from the measured quantities. At the same time, this relationship shows how the volume in the test section changes when there is a change in pressure and the same unchanged temperature everywhere. If the temperature T is variable during the measuring time, ie if the pressures are measured at different temperatures, the former must be corrected, taking into account the temperature response k _τ [bar / K] of the test section. If the pressure p ₃ and the temperature T ₃ at the beginning of the measuring time and p ₄ and T ₄ at the end of the measuring time, the corrected pressure difference results from Δp _Δ τ ⁼ (T ₄ - T ₃ ) • k due to the temperature change _τ [bar / K]. A theoretical pressure at the end of the measuring time, without temperature influence, is p ' ₄ = p ₄ - Δp _ΛT - The formula for the volume change in the test section due to leakage within the measuring time t taking into account the temperature results in ΔV _P = ΔV • ( p ₄ ⁵ - p ₃ ) / (p ₂ - pi) [mm ³ ]. This change in volume corresponds with the opposite sign to the leakage of the test specimen V _leak ⁼ - ΔV _P [mm ³ ], which results in an average leakage in the time unit V _Lec k ⁼ V _Lec / [mm ³ / s]. The compression means provided in the arrangement can advantageously be a piston or, for reasons of tightness, a membrane which is moved into or out of the test section and consequently reduces or increases the volume by a preferably small amount in the cubic millimeter range. Display means are preferably connected to the compression means, which indicate the change in volume of the test section. For calibration of the membrane movement before the actual measuring process the test section can be connected to a reference cylinder and piston with a known diameter and a known stroke in order to bring about a known volume change. The leakage of the test section must also be determined before the measurement process. This is done by connecting a reference part with a blind hole to the test section instead of the test object and pumping the test section designed in this way empty. The vacuum connection is preferably outside the test section. The arrangement according to the invention is equipped with appropriate sensors for measuring the pressures or pressure changes and the temperatures, the measured values of which, like the change in volume, are included in the quantitative determination of the leakage, which can preferably take place automatically by including a suitable evaluation unit.

The invention is explained in more detail below with the aid of a schematic drawing. Show it:

Fig. 1 shows an arrangement according to the invention and

Fig. 2 shows a modified arrangement for testing the tightness of a measuring and test section.

In FIG. 1, in an arrangement 30, an inlet valve 11 for a measuring or test section 12 is arranged downstream of a pump for the hydraulic fluid 10 in a fluid line 25, to which a compression component 13 is connected and at the end of which there is a test object 18 is located, which may include a shut-off valve 14. The compression component 13 is advantageously located in the wall of the measuring and test section 12 and has a membrane 132 clamped in a cylinder 131, which can be moved between end positions defined by stops 134 and 135 with the aid of a plunger (or the like) 133. For this purpose, a force F is applied to the plunger 133, which pushes the membrane 132 up to the stop 135 and thus reduces the volume 136 between the membrane 132 and the stop 135. Since this volume 136 communicates directly with the volume V of the test section 12, its volume is also reduced by ΔV and thus the fluid pressure p in the Test section 12 increased by Δp. A calibrated displacement sensor 137 or another reading device enables the displacement of the plunger 13 or the volume change ΔV to be read, the amount of which is very small in relation to the volume of the test section 12. The pressure change Δp in the test section 12 corresponding to the volume change ΔV is determined by a pressure sensor 15. Since the temperature exerts a considerable influence in this type of leakage determination, the temperature T must either be kept constant over the entire measuring section or it must be measured in order to make appropriate corrections. The latter is carried out with the aid of temperature sensors 16, 17 which are applied to the test section 12, of which the temperature sensor 17 and the shut-off valve 14 are part of the hydraulic component (test object) 18, the leakage of which is to be determined. A vacuum accumulator with oil separator 19 and a vacuum pump 20 with motor M are arranged downstream of the test specimen 18. As is known, the vacuum accumulator is used to quickly build up the vacuum in the measuring and test section 12; the oil separator prevents test liquid from getting into the vacuum pump 20 during evacuation. The diaphragm 132 including the plunger 133 can also be replaced by a piston, but special attention must be paid to the problem of tightness. It is also possible to increase the volume of the measuring and test section 12 by a constant amount and thus to reduce the pressure in this section. After the compression component 13 has been calibrated and the test section 12 from the inlet valve 11 to the test specimen 18 has been adequately sealed, the leakage measurement with the hydraulic fluid is as follows:

First, the inlet valve 11 is blocked, the shut-off valve 14 is opened and a vacuum is created in the test section 12 including the test specimen 18 by means of the vacuum pump 20. Then the shut-off valve 14 is closed, the inlet valve 11 is opened and, with the aid of the pump 10, pressure fluid (for example hydraulic oil) is pumped into the measuring and test section 12, so that a pressure pi is established. The plunger 133 then presses the membrane 132 against the stop 135 within ms and thus reduces the volume by, for example, 11 mm ³ or increases the pressure by 9 bar, so that a Compressibility factor k _p = 11 mm / 9 bar = 1.22 mm / bar after a calming time of a few, for example 2 s. In addition, the arrangement shown in FIG. 1 has a previously determined temperature response of k _τ = 7.3 bar / K (K = Kelvin). For the quantitative determination of the leakage, the pressure in the measuring and test section 12 is initially measured with the pressure sensor 15 with p ₃ = 102.1 bar at an average temperature T ₃ = 23.6 ° C and at the end of the measuring period of 10 s determined with p ₄ = 96.3 bar at an average temperature of T ₄ = 23.8 ° C. The average temperature from the averaging of the temperatures measured by the temperature sensors 16, 17. The measurement time can also be in the minute range (Ibis 5 min).

Due to the temperature change, there is a pressure change of Δp _ΔT = (T ₄ - T ₃ ) • k _τ = (23.8 - 23.6) • 7.3 bar = 1.46 bar. Without a temperature influence, the (theoretical) fluid pressure at the end of the measurement would have been ρ ₄ '= p ₄ • Δp _Δ τ ⁼ (96.3 bar - 1.46 bar) = 94.84 bar. The real pressure change occurring in the measuring and test section 12 due to an existing leak corresponds to a volume change ΔV _P , which changes according to the relationship ΔV _P = ΔV - (p ₄ '- p ₃ ) / (p ₂ - Pi) = 11 , 3 ^• (94.84 - 102.10) / 9 = - 7.26 mm ³ results. This change in volume, with the opposite sign, is the leakage of the test specimen 18 in 10 s, i.e. V _L ec _k ⁼ -ΔV _P = 7.26 mm ³ . In the unit of time, i.e. in one second, this results in an average leakage of V _leak ⁼ V- t = 7.26 / 10 = 0.726 mm ³ / s. The leakage value determined in this way is either sufficient or the test specimen has to be reworked or it must be eliminated as unusable.

The above method of quantitative leakage determination can be carried out manually or partially automatically or fully automatically. In the case of a fully automated method, both the pumps 10 and 20, the valves 11 and 14, the sensors 15, 16, 17 and the displacement sensor 137 and the introduction of the force F are connected to a computing and control device 21. The computing and control device 21 on the one hand receives the sensor data and on the other hand controls the pumps and their motors M, the valves and the initiator of the force F in accordance with the process sequence described above. It stores data Measured values and results to the required extent and displays results.

The measurement and test section 12 can be checked for leaks with the aid of a reference block 22, which is used in place of the test object 18 and ensures complete tightness

Blind hole 23 is provided, see Fig. 2. In the case because of the

Securing the tightness of the vacuum pump 20 with the vacuum accumulator

19 integrated into the fluid line via a ball valve 24 between the hydraulic fluid pump 10 and the inlet valve 11. Otherwise, the test is carried out similarly to that described in FIG. 1: The

Measuring and test section 12 is evacuated and filled with fluid. The

Compressibility is determined. The pressure curve and the temperature are measured over time, with the measurement time being selected to be significantly longer at about 30 minutes than in FIG. 1. Then the leakage of the

Measuring and test section 12 determined and this in consideration of their

Leakage used.

If the test specimen 18 in FIG. 1 does not contain a shut-off valve 14, the vacuum can also be drawn as indicated in FIG. 2, the ball valve 24 having to be replaced by an automatic valve.

All features shown in the description, the following claims and the drawing can be essential to the invention both individually and in any combination with one another.

LIST OF REFERENCE NUMBERS

10 Pump for the hydraulic fluid

11 inlet valve

12 measurement and test section

13 compression component

14 shut-off valve

15 pressure sensor

16, 17 temperature sensors

18 DUT (hydraulic component)

19 vacuum accumulators and oil separators

20 vacuum pump

21 computing and control device

22 reference block

23 blind hole

24 ball valve

25 fluid line

30 arrangement

131 cylinders

132 membrane

133 plungers

134, 135 stops

136 volumes

137 displacement sensor

M engines

Claims

claims

1. A method for the quantitative determination of the leakage of hydraulic components, characterized in that a closed volume including a hydraulic component to be measured is completely filled with a fluid, the volume is changed in a relatively short period of time by a fixed part of its size, a the first change in pressure that occurs as a result of the defined change in volume is measured, after a relatively long period of time a second change in pressure is measured in the closed volume and the leakage is determined from the measured changes in pressure.

2. The method according to claim 1, characterized in that first creates a vacuum in the closed volume and then that

Fluid is let in so that it fills the entire volume.

3. The method according to claim 1, characterized in that the relatively short period is in the millisecond range and that the relatively long period is in the seconds or minutes range.

4. The method according to claim 1, characterized in that temperature changes during the measurement periods are taken into account correctively on the measured pressures and volumes.

5. Arrangement for the quantitative determination of the leakage of hydraulic components, wherein there is a measuring and test section in a fluid line between an inlet valve and a shut-off valve belonging to the hydraulic component, characterized in that the measuring and test section is a

Compression component is assigned to the defined change in volume of the measuring and test section.

6. Arrangement according to claim 5, characterized in that the compression component contains a clamped membrane which acts on a plunger directed essentially at right angles to the membrane.

7. Arrangement according to claim 5, characterized in that the compression component comprises a cylinder in which a piston slides.

8. Arrangement according to claim 6 or 7, characterized in that the conception component is provided with a sensor for displaying the movements of the plunger or the piston.

9. Arrangement according to claim 5, characterized in that sensors for pressure and / or temperature measurement are attached to the measuring and test section.

10. The arrangement according to claim 5, characterized in that the shut-off valve vacuum accumulator and a vacuum pump are arranged downstream.

11. The arrangement according to claim 10, characterized in that the vacuum accumulator is also designed as an oil separator.

12. The arrangement according to claim 5, characterized in that the hydraulic component is interchangeable with a reference part with a blind hole.

13. Arrangement according to claims 5 and 12, characterized in that the vacuum pump is connected to the fluid line outside the measuring and test section.