EP2798225A2

EP2798225A2 - Method for determining a position of a piston in a piston pressure accumulator by resistance measurement and suitably designed piston pressure accumulator

Info

Publication number: EP2798225A2
Application number: EP12816300.3A
Authority: EP
Inventors: Thomas Becker; Christoph Weisser
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2011-12-28
Filing date: 2012-12-27
Publication date: 2014-11-05
Also published as: JP2015508478A; BR112014016016A2; WO2013098311A2; RU2014130909A; US20140352648A1; KR20140105607A; WO2013098311A3; DE102011090048A1; CN104024654A; BR112014016016A8

Abstract

The invention relates to a method for determining a position of a piston (5) in a piston pressure accumulator (1) and a correspondingly designed piston pressure accumulator (1). A housing (3) accommodates a displaceable piston (5). An electrode arrangement (15) having a plurality of 4-point measurement electrode pairs (17) is provided on the electrically conductive housing (3) and is designed to determine a position of the piston (5) inside the housing (3) by measuring a distribution of an electrical resistance or potential between inner electrodes (21) when a current is applied to outer electrodes (19), depending on a position along the housing (3). The position of the piston determined from the measurement of the potential distribution can be used to determine or check a charge state of the piston pressure accumulator (1).

Description

description

Method for determining a position of a piston in a

Piston pressure accumulator by resistance measurement and suitably designed piston accumulator

Field of the invention

The present invention relates to a method for determining a position of a piston within a piston accumulator. The invention further relates to a method for checking information about a charge state of a piston accumulator. Furthermore, the invention relates to a suitably designed piston accumulator and a monitoring device for monitoring a piston accumulator.

State of the art

Piston accumulators are used to mechanically store energy. For example, in hydraulic hybrid vehicles

Piston pressure accumulator used to power, for example, the

Braking wheels is generated to store and make them available, for example, during subsequent acceleration of the vehicle again.

In a piston pressure accumulator can be provided as a separating element between two sub-volumes of the piston accumulator in an example cylindrical housing a displaceable piston. In one of the

Partial volumes, a compressible fluid can be introduced. In the other part volume, a non-compressible fluid can be introduced.

In particular, the incompressible fluid can be replaced by a suitable

Valve system in the appropriate sub-volume on and off again be derived to energy mechanically by compressing the

store or release again compressible fluid.

DE 10 2010 001 200 AI describes a conventional piston accumulator.

In order to determine a state of charge (SOC) of the piston accumulator, i. E. In order to be able to determine how much energy is currently mechanically stored in the piston pressure accumulator, measured variables which determine the energy content, such as, for example, the energy content, can be determined

Piston accumulator prevailing pressure and the prevailing pressure

Temperature, to be measured. Such pressure and temperature measurement is possible with simple sensors.

However, it has been observed that in particular under dynamic

Operating conditions due to e.g. Latency of the temperature measurement can sometimes occur large inaccuracies in determining the state of charge.

Alternatively, the state of charge of a piston accumulator based on the current position of the piston within the housing of the

Piston accumulator can be determined. The position of the piston can be determined, for example, by limit switches, e.g. determine by means of a shift rod, the end position of the piston at one and / or other end of the memory within the housing of the piston accumulator.

Alternatively, the path or location of the piston can be sensed within the housing, for example by means of a piston rod, a cable measuring system or a Ultraschallwegmesssystem.

However, such systems for determining the current position of the piston require a high structural complexity. In particular, it may be necessary

To integrate components such as limit switches or a piston rod in the inner volume of the piston accumulator, it may be necessary to mechanically and / or electrically connect such components to the outside.

Disclosure of the invention The herein proposed method for determining a position of a piston within a piston accumulator and a suitably equipped piston accumulator can make it possible to determine the current position of the piston within the piston accumulator with high accuracy and yet low structural complexity.

In addition, based on the thus determined position of the piston within the piston accumulator information about the state of charge of the piston accumulator memory determined and thus obtained a different way

Information about this state of charge can be checked. The charge state monitoring of the piston accumulator can thus be more reliable. According to a first aspect of the present invention is in a

Piston pressure accumulator having a preferably at least partially electrically conductive housing and a displaceable within the housing, also preferably at least partially electrically conductive piston, determines the current position of the piston within the piston accumulator by measuring a distribution of electrical resistance along the housing.

For this purpose, an electrical current can be locally induced at a plurality of positions in the region of the housing, and then locally a resulting electrical potential distribution can be determined. The current can be considered as

DC generated by applying a DC voltage between two electrodes. Similar to that in geophysics for representation

Underground structures used electrical resistance tomography can be determined with two other electrodes, for example, the distribution of electrical potential, as it is due to the induced current and due to the prevailing between the two electrodes electrical resistance.

Since the position of the at least partially electrically conductive piston within the housing of the piston accumulator has an influence on the on the

Housing measured electrical resistance or self-adjusting has electrical potential distribution can by determining this

Potential distribution information about this position of the piston can be determined.

According to a development of this measuring principle, an electrical alternating current can be locally induced at several positions in the region of the housing. This alternating current leads to a time-varying potential distribution on the housing of the piston accumulator. By local measurement of the resulting time-dependent electrical potential distribution can be similar to the electrical impedance tomography even more accurate information about the current position of the piston within the housing of the

Piston accumulator can be obtained.

In order to carry out the proposed method, a

Piston accumulator on its housing having an electrode assembly which is adapted to determine a distribution of the electrical resistance along the housing in order to draw conclusions about the current position of the piston in the housing can.

An advantage of the proposed position determination method or a correspondingly designed piston accumulator can be seen in the fact that no measuring sensors or other components within the

Storage volume of the piston accumulator need to be arranged. The measured distribution of the electrical resistance or due to the induced electrical current adjusting electrical

Potentials along the housing can be measured using electrodes mounted externally on the housing or integrated into a wall of the housing. Such an external arrangement of

Electrodes can greatly facilitate sealing of the storage volume of the piston accumulator.

In particular, the housing of the piston accumulator of a

Fiber composite material may be formed. Such a trained

Piston pressure accumulator can have a comparatively low weight with high mechanical stability. The fiber composite material can

For example, impregnated with a thermosetting resin carbon fiber fabric include. In particular, in carbon fiber composite materials (carbon fiber reinforced plastics, CFRP), the housing of the piston accumulator can have a high electrical conductivity due to the electrical conductivity of the carbon fibers. This can on the one hand by attaching an electrode

electrical current can be induced within the carbon fiber housing and on the other hand by attaching further electrodes, a distribution of a subsequent adjusting electrical potential can be determined. A self-adjusting local electrical potential will depend on a position of the piston within the housing, since the piston due to its own electrical conductivity and the fact that it rests against the housing, the electrical resistance or the electrical conductivity in the region of Housing in which he is currently, significantly changed. The piston can, like the housing, consist of an electrically conductive material or, at least on its surface facing the housing, have such an electrically conductive material. For example, the piston may be made of metal.

In particular, when the housing of the piston accumulator with a

Fiber composite material is formed, provided for the measurement of the distribution of the electric potential electrode assembly may be integrated directly into the fiber composite material. In other words, electrodes may be integrated in a wall formed by the housing, which surrounds the pressure storage volumes.

For example, in a production of the housing with a

Carbon fiber composite directly corresponding electrodes are implemented in the housing, for example in the form of metallic wires that can be contacted from outside the housing. Such incorporation of electrodes into the fiber composite material may allow for ease of manufacture of the housing of the piston accumulator as well as a reliable means of determining the position of the piston within the accumulator by means of the integrated electrode assembly.

The provided on the housing of the piston accumulator

Electrode assembly may include one or a plurality of 4-point measurement electrode pairs. Any 4-point measurement electrode pair can thereby having two electrodes for inducing the electric current and two electrodes for measuring the distribution of the electric potential between the electrodes. The 4-point measurement electrode pairs may be arranged along the direction of movement of the piston on the housing.

With the aid of the multiplicity of 4-point measuring electrode pairs, it is thus possible in each case to determine a distribution of an electrical resistance or an electrical potential in a partial region of the housing of the piston accumulator along the travel path of the piston within the housing. By a simultaneous or successive measurement of the electrical potential at all 4

Point measurement electrode pairs can thus be closed to a current position of the piston.

A distance of four-point measurement electrode pairs adjacent to the direction of movement of the piston can preferably be smaller than one

Length of the piston in a direction parallel to this direction of movement.

Such a small spacing of adjacent 4-point measurement electrode pairs may cause the piston to be adjacent to at least one of the 4-point measurement positions for any ingestible position.

Electrode pairs is. The respective adjacent 4-point measuring electrode pair is due to the piston a strong change of

detected electrical potential between two electrodes of the 4-point measuring electrode pair, which suggests the presence of the piston in the vicinity of this position.

The previously described method for determining a position of the piston within a piston accumulator can be advantageously used to determine or check information about the state of charge of the piston accumulator based on the specific position of the piston.

Such a method may be carried out in a monitoring device for monitoring the piston accumulator.

For example, in normal operation of the piston accumulator whose state of charge only due to other parameters such as a pressure and a temperature of the piston accumulator stored in the memory Fluids are determined. Based on such easily determinable measures, the state of charge can be simple and generally sufficient

Reliability can be determined. However, it may occur at certain intervals or, for example, under certain working conditions

Be advantageous piston accumulator, which performed so

To monitor or calibrate state of charge measurement by additionally providing information about the actual position of the piston within the

Piston accumulator is determined. This additional information allows a more accurate determination of the state of charge of the piston accumulator or a plausibility of the state of charge determined with other measurement methods.

It should be noted that possible features and benefits of

Embodiments of the invention herein are described in part with reference to the method of determining the position of the piston within the piston accumulator, partially with respect to the method of checking the information about the state of charge of the piston accumulator and partially with respect to a correspondingly configured piston accumulator. One skilled in the art will recognize that the features may be suitably combined and / or interchanged to provide additional ones

Embodiments of the invention and possibly to achieve synergy effects.

Brief description of the drawings

Hereinafter, embodiments of the invention will be described with reference to the accompanying drawings. Neither the description nor the drawings are to be construed as limiting the invention.

Figure 1 shows a side sectional view through a piston pressure accumulator according to an embodiment of the present invention;

Figure 2 shows a cross-sectional view through a piston pressure accumulator according to an embodiment of the present invention.

The figures are only schematic and not to scale. Embodiments of the invention

FIG. 1 shows a piston pressure accumulator 1 according to an embodiment of the present invention. The piston pressure accumulator 1 has a housing 3 in a lightweight construction, the majority of carbon fiber reinforced

Plastics (CFRP) consists. Essentially, these CFRPs consist of electrically conductive carbon fibers and a non-conductive carbon fiber

Plastic matrix, for example in the form of a synthetic resin together. The housing may for example have a cylindrical geometry with a diameter of, for example, 10-30 cm and a length of, for example

50-300 cm.

Within the housing 3 is a piston 5 made of a likewise electrically conductive material such as a metal, e.g. Aluminum, arranged. The piston 5 serves as a separating element between two sub-volumes 7, 9 within the housing 3 and seals them against each other. The piston 5 is displaceable along a direction of movement 23 which corresponds to the center axis of the cylinder of the housing 3, so that the partial volumes 7, 9 can be varied.

In a first sub-volume 7, for example, via a valve system 11, a non-compressible fluid such as a liquid, in particular oil, are introduced or discharged. In the other sub-volume 9, a compressible fluid such as a gas can be on or derived via a valve system 13. The piston 5 can depend on the in the

Partial volume 7 introduced amount of non-compressible fluid along the direction of movement 23 are displaced and store mechanical energy by building up a pressure in the compressible fluid contained in the second partial volume 9.

Due to the electrical conductivity of the material used for the housing 3 can be determined by a determination of the electrical resistance or the impedance at defined locations on the housing 3, a method for determining the position of the piston 5 within the closed housing 3 and, based on this information , a method for determining or

Check a state of charge of the piston accumulator 1 realize. there is used that the electrical resistance or the electrical potential along the housing 3 differs, depending on whether the piston 5 is at the respective measuring position or not. The proposed method is similar to that of the electrical

Resistance tomography or electrical impedance tomography, as used in geophysics, for example, via electrical

Stress measurements between individual electrodes to obtain statements about a condition of layers in a substrate.

For this purpose, along one surface of the housing 3, an electrode arrangement 15 is provided, which is designed to enable determination of a position of the piston by measuring a distribution of the electrical potential along the housing 3. To determine this self-adjusting electrical potential or the potential distribution causing such an electrical resistance along the housing of the piston pressure accumulator, the electrode assembly 15 in this case have one or a plurality of 4-point measurement electrode pairs 17.

Each 4-point measuring electrode pair 17 in this case has two outer electrodes 19, via which a current with a magnitude I can be induced in the conductive housing 3. Due to this current I, a distribution of an electrical potential, which is dependent on the locally prevailing electrical resistance as it is caused by the housing 3 itself and, if appropriate, by an electrically conductive piston 5 adjacent thereto, is formed between the outer electrodes 19.

Between the outer electrodes 19, two further inner electrodes 21 are provided, with which a potential difference ΔΙΙ can be measured.

As shown in FIG. 1, the outer electrodes 19 and the inner electrodes 21 of a 4-point measuring electrode pair 17 may be arranged along a line which is transverse, preferably perpendicular, to the

Movement direction 23 of the piston 5 extends. A distance s between adjacent 4-point measuring electrode pairs 17 may in this case preferably less than or equal to a length L of the piston 5 in the direction parallel to the Movement direction 23 may be selected. In this case, the piston 5 adjoins one of the 4-point measuring electrode pairs 17 provided on the housing 3 for each position which it is capable of receiving within the housing 3. During operation of the piston accumulator 1, it is therefore possible at all four-point measurement Electrode pairs 17 each measured a self-adjusting between the inner electrodes 21 potential difference and thus a distribution of the electrical potential along the housing 3 are determined. Depending on the nature of, for example, the interior of the housing 3, this results in a specific potential difference, which correlates with the presence or absence of the piston 5. With a plurality of distributed over the length of the housing 3 4-point measuring electrode pairs 17 so the piston position can be determined discretely.

As shown in Figure 2, an external monitoring device 25 has both a controllable current source 27 and a

Voltage measuring device 29 on. The power source 27 is electrically connected to the outer electrodes 19. The voltage measuring device 29 is connected to the inner electrodes 21. By applying a predetermined current I from the current source 27 via the outer electrodes 19 to the housing 3, a resistance-dependent potential distribution within the

Housing 3 a. A potential difference between two inner electrodes 21 can be determined with the aid of the voltage measuring device 29.

The information obtainable with the aid of the described method of a current position of the piston 5 within the housing 3 can be used inter alia to directly determine the SOC from the measured piston position, or a calculation model for calculating the current charge state of the piston accumulator 1 from the Initialize and / or correct measured variables pressure and temperature during operation. As a result, a significantly higher accuracy of the calculated state of charge value can be achieved, in particular under dynamic operating conditions.

Claims

claims

A method of determining a position of a piston (5) within a piston accumulator (1), the piston accumulator (1) comprising a housing (3) and a piston (5) displaceable within the housing (5), characterized in that the method comprises :

Determining the position of the piston (5) by measuring a distribution of electrical resistance along the housing (3).

The method of claim 1, wherein at one or more positions in the region of the housing (3) locally an electrical current (I) is induced and locally a resulting electric potential distribution (ΔΙΙ) is determined.

The method of claim 2, wherein at one or more positions in the region of the housing (3) locally alternating electrical current is induced and locally a resulting time-dependent electrical potential distribution is determined.

Method for determining or checking information about a

Charge state of a piston accumulator (1),

characterized in that the method comprises the following steps:

Determining a position of a piston (5) within the

Piston pressure accumulator (1) according to a method according to one of

Claims 1 to 3, and

Determining or checking the information about the state of charge of the piston accumulator (1) taking into account the specific position of the piston (5).

Monitoring device (25) for monitoring a

Piston accumulator (1), characterized in that the monitoring device (25) is adapted to carry out a method according to one of claims 1 to 4.

Piston pressure accumulator (1) comprising:

a housing (3), and

a piston (5) displaceable within the housing (3),

characterized in that

on the housing (3) an electrode arrangement (15) is provided, which is designed to enable determination of a position of a piston (5) by measuring a distribution of an electrical resistance along the housing (3).

Piston pressure accumulator according to claim 6, wherein the housing (3) is formed from a fiber composite material.

Piston pressure accumulator according to claim 7, wherein the electrode assembly (15) is integrated in the fiber composite material.

Piston accumulator according to one of claims 6 to 8, wherein the

Electrode assembly (15) one or a plurality of 4-point measuring electrode pairs (17), which along a line parallel to a direction of movement (23) of the piston (5) on the housing (3) are arranged.

10. piston accumulator according to claim 9, wherein a distance (s) of parallel to the direction of movement (23) of the piston (5) adjacent 4-point measuring electrode pairs (17) is smaller than a length (L) of the piston (5). in a direction parallel to this direction of movement (23).