DE102014200081A1 - Method for detecting a loss of operating medium - Google Patents

Abstract

The invention relates to a method for detecting a loss of operating medium in a fluid system (8) comprising a low-pressure region (6) with a low-pressure accumulator (30) and a high-pressure region (7) with a high-pressure accumulator (40). In order to simplify and / or improve the detection of losses of operating medium in a fluid system, by considering a compressibility of fluid in the low pressure region (6) and fluid in the high pressure region (7), a change in a total fluid volume comprising hydraulic medium and gas is detected ,

Description

The invention relates to a method for detecting a loss of operating medium in a fluid system comprising a low-pressure region with a low-pressure accumulator and a high-pressure region with a high-pressure accumulator.

State of the art

The operating medium is, for example, a hydraulic medium, such as hydraulic oil, or gas. The accumulators are designed for example as a hydraulic accumulator with a gas volume and an oil volume. Such hydraulic accumulators can be designed as a piston accumulator, as a bladder accumulator or as a diaphragm accumulator.

Disclosure of the invention

The object of the invention is to simplify and / or to improve the detection of losses of operating medium in a fluid system comprising a low-pressure region with a low-pressure accumulator and a high-pressure region with a high-pressure accumulator.

The object is achieved in a method for detecting a loss of operating medium in a fluid system comprising a low-pressure region with a low-pressure accumulator and a high-pressure region with a high-pressure accumulator, characterized in that by considering a compressibility of fluid in the low pressure region and fluid in the high pressure region, a change a total volume of fluid is detected, comprising hydraulic medium and gas. The hydraulic medium, in particular hydraulic oil, which is also referred to as oil for short, is present in a hydraulic system which, in addition to the low-pressure accumulator and the high-pressure accumulator, comprises hydraulic lines and valve devices. The gas is preferably arranged on a gas side of the storage. By detecting and considering the compressibility of the fluid in the low-pressure region and in the high-pressure region, it can advantageously be detected not only whether there is a loss of operating medium, but it is even particularly advantageous even possible to identify a loss of operating fluid.

A preferred embodiment of the method is characterized in that a distinction is made between the consideration of the compressibility of the fluid in the low-pressure region and the fluid in the high-pressure region between a hydraulic medium leakage and a gas leakage, wherein a hydraulic medium volume in the low-pressure region and the high-pressure region is monitored model-based. The inventive method can advantageously use existing pressure sensors.

A further preferred exemplary embodiment of the method is characterized in that the hydraulic medium volumes in the low-pressure accumulator and in the high-pressure accumulator are determined with the aid of a simulation model on the basis of input and output variables and on the basis of measured and / or calculated state variables. This can be concluded advantageous to a possible loss of operating medium.

A further preferred exemplary embodiment of the method is characterized in that a differentiation is made between a gas loss and a hydraulic medium loss on the basis of a system reaction. In this case, advantageously, the location at which the loss occurs can be limited. In particular, it can be determined whether there is a defect in one of the hydraulic accumulators.

A further preferred embodiment of the method is characterized in that the method is applied to a fluid system of a hydrostatic drive with at least one hydrostat to detect losses of operating medium, in particular to identify. The hydrostatic drive is, for example, a vehicle that is driven purely hydrostatically. However, it is particularly preferably a vehicle that includes the hydrostatic drive in addition to an internal combustion engine drive. Such a vehicle is also referred to as a hydraulic hybrid vehicle having a hydraulic hybrid powertrain.

A further preferred exemplary embodiment of the method is characterized in that the low-pressure accumulator, the high-pressure accumulator, the hydrostat and fluid lines of the fluid system are modeled with a non-linear state space model, wherein a hydraulic capacity of the hydraulic medium volume is determined continuously with the aid of an estimation algorithm. A state observer adds the model advantageous. Due to the model-based approach, the inventive method is very robust.

A further preferred embodiment of the method is characterized in that it is distinguished by means of a nominal value monitoring of the hydraulic capacity, whether a gas leak or a hydraulic medium leakage is present. A limitation at which the two memory gas loss occurs, can take place at standstill advantageous over a consideration of the isochoric state change of the gas.

A further preferred embodiment of the method is characterized in that a hydraulic medium leakage is identified, wherein the size and / or the location of the hydraulic medium leakage is / are determined with the aid of an estimation algorithm. In the following detailed description, five formulas are given and explained, which are advantageously used in carrying out the method according to the invention.

The invention further relates to a computer program product comprising a computer program having software means for performing a previously described method when the computer program is executed on a computer. The computer is, for example, a control unit that is integrated in a motor vehicle. The control unit is also referred to as an electrical control unit or electronic control unit.

The invention further relates to a control device with such a computer program product. The control unit is preferably installed in a motor vehicle. The motor vehicle is, in particular, a hydraulic hybrid vehicle with a hydraulic hybrid drive, to which the hydraulic system described above is assigned.

Further advantages, features and details of the invention will become apparent from the following description in which, with reference to the drawings, various embodiments are described in detail.

Short description of the drawing

Show it:

1 a simplified hydraulic circuit diagram of a hydrostatic drive according to the invention and the

2 to 4 Cartesian coordinate diagrams with progressions of different sizes over time to illustrate the method according to the invention.

In 1 is a hydrostatic drive 1 simplified represented in the form of a hydraulic circuit diagram. The hydrostatic drive 1 For example, it may be used in a hydraulic hybrid powertrain that includes a hydraulic drive in addition to an internal combustion engine drive.

The internal combustion engine drive is, for example, as an internal combustion engine 4 executed and is also referred to as internal combustion engine. The hydraulic drive comprises, for example, a hydrostatic drive 5 that is drivingly with the internal combustion engine 4 connected is.

The one by the internal combustion engine 4 driven hydrostat 5 includes a hydraulic pump, which is also abbreviated as a hydraulic pump. The hydrostat 5 is on the input side to a low pressure area 6 connected. On the output side is the hydrostat 5 to a high pressure area 7 connected.

The low pressure area 6 and the high pressure area 7 are part of a fluid system 8th , which is also referred to in operation with a hydraulic medium as a hydraulic system. The hydraulic medium is, for example, hydraulic oil, which is also abbreviated as oil. The hydraulic system 8th includes unspecified hydraulic lines and a valve block 9 ,

The hydrostatic drive 1 further comprises a total of four driven wheels 11 to 14 , Each of the driven wheels 11 to 14 is a hydrostat 21 to 24 assigned to the respective wheel hub of the driven wheel 11 to 14 is connected. Between the hydrostats 21 to 24 and the driven wheel 11 to 14 can be connected in each case a transmission.

The hydrostats 21 to 24 can be operated advantageously both as a hydraulic pump and as a hydraulic motor. The hydrostats 21 to 24 are also referred to as hydraulic machines and may for example be designed as hydraulic axial piston machines.

The low pressure area 6 includes a low pressure accumulator 30 with a gas volume or a gas side 31 and an oil side or an oil volume 32 , The oil side 32 the low-pressure accumulator 30 stands with the entrance of the hydrostat 5 in connection. The low pressure accumulator 30 represents a hydraulic medium reservoir, from which the hydraulic system 8th is supplied with hydraulic medium.

The high pressure area 7 includes a high pressure accumulator 40 with a gas volume or a gas side 41 and an oil side or an oil volume 42 , The oil side 42 the high-pressure accumulator 40 stands with the exit of the hydrostat 5 in connection. The oil side 42 the high-pressure accumulator 40 is also in the high pressure area 7 with the hydrostatics 21 to 24 in connection. The oil side 32 the low-pressure accumulator 30 is in the low pressure range 6 with the hydrostatics 21 to 24 in connection.

According to one aspect of the invention, a method is provided with which losses of the operating media of the hydrostatic drive 1 recorded, recognized and evaluated. The hydrostatic drive 1 also known as hydraulic drivetrain, which means hydraulic power train (HPT).

Advantageously comes a model-based monitoring of the oil volume 32 . 42 in low-pressure storage 30 and in high pressure storage 40 for use. A parallel running simulation model determines the oil volume based on the input and output as well as measured and calculated state variables 32 . 42 in the stores 30 . 40 , It can be concluded advantageous to a possible loss of operating media.

Based on the underlying physical relationships, it is possible to differentiate between a gas and an oil loss based on the system reaction. With the help of a subsequent parameter estimation the loss can be further quantified with sufficient accuracy and a decision about a possible endangerment of the environment can be made.

In the in 1 shown hydraulic hybrid system drives the internal combustion engine 4 via a fixed translation the hydraulic pump 5 at. The hydrostats 21 to 24 on the hubs can be operated both as a motor and as a pump. This makes it possible to recuperate braking energy of the vehicle.

mit:

ΔV_H/L

Öl-Volumen im Hoch-(Index H) bzw. Niederdruckspeicher (Index L)

p_min

Minimal zulässiger Betriebsdruck

V_min

Gas-Volumen bei p_min

p_H/L

Druck im Hoch-(Index H) bzw. Niederdruckspeicher (Index L)

κ

Adiabatenkoeffizient des Gases

For a suitable nonlinear state space model, the high and low pressure reservoirs were used 30 . 40 , the hydraulic lines, the hydraulic pumps and motors used 5 . 21 - 24 as well as the vehicle modeled. A condition observer completes the model. In the following, in particular, the physical processes in the hydraulic accumulators 30 . 40 received. Due to their high dynamics, charging and discharging processes in the HPT largely take place without releasing heat to the environment. Therefore, for the pressure-volume relationship in the hydraulic accumulators 30 . 40 be assumed by an adiabatic change in state of the gas. The volume of oil which flows into or out of the respective store during each charging or discharging process can be determined according to formula 1. This corresponds exactly to the gas volume, which is compressed or expanded.

With:

ΔV _{H / L}

Oil volume in high (index H) or low pressure storage (index L)

p _min

Minimum permissible operating pressure

V _min

Gas volume at p _min

p _{H / L}

Pressure in high (index H) or low pressure accumulator (index L)

κ

Adiabatic coefficient of the gas

The simulation model in combination with a state observer makes it possible, even with noisy measurement signals, to be able to make a reliable statement regarding the current oil volume in the storages. Also, unmodeled system dynamics or more complex physical relationships can be captured and considered.

For the detection of the loss of the operating media is a consideration of the oil volumes in the high and low pressure accumulator 40 . 30 crucial. Formula 2a: V _total = ΔV _H + ΔV _L

The _total oil volume V added, formula 2a, is almost constant in the error-free case. Small volume changes are due to the compressibility modulus of the fluid. Two different cases have to be considered.

In the first case that the oil flows out of the system as a result of a leak into the environment, a significant decrease in the volume V _total is expected.

At the same time, the pressure in the memories 30 . 40 lose weight. By means of the adiabatic pressure-volume relationship of Formula 1, a decrease of V _total can be determined from the decreasing pressures in the memories.

In the second case, however, that the gas escapes from the system as a result of a leak in the environment, on the other hand, is to expect no change in the oil volume. However, assuming that the gas leakage does not affect the volume and temperature of the system, a decreasing pressure in the reservoir can be expected. Furthermore, since an adiabatic pressure-volume relationship can be assumed during charge and discharge operations, the modeled _total also decreases in the event of gas leakage.

Consequently, based on the significant decrease in the _overall system volume V, loss of resources, oil and gas, into the environment can be reliably detected.

In both cases, the calculated volume decreases from the time of a leak. A distinction which escapes resources into the environment, is not possible with this consideration.

To determine which resource is lost to the environment, it is necessary to continuously calculate the hydraulic capacity.

For the determination of the hydraulic capacity C _hydr. , Formula 2b, an estimation algorithm (Recursive Least Squares, short RLS) is used. To improve the dynamics new measurements are weighted more. A change is detected faster. By means of a nominal value monitoring of the hydraulic capacity, a gas leakage can be reliably distinguished from an oil leakage.

A limitation at which the two memory gas loss occurs, can be done at a standstill on a consideration of the isochoric state change of the gas. In the error-free case, formula 3 must be fulfilled.

If this is not the case, the loss can be limited to the high or low pressure accumulator.

An example calculation to illustrate the magnitude is in the 2 and 3 shown: In the 2 and 3 the course of the relevant key figures for an oil and gas loss are described.

2 shows one above the other three Cartesian coordinate diagrams. In the uppermost coordinate diagram, the course of a calculated oil volume in the form of a volume balance over time is plotted. The mean coordinate diagram plots the time derivative of the volume balance over time. In the lowermost coordinate diagram, the hydraulic capacity, in particular the hydraulic system capacity, is plotted against loss of oil from a time of two hundred seconds over time.

In 3 the same curves are shown for a calculated gas volume.

The described effects are clearly visible. In both cases V decreases _overall . There is a leakage of about 0.3 liters from the time t = 200 sec recorded.

Considered a vehicle, which first accelerates evenly from 0km / h to 80km / h with fully loaded high-pressure accumulator.

Then it drives at a constant speed (not shown). Finally, the vehicle brakes evenly from 80km / h to 0km / h.

q_Gesamt

Zeitliche Änderung des addierten Öl-Volumens

p₀

Umgebungsdruck

k_{LE_H/L}

Leckage-Koeffizient auf Hoch-(Index H) bzw. Niederseite (Index L)

If it is possible to rule out a gas leakage of the system due to the hydraulic capacity determination, it is possible to identify the existing oil leakage. An RLS algorithm is also used for this. From the moment of detection of a loss of resources, the coefficients for identification k _{LE_H} and k _{LE_L} and limitation of the leakage are used by means of the RLS. For an oil leakage applies:

q _total

Time change of the added oil volume

p ₀

ambient pressure

k _{LE_H / L}

Leakage coefficient on high (index H) or low side (index L)

Using an RLS estimate, the parameters for the leakage can be determined. With the help of the parameters, a statement about the size and the location of the oil leakage can be made.

und der Lösungsvektor y = q_{Leckage_Gesamt}(k) benötigt.For the RLS algorithm, the parameter _vector Θ = [k _{LE_HP} k _{LE_LP} ] ^T , the measurement vector

and the solution vector y = q _{leakage_total} (k) is needed.

In 4 the course of the parameter estimation of the two coefficients of an oil loss from the time t = 100 sec is shown by way of example. It can be seen that the parameters approach a fixed value after a certain delay of the estimation algorithm. The actual value of 8.8e ^-8 is approached sufficiently accurately at the end of the considered time, so that an indication of the location and size of the leak can be made.

Claims (10)

Method for detecting a loss of operating medium in a fluid system ( 8th ), which has a low-pressure area ( 6 ) with a low pressure accumulator ( 30 ) and a high pressure area ( 7 ) with a high-pressure accumulator ( 40 ), characterized in that by considering a compressibility of fluid in the low-pressure region ( 6 ) and high-pressure fluid ( 7 ) detects a change in a total volume of fluid comprising hydraulic medium and gas. Method according to claim 1, characterized in that by considering the compressibility of the fluid in the low-pressure region ( 6 ) and the fluid in the high pressure area ( 7 ) between a hydraulic medium leakage and a gas leakage is distinguished, wherein a hydraulic medium volume in the low pressure region ( 6 ) and in the high pressure area ( 7 ) is monitored model-based. A method according to claim 2, characterized in that with a simulation model based on input and output variables as well as on the basis of measured and / or calculated state variables, the hydraulic medium volumes in the low pressure range ( 6 ) and in the high pressure area ( 7 ) be determined. Method according to one of the preceding claims, characterized in that a differentiated by a system reaction between a loss of gas and a hydraulic medium loss. Method according to one of the preceding claims, characterized in that the method on a fluid system ( 8th ) of a hydrostatic drive ( 1 ) with at least one hydrostat ( 5 . 21 - 24 ) is applied to detect losses of operating medium, in particular to identify. Method according to claim 5, characterized in that the low-pressure accumulator ( 30 ), the high-pressure accumulator ( 40 ), the hydrostat ( 5 . 21 - 24 ) and fluid lines of the fluid system ( 8th ) are modeled with a non-linear state space model, wherein a hydraulic capacity of the hydraulic medium volume is continuously determined by means of an estimation algorithm. A method according to claim 6, characterized in that it is distinguished by means of a nominal value monitoring of the hydraulic capacity, whether a gas leakage or a hydraulic medium leakage is present. A method according to claim 7, characterized in that a hydraulic medium leakage is identified, wherein the size and / or the location of the hydraulic medium leakage is determined by means of an estimation algorithm / is. A computer program product comprising a computer program having software means for performing a method according to any one of the preceding claims when the computer program is run on a computer. Control device with a computer program product according to claim 9.

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