WO2015082189A1

WO2015082189A1 - Method and system for determining parameters of a hydrostatic vehicle drive, which vary over time

Info

Publication number: WO2015082189A1
Application number: PCT/EP2014/074524
Authority: WO
Inventors: Adrian Trachte; Alexandre Wagner; Daniel Seiler-Thull; Carolina Passenberg
Original assignee: Robert Bosch Gmbh
Priority date: 2013-12-04
Filing date: 2014-11-13
Publication date: 2015-06-11
Also published as: DE102013224823A1; CN105960553A

Abstract

The invention relates to a method for determining parameters of a hydrostatic vehicle drive, which vary over time, said hydrostatic vehicle drive comprising at least one primary-side (1) and at least one secondary-side (2) hydrostat. In order to simplify and/or improve the operation of a hydrostatic vehicle drive, the parameters are identified during the operation of the hydrostatic vehicle drive.

Description

description

title

Method and system for determining time-variable parameters of a hydrostatic drive

The invention relates to a method and a system for determining parameters of a hydrostatic travel drive that vary with time, comprising at least one primary-side and at least one secondary-side hydrostatic drive.

State of the art

For a hydrostatic drive, for example, a primary-side axial piston machine and a secondary-side axial piston machine are connected in series. In axial piston machines in swash plate design can be adjusted via an adjustment of the swivel angle of the swash plate of the flow rate. Therefore, such an axial piston machine is also referred to as an adjusting machine. Depending on whether the axial piston machine works as a pump or as an engine, it is also referred to as a variable displacement pump or an adjustment motor. The example driven by an internal combustion engine primary-side axial piston machine, when working as a pump, in particular variable displacement, converts on a drive side mechanical into hydraulic energy. On a driven side, the secondary-side axial piston machine converts, if it works as a motor, in particular as Versteilmotor, hydraulic see mechanical energy. The process can also be reversed, so that is braked by the secondary-side axial piston engine on the output side. The interconnection of the primary-side axial piston machine and the secondary-side axial piston machine can take place both in an open circuit, the low-pressure sides of the two axial piston machines being connected to a pressure-balanced tank, and in a closed circuit, the low-pressure sides of the axial piston machines being directly involved. are connected to each other. Both circuits can be protected by pressure relief valves against excessive pressures. In operation, the primary-side axial piston machine and the secondary-side axial piston machine are adjusted either separately or in a coupled manner.

Disclosure of the invention

The object of the invention is to simplify and / or to improve the operation of a hydrostatic travel drive which comprises at least one primary-side and at least one secondary-side hydrostatic drive.

The object is achieved in a method for determining parameters of a hydrostatic travel drive which vary over time, which comprises at least one primary-side and at least one secondary-side hydrostatic drive, in that the parameters during operation of the hydrostatic drive are identified. For a dynamic driving behavior of the hydrostatic drive, for example, a secondary-side output torque is specified and regulated. As manipulated variables, when using axial piston units of swashplate design, the pivoting angles of the primary side and the secondary side are available as hydrostatic drives. For this purpose, a model-based pressure control can be used. Due to, for example, air bubbles and temperature changes as well as aging effects, parameters such as a compression modulus and the leakage of a hydraulic system of the hydrostatic drive are subject to considerable fluctuations. In order to guarantee a good performance of the pressure control in all operating points, the time-variable parameters during operation or during the term of the hydrostatic drive are identified according to one aspect of the invention. The quantities or parameters may then be provided, for example, to a model-based control or used for monitoring and diagnostics. In principle, the method is also applicable to systems that have more than one on the primary side and / or the secondary side

Hydrostates include, for example, two or more secondary sides

Hydrostats.

A preferred embodiment of the method is characterized in that a compression module of a hydraulic medium and / or a Le ckage a hydraulic system of the hydrostatic drive in operation are identified. Alternatively or additionally, further parameters, in particular physical variables, can be identified. A further preferred exemplary embodiment of the method is characterized in that volume flows over the primary-side and the secondary-side hydrostat are described on the basis of a displacement volume, a rotational speed and a standardized pivoting angle. For example, the volume of hydraulic fluid that displaces one hydraulic machine per revolution is referred to as displacement volume. The number of revolutions per unit time is called the speed. The term swivel angle refers to a swivel cradle or swash plate, which serves in an axial piston machine to adjust the flow rate.

A further preferred embodiment of the method is characterized in that control flow rates are determined by geometries of hydraulic adjusting devices. The control flow rates can be calculated in a simple manner, for example, via the geometry of an adjusting cylinder and / or a counter-cylinder.

A further preferred embodiment of the method is characterized in that the identified parameters are confirmed by a plausibility instance. In a plausibility check, it can be verified, for example by comparison with stored or stored parameter values, whether the currently identified parameters can be correct.

A further preferred exemplary embodiment of the method is characterized in that the identified parameters are used in a model-based pressure regulation in order to adaptively regulate an output torque of the secondary-side hydrostatic drive. By using the identified parameters in the model-based pressure control, the pressure and thus also the output torque on the secondary side can advantageously be regulated independently of environmental influences, tolerances and aging effects. The model-based pressure control comprises, for example, a pilot control and a control loop. A further preferred embodiment of the method is characterized in that the model for the pressure control is calibrated with a pressure measurement. In the pressure measurement, for example, measured values of at least one pressure sensor are detected.

A further preferred embodiment of the method is characterized in that the identified parameters are used for diagnostic purposes. Alternatively or additionally, the identified parameters can be used for other purposes.

The above object is achieved in a system for controlling a pressure of a hydrostatic drive comprising at least one primary side and at least one secondary side hydrostatic, alternatively or additionally solved by the fact that time-variable parameters are identified during operation of the hydrostatic drive, in particular according to a previously described Method.

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.

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

The sole accompanying figure shows a hydraulic equivalent circuit diagram for a hydrostatic drive, which comprises a primary-side and a secondary-side hydrostatic.

Description of the embodiments

In the single accompanying figure, a hydrostatic drive in the form of a hydraulic circuit diagram is shown simplified. The hydrostatic drive includes a primary side hydrostatic 1 and a secondary side

Hydrostat 2. The two hydrostats 1 and 2 are designed as hydraulic machines, in particular as axial piston machine in swash plate design with a swash plate, which is also referred to as a swivel cradle.

A swivel angle of the swash plate or swivel cradle can be changed in order to adjust a delivery volume flow of the hydraulic machine or of the hydrostatic drive. Therefore, the hydraulic machines are also referred to as adjusting machines. Depending on its function, the hydraulic machine 1 is also referred to as a variable displacement pump. Similarly, the hydraulic machine 2 is also referred to as Versteilmotor.

The left side in Figure 1 with the primary side hydrostatic 1 is shortened referred to as the primary side 1. Similarly, the right side in Figure 1 with the secondary side hydrostatic 2 is also referred to as the secondary side 2. The primary-side hydrostat 1 is shortened also referred to as primary unit. Analogously, the secondary-side hydrostat 2 is also referred to as a secondary unit.

The two hydraulic units 1 and 2 designed as hydraulic machines are connected on the input side to a low-pressure region 4. On the output side, the two hydrostats 1 and 2 are connected to a high pressure area. The low-pressure region 4 comprises a pressure-compensated hydraulic medium of the reservoir 6, which is also referred to as low-pressure accumulator. The hydraulic medium is, for example, hydraulic oil.

By a circle 10 in the high-pressure region 5, a connection volume is indicated, which connects the output side of the hydraulic machine 1 with the output side of the hydraulic machine 2. Since the connection volume 10 is in the high pressure region 5, it is a high pressure volume.

For the recuperation of braking energy and the operation in an energy-optimal state, a hydraulic accumulator is advantageously arranged in the high-pressure region 5, which is also referred to as high-pressure accumulator. In this operating state, which is also referred to as Rekuperationszustand, however, the pressure on the high pressure side is directly coupled to the level of the hydraulic accumulator and changes only relatively slowly. So that the mechanical power on the primary side can be transmitted as directly as possible to the secondary side, the hydraulic accumulator is decoupled. There then remains the subsystem shown in the accompanying figure, which can be identified with the inventive method during runtime.

The pressure, and thus also the output torque on the secondary side, can be regulated via a model-based controller using the identified parameters independently of environmental influences, tolerances and aging effects, as will also be explained in more detail below.

By an arrow 1 1, a high-pressure line is indicated, which connects the output of the primary-side hydraulic machine 1 with the high-pressure volume or connection volume 10. By an arrow 12, a further hydraulic line is indicated, which connects the output of the secondary-side hydraulic machine 2 with the high-pressure volume or connection volume 10.

A low-pressure line 13 connects the input of the primary-side hydraulic machine 1 with the hydraulic medium reservoir 6. A low-pressure line 14 connects the input of the secondary-side hydraulic machine 2 with the hydraulic medium reservoir 6. A connecting line 16 with a hydraulic resistance 18 connects the low-pressure region 4 with the high-pressure volume or volume 10. Bei the connection volume 10 is not a real connection line, but an equivalent circuit diagram for a connection, which can be realized for example with the aid of sealing gaps or sealing gaps between high pressure and low pressure.

To illustrate the hydrostatic drive in Figure 1, the primary variable displacement pump 1 and the secondary Versteilmotor 2 are connected in series. The primary unit 1, for example driven by an internal combustion engine, converts mechanical into hydraulic energy. Therefore, the primary side 1 is also called the drive side. The secondary unit 2 converts hydraulic to mechanical energy on the output side. The process can also be reversed, so that is braked by the secondary unit 2 in the recuperation described above on the output side. According to one aspect of the invention, the pressure buildup in the volume 10 between the primary and secondary units is described via a model. The model is calibrated with a pressure measurement to identify the parameters of the modulus of compression and leakage that are slowly changing in the model. The parameters are identified online using a parameter identification method, such as a recursive least-squares (RLS) filter. The estimated parameters are then used in a model-based regulator for pressure control.

For the identification of the unknown parameters, a model for the pressure build-up p point in the connection volume V between primary and secondary unit is needed. For example, this might look like this:

With the compression modulus β, the sum of all known volume flows q, the leakage coefficient with laminar flow /, and the

Leakage coefficients with turbulent flow k _t and the pressure difference between high and low pressure sides Δρ = p - p _ND . In this case, equation (1) is to be understood only as an example; any further empirically motivated terms for the leakage, for example as a function of the pressure, can also be taken into account. With the variable q all known volume flows in and out of the volume V are considered. These are essentially the volume flows of the primary and secondary unit q-ι and q _2, but qi, other volume flows as the control oil flow rates required for the adjustment of the hydrostatic _st and q _{2, st} - A possible calculation of q might look as follows:

Q = fi + Gi _f st + + <? 2, st

The description of the volume flows via primary and secondary unit (s) can be described on the basis of the displacement volume c _qi, the speed ω, and the normalized swivel angle α, - for the ith machine Alternatively, the volume streams can also maps q, = q _(ω ί, _α, ...) are described. The control oil flow rates required to adjust the units can be easily calculated using the geometry of the adjustment and counter cylinders and the normalized tilt angle α.

The following is based on a model approach as defined in equation (1). It should be noted, however, that the approach described below is valid for any model structure that can be transformed into equation (7). Equation (1) can be solved for q and written as a vector product.

If we now take measurement records for q with n-measuring points, the result is the following linear system of equations

Θ

γΤ which can be resolved after the parameter vector Θ

U = Y ^T 0 = Θ = (YY ^T ) ^"l YU. This has translated the problem into a general form for which there are several possible solutions.

In order not to have to store n past measured values for the calculation of equation (7) during runtime and to avoid the partially poorly conditioned matrix inversion, the solution of equation (7) can also be formulated recursively. One possible implementation is described below

T

lik

rp

T

^• « ^• k öt_i H ek.

7k

Where 0 <λ <1 is the forgetting factor and P is the covariance matrix. For initialization, suitable initial values for P ₀ and θ _{0 must be} selected. Through a suitable choice of the Vergessensfaktors also speed influences can be compensated for the leakage, so that meaningful mean leakage coefficients are estimated by the method even at very low speeds.

The combination of this online-enabled parameter identification and a model-based pressure control, for example consisting of pilot control and a control loop, represents an adaptive model-based pressure control. In particular, the identified parameters of the feedforward control and the controller are transferred. When designing model-based pressure control, it must be taken into account that the expected parameter fluctuations in all operating states lead to the desired control behavior, in particular stability. The identified parameters can first be confirmed by a plausibility check. The adaptive pressure control function may be determined by considering the pressure history at different operating conditions affecting the system's leakage and replacement compression modulus.

The method can be applied to hydraulic power transmission hydraulic drives as generally shown in the accompanying figure. This is the case, for example, in a hydraulic hybrid drive, in which at least part of the power is transmitted via a hydraulic path.

Claims

claims

1 . Method for determining parameters which vary with time

Hydrostatic drive, which comprises at least one primary side (1) and at least one secondary side (2) Hydrostaten, characterized in that the parameters are identified during operation of the hydrostatic drive.

2. The method according to claim 1, characterized in that a compression module of a hydraulic medium and / or a leakage of a hydraulic system of the hydrostatic drive are identified during operation.

3. The method according to any one of the preceding claims, characterized in that volume flows are described on the primary side and the secondary side hydrostatic on the basis of a displacement volume, a speed and a normalized pivot angle.

4. The method according to any one of the preceding claims, characterized in that control flow rates are determined by geometries of hydraulic adjusting devices.

5. The method according to any one of the preceding claims, characterized in that the identified parameters are confirmed by a plausibility instance.

6. The method according to any one of the preceding claims, characterized in that the identified parameters are used in a model based on a pressure control to adaptively control an output torque of the secondary side hydrostatic.

7. The method according to claim 6, characterized in that the model for the pressure control is calibrated with a pressure measurement.

8. The method according to any one of the preceding claims, characterized in that the identified parameters are used for diagnostic purposes.

9. A system for controlling a pressure of a hydrostatic drive comprising at least one primary side (1) and at least one secondary side (2) Hydrostat, characterized in that time-varying parameters are identified during operation of the hydrostatic drive, in particular according to a method according to one of previous claims.

A computer program product comprising a computer program comprising software means for performing a method according to any one of claims 1 to 8 when the computer program is run on a computer.