DE102018213455A1 - Method for operating a direct current motor, electronic control module, compressor arrangement and air-sprung undercarriage - Google Patents

Abstract

The invention relates to a method for operating a direct current motor, a predetermined value being specified, an input voltage being applied to the direct current motor as a function of at least the specified value, an armature current being measured and the input voltage being adapted as a function of the armature current. The invention further relates to an associated control module, an associated compressor arrangement and an associated air-sprung chassis for a motor vehicle.

Description

The invention relates to a method for operating a direct current motor, an electronic control module for carrying out such a method, a compressor arrangement with such an electronic control module and an air-suspended chassis with such a compressor arrangement.

DC motors can be used, for example, to drive a compressor that provides compressed air for the compression springs of a chassis. In this way, for example, the vehicle in which the chassis is installed can be lowered or raised. For example, the DC motor can be a brush-commutated, permanently excited DC motor with an input voltage of 12 V, for example. Such is typically switched on and off electromechanically by an electronic control device, that is to say for example with a relay, electronically or for example with a field effect transistor. In contrast to a relay, an electrical switch not only enables the motor to be switched on and off, but also to control the output variably, for example by triggering the field effect transistor with pulse width modulation. An average voltage U _A at the motor can thus be influenced by the pulse duty factor of the pulse width modulation. Such pulse width modulation control of the motor is known in the prior art.

If a DC motor is used, for example, to actuate a compressor, it can happen that the compressor is operated under different pneumatic conditions. For example, the pre-pressure and counter-pressure can change.

This can result in different load torques for the driving motor. If the motor is controlled without feedback of operating variables such as torque, speed, current or electromotive force (EMF), the speed changes as a result of different load torques. Changes in the speed may be undesirable, for example due to a subjectively negative acoustics, and should be avoided by suitable control.

A typical solution would be a classic speed control, for example, in which the motor speed or an electromotive force of the motor proportional to it is measured and fed to a controller, for example a proportional-integral controller, together with a required target speed. The manipulated variable of the controller is then typically the pulse width ratio of the pulse width modulation. Such a regulation is state of the art. However, it has proven to be complicated for various requirements, since an expensive and complex speed sensor must be used, or alternatively the electromotive force is measured, which requires a partial interruption in the power supply to the motor and thus leads to undesirable short-term fluctuations in the current drawn from the vehicle electrical system ,

It is therefore an object of the invention to provide a method for operating a DC motor, which is embodied alternatively and works, for example, without the problems mentioned. It is also an object of the invention to provide an associated electronic control module, an associated compressor arrangement and an associated air-sprung undercarriage for a motor vehicle.

According to the invention, this is achieved by a method, an electronic control module, a compressor arrangement and an air-sprung undercarriage in accordance with the respective main claims. Advantageous refinements can be found, for example, in the respective subclaims. The content of the claims is made express reference to the content of the description.

• - Vorgeben eines Vorgabewerts,
• - Anlegen einer Eingangsspannung an den Gleichstrommotor in Abhängigkeit zumindest von dem Vorgabewert,
• - Messen eines Ankerstroms des Gleichstrommotors, und
• - Anpassen der Eingangsspannung in Abhängigkeit von dem Ankerstrom.

The invention relates to a method for operating a DC motor, the method comprising the following steps:

• - specifying a default value,
• Applying an input voltage to the DC motor as a function of at least the specified value,
• - measuring an armature current of the DC motor, and
• - Adjusting the input voltage depending on the armature current.

It has been found that the armature current is a quantity that can be measured easily and is suitable for regulating the DC motor in typical situations. There is no need to interrupt the operation.

The default value is typically a value which specifies a desired output, a desired torque or a desired speed of the motor. For example, the default value can be proportional to a desired speed.

The DC motor can drive a compressor or drive a compressor for vehicle air suspension. These are typical areas of application of a direct current motor which is operated by means of the method according to the invention and where the method according to the invention has proven to be particularly advantageous.

When adapting the input voltage, the input voltage is preferably adapted such that a load-related speed reduction is completely or partially compensated for in comparison to an idling speed assigned to the preset value. The load driven by the motor can thus be measured by means of the armature current and a corresponding compensation can be carried out so that the motor continues to drive the load taking into account the desired default value.

The default value can preferably be a voltage. This can easily be specified in a circuit.

When adapting the input voltage, the armature current is preferably multiplied by a multiplier and the result of this multiplication is preferably added to the preset value to produce a sum, the input voltage being generated based on the sum. The multiplier is preferably an internal resistance of the DC motor.

The armature current is further preferably low-pass filtered before the multiplication.

The input voltage is preferably generated by means of pulse width modulation depending on the sum. This has proven to be advantageous for typical applications. However, the input voltage can also be generated as a continuous voltage depending on the sum. It can also be generated with the value of the sum.

The sum is preferably subjected to an upper and / or lower limit before the input voltage is generated. This ensures that no input voltages are generated for the motor that are outside of its operating range.

The sum is further preferably subjected to a gradient limitation in the ascending and / or descending direction before the input voltage is generated. This prevents the input voltage from changing too quickly. A gradient means in particular the change in the input voltage over time. In particular, a gradient limitation in the increasing direction has proven to be advantageous, since the motor has a certain inertia with respect to its rotation and therefore it cannot immediately build up a sufficient electromotive force for partial compensation of the voltage if the voltage increases too quickly.

The DC motor is preferably not monitored by means of a speed sensor. In other words, there is no speed sensor. This enables a particularly simple and inexpensive design to be achieved.

The invention further relates to an electronic control module which is configured to carry out a method according to the invention. All versions and variants described here can be used. The advantages explained apply accordingly.

The invention further relates to a compressor arrangement with a compressor, a DC motor for driving the compressor and an electronic control module which is configured to carry out a method according to the invention. With regard to the method according to the invention, all the designs and variants described herein can be used. The advantages described above can be achieved for a compressor arrangement. In particular, a speed sensor can be dispensed with and effective control of the DC motor can be achieved.

The invention further relates to an air-sprung undercarriage for a motor vehicle, the undercarriage having a number of air springs and a compressor arrangement according to the invention, it being possible to use all of the designs and variants described herein with regard to the compressor arrangement. The compressor of the compressor arrangement is connected to the air springs for supplying compressed air to the air springs. This enables the advantages already described above to be achieved.

The air-sprung undercarriage can also have a pressure accumulator. In this case, the compressor can first be connected to the pressure accumulator, and the pressure accumulators can then be connected to the air springs. In principle, different variants are conceivable, it being possible, for example, to use an air spring system with an open air supply or a closed air supply.

• 1: ein luftgefedertes Fahrwerk,
• 2: ein Ersatzschaltbild eines Ankerstromkreises, und
• 3: ein Funktionsplan einer Steuerung eines Motors.

The person skilled in the art will obtain further features and advantages from the exemplary embodiment described below with reference to the attached drawing. Show:

• 1 : an air suspension chassis,
• 2 : an equivalent circuit diagram of an armature circuit, and
• 3 : a functional diagram of a control of an engine.

1 shows purely schematically an air suspension chassis 1 for a motor vehicle. The chassis 1 has a DC motor 10 , a compressor 20 as well as at least one air spring 30 on. These components are only shown schematically here.

DC motor 10 and compressor 20 are about a wave 15 connected with each other. To control the DC motor 10 is also an electronic control module 12 provided which is configured to carry out a method according to the invention. These components together form a compressor arrangement 2 ,

Bei typischen Anwendungen, welche hier betrachtet werden, kann diese Änderung des Stroms vernachlässigt werden, so dass die über der Induktivität abfallende Spannung ebenfalls vernachlässigt werden kann. 2 shows an equivalent circuit diagram of an armature winding of the DC motor 10 , Between two connection points A1 . A2 becomes an input voltage U _A created. This leads to an armature current I _A , The input voltage U _A split over an inductor L _A whose internal resistance R _A as well as the electromotive force U _EMK . The voltage drop across the inductance is proportional to the change in current $\frac{d{I}_A}{dt},$

In typical applications, which are considered here, this change in the current can be neglected, so that the voltage drop across the inductance can also be neglected.

A typical relationship between an angular velocity ω of the motor 10 and the electromotive force UEMK and an engine parameter k _M and a variable n, which corresponds to a speed in rpm, results as follows: $$\mathrm{\omega }=\frac{2\pi \text{n}}{60}=\frac{{\text{U}}_{\text{EMK}}}{{\text{k}}_{\text{M}}}$$

Ankerstrom I_A und Drehmoment M_i sind somit proportional.The torque of the engine 10 M _i results from the following formula: $${\text{M}}_{\text{i}}={\text{K}}_{\text{M}}\cdot {\text{I}}_{\text{A}}\Rightarrow {\text{M}}_{\text{i}}~{\text{I}}_{\text{A}}$$

armature current I _A and torque M _i are therefore proportional.

From the equivalent circuit diagram of 2 the following mesh equation results: $${\text{U}}_{\text{A}}={\text{L}}_{\text{A}}\cdot \frac{{\text{dI}}_{\text{A}}}{\text{dt}}+{\text{I}}_{\text{A}}\cdot {\text{R}}_{\text{A}}+{\text{U}}_{\text{EMK}}$$

Assuming that the armature current I _A the mesh equation can be simplified to the following formula: $${\text{U}}_{\text{A}}={\text{I}}_{\text{A}}\cdot {\text{R}}_{\text{A}}+{\text{U}}_{\text{EMK}}$$

On the left is the armature voltage at the motor terminals, on the right is a sum of the voltage drop at the armature resistance, which is proportional to the torque, and the electromotive force, which is proportional to the speed.

The aim now is to keep the electromotive force and thus the speed as constant as possible regardless of the load.

With increasing load torque or torque M _i the product of current and resistance becomes larger, which is why the armature voltage U _A should be increased by the same amount so that the speed and thus the electromotive force remain the same. A corresponding regulation is in 3 shown. In this context, a voltage U _REQ is first specified as part of a control function, which represents a specified value. This specifies the desired output or speed. The input voltage is via an adder, the further input of which will be described in more detail below U _A calculated for the engine, which in 3 is shown with the letter M. The input voltage U _A is first subjected to a limitation of the absolute value to ensure that the amount of the input voltage U _A is not greater than a maximum input voltage U _{A, max} . The maximum input voltage can be 13.5 V, for example. A minimum input voltage U _{A, min} can also be specified. Then the input voltage U _A subjected to a gradient limitation to ensure that the change over time is not greater than one with | dU _A / dt | _max is the maximum value that can be, for example, 40 V / s. Then the input voltage U _A a pulse width modulator PWM, which has an operating voltage U _B modulated so that the input voltage U _A is present on the motor M on average.

The armature current is then at the motor M. I _A measured and first fed to a low-pass filtering with a time constant T ₁ , wherein the time constant T _{1 can be,} for example, 1.5 s. The output of the low-pass filtering is with the value of the internal resistance R _A multiplied and the result as a correction voltage U _CORR the adder mentioned above for summation with the voltage value U _REQ fed. In this way, when the motor M reduces its speed due to the load, the input voltage becomes U _A increased, with exactly the value that is required to compensate for the load-related drop in speed.

The tension value U _REQ can be understood in particular as a default value of a desired electromotive force.

Due to the described embodiment, there is no need to measure the speed by means of a sensor. There is also no need to measure the electromotive force. An interruption in engine operation for measuring the electromotive force can thus be avoided. Only an electrical current measurement is carried out, for example by means of a shunt resistor and an AD converter.

It is also not necessary to adapt or parameterize a controller, such as a PI controller, to a controlled system. The necessary function parameters largely result from the engine parameters.

It should be mentioned that the parameters and other values mentioned here are only mentioned as examples and in principle other parameters or values can also be used.

Mentioned steps of the method according to the invention can be carried out in the order given. However, they can also be carried out in a different order if this makes technical sense. The method according to the invention can be carried out in one of its embodiments, for example with a specific combination of steps, in such a way that no further steps are carried out. In principle, however, further steps can also be carried out, even those that are not mentioned.

The claims belonging to the registration do not constitute a waiver of further protection.

If it emerges in the course of the method that a feature or a group of features is not absolutely necessary, the applicant is already attempting to formulate at least one independent claim which no longer has the feature or group of features. This can be, for example, a sub-combination of a claim existing on the filing date or a sub-combination of a claim existing on the filing date, which is restricted by further features. Such new claims or combinations of features are to be understood as being covered by the disclosure of this application.

It should also be pointed out that configurations, features and variants of the invention, which are described in the various designs or exemplary embodiments and / or shown in the figures, can be combined with one another as desired. Individual or multiple features can be interchanged with one another. Combinations of features resulting from this are to be understood as being covered by the disclosure of this application.

Back references in dependent claims are not to be understood as a waiver of the achievement of independent, objective protection for the characteristics of the back dependent claims. These features can also be combined with other features.

Features that are only disclosed in the description or features that are only disclosed in the description or in a claim in connection with other features can in principle be of independent importance of the invention. They can therefore also be included individually in order to differentiate them from the prior art.

Claims (15)

Method for operating a DC motor (10), the method comprising the following steps: - Specifying a default value (U _REQ ), - Applying an input voltage (U _A ) to the DC motor (10) depending on at least the default value (U _REQ ), - Measuring an armature current (I _A ) of the DC motor (10), and - Adjusting the input voltage (U _A ) depending on the armature current (I _A ). Procedure according to Claim 1 , - The DC motor (10) drives a compressor (20), or drives a compressor (20) for vehicle air suspension. Method according to one of the preceding claims, - wherein when adapting the input voltage (U _A ), the input voltage (U _A ) is adapted in such a way that a load-related speed reduction compared to an idle speed assigned to the default value (U _REQ ) is fully or partially compensated. Method according to one of the preceding claims, - wherein the default value (U _REQ ) is a voltage. Procedure according to Claim 4 , - When adjusting the input voltage (U _A ) the armature current (I _A ) is multiplied by a multiplier (R _A ) and the result of this multiplication is added to the default value (U _REQ ) to produce a sum, the input voltage (U _A) is generated based on the sum. Procedure according to Claim 5 , - wherein the multiplier (R _A ) is an internal resistance of the DC motor (10). Procedure according to one of the Claims 5 or 6 , - the armature current (I _A ) being low-pass filtered before the multiplication. Procedure according to one of the Claims 5 to 7 , - whereby the input voltage (U _A ) is generated by pulse width modulation depending on the sum. Procedure according to one of the Claims 5 to 7 , - whereby the input voltage (U _A ) is generated as a continuous voltage depending on the sum. Procedure according to one of the Claims 8 or 9 , - The sum before the generation of the input voltage (U _A ) is subjected to an upper and / or lower limit. Procedure according to one of the Claims 8 to 10 , - the sum being subjected to a gradient limitation in the ascending and / or descending direction before the generation of the input voltage (U _A ). Method according to one of the preceding claims, - The DC motor (10) is not monitored by means of a speed sensor. Electronic control module (12) which is configured to carry out a method according to one of the preceding claims. Compressor arrangement (2), comprising - a compressor (20), - a direct current motor (10) for driving the compressor (10), and - an electronic control module (12) which is configured to implement a method according to one of the Claims 1 to 12 perform. Air-sprung undercarriage (1) for a motor vehicle, the undercarriage (1) comprising: - a number of air springs (30), and - a compressor arrangement (2) according to Claim 14 , - The compressor (20) of the compressor arrangement (2) for supplying compressed air to the air springs (30) is connected to the air springs (30).

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