WO2021115647A1

WO2021115647A1 - Electrical orbiter vacuum pump having optimised control

Info

Publication number: WO2021115647A1
Application number: PCT/EP2020/075959
Authority: WO
Inventors: Conrad Nickel; Jakob Schnitzer; Franz Pawellek
Original assignee: Nidec Gpm Gmbh
Priority date: 2019-12-10
Filing date: 2020-09-17
Publication date: 2021-06-17
Also published as: DE102019133743A1

Abstract

The invention relates to an electrical orbiter vacuum pump having optimised control for cost-effectively improving the efficiency and acoustics. The orbiter vacuum pump is characterised in that, in order to compensate for angular speed changes of the eccentric piston (3) of the orbiter, the control device (10) is configured to control a drive torque of the electric motor (8) on the basis of an angular position of the rotor, which angular position is interpreted from a reactive electromotive force. The reactive electromotive force is detected by the control device (10), which results in sensor-free implementation of the improvement to the control.

Description

description

Electric orbiter vacuum pump with optimized control

The invention relates to an electric vacuum pump for gaseous media of the orbiter pump type with an optimized electromotive control.

Electric vacuum pumps are required in the automotive sector, for example, to generate and maintain a vacuum in a brake booster, or for the pneumatic adjustment of exhaust gas recirculation valves, exhaust flaps, guide vanes on turbochargers with variable turbine geometry, and a bypass for boost pressure control with a wastegate as well to operate a central locking system or to open and close headlight flaps. In plant engineering, vacuum pumps can generally be used to supply negative pressure to electropneumatic valves or pneumatic actuators.

Circulating displacement pumps, such as vane pumps or rotary vane pumps, which have a large number of working chambers, are widespread. The higher the number of working chambers on which the volume displaced during one revolution of the pump shaft is divided, the lower the pressure fluctuation in the delivery flow of the gaseous medium. More precisely, a pulsation of the delivery flow has a higher frequency, but a lower intensity, which is positively noticeable, for example, in a sensitive control of pneumatic actuators or in the acoustics of the operating noise.

V acuumpumps with a large number of working chambers generally have a comparatively complex structure or a correspondingly high number of movable and sealing components, such as, for example, blades mounted in a radially sliding manner. As a result, pump types of this type are associated with comparatively higher manufacturing costs for the components and assembly. Also are Corresponding pump structures with filigree, moving components are comparatively less robust and more susceptible to contamination in the gaseous pumping medium.

Furthermore, various types of rotary lobe pumps are known which are characterized by a simple and robust construction with a one-piece piston which executes an eccentric orbital movement in a cylindrical pump chamber. Such types of pumps can have few or only one working chamber.

DE 102015 010 846 A1 by the same applicant describes an orbiter vacuum pump whose structure of the pump assembly is similar to the structure of the pump assembly of the present invention.

In the case of a single working chamber, only a single volume displacement occurs during one revolution of the pump shaft. The pulsation of the delivery flow has a low frequency and a high intensity, which has a negative effect on an electromotive drive characteristic. Strictly speaking, the comparatively larger accumulated volume of the single working chamber increases a fluctuation in the required drive torque on the pump shaft. With a constantly applied drive torque, a negative and a positive acceleration of the piston occur cyclically during one revolution of the pump shaft, as a result of which the efficiency of the electrical drive power and the resulting acoustics of the operating noise deteriorate.

EP 1 519 046 B1 discloses a rotary lobe pump with a working chamber. The pump comprises a device for compensating for a speed deviation of a motor, more precisely for reducing a speed ripple due to a load characteristic, whereby vibrations and noise can also be reduced. One revolution of a rotor of the motor is divided into rotation sections in which a speed deviation is calculated. Based on the comparison, a controller outputs a current to compensate for the speed deviation. A position sensor is required for the technical implementation, which records the position of the rotor detected. There is a need for a similar improvement to the aforementioned Orbiter vacuum pump.

The object of the invention is to develop an electric orbiter vacuum pump in such a way that electromotive efficiency and acoustics are improved in a cost-effective manner.

This object is achieved by an electric orbiter vacuum pump with the features of the main claim of the present invention. The electric orbiter vacuum pump is characterized in particular by the fact that a control device of the orbiter vacuum pump is set up to compensate for changes in the angular velocity of the orbiter eccentric piston to regulate a drive torque of the electric motor based on an angular position of the rotor that is evaluated from a retroactive electromotive force .

The invention thus provides for the first time an electric orbiter vacuum pump which enables sensorless torque control in relation to the rotating displacement process.

It is essential to the invention that the opposite electromotive force or “back EMF” is recorded, evaluated and used as an input parameter of a torque control with regard to the orbiter battery pump. This makes it possible to implement an electromotive control on the drive side in response to the required dynamic torque of the displacement process on the pump side. It is provided according to the invention that the orbiter eccentric piston maintains a constant angular speed over one revolution of the shaft despite a fluctuation in a torque required for the displacement process.

According to the invention, depending on the detected retroactive electromotive force or back-EMF and an instantaneous angular position of the rotor evaluated therefrom, the control device controls the stator current, which sets the drive torque in relation to an angular position of the Rotor influences. A constant angular speed of the orbiter eccentric piston is therefore regulated based on sensorless detection.

This prevents a deceleration and an acceleration of the orbiter eccentric piston before and after a resistance to the gas displacement. As a result, vibrations in the electric drive are reduced, whereby an efficiency of the electric drive is improved. Furthermore, sound waves in the gaseous delivery flow are reduced, as a result of which the acoustics of the operating noise are improved.

According to the invention, these advantages are achieved without the need for a position encoder, i.e. sensor-based position detection of the motor rotor or the pump piston. Costs for a sensor and its orientation feature as well as installation effort, installation space and wiring of the sensor can be saved. Furthermore, the susceptibility to failure or failure safety of the system is improved by minimizing the hardware components, in particular the elimination of cables, plugs and sensitive electronic measuring circuits.

Advantageous further developments of the invention are the subject of the dependent claims.

According to one aspect of the invention, the control device can be set up to regulate the drive torque of the electric motor by a field-oriented regulation based on the angular position of the rotor evaluated from the retroactive electromotive force.

Due to the principle of field-oriented control (FOR) or field-oriented control (FOC), a stator and rotor field are always kept at right angles to one another. For this purpose, the stator currents are measured and adjusted in such a way that the angle between the rotor and stator flux is always 90 °, resulting in maximum torque and optimum efficiency. Furthermore, the field-oriented Regulation regulate the torque and the flux independently, which enables a fast, dynamic response to load fluctuations.

According to one aspect of the invention, the control device can have a temperature sensor that detects a temperature with respect to the control device; and the control device can be set up to regulate the drive torque of the electric motor at a constant speed as a function of a profile of the temperature detected by the temperature sensor.

With constant operating parameters of the electric drive, a more efficient control and a more inefficient control of a dynamic drive torque with regard to the maximum torque within one revolution of the shaft can be compared and qualitatively differentiated by the fact that the more efficient control results in less waste heat from electrical power loss and from the more inefficient regulation generates greater waste heat. This knowledge results in a further methodology for optimizing an efficient control, the implementation of which is based on a physical, directly measurable variable. In order to avoid thermal damage in the event of overheating, a temperature sensor for the function of an emergency shutdown is usually already available in standard versions of control devices with the mentioned application reference. Based on such standard designs, the existing hardware can also be used for the mentioned methodology to optimize the efficiency of the regulation, so that no additional components such as a sensor or wiring of a measuring circuit are required.

The invention is described below using an embodiment of an orbiter vacuum pump with reference to the accompanying drawing. In the drawing show:

1 shows a cross section through the pump chamber of an Orbiter V acuumpump, in which the regulation according to the invention is implemented; FIG. 2 shows an axial cross section through the orbiter vacuum pump according to the invention through the section line BB in FIG. 1.

As shown in FIGS. 1 and 2, the orbiter vacuum pump, driven by an electric motor, is formed from a pump housing 1 which comprises a pump chamber 2 with a cylindrical chamber wall, which is arranged in the pump housing 1 and is closed off by a pump cover. In the pump housing 1, a shaft 9 is rotatably mounted by means of a shaft bearing 11. An eccentric disk 12 with an eccentrically arranged crank pin is fixed on the shaft 9. The eccentric disk 12 engages with the crank pin in the center of a cylindrical orbiter eccentric piston 3 designed as a piston drum.

The eccentric disk 12 executes a rotary movement of the orbiter eccentric piston 3 through the pump chamber 2, a circumferential sliding contact of the orbiter eccentric piston 3 with the cylindrical chamber wall being maintained. In the orbiter eccentric piston 3, a guide slot 4 is arranged, which slidably receives a locking slide 5. The locking slide 5 is pivotably mounted at a free end in the chamber wall and extends through the pump chamber 2 to the orbiter eccentric piston 3. For this purpose, a pivot bearing 15 is arranged between an inlet opening 6 and an outlet opening 7 in the chamber wall. Depending on a position of the orbiter eccentric piston 3 on the orbital movement in the pump chamber 2, a section of the locking slide 5, which is opposite the pivotably mounted end, slides into and out of the guide slot 4. The pump chamber 2 is divided into two volumes on both sides of the locking slide 5, one of which communicates with the inlet opening 6 and one with the outlet opening 7.

The volumes on both sides of the locking slide 5 change with the circumferential sliding contact between the orbiter eccentric piston 3 and the cylindrical chamber wall in equal proportions in opposite directions, so that a cyclical displacement process within one revolution of the shaft 9 or one Orbital movement of the orbiter eccentric piston 3 is completed. In this case, a torque required for the displacement process increases during the orbital movement of the orbiter eccentric piston 3 during the increase in the volume communicating with the inlet 6 and drops abruptly when a maximum volume is reached. The illustration in FIG. 1 shows a position of the orbiter eccentric piston 3 shortly before top dead center, in which the volume of the pump chamber 2 communicating with the inlet 6 has reached an almost maximum volume and is then pushed out of the outlet 7.

The shaft 9 is driven by an electric motor 8 of the type of a brushless direct current motor or a BLDC motor. The rotor 14 of the electric motor 8 is equipped with permanent magnets. The stator 13 comprises stator coils for generating circumferentially rotating electrical fields, with which the rotor 14 rotates synchronously. For this purpose, the stator coils are controlled by a control device 10, which is connected to an electrical power supply and three phases of the stator 13.

The control device 10 of the orbiter vacuum pump is described in more detail below.

In order to drive the brushless electric motor 8, the control device 10 must commutate the power supply to the stator coils. The electronic commutation successively excites the stator coils, which generate a rotating electrical field which the rotor 14 with its permanent magnet follows. Efficient operation depends on correct timing at which the stator coils are energized. For this, however, the control device 10 requires information about the current position of the rotor 14, which in the present case is obtained without sensor support, such as a Hall sensor as a position encoder. For this purpose, a control method of the control device 10 determines the rotor position directly on the basis of current and voltage information recorded from the electric motor 8. When magnetic field lines of the permanent magnets on the rotor 14 intersect the stator coils, a voltage is also induced in the stator coils during operation according to the generator principle. This induced voltage has the same polarity as the applied operating voltage and counteracts an induced current of the rotor 14. It can be measured as the counter voltage occurring in current values at the stator coils and is referred to as the retroactive electromotive force or back EMF. The electromotive force, measured as the counter voltage in volts, generates a magnetic field in accordance with Lenz's law, which is opposite to the original change in the magnetic flux that causes the rotor 14 to rotate. In other words, the electromotive force opposes the rotation of the rotor 14 and is consequently referred to as a retroactive electromotive force or back EMF.

Due to the fixed number of windings and a constant magnetic flux in an electric motor 8, the magnitude of the retroactive electromotive force is proportional to the angular speed of the rotor 14. A specific parameter for the electric motor 8, a back EMF constant , can be used by the control device 10 to determine a speed of the electric motor 8 from the proportional ratio of the retroactive electromotive force.

A potential at a stator coil can be calculated by subtracting the retroactive electromotive force from the supply voltage. A resulting voltage, which results from a potential difference between the retroactive electromotive force and the supply voltage, causes a current flow that is referred to as the rated current. When the electric motor 8 runs at a nominal speed when the nominal current is supplied, the electric motor 8 generates a nominal torque. With no sensor support, the control method of the control device 10 uses directly recorded current and voltage information from the electric motor 8 to determine a change in the angular position or angular speed, which is also used for speed control. The control device 10 controls the current, which influences the drive torque in relation to an angular position of the rotor 14 of the electric motor 8, as a function of the variables mentioned. More precisely, the control modifies a pulse width modulation, which is indicative of an intermittently supplied electrical power to each stator coil, and its timing in relation to an angular position of the rotor 14, which is based on the previously described sensorless detection of the retroactive electromotive force or counter -EMK is determined to the effect that a constant angular velocity of the orbiter eccentric piston 3 is sought. As a result, the orbiter eccentric piston 3 maintains an essentially constant angular speed within one revolution of the shaft 9 despite a fluctuation in a torque of the displacement process required for the displacement process.

According to the principle of field-oriented control (FOR) or field-oriented control (FOC), stator currents are measured and adjusted so that the angle between rotor and stator flux is always 90. As long as a resulting stator and rotor field are always held at right angles to one another, a maximum torque can be achieved, which is synonymous with an optimal degree of efficiency. Furthermore, the field-oriented control enables a fast dynamic response behavior of the torque to load fluctuations, which has a positive effect in particular in the present application as a vacuum pump, as will be explained below.

This is because during an evacuation the dynamics of a load fluctuation increases with the ongoing operating time, since with decreasing pressure in a gas volume to be evacuated, a maximum torque required for the displacement process increases within one revolution of the shaft 9. For the orbiter vacuum pump according to the invention, the sensorless control method together with a field-oriented regulation offers a preferred implementation of the control and regulation technology for the effective suppression of a ripple in the angular velocity of the orbiter eccentric piston 3. Apart from the field-oriented regulation (FOR), the control device 10 carries out a further method for optimizing the regulation during an operating period with relatively constant operating parameters. For this purpose, a temperature profile is included which is related to electronics of control device 10, in particular power electronics for controlling the stator currents from an electrical power supply.

After reaching an operating temperature at an operating point with constant operating parameters, such as in particular the speed and the pressure difference of the delivery flow upstream and downstream of the vacuum pump, a curve of comparative values of waste heat from electrical power loss on capacitors, transistors or the like in a control circuit can be used Draw conclusions with a qualitative evaluation of the electromotive efficiency of a control that can be assigned to the comparison values over time.

Accordingly, the control device 10 is able to optimize the efficiency of the regulation of the dynamic drive torque at a constant operating point of the electric motor 8, taking into account a temperature profile which is detected by means of a temperature sensor (not shown) in the vicinity of power electronics or the like in the control device 10 . For this purpose, variable parameters of the control, in particular values of the stator currents depending on an angular position of the rotor 14 or a timing, in feedback to an observed increase or decrease in the recorded temperature, as well as a slope of the temporal temperature change, are varied so that the lowest constant achievable temperature results from the regulation.

The described preferred embodiment of the invention includes both the feature of a field-oriented control (FOR) and the feature of a thermally controlled methodology for optimizing the electromotive control. In alternative embodiments of the invention, the orbiter vacuum pump can also be equipped without one of these features or without both features. For example, instead of the field-oriented control (FOR), another control, such as known principles of so-called vector-related controls for controlling brushless electric motors 8, can be implemented, as long as this is a suitable connecting control element between the sensorless detection and evaluation of a rotor position based on the retroactive electromotive force (counter -EMK) and a torque control to achieve an essentially continuous angular velocity of the orbiter eccentric piston 3. Likewise, in an alternative embodiment, optimization of the regulation taking into account the temperature in the control device 10 can be dispensed with.

List of reference symbols:

1 pump housing

2 pump chamber

3 orbiter eccentric pistons

4 guide slot

5 locking slide

6 inlet

7 outlet

8 electric motor

9 wave

10 control device

11 shaft bearings

12 eccentric disc with crank pin

13 stator

14 rotor

15 pivot bearings

Claims

Expectations

1. Orbiter electric vacuum pump, comprising: a pump housing (1) with a cylindrical pump chamber (2); an orbiter eccentric piston (3) with a guide slot (4) and a cylindrical outer surface, a cylindrical cross section of the orbiter eccentric piston (3) being smaller than a cylindrical cross section of the pump chamber (2); a locking slide (5) which is received in the guide slot (4), one end of the locking slide (5) being pivotably mounted on the pump housing (1) between an inlet (6) and an outlet (7); a brushless permanent magnet electric motor (8) with a stator (13) and a rotor (14) for driving the orbiter eccentric piston (3) via a shaft (9); and a control device (10) for controlling the electric motor (8) from an electrical power supply, the control device (10) being set up to detect a retroactive electromotive force from a voltage of a stator current; characterized in that the control device (10) is set up to compensate for changes in the angular velocity of the orbiter eccentric piston (3) to regulate a drive torque of the electric motor (8) based on an angular position of the rotor (14) evaluated from the retroactive electromotive force.

2. Electric orbiter vacuum pump according to claim 1, wherein the control device (10) is configured to regulate the drive torque of the electric motor (8) by a field-oriented control based on the angular position of the rotor (14) evaluated from the retroactive electromotive force.

3. Electric Orbiter- V acuumpump according to claim 1 or 2, wherein the control device (10) comprises a temperature sensor which detects a temperature with respect to the control device (10); and the control device (10) is set up to control the

To regulate the drive torque of the electric motor (8) as a function of a profile of the temperature detected by the temperature sensor.