Control method and control unit for a DC pump motor

Abstract

A method for controlling a DC pump motor, preferably a brushed DC motor for pumping lubricant, which motor is controlled by a pulse-width modulated (PWM) control signal, wherein current parameters are acquired in an acquisition step and a duty cycle (D) of the PWM control signal (S.sub.PWM) is adapted and/or changed on the basis of the detected parameters in an adaptation step, wherein the acquisition of current parameters comprises at least the acquisition of a current input voltage (U.sub.B).

Claims

1. Method for controlling a DC pump motor by a pulse-width modulated (PWM) control signal, wherein current parameters are acquired in an acquisition step, and a duty cycle (D) of the PWM control signal (S.sub.PWM) is adapted and/or changed with the aid of the acquired parameters in an adaptation step, the acquisition of current parameters comprising at least the acquisition of a current input voltage (U.sub.B), wherein the acquisition of current parameters further comprises the acquisition of a motor current (I.sub.m) of the DC pump motor and/or of an outside temperature (T.sub.A), wherein the parameter acquisition units have at least one input voltage sensor for acquiring an input voltage and one or more of the following sensors: a motor current sensor for detecting a motor current of the DC pump motor; and an outside temperature sensor for acquiring an outside temperature, wherein the current parameters comprises an input voltage (U.sub.B) and the motor current (I.sub.m) of the DC pump motor, and an external temperature (T.sub.A).

2. Method according to claim 1, wherein in the adaptation step the duty cycle (D) of the PWM control signal is adapted independently of the input voltage (U.sub.B) if the input voltage (U.sub.B) acquired in the acquisition step falls below a lower threshold value (U.sub.Schw).

3. Method according to claim 1, wherein in the adaptation step the duty cycle (D) of the PWM control signal is adapted in such a way that a substantially identical rotational speed (UN) of the direct-current pump motor, which speed is predetermined as constant, is achieved.

4. Method according to claim 3, wherein the adaptation of the duty cycle (D) of the PWM control signal is carried out in order to achieve an at least substantially constant rotational speed without recourse to the measured values of a rotational speed sensor.

5. Method according to claim 1, wherein the acquisition step can take place in an event-controlled manner at irregular intervals and/or at cyclic intervals.

6. Method according to claim 1, wherein in the adaptation step the duty cycle (D) is set to a value from zero to one in accordance with a predetermined formula as a function of the detected input voltage (U.sub.B) and the optionally acquired outside temperature (T.sub.A), as well as the optionally acquired motor current (I.sub.m) of the DC pump motor, wherein the values zero and one are included in particular.

7. Method according to claim 1, wherein, in the acquisition step, a rotational speed (n) of the DC pump motor is detected by a rotational speed sensor, and wherein in the adaptation step the duty cycle (D) of the PWM control signal (S.sub.PWM) is adapted such that an at least substantially constant rotational speed of the DC pump motor is achieved.

8. Method according to claim 7, wherein, when the method is applied in a pump element for pumping lubricant from a lubricant reservoir, a pumping quantity of the pump element is determined from a pump stroke and the substantially constant rotational speed of the DC pump motor.

9. Method according to claim 8, wherein a filling level of the lubricant reservoir is determined on the basis of the pumping quantity of the pump element.

10. Control unit for controlling a DC pump motor, wherein the control unit is controlled according to the method according to claim 1 and has the following: a DC pump motor which is designed in particular as a brushed DC motor; one or more switching element(s); and a control module adapted to switch the switching element(s) into a conductive or a non-conductive state; wherein the drive unit further comprises parameter acquisition units adapted to acquire current parameters and wherein the switching element(s) are switched by the control module such that the DC pump motor is controlled by a pulse-width modulated (PWM) control signal (S.sub.PWM), wherein a duty cycle (D) of the PWM control signal (S.sub.PWM) is adapted and/or changed on the basis of the detected current parameters, wherein the parameter acquisition units have at least one input voltage sensor for acquiring an input voltage and preferably one or more of the following sensors: a motor current sensor for detecting a motor current of the DC pump motor; and preferably an outside temperature sensor for acquiring an outside temperature, wherein the current parameters comprises an input voltage (U.sub.B) and the motor current (I.sub.m) of the DC pump motor, and preferably an external temperature (T.sub.A).

11. Control unit (1) according to claim 10, wherein the PWM control signal (S.sub.PWM) is adapted as a function of one or more parameters acquired by the parameter acquisition units, preferably without recourse to measured values of a rotational speed sensor, in such a way that an at least substantially constant rotational speed of the DC pump motor is achieved.

12. Control unit according to claim 10, which further has no rotational speed sensor or does not interact with any rotational speed sensor.

13. Control unit according to claim 10, which further comprises a rotational speed sensor which detects the rotational speed of the DC pump motor, wherein the PWM control signal (S.sub.PWM) is adapted such that an at least substantially constant rotational speed of the DC pump motor is achieved.

14. Control unit according to claim 10, wherein the control unit, if the control unit is integrated in a pump element for pumping lubricant from a lubricant reservoir, is adapted to determine a pumping quantity of the pump element on the basis of a pump stroke and the substantially constant rotational speed of the DC pump motor.

15. Pump system comprising the following: a pump element operated with a DC pump motor; the DC pump motor, which is preferably designed as a brushed DC motor; a lubricant reservoir to which the pump element is connected; a control unit according to claim 10 for controlling the DC pump motor; and a display for displaying a filling level of the lubricant reservoir determined by the control unit.

16. Method for calibrating a control unit according to claim 10, wherein initial parameters, such as a stored formula for determining the duty cycle (D) of the PWM control signal (S.sub.PWM), and preferably a pump stroke value, are provided by the manufacturer, and wherein the initial parameters are calibrated by means of test measurements in a plurality of calibration steps under specific conditions.

17. Method according to claim 16, comprising the following calibration steps: applying certain calibration voltages to the control unit; controlling the DC pump motor with the control unit; performing test measurements by determining an actual rotational speed under a predetermined load; comparing the actual rotational speed with a target rotational speed to be reached under the predetermined load; and adjusting the initial parameters so that the actual rotational speed and the target rotational speed match.

18. Method for controlling a DC pump motor according to claim 1, wherein the DC pump motor is a brushed DC motor for pumping lubricant.

19. Control unit (-) according to claim 10, wherein a filling level of the lubricant reservoir is determined on the basis of the pumping quantity of the pump element.

Description

(1) In the following, the disclosure is described by reference to embodiment examples, which are explained in more detail using the figures, wherein:

(2) FIG. 1 shows a circuit diagram of a first embodiment of the control unit according to the disclosure;

(3) FIG. 2A shows a signal characteristic of an embodiment of the control unit according to the disclosure;

(4) FIG. 2B a signal characteristic of a further embodiment of the control unit according to the disclosure;

(5) FIG. 3 shows a cross-sectional view of a pump system according to the disclosure, and

(6) FIG. 4 shows a sequence diagram of the steps of an embodiment of the method according to the disclosure for controlling a DC pump motor.

(7) FIG. 1 shows a circuit diagram of a first embodiment of the control unit 1 according to the disclosure. The control unit has a control module 20 which controls the DC pump motor 4 with a PWM control signal S.sub.PWM. In this embodiment example, control unit 1 has two switching elements 23 which are connected in series and controlled by control module 20. The switching elements 23 essentially function as switches and can be designed as bipolar transistors or metal oxide semiconductor field effect transistors (MOSFET), for example, or optionally as insulated gate bipolar transistors (IGBT). The DC pump motor 4 is supplied with a voltage u(t) which is applied above the upper switching element 23, i.e. applied to the PWM control signal S.sub.PWM. In addition, the motor current I.sub.m is measured with the motor current sensor 22. The measured motor current I.sub.m is passed on to the control module 20. Furthermore, in FIG. 1, a smoothing capacitor 24 is electrically connected to a connection of the DC pump motor 4 (the positive connection) and ground to smooth the PWM control signal S.sub.PWM.

(8) In addition, the circuit diagram illustrated in FIG. 1 shows an input voltage sensor 21, to which an input voltage U.sub.B, which can also be referred to as operating voltage, is applied. The input voltage sensor 21 measures the applied input voltage U.sub.B and transmits the measured value of the input voltage U.sub.B to the control module 20. The input voltage U.sub.B is passed directly (unchanged) to the series connection of the switching elements 23. The illustrated embodiment example is implemented as a 2-quadrant actuator, but it is also possible to realize control unit 1 as a 1-quadrant actuator (with only one switching element 23 and one diode instead of the upper switching element 23) or as a 4-quadrant actuator (with a total of four switching elements 23, which together with the DC pump motor form an H-bridge circuit) according to the disclosure.

(9) It is also possible that the control unit, consisting of the control module 20, the input voltage sensor 21, the motor current sensor 22, the switching elements 23, the smoothing capacitor 24 and/or the outside temperature sensor 3, is realized in particular on a circuit board.

(10) In addition, an outside temperature sensor 3 is shown in FIG. 1. The outside temperature sensor 3 supplies a temperature value T.sub.A, which is transmitted directly to the control module 20. Depending on the embodiment example, the outside temperature sensor 3 can be mounted on a housing of the control unit or integrated in the housing. It would also be possible that the outside temperature sensor 3 is arranged in a lubricant reservoir (not shown in FIG. 1) if this is present in the pump system in which the control unit 1 is integrated.

(11) The control unit 1 can preferably have a memory (not shown) to which initial parameters, such as the stored formula for determining the duty cycle of the PWM control signal, and preferably a pump stroke value or different routines for certain operating modes, can be stored.

(12) In addition, FIG. 1 shows a display 5, which makes it possible to display information that is important for the operation of the electric pump. For example, information available to control module 20 may be displayed on display 5. This information can include the current parameters, such as the input voltage, the motor current I.sub.m, or the outside temperature T.sub.A, or it can conversely include additional information, such as the speed of the DC pump motor, the pumping quantity, the pump stroke, or the level of the lubricant reservoir. It would also be conceivable that display 5 could also display several pieces of information at the same time in order to provide as much clarity as possible. Furthermore, it would also be conceivable that an input unit (not illustrated) could communicate with control unit 1 (e.g. via cable or wireless), so that initial parameters, such as the stored formula for determining the duty cycle of the PWM control signal, and preferably a pump stroke value, or different routines for certain operating modes, can optionally be uploaded to the control unit.

(13) FIG. 2A shows a signal curve of a PWM control signal S.sub.PWM. FIG. 2A shows the time-varying voltage signal u(t) over time t.

(14) In this embodiment example, an input voltage U.sub.B1 is shown which is used in the predetermined formula for adapting the duty cycle D of the PWM control signal S.sub.PWM1. The duty cycle D is defined as the ratio of the pulse width t.sub.e1 to the period duration T of the PWM control signal S.sub.PWM1. In FIG. 2A the duty cycle D is 0.5 (i.e. 50%).

(15) FIG. 2B shows a further signal curve of the PWM control signal S.sub.PWM2. This embodiment example shows another input voltage U.sub.B2 which is smaller than the input voltage U.sub.B1 from FIG. 2A. The input voltage U.sub.B2 is below a lower threshold value U.sub.Schw (not shown), whereby the duty cycle D is adjusted and/or changed independently of the input voltage U.sub.B2 according to the predetermined formula for adjusting the duty cycle D. FIG. 2B shows that the pulse width t.sub.e2 tends to be wider than the pulse width t.sub.e1 determined from the predetermined formula and the first higher input voltage UB1. The period duration T of duty cycle D, on the other hand, remains unchanged. The duty cycle D shown in FIG. 2B is approximately 0.9 (i.e. 90%).

(16) FIG. 3 shows a cross-sectional view of a typical lubricant pump, as used in connection with the present disclosure, with DC pump motor 4 and integrated control unit 1 for pumping lubricant.

(17) The lubricant reservoir (7) contains a predetermined amount of lubricant, lubricating agent or grease. The pump element 6 is in fluid connection with the lubricant reservoir 7 in a suction area 61, so that lubricant, lubricating agent or grease can be sucked out of the lubricant reservoir. In addition, pressure output 62 of pump element 6 is shown schematically on the side of pump element 6.

(18) Furthermore, FIG. 3 shows an eccentric unit 41 which is driven by the DC pump motor 4. The eccentric unit 41 converts the (rotary) rotational motion of the DC pump motor 4 into a (translatory) pumping motion and transmits the pumping motion to the pump element 6. The pump element 6, the eccentric unit 41 and the DC pump motor 4 are mounted on a base plate 80 and housed in a housing 81 with a cover 82.

(19) FIG. 4 shows a sequence diagram of an embodiment example of the method for controlling a DC pump motor as a control path. The control path comprises steps S1, S2, S3 and S4, wherein steps S1 to S4 are repeated cyclically in this embodiment example.

(20) In a concrete embodiment example, steps S1 to S4 can be repeated cyclically, especially every 50 ms to 200 ms. Preferably steps S1 to S4 are repeated every 100 ms.

(21) In FIG. 4, the input voltage of the control unit according to the disclosure is acquired in step S1. This is followed by step S2, in which the duty cycle D is calculated in particular on the basis of a stored formula and/or determined calibration values from production. In the following step S3, a temperature compensation is carried out on the basis of the optionally acquired temperature. In step S4, the duty cycle D is now changed and output to the control module (20) in particular.

REFERENCE CHARACTER LIST

(22) 1 Control unit; 20 Control module; 21 Input voltage sensor; 22 Motor current sensor; 23 Switching elements; 24 Smoothing capacitor; 3 Outside temperature sensor; 4 DC pump motor (brushed DC motor); 41 Eccentric unit; 5 Display; 6 Pump element; 61 Suction area; 62 Pressure output; 7 Lubricant reservoir; 80 Base plate; 81 Housing; 82 Cover; D Duty cycle; I.sub.m Motor current; S1, S2, Process steps of the control path; S3, S4 S.sub.PWM PWM control signal; S.sub.PWM1, S.sub.PWM2 Adapted PWM control signal; t Time; TA Outside temperature (temperature); te1, te2 Pulse width; T Period duration of the PWM signal; U.sub.B, U.sub.B1, U.sub.B2, Input voltage (operating voltage); u(t) Time-varying voltage signal;