Operating method and actuation device for a piston pump

Abstract

The invention relates to a method for operating a piston pump (10) which is driven by means of a coil (1) of an electromagnet. A piston (2) of the piston pump (10) can be moved in a cylinder (3) for pumping purposes by means of the electromagnet. A voltage (U) is applied to the coil (1) during a switch-on period such that a current flows through the coil (1) and the piston (2) is accelerated, said voltage being applied by means of an actuation device (11). A time curve of an electric state variable (I, U) of the coil (1) is qualitatively detected, and the curve or a curve derived therefrom is analyzed in order to detect an impact of the piston (2) against a stop. The invention further relates to an actuation device and a piston pump.

Claims

1. A method for operating a piston pump (10), which is driven by means of a coil (1) of an electromagnet, wherein, by means of the electromagnet, a piston (2) of the piston pump (10) is moveable in a cylinder (3) for the execution of a pump action, wherein, during a switch-in time, a voltage (U) is applied to the coil (1), such that a current flows in the coil (1) and the piston (2) is accelerated, wherein the voltage is applied by means of an semiconductor switch of an actuation device (11), and wherein a time characteristic of an electrical state variable (I, U) of the coil (1) is qualitatively determined by measuring a voltage drop across an internal resistance of the semiconductor switch (LS) and determining the current in the coil from the measured voltage drop, and the time characteristic, or a characteristic derived therefrom, is evaluated in order to determine the impact of the piston (2) on a limit stop (8), control the voltage applied to the coil (1) to accelerate the piston according to the determined time characteristic, wherein a conveyance of vapor is detected on the basis of a time characteristic of the voltage.

2. The method as claimed in claim 1, wherein an impact time point (tA) of the piston (2), at which the piston (2) engages with the limit stop (8), is determined on the basis of the time characteristic of the electrical state variables (I, U).

3. The method as claimed in claim 2, wherein the impact time point (tA) is detected and, in a first temporal derivation of the characteristic of the electrical state variables (I, U), an extreme value is temporally determined, in a second temporal derivation of the characteristic of the electrical state variables (I, U), a zero-crossing is temporally determined, or both the extreme value and the zero-crossing are determined.

4. The method as claimed in claim 2, wherein the time characteristic of the state variables (I, U) is subtracted from a temporal reference characteristic, which simulates a theoretical characteristic of the state variables (I, U) in the absence of motion of the piston, or with the piston in motion but in the absence of impact of the piston (2), and the difference is compared with a threshold value, wherein the impact time point (tA) is detected by an extreme value in said difference.

5. The method as claimed in claim 2, wherein a detected impact time point (tA) is saved.

6. The method as claimed in claim 2, wherein, upon the detection of the impact time point (tA), the voltage supply to the coil (1) is terminated or, on the basis of a previously detected and saved impact time point (tA), a time point is determined at which the voltage supply to the coil (1) is terminated, wherein, specifically after a time interval (IIa), which commences upon the termination of the voltage supply, the voltage supply is switched-in once more.

7. The method as claimed in claim 2, wherein the voltage supply is terminated before the determined impact time point (tA) is reached, or when the determined impact time point (tA) is reached.

8. The method as claimed in claim 7, wherein a voltage supply time (II) of the coil (1) is set such that, further to the end of the voltage supply time (II), the piston (2) reaches the limit stop (8) as a result of its momentum, and reaches the limit stop (8) at a substantially lower speed in comparison with its maximum speed.

9. The method as claimed in claim 1, wherein the conveyance of vapor is detected on the basis of the time characteristic of the electric voltage (U) on the coil (1).

10. The method as claimed in claim 9, wherein, further to the commencement of a discharge process of fluid from the piston pump (10), a dip (E) in the voltage characteristic (U) on the coil (1) is detected, specifically wherein a difference between the voltage characteristic and a characteristic of a reference voltage at an average value of the voltage (U) during a time interval following decay of the current in the coil (1) is determined, and an extreme value is identified in said difference which exceeds a threshold value.

11. An actuation device (11) for a piston pump (10) for the conveyance of a fluid, specifically a fuel, having a cylinder (3), a piston (2) and an electromagnet with a coil (1) for the movement of the piston (2) in the cylinder (3), wherein the actuation device (11) comprises a semiconductor switch (LS), by means of which a voltage is applied to the coil (1), and the actuation device (11) is configured to; apply, during a switch-in time, a voltage (U) to the coil (1), such that a current flows in the coil (1), accelerating the piston (2); qualitatively determine a time characteristic of an electrical state variable (I, U) of the coil (1) by measuring a voltage drop across an internal resistance of the semiconductor switch (LS) and determining a current in the coil from the measured voltage drop; determine an impact of the piston (2) on a limit stop (8) by evaluating the characteristic, or a characteristic derived therefrom; and control the voltage applied to the coil (1) to accelerate the piston according to the determined time characteristic wherein a conveyance of vapor is detected on the basis of a time characteristic of the voltage (U) to the coil (1).

12. The actuation device (11) as claimed in claim 11, wherein the voltage (U_DS) across the internal resistance of the semiconductor switch (LS) is executed between a ground potential (GND) and one terminal of the semiconductor switch (LS) or between a voltage supply potential (+UB) and one terminal of the semiconductor switch (LS).

13. The actuation device (11) as claimed in claim 11, wherein one terminal of the semiconductor switch (LS) is connected to the same potential as a first terminal of the coil (1), and wherein a second terminal of the coil (1) is connected to a voltage supply potential or to a ground potential, wherein the actuation device (11) is configured to calculate a voltage on the coil (1) from the difference between a voltage on the terminal of the semiconductor switch (LS) and the supply voltage potential or the ground potential.

14. A piston pump (10), wherein it comprises an actuation device (11) as claimed in claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are described in detail hereinafter, with reference to the attached drawings. In the drawings:

(2) FIG. 1 shows a cross section of a piston pump according to the prior art,

(3) FIG. 2 shows a circuit diagram of an actuation device according to the prior art,

(4) FIG. 3 shows a circuit diagram of a first form of embodiment of an actuation device according to the invention,

(5) FIG. 4 shows a circuit diagram of a second form of embodiment of an actuation device according to the invention,

(6) FIG. 5 shows a circuit diagram of a third form of embodiment of an actuation device according to the invention,

(7) FIG. 6 shows a double diagram, in which a voltage on the coil and a current in the coil are plotted over a time interval which is common to both, wherein a conventional current and voltage characteristic is represented,

(8) FIG. 7 shows a double diagram, in which a voltage on the coil and a current in the coil are plotted over a time interval which is common to both, wherein a current and voltage characteristic is represented according to the application of a first form of embodiment of the invention,

(9) FIG. 8 shows a double diagram, in which a voltage on the coil and a current in the coil are plotted over a time interval which is common to both, wherein a current and voltage characteristic is represented according to the application of a second form of embodiment of the invention,

(10) FIG. 9 shows a double diagram, in which a voltage on the coil and a current in the coil are plotted over a time interval which is common to both, wherein a conventional current and voltage characteristic is represented but wherein, however, a liquid fluid and vapor are conveyed.

DETAILED DESCRIPTION

(11) FIG. 3 shows a circuit diagram of an actuation device, as an element of the invention. This element of the invention is of independent significance. The applicant reserves the option to file a separate application in respect of this subject matter. The actuation device represented can form part of a more extensive unit. Between a supply voltage potential +UB and a ground potential GND, a coil of an electromagnet of a piston pump and a semiconductor switch LS are connected in series. The semiconductor switch LS is configured as a n-channel MOSFET transistor. Alternatively, the semiconductor switch LS can also be configured as a p-channel MOSFET transistor. A source terminal S of the transistor is connected to the ground potential GND. A drain terminal D is connected to one terminal of the coil. The gate terminal G is connected to an actuation potential via a series resistor Rv_LS. A voltage drop U_DS can be tapped-off between the drain D and the source S. The voltage drop can be employed from the measurement of a current flowing in the coil L_coil. The coil comprises an inductive element L_coil and a resistive element R_coil, which are connected in series. One terminal of the coil is connected to the supply voltage potential +UB, whereas the other terminal is connected to the semiconductor switch HS.

(12) FIG. 4 shows a circuit diagram of a second form of embodiment of the actuation device. In many respects, the second form of embodiment is identical to the first form of embodiment, which is represented in FIG. 3. Equivalent characteristics are identified by the same reference symbols, and reference is made to FIG. 3 in relation thereto. Only the differences from FIG. 3 will be described hereinafter. The second form of embodiment is additionally provided with a Zener diode, which is connected to the drain and source of the semiconductor switch LS and, with respect to the supply voltage potential +UB, is connected in a blocking direction. The actuation device is further provided with an additional current path, having a series-connected arrangement of a further semiconductor switch HS and a diode D1 which, with respect to the supply voltage potential +UB, is arranged in the blocking direction. The drain of the semiconductor switch HS is connected to the supply voltage potential +UB. The anode of the diode D1 is connected to the drain of the semiconductor switch LS. The source of the semiconductor switch HS and the cathode of the diode D1 are interconnected. The semiconductor switch HS can be actuated via its gate and a series resistor Rv_HS. The circuit incorporates a shunt resistor, on which a voltage U_shunt can be tapped for the measurement of a current flowing in the coil L_coil.

(13) For the energization of the coil L_coil, the semiconductor switch LS is switched to a conducting state. Once a switch-in time has expired, the semiconductor switch LS is opened. The coil L_coil then generates a voltage U_coil_pump. This drives a current through a freewheeling circuit. The function of the semiconductor switch HS is the activation of a freewheeling circuit with a low impact, which runs through the diode D1 and the closed semiconductor switch HS connected thereto. As the voltage drop on the closed semiconductor switch HS and the diode D1 is small, energy is only discharged slowly from the coil L_coil, such that the coil current is extinguished slowly. Conversely, if the semiconductor switch is open, a strong extinction effect is generated. The current path of the current driven by the coil is then routed via the Zener diode ZD, the shunt resistor R_shunt and a power supply device, which delivers the supply voltage potential +UB. The high energy loss results in the rapid extinction of the current flowing in the coil L_coil.

(14) FIG. 5 shows a variant form of embodiment of the form of embodiment represented in FIG. 4. Equivalent characteristics are identified by the same reference symbols, and reference is made to FIG. 4 in relation thereto. Only the differences will be described hereinafter. By way of a difference from FIG. 4, the form of embodiment represented in FIG. 5 is lacking the shunt resistor R_shunt. In its place, as in the form of embodiment represented in FIG. 3, a voltage U_DS across the closed semiconductor switch LS is employed for the measurement of the current flowing in the coil L_coil.

(15) FIG. 6, in a double diagram, represents a characteristic of a voltage U, which is present on the coil of an electromagnet of a piston pump, and a characteristic of a current I flowing in the coil, wherein the current I and the voltage U are plotted against time t and are represented over the same time interval. An actuation device in one of the forms of embodiment according to FIG. 4 or 5 is employed. In a first time segment I, the voltage U assumes an approximately constant value of zero, and the current I likewise is essentially at zero. The piston lies against a rest stop, or executes a slow expulsion motion for the pumping of fluid. At the transition from time segment I to time segment II, the supply voltage is applied to the coil, such that the voltage U shows a rapid and substantial rise. As a result of the inductance and the internal resistance of the coil, there is a time lag in the trailing current in the coil I, which rises slowly and reaches its maximum value at the end of the time segment II. The rising ramp commences with an approximately constant gradient which, however, is impaired by a minor irregularity at the kink K. This is attributable to the fact that, at the start of the kink, at an impact time point tA, the piston of the piston pump engages with a limit stop, as a result of which its speed is strongly reduced and the piston thus generates no further counter-voltage. The time point of the kink thus corresponds to an impact time point. In accordance with the strong reduction in the speed of the piston, a larger effective voltage is present on the coil, such that the current I, with effect from this impact time point, rises with a steeper ramp. This rising ramp becomes progressively less steep up to the end of time segment II. At the end of time segment II, the coil is isolated from the supply voltage. To this end, the semiconductor switch LS is switched to a blocking state. The semiconductor switch HS is switched to a conducting state, such that only a weak extinction of the coil current occurs. Accordingly, the voltage U drops very rapidly to a sub-zero value, where it remains during time segment III. In time segment III, as a result of the aforementioned setting of the semiconductor switches LS and HS, the current I decays slowly. In time segment IV, the voltage U drops rapidly and very strongly, which is associated with a rapid and strong reduction in the current I to a value close to zero. This is effected by the switch-out of the semiconductor switch HS which, as described above, is associated with a strong extinction of current. At the end of the drop in current, the voltage U rapidly rises again to an approximate value of zero. In time segment V, the piston, as a result of the termination of the magnetic action of the coil, is reset in motion by the spring bias. This results in the generation of a counter-voltage in the coil, which can be identified by a dip in the characteristic of the voltage U. Although the piston is accelerated, the action of the motion of the piston in the time characteristic declines up to the end of time segment V. During the latter, the current I is close to zero. At the end of the time segment V, the cycle begins again from the start with time segment I.

(16) FIG. 7 shows a variant of the double diagram of voltage U and current I plotted against time t, as represented in FIG. 6. The same time period is represented as in FIG. 4. The characteristics of the voltage U and the current I substantially correspond to the characteristics represented in FIG. 6. Consequently, only the differences will be described here. The main difference between FIGS. 6 and 7 is that the transition between time segments II and III occurs at an earlier time. Time segment II is thus shortened, whereas time segment III is extended. Time segment II ends approximately after the time of the kink K, wherein the coil is isolated from its supply voltage. The acceleration of the piston is thus terminated early, such that the latter, as a result of this load step, and as a result of the only slow decay in the magnetic action and in the current I which continues to flow in the coil, continues to run, and engages with its limit stop at a comparatively reduced speed. This results in a reduction in noise, and a reduction in wear. In time segment III, the voltage U drops to a sub-zero value. The current I thus decays slowly to lower values. The remainder of the cycle for the voltage U and the current I corresponds to that represented in FIG. 6. Overall, substantially lower energy consumption is achieved in comparison with figure three, as a result of the abbreviated duration of application of the supply voltage and the lower maximum current strength, together with the reduced charging flux, as can be seen from the area below the characteristic current curve I.

(17) FIG. 8 shows a variant of the double diagram of voltage U and current I plotted against time t, as represented in FIG. 6. The same time period is represented as in FIG. 6. The characteristics of the voltage U and the current I substantially correspond to the characteristics represented in FIG. 6. Consequently, only the differences will be described here. The main difference between FIGS. 6 and 8 is that, in the voltage characteristic represented in FIG. 8, an additional time segment IIa is incorporated in the characteristic of time segment II. During time segment IIa, the supply voltage falls to zero. To this end, the semiconductor switch LS is open. The semiconductor switch HS remains closed or is opened, depending upon whether a strong or a weak current extinction is required. The time segment IIa corresponds to a temporal braking segment, during which the speed of the piston and/or the acceleration thereof is reduced, wherein the supply voltage to the coil is switched-out. During time segment IIa, the current I declines somewhat, whereas during time segment II, which encompasses time segment IIa, it rises rapidly. Preferably, time segment IIa commences at the kink K, at the point where the piston engages with its limit stop. Overall, a significantly lower energy consumption is achieved, specifically in that the current reaches a lower maximum value. The overall charging flux is reduced. During time segment IIa, moreover, the supply voltage is switched-out such that, during this time interval, there is no input of energy. As a result of the lower input of energy to the piston, the latter engages with its limit stop at a lower speed, thereby reducing noise and wear. The length of time segment IIa can serve as a manipulated variable for the setting of an optimum duration of energization of the coil, in order to achieve the optimum operation of the piston pump. The remainder of the time segments in a cycle represented in FIG. 8 correspond to those represented in FIG. 6.

(18) FIG. 9 shows a variant of the double diagram of voltage U and current I plotted against time t, as represented in FIG. 6. The same time period is represented as in FIG. 6. The characteristics of the voltage U and the current I substantially correspond to the characteristics represented in FIG. 6. Consequently, only the differences will be described here. The main difference between FIGS. 6 and 9 is that the dip E in time segment V is significantly more prominent. This is due to the fact that FIG. 9 represents the conveyance of a mixture of a liquid fluid and a vapor thereof. At the start of time segment V, the piston is strongly accelerated, until the vapor is compressed by the rising pressure, and a medium which can be compressed no further is expelled. With reference to the magnitude or the temporal gradient of the dip E, it can be established whether or not vapor is present in the pump body. To this end, specifically, an amplitude of the dip E and/or a temporal gradient of the dip E can be compared with a threshold value.