Method for operating a dosing pump and device having a dosing pump

Abstract

A method for operating a vehicle heater dosing pump for conveying fuel having a piston which can be moved back and forth between a start position and an end position, and a drive unit which can be electrically excited by applying a voltage, having the following procedure: controlling and/or regulating the voltage for generating an effective voltage to transfer the piston from the start position to the end position, wherein the effective voltage reaches a first maximum (U.sub.1) in a start phase (t.sub.0-t.sub.1), and is lower than the first maximum in a subsequent intermediate phase (t.sub.1-t.sub.2). The effective voltage reaches a second maximum (U.sub.3) in an end phase (t.sub.2-t.sub.3) following the intermediate phase. A device is also provided having a dosing pump and a control/regulation unit. The control/regulation unit is suitable for controlling voltage applied to a drive unit of the dosing pump.

Claims

1. A method for operating a dosing pump, wherein the dosing pump comprises a piston, which for delivery is movable back and forth between a starting position and an end position, and a drive unit which can be electrically excited by the application of a voltage, the method having the step of: controlling the voltage so as to generate an effective voltage in order to move the piston from the starting position into the end position, that differs from the starting position, wherein the effective voltage assumes a first local maximum (U.sub.1) in a starting phase (t.sub.0-t.sub.1) and is lower than the first local maximum in a subsequent intermediate phase (t.sub.1-t.sub.2), and wherein the effective voltage assumes a second local maximum (U.sub.3), higher than the effective voltage applied during the intermediate phase, in an end phase (t.sub.2-t.sub.3) which follows the intermediate phase, wherein the piston reaches its end position during the intermediate phase, and wherein the piston stays in its end position during the end phase.

2. The method of claim 1, wherein the second local maximum (U.sub.3) is lower than the first local maximum (U.sub.1).

3. The method of claim 1 wherein, during the starting phase and/or the intermediate phase and/or the end phase, the effective voltage is in each case constant or defined by a step function.

4. The method of claim 1, wherein the effective voltage is zero during the intermediate phase.

5. The method of claim 1, wherein the voltage is controlled independently of the movement of the piston.

6. The method of claim 1, wherein the voltage is at least intermittently pulse-width-modulated.

7. The method of claim 1, wherein a control unit accesses stored items of information which define a profile of the effective voltage for the starting phase, the intermediate phase and the end phase, and controls the voltage on the basis of said items of information.

8. The method of claim 7, wherein the control unit does not use any information from which it is possible to infer an actual position or speed of the piston.

9. The method of claim 1, wherein a restoring force causes a return of the piston into the starting position.

10. A device comprising: a dosing pump, wherein the dosing pump comprises a piston, which for delivery is movable back and forth between a starting position and an end position, that differs from the starting position, and a drive unit which can be electrically excited by the application of a voltage, and a control unit suitable for carrying out the following measure: controlling the voltage so as to generate an effective voltage in order to move the piston from the starting position into the end position, wherein the effective voltage assumes a first local maximum (U.sub.1) in a starting phase (t.sub.0-t.sub.1) and is lower than the first local maximum (U.sub.1) in a subsequent intermediate phase (t.sub.1-t.sub.2), wherein the piston reaches its end position during the intermediate phase and wherein the piston stays in its end position during the end phase, wherein the effective voltage assumes a second local maximum (U.sub.3), higher than the effective voltage applied during the intermediate phase, in an end phase (t.sub.2-t.sub.3) which follows the intermediate phase.

11. The device of claim 10, wherein the control unit comprises a memory and a processor and a profile of the effective voltage is at least partially defined by items of information which are present in the memory and which can be read by the processor.

Description

(1) The invention will now be explained on the basis of exemplary embodiments and with reference to the appended drawings. Here, identical or similar components are denoted by the same reference numerals.

(2) In the drawings:

(3) FIG. 1 shows a dosing pump at a first time during a pump cycle.

(4) FIG. 2 shows the dosing pump at a second time during the pump cycle.

(5) FIG. 3 shows the profile of an effective voltage.

(6) FIG. 4 shows a flow diagram of the operation of a dosing pump.

(7) FIG. 5 shows the profile of an effective voltage according to a second embodiment.

(8) FIG. 1 schematically shows an example of a device 10 for pumping a liquid, for example a fuel, from an inlet line 22 to an outlet line 24 by means of a dosing pump 12. The dosing pump 12 comprises a housing and a piston 14 which, together with the housing, defines a pump chamber 16. The present position of the piston 14 relative to the housing defines a present volume of the pump chamber 16. FIG. 1 shows the piston 14 in a starting position, in which the pump chamber 16 assumes its maximum volume.

(9) FIG. 2 shows the piston 14 in an end position in which the volume of the pump chamber 16 is zero. The piston 14 is connected to an electric drive unit 18. The drive unit 18 is suitable for cyclically or periodically exerting a force F on the piston 14 in order to move the piston 14 back and forth between its starting position and its end position. The dosing pump 12 may have a spring (not illustrated) which causes a return of the piston 14 from the end position into the starting position without the drive unit 18 having to exert a force for this purpose. The drive unit 18 has a coil to which an electrical voltage U can be applied in order to generate a current and thus the force F. The voltage U which is applied to the coil is controlled/regulated by a control/regulating unit 20. The voltage U may be amplitude-modulated. It may alternatively be pulse-width-modulated.

(10) FIG. 3 illustrates by way of an example the time profile of an effective voltage U.sub.eff which corresponds to the voltage U applied to the coil of the drive unit 18. The effective voltage is periodic, with a period duration T. At the time t.sub.0, the piston 14 is situated in its starting position. At said time, an effective voltage of magnitude U.sub.1 is applied. Said voltage sets the piston 14 in motion in the direction of the end position. At a later time t.sub.1, the effective voltage is reduced to a value U.sub.2 (U.sub.2<U.sub.1). At a later time t.sub.2, the effective voltage is increased to a value U.sub.3. At a later time t.sub.3, the effective voltage is reduced to zero. At the time t.sub.4, a new pump cycle begins in which an effective voltage is applied analogously to the effective voltage in the interval [0, t.sub.4]. The intervals t.sub.0 to t.sub.1, t.sub.1 to t.sub.2, t.sub.2 to t.sub.3 and t.sub.3 to t.sub.4 are referred to in each case as the starting phase, intermediate phase, end phase and off phase (off period). For given lengths of said phases and given voltage values U.sub.1, U.sub.2 and U.sub.3, the movement of the piston is dependent on the electrical resistance of the drive unit, on the viscosity of the liquid being delivered and on the outlet pressure. In particular, the electrical resistance and the viscosity may in turn be dependent on the ambient temperature.

(11) Under normal conditions (for example at normal temperature, low or normal viscosity and normal outlet pressure), the piston moves as follows. In the starting phase [t.sub.0, t.sub.1], the piston is set in motion by the high effective voltage U.sub.1. In the subsequent intermediate phase [t.sub.1, t.sub.2], the piston is braked by friction forces and/or by the outlet pressure, which cannot be fully compensated by the lower voltage U.sub.2 which is now applied, and reaches its end position approximately at the time t.sub.2, preferably precisely at the time t.sub.2. Here, the end speed of the piston, that is to say the speed of the piston when it reaches the end position, is preferably low, if possible zero. The effective voltage pulse of magnitude U.sub.3 which is applied in the end phase [t.sub.2, t.sub.3] which follows acts on the piston only so as to prevent an immediate return of the piston into its starting position. By contrast, said effective voltage pulse does not lead to a louder impact noise, because the piston has already impacted or is already situated close to the stop. During the off period [t.sub.3, t.sub.4], the piston finally returns into its starting position under the action of a restoring force.

(12) Under adverse operating conditions (for example at elevated temperature, elevated viscosity of the liquid to be delivered or elevated outlet pressure), the piston moves slightly differently. In the starting phase [t.sub.0, t.sub.1], it is accelerated. Owing to the adverse operating conditions, it has not yet reached its end position at the time t.sub.2. Its speed at the time t.sub.2 is zero or even negative. As a result of the voltage pulse of magnitude U.sub.3 which starts at the time t.sub.2, the piston is accelerated again and reaches the end position during the end phase [t.sub.2, t.sub.3] or possibly first during the off period [t.sub.3, t.sub.4]. The provision of an elevated effective voltage in the end phase [t.sub.2, t.sub.3] thus ensures that the piston reaches the predefined end position even under the adverse operating conditions.

(13) The flow diagram in FIG. 4 illustrates the activation of the dosing pump 12 in accordance with the effective voltage profile depicted in FIG. 3. At the time t.sub.0, an effective voltage of magnitude U.sub.1 is applied (step S1). At the subsequent time t.sub.1, the effective voltage is reduced to the value U.sub.2 (step S2). At the subsequent time t.sub.2, the effective voltage is increased to the value U.sub.3 (step S3), wherein U.sub.3 is lower than U.sub.1. At the subsequent time t.sub.3, the effective voltage is reduced to zero in order to permit a return of the piston into its starting position (step S4). At the subsequent time t.sub.4, the method returns to step S1.

(14) FIG. 5 schematically shows the effective voltage profile according to a further embodiment. In the starting phase [t.sub.0, t.sub.1], the intended effective voltage assumes the constant high value U.sub.1. In the subsequent intermediate phase [t.sub.1, t.sub.2], the effective voltage is zero. In the end phase [t.sub.2, t.sub.3] which follows, the effective voltage is characterized by a rising step function. In this way, the dosing pump is optimized for different operating conditions. The three different voltage levels during the end phase [t.sub.2, t.sub.3] may for example be assigned to three different temperature values or viscosity values. Here, the highest and latest voltage level in the end phase [t.sub.2, t.sub.3] has an advantageous effect in the presence of the highest temperature or viscosity. A different number of voltage levels during the end phase [t.sub.2, t.sub.3] is self-evidently also conceivable. For example, the effective voltage could be defined, during the end phase, by a step function and in particular by a rising step function with two, three, four or five steps. Embodiments may also be realized in which, by contrast to FIG. 3 and FIG. 5, the effective voltage is not constant in portions but rather varies continuously.

REFERENCE SYMBOLS

(15) 10 Device 12 Dosing pump 14 Piston 16 Pump chamber 18 Drive unit 20 Control/regulating unit 22 Inlet line 24 Outlet line U Voltage Ueff Effective voltage t Time