METHOD FOR OPERATING A PUMP, AND FLUID SUPPLY SYSTEM HAVING A PUMP OF SAID TYPE

Abstract

A method for operating a pump of a delivery unit, in particular of a fluid supply system, having a pump chamber and an actively controllable inlet valve and an actively controllable outlet valve for the pump chamber, wherein, for the delivery of a fluid, a pressure (p), which is to be provided by the pump, of the fluid for delivery is controlled in closed-loop fashion on the basis of a manipulated variable (V), and wherein, within one full cycle (Z) of the pump (200), at least one of inlet valve (211) and outlet valve (212) is activated only if fluid is to be delivered, and is not activated if no fluid is to be delivered, and to a fluid supply system.

Claims

1. A method for operating a pump (200) of a delivery unit (110) of a fluid supply system (100), having a pump chamber (210) and an actively controllable inlet valve (211) and an actively controllable outlet valve (212) for the pump chamber (210), the method comprising: controlling a pressure (p) of a fluid (121), which is to be provided by the pump (200), in a closed-loop fashion on the basis of a manipulated variable (V, f, f.sub.W), and within one full cycle (Z) of the pump (200), activating at least one of inlet valve (211) and outlet valve (212) only if fluid is to be delivered, and not activating at least one of inlet valve (211) and outlet valve (212) if no fluid is to be delivered.

2. The method according to claim 1, wherein, if no fluid is to be delivered, a zero delivery state is implemented by means of the pump.

3. The method according to claim 1, wherein the pressure (p) of the fluid (121), at least in a part of an available mass flow range of the fluid, controlled in closed-loop fashion by means of two-point closed-loop control, in which a use (V) of an activation of the inlet valve (211) and of the outlet valve (212) is used as manipulated variable, and wherein a pump frequency (f) is set to a predetermined value (f.sub.min) greater than zero.

4. The method according to claim 1, wherein the pressure (p) of the fluid (121) is, at least in a part of an available mass flow range, controlled in closed-loop fashion by means of a closed-loop controller, in which a repetition frequency (f.sub.W) of activation cycles of the inlet valve (211) and of the outlet valve (212) is used as manipulated variable.

5. The method according to claim 1, wherein the pressure (p) of the fluid (121) is, at least in a part of an available mass flow range, controlled in closed-loop fashion by means of a closed-loop controller, in which a pump frequency (f) is used as manipulated variable, and wherein an activation of the inlet valve (211) and of the outlet valve (212) is performed.

6. The method according to claim 3, wherein the two-point closed-loop control is used for a first mass flow range (B.sub.1), and the closed-loop control in the case of which the pump frequency (f) is used as manipulated variable is used in a second mass flow range (B.sub.2), wherein the second mass flow range (B.sub.2) at least partially comprises higher mass flows than the first mass flow range (B.sub.1).

7. The method according to claim 4, wherein the closed-loop control in which the repetition frequency (f.sub.W) of activation cycles is used as manipulated variable is used for a first mass flow range (B.sub.1), and the closed-loop control in which the pump frequency (f) is used as manipulated variable is used in a second mass flow range (B.sub.2), wherein the second mass flow range (B.sub.2) at least partially comprises higher mass flows than the first mass flow range (B.sub.1).

8. The method according to claim 3, wherein, in the case of an activation, an activation time (t.sub.1) of the inlet valve, an activation angle of the inlet valve, an opening time of the inlet valve, an opening angle of the inlet valve, an activation duration (b) of the inlet valve, an activation angle range of the inlet valve, an opening duration of the inlet valve, an opening angle range of the inlet valve, an activation time (t.sub.2) of the outlet valve, an activation angle of the outlet valve, an opening time of the outlet valve, an opening angle of the outlet valve, an activation duration (d) of the outlet valve, an activation angle range of the outlet valve, an opening duration of the outlet valve and an opening angle range of the outlet valve are used as activation parameter (A.sub.P) of inlet valve and/or outlet valve, which are in each case set to a predetermined value which is in particular dependent on the pump frequency (f).

9. A fluid supply system (100), having a pump (200) with a pump chamber (210) and an actively controllable inlet valve (211) and an actively controllable outlet valve (212) for the pump chamber, and having a processing unit (150) configured to operate the pump (200) by: controlling a pressure (p) of a fluid (121), which is to be provided by the pump (200), in a closed-loop fashion on the basis of a manipulated variable (V, f, f.sub.W), and within one full cycle (Z) of the pump (200), activating at least one of inlet valve (211) and outlet valve (212) only if fluid is to be delivered, and not activating at least one of inlet valve (211) and outlet valve (212) if no fluid is to be delivered.

10. A non-transitory, computer-readable medium containing instructions that when executed by a computer cause the computer to control a fluid supply system (100) having a pump (200) with a pump chamber (210) and an actively controllable inlet valve (211) and an actively controllable outlet valve (212) for the pump chamber, by: controlling a pressure (p) of a fluid (121), which is to be provided by the pump (200), in a closed-loop fashion on the basis of a manipulated variable (V, f, f.sub.W), and within one full cycle (Z) of the pump (200), activating at least one of inlet valve (211) and outlet valve (212) only if fluid is to be delivered, and not activating at least one of inlet valve (211) and outlet valve (212) if no fluid is to be delivered.

11. The method according to claim 1, wherein, if no fluid is to be delivered a drive of the pump (200) is not actuated.

12. The method according to claim 1, wherein, if no fluid is to be delivered the inlet valve (211) remains permanently open.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 schematically shows a fluid supply system according to the invention in a preferred embodiment.

[0033] FIG. 2 schematically shows a sequence of a possible activation of active valves and a pump.

[0034] FIGS. 3 to 6 show sequences of methods according to the invention in various preferred embodiments, and explanations thereof.

DETAILED DESCRIPTION

[0035] FIG. 1 schematically illustrates, by way of example, a fluid supply system 100 according to the invention in a preferred embodiment. The fluid supply system 100 is configured in particular as an SCR system and comprises a delivery unit 110 which has a pump or delivery pump 200, which pump or delivery pump is configured to deliver reducing agent 121 (or a reducing agent solution) as fluid for delivery from a reducing agent tank 120 via a pressure line 122 to a dosing module or dosing valve 130 and will be described in more detail further below. At the dosing module or dosing valve, the reducing agent 121 is then sprayed into an exhaust-gas tract 170 of an internal combustion engine.

[0036] Also provided is a pressure sensor 140 (this may also be accommodated in the delivery module) which is configured to measure a pressure at least in the pressure line 122. A processing unit 150, which is configured for example as an exhaust-gas aftertreatment control unit, is connected to the pressure sensor 140 and, from this, receives information relating to the pressure in the pressure line 122. Furthermore, the exhaust-gas aftertreatment control unit 150 is connected to the delivery module 110, and in particular to the pump 111 and to the dosing module 130 therein, in order to be able to activate said delivery module.

[0037] The fluid supply system 100 furthermore comprises, by way of example, a return line 160, through which the reducing agent can be conducted from the system back (cf. Q.sub.RL) into the reducing agent tank 120. In said return line 160, there is arranged, by way of example, an aperture or restrictor 161 which provides a local flow resistance. It is however to be noted here that such a return line may also be omitted in the case of the proposed method with actively controlled valves.

[0038] The exhaust-gas aftertreatment control unit is configured to, on the basis of relevant data, for example data received from the engine control unit or from sensors for temperature, pressure and nitrogen oxide content in the exhaust gas, coordinate the actuators of the system in order to introduce the urea-water solution into the exhaust-gas tract upstream of the SCR catalytic converter in accordance with the operating strategy. Furthermore, it is for example the case that an on-board diagnosis (OBD) arrangement monitors those components and assemblies of the exhaust-gas aftertreatment system which are relevant for adherence to exhaust-gas limit values.

[0039] The pump 200 has a pump chamber 210, which is incorporated by way of an inlet valve 211 and an outlet valve 212 into the corresponding line. Both the inlet valve 211 and the outlet valve 212 are in this case actively controllable or activatable, that is to say these two valves can be opened or closed as required. It is in particular also possible for the exhaust-gas aftertreatment unit 150 (or possibly also some other suitable processing unit; it is also conceivable for this to be integrated into a set of electronics of the pump, in particular of the motor or valve thereof) to be used for this purpose.

[0040] Furthermore, the pump 200 has a delivery element 220 with a drive in order to increase and decrease the volume of the pump chamber 210. It is to be noted at this juncture that the specific form of the delivery element 220, for example piston or the like, is not relevant for the proposed method.

[0041] FIG. 2 schematically illustrates a sequence of a possible activation of active valves in a pump, such as is used for example in the case of the fluid supply system shown in FIG. 1. For this purpose, a course B of a position or setting of the delivery element of the pump is illustrated versus the time t, said course moving between a top dead centre OT and a bottom dead centre UT and in so doing also representing a measure for the volume (course between maximum and minimum volume).

[0042] Activation signals S.sub.E for the inlet valve and S.sub.A for the outlet valve are also illustrated versus the time t. It can be seen here that, after bottom dead centre UT, that is to say when the volume of the pump chamber is then increasing again, the inlet valve is activated such that fluid can be drawn in. Correspondingly, after top dead centre OT, that is to say when the volume of the pump chamber is then decreasing again, the outlet valve is activated such that fluid can be forced out.

[0043] Here, the valves are activated for opening at a particular time, the inlet valve at the time t.sub.1 and the outlet valve at the time t.sub.2. It can also be seen that the times t.sub.1 and t.sub.2 are spaced apart from the preceding dead centre by a time period a and c respectively. In this context, the activation time t.sub.1 and t.sub.2 can also be defined as a delay in relation to the corresponding dead centre.

[0044] The durations of the activation signals are denoted by b and d respectively. In this way, it is thus possible for four activation parameters a, b, c and d (or else t.sub.1 and t.sub.2 instead of a and c) of the valves to be used for the operation of the pump, which activation parameters can in particular each be set to particular values, as will also be discussed in more detail below.

[0045] It is pointed out at this juncture that the actual opening durations of the valves may in practice sometimes deviate, owing to necessary actuator movements, from the corresponding durations of the activation signals, but this can correspondingly be taken into consideration in the configuration of a control unit.

[0046] Also shown is a pump frequency of the pump, which, in the context of the invention, may also be used in certain embodiments as manipulated variable for the closed-loop control of the pressure. This is indicated by the period of the course B, which corresponds to the reciprocal of the pump frequency f. The period in turn corresponds to one full cycle Z of the pump, as has been discussed in the introduction.

[0047] FIGS. 3 to 6 illustrate sequences of methods according to the invention in various preferred embodiments, and explanations thereof. Firstly, in FIG. 3, a pump frequency f, which may for example correspond to a rotational speed, and a fluid mass flow or mass flow M of the fluid for delivery, are shown schematically and without specific scaling.

[0048] In the case of the mass flow M, it can be seen that this rises continuously from zero (on the left) in linear fashion (to the right), which is intended to make it clear that, with such a pump, the mass flow can basically be varied arbitrarily from zero up to a certain maximum value, and that this is furthermore desired during normal operation.

[0049] By contrast, in the case of the pump frequency f, it can be seen that this cannot fall below a particular minimum value f.sub.min. As already mentioned in the introduction, this is inter alia because, below this minimum value, which may for example be 500 rpm or approximately 8 Hz, the required friction force of the drive cannot be overcome. The resultant torque exerted on the drive by the pump pressure can likewise be a problem here. There thus remains a mass flow range B.sub.1 in which, with constant pump frequency, that is to say for example f.sub.min, the mass flow must be varied from zero up to a particular value M.sub.1, whereas, in a mass flow range B.sub.2 that covers the rest of the range, the mass flow can be varied for example by means of the pump frequency (as manipulated variable).

[0050] In a preferred embodiment of the method according to the invention, it is thus the case that, in the mass flow range B.sub.1, two-point closed-loop control is used, by means of which the pressure of the fluid for delivery is controlled in closed-loop fashion.

[0051] In this regard, FIG. 4 illustrates the pressure p versus the time t, wherein a setpoint value p.sub.soll for the pressure and an upper threshold value p.sub.O and a lower threshold value p.sub.U are shown. The value of the associated manipulated variable V for this two-point closed-loop control is also shown, likewise versus the time t, which value can assume the two values 1 for on, that is to say an activation of the valves is performed, and 0 for off, that is to say no activation of the valves is performed.

[0052] The pressure p is initially zero, that is to say the manipulated variable is set to 1, and an activation of the valves is performed. In particular, each valve is opened and closed once in every full stroke of the delivery element. Only when the upper threshold value p.sub.O is reached is the manipulated variable set to 0, that is to say the activation is stopped, and full strokes of the delivery element are thus performed without activation of the valves. Only when the pressure reaches the lower threshold value p.sub.U again is the activation of the valves started again, that is to say the manipulated variable is set to 1.

[0053] This two-point closed-loop control is, as mentioned, used in particular in the mass flow range B.sub.1. If a mass flow in the mass flow range B.sub.2 is desired, then a switch can be made from the two-point closed-loop control to closed-loop control with the pump frequency as manipulated variable, in particular PI(D) closed-loop control, in order to control the pressure in closed-loop fashion.

[0054] During the closed-loop control in the mass flow range B.sub.2, but for example also in the case of the two-point closed-loop control in the mass flow range B.sub.1, the activation parameters of the valves (for example the parameters a, b, c, d as discussed with regard to FIG. 2) are preferably set to the most optimum values possible, which are in particular dependent on the present pump frequency.

[0055] In this regard, in FIG. 5, the mass flow M is plotted versus the pump frequency fin rpm, which is for example used as manipulated variable. Here, the two curves represent—from left to right—activation parameters a, b, c, d, which are each kept constant but which differ, of the valves. It can be clearly seen here that the mass flow M can be very greatly varied even with the pump frequency f alone, but also that there is in each case a set of activation parameters in the case of which the mass flow is particularly high, that is to say particularly efficient operation is possible. In this regard, AP is used by way of example to indicate four sets of activation parameters for a respective particular pump frequency f, which activation parameters allow optimum operation at the respective pump frequency and should therefore be used as far as possible.

[0056] In FIG. 6, a mass flow M and a repetition frequency f.sub.W are schematically plotted in each case versus a time t. Here, the repetition frequency f.sub.W indicates how often one (full) activation cycle of the valves, with opening and closing, is performed per unit of time. From the two courses, it can be clearly seen that the mass flow M can also be varied through the variation of the repetition frequency f.sub.W.

[0057] In a further preferred embodiment of the method according to the invention, it is thus the case that, in the mass flow range B.sub.1, closed-loop control is used, in the case of which this repetition frequency f.sub.W is used as manipulated variable in order to perform closed-loop control of the pressure of the fluid for delivery.

[0058] This closed-loop control, which may in particular be PI(D) closed-loop control, is, as mentioned, used in particular in the mass flow range B.sub.1. By contrast, the closed-loop control with the pump frequency as manipulated variable, as already mentioned above, may be used in the mass flow range B.sub.2. In this embodiment, too, the above-discussed activation parameters for the valves may be used.