Fluid conveying system and method for conveying a fluid

Abstract

Fluid delivery system (1), in particular for an injection system, comprising: a fluid reservoir (2) for storing the fluid (3) to be delivered, a fluid delivery pump (8), a pressure line (12) and a return line (20) which enables a fluid flow from the pressure line (12) into the fluid reservoir (2), wherein the fluid delivery pump (8) is designed, during operation, to withdraw fluid (3) from the fluid reservoir (2) and to discharge it under increased pressure into the pressure line (12), wherein a controllable return valve (22) is arranged in the return line (20), wherein the return valve (22) in an open state enables a return flow of fluid (3) from the pressure line (12) into the fluid reservoir (2) and in a closed state prevents a return flow of fluid (3) from the pressure line (12) into the fluid reservoir (2), characterized in that parallel to the return valve (22) a fixed choke (24) is connected.

Description

[0001] The invention relates to a fluid conveying system, in particular for an injection system, and a method for conveying a fluid. State of the art

[0002] In vehicles with internal combustion engines, especially diesel engines, the pollutant NOx must be reduced, particularly due to stricter emissions legislation. One method used for this is the so-called SCR process, in which the pollutant NOx is reduced to N2 and H2O using a liquid, urea-containing reducing agent ("AdBlue") in a catalytic converter. To achieve good efficiency, the liquid reducing agent should be added to the exhaust gas in as fine a distribution as possible. In order to achieve the finest possible atomization of the reducing agent when it is injected into the exhaust system, there is a need for fluid delivery and injection systems that deliver the reducing agent at sufficiently high pressure. Known fluid delivery systems have a fluid delivery pump and a return throttle. The injection pressure of the fluid is adjusted by varying the speed of the fluid delivery pump.Excess fluid not required for injection flows back into the fluid tank through the return throttle.

[0003] DE 10 2006 060 838 A1 discloses a dosing system for metering a liquid into an exhaust line connected to an internal combustion engine of a motor vehicle. In a ventilation mode, actuation of a liquid pump causes the liquid present in a supply line to be displaced by ambient air. DE 10 2008 060 373 A1 shows an exhaust gas purification device for vehicles. DE 10 2009 037 564 A1 discloses a device and a method for metering a reducing agent into an exhaust tract of an internal combustion engine. DE 10 2011 075 298 A1 describes a pump device for a dosing system. DE 10 2009 046 802 A1 discloses a device for injecting fluid into an exhaust system. Disclosure of the invention

[0004] One object of the invention is to provide a more efficient fluid delivery system and a more efficient method for delivering a fluid. A fluid delivery system according to the invention has a fluid reservoir for storing the fluid to be delivered, a fluid delivery pump, and a pressure line.

[0005] The fluid delivery pump is designed to suck fluid from the reservoir during operation and discharge it into the pressure line under increased pressure. A return line with an adjustable check valve is arranged between the pressure line and the reservoir. When open, the check valve allows fluid to flow back from the pressure line into the reservoir, and when closed, prevents fluid from flowing back from the pressure line into the fluid reservoir.

[0006] The fluid pressure in the pressure line is adjusted by varying the opening cross-section or the opening duration (“duty cycle”) of the return valve; the amount of fluid required in the pressure line is determined by the speed of the fluid delivery pump.

[0007] In a delivery system according to the invention, the amount of fluid flowing back into the reservoir through the return line is significantly smaller than in a conventional fluid delivery system because the fluid pressure in the pressure line is not adjusted by changing the speed of the fluid delivery pump. Rather, the speed and thus the delivery rate of the fluid delivery pump can be adjusted as a function of the amount of fluid actually required in the pressure line. Since in this way less fluid is delivered that is not injected into the exhaust system but flows directly back into the reservoir than is delivered in a conventional delivery system, a fluid delivery system according to the invention operates with greater efficiency than conventional fluid delivery systems. A fixed throttle is connected parallel to the return valve.A fixed throttle arranged parallel to the return valve allows air to be removed from the delivery system, in particular from the working chamber of the fluid delivery pump, and, when the fluid delivery pump is at a standstill, achieves a balanced system pressure by equalizing pressure with the ambient air. The fixed throttle in a fluid delivery system according to the invention has a significantly smaller flow rate than a return throttle used in a conventional fluid delivery system.

[0008] In one embodiment, the return valve is designed as an adjustable pressure-maintaining valve. This allows a predetermined pressure to be set in the pressure line. In one embodiment, the pressure-maintaining valve is continuously adjustable.

[0009] In one embodiment, the fluid delivery pump is connected to a switchable non-return valve. Such a non-return valve allows the flow direction to be reversed, allowing fluid to be pumped from the pressure line back into the tank or fluid reservoir when needed, thus completely draining the system.

[0010] In one embodiment, a (heatable) filter and / or a pressure sensor are arranged in the pressure line. A filter makes it possible to filter out particles contained in the fluid that could clog or damage injection nozzles connected to the pressure line. A pressure sensor makes it possible to measure and monitor the pressure in the pressure line.

[0011] In one embodiment, the maximum flow rate of the fluid pump is greater than the maximum fluid volume flowing out of the pressure line. A flow rate of the fluid pump that is greater than the maximum fluid volume flowing out of the pressure line is necessary to maintain the desired pressure in the pressure line under all operating conditions.

[0012] In one embodiment, the pumping capacity of the fluid delivery pump is at least 5 kg / h. A pumping capacity of 5 kg / h has proven sufficient in many cases to maintain the desired pressure in the pressure line under all operating conditions and to provide the required amount of fluid.

[0013] The invention is explained in more detail below with reference to the accompanying figures.

[0014] It shows: Fig. 1 is a schematic representation of a conventional fluid conveying system; Fig. 2 a schematic representation of an embodiment of a fluid conveying system according to the invention; and Fig. 3 shows, by way of example, the delivery characteristics of a fluid delivery pump and a return valve in a fluid delivery system according to the invention.

[0015] Fig. 1 shows a schematic representation of a conventional fluid conveying system 5.

[0016] A conventional fluid delivery system 5 comprises a tank or fluid reservoir 2 in which the fluid 3 to be delivered is stored. For withdrawing the fluid 3 from the tank 2, a fluid withdrawal line 4 is provided, which is arranged with a first end in a lower region of the tank 2 and whose second end is connected to a fluid delivery pump 8 via a non-return valve 6.

[0017] An outlet of the fluid feed pump 8 is connected to a pressure line 12 via the non-return valve 6, so that when the fluid feed pump 8 is operating, the fluid 3 is withdrawn from the tank 2 through the fluid withdrawal line 4 and discharged into the pressure line 12 under increased pressure.

[0018] By switching the non-return valve 6, the connections of the fluid extraction line 4 and the pressure line 12 to the fluid feed pump 8 are swapped so that when the fluid feed pump 8 is operating, fluid 3 is pumped from the pressure line 12 back into the tank 2 in order to completely empty the system, e.g. to protect against frost damage or for maintenance work, without reversing the direction of rotation of the fluid feed pump 8 itself.

[0019] Downstream of the suction valve 6, a filter 10 is arranged in the pressure line 12, which filter is designed to filter out particles contained in the fluid 3 and thus prevent clogging or damage to injection devices connected to the pressure line 12, not shown in the figure.

[0020] The filter 10 and / or the non-return valve 6 are preferably heatable in order to prevent fluid from freezing in the filter 10 or the non-return valve 6, even at low ambient temperatures.

[0021] In the flow direction between the filter 10 and the pressure sensor 18, a return line or return flow line 20 is connected to the pressure line 12, which allows fluid 3 pumped from the tank 2 by the fluid pump 8 to flow back into the tank 2. A throttle 14 and a check valve 16 are arranged in series in the return line 20 to limit the amount of fluid 3 flowing back from the pressure line 12 into the tank 2 and to prevent an undesired flow of fluid 3 or air from the tank 2 through the return line 20 into the pressure line 12.

[0022] In such a conventional delivery system 5, the pressure in the pressure line 12 is adjusted by selecting the speed of the fluid delivery pump 8. A significant portion of the fluid 3 delivered by the fluid delivery pump 8 always flows through the throttle 14 and the return line 20 back into the tank 2. The operation of such a system is not very efficient, since a fluid quantity that must always be delivered is considerably greater than the fluid quantity required in the pressure line 12.

[0023] Downstream of the filter 10, a pressure sensor 18 is connected to the pressure line 12. The pressure sensor 18 makes it possible to measure the pressure of the fluid 3 in the pressure line 12 and to adjust it to a desired value by varying the speed of the fluid feed pump 8.

[0024] Fig. 2 shows a schematic representation of a fluid conveying system 1 according to the invention.

[0025] The components of the fluid conveying system 1 according to the invention, which are identical to the components of a conventional fluid conveying system 5 as shown in Fig. 1, are provided with the same reference numerals and will not be described in detail again.

[0026] A fluid conveying system 1 according to the invention differs from a conventional fluid conveying system 5 in that no throttle 14 and no check valve 16 are provided in the return line 20.

[0027] Instead of the throttle 14 and the check valve 16, a controllable return valve 22 is provided in the return line 20, which is designed in particular as a pressure holding valve 22.

[0028] In a fluid delivery system 1 according to the invention, in contrast to a conventional fluid delivery system 5, the pressure in the pressure line 12 is not adjusted by regulating the speed of the fluid delivery pump 8, but by selecting the opening cross-section or the opening duration of the return valve 22.

[0029] The speed of the fluid feed pump 8 is not selected as a function of the desired fluid pressure in the pressure line 12, but rather as a function of the fluid quantity required in the pressure line 12. The fluid quantity delivered by the fluid feed pump 8 can be adjusted so that it is always only slightly larger than the fluid quantity required in the pressure line 12 in order to maintain the desired pressure in the pressure line 12.

[0030] A fixed throttle 24 is arranged parallel to the return valve 22. The fixed throttle 24 makes it possible to discharge air from the fluid delivery system 1, in particular from the working chamber of the fluid delivery pump 8, and to achieve a balanced system pressure by equalizing pressure with the ambient air when the fluid delivery pump 8 is at a standstill. The fixed throttle 24 of a delivery system 1 according to the invention has a significantly smaller opening cross-section than the return throttle 14 of a conventional delivery system 5, so that the amount of fluid flowing back into the tank 2 through the fixed throttle 24 is significantly smaller than in a conventional delivery system 5.

[0031] Fig. 3 shows, as an example, the delivery characteristics of the fluid feed pump 8 (dashed line) and the return valve 22 (solid line).

[0032] In particular, the dashed line describes the flow rate Q of the fluid feed pump 8 as a function of the speed n of the fluid feed pump 8 in relation to the maximum speed n0 of the fluid feed pump 8 and the solid line describes the fluid quantity Q discharged through the return line 20 as a function of the relative opening duration A / A0 of the return valve (metering valve) 22 (0-100% duty cycle at x Hz dosing frequency).

[0033] For the function of a fluid conveying system 1 according to the invention, it is necessary that the fluid quantity Q conveyed by the fluid conveying pump 8 is always greater than the fluid quantity discharged through the return line 20 (Δ > 0), since otherwise the desired fluid pressure in the pressure line 12 cannot be maintained.

[0034] A fluid delivery system 1 according to the invention leads to a stable pressure in the pressure line 12 even in the case of dynamic changes in the dosing quantity and avoids undesirable pressure fluctuations and pressure pulses, the peaks of which exceed the maximum permissible pressure for the individual components and can thus lead to damage to the components.

[0035] Since, according to the invention, no check valve 16 is present in the return line 20, pressure equalization with the environment can take place via the tank 2, the return line 20, and the throttle 24 after the fluid delivery pump 8 is switched off. Such pressure equalization prevents an undesirable negative pressure from developing and being maintained in the fluid delivery system 1 after the fluid delivery pump 8 is switched off and the system has cooled down.

Claims

[1] A fluid delivery system (1), in particular for an injection system, comprising: a fluid reservoir (2) for storing the fluid (3) to be delivered, a fluid delivery pump (8), a pressure line (12) and a return line (20) which enables a fluid flow from the pressure line (12) into the fluid reservoir (2), wherein the fluid delivery pump (8) is designed, during operation, to withdraw fluid (3) from the fluid reservoir (2) and to discharge it under increased pressure into the pressure line (12), wherein a controllable return valve (22) is arranged in the return line (20), wherein the return valve (22) in an open state enables a return flow of fluid (3) from the pressure line (12) into the fluid reservoir (2) and in a closed state prevents a return flow of fluid (3) from the pressure line (12) into the fluid reservoir (2), characterized by that a fixed throttle (24) is connected parallel to the return valve (22). [2] Fluid conveying system (1) according to claim 1, wherein the return valve (22) is designed as a, preferably continuously adjustable, pressure-maintaining valve which makes it possible to set a predetermined pressure in the pressure line (12). [3] Fluid delivery system (1) according to one of the preceding claims, wherein the fluid delivery pump (8) is connected to a switchable non-return valve (6) which enables a reversal of the delivery direction of the fluid delivery pump (8) in order to pump fluid (3) from the pressure line (12) back into the fluid reservoir (2). [4] Fluid conveying system (1) according to one of the preceding claims, wherein a filter (10) is arranged in the pressure line (12). [5] Fluid conveying system (1) according to one of the preceding claims, wherein a pressure sensor (18) is arranged in the pressure line (12). [6] Fluid delivery system (1) according to one of the preceding claims, wherein the maximum delivery rate of the fluid delivery pump (8) is greater than the maximum amount of fluid flowing out of the pressure line (12). [7] Method for conveying a fluid (3) with a conveying system according to one of the preceding claims, wherein the speed of the fluid conveying pump (8) is adjusted as a function of the amount of fluid required in the pressure line (12). [8] Method according to claim 7, wherein the pressure in the pressure line (12) is adjusted by adjusting the return valve (22). [9] Method according to claim 7 or 8, wherein the amount of fluid delivered by the fluid delivery pump (8) is greater than the amount of fluid required in the pressure line (12).

Images