DE102014211978A1 - Low pressure circuit for a fuel injection system with a temperature controlled bypass - Google Patents

Abstract

The invention relates to a low-pressure circuit for a fuel injection system of an internal combustion engine, comprising a fuel line (1) which is relieved via a pressure-dependent controllable valve (2), which is preceded by a fuel filter (3). According to the invention, a temperature-dependent controllable valve (4) is arranged upstream of the fuel filter via which at low fuel temperatures a connection of the fuel line (1) with a bypass line (5) for bypassing the fuel filter (3) and / or the pressure-dependent controllable valve ( 2) can be produced.

Description

The invention relates to a low pressure circuit for a fuel injection system of an internal combustion engine having the features of the preamble of claim 1. The fuel injection system is preferably a common rail injection system for injecting diesel fuel into a diesel engine.

State of the art

At low temperatures, especially during the cold start of a diesel engine, paraffin crystals are formed in the diesel fuel. These can lead to a blockage of a fuel filter arranged in the fuel injection system. For example, a fuel filter may be located upstream of a valve to protect it from damaging particles. The upstream fuel filter can thus increase the life of the valve. This is accompanied by an increase in the robustness of the injection system. However, if such a fuel filter at low temperatures, its functionality and that of the valve is no longer guaranteed. This can ultimately lead to failure of the system.

To solve the problem, which occurs in particular during cold start of the engine or the internal combustion engine, a fuel filter arranged upstream of a valve can be removed or a valve without upstream fuel filter can be used. However, this suffers the robustness of the system, because harmful particles are no longer intercepted. Alternatively, a throttled bypass line can be provided to bypass the fuel filter. However, this reduces the efficiency of the system, as constantly flows through the throttled bypass line fuel.

From the publication DE 198 57 249 A1 is fuel injection system, in particular a common rail injection system, known with a prefeed pump, which is a fuel filter upstream or downstream. To protect the prefeed pump and a high-pressure pump, which is supplied via the prefeed pump fuel from a fuel tank, a valve device is provided which the pumped by the priming pump fuel - depending on the pressure difference between the pressure upstream and downstream of the fuel filter - either back into the Fuel tank or promotes the high-pressure pump. A connection to the fuel tank is established when the pressure upstream of the fuel filter, for example due to clogging, exceeds a permissible limit. In this case, no fuel is supplied to the high-pressure pump. However, in order to ensure supply of the high-pressure pump with fuel at low temperatures and turbulated fuel, which may also cause an impermissible pressure increase upstream of the fuel filter, a bypass with an expansion element is provided to bypass the valve means. The expansion element opens the bypass at low temperatures and ensures that the pumped by the feed pump fuel flow passes through the fuel filter to the high pressure pump. However, this assumes that the fuel filter continues to let the spilled fuel through.

The object of the present invention is to provide a low pressure circuit for a fuel injection system, in particular a common rail injection system, which ensures high efficiency and at the same time a high degree of robustness of the system. The proposed low-pressure circuit is also intended in particular to remedy the cold-start problem mentioned above.

To solve the problem, the low-pressure circuit for a fuel injection system with the features of claim 1 is proposed. Advantageous developments of the invention can be found in the dependent claims.

Disclosure of the invention

The low-pressure circuit proposed for a fuel injection system of an internal combustion engine comprises a fuel line which can be relieved via a pressure-dependent controllable valve, wherein a fuel filter is connected upstream of the pressure-dependent controllable valve. According to the invention, a temperature-dependent controllable valve is arranged upstream of the fuel filter, via which a connection of the fuel line with a bypass line for bypassing the fuel filter and / or the pressure-dependent controllable valve can be produced at low fuel temperatures. This means that at low fuel temperatures and possibly clogged fuel filter opens the temperature-dependent controllable valve and can flow fuel from the fuel line into the bypass line. This ensures relief of the fuel line even with a clogged fuel filter, since it can be bypassed via the bypass line.

Preferably, the fuel line is a supply line in the inlet region of a high-pressure pump. For this purpose, the fuel line may be formed as a bore in a housing part of the high-pressure pump. In the inlet region of a high-pressure pump is usually at least one valve, for example, for flow control or pressure control, arranged, which is often preceded by a fuel filter to protect against harmful particles. Thus, at low temperatures there is a risk that this fuel filter due to the Added paraffin crystals in the fuel. However, if a temperature-dependent controllable valve is arranged upstream of this fuel filter, which opens at low temperatures and connects the supply line to a bypass line, the fuel filter can be bypassed. This ensures that the pressure in the supply line to the high-pressure pump does not exceed a permissible limit and the high-pressure pump is further supplied with fuel in order to maintain the operation of the internal combustion engine or to start the internal combustion engine.

Further preferably, the pressure-dependent controllable valve is an overflow valve, via which the preferably serving as a feed line fuel line with a return line is connectable. The overflow valve is used to control the pressure in the fuel line, since it opens when a predetermined limit pressure is exceeded and discharges fuel into the return line. The overflow valve may in particular be designed as a spring-loaded check valve, so that it can only be flowed through in one direction, namely by the fuel or feed line to be relieved in the direction of the return line. The bypass line for bypassing the fuel filter upstream of the overflow valve preferably opens downstream of the overflow valve into the return line, so that, moreover, the overflow valve can be bypassed. This ensures that any harmful particles contained in the fuel do not get into the valve.

Advantageously, the bypass line is at least partially designed as a throttle bore. The discharge of fuel from the fuel line to be relieved is thus throttled when the temperature-dependent controllable valve is opened. This prevents the pressure from dropping below the level required to operate the high pressure pump. Furthermore, the amount of fuel removed via the temperature-dependent valve does not adversely affect the efficiency of the system. The at least partially designed as a throttle bore bypass line is preferably formed in a housing part of the high-pressure pump.

It is also proposed that the temperature-dependent controllable valve is arranged in the fuel line, in the bypass line or in a fuel-carrying region between the fuel line and the bypass line, preferably in an engine room of the high-pressure pump. An appropriate arrangement ensures that the temperature dependent valve comes in contact with the fuel to open at low fuel temperatures.

The temperature-dependent controllable valve preferably comprises a temperature-active element which changes its shape and / or size when the temperature changes. This has the consequence that via the temperature-active element, a cross-section is opened, which opens the bypass. With regard to the design of the temperature-active element, there are a variety of ways. Two concrete embodiments are mentioned below.

Ideally, the temperature-active element is an expansion element, a bimetallic element or an element made of a material with a high coefficient of thermal expansion, such as aluminum. All of these elements change shape and / or size as the ambient temperature rises or falls. The change in shape and / or size can be manifested, for example, by stretching or bending of the temperature-active element. This in turn can lead to a Absteuerquerschnitt is opened to relieve the fuel line in the bypass line.

According to a first preferred embodiment of the invention, the temperature-active element is an open bimetallic ring, which has on the outer circumference in the region of a bending at a temperature change end cooperating with a flow-through sealing contour. At normal operating temperature, the sealing contour closes the flow-through opening, so that no fuel can flow out of the fuel line into the bypass line. The flow-through opening can be formed by the flow cross-section of the bypass line itself. Preferably, however, it is formed in a surrounding the bimetal ring support ring. The flow-through opening formed in the support ring overlaps at least in regions with the flow cross-section of the bypass line.

Alternatively, the temperature-active element may be an open ring, which is made of a material having a high coefficient of thermal expansion, preferably made of aluminum, and at least temporarily defined between its ends a flow opening whose cross section changes with a change in temperature. For this purpose, the ring is preferably designed slotted, wherein the slit or gap serving as flow opening is closed at normal operating temperatures and only opens at low temperatures in order to discharge fuel from the fuel line into the bypass line.

Preferred embodiments of the invention will be explained in more detail with reference to the accompanying drawings. These show:

1 a hydraulic circuit diagram of a low pressure circuit according to the invention,

2 a hydraulic circuit diagram of a fuel injection system with inventive low-pressure circuit according to the 1 .

3a) a perspective view of a temperature-active element of a first preferred embodiment of a temperature-dependent controllable valve and b) the temperature-active element after installation,

4a) a perspective view of a temperature-active element of a second preferred embodiment of a temperature-dependent controllable valve and b) the temperature-active element after installation and

5 a perspective view of a high-pressure pump with open engine compartment, in which the temperature-dependent controllable valve 4 is used.

Detailed description of the drawings

Like the wiring diagram of the 1 can be seen, a low pressure circuit according to the invention a fuel line 1 and a return line 8th having, via a pressure-dependent controllable valve 2 , are connectable. The pressure-dependent controllable valve 2 is presently designed as a spring-loaded check valve, which is a fuel filter 3 upstream. In case of a blockage of the fuel filter 3 a connection of the fuel line 1 to the return line 8th to be able to produce, is a bypass line 5 to bypass the fuel filter 3 intended. The bypass line 5 opens downstream of the pressure-dependent controllable valve 2 in the return line 8th , To the over the bypass line 5 to reduce the amount of fuel removed is in the bypass line 5 a temperature-dependent controllable valve 4 provided that the bypass line 5 only releases when a given temperature of the fuel in the fuel line 1 is fallen short of.

Like in the 2 shown by way of example, the low-pressure circuit of 1 Be part of a fuel injection system. The fuel line 1 serves in this case as a supply line, which in an inlet area 6 a high pressure pump 7 is arranged. With the pressure-dependent controllable valve 2 it is preferably an overflow valve in the inlet area 6 the high pressure pump 7 is added to the pressure in the inlet area 6 in front of a metering unit 16 of the fuel injection system. The metering unit 16 supplies the high-pressure pump 7 with the required amount of fuel in the high pressure pump 7 conveyed to high pressure and a high-pressure accumulator (not shown) is supplied. The high pressure pump 7 for this purpose comprises two pump elements 17 , each one on a cam drive 18 supported liftable pump piston 19 include. In the suction stroke of the pump piston 19 will fuel through an inlet valve 20 in one of the pump piston 19 limited pump work space 21 aspirated, compressed in the delivery stroke and then via an outlet valve 22 supplied to the high-pressure accumulator. About the connected to the high-pressure accumulator injectors then the compressed fuel in the combustion chamber of the internal combustion engine (not shown) is injected. All in the 2 Components shown can be components of the high-pressure pump 7 be, ie in the high pressure pump 7 be integrated.

If diesel fuel is used as fuel, at low temperatures, especially during cold start, paraffin crystals can form in the fuel, so that there is a risk that the valve 2 upstream fuel filter 3 added. A pressure control via the valve 2 in the inlet area 6 the high pressure pump 7 is then no longer guaranteed. A relief of the fuel line 1 in the inlet area 6 but is via the bypass line 5 causes, as the temperature-dependent controlled valve 3 opens and the bypass line 5 releases.

The temperature-dependent controlled valve 3 has a temperature-active element for this purpose 11 , This can be made of different materials and have different shapes. In the 3 and 4 are concrete embodiments of such a temperature-active element 11 shown.

3a) shows, for example, a bimetallic ring which is interrupted and has at least one freely movable end. At this end, the outside circumference is a cam-shaped sealing contour 13 formed with a flow opening 12 in a support ring 14 cooperates, which surrounds the bimetallic ring. When a predetermined temperature is exceeded, the movable end of the bimetallic ring bends radially inwards, so that the flow-through 12 is released. If the temperature falls below a predetermined value, the end of the bimetallic ring moves radially outward, so that the flow-through 12 from the cam-like sealing contour 13 is closed.

In the 3b) the bimetallic ring is shown in the installed state. To open flow opening 12 the connection of the fuel line 1 with the bypass line 5 ensure is the flow opening 12 in overlap with the flow cross section of the bypass line 5 brought. The connection of the fuel line 1 with the bypass line 5 can be indirectly via an engine room 10 the high pressure pump 7 be made in a housing part 9 the high pressure pump 7 for receiving the cam drive 18 is trained. This can - as in the 5 shown - the bimetallic ring in the engine room 10 be used.

Of the 4 is an alternative embodiment of a temperature-active element 11 refer to. This is also designed annular and has a slot as a flow opening 15 on. The ring consists in the present case of aluminum, which has a high coefficient of thermal expansion and expands at a temperature rise. If the temperatures go down, the material contracts. The annular temperature-active element behaves accordingly 11 of the 4a) such that in normal operation, when the fuel temperature is high, the flow opening 15 closed and at low temperatures, for example when cold starting the engine, is open. In this case, connect to the bypass line 5 produce is the flow opening 15 again in overlap with the flow cross section of the bypass line 5 brought (see 4b ). The ring of 4 can also according to the 5 in the engine room 10 a high pressure pump 7 be used. For support or guidance of the ring both outside and inside circumference each of a support ring 14 . 14 ' be surrounded.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19857249 A1 [0004]

Claims (9)

Low pressure circuit for a fuel injection system of an internal combustion engine, comprising a fuel line ( 1 ), which via a pressure-dependent controllable valve ( 2 ) to which a fuel filter ( 3 ) is relieved, characterized in that upstream of the fuel filter ( 3 ) a temperature-dependent controllable valve ( 4 ) is arranged, over which at low fuel temperatures a connection of the fuel line ( 1 ) with a bypass line ( 5 ) for bypassing the fuel filter ( 3 ) and / or the pressure-dependent controllable valve ( 2 ) can be produced. Low pressure circuit according to claim 1, characterized in that the fuel line ( 1 ) a supply line in the inlet area ( 6 ) a high pressure pump ( 7 ). Low pressure circuit according to claim 1 or 2, characterized in that the pressure-dependent controllable valve ( 2 ) is an overflow valve, via which the preferably serving as a feed line fuel line ( 1 ) with a return line ( 8th ) is connectable. Low-pressure circuit according to one of the preceding claims, characterized in that the bypass line ( 5 ) is designed at least in sections as a throttle bore, which is preferably in a housing part ( 9 ) of the high-pressure pump ( 7 ) is trained. Low-pressure circuit according to one of the preceding claims, characterized in that the temperature-dependent controllable valve ( 4 ) in the fuel line ( 1 ), in the bypass line ( 5 ) or in a fuel-carrying area between the fuel line ( 1 ) and the bypass line ( 5 ), preferably in an engine room ( 10 ) of the high-pressure pump ( 7 ) is arranged. Low-pressure circuit according to one of the preceding claims, characterized in that the temperature-dependent controllable valve ( 4 ) a temperature-active element ( 11 ) which changes shape and / or size upon a temperature change. Low pressure circuit according to claim 6, characterized in that the temperature-active element ( 11 ) is a Dehnstoffelement, a bimetallic element or an element made of a material having a high coefficient of thermal expansion, such as aluminum. Low pressure circuit according to claim 6 or 7, characterized in that the temperature-active element ( 11 ) is an open bimetallic ring, the outer peripheral side in the region of a bending at a temperature change end with a flow-through ( 12 ) cooperating sealing contour ( 13 ), wherein preferably the flow-through opening ( 12 ) in a surrounding the bimetallic ring support ring ( 14 ) is trained. Low pressure circuit according to claim 6 or 7, characterized in that the temperature-active element ( 11 ) is an open ring, which is made of a material with a high coefficient of thermal expansion, preferably made of aluminum, and at least temporarily between its ends a flow-through ( 15 ) whose cross-section changes as the temperature changes.

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