DE102020000253A1 - Fuel system, method for avoiding the boiling of fuel with a boiling point below 90 ° C on a low-pressure fuel pump of a fuel system operated by an internal combustion engine, and vehicle with a fuel system - Google Patents

Abstract

The invention relates to a fuel system (4) for an internal combustion engine (2) of a vehicle (1), suitable for a fuel with a boiling point below 90 ° C, the fuel system having: a main fuel line (18) which has an internal combustion engine-operated low-pressure pump (12) followed by a fuel tank (11) upstream of the low-pressure pump (12), a fuel filter (17) downstream of the low-pressure pump (12) and a high-pressure pump (19) downstream of the fuel filter (17), the high-pressure pump (19) being set up to fuel an injection system feed, which is connected to the internal combustion engine. The fuel system (4) has a cooling flow recirculation line (15) which is connected to the main fuel line (18) and is configured to recirculate some of the fuel downstream of the low pressure pump (12) and upstream of the high pressure pump (19) back to the fuel tank (11), whereby cooling of the low-pressure pump can be achieved, especially when the engine of the vehicle is braking.

Description

TECHNICAL AREA

This description relates to a fuel system for an internal combustion engine of a vehicle, which is designed for a fuel with a boiling point below 90 ° C. The description further relates to a method for preventing the boiling of fuel, which has a boiling point temperature below 90 ° C., on a low-pressure fuel pump driven by an internal combustion engine of a fuel system connected to the internal combustion engine of a vehicle.

THE PRIOR ART

Internal combustion engines, such as diesel engines, are used, for example, in trucks, buses, passenger cars, motor boats, ships, ferries and other watercraft. Internal combustion engines of this type are also used in industrial machines and / or machines for operating industrial robots, as well as in power plants, such as power generation plants with a diesel generator, or also in locomotives. Internal combustion engines of this type are provided with a fuel system which is set up to convey fuel from one or more fuel tanks via an injection system to the internal combustion engine. The fuel system has one or more fuel pumps which can be driven mechanically by the internal combustion engine. The fuel pumps generate a fuel flow and pressure to deliver the fuel to the injection system. The injection system then delivers the fuel to the internal combustion engine.

Internal combustion engines can run on fuel, which can be diesel, gasoline, or ethanol, or some other type of biofuel. Ethanol and certain other types of biofuels can have a low boiling point (a low boiling point temperature), usually below 90 ° C, which can result in the fuel boiling when the temperature of the engine rises, for example when the vehicle brakes when there is no Fuel is injected into the engine. If the fuel boils, the gas phase of the fuel can no longer be pressurized sufficiently with the fuel pumps which are used to deliver fuel from the fuel tank to a high-pressure fuel pump which is connected to the internal combustion engine and which is set up, the fuel to the engine feed. This creates risks with regard to malfunctions and vehicle failures ("VOR"). There is thus a need for a solution to the problem that reduces the risk of fuel boiling in given fuel systems.

BRIEF DESCRIPTION OF THE INVENTION

The aim of the present invention is thus to reduce the risk of malfunctions in a fuel system which is designed for fuels with a boiling point of 90 ° C. or less.

In particular, one aim is to prevent malfunctions at high engine temperatures, for example when the vehicle brakes on the engine.

Another goal is to provide a robust fuel system.

These goals are achieved with a fuel system for an internal combustion engine of a vehicle according to the appended claims. The fuel system is set up for fuels with a boiling point below 90 ° C. The fuel system has a main fuel line connecting an engine driven low pressure pump, a fuel tank upstream of the low pressure pump, a fuel filter downstream of the low pressure pump and a high pressure pump downstream of the fuel filter. The high pressure pump is set up to supply fuel to the injection system, which interacts with the internal combustion engine. The fuel system has a cooling flow recirculation line connected to the main fuel line and configured to recirculate a portion of the fuel downstream of the low pressure pump and upstream of the high pressure pump back to the fuel tank. By returning a small portion of the fuel back to the tank, the low pressure pump can draw cool fuel out of the tank and maintain a flow of cool fuel through the pump at a certain level. “Cooling flow” here means a flow with a flow rate that is sufficient to cool the low-pressure pump, for example in a state in which the vehicle is braked by the engine. Thus, the low pressure pump is cooled and the fuel will not boil, especially when the vehicle is braking the engine if no fuel is introduced into the engine.

The cooling flow recirculation line may be connected to a drain opening in the main fuel line. This results in a simple structure. The drain opening can have a diameter of more than 0.5 mm. In this way, the flow through the low pressure pump can the desired level are maintained, even in an operating state with engine braking.

The low pressure pump can be linked to an internal recirculation line which is provided with a pressure adjustment valve. In this way, excess fuel generated by the low pressure pump can be recirculated to the inlet of the low pressure pump.

The fuel system may further include a main fuel return line configured to return fuel to the fuel tank and having a fuel filter return line and / or a high pressure pump return line and / or an accumulator return line, the cooling flow recirculation line cooperating with the main fuel return line. This means that existing fuel return lines can be used in the systems for the cooling flow and its return to the tank.

The cooling flow recirculation line can have a flow restriction valve and optionally also a check valve. In this way, the flow can be controlled efficiently and the check valve can prevent fuel from flowing back into the main fuel line.

The cooling flow recirculation line may have a capacity that is less than the capacity of the main flow line. This reduces the risk of the engine not starting successfully.

The cooling flow return flow line may be connected to the main fuel line between the low pressure pump and the fuel filter. This means that the filter is not loaded with hot fuel, which could affect it.

The cooling flow return line may alternatively or additionally be connected to the main fuel line between the fuel filter and the high pressure pump. This allows the cooling flow to be returned to the tank before it reaches the high pressure pump.

The fuel system can be designed for an ethanol-based fuel.

The above objects are also achieved by a method for preventing the boiling of fuel with a boiling point below 90 ° C on an internal combustion engine-operated low-pressure fuel pump in a fuel system which is connected to the internal combustion engine of a vehicle. The method is particularly suitable for a vehicle that is in the engine braking state. The fuel system has a main fuel line that includes an internal combustion engine powered low pressure pump, a fuel tank upstream of the low pressure pump, a fuel filter downstream of the low pressure pump, and a high pressure pump upstream of the fuel filter. The high pressure pump is set up to supply fuel to an injection system which is connected to the internal combustion engine. In the method, a cooling flow recirculation line for the fuel is placed downstream of the low pressure pump and upstream of the high pressure pump for returning fuel to the tank. The flow rate for the cooling flow is set up in such a way that the low-pressure pump is adequately cooled when the vehicle brakes the engine. The fuel system can be of the type described above.

The invention also relates to a vehicle with a fuel system of the type described above.

Further features and advantages are described in more detail below.

Figure list

• 1 schematically shows a vehicle with a fuel system according to the present description;
• 2nd shows schematically a part of the drive train of the vehicle according to 1 ;
• 3rd shows schematically a road section with a course uphill and downhill and the given temperature curve for the fuel; and
• 4th schematically shows an example of the configuration of the fuel system according to the present description.

DESCRIPTION OF DETAILS

The invention will now be described in more detail in connection with exemplary embodiments and the accompanying figures. However, the invention is not limited to the exemplary embodiments described and / or shown in the figures, but can be modified within the scope of the appended claims. The figures are not necessarily to scale and some features may be shown enlarged in order to emphasize features of the invention.

1 shows schematically a side view of a heavy duty vehicle 1 , here a truck with an internal combustion engine 2nd with a fuel system 4th which is connected Fuel tank 11 having. Although the exemplary embodiment shown is a truck, the vehicle can also be another type of heavy-duty vehicle, such as a bus. The vehicle 1 has a gearbox 6 which with drive wheels 10th of the vehicle 1 via a drive shaft 8th connected is.

2nd shows schematically parts of the drive train of the vehicle 1 . The drive train contains the internal combustion engine 2nd which here is mechanical via a clutch 3rd and a shaft with a first input of the transmission 6 connected is. The gear 6 is mechanical with its output with the drive shaft 8th about a differential 5 connected, which in turn is connected to the drive axle. The drive axle has left and right drive shafts 7 which the drive wheels 10th drive.

With this well-known arrangement, the mechanical work of the internal combustion engine 2nd via a number of transmission devices, such as the clutch 3rd , The gear 6 , the drive shaft 8th , the differential 5 and the drive shaft 7 to the drive wheels 10th to drive the vehicle 1 transfer. The gear 6 is a transmission device with a number of forward gears for propelling the vehicle and usually also with one or more reverse gears. The number of forward gears varies, but is usually twelve for trucks.

Furthermore, the vehicle 1 with a control device 50 be connected or have one which has one or more electronic control units (ECU). The purpose of this control device is to control one or more functions in the vehicle 1 , for example the speed, by means of one or more actuators which control the various functions of the vehicle 1 relate to, such as engine control, gear change, cruise control, suspension configurations, etc. The control device 50 can use various parameters, such as the current engine speed, the current accelerator pedal position, the current engine torque, data from various sensors and map data for controlling the individual functions of the vehicle 1 .

In the present description, the term “drive train” encompasses the internal combustion engine and the propulsion components of the vehicle.

The vehicle can be operated in a state with engine braking, for example on downhill sections of a road. The term "engine braking" means an operating state of the vehicle in which the vehicle drive train is closed, i.e. the internal combustion engine is connected to the drive wheels of the vehicle via the transmission devices, but no fuel is introduced into the internal combustion engine. The gas actuator is therefore not activated and the friction brakes of the vehicle are not necessarily in use. When the engine is braking, the vehicle is moved by its kinetic energy, which depends, among other things, on the weight of the vehicle, its speed and the inclination of the road. Since the drive train is not active when the engine is braking (it is closed), the drive shaft of the internal combustion engine rotates, ie it has a rotational speed. This means: a component or a device which is described in this description as being driven by the internal combustion engine can also be in operation during engine braking, unless expressly stated otherwise.

According to the present description, a method is provided with which the boiling of fuel having a boiling temperature below 90 ° C. is prevented on a low-pressure pump of a fuel system of a vehicle, in particular when the vehicle is in a state with engine braking. In general, the fuel system has a fuel tank, which is arranged upstream of the low-pressure pump, which in turn is set up to draw fuel from the tank. The low-pressure pump is set up to pressurize the fuel and to convey it to a high-pressure pump, which is arranged downstream of the low-pressure pump and is connected to the internal combustion engine via an accumulator and an injection arrangement, so that fuel is supplied to the internal combustion engine. The low pressure pump puts the fuel under a pressure in the range of 9-14 bar, but there is no restriction in this regard. The high-pressure pump is connected to the engine block and is arranged and set up in its immediate vicinity, the fuel under high pressure of e.g. 500-2400 bar to be set, but there is also no restriction in this regard. Thus, the low pressure pump sets the fuel to a pressure that is 10 or 20 or even more than 30 times less than the operating pressure of the high pressure pump. The tank, the low pressure pump and the high pressure pump are connected by a main fuel line.

A fuel filter, also referred to as a pressure filter or main fuel filter, is arranged in the main fuel line between the low pressure pump and the high pressure pump, that is to say downstream of the low pressure pump and upstream of the high pressure pump. Another fuel filter can be arranged on the suction side of the low pressure pump, i.e. between the tank and the low pressure pump.

The low pressure pump is connected to the internal combustion engine and is driven by it. The low-pressure pump is therefore also in operation when the vehicle is in the state with engine braking. In the state with engine braking, however, no fuel is introduced into the internal combustion engine and an inlet quantity control valve of the high-pressure pump is closed, which is why no fuel is fed into the high-pressure pump. Since no further fuel is drawn into the fuel system and the engine energy in the form of heat propagates from the engine block to the low pressure pump via the high pressure pump, the temperature at the low pressure pump rises when the vehicle is in an engine braking condition. The fuel can therefore be heated to its boiling point very quickly, for example to around 90 ° C. There is therefore a risk that the fuel, which may be ethanol of the designation “ED95”, will start to boil and evaporate, which in turn can lead to malfunctions, since the gas phase of the fuel by the low-pressure pump is insufficient Pressure can be put. Therefore, fuel in the fuel system cannot be led to the high pressure pump when the vehicle returns from the engine braking state to the normal state in which fuel is injected into the engine.

According to the present description, boiling of fuel with a boiling temperature below 90 ° C at the low pressure pump is prevented by recirculating part of the fuel flow downstream of the low pressure pump and upstream of the high pressure pump back to the fuel tank. A cooling flow recirculation line is thus connected to the main fuel line of the fuel system. The flow rate in the cooling flow recirculation line can be set such that the flow cools the low-pressure pump, in particular in an operating state of the vehicle with engine braking. This can be achieved, for example, by connecting the cooling flow recirculation line to a drain opening in the main fuel line. Therefore, there is a continuous drain flow corresponding to the cooling flow through the opening when the vehicle is operating. The diameter of the discharge opening can be set in such a way that a flow rate that can be determined in advance is achieved, which is sufficient to sufficiently cool the low-pressure pump. For example, this diameter can be greater than 0.5 mm, for example in the range from 0.5 mm to 1 mm. Part of the hot fuel is thus returned to the fuel tank, the flow being so small that there are no malfunctions, for example when the vehicle is started.

When the engine brakes, fuel is sucked out of the tank by the low pressure pump in an amount corresponding to the cooling flow or the discharge flow. The low pressure pump can be connected to an internal recirculation line which is connected to a pressure setting device, in particular a pressure regulator, e.g. a pressure control valve can be provided. For example, an input of the recirculation line can be arranged at or connected to an outlet of the low pressure pump, and an outlet of the recirculation line can be connected to the inlet of the low pressure pump. The pressure adjustment valve, in particular pressure control valve, opens, so that excess fuel generated by the pump is recirculated back to the inlet of the pump. When the vehicle brakes the engine, when no fuel is requested from the high-pressure pump, but the low-pressure pump continues to operate, the pressure adjustment valve causes a constant flow through the pump. Thus, a fuel flow corresponding to the cooling flow is sucked out of the tank through the low pressure pump, thereby cooling the low pressure pump and reducing the risk of the fuel boiling. The recirculation can be set up such that the discharge flow flows continuously when the low pressure pump is operating.

3rd explains an example of a driving situation in which engine braking occurs. The vehicle shown in the figure 1 runs on a road with an uphill section UH and a downhill section DH. If the vehicle is traveling upwards, high engine outputs are often used. In the event of a large fuel requirement from the engine, the temperature of the fuel on and in the low pressure pump can be kept at a relatively constant level below the boiling point of the fuel, since the low pressure pump is cooled by fresh fuel that is drawn into the system from the fuel tank. If the vehicle is on the hilltop HT of the hill and has reached a certain speed, for example in accordance with the speed limit of the road, the vehicle can be brought into a state with engine braking. This can reduce the use of friction-based brakes. When the engine is braking, there is no fuel injection into the internal combustion engine. Therefore, the temperature at the low pressure pump rises rapidly from the initial engine braking temperature T _eb because the high pressure pump does not request fuel and no fuel is fed into the engine. Therefore, heat is conducted from the engine block to the low-pressure pump, and therefore the fuel at or in the low-pressure pump can be quickly heated to a boiling point temperature T _bp .

By arranging the cooling flow recirculation line in connection with the main fuel line to recirculate a part of the fuel downstream of the low pressure pump and upstream of the high pressure pump back to the fuel tank, the low pressure pump can use cooling fuel from the tank in an amount corresponding to the amount of the cooling flow returned to the tank. The cooling flow can be a continuous flow, in particular a continuous discharge flow. The continuous bleed flow can be established by connecting the cooling flow recirculation line to an opening in the main fuel line. In this way, fuel is passed passively and continuously back to the tank. A small part of the fuel flow from the main fuel line is continuously removed. Since the low-pressure pump has overcapacity, the drain flow does not affect the normal operation of the fuel system, but does provide sufficient cooling for the pump when braking the engine. The capacity of the cooling flow recirculation line is smaller than the capacity of the main fuel line and can be set in the range of about 1/20 to 1/10 of the capacity of the main fuel line. This results in a simple construction of the fuel system.

4th shows an example of a fuel system 4th according to the present description. The fuel system 4th has a fuel tank 11 , from the fuel using the low pressure pump 12th to a high pressure pump 19th is sucked, the high pressure pump 19th Fuel under high pressure an accumulator 20 feeds. The fuel system is also provided with a main fuel line 18th which the tank 11 who have favourited Low Pressure Pump 12th and the high pressure pump 19th of the fuel system connects. When in 4th In the example shown, the fuel system also has a fuel filter 17th in the main fuel line downstream of the low pressure pump 12th and upstream of the high pressure pump 19th , ie on the pressure side of the low pressure pump 12th . Another fuel filter can be found on the suction side of the low pressure pump 12th be provided, ie upstream of the low pressure pump and downstream of the tank 11 . The high pressure pump 19th can with a high pressure pump return line 25th connected, which in turn can be connected to the main fuel return line 28 of the fuel system.

The accumulator 20 , which can be a common rail type, fuel leads to fuel nozzles 22 what fuel in the internal combustion engine 2nd inject. So excess fuel from the accumulator 20 back to the tank 11 can be recirculated is an accumulator return flow line 24th with a check valve 21 connected to the accumulator. In this way, fuel can be returned from the accumulator to the fuel tank using the check valve 21 prevents backflow to the accumulator. The accumulator return flow line 24th can with the main fuel return line 28 connected to the fuel system.

The fuel system is used to reduce the risk of fuel boiling, especially when an engine is braking 4th as described herein with a cooling flow recirculation line 15 provided with the main fuel line 18th is connected and set up, part of the fuel downstream of the low pressure pump 12th and upstream of the high pressure pump 19th back to the fuel tank 11 to recirculate. The cooling flow recirculation line 15 is with the main fuel line 18th downstream of the low pressure pump 12th connected.

The low pressure pump 12th can have an internal pressure setting arrangement, in particular a control arrangement, with a recirculation line 14 and a check valve 13 which are set up to open any of the low pressure pumps 12th generated excess fuel back to the low pressure pump 12th to recirculate. The entrance of the recirculation line 14 can at the outlet of the low pressure pump 12th be arranged and the output of the recirculation line 14 can be at the inlet of the low pressure pump 12th to be ordered. The pressure setting arrangement can be integrated with the low pressure pump 12th . The cooling flow recirculation line 15 can downstream of the entrance of the recirculation line 14 be arranged, which with the main fuel line 18th can be connected.

The fuel filter 17th can also be used with the fuel filter return line 27 be connected, which in turn is connected to the main fuel return line 28 can be connected. The cooling flow recirculation line 15 can be upstream of the fuel filter return line 27 be connected, which in turn is connected to the main fuel return line 28 can be connected. The cooling flow recirculation line 15 can be upstream of the fuel filter return line 27 in the main fuel line 18th be arranged. The cooling flow recirculation line may have a capacity that is less than the capacity of the main fuel line 18th , wherein the amount of fuel flowing through the return flow line can be easily passively controlled. For example, but not by way of limitation, the capacity can range from 1/20 to 1/10 of the flow capacity of the main flow line.

The cooling flow recirculation line 15 can be connected to a drain opening in the main fuel line 18th , which here with the reference symbol 16 is marked. The opening should have a diameter that allows a flow that is sufficient for sufficient cooling of the low-pressure pump, but is also small enough to keep the flow at a level that cannot cause malfunctions, for example when the engine is started. For example, the diameter can be 0.5 mm or larger, such as 0.6 mm. The main fuel line may, for example, have an inner diameter of approximately 9 mm and an outer diameter of approximately 12 mm. The diameter of the opening can thus be approximately 10 to 20 times smaller than the inside diameter of the main fuel line. The cooling flow recirculation line 15 can, on the other hand or in addition, a flow restriction valve and / or a check valve 16 ' exhibit. In this way there is a back flow into the main fuel line 18th prevented.

In the embodiment according to 4th is the cooling flow recirculation line 15 upstream of the fuel filter 17th to the main fuel line 18th connected, ie between the low pressure pump 12th and the fuel filter 17th . An existing main return flow line 28 can be used at least partially for the cooling flow with which fuel from the low pressure pump 12th is returned to the fuel tank 11 . This results in a more compact and inexpensive solution because existing return flow lines can be used. It should be noted that the cooling flow recirculation line 15 on the other hand or can also be connected to the main fuel line 18th between the fuel filter 17th and the high pressure pump 19th . Also, the cooling flow recirculation line can be connected to the main fuel return line 28 be connected, the latter at least one of the above components: fuel filter return line 27 , High pressure pump return line 25th and accumulator return line 24th can have.

Although in 4th not shown, the fuel system 4th have one or more fuel tanks. The fuel system can also have additional fuel pumps. For example, the fuel system 4th have an additional pump that is set up to convey fuel from a second fuel tank to the in 4th shown fuel tank 11 . On the other hand, when using several fuel tanks, it can be provided that these bring about a self-regulating flow between the tanks via a line connecting the fuel tanks. Furthermore, the fuel system can have further fuel filters, for example a pre-filter arrangement, within the fuel tank 11 . Such a prefilter arrangement can have a coarse mesh screen for the purpose of filtering particles from the fuel which have a predetermined size or are larger. On the other hand or in addition, an additional filter, which can be referred to as a suction filter, can also be arranged between the tank and the low-pressure pump. The fuel filter, the low pressure pump and the high pressure pump with the accumulator and the nozzles are typically arranged on the internal combustion engine while the fuel tank 11 is usually arranged in the body of the vehicle.

Claims (13)

Fuel system (4) for an internal combustion engine (2) of a vehicle (1), suitable for a fuel with a boiling point below 90 ° C, the fuel system comprising: a main fuel line (18) which connects a low-pressure fuel pump (12) operated by an internal combustion engine, a fuel tank (11) upstream of the low pressure pump (12), a fuel filter (17) downstream of the low pressure pump (12) and a high pressure pump (19) downstream of the fuel filter (17), the high pressure pump (19) being set up to form a fuel connected to the internal combustion engine To promote the injection system, characterized in that the fuel system (4) has a cooling flow recirculation line (15) which is connected to the main fuel line (18) and is set up to recirculate part of the fuel downstream of the low pressure pump (12) and upstream of the high pressure pump (19) back to the fuel tank (11). Fuel system according to Claim 1 , characterized in that the cooling flow recirculation line (15) is connected to a drain opening in the main fuel line (18). Fuel system according to Claim 2 , characterized in that the drain opening has a diameter greater than 0.5 mm. Fuel system according to one of the preceding claims, characterized in that the low-pressure pump (12) is connected to an internal recirculation line (14) which is provided with a pressure adjusting valve (13). Fuel system according to one of the preceding claims, characterized in that the fuel system (4) further has a main fuel return line (28) which is set up for returning fuel back to the fuel tank (11) and the at least one of the comprising the following components: a fuel filter return line (27), a high pressure pump return line (25) and an accumulator return line (24), the cooling flow recirculation line (15) being connected to the main fuel return line (28). Fuel system according to one of the preceding claims, characterized in that the cooling flow recirculation line (15) has a flow limiting valve (16) and optionally also a check valve (16 '). Fuel system according to one of the preceding claims, characterized in that the cooling flow recirculation line (15) has a capacity which is smaller than the capacity of the main fuel line (18). Fuel system according to one of the preceding claims, characterized in that the cooling flow recirculation line (15) is connected to the main fuel line (18) between the low-pressure pump (12) and the fuel filter (17). Fuel system according to one of the preceding claims, characterized in that the cooling flow recirculation line (15) is connected to the main fuel line (18) between the fuel filter (17) and the high pressure pump (19). Fuel system according to one of the preceding claims, characterized in that the fuel system is suitable for an ethanol-based fuel. Method for preventing the boiling of fuel with a boiling point below 90 ° C on an internal combustion engine-operated low-pressure pump (12) of a fuel system (4) which is connected to an internal combustion engine (12) of a vehicle (1) when the vehicle is in a state with Engine braking is located, the fuel system comprising: a main fuel line (18), which connects an internal combustion engine-operated low pressure pump (12), a fuel tank (11) upstream of the low pressure pump (12), a fuel filter (17) downstream of the low pressure pump (12) and a high pressure pump ( 19) downstream of the fuel filter (17), the high-pressure pump (19) being set up to supply fuel to an injection system of the internal combustion engine, characterized by the establishment of a cooling flow which draws part of the fuel downstream of the low-pressure pump (12) and upstream of the high-pressure pump (19) recirculated back to the fuel tank (11), and by adjustment the flow rate so that the flow cools the low-pressure pump (12) when the vehicle brakes on the engine. Procedure according to Claim 11 , characterized by carrying out the method in a fuel system according to one of the Claims 1 to 10th . Vehicle (1) characterized in that it is a fuel system according to one of the Claims 1 to 10th having.

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