DE102018211173A1 - Method for operating a fuel delivery device for cryogenic fuels, fuel delivery device for cryogenic fuels - Google Patents

Abstract

The invention relates to a method for operating a fuel delivery device (20) for cryogenic fuels, comprising a piston pump (1) for delivering the cryogenic fuel to high pressure, the piston pump (1) having a reciprocating pump piston (2) which is acted upon a pressure chamber (3) on the drive side is hydraulically driven with a liquid fuel, in particular with diesel fuel. According to the invention, a liquid fuel, in particular diesel fuel, is used as the hydraulic fluid, which is removed from a pressure-controlled high-pressure accumulator (4) and fed to the pressure chamber (3) via a high-pressure line (5), with the aid of a high-pressure pump (6) conveying into the high-pressure accumulator (4). the liquid fuel is subjected to high pressure. The invention further relates to a fuel delivery device (20) for cryogenic fuels for carrying out the method according to the invention.

Description

The invention relates to a method for operating a fuel delivery device for cryogenic fuels with the features of the preamble of claim 1. Furthermore, the invention relates to a fuel delivery device for cryogenic fuels which is suitable for carrying out the method. The cryogenic fuel is used to operate an internal combustion engine, which can in particular be the internal combustion engine of a vehicle, preferably a commercial vehicle.

The proposed fuel delivery device comprises a piston pump with a reciprocating pump piston for delivering the cryogenic fuel to high pressure. In order to prevent transverse forces acting on the pump piston, a hydraulic drive for the piston pump is proposed.

State of the art

From the EP 2 923 062 B1 A method and a system for supplying an internal combustion engine with a gaseous fuel with the aid of a fuel pump which is driven hydraulically are known. For this purpose, the fuel pump comprises a hydraulic drive unit which can be supplied with hydraulic fluid from a hydraulic fluid tank by means of a hydraulic pump. In order to enable the hydraulic pump to be operated independently of the operation of the internal combustion engine, a hydraulic pump driven by an electric motor is proposed. Furthermore, at least one further hydraulic pump is proposed in order to increase the hydraulic fluid flow rate in the direction of the hydraulic drive unit if necessary.

Starting from the prior art mentioned above, the present invention is based on the object of improving the efficiency of a hydraulic drive of a fuel pump for cryogenic fuels. In particular, large volume flows that require a large hydraulic pump or several hydraulic pumps are to be avoided on the drive side.

To achieve the object, the method with the features of claim 1 and the fuel delivery device with the features of claim 7 are proposed. Advantageous developments of the invention can be found in the respective subclaims.

Disclosure of the invention

A method is proposed for operating a fuel delivery device for cryogenic fuels, which comprises a piston pump for delivering the high-pressure cryogenic fuel. The piston pump has a reciprocating pump piston which is hydraulically driven by the application of a hydraulic fluid to a pressure chamber on the drive side. According to the invention, a liquid fuel, in particular diesel fuel, is used as the hydraulic fluid, which is removed from a pressure-controlled high-pressure accumulator and fed to the pressure chamber via a high-pressure line, the high-pressure liquid being applied to the liquid fuel with the aid of a high-pressure pump delivering the high-pressure accumulator.

The use of liquid fuel as hydraulic fluid has the advantage that liquid fuel is usually already available on board a vehicle. This is carried as additional fuel and injected into the internal combustion engine in order to ignite the cryogenic fuel and / or to enable emergency operation in the event of a fault. This means that liquid fuel is also burned. In order to replace the amount supplied to the combustion, liquid fuel is regularly refilled. This means that there is not only a sufficient, but constantly renewing amount of liquid fuel available for the hydraulic drive of the piston pump. A regular change of the hydraulic fluid can therefore be omitted, which proves to be a further advantage.

High-pressure liquid fuel is used according to the invention for the hydraulic drive of the piston pump. The high pressure is applied by means of a high pressure pump, which conveys to a pressure-controlled high pressure accumulator, from which the liquid fuel is taken and fed to the piston pump via a high pressure line. Due to the pressure-controlled high-pressure accumulator, the piston pump can be operated asynchronously to the internal combustion engine and therefore as required. This is because the pressure-controlled high-pressure accumulator ensures that a permanently high pressure, which is preferably at least 300 bar, is present in the high-pressure line and can be used to operate the piston pump. Volume decreases through the piston pump are compensated for by the pressure-controlled high-pressure accumulator.

The pressure level in the high-pressure accumulator is preferably 500 bar. Due to the high pressure, comparatively small volume flows are sufficient to apply the required drive power. This means that a smaller high-pressure pump can be used. A suction-throttled high-pressure pump is preferably used, so that the drive power can be reduced at part load. As a result, an increase in the Efficiency of the hydraulic drive of the piston pump can be achieved.

Furthermore, the pressure of the cryogenic fuel and the liquid fuel pressure are each preferably set permanently to approximately 500 bar. This means that the return and return times of the pump piston are always the same (analog "rated point", maximum quantity = maximum frequency). Only the time interval between two strokes changes when there is a load change. Rapid conveying and unloading, in turn, reduces the heat input into the piston pump housing under partial load compared to a sinusoidal piston movement. This also reduces the risk of cryogenic fuel evaporating when drawn in.

The liquid fuel is preferably stored in a liquid fuel tank and fed to the high-pressure pump with the aid of at least one prefeed pump. An electric fuel pump is preferably used as the pre-feed pump, since this enables a quantity metering or regulation as required. Alternatively or in addition, a simple mechanical pump, in particular a gear pump, can be used as the pre-feed pump. If no liquid fuel is required to drive the piston pump, only the gear pump has to be driven in order to replace lost quantities due to leakage.

A radial piston pump is preferably used as the high pressure pump, which comprises at least one pump element with a pump piston which is driven in one stroke movement via a cam or eccentric drive. High-pressure pumps of this type are also used in common-rail injection systems, so that they can be used. If the high-pressure pump has a plurality of pump elements, at least one pump element can be used to convey liquid fuel into a rail, to which at least one fuel injector for injecting the liquid fuel into a combustion chamber of the internal combustion engine is connected. Function integration means that there is no need for a further high-pressure pump. If a further high-pressure pump is provided, at least both high-pressure pumps can be connected to the internal combustion engine via a common power take-off. In this way, a compact arrangement of the two high-pressure pumps can be created.

At least one metering unit, which is connected upstream of at least one pump element of the high-pressure pump, is advantageously used for metering liquid fuel. The delivery rate of the high pressure pump can be regulated by means of the metering unit. If only one high-pressure pump is provided as a drive pump and for conveying liquid fuel into a rail, it is proposed that at least one further pump element of this high-pressure pump be preceded by a further metering unit. Via the two metering units, the quantity of liquid fuel delivered from the liquid fuel tank by means of the prefeed pump can be allocated to the several pump elements as required. If a further high-pressure pump for conveying liquid fuel is provided in a rail, the further metering unit is connected upstream of the further high-pressure pump.

Furthermore, the action on the drive-side pressure chamber of the piston pump with liquid fuel is preferably controlled with the aid of a valve arrangement. For this purpose, the valve arrangement is arranged between the pressure chamber on the drive side and the high-pressure line connected to the high-pressure accumulator. Liquid fuel as hydraulic fluid can thus be supplied to the pressure chamber as required. If liquid fuel is supplied to the pressure chamber, the pressure in the pressure chamber rises, so that a hydraulic pressure force acts on the pump piston of the piston pump, which leads to a working stroke of the pump piston. In order to then reset the pump piston, liquid fuel must be removed from the pressure chamber. It is therefore proposed as a further development measure that the pressure chamber is alternately connected to the high-pressure line and a low-pressure line via the valve arrangement. Liquid fuel can be discharged from the pressure chamber via the low-pressure line, so that the pressure is relieved and the pump piston is returned to its starting position, for example mechanically by means of the spring force of a spring. If the resetting is effected mechanically by means of a spring, the valve arrangement can be designed as a 3/2-way valve or can include one. If there is no spring to reset the pump piston, the reset can be carried out hydraulically. In this case, the proposed valve arrangement is preferably designed as a 4/2-way valve or comprises one. Via the 4/2-way valve, a further pressure chamber on the drive side, which is preferably opposite the first pressure chamber on a piston section of the pump piston that serves for the drive, can be acted upon or relieved of liquid fuel, specifically opposite the first pressure chamber. The liquid fuel discharged from a pressure chamber is preferably fed back into the liquid fuel tank via the low-pressure line or a return line connected to the low-pressure line, so that this amount is not lost, but is still available as hydraulic fluid or fuel.

To achieve the object mentioned above, a fuel delivery device is also used proposed for cryogenic fuels, which comprises a piston pump to deliver the cryogenic fuel to high pressure. The piston pump has a reciprocating pump piston, which can be driven hydraulically by acting on a drive-side pressure chamber with a hydraulic fluid, preferably with a liquid fuel, in particular with diesel fuel. According to the invention, the fuel delivery device further comprises a pressure-controlled high-pressure accumulator and a high-pressure line for connecting the high-pressure accumulator to the drive-side pressure chamber of the piston pump, and a high-pressure pump delivering into the high-pressure accumulator.

The proposed fuel delivery device is particularly suitable for carrying out the method according to the invention. The same advantages can thus be achieved with it. In particular, demand-driven operation of the piston pump for cryogenic fuels is made possible, since the pressure level in the high-pressure line can be kept largely constant via the pressure-controlled high-pressure accumulator. This is because the quantity supplied to the pressure chamber via the high-pressure line is compensated for by the high-pressure accumulator. Furthermore, due to the comparatively high pressure in the high-pressure line, the volume flows required for driving the piston pump can be reduced. In this way, the efficiency can be increased since the high-pressure pump for the high-pressure application of the hydraulic fluid can also become smaller with the volume flows.

Liquid fuel, in particular diesel fuel, which is stored in a liquid fuel tank, is preferably used as the hydraulic fluid. Since combustion engines operated with a cryogenic fuel, in particular gas engines, carry liquid fuel as a further fuel and / or as a control medium for the hydraulic control of valves, such as fuel injectors, in this case only liquid fuel has to be kept available as a further medium. This means that in addition to the cryotank, only one additional tank is required for the liquid fuel. Since liquid fuel is also burned when the internal combustion engine is in operation, it must be refueled regularly. The hydraulic fluid used to drive the piston pump is therefore also regularly renewed.

At least one prefeed pump is preferably provided, by means of which liquid fuel can be removed from a liquid fuel tank and can be supplied to the high-pressure pump as hydraulic fluid. The structure of the system used to drive the piston pump hydraulically is thus the same as that of a common rail injection system, so that appropriate components can be used. Furthermore, the systems can be merged if a common rail injection system for the injection of liquid fuel or diesel fuel is present. The at least one pre-feed pump is preferably designed as an electric fuel pump. With the help of the electric fuel pump, quantity pre-control can also be implemented. Alternatively or in addition, a gear pump can be provided as a pre-feed pump. Gear pumps are particularly robust and therefore fail less often. If the gear pump is operated in combination with an electric fuel pump, the base load is preferably supplied by the gear pump. In the event of a start and under high load, the electric fuel pump can then be switched on for support.

The high-pressure pump is preferably designed as a radial piston pump and comprises at least one pump element with a pump piston, which can be driven in one stroke movement via a cam or eccentric drive. The high-pressure pump thus resembles a high-pressure pump of a common rail injection system. This means that if several pump elements are available, at least one pump element can be used to deliver liquid fuel into a rail. In this way, multiple functions can be implemented with just one high-pressure pump. To increase the pump frequency, the pump pistons of a pump unit can be supported on a multiple cam, for example a double or triple cam, via the cam drive, so that the number of pump elements can be kept small.

It is further proposed that a metering unit is connected upstream of at least one pump element of the high-pressure pump. The metering unit enables a quantity to be metered regardless of the type of pre-feed pump. A further metering unit is preferably connected upstream of at least one further pump element of the high-pressure pump or a further high-pressure pump for conveying liquid fuel into a rail. This means that at least two metering units are provided, which allow the quantity of liquid fuel withdrawn from the liquid fuel tank to be allocated to the pump elements or high-pressure pumps serving different functions as required.

A valve arrangement is preferably provided between the drive-side pressure chamber of the piston pump and the high-pressure line for supplying the drive-side pressure chamber with liquid fuel, by means of which the drive-side pressure chamber can be alternately connected to the high-pressure line and a low-pressure line. This means that the pressure chamber on the drive side can be acted upon and relieved of high pressure alternately via the valve arrangement. This ensures that the pump piston of the piston pump can be returned to its starting position after a working stroke. A simple spring can be used for resetting, for example. In this case, the valve arrangement for connecting the pressure chamber to the high-pressure line can be designed as a 3/2-way valve or can include one. If the resetting is to be effected hydraulically, the valve arrangement can be designed as a 4/2-way valve or comprise such a valve. Another 4/2-way valve can then be used to alternately connect a further pressure chamber on the drive side to the high-pressure line and the low-pressure line, in opposite directions to the first pressure chamber. The two pressure chambers are preferably located opposite one another on a piston section of the pump piston, so that the hydraulic pressure forces generated via the pressure in the pressure chambers act in opposite directions. The low-pressure line is preferably connected directly or indirectly to the liquid fuel tank via a return line, so that the amount discharged from the at least one pressure chamber is returned to the tank. It is then still available as hydraulic fluid or as fuel.

In order to prevent the pressure in the high-pressure line from exceeding a permissible limit value in the event of a fault, in particular in the event of a fault on the part of the metering unit, a pressure relief valve can be provided upstream of the valve arrangement described above. In this way, the pressure relief valve enables emergency operation or a “limp home” function with a reduced pressure level. The quantity of liquid fuel that is controlled via the pressure relief valve is preferably fed back into the liquid fuel tank via a return line, so that it is still available to the system.

A preferred embodiment of the invention is explained below with reference to the accompanying drawings. This shows a schematic representation of a fuel delivery device according to the invention in connection with a common rail injection system for a liquid fuel, which is diesel fuel.

Detailed description of the drawing

The fuel delivery device according to the invention shown in the figure 20 serves to supply an internal combustion engine (not shown) of a vehicle, in particular a commercial vehicle, with a cryogenic fuel, for example with natural gas. The fuel delivery device shown 20 includes a piston pump 1 with a reciprocating pump piston 2 , the drive side a pressure chamber 3 limited. The pressure room 3 is about a valve assembly 14 alternating with a high pressure line 5 and a low pressure line 15 connectable so that the pressure in the pressure chamber 3 can be alternately raised and lowered. The pressure in the pressure chamber 3 raised, this leads to one on the pump piston 2 acting hydraulic pressure force, so that it performs a working stroke. The subsequent resetting of the pump piston 2 is also effected hydraulically in the present case. The pressure room is located for this 3 on a piston section 21 another pressure room 22 opposite, also via the valve arrangement 14 alternating with the high pressure line 5 and the low pressure line 15 is connectable, namely opposite to the first pressure chamber 3 , The valve assembly 14 is designed as a 4/2-way valve. On the other hand, the pump piston 2 a compression room 25 limited, even after a working stroke of the pump piston 2 a residual amount of fuel and thus a certain residual pressure remains on the pump piston 2 an additional restoring pressure force. During the subsequent suction stroke of the pump piston 2 becomes the compression space 25 refilled with cryogenic fuel so that the pressure in the compression chamber 25 increases. This also leads to one on the pump piston 2 acting restoring force, which is the hydraulic return of the pump piston 2 supported.

For pressurizing the pressure rooms 3 and 22 In the present case, a liquid fuel is used which is in a liquid fuel tank 7 stocked and by means of a high pressure pump 6 is pressurized with high pressure. The high pressure pump 6 conveys into a high pressure accumulator 4 connected to the high pressure line 5 connected. The high-pressure pump is designed as a radial piston pump and in the present case has two pump elements 9 . 9 ' with one pump piston each 10 . 10 ' on. Every pump piston 10 . 10 ' is via a cam drive 11 . 11 ' supported on a multiple cam. The high pressure pump 6 is via a pre-feed pump 8th , which is designed as an electric fuel pump, liquid fuel from the liquid fuel tank 7 fed. In addition to the pre-feed pump 8th is another pre-feed pump 8th' provided that is designed as a simple gear pump. This feed pump 8th' can, for example, with a non-delivering piston pump 1 to compensate for leakage quantities. The pre-feed pump designed as an electric fuel pump 8th In this case, it does not have to be put into operation.

The pre-feed pumps 8th . 8th' not only supply the high pressure pump 6 , but also another high pressure pump 6 ' with liquid fuel from the liquid fuel tank 7 , The further one high pressure pump 6 ' supports in a rail 13 , to the fuel injectors 17 are connected, by means of which the liquid fuel can be injected into a combustion chamber (not shown) of the internal combustion engine. The liquid fuel can thus also be used to ignite the cryogenic fuel and / or to implement emergency operation if, for example, diesel fuel is used as the liquid fuel. The fuel injectors 17 can in particular be designed as dual-fuel injectors.

Since the fuel delivery device shown 20 two high pressure pumps 6 . 6 ' it is important to ensure that both high pressure pumps 6 . 6 ' with enough liquid fuel from the liquid fuel tank 7 be supplied. Both high pressure pumps 6 . 6 ' is therefore a metering unit 12 . 12 ' upstream for quantity metering or regulation. Excess quantities of the pilot-controlled pre-feed pumps 8th . 8th' are via an overflow valve 23 in the liquid fuel tank 7 recycled.

To in the high pressure line 5 A pressure relief valve is also to prevent a pressure rise above a permissible maximum value 16 provided on the control side via a return line 19 with the liquid fuel tank 7 is connected so that the tax amount back into the liquid fuel tank 7 arrives. To the return line 19 is also the low pressure line 15 connected, so that also from the pressure rooms 3 . 22 amount of liquid fuel in the liquid fuel tank 7 is dissipated.

In addition, there is a leakage line 18 provided about which a tour 24 of the pump piston 2 the piston pump 1 as well as the valve arrangement 14 to return the tax amount with the liquid fuel tank 7 connected is. This means that these quantities also get back into the liquid fuel tank 7 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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.

Patent literature cited

• EP 2923062 B1 [0003]

Claims (10)

Method for operating a fuel delivery device (20) for cryogenic fuels, comprising a piston pump (1) for delivering the cryogenic fuel to high pressure, the piston pump (1) having a reciprocating pump piston (2), which by acting on a drive-side pressure chamber ( 3) is driven hydraulically with a hydraulic fluid, characterized in that a liquid fuel, in particular diesel fuel, is used as the hydraulic fluid, which is removed from a pressure-controlled high-pressure accumulator (4) and fed to the pressure chamber (3) via a high-pressure line (5), with the aid of a high pressure pump (6) delivering liquid fuel to high pressure in a high pressure accumulator (4). Procedure according to Claim 1 , characterized in that the liquid fuel is stored in a liquid fuel tank (7) and is fed to the high pressure pump (6) with the aid of at least one prefeed pump (8), preferably an electric fuel pump and / or a gear pump being used as the prefeed pump (8). Procedure according to Claim 1 or 2 , characterized in that a radial piston pump is used as the high pressure pump (6), which comprises at least one pump element (9) with a pump piston (10) which is driven by a cam or eccentric drive (11) in a lifting movement. Method according to one of the preceding claims, characterized in that for metering liquid fuel at least one metering unit (12) is used, which is connected upstream of at least one pump element (9) of the high pressure pump (6), preferably another pump element (9 ') of the high pressure pump (6) or a further high-pressure pump (6 ') for conveying liquid fuel into a rail (13) is connected upstream of a further metering unit (12'). Method according to one of the preceding claims, characterized in that the application of liquid fuel to the pressure chamber (3) is controlled with the aid of a valve arrangement (14), the pressure chamber (3) preferably alternating with the high-pressure line (5) via the valve arrangement (14). and a low pressure line (15) is connected. Fuel delivery device (20) for cryogenic fuels, comprising a piston pump (1) for delivering the cryogenic fuel to high pressure, the piston pump (1) having a reciprocating pump piston (2), which is acted upon by a pressure chamber (3) on the drive side Hydraulic fluid can be driven hydraulically, characterized in that the fuel delivery device further includes a pressure-controlled high-pressure accumulator (4) and a high-pressure line (5) for connecting the high-pressure accumulator (4) to the pressure chamber (3) on the drive side of the piston pump, as well as a high-pressure pump delivering the high-pressure accumulator (4) (6) includes. Fuel delivery device (20) after Claim 6 , characterized in that at least one pre-feed pump (8) is provided, by means of which liquid fuel can be removed from a liquid fuel tank (7) and the high-pressure pump (6) can be supplied as hydraulic fluid, preferably at least one pre-feed pump (8) as an electric fuel pump and / or as Gear pump is executed. Fuel delivery device (20) after Claim 6 or 7 , characterized in that the high-pressure pump (6) is designed as a radial piston pump and comprises at least one pump element (9) with a pump piston (10) which can be driven in a lifting movement via a cam or eccentric drive. Fuel delivery device (20) according to one of the Claims 6 to 8th , characterized in that at least one pump element (9) of the high-pressure pump (6) is preceded by a metering unit (12), preferably another pump element (9 ') or another high-pressure pump (6') for conveying liquid fuel into a rail (13 ) a further metering unit (12 ') is connected upstream. Fuel delivery device (20) according to one of the Claims 6 to 9 , characterized in that a valve arrangement (14) is provided, by means of which the pressure chamber (3) can be alternately connected to the high-pressure line (5) and a low-pressure line (15).

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