EP2333283A1

EP2333283A1 - A method and system for controlling pressure in a pressure accumulator

Info

Publication number: EP2333283A1
Application number: EP09252726A
Authority: EP
Inventors: Michael David Smith
Original assignee: Perkins Engines Co Ltd
Current assignee: Perkins Engines Co Ltd
Priority date: 2009-12-04
Filing date: 2009-12-04
Publication date: 2011-06-15

Abstract

This disclosure relates to a method and system for controlling pressure in a pressure accumulator, such as a common rail, of a fuel injection system in the event of valve failure during cranking. The method comprises the steps of monitoring the speed of the engine and the valve to determine a fault which would cause the valve to remain open. When such a fault is detected, and the engine speed is in a predetermined cranking range, the continuous activation and deactivation of one or more injectors is effected. The duration and frequency of the activation is such as to enable fuel to leak from the injectors into a fuel return path without injection into the combustion chambers to reduce pressure in the accumulator. The system comprises means for effecting the method.

Description

Background

This disclosure relates to a method and system for controlling pressure in a pressure accumulator, such as a common rail, of a fuel injection system in the event of valve failure during cranking.
Many fuel injection systems for internal combustion engines include a pressure accumulator, such as a common rail, and a high pressure fuel pump for supplying fuel at high pressure to the pressure accumulator. A number of injection nozzles are supplied with high pressure fuel by the pressure accumulator. A corresponding number of fuel supply lines branch off from the pressure accumulator and lead to respective injection nozzles.
Common rail technology is increasingly being used in heavy duty engines such as those used to drive construction machinery, large ships or vessels and the like. The fuel within the common rail, e.g. diesel or heavy fuel oil, has a very high pressure. For various reasons, the pressure within the common rail may possibly exceed a predetermined level that may cause damage or perhaps even destruction of the common rail, as well as possibly equipment operating in communication with the common rail.
Consequently various systems have been developed which enable the pressure in the accumulator to be maintained at a safe level. EP-A-2110543 discloses a safety valve attached to a common rail which provides a drain path for pressurised fluid if the pressure exceeds a predetermined level.
EP-A-1024274 describes fuel pressure control apparatus which is designed to use the limited period during which normal fuel injection is not carried out to control the fuel pressure. The system has "normal" injection periods for injecting fuel accumulated in the accumulator line to the combustion chamber as "invalid" injection periods between the normal injection periods for releasing fuel pressure accumulated in the accumulator line. The initial injection periods are such that injectors are opened for such as short time line that the fuel is not injected into the combustion chamber, but spills out at a low pressure side of the fuel system. This is known as "dry firing" the injectors and the apparatus includes means for adjusting timings for driving the fuel injection valve to effect dry firing when an injection of fuel through the injector is not normally required.
US-6273067 describes a system of controlling the pressure in a common rail system which also uses dry firing of the injectors. In this system the fuel pressure within the common rail is monitored and, in the event that the measured common rail fuel pressure exceeds a predetermined threshold, the pressure is relieved by actuating the control valve of at least one of the injectors to allow fuel to flow from the common rail, through the control chamber of the injector to the fuel reservoir. The control valves are arranged so as to control the fuel pressure within the control chambers of the injectors in such a manner as to ensure that injection of fuel through those injectors into the combustion chamber does not commence.
However each of these prior art systems is dependent on the measurement of the fuel pressure within the accumulator during normal operation of the engine.

Summary

The disclosure provides a method of controlling pressure in a pressure accumulator of a fuel injection system comprising a plurality of activatable fuel injectors for injecting high pressure fuel from the accumulator into a plurality of combustion chambers, a high pressure pump for delivering fuel at high pressure to the accumulator and a valve for controlling the flow of fuel to the high pressure pump, the method comprising the steps of:-

monitoring the speed of the engine;
monitoring the valve to determine a fault which would cause the valve to remain open; and
effecting the continuous rapid activation and deactivation of one or more injectors on an alternating basis when such a fault is detected and the engine speed is in a predetermined cranking range, the duration and frequency of the activation being such as to enable fuel to leak from the injectors into a fuel return path without injection into the combustion chambers and to reduce pressure in the accumulator.

The disclosure also provides a system for controlling pressure in a pressure accumulator of a fuel injection system comprising a plurality of activatable fuel injectors for injecting high pressure fuel from the pressure accumulator into a plurality of combustion chambers, a high pressure pump for delivering fuel at high pressure to the accumulator and a valve for controlling the flow of fuel into the high pressure pump, comprising:-

a controller connected to monitor the speed of the engine;
said controller also being connected to monitor the valve to determine a fault which would cause the valve to remain open;

Whilst there are known pressure relief systems, which utilise a pressure relief valve, which are effective during normal operation of the engine, they are not effective during cranking (start up) of the engine. This is because, at lower pump speeds, the high pressure pump is not capable of generating fuel pressures high enough to open the pressure relief valve. The pump capability is limited at lower speeds due to the swept volume of the pump per unit time being lower. During cranking, when the high pressure pump is at maximum capability, the pressure is above the threshold that can cause pump damage, but below the pressure required to open the pressure relief valve. This is only applicable for a high pressure pump with a normally open suction control valve.
The method and system will now be described, by way of example only, with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 is a schematic representation of the elements of a common rail fuel system for an internal combustion engine; and
Figures 2 and 3 are flow charts illustrating the "decisions" made by the electronic control module.

Detailed Description

Referring to Figure 1, a fuel system 10 for an internal combustion engine (not shown) utilising a pressure accumulator in the form of a common rail 11 is shown. Such a system 10 may comprise a reservoir 12 containing fuel at ambient (low) pressure and a low pressure pump 13 which draws the low-pressure fuel from the reservoir 12 through a first fuel supply line 14 and feeds it to a high pressure pump 15. The high pressure pump 15 pressurises the fuel to the desired fuel injection pressure level and delivers it to the common rail 11 via a second fuel supply line 23. The pressure in the common rail 11 may partly be controlled by a pressure relief valve 16, which diverts fuel to a fuel return line 17 if the pressure in rail 11 is above a desired pressure during operation of the engine. The fuel return line 17 returns fuel to the low pressure reservoir 12.
A plurality of fuel injectors 18 draw high pressure fuel from the common rail 11 and inject it into the combustion cylinders (not shown) of the engine. The injectors 18 typically include a needle valve and a solenoid which moves the needle valve to open or close spray holes. The opening of the spray holes to inject a required quantity of fuel into the engine at a required time is achieved by energizing the solenoid coil. Fuel not injected by injectors 18 is diverted to the fuel return line 17.
A controller, usually in the form of an electronic control module (ECM) 19, provides general control for the fuel system 10. The ECM 19 is connected to receive various input signals, such as fuel pressure and temperature from sensors 20,21 connected to the common rail 11, and the rotational speed of the engine etc. to determine operational conditions. One of the functions nf the ECM 19 is to calculate the correct fuel injection timing during normal running of the engine and send out control signals to, inter alia, activate and deactivate the fuel injectors 18.
The high pressure pump 15 incorporates a suction control valve 22, preferably in the form of an electrically operated solenoid valve. The suction control valve 16 is responsive to a control signal from the ECM 19, to which it is connected, to regulate the amount of fuel to be sucked into the high pressure pump 15. The suction control valve 22 is of the normally open type, such that when the solenoid is de-energised, the fuel supply line 14 is opened fully. Energisation of the solenoid causes the suction control valve 22 to close.
As the suction control valve 22 is a solenoid valve, a fault in the electrical supply thereto will result in the valve 22 failing in the open position. In this case the high pressure pump 15 will continue to pump at the maximum flow rate and the pressure in the common rail 11 will continue to rise. The high pressure pump 15 is capable of generating very high pressures, for example well above 50MPa, which can cause the pump 15 and/or the common rail 11 to fail at low engine speeds. At higher speeds these pressures are unlikely to cause the same sort of damage because there is sufficient lubrication from the fuel, whereas at lower speeds the lubrication film has a lower load capability. The ECM 19 is therefore configured to detect a fault with the suction control valve 22 which results in it failing in the open position.
When the engine is switched on, the ECM 19 commences a "pressure minimisation decision cycle" which checks to determine whether the pressure relief is required during cranking. This is illustrated in the flow chart of Figure 2. In the event of the detection, by the ECM 19, of a fault with the suction control valve 22 during cranking, the ECM 19 activates one or more of the fuel injectors 18 such that they dry fire continuously (as described in more detail below) to relieve the fuel pressure in the common rail 11. The ECM 19 is programmed with the cranking speed threshold speed for the engine in question; the cranking speed threshold is the maximum speed that it would be expected that the engine would be cranked at. Above this speed it would normally be assumed that combustion is taking place in the cylinders. A typical speed would be 300rpm. This speed threshold would be considered generic and would apply to virtually any engines used in off highway application although it may vary for engines used in other applications.
If the engine ceases cranking the ECM 19 deactivates the dry firing of the fuel injectors 18. This can happen if the engine is switched off and the speed drops to 0rpm, which will cause the high pressure pump 15 to deactivate, or if the engine speed is increased past the cranking threshold. At this point the pressure minimisation decision cycle of the ECM 19 is ended.
Additionally, as shown in Figure 3, the ECM 19 can be set to activate the dry firing of the fuel injectors 18 if the aforementioned conditions are met and the measured rail (accumulator) pressure lies between a minimum rail pressure limit and a maximum rail pressure limit. The ECM 19 computes the fuel rail pressure (FRP) map taking account of engine speed, and is calibrated with a maximum fuel rail pressure before there is a risk of mechanical damage to the high pressure pump for a given engine speed. If the measured rail pressure goes above this maximum fuel rail pressure, then it is assumed that the pressure reduction strategy is not working and it would probably cause less risk of damage to stop the pressure reduction strategy and allow the engine to start and open the pressure relief valve.
If the measured rail pressure is less than a preset minimum rail pressure, the pressure relief system may also be set to be switched off as it is considered that there is no risk of damage.
The ECM 19 may also be configured to detect a fault with the fuel pressure sensor 20, which would mean that the rail pressure cannot be monitored. If such a fault is detected and the ECM 19 detects valve failure during cranking, the ECM 19 activates the continuous dry firing of the fuel injectors 18.
During dry firing of the fuel injectors 18, the needle valves are opened for such a short time so that the fuel is not injected into the engine combustion chamber, but spills out at a low pressure side of the fuel system. When the ECM 19 activates the fuel injectors 18 to dry fire continuously, In one embodiment the ECM 19 instructs a pattern of alternate sets of injectors 18, e.g. three injectors out of the six injectors on a six cylinder engine, to be dry fired so that the injectors 18 in each set are activated simultaneously for a first preset "on duration" time period (T1) and deactivated for a second preset "dwell" time period (T2). This pattern cycles continuously, with the first set on and the second set off and vice versa, whilst the dry firing program is activated.
The range for the on duration is defined by the injector hardware design, but would typically this would be about 200usec. The dwell time is also defined by the injector hardware design and would have more variation than the on time. Typically the minimum dwell time would be in the range 200usec to 1000usec. This time could be set to be longer than 1000usec if sufficient leakage can be achieved at a lower frequency of injection pulses.
In alternative embodiments, the pattern need not be of alternating sets of injectors 18, but could range from firing all injectors 18 simultaneously, to firing each injector 18 in turn or repeated firing one or a limited number of injectors 18. The limitation on this is the way the injector drivers within the ECM 19 have been designed.
The first preset time period (T1) is based on the "dry fire injection duration map" which is an input of rail pressure and an output of the injection duration. This map is calibrated so that the injection duration is the maximum duration at the given pressure without delivery of any fuel to the cylinder. The second preset time period (T2) is the output from the "dry fire dwell map" which has an input of engine speed. This map is calibrated to define the frequency of the injection pulses which in turn defines the leakage flow rate that is required for the engine. In an engine used in an off road application, this could be calibrated to be as high as, approximately, 200mm³ per pump revolution.
In a test system the preset time periods (T1) and (T2) were calculated so as to provide 12 injection events per revolution of the high pressure pump 15, with T1 set at 200 microseconds and T2 at 1000 microseconds. With the engine speed set at 200rpm and the rail pressure at 50MPa this gave a sufficient leakage flow rate.
Element List

10: fuel system
11: common rail
12: reservoir
13: low pressure pump
14: fuel supply line
15: high pressure pump
16: safety valve
17: fuel return line
18: fuel injector
19: ECM
20: pressure sensor
21: temperature sensor
22: suction control valve
23: fuel supply line

Claims

A method of controlling pressure in a pressure accumulator (11) of a fuel injection system (10) comprising a plurality of activatable fuel injectors (18) for injecting high pressure fuel from the pressure accumulator (11) into a plurality of combustion chambers, a high pressure pump (15) for delivering fuel at high pressure to the accumulator (11) and a valve (22) for controlling the flow of fuel into the high pressure pump (15), the method comprising the steps of:-
monitoring the speed of the engine;

monitoring the valve (22) to determine a fault which would cause the valve (22) to remain open; and

effecting the continuous activation and deactivation of one or more injectors (18) when such a fault is detected and the engine speed is in a predetermined cranking range, the duration and frequency of the activation being such as to enable fuel to leak from the injectors (18) into a fuel return path without injection into the combustion chambers to reduce pressure in the accumulator(11).
A method as claimed in claim 1 in which at least two sets of injectors are alternately activated and deactivated.
A method as claimed in claim 1 in which all the injectors are alternately activated and deactivated.
A method as claimed in any one of the preceding claims in which the predetermined cranking range of the engine speed lies between 0 rpm and a predetermined cranking speed threshold for the engine.
A method as claimed in any one of the preceding claims further comprising the step of monitoring the pressure in the accumulator (11), such that the continuous activation and deactivation of the one or more injectors (18) is effected when the pressure in the accumulator lies in a predetermined range.
A method as claimed in any one of the preceding claims further comprising the step of monitoring a sensor (20) which measures the accumulator pressure to determine a fault in the sensor (20) and, in the event that a fault is detected, to effect the continuous activation and deactivation of the one or more injectors (18).
A system for controlling pressure in a pressure accumulator (11) of a fuel injection system (10) comprising a plurality of activatable fuel injectors (18) for injecting high pressure fuel from the pressure accumulator (11) into a plurality of combustion chambers, a high pressure pump (15) for delivering fuel at high pressure to the accumulator (11) and a valve (22) for controlling the flow of fuel into the high pressure pump (15), comprising:-
a controller (19) connected to monitor the speed of the engine;

said controller (19) also being connected to monitor the valve (22) to determine a fault which would cause the valve (22) to remain open;
wherein the controller (19) effects the continuous rapid activation and deactivation of one or more injectors (18) on an alternating basis when such a fault is detected and the engine speed is in a predetermined cranking range, the duration and frequency of the activation being such as to enable fuel to leak from the injectors (18) into a fuel return path without injection into the combustion chambers and reduce the pressure in the accumulator (11).
A system as claimed in claim 7 in which the controller (19) is further connected to monitor the pressure in the accumulator (11) and effects the continuous rapid activation and deactivation of the one or more injectors (18) when the pressure in the accumulator lies in a predetermined range.
A system as claimed in claim 7 or claim 8 further comprising a pressure sensor (20) which measures the accumulator pressure and the controller (19) is further connected to monitor the sensor (2) to determine a fault in the sensor (20) and effecting the continuous activation and deactivation of the one or more injectors (18) in the event that a fault is detected.