Abstract:
A fuel injection system includes a fuel pressure boost pump having a pump body that defines a pump cylinder and a pump chamber. A piston structure is movable in the pump cylinder along a longitudinal axis of the piston structure. A fuel inlet conduit and a fuel outlet conduit are in flow connection with the pump chamber, the fuel inlet conduit being provided with a first one-way valve and the fuel outlet conduit being provided with a second one-way valve. A temperature sensor is in thermally conductive contact with the pump body.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a fuel injection system comprising a pressure boost pump having a pump body defining a pump cylinder and a pump chamber, and also comprising a fuel inlet conduit and a fuel outlet conduit in flow connection with the pump chamber, the conduits each having a one-way valve, and further a piston structure (which may be a simple piston member or a more complex apparatus) inside the pump cylinder and movable along the longitudinal axis of the piston structure. 
   In addition, the invention relates to a method of operating a fuel injection system that comprises a pressure boost pump having a pump body defining a pump chamber and a pump cylinder and also comprising a fuel inlet conduit and a fuel outlet conduit in flow connection with the pump chamber, the conduits each having a one-way valve, and further a piston structure arranged inside the pump cylinder, in which method during the intake stroke of the piston structure fuel flows into the pump chamber and during the power stroke of the piston structure fuel flows away from the pump chamber via the one-way valve in elevated pressure and temperature. 
   Such fuel pressure boost pumps are commonly used in so-called common rail fuel injection systems. A known common rail fuel injection system is disclosed in the applicant&#39;s U.S. Pat. No. 6,240,901. In the known system, fuel is fed from the fuel tank to the pressure accumulator by means of a high pressure pump, subsequent to which the fuel is injected into cylinders of the engine by means of injectors. 
   A problem with a pump like this is that lateral forces acting on the piston structure of the pump cause wear of the piston structure and increase the risk of seizure. 
   It is an aim of the present invention to provide a fuel injection system minimizing the problems associated with prior art. It is an especial aim of the invention to provide a capability for efficiently detecting pressure boost pump malfunctions in a so-called common rail fuel injection system. 
   SUMMARY OF THE INVENTION 
   In an embodiment of the invention, the fuel injection system comprises a pressure boost pump, in which the pump cylinder and the pump chamber have been arranged in connection with the body part thereof, and a fuel inlet conduit and a fuel outlet conduit in flow connection with the pump chamber, the conduits each having a one-way valve, and further a piston structure arranged inside the pump cylinder, the piston structure being movable along its longitudinal axis. The fuel injection system further comprises a temperature sensor arranged in the body part for monitoring the operation of the pump. 
   In a preferred embodiment of the invention, the fuel injection system comprises a number of pressure boost pumps, each of which pumps is provided with a temperature sensor, and additionally the system comprises an analysis apparatus for comparing the data read provided by the pressure boost pump temperature sensors. Advantageously the pressure boost pumps are arranged to pump fuel into a functionally common pressure accumulator space. 
   A method embodying the invention is performed with a fuel injection system comprising a pressure boost pump, in which the pump cylinder and the pump chamber have been arranged in connection with the body part thereof, and a fuel inlet conduit and a fuel outlet conduit in flow connection with the pump chamber, the conduits having a one-way valve, and further a piston structure arranged inside the cylinder, and in accordance with the method during the intake or suction stroke of the piston structure fuel flows into the pump chamber and during the power or pressure stroke of the piston structure fuel flows away from the pump chamber via the one-way valve at elevated pressure and higher temperature and in which method the temperature of the pressure boost pump is measured for monitoring the operation of the pressure boost pump. The temperature of the pressure boost pump is measured using a temperature sensor arranged in connection with the pressure boost pump. 
   Typically the part in which a malfunction occurs is the one-way valve of the outlet conduit. In the event of a malfunction, this one-way valve may allow fuel to move into and out of the pump chamber. Therefore, the temperature sensor is preferably arranged adjacent the pump chamber or the channel connecting the pump chamber and the one-way valve of the outlet conduit, or, for example adjacent the one-way valve of the outlet chamber so that a temperature increase caused by the above-mentioned malfunction can be detected. 
   In the event that the system comprises only one pressure boost pump, the rate of change of the measurement data read from the temperature sensor is compared with a setpoint of the rate of change, and in case the measured rate of change exceeds the setpoint, an alarm condition is activated. 
   If the fuel injection system comprises a number of pressure boost pumps arranged to pump into a functionally common pressure accumulation space and each pump is provided with at least one temperature sensor, and the injection system further comprises an analysis apparatus for comparing the measurement data read from the temperature sensors of the several pressure boost pump, the temperature of each pressure boost pump is read into the analysis apparatus, in the analysis apparatus the temperature of each pressure boost pump is compared with the temperature of at least one other pressure boost pump and if the temperature difference is larger than a setpoint, an alarm condition is activated. 
   The temperature of each pressure boost pump is regularly read while the fuel injection system is in operation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following the invention is described by way of example and with reference to the appended drawings, of which 
       FIG. 1  shows an exemplary embodiment of the fuel pressure boost pump; and 
       FIG. 2  shows another exemplary embodiment of the fuel pressure boost pump. 
   

   DETAILED DESCRIPTION 
   In the appended drawings, reference numeral  1  refers to a piston engine fuel pressure boost pump  1  of a fuel injection system. The fuel injection system comprises a source for the fuel, such as a fuel tank  3 , to which the fuel pressure boost pump is connected by means of a channel  4  which may be provided with a transfer pump  4 . 1 . The fuel pressure boost pump  1  comprises a body part  5 , which defines a pump cylinder  6  and a pump chamber  7 . Both a fuel inlet conduit  8  and a fuel outlet conduit  9  are in flow connection with the pump chamber  7 . The conduits  8 ,  9  are provided with respective one-way valves  8 . 1 ,  9 . 1  so that in normal operation the one-way valve  8 . 1  of the inlet conduit  8  allows fuel to flow into the pump chamber  7  but does not allow it to flow away from the pump chamber  7 , and the one-way valve  9 . 1  of the outlet conduit  9  allows fuel to flow away from the pump chamber  7  but does not allow fuel to flow back to the pump chamber  7 . The flow takes place through the channel  7 . 1  connecting the pump chamber and the one-way valve of the outlet conduit. In a fuel pressure boost pump  1  embodying the invention there further is a piston structure  2  provided inside the cylinder  6 , advantageously arranged freely rotatable around its longitudinal axis. Further, the piston structure is functionally connected to the camshaft  14  or a corresponding arrangement for causing its reciprocating movement. During normal operation, as the piston reciprocates in the direction of its longitudinal axis, the one-way valve  8 . 1  allows fuel to pass from the pump chamber into the pump chamber  7  during the suction stroke, while during the pressure increase stroke the one-way valve  9 . 1  allows fuel to pass through it into the common pressure accumulator  11 . The pressure of the common pressure accumulator is higher, so the pressure of the fuel pump chamber will have to increase sufficiently for the one-way valve  9 . 1  to open. 
   The channel  4  transferring fuel from the fuel tank  3  is connected to the inlet conduit  8  from which fuel can flow unidirectionally through the one-way valve  8 . 1  to the pump chamber  7 . From there, fuel is conveyed unidirectionally via the one-way valve  9 . 1  and the outlet conduit  9  to the fuel transfer channel  10  connecting the pressure boost pump  1  and the common pressure accumulator  11 . From the common pressure accumulator  11 , fuel is transferred to the engine combustion chamber  13  by means of an injector nozzle  12 . 
   The fuel injection apparatus comprises a temperature sensor module  15 , arranged in the body part  5  of the fuel pressure boost pump  1 , the temperature sensor module being connected to analysis apparatus  16 . Preferably, the temperature sensor module  15  includes a sensor, such as a thermocouple, and an analog-to-digital converter which converts the analog signal to digital form and supplies temperature measurement data to the analysis apparatus  16 . It should be understood, however, that other arrangements are possible. For example, the temperature sensor module may include only the sensor, in which case the analog-to-digital converter for converting the analog signal to digital form would be included in the analysis apparatus. Measurement data is regularly read from the temperature sensor module  15  into the analysis apparatus  16  while the engine is in operation. Temperature measurement setpoint data is stored in the analysis apparatus  16  or elsewhere to be used by it, the data being used in monitoring the operation of the fuel pressure boost pump. 
   During normal operation fuel flows into the pump chamber  7  via the one-way valve  8 . 1  of the fuel inlet conduit  2  during the intake stroke of the piston structure, and fuel flows at elevated temperature and pressure away from the pump chamber via the one-way valve  9 . 1  of the outlet conduit  9  into the common pressure accumulator  11  during the power stroke of the piston structure. During this operation the temperature of the fuel pressure boost pump is measured by means of the temperature sensor module  15  to monitor the operation of the one-way valve  9 . 1  of the outlet conduit  9 . The monitoring is based on the observation that if the one-way valve  9 . 1  malfunctions and allows fuel to flow back to the pump chamber  7 , whereby the same fuel is pumped many times back and forth, this sequential pumping back and forth will cause a rapid increase in fuel temperature. This can be detected by means of the analyzing apparatus  16  and necessary actions can be taken. 
   The apparatus shown in  FIG. 1  comprises only one fuel pressure boost pump  1 , whereby the rate of change of the measurement data read from the temperature sensor module  15  is compared with the setpoint of the rate of change, stored in the analysis apparatus  16  or available to it somewhere else in the system. If the measured rate of change is larger than the setpoint, predefined alarm procedures are triggered. Such procedures can include, for example alarming the control room of the installation and/or storing the alarm information into the control system. 
   In the embodiment shown in  FIG. 2  the fuel injection system comprises multiple fuel pressure boost pumps  1  arranged to pump into the respective pressure accumulator vessels  11  that are in flow connection with each other by means of a channel  11 ′, forming a common pressure accumulation space. Connecting the pressure accumulation vessels together in this manner allows the fluctuation of the fuel pressure to be decreased. Each fuel pressure boost pump  1  is provided with at least one temperature sensor module  15 . The fuel injection system in this case comprises an analysis apparatus  16  which is electrically connected to each of the temperature sensor modules  15  of the fuel pressure boost pumps  1 . Measurement data is continuously read into the analysis apparatus  16  from each of the temperature sensor modules  15  and in the analysis apparatus the temperature of each separate fuel pressure boost pump is compared to that of at least one other fuel pressure boost pump. If the temperature difference is larger than the setpoint stored in the analysis apparatus or somewhere else to be used by it, an alarm condition is triggered. 
   In a system as that shown in  FIG. 2 , comprising a number of fuel pressure boost pumps, the sequential temperature measurement data does not necessarily have to be stored, because a fault in the one-way valve  9 . 1  can be detected by comparing the temperatures read from various locations. The analysis apparatus  16  can be implemented by, for example, the engine control computer or the like. 
   The invention is not limited to the embodiments described here, but a number of modifications thereof can be conceived of within the scope of the appended claims.