The present invention relates to the field of variable discharge pumps. Particularly, though not exclusively, the invention relates to a variable discharge pump suitable for pumping fuel into the common rail of a common rail fuel injection system.
The present invention relates to the field of variable discharge pumps. Particularly, though not exclusively, the invention relates to a variable discharge pump suitable for pumping fuel into the common rail of a common rail fuel injection system.
Each downward stroke of the plungers feeds fuel from the fuel feed port into the pumping chamber. When the control valve member is open, the fuel passes through the valve and back to the feed port via the return passage when the plungers move upward. When pressurized fuel is to be fed into the common rail, a control pulse moves the control valve member into the closed position. At the same time, the plunger is undertaking an upward stroke. Because the control valve is closed, pressurization of the fuel takes place in the pumping chamber. When the fuel pressure reaches a certain level, the discharge valve opens and the pressurized fuel passes from the pumping chamber into the common rail. The consequent drop in fuel pressure in the pumping chamber allows the valve spring to push the control valve member into its open position, whereupon it comes into contact with a valve stop.
In order to maintain fuel pressure in the common rail, the control valves in the pump are required to very frequently pressurize fuel in the pumping chambers. For each rotation of the pump camshaft, each control valve will be required to pressurize fuel several times depending upon the number of lobes on the cam. This means that the control valve member is being energized and de-energized extremely frequently. Every time that the valve member is de-energized, it impacts the valve seat under the action of the spring. Over a long period of time, this impact between the valve member and valve seat may damage the valve member. This may lead to a shortening of valve life and deterioration of the seal effected by the valve member when closed. Such seal deterioration may lead to variation in fuel pressure in the pumping chamber and consequent variation in overall pump performance.
It is an aim of the present invention to obviate or mitigate one or more disadvantages associated with prior art devices and methods.
According to a first aspect of the invention, there is provided a pump comprising a first pumping chamber and a first reciprocating plunger disposed within a first plunger bore so as to reciprocate within the first pumping chamber. The pump includes a first electrically actuated spill control valve adapted to open or close fluid communication between the first pumping chamber and a low pressure area. The pump also includes a controller adapted to operate the first control valve for a first period of time extending from a first time point occurring after the first plunger passes bottom dead center to a second time point occurring before the first plunger passes top dead center. The controller may also be adapted to operate the control valve for a second period of time extending from a third time point occurring between the second time point and the passing of the first plunger through top dead center to a fourth time point occurring after the first plunger has passed top dead center.
According to a second aspect of the present invention, there is provided an internal combustion engine including a pump according to the first aspect of the present invention.
According to a third aspect of the present invention, there is provided a method of pressurizing fluid in a pump, the method comprising the steps of supplying low pressure fluid to a pumping chamber and reciprocating a plunger within the pumping chamber so as to force fluid from the pumping chamber. The fluid may be returned from the pumping chamber through an electrically actuated spill control valve. The control valve may be operated to pressurize the fuel in the pumping chamber during a forward stroke of the plunger. The pressurized fuel may be discharged through a discharge port in communication with the pumping chamber. The operating step may include operating the control valve for two separate periods of time, a first period of time extending from a first time point occurring after the plunger passes bottom dead center to a second time point occurring before the plunger passes top dead center, and a second period of time extending from a third time point occurring between the second time point and the passing of the plunger through top dead center to a fourth time point occurring after the plunger has passed top dead center.
Referring to
When the first plunger 45 is undergoing its retracting stroke, fresh low pressure fuel is drawn into pumping chamber 46 past a first inlet check valve 48 from a low pressure area, or gallery, 37 fluidly connected to the inlet 33. Similarly, when the second plunger 55 is undergoing its retracting stroke, fresh low pressure fuel is drawn into the second pumping chamber 56 past a second inlet check valve 58 from the gallery 37. When the first plunger 45 is undergoing its pumping stroke, fuel is displaced from the pumping chamber 46 either into the low pressure gallery 37 via a first portion 41 of a spill passage and spill control valve 38, or into a high pressure gallery 39 past a first outlet check valve 47. Similarly, when the second plunger 55 is undergoing its pumping stroke, fuel is displaced from the second pumping chamber 56 either into the low pressure gallery 37 via a second portion 51 of a spill passage and spill control valve 38, or into the high pressure gallery 39 past a second outlet check valve 57.
Referring in particular to
The spill control valve 38 includes a spill valve member 60 that includes a closing hydraulic surface 62. The spill valve member 60 is normally biased downward towards its open position via a biasing means, here represented by a biasing spring 64. The valve member 60 rests upon a valve stop 63 when in its open position. The spill valve member 60 can be moved upward to close by energizing an electrical actuator 28. In the illustrated embodiment, the actuator 28 is a solenoid having an armature 36 adapted to move the spill valve member 60. That said, those skilled in the art will appreciate that the actuator 28 could take a variety of forms, including piezo and/or piezo bender actuators.
The present device and method may be used in any fluid system where there is a desire to control discharge using a pump having reduced valve wear and damage. In particular, the present device and method may be used with common rail fuel injection systems. However, those skilled in the art will appreciate that the present device and method may also be used in other hydraulic systems that may or may not be associated with an internal combustion engine.
Referring to
As the pressurized fuel is discharged through one of the check valves 47,57, the pressure in the pumping chamber 46,56 rapidly drops. As a result, the forces on the valve member 60 are now unbalanced, with the force of the valve spring 64 outweighing the hydraulic forces on the lifting surface 62 of the valve member 60. The second control signal C2 is generated for a second period of time extending from a third time point occurring after the second time point (the end of first control signal C1) but before the passing of the plunger through TDC, to a fourth time point occurring after the plunger has passed TDC. In this way, the second control signal C2 is generated just as the pressurized fuel is discharged from the pumping chamber. The purpose of the second control signal C2 is to partially counter the force of the spring 64. In this way, the second control signal C2 decelerates the valve member as it returns towards the open position, ensuring that the impact of the valve member 60 on its valve stop 63 is significantly reduced compared with conventional arrangements in which the valve returns to the open position unchecked under the force of the spring 64.
It will be appreciated that the timing of the control signals, and the first control signal C1 in particular, determines what fraction of fuel displaced by the plungers enters the high pressure gallery 39 and what fraction returns to the low pressure gallery 37. This operation ensures that the pressure can be maintained and controlled in the common rail. While one plunger is advancing (pumping), the other plunger is retracting and drawing low pressure fuel into its pumping chamber past one of the respective inlet check valves 48,58.
By generating a second control signal, the pump of the present invention ensures that wear and damage on the control valve member is reduced compared with previous proposals for variable discharge pumps. This will ensure that maintenance and replacement of pumps according to the present invention will be less than at present, with associated cost savings for users of such pumps. In addition, with less wear and damage on the valve member, the performance of the pump will be more consistent over its operating life than is the case at the moment.
It will be understood by those skilled in the art that the duration of the second control signal C2, i.e. the position of the fourth time point, and the dwell d between the end of the second control signal C2 and the beginning of the subsequent first control signal C1, can be varied by the ECU. The ECU can be provided with a receiving means which allows the ECU to receive data relating to fluid pressurization parameters from an external device, e.g. an engine speed sensor on an internal combustion engine. In addition, reference data relating to fluid pressurization parameters can be stored either by the ECU or by a data storage device connected to the ECU. This allows the ECU to vary the fourth time point for particular engine speeds (received data) and desired rail pressures (stored data). In addition, the ECU can vary the dwell d depending on data received for the external device.
Although the preferred embodiment of the pump described above comprises a pair of pumping chambers with associated plungers and plunger bores, it will be understood that the present invention could be provided with only a single pumping chamber with an associated plunger and plunger bore if desired.
Additionally, although the preferred embodiment of the present invention described above includes a single spill control valve opening and closing fluid communication between the pumping chambers and the low pressure area, the present invention may be modified to include a second spill control valve. In such an arrangement, the present invention includes first and second control valves opening and closing fluid communication between their respective first and second pumping chambers and the low pressure area. The controller is consequently adapted to operate each of the first and second control valves for first and second time periods dictated by the reciprocating movements of the respective first and second plungers, in the manner described above.
These and other modifications and improvements may be incorporated without departing from the scope of the present invention.