Pumps – Processes
Reexamination Certificate
1999-01-08
2001-09-25
Tyler, Cheryl J. (Department: 3746)
Pumps
Processes
C417S462000, C123S456000, C123S447000, C123S497000
Reexamination Certificate
active
06293757
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 10-28738 filed on Feb. 10, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for controlling a fluid pump.
2. Description of the Related Art
There is known a common rail-type fuel injection apparatus wherein a common rail (pressure accumulating chamber) for storing high pressure fuel is provided and a fuel injection valve is connected to the common rail so that fuel is injected into an internal combustion engine.
In the common rail-type fuel injection apparatus, the rate of fuel injection from the fuel injection valve varies in accordance with the common rail pressure, that is, the pressure inside the common rail. Therefore, it is necessary to control the common rail pressure with high precision so that an optimal fuel injection rate can be achieved in accordance with the engine operating conditions.
The common rail pressure is controlled typically by controlling the amount of fuel ejected, i.e., the fuel pumping amount, from a high-pressure fuel supply pump that supplies fuel to the common rail. A plunger-type pump is normally used as the high-pressure fuel supply pump.
In the common rail-type fuel injection apparatus, high pressure fuel stored in the common rail is injected into cylinders from fuel injection valves provided separately for the individual cylinders. Therefore, the pressure in the common rail decreases every time fuel injection is performed. Consequently, there is a need for a fuel pump control apparatus to cause the fuel pump to pump a required amount to the common rail after each fuel injection so as to hold the pressure in the common rail at a target pressure. Moreover, in actual operation, the target common rail pressure itself is sharply varied over a wide range in accordance with the operating condition of the engine during transitional operation, during which the engine operating condition sharply changes. Therefore, during the transitional period, the fuel pump control apparatus needs to control the amount of fuel to be pumped out from the fuel pump, i.e., fuel pumping amount, so as to prevent the pressure in the pressure accumulating chamber from overshooting or undershooting following changes in the target pressure, that is, so as to achieve good controllability of the pressure in the pressure accumulating chamber.
The plunger pump used as the common rail-type fuel pump is normally an inner cam-type plunger pump as shown in FIG.
11
. Since the fuel pump needs to pump fuel for the fuel injection into each cylinder of the engine, the number of times of pumping out fuel during one revolution of the pump needs to correspond to the number of cylinders. The pump shown in
FIG. 11
has four cam lobes and four plungers. In the pump shown in
FIG. 11
, the plungers simultaneously pump out and draw in fuel during each cycle, that is, 90° rotation of the pump drive shaft. Therefore, the fuel pump pumps out fuel four times per revolution. In four-stroke engines, the fuel injection into all the cylinders is completed in two engine revolutions. Consequently, the pump shown in
FIG. 11
can be used for a four-stroke eight-cylinder engine by driving the pump at the revolution speed equal to that of the crank shaft. The pump can also be used for a four-stroke four-cylinder engine by driving the pump at half the revolution speed of the crank shaft. However, with the four cam lobes of the inner cam as shown in
FIG. 11
for driving the plungers, it becomes necessary to set a large changing rate of the cam profile of each cam lobe, which results in greater fluctuation of the pump driving torque. Greater fluctuation of the pump driving torque increases the load on the component parts of the pump driving system, such as the chain or the belt, and therefore may reduce the service life of the pump driving system.
In order to reduce the pump driving torque fluctuation, it is necessary to reduce the number of cam lobes and therefore reduce the changing rate of the cam profile.
FIG. 2
shows a two-lobe cam pump in which the number of cam lobes is reduced to two. This cam pump has four plungers, and it is designed so that each oppositely positioned pair of cam lobes simultaneously perform pumping and intake strokes. Each plunger operates at cycles of 180° rotation of the pump drive shaft. With two pairs of plungers, the pump device pumps out fuel four times per rotation of the pump.
As for the method for controlling the amount pumped out of a plunger pump, there are known a pre-stroke adjusting method and an intake adjusting method.
The pre-stroke adjusting method controls the amount pumped from each plunger by holding the intake valve for each plunger at an open position until an intermediate stage of the pumping stroke of the plunger. More specifically, in the pre-stroke adjusting method, each plunger draws an amount of fuel corresponding to the entire stroke of the plunger into the corresponding cylinder during the intake stroke. In an early stage of the pumping stroke, a certain amount of taken-in fuel is discharged from the cylinder through the intake valve. After the intake valve is closed during the pumping stroke, the amount of fuel contained in the cylinder at that time is pressurized by the plunger. When a predetermined fuel pressure is reached, an ejection valve urged by a spring is forced to open, so that fuel is pumped into the common rail.
The intake adjusting method draws a necessary amount of fuel into each cylinder by closing the intake valve for each plunger at an intermediate stage of the intake stroke. Therefore, the entire amount of fuel drawn into each cylinder is ejected from the cylinder during the pumping stroke.
Since the pre-stroke adjusting method closes each intake valve during the pumping stroke, the method needs to employ intake valves designed for use under higher pressures than the intake valves employed by the intake adjusting method. Thus, the cost of the apparatus for the pre-stroke adjusting method becomes comparatively high. Moreover, in the pre-stroke adjusting method, a surplus of the amount of fuel drawn into each cylinder must be discharged from the cylinder by using the corresponding plunger in the early stage of the pumping stroke. Therefore, the pre-stroke adjusting method has a danger of increasing the pump driving power loss, in comparison with the intake adjusting method.
Therefore, it is preferable that the common rail fuel pump be a two-lobe cam pump, which reduces the driving torque fluctuation, and the amount of fuel to be pumped out of the cam pump be controlled by the intake adjusting method, which reduces the apparatus cost and the power loss.
However, the combination of a two-lobe cam pump and the intake adjusting method conventionally causes the problem of deterioration of responsiveness in the common rail pressure control.
Whereas the pre-stroke adjusting method determines the amount of fuel to be pumped from each plunger on the basis of the intake valve closing timing during the pumping stroke of the plunger, the intake adjusting method determines the amount of fuel to be pumped from each plunger on the basis of the intake valve closing timing, i.e., the intake valve open period, during the intake stroke of the plunger. Therefore, the pre-stroke adjusting method allows control of the pumping amount in accordance with the engine operating condition and the common rail pressure immediately before the start of pumping, that is, immediately before the start of closing the intake valve. On the other hand, the intake adjusting method necessitates determining the pumping amount in an early stage of the intake stroke. Therefore, in the intake adjusting method, a time interval between the determination of the pumping amount and the actual start of pumping becomes long. If, during the time interval, the engine operating condition or the common rail pressure changes, such a change
Fukuma Takao
Harada Yasuo
Oda Tomihisa
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Tyler Cheryl J.
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