Internal-combustion engines – Charge forming device – With fuel pump
Reexamination Certificate
2000-03-14
2002-03-26
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
With fuel pump
C123S447000
Reexamination Certificate
active
06360727
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to diesel fuel injectors and fuel injection pumps. The invention is applicable to unit injectors used on locomotive, automotive, marine and stationary engines, in which the pump, nozzle and holder assembly are a single unit. The invention is also applicable to injection systems in which the fuel is fed from the pump through tubing to a separate nozzle-and-holder assembly.
BACKGROUND
A known type of fuel injector for diesel engines comprises a fuel pump and an injection nozzle associated with the fuel pump. The fuel pump includes a pump cylinder and a pump plunger reciprocatable in the cylinder. The cylinder and plunger together define a pump chamber open at one end for the discharge of fuel during a pump stroke and for fuel intake during a suction stroke of the plunger. The injection nozzle is associated with a valve body having a spray outlet at one end for the discharge of fuel at the nozzle tip. The nozzle valve is movable in the nozzle body between open and closed positions to control flow through the spray outlet. The valve is spring-biased to closed position and openable when such discharge of fuel during a pump stroke reaches a given level of pressure. The valve then remains open until pressure drops to a closing pressure somewhat below the opening pressure. The closing pressure is below the opening pressure because the valve face area subject to opening pressures is somewhat greater when the valve is open and unseated than when it is closed and seated.
Fuel is supplied to the pump and excess fuel is returned from the pump to reservoir through low pressure passages communicating with the pump chamber. The low pressure passages constitute fill and spill passages. The inlet port area is large enough to fill the pump chamber under the highest engine operating speeds. The flow area of the spill port is large enough that the fuel is spilled back into the fuel supply ducting of the low pressure supply system (or into the return to reservoir, which for present purposes counts as part of the fuel supply ducting) at a rate high enough to prevent the discharge of fuel, resulting from the pump stroke, from reaching the given pressure at which the nozzle valve opens to commence fuel injection, or from remaining above the somewhat lower given pressure at which the open injection valve closes. The ports close and then open during each stroke of the pump plunger to thereby establish, between the closing and opening, the portion of the pump stroke during which such discharge of fuel occurs at pressures above the closing pressure of the injection nozzle.
In purely mechanical injectors, the spill referred to is wholly mechanical, generally in the form of edges and cut-outs formed on the pump plunger which interact with ports opening into the pump bore from the low pressure passages. In other injectors, the spill valving is controlled by a solenoid which opens and shuts a spill passage valve.
Fuel injection, that is, delivery of fuel to the injection nozzle downstream of the plunger chamber at a high enough pressure to cause the nozzle valve to open, occurs during that part of the pump stroke during which the spill passages are closed.
The initial rate of fuel injection has a profound influence on the maximum combustion pressure and temperature generated in a diesel engine combustion chamber during engine operation. When combustion pressure and temperature are elevated above certain limits, nitrogen is oxidized to form nitrous oxide. Ignition delay is the principal reason for generation of such excessively high pressure and temperature. Improved ignition quality of fuel and higher compression pressures can reduce the ignition delay period, but there is a limit to the improvement that can be achieved with improved fuel quality which also carries a cost penalty. Higher compression pressures also have the adverse effect of increasing maximum combustion pressure which in turn tends to increase the formation of nitrous oxide.
Various proposals have been made to deliver injected fuel at a lower rate during the early part of the injection portion of the pump stroke corresponding to the ignition delay period. For example, it has been attempted to deliver fuel at an initially reduced rate by using a two stage lift-cam whereby the initial portion of the cam lift is limited to produce a fixed quantity of fuel delivery by the plunger and then the cam lift ceases for a small period, or slows down, and then resumes its lift at the normal rapid rate to complete the plunger stroke. This two-stage lift method has not been successful because the initial pressure wave generated at port closing is a function of engine speed and injection is inconsistent in the low and intermediate engine speed ranges.
Another previous method has used a separate small plunger to inject a small pilot quantity of fuel preceding the delivery by the main plunger of the main quantity of fuel required by the engine to develop the power required. This is a mechanically complicated and relatively costly system and has not been successful.
It has also been known in the prior art to provide auxiliary spill porting for a reduced rate of fuel feed in the early part of the injection portion of the plunger stroke, but such arrangements were intended to minimize initial injection pressure and were not successful. An example is seen in U.S. Pat. No. 2,513,883 to J. F. Male. It has also been known to use auxiliary spill porting arrangements effective at varying proportions of the injection portion of the feed stroke, as for example in U.S. Pat. No. 4,741,314 to Hofer in which auxiliary porting is arranged so there is a declining duration of leakage as the engine load increases in a straight line relationship with load such that maximum duration of leakage is at idle and there is zero duration of leakage at full load.
Other spill porting systems have been proposed as for example in my U.S. Pat. Nos. 5,870,996 and 6,009,850. These systems are effective, but may be too costly or difficult to fabricate in smaller injector sizes.
Another alternative proposed in the prior art is subtract-then-add-back porting, wherein instead of spilling some of the fuel during the injection portion of the plunger stroke, a portion of the fuel is temporarily diverted from the pump chamber to a fuel subtraction chamber and then during the return stroke of the plunger is returned (added back) from the subtraction chamber to or toward the pump chamber. An example is seen in U.S. Pat. No. 4,811,715 to Djordjevic et al. in which the volume of the fuel subtraction chamber
134
expands and contracts as the pin
128
is forced up into the accumulator chamber
136
and back down again by varying pressures according to the load and speed conditions of the injection pump. However, in this patent, the subtracted fuel is not contained entirely in the subtraction chamber, but in very small part leaks back and forth past the pin
128
into and out of the accumulator chamber
136
. Fuel can start to be subtracted from the system before injection begins because the pressure in the accumulator chamber can drop below the nozzle opening pressure during the residual pressure phase of the injection cycle (which is much longer in duration than the injection phase), depending upon the clearance between the plunger and its guide. Also, the condition can vary from injector to injector depending upon the respective clearances of the plungers in the injectors.
British Patent 634,030 also shows a form of subtract-then-add-back porting. Although the patent does not describe itself in those terms, it does contain a fuel subtraction chamber m (not denominated as such) to which a portion of the fuel is diverted as the pump stroke begins and from which the diverted fuel is returned (added back) during the return stroke of the pump. However, the operation of the disclosed device is necessarily such that injection is interrupted and then resumed during the pump stroke (although interruption is not mentioned in the patent description). Such interruption
Buescher Alfred J.
Gimie Mahmoud
Pearne & Gordon LLP
LandOfFree
Reduce initial feed rate injector with fuel storage chamber does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Reduce initial feed rate injector with fuel storage chamber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reduce initial feed rate injector with fuel storage chamber will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2890247