Internal-combustion engines – Two-cycle – Rear compression
Patent
1997-12-16
2000-05-23
Moulis, Thomas N.
Internal-combustion engines
Two-cycle
Rear compression
123DIG5, 123495, 417380, F02M 3704
Patent
active
060654333
DESCRIPTION:
BRIEF SUMMARY
This invention relates to pumps and, in particular, to pumps suitable for metering fuel to an internal combustion engine.
Direct injected internal combustion engines have been devised as a means of achieving efficient combustion of fuel so as to minimise exhaust emissions, especially in automotive engines. The efficiency with which direct injected internal combustion engines achieve this objective depends very much on the accuracy of metering of quantities of fuel for delivery to the combustion chamber(s) of such engines.
This imposes a requirement on pumps designed for metering fuel for delivery to the combustion chamber(s) of the engine that the volume of fuel delivered thereby is able to be carefully controlled. In this manner, a greater accuracy of the quantity of fuel delivered to the combustion chamber(s) may be achieved.
This need for accurate fuel control is particularly acute in systems which run "open-loop" on fuelling rate. In such open loop systems, the operator demand is translated directly into a required fuel metering rate, with the air flow to the engine being controlled as a secondary variable.
Some fuel metering pumps presently used in internal combustion engines are variable displacement pumps in which the volume of fuel delivered thereby is controlled by the stroke of a piston provided in the pump. To ensure that the correct stroke setting is attained, a cam or other positive physical stop means may also be employed in the pump. Such a cam or physical stop means typically will be arranged to alter the displacement of the piston within its working cylinder within the pump. Hence, any trimming used to control fuelling level, especially at idle or under high speed conditions, requires mechanical adjustment of the position of the physical stop means. In the past, such mechanical adjustment has been achieved on certain fuel systems by an electro-mechanical device such as a stepper motor which adjusts the position of a cam acting on the piston of the fuel metering pump. The operation of the stepper motor has typically been under the control of an electronic control unit (ECU).
Such control generally results in complexity with respect to both hardware requirements and the design of suitable control algorithms therefor. With such complexity has arisen expense associated with the cost of the stepper motor and, to a generally lesser extent, the necessary driver circuitry therefor required within the ECU. It will also be understood that the electrical power required to drive the stepper motor may prove problematic in situations where batteries are not provided on particular engine configurations, the purchaser is cost sensitive or there is little electrical power available. Smaller engine applications such as chainsaws, lawn mowers and other small engine apparatus are particularly susceptible to the above problems. Stepper motors may also suffer problems in regard to long term durability and accuracy. In this respect, it is known from prior art systems that steps may be lost under high speed conditions. Further, being mechanical devices subject to certain lags, stepper motors may have a reasonably slow response. Hence, there is a need for functionally similar systems that are cheaper and technically simpler in operation.
It is the object of the present invention to provide a fuel metering pump in which the stroke of the pump may be adjusted in a manner to overcome at least some of the problems present in prior art systems.
With this object in view, the present invention provides a variable displacement metering pump for metering a fluid comprising a fluid chamber in communication with a fluid supply; and a control chamber in communication with a pressurised working fluid source wherein the relative volumes of the fluid chamber and the control chamber are variable in accordance with reciprocation of a pumping means and wherein a portion of the pumping means, which at least in part defines the control chamber, is arranged to be subject to pressure from the pressurised working fluid source, the press
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Patent Abstracts of Japan, M364, pp. 45, JP 59-19074A.
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