GB2307513A

GB2307513A - Solenoid fuel injector with heating

Info

Publication number: GB2307513A
Application number: GB9524163A
Authority: GB
Inventors: Melvin Coldwell
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1995-11-25
Filing date: 1995-11-25
Publication date: 1997-05-28
Also published as: GB9524163D0

Abstract

Fuel is heated in an injector 2 by maintaining a current in the winding of the solenoid coil 10 which is insufficient to cause fuel injection but which generates heat. Additionally, or alternatively, a greater current may be used than necessary to cause fuel injection, to provide more heat than normal when the injector 2 is injecting fuel.

Description

HEATED FUEL INJECTOR The present invention relates to a method of heating fuel in a fuel injector, and particularly in a fuel injector for an internal combustion engine. The invention also provides a fuel injector system for use in the method.

The flow of fuel from a fuel injector is affected by the temperature of the fuel. In order to provide a more consistent engine performance and improve fuel economy it is known to heat fuel when it is in the fuel pump so as to bring the fuel to a preferred temperature. However the fuel will be cooled when it enters the injector unless means are also provided for heating the fuel injectors.

The provision of one or more heaters to warm up the fuel injectors adds to the complexity of the fuel injection system and increases manufacturing costs.

The present invention provides a method of heating fuel in a solenoid operated fuel injector, the method comprising causing a current to flow through the solenoid during at least a part of the operating cycle of the injector, which current is greater than is necessary for the performance of that part of the operating cycle.

The term "operating cycle" is used to refer to the sequence of opening of the fuel injector for the injection of fuel, and the closing of the fuel injector to stop the injection of fuel.

By using extra current over at least a part of the operating cycle, heat is generated which warms up the fuel injector.

When sufficient current flows through the solenoid to cause fuel injection, heat is also generated. However additional heat may be generated by causing a greater current to flow than is necessary to open the fuel injector.

When the injector is closed, and fuel is not flowing, the injector may be heated by maintaining a current through the solenoid which is insufficient to cause fuel injection but which generates heat. This allows the injector to be heated during all of the operating cycle. For convenience hereinafter the invention will be described with reference to this preferred embodiment.

By maintaining a current in the solenoid winding when fuel is not being injected, fuel in the injector may be heated so as to maintain it in a preferred temperature range.

Fuel may therefore be heated in the injector by the use of existing electrical connections, and without the provision of a dedicated heater.

The term "maintaining a current" is used herein to mean that a current is made to flow through the solenoid winding at a level insufficient to cause fuel injection, but sufficient to generate heat, for longer periods of time than the transitory moments when the current builds up or decays in the conventional operation of a solenoid operated fuel injector.

It is particularly important that diesel fuel be maintained at a sufficiently high temperature to prevent paraffin crystals forming and blocking the fuel injector.

However heating petrol in the injector is also of benefit because this helps to reduce flow variability between operation of the fuel injector in hot and in cold conditions.

The current in the solenoid winding may be maintained continuously at a pre-set value when fuel is not being injected, and increased to a level sufficient to open up the needle or other valve when fuel is to be injected.

Alternatively the current may be varied or switched on and off at intervals when fuel injection is not taking place, so as to attain a preferred operating temperature. In a preferred embodiment the amount of heat generated is controlled by a thermostat so as to maintain the fuel in a preferred temperature range.

An AC, DC, or chopped DC current may be used for the heating effect. If an AC current is used, it should be of a frequency which is too high for the injector to be actuated. Suitable frequencies will vary depending on the nature of the injector, but a frequency of over 3000 Hz will typically be required. A magnetically polarised armature may be used when AC current is employed.

The fuel injector may also be heated when fuel is being injected, by maintaining a current in the solenoid which is greater than that required for fuel injection. Where the injector is open almost continuously the body temperature can rise by 300C.

The invention will now be further described, by way of example, with reference to the following drawing in which: Figure 1 is a cross section through a conventional fuel injector.

The fuel injector 2 shown in Figure 1 is of known design (EAO CDW-27 side feed fuel injector, Ford Motor Company Limited). A needle 6 is urged into sealing contact with a valve body 4 by a spring 14 so as to prevent pressurised fuel from leaving the valve body via a nozzle 16.

An armature 8 is disposed between the spring 14 and the needle 6. A solenoid coil 10, mounted in a housing 12, is coupled to the armature 8 and, when sufficient current passes through the winding of the coil 10, the armature 8 moves away from the nozzle 16 against the force of the spring 14, allowing fuel to be ejected through the nozzle 16. When current stops flowing in the winding of the coil 10, or when the current drops to below a pre-set value, the armature 8 moves back to its rest position and the needle 6 re-seals the nozzle 16.

Heat is generated in the coil 10 when current passes, in proportion to the square of the current. Thus by maintaining a current in the coil 10 which is insufficient to move the armature 8, the injector 2 and fuel in the injector 2 may be heated.

The invention therefore provides a simple method of heating fuel in a solenoid operated fuel injector, without the need for additional wiring.

Claims

1. A method of heating fuel in a solenoid operated fuel injector, the method comprising causing a current to flow through the solenoid during at least a part of the operating cycle of the injector, which current is greater than is necessary for the performance of that part of the operating cycle.

2. A method as claimed in Claim 1, comprising maintaining a current in the solenoid winding which is insufficient to cause fuel injection but which generates heat.

3. A method as claimed in Claim 1 or Claim 2, wherein the current is maintained continuously at a pre-set value when fuel is not being injected.

4. A fuel injection system which comprises a solenoid operated fuel injector and means for maintaining a current in the solenoid winding which is insufficient to cause fuel injection but which generates heat.

5. A method of heating fuel in a solenoid operated fuel injector substantially as herein described.