GB2179097A - A fuel system for a road vehicle - Google Patents

Abstract

A fuel system for a road vehicle, which fuel system comprises a valve (12) for reducing vacuum levels in an inlet manifold (130) of an engine during periods when the engine is decelerating, a fuel tank (152), apparatus (pipes 166, 156 and valve 22) for communicating an air space (148) above fuel (150) in the fuel tank (152) of the vehicle with the inlet manifold (130) whereby usable fuel vapour in the air space (148) above the fuel (150) can be introduced to the engine, and apparatus (8), Fig. 1, for providing plasma ignition during operation of the engine. The system may be responsive to engine and vehicle speed, manifold vacuum, throttle position, gear engaged and the oxygen content of the exhaust gases. The plasma ignition apparatus may include energy and spark duration control means responsive to the engine operating conditions. <IMAGE>

Description

SPECIFICATION A fuel system for a road vehicle This invention relates to a fuel system for a road vehicle.

Known fuel systems for road vehicles are often defective in one or more areas relating to increased fuel consumption and/or loss of engine performance.

The present invention aims to provide a fuel system which deals at the same time with the problem of reducing vacuum levels in an inlet manifold of the engine, with the problem of neglect of the fuel source represented by hydrocarbon vapours from a fuel tank of the road vehicle, and with the problem of poor spark ignition conditions effecting engine performance.

Accordingly, this invention provides a fuel system for a road vehicle, which fuel system comprises apparatus for reducing vacuum levels in an inlet manifold of an engine during periods when the engine is decelerating, a fuel tank, apparatus for communicating an air space above fuel in the fuel tank of the road vehicle with the inlet manifold of the engine whereby usable fuel vapour in the air space above the fuel can be introduced to the engine, and apparatus for providing plasma ignition during operation of the engine.

The apparatus for reducing the vacuum levels in the inlet manifold of the engine enables the vacuum levels to be reduced during overrun conditions. More specifically, whilst developing a desired engine power output, engine vacuum conditions in the inlet manifold are at their highest. On release of the vehicle accelerator, the vacuum will continue to draw fuel from the carburettor. This fuel that is drawn in will not generate any useful energy conversion and the absence of air will prevent the formation of a balanced combustible mixture.

The provision of the apparatus for communicating the air space above the fuel in the fuel tank of the road vehicle with the inlet manifold of the engine is based upon the reaiisation that the air space is saturated with fuel vapour which represents a mostly hitherto unused source of hydrocarbons. Usually this source of hydrocarbons is neglected as a fuel additive and some may be lost. Clearly the using of the hitherto unexpoited hydrocarbons will effect fuel economy savings.

The provision of the apparatus for providing the plasma ignition is based upon the realisation that conventional spark ignition systems for internal combustion engines such for example as 2- and 4-stroke engines comprise an ignition coil for providing a high induced voltage spike which strikes an arc for ignition purposes between the electrodes of one or more spark plugs. It has long been appreciated that it is desirable to strike a high energy arc if engine efficiency is to be optimised but known systems are something of a compromise and they are not able to provide high spark energy levels at the high voltage required initially to strike the arc. The provision of the plasma ignition may be effective to enable the fuel system to improve overall fuel combustion efficiency, drivability, pulling power at low speeds in high gears, and cold starting performance.The plasma ignition may be designed particularly to respond to the continually varying air/fuel proportions encountered at different engine speeds and loadings.

Thus, for example, the fuel system may take into account ambient temperatures, humidity and air pressures.

The apparatus for reducing the vacuum levels in the inlet manifold of the engine may include valve means positioned between an air filter and the inlet manifold.

The fuel system may be one in which the valve means is actuated by a microswitch, and in which the valve means is effective on actuation to allow air from the air filter to pass into the inlet manifold to reduce the vacuum levels in the inlet manifold and thus the amount of fuel drawn from a carburettor of the engine.

The fuel system may include a road speed sensing device which is effective to prevent operation of the apparatus for reducing the vacuum levels in the inlet manifold of the engine under engine idling conditions.

The apparatus for communicating the air space above the fuel in the fuel tank with the inlet manifold may includes a valve adapted normally to permit gas flow from the air space to the inlet manifold but to prevent flow in the opposite direction.

The apparatus may also include a solenoid valve in dependence upon the operative state of which a passageway from the fuel tank to the inlet manifold is opened or closed.

The apparatus for communicating the air space with the inlet manifold may include conduit means via which atmospheric air is fed to the inlet manifold.

The apparatus for communicating the air space with the inlet manifold may further include an electrical switch operating in accordance with engine throttle position to control operation of the solenoid valve.

The said apparatus for communicating the air space with the inlet manifold may include a sensing device responsive to engine operating conditions for preventing effective operation of the electrical switch when a predetermined operating condition obtains. The sensing device may be responsive, for example, to vehicle road speed, engine revolutions per minute, or predetermined selected gears.

The apparatus for providing the plasma ignition may comprise a transformer and a d.c. to d.c. convertor which in use converts a low tension d.c. electrical supply to a high tension d.c. electrical supply for use in manintaining a plasma arc.

The d.c. to d.c. convertor may comprise an inverter which responsively to the application of a low tension d.c. supply produces a high tension a.c. supply and a full wave rectifier arrangement fed with the high tension a.c.

supply to provide the said high tension d.c.

supply.

The inverter may comprise, for example, an oscillator which is fed from the low tension d.c. supply to provide an a.c. signal, the voltage of which is stepped up by transformer means to provide the a.c. high tension voltage.

The plasma ignition appartus may be associated with a low tension current interrupter means in the form of mechanical contact breaker points or an electronic switch, whereby generation of sparks is synchronised with engine operation.

Additionally, the plasma ignition apparatus may be such as to include energy and spark duration control means which are responsive to engine operational characteristics for modifying the energy in and/or the duration of the plasma arc, electrical power for which is supplied by the d.c. to d.c. converter.

Thus, means may be provided to sense engine exhaust gas characteristics and/or engine load characteristics whereby controlled signals may be provided for modifying the characteristics of the plasma produced by electrical power supplied to the d.c. to d.c. convertor.

The exhaust gas characteristic sensing apparatus may comprise means for sensing oxygen level, and the means for sensing the engine load may comprise manifold depression sensing means which senses the pressure at a region within or associated with the inlet manifold of the engine.

An embodiment of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows an electrical circuit for providing reduced vacuum levels in an inlet manifold of an engine, for providing desired communication of an air space above fuel in a fuel tank with the inlet manifold of the engine, and for providing plasma ignition during operation of the engine; and Figure 2 shows a mechanical arrangement for reducing vacuum levels, and for communicating the air space in the fuel tank with the inlet manifold of the engine.

Referring to Fig. 1, there is shown to the left of the dotted line 2 a schematic circuit for enabling the reduction of vacuum levels (hereinafter sometimes referred to as vaccum dumping) in the inlet manifold of the engine during periods when the engine is decelerating, and for enabling hydrocarbons in the air space above the fuel in the fuel tank to be obtained. The block 4 is a speed control circuit. The block 6 is a plasma generation circuit, and the block 8 which is within the block 6 gives the circuit for the actual generation of the plasma.

Referring firstly to the circuitry to the left of the line 2, there is shown a speed sensor detector 10, a main valve 12 for controlling vacuum dumping, a warning light 14 (which is operative when the main valve 12 is operative), and first second and third relays 16, 18, 20 respectively. Also shown is a small valve 22 for permitting the hydrocarbons to be obtained from the air space above the fuel tank.

When the valve 22 is operative, a warning light 24 shines. The system may be operated by means of a throttle switch 26. The throttle switch 26 is preferably a microswitch. The throttle switch 26 may be arranged to be open at engine idle conditions. Directly the engine is caused to accelerate, the throttle switch 26 can be caused to close so that the circuit can operate. However, the circuit will not be permitted to operate until such time as an appropriate speed is detected by the speed sensor detector 10. Thus the speed sensor detector 10 is effective to override the system until such time as appropriate engine speed conditions appertain. The throttle switch 26 can be arranged to operate off a pivoting part of the carburettor mechanism. The valves 12 and 22 can be arranged to work in synchronism.

Referring now to the block 4, the illustrated speed control circuit comprises a frequency control chip 28, a relay 30, diodes 32, 34, capacitors 36, 38, 40, and resistors, 42, 44, 46 and 48. The circuit also includes a coil 50 as illustrated and a trimmer potentiometer 52.

The trimmer potentiometer 52 is for enabling final adjustments for the speed control. The coil 50 forms the winding circuit of the relay 30. The capacitor 40 together with the diodes 32 and 34 are effective to remove input ripple to the circuit. The relay 30 drives the solenoid which controls the obtaining of the hydrocarbons from the fuel tank together with the solenoid that controls the operation of the vacuum dumping.

The sensor input 54 may be a magnetic sensor. The sensor input 54 may be provided on the propellor shaft of the vehicle or on a vehicle wheel, or on the drive shaft of the vehicle. Alternatively, the input sensor 54 may be provided on a bracket of the gearbox. The input sensor 54 may be effective to sense four bits of a rotating magnetic tape. Advantageously, the input sensor 54 is arranged to be compatible with front and rear wheel drivevehicles to allow for difference in rotational speeds between front and rear wheel drive vehicle parts.

Referring now to the block 8, there is shown a main drive transformer 56. A capacitor 58, a diode 60 and a pair of transistors 62, 64 form a push/pull oscillator circuit giv ing an a.c. frequency. This frequency may be 12 kilocycles. Input leads 66, 68 are available for connecting engine management systems.

The block 8 also includes a main output transformer 70 which is connected as shown to a four way bridge circuit 72. The bridge circuit 72 is connected to a series 74 of smoothing capacitors. The smoothing capacitors are arranged to be charged during delivery pulses.

The driver push/pull oscillator circuit is arranged to be shut down if a short -circuit occurs on a resistor 76. Also shown in the block 8 is the ignition coil of the vehicle and this is shown as ignition coil 78 having a primary winding 80 and a secondary winding 82.

The block 8 forms a d.c. generator for the plasma.

The remainder of the block 6 comprises a function indicator 84, and capacitors 86, 88, 92, 94 and 96. The capacitors 92, 94, 96 are associated as shown with diodes 98, 100 and resistors 102, 104. The capacitors 86, 88, 90 are associated as shown with resistors 106, 108 and 110. The resistors 108, 110 are connected as shown to a switch 112. The block 6 further includes a transformer 114 which is associated as shown with a circuit involving diodes 116 and 118 and two transistors 120 and 122. This circuit also includes a resistor 124.

The vehicle 12 volt supply is connected to line 126.

Generally, the vacuum dumping is effected by the large valve 12, positioned between the central plenum of the inlet manifold and the air filter. When the vehicle accelerator is released, a microswitch operates the main valve, allow ing air to pass into the inlet manifold via the air filter. This reduces the vacuum level in the inlet manifold and so reduces the amount of fuel being drawn off from the vehicle carburettor. The control is effected by the road speed sensor ensuring that the main valve does not remain open at engine idle/tick-over conditions. A relay is provided to isolate the system during vehicle breaking, providing the servo with maximum vacuum.

The obtaining of the fuel vapour from the fuel tank improves the homogeneity of the petrol/air mixture required for good combustion.

The obtaining of the fuel vapour with its advantageous hydrocarbons is controlled by the valve 22 and the function of the valve 22 is limited by the speed sensor detector 10. The hydrocarbon vapours are only admitted to the engine above a predetermined engine speed so that the light vapours are not wasted. The throttle switch 26 is effective to switch off the hydrocarbon obtaining system when the vehicle engine is slowing down or is at idle conditions. The plasma ignition system provided by the block 6 may be effective to improve overall combustion and drivability, particularly during engine start-up conditions and under various air/fuel variations which occur during varying engine speeds and loads.

Referring now to the mechanical apparatus shown in Fig. 2, it will be seen that there is illustrated an inlet manifold 130. The inlet manifold 130 has four ports 132, 134, 136 and 138. The inlet manifold 130 has a central plenum chamber 140. A pipe 142 leads into the inlet manifold 130 and this pipe 142 is provided with the valve 12 shown in Fig. 1. It will be apparent that the valve 12 as shown in Fig. 2 is then provided with the appropriate circuitry shown in Fig. 1, this circuitry being provided via input leads 144.

A further pipe 146 also connects to the inlet manifold 130 and more specifically the pipe 146 connects to the central plenum chamber 140. The pipe 146 is provided with the valve 22 shown in Fig. 1, this valve 22 being effective to control the hydrocarbon fuel vapour obtained from an air space 148 above fuel 150 in a fuel tank 152. It will be apparent that the valve 22 is provided with the circuitry illustrated in Fig. 1, this circuitry being connected to the valve 22 via leads 154. A small bore pipe 156 connects the valve 22 to a Tpiece 158. One leg of the T-piece 158 connects to a pipe 160 which is a large bore vent pipe 160. The other leg of the T-piece 158 connects to a pipe 162. The pipe 162 itself connects to a T-piece 164. One leg of the T-piece connects to a balancing pipe 166 whilst the other leg of the T-piece connects to a pipe 168 which communicates with a spout portion 170 of the fuel tank 152. When the valve 22 is open, the hydrocarbon fuel vapours can be obtained from the space 148 and led directly to the central plenum chamber 140 of the inlet manifold 130.

It is to be appreciated that the embodiment of the invention described above with reference to the accompanying drawings has been given by way of example only and that modifications may be effected. Thus, for example, various parts of the circuitry illustrated in Fig.

1 may be varied as desired. Furthermore, the precise mechanical layout illustrated in Fig. 1 and giving the connections to the vauum dumping valve 12 and the hydrocarbon lead valve 22 may be varied.

Claims (17)

1. A fuel system for a road vehicle, which fuel system comprises apparatus for reducing vacuum levels in an inlet manifold of an engine during periods when the engine is decelerating, a fuel tank, apparatus for communicating an air space above fuel in the fuel tank of the road vehicle with the inlet manifold of the engine whereby usable fuel vapour in the air space above the fuel can be introduced to the engine, and apparatus for providing plasma ignition during operation of the engine.

2. A fuel system according to claim 1 in which the apparatus for reducing the vacuum levels in the inlet manifold of the invention includes valve means positioned between an air filter and the inlet manifold.

3. A fuel system according to claim 2 in which the valve means is a microswitch, and in which the valve means is effective on actuation to allow air from the air filter to pass into the inlet manifold to reduce the vacuum levels in the inlet manifold and thus the amount of fuel drawn from a carburettor of the engine.

4. A fuel system according to any one of the preceding claims and including a road speed sensing device which is effective to prevent operation of the apparatus for reducing the vacuum levels in the inlet manifold of the engine under engine idling conditions.

5. A fuel system according to any one of the preceding claims in which the apparatus for communicating the air space above the fuel in the fuel tank with the inlet manifold includes a valve adapted normally to permit gas flow from the air space to the inlet manifold but to prevent flow in the opposite direction.

6. A fuel system according to any one of the preceding claims and including a solenoid valve in dependence upon the operated state of which a passageway from the fuel tank to the inlet manifold is opened or closed.

7. A fuel system according to any one of the preceding claims in which the apparatus for communicating the air space with the inlet manifold includes conduit means via which atmospheric air is fed to the inlet manifold.

8. A fuel system according to any one of the preceding claims in which the apparatus for communicating the air space with the inlet manifold includes an electrical switch operating in accordance with engine throttle position to control operation of the solenoid valve.

9. A fuel system according to claim 8 in which the apparatus for communicating the air space with the inlet manifold includes a sensing device responsive to engine operating conditions for preventing effective operation of the electrical switch when a predetermined operating condition obtains.

10. A fuel system according to any one of the preceding claims in which the apparatus for providing the plasma ignition comprises a transformer and a d.c. to d.c. convertor which in use converts a low tension d.c. electrical supply to a high tension d.c. electrical supply for use in maintaining a plasma arc.

11. A fuel system according to claim 10 in which the d.c. to d.c. convertor comprises an inverter which responsively to the application of a low tension d.c. supply produces a high tension a.c. supply and a full wave rectifier arrangement fed with the high tension a.c.

supply to provide the said high tension d.c.

supply.

12. A fuel system according to claim 11 in which the inverter comprises an oscillator which is fed from the low tension d.c. supply to provide an a.c. signal, the voltage of which is stepped up by transformer means to provide the a.c. high tension voltage.

13. A fuel system according to any one of the preceding claims in which the apparatus for providing the plasma ignition is associated with a low tension current interrupter means in the form of mechanical contact breaker points or an electronic switch, whereby generation of sparks is synchronised with engine operation.

14. A fuel system according to claim 10 in which the apparatus for providing the plasma ignition includes energy and spark duration control means which are responsive to engine operational characteristics for modifying the engine in and/or the duration of the plasma arc, electrical power for which is supplied by the d.c. to d.c. convertor.

15. A fuel system according to claim 14 and including means for sensing engine exhaust gas characteristics and/or engine load characteristics whereby controlled signals may be provided for modifying the characteristics of the plasma produced by electrical power supplied to the d.c. to d.c. convertor.

16. A fuel system according to claim 15 in which the exhaust gas characteristic sensing apparatus comprises means for sensing oxygen level, and in which the means for sensing the engine load comprises manifold depression sensing means which senses the pressure at a region within or associated with the inlet manifold of the engine.

17. A fuel system for a road vehicle, substantially as herein described with reference to the accompanying drawings.