Aug. 15, 1967 G N. BEDDOES ETAL 3,335,708
DISCRIMINATOR DEVICES Filed'Jan. 14, 1965 2 Sheets-Sheet :1
THROTTLE 2 PEDAL ACCELERATION I T A ND IDL E 17 24a TRANSDUCER com START TRANSDUtER 14 INTECT 23 22d MAN/FOLD PRESJURE TRANSDUCER COMPUTER O ISCRIM/NATOR TRIGGE DIS TRI B U TOR Fig.3
Inventors G. N- BElwoEs (l 3L IA WESTBROOK y km, W i
ttorneys United States Patent Claims (Cl. 123-32 The present invention relates to fuel injection systems for internal combustion engines and more particularly to systems comprising at least one electromagnetically operated fuel injection valve and a control circuit producing electrical pulses for energising said at least one valve to pass fuel to an engine. Such systems are described in US. Patents No. 3,240,191 issued Mar. 15, 1966 and No. 3,272,187 issued Sept. 13, 1966.
In such injection systems, in order to adjust the fuel flow to the engine so as to obtain the most economical operation it is necessary to take account of the speed of rotation of the engine, that is to say, the energising pulses must vary in duration as a function of engine speed and hence vary the time for which each injection valve is open to pass fuel to the engine. In the systems as described in the aforementioned US. patents, this has been achieved by means of an electronic discriminator. circuit which produces an output voltage which is a function of the frequency at which the system is operating and hence of engine speed. This output voltage is then used to vary the duration of the energising pulses applied to the fuel injection valves. However, such electronic discriminator circuits have limitations in the range of characteristics which they can produce.
It is an object of the present invention to provide another form of discriminator, other than an electronic circuit, for use in fuel injection systems.
According to the present invention, in a fuel injection system for internal combustion engines comprising at least one electromagnetically operated fuel injection valve and a control circuit producing electrical pulses for energising said at least one valve to pass fuel to an engine and wherein said pulses vary in duration as a function of the speed of the engine, a mechanical discriminator device is provided comprising a resistance element having a predetermined characteristic, a relatively movable contact for deriving an output from the resistance element when a voltage is applied across said element and driving means responsive to engine speed for effecting relative movement between said contact and said resistance element, whereby the output derived from said resistance element varies as a function of engine speed.
In order that the invention may be more fully understood, reference will now be made to the accompanying drawings, in which:
FIGURE 1 is a diagrammatic representation of one embodiment of mechanical discriminator according to this invention,
FIGURE 2 is a sectional view through one construction of the discriminator shown in FIGURE 1, and
FIGURE 3 is a block diagram of one embodiment of fuel injection system with which the discriminator may be used.
As shown in FIGURE 1, the mechanical discriminator consists of a number of equally spaced fixed contacts 1 arranged on an arcuate path and having resistances 2 connected between them to form the resistance element. Supply voltages can be fed to the terminals 3 at chosen points on the resistance element in order to produce the desired voltage characteristics across the resistance element. A double-ended rotatable wiper 4 is mounted so 3,335,708 Patented Aug. 15, 1967 ice that its end 4a can move over the fixed contacts 1, whilst its end 4b is in continuous engagement with an arcuate contact 5 forming the output convection.
Referring now to FIGURE 2 the discriminator comprises a housing 6 of insulating material which is rotat ably mounted on a shaft 7 which is driven from the engine, either directly or indirectly, and which carries a rotatable magnet 8. The housing also contains a rotatable drag cup 9 which carries the movable contact 4 whose ends 4a and 4b respectively engage with the fixed contacts 1 and 5 carried by an insulating plate member 10 on which the resistances 2 are mounted. The drag cup 9 surrounds the rotatable magnet 8 and is itself surrounded bf the magnetic flux return path member 11 carried by the housing 6.
Rotation of the magnet 8, when the shaft 7 is driven from the engine, induces eddy currents in the drag cup 9 which is thereby caused to rotate and drive the wiper 4 attached thereto. The wiper moves against the action of a spring, which may be a coil spring as shown at 12. As the engine speed varies, the movement of the wiper 4 across the contacts 1 also varies and therefore the output voltage derived from the output contact 5 also varies. The variation is in accordance with the characteristic given to the resistance element by the values of the resistances 2 and the voltages applied through the terminals 3. The output voltage is employed to vary the duration of the energising pulses, which operate the fuel injection valves, as a function of the speed of the engine.
In an alternative arrangement the wiper 4 may be driven through a centrifugal governor device, or a hydraulically operated mechanism, instead of using the eddy current coupling device.
The construction and arrangement of the resistance element may also be varied, for example it may be formed as a wound resistance element with the wiper in direct engagement therewith or it may be formed by a printed circuit technique. The resistance element and wiper may also be so disposed that the latter travels over a linear path and not over an arcuate path.
Referring now to FIGURE 3 which illustrates a fuel' injection system which may incorporate the discriminator of the present invention; the fuel injection system is of the type described in US. Patent No. 3,272,187 and is intended for a four cylinder internal combustion engine. It comprises a fuel tank 11 from which fuel is pumped under pressure by the pump 12, through a filter 13 to a common rail 15 supplying fuel at constant pressure to four individual electromagnetically operated fuel injection valves, shown at 14.
A separate injection valve is provided for each cylinder, either mounted in the inlet manifold of the engine or in.the case of direct injection using higher pressures, in the cylinder head or cylinder. A return pipe 16 'from the common rail 15 bypasses fuel back to the tank 11 through a control valve 17 which determines the actual pressure in the rail 15.
Since the injection valves 14 are supplied with fuel at constant pressure, a periodic activation of an injection valve for a time duration dependent upon engine operating conditions will meter the fuel supplied to the engine through each injection valve. Each valve is energised by a current pulse of predetermined duration, which pulse is derived from the control pulse generator 18 and allocated by the distributor 19 according to the firing sequence of the engine. A quantity of fuel proportional to the electrical pulse duration is delivered in an atomised form into the cylinder through the open inlet valve, or directly into the combustion chamber, in the case of the high pressure application, at a predetermined point in the engine cycle.
The duration of the pulses fed to the valves via the distributor is controlled by the control pulse generator 18, which in turn is controlled by two voltages V1 and V2 from the computer 20. The control pulse generator is triggered from a trigger contact assembly 21 mounted in the distributor housing and operating at the firing frequency of the engine.
The computer 20 is fed with information supplied by a number of transducers 22, 23 and 24 each responsive to one or more conditions of engine operation. In this embodiment the individual transducers are arranged to sense the following conditions of engine operation:
Transducer 22-Manifold pressure Transducer 23Engine water jacket temperature (cold start and warm up) Transducer 24Acceleration and idling transducer.
In operation, the driver primarily controls a valve, located in the induction manifold from a conventional throttle pedal 25 which in turn influences the behaviour of the transient transducers in response to the engine operation, and hence the fuel quantity is computed by the system to satisfy the required operating condition.
The manifold absolute pressure transducer 22 comprises a resistance winding 22a and wiper 22b contained within a casing 220 sealed by a diaphragm 22d responsive to manifold pressure and containing a quantity of gas so that movement of the diaphragm and thus the position of the wiper is influenced by ambient temperature as well as manifold absolute pressure.
The cold start transducer 23 for fuel enrichment during the engine warm up period comprises a thermistor connected into the computer circuit. The arrangement is such that when the engine starter is operated, the degree of enrichment is increased for so long as the starter is engaged.
The acceleration and idling transducer 24 provides fuel enrichment on acceleration by means of a potentiometer 24b whose wiper 24a is mechanically coupled to the throttle pedal 25 and electrically connected to the computer circuit. The transducer 24 also includes contacts which are closed under engine idling conditions.
The control pulse generator is further controlled by an output voltage from a discriminator 26, which produces a voltage proportional to engine speed. This discriminator may be constructed in accordance with the present invention and includes a resistance element having a predetermined characteristic, whereby the duration of the output pulses from the control pulse generator varies as a function of engine speed in accordance with this characteristic.
It will thus be seen that the present invention provides constructions of mechanical discriminator devices for obtaining an output voltage varying as a function of engine speed and whose characteristics can be designed to match a desired range of engine characteristics and furthermore the characteristics of the devices may also be readily altered at will.
1. In a fuel injection system for internal combustion engines comprising at least one electromagnetically operated fuel injection valve and a control circuit producing electrical pulses for energising said at least one valve to pass fuel to an engine and wherein said pulses vary in duration as a function of the speed of the engine, the improvement which consists of a mechanical discriminator device comprising a resistance element having a predetermined characteristic related to the engine with which the system is to be used, a relatively movable contact for deriving an output from the resistance element when a voltage is applied across said element and driving means responsive to engine speed for effecting relative movement between said contact and said resistance element whereby the output derived from said resistance element varies as a function of engine speed.
2. A system as claimed in claim 1, wherein the resistance element comprises a plurality of separate resistances connected between a series of fixed contacts and including a movable contact comprising a wiper which is adapted to move in succession over the fixed contacts.
3. A system as claimed in claim 2, in which the wiper is mounted for rotation and the series of fixed contacts are disposed in an are so that one end of the wiper travels over said contacts as it rotates, the other end of the wiper engaging a further contact forming the output connection and said arrangement including spring means acting against the movement of the wiper in one direction of movement.
4. A system as claimed in claim 1, in which the driving means responsive to engine speed comprises an eddy current coupling device.
5. In a fuel injection system for internal combustion engines comprising at least one electromagnetically operated fuel injection valve and a control circuit producing electrical pulses for energising said at least one valve to pass fuel to an engine and wherein said pulses vary in duration as a function of the speed of the engine, the improvement which consists of a mechanical discriminator device comprising a fixed resistance element having a predetermined characteristic related to the engine with which the system is to be used, a rotatable contact for deriving an output from the resistance element when a voltage is applied across said element, driving means responsive to engine speed for rotating said contact whereby the output derived from said resistance element varies as a function of engine speed, and spring means opposing said rotation of said contact.