DESCRIPTION
"POWER CONTROL SYSTEM FOR AN INTERNAL COMBUSTION ENGINE" This invention relates to poorer control systems for internal combustion engines.
According to the present invention there is provided a power control system for an internal combustion engine having a crankshaft driven by n pistons (where n is an integer greater than 1) each piston being reciprocable in a cylinder to which fuel is supplied by one or more electrically operable fuel injectors, the control system comprising means for generating a periodic control signal which is composed of a series of actuating signals for operating the or each fuel injector to supply fuel to the cylinders in timed relationship with the rotation of the crankshaft and means for progressively increasing and decreasing in a plurality of incremental steps the number of actuating signals per period of the control signal whereby the number of cylinders to which fuel is supplied may be varied.
Preferably the periodic control signal operates n fuel injectors, each of which is associated with a respective cyHinder. In order to keep each cylinder in use and therefore at its operating temperature, the periodic control signal preferably actuates the or each fuel injector so that fuel is supplied to each cylinder at least once in every predetermined number of cycles of crankshaft, and, preferably, at least once in every n periods of the actuating signal. This can be achieved by limiting the maximum number of actuating signals in each period of the control signal to a value m where m is an integer but not an integral multiple of n or of an integral factor thereof greater than 1. Usually the maximum number of actuating signals per period of the control signal will be greater than n.
The number of actuating signals in each period of the control signal may be permitted to vary in steps of 1 between 0 and m according to the power requirement. In the case of an unthrottled engine, this will produce a variation in power from zero to 100% of the maximum power output in steps of (1/m) of the maximum power output. The larger the value of m, the greater the number of incremental steps, and therefore the smaller the difference in the modulated power output of the engine between successive steps.
Further reduction in the size of the incremental steps may be provided without increasing the maximum number of actuating signals in the periodic control signal by controlling the quantity of air flowing into the cyliners e.g. by means of a throttle. With such an arrangement, the power output of the engine can be increased in m incremental steps for each setting of the throttle. Preferably the quantity of air flowing into the engine may be varied in discrete steps, for example by providing 2. plurality of orifices through which air flows into the engine and means for selectively closing the orifices.
Fine adjustment of the power output may be achieved by varying the air/fuel ratio or spark timing of the engine within limits of ignitability and acceptable combustion without varying the number of actuating signals per period of the control signal. In one embodiment of the invention the generation of the periodic control signal is controlled by a selector movable by an accelerator control for the engine, and an electronic circuit operable in response to changes in the position of the selector to vary the number of actuating signals per period of the control signal, and to vary the air/fuel ratio or spark timing of the engine.
In one embodiment of the invention the Elector comprises a simple position transducer e.g. a rotary potentiometer, operable by the accelerator control, the appropriate number of actuating signals and air/fuel ratio or spark timing being determined from the position of the transducer.
In an alternative embodiment, the selector comprises a switchhavinga plurality of adjacent operating positions corresponding to different numbers of actuating signals per period of the control signal, and a linkage between the switch and the accelerator which incorporates a lost-motion mechanism, and the electronic circuit includes means operable in response to the position of the switch to vary the number of actuating signals per cycle of the control signal, and means operable in response to movement of the lost motion mechanism for varying the air/fuel ratio or spark timing of the engine.
A preferred embodiment of the invention will now be deseribed, by way of example only, with reference to the accompanying drawings, in which:-
Figure 1 is a diagram of an engine incorporating a power modulation control system in accordance with the invention.
Figure 2 is a diagram of a throttle mechanism forming part of the system of Figure 1. Figure 3 is a graph illustrating the operation of the system of the Figure 1.
Figure 4 is a diagram of part of the system of Figure 1 and
Figure 5 is a diagram of another part of the system of Figure 1, and
Figure 6 is a graph illustrating the operation of the engine of Figure 1.
Referring to the drawings, an internal combustion engine comrpises an engine block of conventional construction having four cylinders 1,2,3,4 to each of which fuel is respectively supplied by four fuel injectors 5,3,7,8 mounted adjacent the inlet ports of the cylinders. The engine block carries an. inlet manifold 9 through which air is drawn into the cylinders and an exhaust manifold 10. The inlet manifold includes a throttle mechanism 12
(Figure 2) for varying the quantity of air flowing into the cylinder. The throttle mechanism comprises a plate 13 having three orifices 14,15,16 of diminishing size, and a shutter 17 εlidablε over the plate 13 by means of an electrical drive motor 13. In the first position of the shutter 17, illustrated, the throttle is fully open. When the shutter 17 covers the first or largest orifice 14, the throttle is half open. When the plate covers the first and second orifices 14,15 the throttle is one quarter open. The throttle mechanism 12 and the fuel injectors 5-8 are all controlled by an electronic control unit 20 which is operated by a selector switch 21 connected to the accelerator pedal of the vehicle.
The electronic control unit 20 comprises a micro - processor which receives input signals in a conventional manner from engine speed, engine load and engine timing sensors to generate a train of actuating signals in the form of pulses which are fed to the fuel injectors 5-8 in the form of a periodic control signal, the nature of which is illustrated in Figure 3. The control signal is periodic, each containing 21 time slots. The actuating signals in each time slot may be on either of two levels corresponding to a 0 level or "off" signal and a 1 level or "actuate" signal. The duration, or pulse width, of the signal in each time slot is controlled in a conventional manner in accordance with the engine speed and load conditions to provide appropriate air/fuel ratios, and the signal in each time slot is supplied through a conventional distributor in sequence to the fuel injectors 5-8 in timed relationship with the engine crankshaft and in the firing order of the cylinders 1 to 4 so that each injector supplies fuel to the associated cylinder only if the signal from the control program is at the "1" level. The firing order of the cylinders 1 to 4 is indicated by the numbers along the top of Figure 3.
If the control signal v.-ere to contain only one signal per period, only one cylinder would be actuated in each period, as illustrated in Figure 3a. Since the number of actuating signals per period (21) is not a multiple of the number of cylinders (4) (or of a non-unitary integral factor thereof) a different injector is actuated on successive periods. When the control signal contains only one signal per period, with four cylinders and a 21-slot period, each cylinder will be actuated once every four periods.
For each position of the throttle mechanism the power output of the engine can be increased by increasing the number of actuating signals per period until, when 21 actuating signals are generated per period, the engine is operating at full output power for that position of the throttle mechanism. Intermediate power outputs are obtained by varying the number of actuating signals per period. The number of actuating signals generated per period is controlled by a selector switch 21 illustrated in Figure 4. The selector switch 21 comprises a hub 31 having a wiper 32 arranged to sweep a selector band 33 which is itself divided into a plurality of discrete positions corresponding to different numbers of actuating signals per period. The selector band 33 is divided into three operating segments 34,35,36. In the first segment 34, the wiper 32 may occupy any one of iβ discrete positions 38. In the first position 38a, corresponding to the engine idle condition, the selector switch 21 conditions the control unit 20 to produce 4 actuating signals per period as illustrated in Figure 3b. The signals are so spaced that the intervals between the actuating signals are approximately equal, and each cylinder is fired once per period of the control signal. As the wiper 32 is moved clockwise over the first segment 34 of the selector band 33 , the selector switch conditions the control unit 20 to increase by one the number of actuating signals for each of the positions 38 swept by the wiper 32.
The precise sequence in which the actuating signals appear in each period of the control signal can be varied as desired when the engine is operating at less than full output power. Normally the actuating signals will be evenly spaced in the period so as to provide even operation in the engine.
At the intermediate position 38b, the control unit produces 10 actuating signals per control program period as illustrated in Figure 3c. Then the wiper 32 occupies the last position 38c in the segment 34, the control unit produces 20 pulses per period (Figure 3d) .
Throughout the movement or the wiper 32 across the first section of the selector band 33, the control unit 20 is also conditioned to position the shutter 17 to cover two of the three orifices 14,15 in the throttle plate 13 so that the throttle is one-quarter open, as iπcicated by the thick part of the black strip 39 on the selector band 33 in Figure 4. The control unit 20 is also conditioned to vary the pulse widths of the actuating signals in proportion with the throttle condition to maintain the required air/fuel ratio.
When the wiper 32 is in the first position 38d of the second segment 35 of the selector band 33 the control unit 20 is conditioned to produce 12 actuating signals per period, but, at the same time, 1he tnrottle mechanism is adjusted to move the shutter 17 so that the throttle is half open. Tnis is indicated by the narrower part of the black strip 39 on the selector band 33 in Figure 4. The pulse width is also adjusted accordingly to match the new air flow into the engine.
As the wiper 32 traverses the second segment 35 of the selector band 33, the control unit 20 is conditioned to increase the number of actuating signals per period of the control signal in incremental steps of 1 up to 20 once again. Thus, although the number of actuating signals per period is decreased from position 38c to 38d, since the throttle 12 is open wider, the power output of the engine continues to increase beyond that set by the control unit 20 when the wiper occupied the last position 38c of the first segment. When the wiper 32 is moved into the first position 38e on the third segment 36 of the selector band 33, the number of actuating signals per period is reduced again to 12, but the throttle 12 is adjusted so that it is fully open, and the injectors pulse width is increased to maintain air/fuel ratio, thereby producing a further increment in power output. As the wiper 32 traverses the third segment 36 of the selector band 33, the control unit 20 is conditioned to increase the number of actuating signals per period of the control signal to 21 in incremental steps of 1. When the wiper 32 occupies the end position 38+ of the third segment, 21 actuating signals are generated per period so that the engine operates at its maximum power output.
The hub 31 of the selector 21 is rotated by a collar 40 which is connected to an accelerator control (not shown) by a cable 4 1. The collar includes a slot 42 through which the arm of the wiper 32 projects and which provides a lost motion mechanism allowing a limited amount of relative movement between the collar 40 and the hub 31 . The amount of this relative movement corresponds approximately to the movement of the wiper 32 across one position 38 of the selector band. As best seen in Figure 5 the relative movecent operates a potentiometer 45. The potentiometer is connected to a control device (not shown) for varying the power of the engine within predetermined limits for each position of the wiper 32. For example the device may advance or retard the engine spark timing or, alternatively may vary the air/fuel ratio of the mixture supplied to the cylinders, e.g. by adjustment of the pulse widths of the actuating signals. Hence the driver can effect fine adjustments in power output between the two discrete power steps selected by the wiper 32 in adjacent positions on the selector band. A variable resistance 50 is connected insries with the potentiometer 45 and is normally short-circuited by a switch 51. As the wiper 32 is returned to the idle position 38a, the switch 51 is opened, so that the resistance 50 is switched into the circuit for the control device. Since the potentiometer 45 is arranged to provide its minimum resistance as the wiper is moved down the selector band 33 into the idle position 38a, the resistor 50 provides a predetermined setting for the control device corresponding to the desired idle setting.
The complete operation of the system is illustrated graphically in Figure 6 in which the power output of the engine is plotted on the left-hand ordinate of the graph and the positiccs of the wiper 32 on the selector band 33 are plotted on the abscissa.
For convenience, the plots for the second and third segments of the selector band 33 are shown above those for the first segment. The arrows A,B and C on the right-hand ordinate represent the ranges in which the throttle 12 is ¼, ½ or fully open respectively.
When the engine is idling, the wiper is at the first position 38a in the first segment of the selector band 33. The collar 40 has been rotated anticlockwise relative to the hub 31 so that the potentiometer 45 is in its minimum position. Switch 51 is open and the control device for the engine spark timing or air/fuel ratio is therefore at the appropriate predetermined idle setting.
TThen the accelerator control is operated, the collar 40 is first rotated clockwise relative to the hub 31 and the switch 51 is closed to short-circuit the resistance 50. The resistance provided by the potentiometer in the control circuit of the engine spark timing or air/fuel ratio control device increases to a maximum value, thereby increasing the power output of the engine as indicated by the broken line 60 in Fig. 6.
Thereafter, as the wiper 32 traverses the various positions 38 on the selector band 33, the power output of the engine increases in incremental steps corresponding to increases in the number of actuating pulses per period of the control signal, as described previously, following the solid line E in Figure 6. When the engine reaches a desired power value, the operator will move back slightly the accelerator control thereby moving the collar 40 relative to the hub 31 without altering the position of the wiper 32 on the selector band 33 (line F), The engine spark timing or air/fuel ratio is thereby altered to reduce the power of the engine by fine adjustments to the precise desired level without altering the number of actuating signals generated per period.
Subsequent reduction in power called for by the operator causes the collar 40 to move fully anticlockwise relative to the hub 31, as seen in line G in Figure 6, thereby causing a further smooth decrease in power. Thereafter the engine power is reduced in incremental steps as the wiper 32 traverses backwards the selector band 33 and the power output of the engine decreases as illustrated by the solid line H in the graph. Smooth changes in power output are therefore obtained on both acceleration and deceleration.