Speed Controls

Abstract

The invention relates to speed control systems for controlling the rotational speed of an internal combustion engine and provides means for controlling the engine utilizing a fuel injection system idling speed so as to maintain it at a substantially constant pre-selected value which is virtually independent of ambient conditions and engine load conditions. Different types of valve means are described for controlling the flow of air from a point at substantially atmospheric pressure to a point downstream of the engine throttle valve. Control circuits are also described for controlling the valve means in accordance with the difference between a pre-selected value of engine idling speed and the actual engine idling speed.

Description

This invention relates to speed control systems for controlling the rotational speed of an internal combustion engine.

In accordance with this invention, means are provided for controlling the idling speed of an internal combustion engine so as to maintain a substantially constant preselected value of idling speed which is virtually independent of ambient conditions and engine load conditions.

In accordance with a feature of the invention, said means for controlling the idling speed includes valve means controlling a flow of air from a point at substantially atmospheric pressure, e.g. from a point in the induction system of the engine upstream of the engine throttle valve means therein, to a point downstream of said engine throttle valve.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a simplified diagram of a basic speed control arrangement,

FIG. 2 is a diagrammatic drawing of a control valve unit,

FIG. 3 is a diagram of one embodiment of the arrangement of FIG. 1,

FIG. 4 is a diagram of a motor driven control valve;

FIG. 5 is a diagram of a further embodiment of the arrangement of FIG. 1 and

FIG. 6 shows a further embodiment.

Referring to FIG. 1 of the drawings, a reciprocating internal combustion engine 8 has an air cleaner 9 at the inlet to the engine induction pipe 10. The idling speed control includes a control valve unit 11, shown in greater detail in FIG. 2, the valve unit being controlled in accordance with the difference between the actual idling speed and the required idling speed. For this purpose, a tachometer generator 12 is driven by the engine and produces an electrical output, e.g. a voltage V.sub.S, which is a function of the actual engine speed. A device 13 produces a voltage V.sub.R which is a measure of the required idling speed. The two voltages are fed to a comparator device 14, the output from which represents the difference of the voltages. This output is amplified in an amplifier 15 and the amplified signal is fed to control the valve unit 11, and hence to control the admission of air into the induction system of the engine.

Referring to FIG. 2, the control valve unit 11 is shown in detail. This unit is positioned upstream of a conventional fuel injection system such, for example, as one of those described in U.S. Pat. Nos. 3,272,187 and 3,240,191, which system is responsive to manifold pressure and engine speed. The unit is associated with the engine induction pipe 10, and includes a casing 16, the interior of which is divided by a diaphragm 17 into two chambers 18, 19. The diaphragm carries a central disc valve 20 which co-operates with a valve seat 21, and a coil spring 22 loads the disc valve in the opening direction.

The valve seat 21 surrounds the outlet of a duct 23 which is preferably connected to the induction system just downstream of the engine air cleaner, and thus has its inlet effectively at substantially atmospheric pressure. A branch pipe 24 from duct 23 is connected to chamber 18, and contains a restrictor 25. The other chamber 19 is connected by a duct 26 to a point in the engine induction system 10 downstream of the throttle valve 7, where the pressure is below atmospheric pressure.

A further pipe or conduit 27 leads from chamber 18 to duct 26 (or direct to the induction system downstream of the throttle valve 7), and conduit 27 contains an electrically operated normally-closed valve 28. The operation of the valve 28 is controlled by the amplified electrical signal from the amplifier 15, which is fed to the valve operating solenoid 29.

In operation of an engine provided with an idling speed control as described above, if the actual idling speed sensed by the tachometer 12 is greater than the required idling speed for which the device 13 is set, an error signal produced by the comparator 14 and amplified by amplifier 15, maintains the valve 28 in the normally closed position. Since the pressure drops across restrictor 25 and the orifice 28a of valve 28 are an inverse function of the respective areas, this causes an increase of pressure in chamber 18, which in turn tends to load disc valve 20 onto its seating 21 against the load of spring 22. This reduces the flow of air through duct 23, chamber 19, and duct 26, from atmosphere to a point in the engine induction system 10 on the downstream side of the throttle 7, and consequently reduces the engine idling speed.

Conversely, if the actual idling speed is less than the selected speed, an error signal is produced causing valve 28 to open, the pressure in chamber 18 reduced, the valve 20 opens further, and the air flow through duct 23 increases until the idling speed has increased to the selected value.

One particular embodiment of the basic arrangement of FIG. 1 is shown in FIG. 3, wherein like parts bear the corresponding reference numerals to those in FIG. 1. The reference voltage V.sub.R, which is a measure of the required idling speed, is derived from a tapping T on a potentiometer P connected across a D.C. source, such as a battery B. The tapping T, and hence the output voltage from device 13, is made variable so that the value of the pre-selected idling speed of the engine can be varied. The D.C. voltage V.sub.S from the tachometer generator 12, which is a function of the actual engine speed, is fed through a filter network F and combined, with opposite polarity, with the voltage V.sub.R at the input to the comparator device 14. This device comprises an operational amplifier A1 which produces an output error signal representing the difference between the two applied voltages. The output of amplifier A1 is fed through a further operational amplifier A2 functioning as a level detector, and a buffer stage BF. These two stages correspond to the amplifier 15 of FIG. 1. The output from the buffer stage is employed to energize the operating solenoid 29 of the valve 28, and hence controls the operation of the valve unit 11, as previously described.

It will be appreciated that in the arrangements so far described, the valve 28 is either closed or open, depending upon whether the engine idling speed is above or below the pre-selected value. In practice, the valve 28 may be caused to operate fairly rapidly if the idling speed is fluctuating closely about the pre-selected value.

In an alternative arrangement, instead of a solenoid controlled valve, a motor driven valve may be used which can gradually vary the area of the valve orifice 28a (FIG. 2) between a fully closed and a fully open position. Such an arrangement is shown in FIG. 4 which reproduces a part of the duct 26 and pipe or conduit 27 which are interconnected by the valve orifice 28a. This orifice is controlled by a valve member 30 connected to a worm gear 31 driven by a gear 32 mounted on the output shaft of an electric motor 33. The rotation of the motor in either direction to vary the position of the valve member 30 with respect to the orifice 28a is controlled by a signal depending on the difference between the voltages V.sub.R and V.sub.S as previously described.

FIG. 5 shows one particular arrangement for controlling such a motor driven valve. Once again like parts bear corresponding reference numerals. As in the arrangement of FIG. 3, the reference voltage V.sub.R is derived from the tapping T of a potentiometer P connected across a battery B. This reference voltage is applied to the input of an operational amplifier A1 together with the voltage V.sub.S derived from the tachometer generator 12 and which is a function of actual engine speed. The error signal output voltage produced by the operational amplifier A1 is fed through a further operational amplifier A3 which in turn produces an output voltage controlling the operation of the motor 33. This motor controls the valve 30, as previously described, so as to maintain the engine idling speed at the pre-selected value.

According to a further embodiment shown in FIG. 6 and employing a motor driven valve similar to that shown in FIG. 4, the motor driven valve itself may directly control the admission of air to the engine induction pipe 10. In such an arrangement the valve must be arranged to be closed, except when controlling engine idling speed.

A further feature which may be incorporated is a circuit which differentiates the output of the tachometer generator with respect to time, feeding the resultant signal to the comparator, so that the error signal takes account not only of the magnitude of the difference between the actual speed and the required speed, but also of the magnitude and sense of the rate of change of the actual speed.

The invention may be applied to engines which employ fuel injection, for example, into the induction manifold upstream of the inlet valves.

Claims

I claim:

1. An idling speed control system for an internal combustion engine having an inlet manifold, a main engine throttle valve disposed in the inlet manifold for controlling the flow of motive fluid therethrough, and a fuel injection system responsive to manifold pressure and engine speed, said system comprising electrically operable valve means for controlling the flow of motive fluid from a point at substantially atmospheric pressure to a point in the inlet manifold downstream of the main engine throttle valve but upstream of said fuel injection system, selector means for producing a first electrical signal representative of a pre-selected value of engine idling speed, means for producing a second electrical signal representative of actual engine speed and a comparator device connected to receive the first and second signals and arranged to produce an electrical output signal representative of the difference therebetween, said output signal being applied to the electrically operable valve means to control the operation thereof, whereby to maintain the engine idling speed substantially constant at said pre-selected value virtually independently of ambient conditions and engine load conditions.

2. A system as claimed in claim 1, wherein the electrically operable valve means comprises first and second chambers each having a respective outlet which is adapted to be connected to the inlet manifold downstream of the main engine throttle valve, a diaphragm separating said chambers and carrying a valve member which co-operates with a valve seat to control the admission of motive fluid at substantially atmospheric pressure to the first chamber, a conduit for establishing restricted communication between said first and second chambers, and an electrically operable valve connected to the outlet of the second chamber for controlling the pressure therein, whereby to influence said diaphragm.

3. A system as claimed in claim 1, wherein the motive fluid at substantially atmospheric pressure is derived from a point in the induction system of the engine upstream of the throttle valve.

4. A system as claimed in claim 1, wherein said valve means comprises a solenoid operated valve.

5. A system as claimed in claim 1, wherein said valve means comprises a motor driven valve.

6. A system as claimed in claim 5, wherein the motor driven valve directly controls the admission of motive fluid to the induction system of the engine at a point downstream of the throttle valve.

7. A system as claimed in claim 1, wherein the second signal representative of actual engine speed is a voltage signal derived from a tachometer generator driven by the engine and the first signal representative of the required idling speed is a reference voltage.

8. A system as claimed in claim 7, wherein the voltages are D.C. voltages.

9. A system as claimed in claim 8, wherein the comparator device is an operational amplifier whose output is applied to a level detector circuit which produces an output employed to control the operation of a solenoid operated valve means.

10. A system as claimed in claim 9, wherein the level detector is a further operational amplifier.

11. A system as claimed in claim 8, wherein the comparator device is an operational amplifier whose output is fed to a second operational amplifier producing an output which controls an electric motor driving the valve means.