GB2101683A - Multi-cylinder internal combustion engine - Google Patents

Abstract

A plurality of cylinders are supplied with air via a common throttle valve 6 and a control unit 5 regulates the number of cylinders operating by intercepting the air supply to some of the cylinders under certain operating conditions. The output of the engine with a first number Z1 of cylinders operating coincides with the output with a second number Z2 of cylinders operating at a certain engine speed and the same throttle valve opening or manifold pressure or air flow rate. The engine is switched between Z1-cylinder and Z2-cylinder operation in the proximity of the point where said outputs coincide in response to the throttle valve opening, the manifold pressure or the inlet air flow rate and in response to the engine speed. <IMAGE>

Description

SPECIFICATION Multi-cylinder internal combustion engine The present invention relates to internal combustion engines which are capable of changing the number of cylinders in operation at any one time.

There have been known in prior art multi-cylinder engines which can increase the combustion efficiency of cylinders in operation to prevent toxic exhaust gas or which can reduce pumping loss through an increase in load rate to better fuel economy, by shifting the number of operating cylinders from the total at low-load to a given number.

There are conventionally known various methods for suspending the operation of cylinders such as disclosed in United States Patent Specification Nos.

4,221,200, and 4,221,201 and UK Patent Specification No. 2,075,118. In one such method, the operation of the intake and exhaust valves is suspended; it is also known to stop the operation of a fuel supply system provided for each cylinder (in many cases an electrically controlled fuel injection valve provided on branched pipes ofthe intake manifold) or the like.

These multi-cylinder engines, however, are deficient in that the output of the engine would fluctuate when the operation of cylinders is suspended, and when carried on automotive vehicles, it might cause a shock or jerk, presenting difficulties in smooth driving.

The present invention aims to provide a multicylinder internal combustion engine provided with a control unit which is capable of shifting an operational state with a first number of cylinders in operation (hereinafter called Z,-cylinder operation) to another operational state with another number of cylinders (hereinafter called Z2cylinder operation) with reduced output fluctuation and reduced shock.

In accordance with one aspect of the present invention, there is provided a multi-cylinder internal combustion engine ofthetype comprising a plurality of cylinders which are supplied with air via one common throttle valve and a control unit for regulating the number of cylinders in operation which can suspend the operation of a number of the cylinders by intercepting the air supplyto those cylinders, said control unit being so constructed as to switch the number of cylinders in operation from one number to another number at an operating condition when the engine outputs before and after switching the number of operating cylinders substantially coincide at a given rate of rotation of the engine at the same degree of opening of the throttle valve.

In accordance with another aspect of the present invention, there is provided a multi-cylinder internal combustion engine comprising a plurality of cylinders which are supplied with air through one com mon throttle valve and a control unit for regulating the number of cylinders which in operation can sus pend the operation of number of the cylinders by intercepting the air supply to those cylinders, wherein in order to change the number of operating cylinders at a particular rotational speed of the engine under an operating condition where the engine outputs before and after the change substantially coincide for a particular degree of opening of the throttle valve, a first number of operating cylinders will be changed to a second number of operating cylinders at or around a pressure value at an intake manifold of the engine where said engine output is substantially the same for operation with either number of cylinders by detecting said pressure, and vice versa, said second number of cylinders being switched back to said first number by detecting the pressure atthe intake manifold at which the engine output under said second number of cylinders in operation takes said substantially coinciding output value.

In accordance with a yet further aspect of the present invention, there is provided an internal combustion engine having a plurality of combustion cylinders, means for feeding air to said cylinders, via a commonly adjustable throttling means, cut-off means which can be selected to cut-off the air supply to one or more of the cylinders to prevent combustion in that or those cylinders, the engine being such that for certain operating conditions of the engine the output ofthe engine is substantially independent of whether or not said cylinder is cut-off, means for detecting whether or not the engine is operating substantially at such a certain operating condition and control means responsive to the detecting means to control the cut-off means such that, as the operating condition of the engine departs from said certain operating condition, said one cylinder is cut-off or not depending upon whether a higher engine output is obtained from the engine from that cylinders being cut-off or not.

Examples of the present invention will now be described with reference to the accompanying drawings in which: Fig. 1 shows a graph explaining a cross point; Figure 2 shows a first embodiment of the present invention diagrammatically.

Fig. 3 is a block diagram of the control unit in Figure 2.

Figs. 4(a), (b) and (c) are graphs of measured pressures at the intake manifold of the engine with various numbers of cylinders held in suspension.

Fig. 5 shows diagramaticallythe structure of a second embodiment according to the present invention.

Fig. 6 shows a circuit diagram of the control unit of the second embodiment.

Figs. 7(a) - (i) are the time charts of the signals at various parts in the circuit shown in Figure 6.

Fig. 8 is the output curve to show one example of operation with a number of cylinders suspended.

Fig. 9 shows diagramatically a third embodiment according to the present invention.

Fig. 10 is an explanatory diagram of the operation of the pressure switch of the third embodiment.

Fig. 11 shows the time charts of the signals at vari ous parts of the circuit shown in Figure 9.

Fig. 12 shows the structure of a fourth embodi ment according to the present invention.

Fig. 13 is the output curve of an example of operation ofthe fourth embodiment with a number of cylinders held in suspension.

The present invention will now be described by way ofthe first embodiment with reference to Figs. 1 -3.

In a variable displacement engine having a plurality of cylinders which is supplied with air via one common throttle valve and a system which interceptsthe airsupplyto said cylinders held in suspension via said valve by methods such as the mechanism for stopping intake/exhaust valve operation, the method to introduce atmospheric air, the mechanism to recycle the exhaust gas, etc., there exists a point (hereinafter called the cross point) as shown in Fig. 1 where the output underZ1-cylinder operation, i.e. 4-cylinder operation in Fig. 1, coincides with the output of Z2-cylinder operation, i.e. 2-cylinder operation, when the degree of the throttle valve opening is varied at a given constant rate of the engine rotation.

This is because while, in the driving range with reduced throttle valve opening, the combustion efficiency of 4-cylinder operation decreases the pump- ing loss increases, such defects are alleviated in 2cylinder operation.

It will therefore be possible to achieve smooth shifting of the driving without fluctuation in the out put if such shifting is conducted at a point where the outputs underZ1- and Z2cylinder operations at the same degree ofthe throttle valve opening coincide at respective rate of the engine rotation, or in other words at the cross point. In orderto do this, a memory may be provided for storing in advance the out puts corresponding to said cross point in terms of such parameters as the degree ofthe throttle valve opening, the negative pressure at the intake manifold and the like for respective rate ofthe engine rotation, whereby the engine is controlled by a command signal for suspending the cylinders produced by comparing the value in the memory with the actual value of the parameter.Theoretically, this shifting is best conducted at the cross point. "Hunting", however, occurs by shifting to and from just at the cross point and renders the engine unstable to make a smooth shifting impossible. In actual operation therefore a hysteresis is provided so as to conduct said shifting at two points, a andb on the both sides ofthe cross point in Fig. 1.

The control unit for shifting between Z1-cylinder operation and Z2-cylinder operation will now be described referring to Fig. 2.

The control unit to be provided on a 4-cylinder engine 1 comprises a magnet pickup 3 for detecting the rotational pulse ofthe engine located opposing the ring gear 2 of the flywheel within the flywheel housing 4, and the outputtherefrom is transmitted to the control unit 5. As a detector means for detect ing the output of the engine 1 at the cross point, a throttle sensor 7 is provided to determine the degree of the throttle valve opening as a parameter. A diffe rential transformer or the like to be provided on the rotational axis of the throttle valve 6 at its movable part may be used for this purpose. The output signal of the throttle sensor 7 is also transmitted to the control unit 5.

As shown in the block diagram of Fig. 3, the control unit 5 comprises: a memory 8 ofthe shifting engine load which receives as input the the engine rotation rate and which stores loads at the switching points at each rotation rate or in other words, the output at the point a in Fig. 1 where operation is shifted from 4 cylinders to 2 cylinders, in terms of the degree of the throttle valve opening, a memory 9 of the engine load at the cylinder suspension releasing point which stores the output at the point where the suspended cylinders are resumed, in other words the output at the point ofb in Fig. 1, in terms ofthe degree b' of the throttle valve 6 opening and, two comparators 10 and 11 which compare the output signals from these two memories with the output signal from the throttle sensor7 indicating the degree of the opening of the throttle valve 6.One of said comparators 10 detects the point where 4cylinder operation is switched to 2-cylinder operation while the other compartment 11 detects the point where 2-cylinder operation is switched back to 4-cylinder operation. The outputs from these two comparators 10 and 11 are transmitted to a unit 12 to determine the number of operating cylinders and to transmit a signal to a unit 13 for suspending the valve. A conventional device such as the mechanism for stopping intake/exhaust valve operation may be used as said unit 13. It is noted that such a device must be able to prevent air from coming into the suspended cylinders via the throttle valve. The detecting means for the output of the engine at the cross point is not limited to the throttle sensor 7 which detects the opening degree of the valve 6, but a pressure sensor 14 may be used to detect the pressure at the intake manifold.Further in the case of a 4-cycle engine, the amount of air intake per one cylinder, one cycle is expressed as total air intakel (number of cylinder x number of rotation / 2), and is proportional to the pressure at the intake manifold. It is therefore possible to detect the amount of intake by an air flow sensor 15. When the pressure sensor 14, orthe airflow sensor 15 is employed, it goes without saying that the outputs at the cross point in correspondence with the values in the sensors must be stored in the memories 8 and 9. It is also possible to detect the rate ofthe engine rotation through the ignition pulse at the distributor.

Although the embodiment has been explained in terms of shifting 4-cylinder operation (Z1 = 4) to 2-cylinder operation (Z2 = 2), it is not limited to a 4-cylinder engine but the numberofZ, and Z2 may be an arbitrary number. For example, a 4 cylinder engine can be operating using 4 cylinders, 3 cylinders of 2 cylinders in operation.

Next, the second embodiment according to the present invention will be described with reference to Figs. 4 -8. Various parts identical in function to those in the above embodiment are given the same reference number. This applies to other embodi ments to be described below.

Noting the cross point exists as mentioned in the first embodiment, the present inventors have simu lated the operation of an engine at the cross point to theoretically analyze the state of the engine. It was found that the characteristics of the cross point, or in other words, the point where outputs of Z, - and Z2cylinder operations of an engine operating at a constant rate of rotation become coincided atthe same degree of opening of the throttle valve, lies in that the value P, orthe pressure atthe intake manifold under Z1-cylinder operation and the value P2, or the pressure at the intake manifold underZ2 operation are simply determined by the value Z2/Z, and the atmospheric pressure P3 and are irrespective of the ratio of rotation of the engine, capacity of the cylinder and the absolute number of the cylinders. In other words, regardless of whetherthe displacement is 1000 cc or 2000 cc, or whether the number of cylinders is 6 or4, the pressures P1 and P2 at the intake manifold at the cross point take the same value if the ratio of the number of cylinders Z2/Z before and after shifting between Z1- and Z2cylinders remains the same.

The pressure P at the intake manifold was measured using a 4cylinder engine with 2000 cc displacement, and the results are shown in Figs. 4(a), (b) and (c). In these figures, the abscissa denotes the rate of rotation of the engine (rpm) respectively while the ordinate denotes the pressure (mm Hg abs) at the intake manifold of the engine rotating at a given rate wherein the output and the degree of the valve opening become the same in both operations.

Fig. 4(a) shows the shifting down from 4 cylinders to 2 cylinders; (b) from 4 to 3 cylinder; and (c) from 3 cylinders to 2 cylinders. As is evident from the graphs, the result (a) of shifting from 4 cylinders to 2 cylinders coincides well with the result of the theoretical analysis, and it is found thatthe pressure P1 at the intake manifold under 4cylinder operation when Z1 = 4 remains substantially constant in the range of between 330 and 340 mm Hg abs and the pressure P2 at the intake manifold under 2-cylinder operation remains substantially constant between 560 and 570 mm Hg abs. In the case of (b) and (c), the results differ from that of the theoretical analysis probably because the intake stroke cycles at an irregular interval.

The results of the theoretical analysis and experiments indicate that the pressures P1 and P2 at the intake manifold at the cross point maintain a constant value respectively for over a wider range of rate of rotation of the engine. It is therefore possible to shift the number of operating cylinders from Z1 to Z2 and vice versa in a smooth manner without causing fluctuation in the output by detecting said pressure at the intake manifold. Moreover, the control unitforthis purpose can be made simple as it only involves detection of the pressure at the intake man ifold.

Referring now to Fig. 5, the second embodiment of the variable displacement engine according to the present invention will now be described.

The control unit to be provided on a 4-cylinder engine comprises a pressure sensor 14 which is connected to an intake manifold 18 and which con tinuouslyconvertsthe pressure P atthe intake manifold into an electric signal to be transmitted to the control unit 5. The control unit 5 transmits to the cylinder suspension mechanism 13 a command signal for suspending the cylinders, or a signal for releasing the suspended cylinders obtained from the operational state of the engine 1 at the moment and said pressure P at the intake manifold.

As shown in Fig. 6, the control unit 5 comprises a comparatorCOMP 1 which is provided in advance with a reference voltage Vref 2 which corresponds with the pressure P2 = 580 mm Hg abs, at which value 2-cylinder operation is shifted to 4-cylinder operation and compares the voltage with the input signal; a comparator COMP 2 which is provided in advance with a reference voltage Vref 1 and compares the same with the input signal; and a logic circuit of AND gate 1,NOR gate 1 and OR gate 1 which transmits a command signal for suspending the cylinders on the basis of the data from these comparators COMP 1 and COMP 2. The output of the control unit 5 is necessarily "1" when the input signal is smaller than the reference voltage Ref 1, and "0" when the input signal is greater than the reference voltage Vref 2.When the input signal takes an intermediate value between the reference voltages Ref 1 and Vr,,t, the output will vary depending on the situation. In other words, when the output of the control unit 5 is "1 " because the outputs of COMP 1 and COMP 2 are both "1" and the output of NOR 1 is "0", then the output of AND 1 becomes "1 " and the output remains to be "1". When the output of the control unit 5 is "0", on the other hand, the output of AND 1 becomes "0" and the output of the control unit 5 remains to be "0".

Under the operation in which fluctuation of the output assumes the curve A as shown in Fig. 8, the throttle valve would be manipulated in the manner as shown in Fig. 7(a) with signals at various parts as shown in Figs. 7(d)-(h), whereby a command signal for suspending the cylinders as shown in Fig. 7(i) will be transmitted and the pressure atthe intake manifold will fluctuate as shown in Fig. 7(b).

The reference voltages Vref 1 and Vref 2 to be set in the comparators COMP 1 and COMP 2 are slightly deviated from the actually measured pressures at the cross point, or by about 10 mm Hg in the present embodiment. This is to prevent unstable operation due to occurrence of "hunting" in the engine as is in the first embodiment.

As the cylinder suspension mechanism 13 which is driven by the command signal for suspending the operating cylinders from the control unit 5, the device such as the mechanism for stopping intake/exhaust valve operation mentioned in the first embodiment may be used.

Referring now to Figs. 9 - 11, the third embodiment according to the present invention will be described.

In the embodiment shown in Fig. 9, pressure switches VS 1 and VS 2 which switch on and off at a pre-determined point are used in place of the pressure sensor of the above embodiment. Transistors Tr 1 and Tor 2 function as the comparators. The construction is identical with the above embodiment in other respect, and the identical parts are given the same reference numbers and overlapping description is omitted. As shown in Fig. 10, the pressure switches VS 1 and VS 2 switch on and offatthe pressures at the intake manifold P1 = 330 mm Hg abs and P2 = 580 mm Hg at the cross point. Hysteresis is provided to prevent "hunting" in the engine 1.When the throt tle valve is manipulated in the manner as shown in Fig. 11(a), the signals at various parts become as shown in Figs. 11 (b) - (k) to thereby achieve the con trol as mentioned above.

In the foregoing, the second and the third embod iments were described in terms of shifting between 4-cylinder (orZ1 = 4) and 2 cylinder (orZ2 = 2) operations where there exists a relation of Z, 2Z2 and where intake stroke in both Z1- and Z2-cylinder operations cycles at a regular interval, these conditions being approximately the same as those ofthe theoretical model with the pressures P1 = 330, P2 580 respectively at the intake manifold at the cross point. The fourth embodiment to be described below relates to shifting between 4 cylinders, 3 cylinders and 2 cylinders. In these cases, as has already been mentioned with respect to Figs. 4(a), (b) and (c), the pressures P1 and P2 at the intake manifold do not maintain a constant value except at the shifting point.The pressures at the intake manifold are therefore established with due consideration to the rate of rotation ofthe engine, as shown in Table 1.

Table 1

Cylinders Pressure at the Rate of engine in operation intake manifold rotation 2 ~4 cylinders 580 mm Hg abs 500 rpm and less 42 330 23 540 500 3 ~2 360 34 500 3~4 500 4 ~3 330 2500 500 and more Fig. 12 shows an embodiment in diagram for the control ofthe number of cylinders according to the valves of Table 1 above.The second embodiment shown in Fig. 5 is further provided with a distributor 20 which transmits ignition pulse to be transmitted to the control unit 5 by detecting the rate of rotation of the engine. Various means can be used to detect the rate of rotation of the engine such as a magnet pickup 3 which can be provided opposing the ring gear 2 of the flywheel, as in the first embodiment.

The output of the engine 1 of this construction is controlled in various regions as shown in Fig. 13. By controlling in such a fine manner, the features of variable displacement engine will be enhanced, and a smooth driving of the engine will be ensured as there is no fluctuation in the output at the time of shifting.

As has been described above by way of embodiments, the present invention enables a smooth driving without any shocks due to fluctuation in the out put since shifting between Z1- and Z2-cylinder operations is conducted at or around the cross point where the outputs before and after shifting the number of cylinders coincide. Further, the control unit for such shifting can be made simple as it only need to detect the pressure atthe intake manifold to check the cross point.

Claims (9)

1. A multi-cylinder internal combustion engine of the type comprising a plurality of cylinders which are supplied with air via one common throttle valve and a control unit for regulating the number of cylinders in operation which can suspend the operation of a number ofthe cylinders by intercepting the airsupply to those cylinders, said control unit being so constructed as to switch the number of cylinders in operation from one number to another number at an operating condition when the engine outputs before and after switching the number of operating cylinders substantially coincide at a given rate of rotation ofthe engine atthe same degree of opening ofthe throttle valve.

2. The multi-cylinder internal combustion engine as claimed in claim 1 in which said control unit comprises an electric means for storing or for calculating a signal dependent on the degree of opening of the throttle valve which corresponds to the operating condition where said outputs before and after switching the number of operating cylinders substantially coincide as a function ofthe rotational speed ofthe engine controls the number of operating cylinders by comparing a signal dependent on the actual opening degree of the throttle valve transmitted from a detecting means for the actual opening degree ofthe throttle valve with the signal from said electric means.

3. The multi-cylinder internal combustion engine as claimed in claim 1 in which said control unit comprises an electric means storing or for calculating a signal dependent on the pressure at an intake pipe of the engine which corresponds to the operating condition when said outputs before and after switching the number of operating cylinders substantially coincide as a function ofthe number of operating cylinders and the rotational speed of the engine and controls the number cf operating cylinders by comparing a signal dependent on the actual pressure at the intake pipe transmitted from a detecting means forth actual intake pipe pressure with the signal transmitted from said electric means.

4. The multi-cylinder internal combustion engine as claimed in claim 1 in which control unit comprises an an electric means for storing or calculating a signal dependent on the amount of air intake which corresponds with the operating condition when the outputs before and after switching said number of operating cylinders substantially coincide as a function ofthe number of operating cylinders and the rotational speed ofthe engine, and controls the number of operating cylinders by comparing a signal dependent upon the actual amount of air intake transmitted from a detecting means for the actual air intake amount with the signal transmitted from said electric means.

5. A multi-cylinder internal combustion engine comprising a plurality of cylinders which are supplied with air through one common throttle valve and a control unit for regulating the number of cylinders which in operation can suspend the operation of a number ofthe cylinders by intercepting the air supply to those cylinders, wherein in order to change the number of operating cylinders at a particular rotational speed of the engine under an operating condition where the engine outputs before and after the change substantially coincide for a particular degree of opening of the throttle valve, a first number of operating cylinders will be changed to a second number of operating cylinders at or around a pressure value at an intake manifold at the engine where said engine output is substantially the same for operation with either number of cylinders by detecting said pressure, and vice versa, said second number of cylinders being switched back to said first number by detecting the pressure at the intake manifold at which the engine output under said second number of cylinders in operation takes said substantially coinciding output value.

6. The multi-cylinder internal combustion engine as claimed in claim 5 in which said control means comprises a pressure detecting means for transmit- ting electric signals corresponding to the pressure at the intake manifold, a comparator for comparing a reference electric signal corresponding to the intake-manifold pressure at the time of switching the number of operating cylinders with the electric signal from said pressure detecting means, and an electric means having a logic circuit for transmitting to the control unit a command signal corresponding to the output from said comparator for changing the number of operation cylinders.

7. The multi-cylinder internal combustion engine as claimed in claim 5 in which said control unit comprises a pressure switch which switches on and off at or around the pressure atthe intake manifold where the outputs under the first number of operating cylinders takes said substantially coinciding output value, a pressure switch which switches on and off at or around the pressure at the intake manifold where said output under said second number of cylinders in operation takes said substantially coinciding output value, and an electric means which transmits to said control unit a command signal for switching the number of operating cylinders for regulating the number of operating cylinders in correspondence with the electric signals from said two pressure switches.

8. An internal combustion engine having a plur alityofcombustion cylinders, means for feeding air to said cylinders, via a commonly adjustable throttling means, cut-off means which can be selected to cut-off the air supply to one or more of the cylinders to prevent combustion in that or those cylinders, the engine being such that for certain operating conditions of the engine the output of the engine is substantially independent of whether or not said cylinder is cut-off, means for detecting whether or not the engine is operating substantially at such a certain operating condition and control means responsive to the detecting means to control the cut-off means such that, as the operating condition of the engine departs from said certain operating condition, said one cylinder is cut-off or not depending upon whether a higher engine output is obtained from the engine from that cylinder being cut-off or not.

9. A multi-cylinder internal combustion engine substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.