GB2128318A - Cooling of internal combustion engines - Google Patents

Abstract

This invention provides means to improve control of the temperature of the internal cylinder surfaces of an IC engine so that those temperatures are maintained closer to their optimum values at each combination of engine load and speed, and particularly to enhance engine cooling whenever the co-ordinates of the engine load and engine speed approach a value at which detonation would tend to occur in the absence of such enhancement. The setting of a valve controlling the rate of flow of coolant through ducts formed in the engine structure is determined by the output of a control device having two inputs (10, 13), related to engine load and speed respectively. The control device may be a movable plate (35) connected to the control valve and presenting two shaped surfaces which maintain contact with followers (29, 32) carried by levers (27, 31) movable in response to engine load and engine speed respectively. Means to vary ignition timing in response to particularly rapid changes in engine demand are also described. <IMAGE>

Description

SPECIFICATION Improvements in or relating to the cooling of internal combustion engines This invention relates to internal combustion engines and seeks in general to provide improved control of the temperatures of the internal cylinder surfaces so that, at each combination of engine speed and engine load, the surface temperatures approach those producing the most satisfactory conditions for combustion, as judged by criteria such as engine performance and durability, exhaust gas emissions and noise. A particular case in which such improved control of internal surface temperatures is especially desirable is that of the spark-ignition engine, using liquid or gaseous fuel or both.In this type of engine, the compression ratios that can be used, and hence the power and economy of the engine, are limited by the occurrence of detonation when the compression ratio is raised beyond a certain value.

In Figure 1 of the accompanying drawings, which is a diagrammatic graph, ordinates represent engine speed and abscissae represent load. By load we mean that quantity, normally expressed as brake mean effective pressure, which is equal to a constant times the torque (as measured during engine testing by a dynamometer) existing at the output end of the crankshaft of a typical engine. More colloquially, the same term "load" is also applied to the resistance -- in practice, always the sum of several opposing forces -- against which the engine works. For a better understanding of what follows it is important to appreciate that these two uses of the term "load" are consistent with each other. A simple movement of the engine throttle does change the resistance against which the engine is working.The explanation is that an increase (say) in throttle opening results immediately in an increase in the Bmep and torque and thus produces an acceleration of the body - a vehicle say - that the engine is driving. The inertia of that vehicle thus provides immediately an increase to the load under which the engine is already working, this increase comprising a force equal to the product of the mass of the vehicle and the acceleration. The acceleration of the vehicle continues until the increase in frictional forces, including air resistance, baiances the increase in torque.

Every point on the graph of Figure 1 represents a particular combination of speed and load for a particular engine. The shaded area covers those combinations of speed and load under which, in the absence of enhanced cooling, detonation would occur in that engine.

At some point, such as X, the tendency to detonate is greatest. It will be noted that below a certain load (Ll) the engine will operate over the whole speed range without detonation, and that it will operate over the whole load range without detonation at speeds below and above certain values (S, and S2). It is known that the detonation limited mean effective pressure increases with reduction of coolant temperature as a result of the reduction of the internal surface temperatures, and one aim of the present invention is to reduce the temperatures of some of the internal surfaces below the values they would have had with conventional cooling systems so as to permit the engine to run without detonation at combinations of speed and load that would otherwise have given rise to it.

A conflicting requirement of the spark ignition engine, however, is that higher than normal internal surface temperatures are needed during idling and low power running in order to reduce the concentration in the exhaust gases of the products of incomplete combustion. The incomplete combustion is largely due to the quenching of the combustion flame by the relatively cool combustion chamber surfaces, the temperatures of which, with conventional cooling arrangements including thermostatic control of the coolant temperature, fall at low powers far below those at high powers.

The present invention seeks to go some way towards meeting both of those conflicting requirements and according to the invention an internal combustion engine, particularly of sparkignition type, has a fluid coolant circuit including a pump and cooling ducts, the ducts being formed within the engine structure close to those internal surfaces where excessive temperature can lead to detonation. The circuit includes a flow control valve to regulate the rate of flow of coolant through the ducts and the setting of that valve is determined by the output of a control device, this output being a function of at least two inputs to the device. One of those inputs is related to the instantaneous load of the engine, and the other to the instantaneous engine speed.

The circuit may also include a radiator and the control device may be located between the radiator outlet and the ducts and may operate as a variable two-way valve to direct only a variable proportion of the total coolant flow through the ducts, diverting the balance of the flow back to the radiator inlet without passing through the ducts.

A rise in the output of the control device is reflected in a rise in the proportion of the coolant flow that passes through the ducts, and a fall in output in a fall in that flow.

The function of the control device may be to produce the following pattern of changes in its output, in accordance with variation in the two inputs which represent engine speed and engine load. When both these inputs are minimal, the output is minimal also. Below a vertain value of each input, an increase in either input causes the output of the device to increase steadily. As the co-ordinates (see Figure 1) of engine load and speed approach close to the shaded area in which detonation occurs, output increases rapidly. The output reaches a maximum as the co-ordinates approach point X.The output falls again when subsequent changes -- either reductions or further increases -- in either or both of the two inputs indicate that the engine running condition has moved firstly well clear of point X, and secondly out of the entire shaded area.

The control device may comprise a first lever movable in response to a first input related to engine load and a second lever movable in response to a second input related to engine speed, and an output member in the form of a movable plate presenting two shaped surfaces which maintain contact with followers carried by the first and second levers respectively, the output member being connected to the control valve. The first lever may be connected to the engine throttle cable, and the second lever may be connected to speed-responsive mechanism, for instance to spring-loaded flyweights pivotally mounted on the drive wheel of the customary camshaft which operates the valves of the cylinders.The surface of the output member which engages with the second lever may be shaped so as to provide an increasing output as engine speed rises from minimum to a first value, then a substantially constant output as speed continues to rise to a second value, and then a lesser and generally decreasing output if engine speed rises yet further.

The first and second speed values just referred to may be related to the lower and upper boundaries, respectively, of that range of engine speed (see Figure 1) within which detonation can occur.

In addition there may also be means to vary ignition timing in response to particularly rapid changes in demand.

The invention is further defined by the claims and will now be described, by way of example, with reference to the further Figures of accompanying drawings in which: Figure 2 is a diagrammatic plan view of a four cylinder, naturally-aspirated, automotive petrol engine and its radiator; Figure 3 is a side view of the same engine; Figure 4 is a section through the control device, taken at the level of the cables; Figures 5 and 6 are respectively a horizontal section and a vertical section through a flow control valve; Figure 7 is a vertical transverse section through the axis of the spark plug hole of the cylinder head of the engine shown in Figures 2 and 3;; Figure 8 is a horizontal section through the lower deck coolant ducts serving one cylinder of that engine, and Figure 9 is a diagrammatic view of mechanism whereby ignition timing may be varied in response to particularly rapid changes in load.

In Figure 2 the radiator hoses, water pump, cooling fan and some other features, which are of known design and are not pertinent to the present invention, have been omitted for clarity.

Conventional but illustrated features of the engine include the crankcase 1, the top surface 2 of the cylinder head, the valve gear cover 3, the air manifold 4, the carburettor 5, the air filter 6 and the radiator 7.

Reference 8 indicates a control device according to the invention, in the form of a shallow box containing a mechanical arrangement for controlling a flow control valve 9. The throttle cable 10 passes through one end of the control box 8, and is connected in the normal manner to the arm 11, seen end-on in the vertical position, which turns the throttle shaft. 12 is an enlarged part of the camshaft drive cover surrounding the camshaft driving wheel, which is modified to carry spring-loaded flyweights of known type which swing on their pivots under centrifugal force and draw in a central non-rotating spindle to which is attached one end of a cable 13 which, like the throttle cable, is of the conventional Bowden type, with an outer sheath.The other end of the cable enters the box 8. 14 is a further Bowden cable which carries the movement produced by the mechanism in 8 to the arm 15, seen in the vertical position, of the flow control valve 9.

Figure 3 shows a conventional pump 16, driven from the engine by a shaft 17, and drawing coolant from the bottom of the radiator 7 via a connecting hose 18, a T-piece 1 9 through which the coolant passes from the cylinder head via connecting hoses 20 to the tope of the radiator in the usual way, except that no thermostat is used at the cylinder head outlet, and hoses 21 and 22 via which some of the coolant leaving the control valve 9 passes to the coolant inlet in the cylinder block and the remainder returns directly to the radiator, the distribution depending on the position of the control valve arm 1 5.

As Figure 4 shows, cable 10 lies in the slotted end of one arm of an angled lever 23. An attachment 24 on the cable abuts the side of the arm so that movement of the cable to open the throttle by the arm 11 on the throttle shaft moves the lever 23 which is mounted on a pivot 25 projecting from the bottom of the box 8. The end of the other arm of the lever is connected pivotally by a link 26 to an arm 27 mounted at one end on a pivot 28. The other end of the arm 27 carries a roller 29. The end of the cable 1 3 is connected pivotally at 30 to a pivoted arm 31 similar to 27 and also carrying a roller, 32, at its free end. The two arms 27 and 31 which are shown in the engine idling position are provided with tension springs 33 and 34 tending to draw them towards one another.The two rollers roll across two parts of the shaped edge of an output member in the form of a plate 35 mounted on a pivot 36 projecting from a sliding bar 37 which moves freely between two guides 38 projecting from the bottom of the box. The end of the cable 1 4 which operates the flow control valve is connected either to a pivot on the plate at 39 as shown, or to the sliding bar 37. The three cables have conventional adjustable end housings 40, 41 and 42, one of which is shown in section.

The flow control valve 9, shown in detail in Figures 5 and 6, comprises a body 43, a cylindrical rotor 44, end covers 45 and 46 and a shaft seal 47. Rotor 44 has stub shafts 48 housed in bores in the covers, forming bearings. A circular spring 49 urging the valve towards its fully open position is fitted to the projecting stub shaft which also carries the operating arm 1 5 to which the cable 14 is attached.

The body 43 has three ports. Port 50 is connected by a short length of hose 21 to the engine coolant inlet. Port 51 is connected by a hose 22 to the T-piece 1 9 which connects the engine outlet and the radiator inlet. The crosssection of both the ports changes from circular at the outer end of the projecting hose connection to rectangular at the interface with the rotor, so that turning the rotor through a small angle is sufficient to switch almost the whole flow from one port to the other.

The inlet port 52 which is connected directly to the pump outlet opens out into a passage 53 which subtends an angle large enough to keep the rotor inlet always fully open.

As seen in Figure 5, the passage 54 through the rotor extends axially to match the inner ends of the three ports. Figure 6 shows that the corners of the inlet end of the passage are rounded to improve flow. The outlet end subtends an angle of 900, as do the axes of the two outlet ports. In the position shown, the two outlet ports are equally open. A small movement of the rotor in either direction from this position almost closes one port and almost fully opens the other.

Figures 7 and 8 show the coolant ducts of the engine now being described. In this particular engine the cylinder block has conventional cooling passages (not shown), and in practice this restricted arrangement of the distinctive layout of ducts as shown in these Figures will often be sufficient to obtain the control sought by the present invention, because the hot surfaces of the part of the cylinder head forming the top or "flame plate" of each individual cylinder have the greatest tendency to cause premature detonation. However ducts of this distinctive layout could, if desired, also be used in the upper structure of the cylinder block without departing from the invention.

Figures 7 and 8 show that coolant ducts in the form of flow passages run lengthwise through the deck in two groups, 55 and 56, one on each side of the line of exhaust and air valves, and are of small cross-sectionai area to obtain very high rates of heat transfer when a high coolant flow rate is used. The deck portions such as 57 below the passages (Figure 7) are thinner than normal in order to minimise the amount of metal that need be heated or cooled in accordance with changes of engine running conditions and thus to minimise the response time.

From the outlet of radiator 7, coolant reaches the passages 55 and 56 by way of hose 18, pump 16, flow control valve 9 and hose 21 and then passes into the cylinder block through which it flows to the left-hand end as shown in Figure 3, then rising to pass through two conventional transfer passages 58 and 59 (Figure 8) and then into the space 60 at the end of the cylinder head.

Part of the coolant then enters the deck passages 55 and 56. The remainder of the coolantflows upwards through a rising passage indicated by a broken line in Figure 8 and into and along two drilled passages 61 and 62 which cool the valve guides.

On reaching the outlet ends of the deck passages, the coolant flows into a collecting space similar to 60, but without the transfer passages 58 and 59. It then enters a similar rising passage (broken line) where it is joined by coolant leaving the outlet ends of valve guide cooling passages 61 and 62. The combined flow then leaves the cylinder head through a hole in the end wall and passes through the T-piece 1 9 and hoses 20 (Figure 3) back to the radiator 7.

Referring again to Figures 1 and 4 the effects on the behaviour of the cooling system of various changes of engine speed and load will now be considered.

Under idling conditions, the throttle will be nearly closed, so that the slotted arm of the angled lever 23 (Figure 4) will be at its extreme right-hand position as shown in full line. The tension spring 33 attached to the arm 27 will have drawn the roller 29 to the inner end of its range of travel across the contoured edge of the plate 35. The other end of the range of travel of the components is shown in broken lines.

At the idling speed, the flyweights of the speedsensing device will be exerting minimal force on the cable 13, so the roller 32 on the arm 31 will likewise be at the inner end of its travel. Taking account of the arcuate paths of the rollers and the contours of the two parts of the plate edge, it will be seen that in this condition the plate and with it the cable 14 will be drawn powerfully to their extreme left-hand positions, the function of the pivot 36 and slider 37 being to prevent movement of the plate 35 in the direction of the roller movements while permitting movement in the direction of the slider movement.The adjusting screw 41 of the cable 14 is set so that when the plate 35 is in this position the flow control valve passes coolant to the engine at a minimum flow rate and the remainder flows to the radiator to be cooled in readiness for use during subsequent vehicle acceleration.

The adjusted minimum rate of flow of coolant through the engine is such that at idling and low powers the coolant temperature rises to a value in excess of that conventionally produced by a thermostat. With the radiator pressure relief valve set to a higher value than normal and the pump shaft seal, hoses, etc. modified if necessary to withstand higher pressure, the system is selfpressurised by the build-up of the pressure of the vapour in the space above the coolant in the radiator. Boiling in the coolant passages is therefore avoided despite the raised temperature, and the effect is that the temperatures of the internal surfaces of the combustion chambers and cylinder walls are higher than normal with the result that flame quenching is reduced and the concentrations in the exhaust gases of the products of incomplete combustion are reduced.

This is in addition to the established beneficial effect of allowing chemical reactions to continue at a higher than normal rate in the exhaust passages by confining coolant passages to critical regions in accordance with the teaching of U.K.

Patent No. 1479139, thus leaving the exhaust passage 63 uncooled.

An increase of throttle opening moves the roller 29 across the contoured edge of the plate 35 and, as will be seen from the plate contour and the arcuate path of the roller, this allows the plate to make an increment of movement to the right so that the flow control valve spring can move the valve to increase the coolant flow through the engine.

An increase of engine speed directly causes an increase of flow through both engine and radiator when the coolant pump 1 6 is directly driven, as it is here by shaft 1 7. Within cover 12, but not illustrated, flyweights are pivotally mounted on the drive wheel of the camshaft to act as a mechanism responsive to engine speed, and the increase of speed just referred to causes these flyweights to increase the force in cable 13, so causing roller 32 to begin moving across the other part of the edge of plate 35. Because of the shaping of this part, this movement causes the plate as a whole to make a further increment of movement to the right, this increment being added to the one produced by the increase of load.

By the time the engine speed reaches S,, represented graphically in Figure 1 and related to a particular location 35a on the edge of plate 35 in Figure 4, the temperature and flow rate of the coolant in the engine are such as to provide nearly normal internal surface temperatures at loads less than L1 (Figure 1) and increase of speed between S, and S2 (which corresponds with location 35b in Figure 4) requires no further plate movement because the increase in pump speed provides the necessary further increase of coolant flow. The plate contour therefore runs parallel to the arcuate path of the roller 32 in this part of the roller movement between 35a and 35b. Beyond point 35b the contour changes to withdraw the plate so that the coolant temperature rises again.

The nearly normal temperatures and flow rates of the coolant in the speed range S, to S2 are necessary even at light loads because with the speed already in the potential detonation range, a rapid opening of the throttle to accelerate the vehicle will rapidly bring the engine load into the potential detonation zone. For this same reason, the contour of the part of plate 35 that engages with roller 29 is shaped to increase opening rapidly after load L, (which corresponds with location 35c, Figure 4) is reached, which is somewhat less than L2 (35d, Figure 4) at which detonation could possibly occur, and to produce its full contribution (at loaction 35e) towards increasing engine coolant flow when a load such as L3 is reached which is less than at X where the detonation tendency is greatest.Since the speed related flow valve movement is also at maximum in the range S1 to S2, the desired maximum cooling effect is produced in the potential detonation zone. Because the thickness of the cylinder head deck below the cooling passages (Figure 7) is small, and the passages are of small cross-sectionai area, the temperature of the surface exposed to the combustion chamber falls rapidly as the coolant flow rate increases.

The engine described so far has been one in which the detonation tendency is moderate, so that, with the provisions described, only very brief incipient detonation, if any, occurs on the most sudden opening of the throttle in service. In some engines, however, such provisions alone may not cause surface temperature to fall quickly enough to avoid serious detonation. In such cases, the device shown in plan view in Figure 9 may be used. The device consists of a small dash-pot comprising a cylinder 63, closed at one end by an integral end 64 and at the other by a plug 65 having a projecting rod 66 and one or more holes 67, a piston 68 with holes 69 covered, when the piston moves to the right, by a flexible disc valve 70, a rod 71 passing through a bore in the end wall 64 of the cylinder, and a small hole 72 in the end wall.The projecting rod 66 on the plug 65 passes through a slot in the wall 73 of the spark distributor 73a (cap removed) and its end, which is bent downwards, engages a hole 74 in the contact breaker plate 75. The rod 71 is connected to any suitable point in the connections between the accelerator pedal and the throttle, e.g. by a Bowden cable 76, the adjustable housing 77 for the sheath of which is mounted in an arm 78 attached to the side of the engine.

The action of the device is as follows. When the accelerator pedal is moved fairly slowly when accelerating, as during most of a journey, the accompanying movement of the piston 68 imparts only negligible force to the cylinder 63, because the trapped air requires little pressure to force it out at low velocity through the hole 72. The large hole or holes 67 in the plug at the other end of the cylinder ensure that even with rapid pedal movements no appreciable change of pressure occurs in the adjacent chamber. On rapid movement of the pedal to accelerate, the rapid compression of the trapped air on the right of the piston produces a substantial force on the cylinder and this force is applied by the rod 66 to the contact breaker plate 75 so that ignition timing is retarded in relation to the timing which would be produced by the normal vacuum and speed operated devices. As a result of the expulsion of the compressed air through the hole 72 (together with the leakage past the piston and rod), the other forces acting on the contact breaker plate draw the plate to its normal position for the new engine speed and load and the normal ignition timing is established. By appropriate choices of piston area and discharge hole diameter, the amount of retardation and the rate at which the normal ignition timing is established are made sufficient to prevent detonation under the worst conditions and to allow sufficient time for the increased coolant flow to reduce the surface temperatures sufficiently to make the retardation unnecessary.

When the accelerator pedal is released partly or wholly, the piston 68 moves freely to the left in the cylinder 63 because the flexible disc valve 70 uncovers holes 69 and a negligible force only is exerted on the contact breaker plate 75. The cylinder 63 is made long enough to ensure that whatever the position of the contact breaker plate prior to acceleration, the piston 68 will be at an adequate distance from the end 64 of the cylinder.

The invention is not limited to engines in which the control device, and the inputs to it, are of the purely mechanical type shown in the drawings.

Engine speed and engine load could both be sensed in many other ways, especially electronically, and in particular the engine load could be sensed not by a mechanical connection to the throttle cable but by a simple form of electric torque meter connected to the crankshaft and delivering an electric signal which constitutes one of the inputs to an electric control device in place of the box 8 of purely mechanical components shown in the Figures.

Claims (9)

CLAIMS 1. An internal combustion engine having.a fluid coolant circuit including a pump and cooling ducts, the ducts being formed within the engine structure close to those internal surfaces where excessive temperature can lead to detonation, and a flow control valve in the circuit to regulate the rate of flow of coolant through the ducts, in which the degree of opening of the flow control valve bears a direct relationship to the output of a control device, this output being a function of at least first and second inputs to the device the first of which is related to the instantaneous load of the engine and the second of which to the instantaneous engine speed. 2. An internal combustion. engine according to Claim 1 in which the circuit also includes a radiator, and the control device is located between the radiator outlet and the ducts and operates as a variable two-way valve to direct only a variable proportion of the total coolant flow through the ducts, diverting the balance of the flow back to the radiator inlet without passing through the ducts. 3. An internal combustion engine according to Claim 1 in which the output of the control device obeys the following law in accordance with variation of the first and second inputs:

1. when both these inputs are minimal, the output is minimal also;

2. an increase in either input, up to a certain value, causes the output to increase steadily;

3. as the co-ordinate value of engine load and engine speed approaches close to the range of values within which detonation tends to occur, output increases rapidly;

4. as the co-ordinates of engine load and engine speed approach the value at which the tendency to detonation is greatest, output reaches a maximum, and

5. output falls in response to a subsequent change of either input tending to take the coordinate value of the two inputs further away from that at which the tendency to detonation is greatest.

4. An internal combustion engine according to Claim 1 in which the control device comprises a first lever movable in response to the first input, a second lever movable in response to the second input, and an output member presenting two shaped surfaces which maintain contact with followers camed by the first and second levers respectively, the output member being connected to the control valve.

5. An internal combustion engine according to Claim 4 in which the first lever is connected to the engine throttle cable, and the second lever to a device responsive to engine speed.

6. An internal combustion engine according to Claim 5 including a camshaft operating the engine valves and a drive wheel driving that camshaft, and in which the device responsive to engine speed comprises spring-loaded flyweights pivotally mounted on that drive wheel.

7. An internal combustion engine according to Claim 4 in which the surface of the output member which engages with the second lever is shaped so as to provide, for constant engine load: an increasing output as engine speed rises from minimum to a first value; then a substantially constant output as speed continues to rise to a second value; and then a lesser and generally decreasing output if engine speed rises yet further.

8. An internal combustion engine according to Claim 1, including also means to vary ignition timing in response to particularly rapid changes in engine demand.

9. An internal combustion engine according to Claim 1, substantially as described with reference to the accompanying drawings.