GB2044851A - Turbocharged engine braking system - Google Patents

Abstract

Engine braking by opening the exhaust valves on the compression strokes is enhanced by increasing the charging pressure and the exhaust back pressure. The exhaust gases are diverted by a valve 22 to flow through only one of the turbine inlet volutes simultaneously with fuel supply cut-off and exhaust valve opening. Engine braking may varied by selecting the number of exhaust valves which are opened and operation of the valve 22. <IMAGE>

Description

SPECIFICATION An engine braking system and method of braking This invention relates generally to an engine braking system and to a method of braking.

More particularly, the invention relates to a braking system which is characterized by the combination of the compression relief type engine brake and a turbocharger comprising an exhaust gas turbine having a divided volute and an air compressor, this combination providing as will be seen from the disclosure to follow, improved engine braking and improved engine performance.

A turbocharger in turbocharged engines is normally not required during braking because the engine is not fueled. Because of this, both the volume and the temperature of the exhaust gases are reduced. This produces two adverse effects: (1) the operating temperature of the engine drops below the desired point since the cooling system removes more heat than is being generated and (2) a decrease in exhaust gas volume generated (because of the lack of combustion) and the decrease in gas volume (due to the drop in temperature of the gas) cause a decrease in the speed of the turbocharger. These adverse effects are experienced when engine braking is required, for example, while negotiating a long decline. By the time the bottom of the decline is reached, the engine temperature will have been considerably decreased and the turbocharger slowed down.Under these conditions, it is difficult to accelerate the engine rapidly as may be required to negotiate a steep rise which usually follows a decline.

These adverse effects are generally overcome by providing a braking system which combines the turbocharger comprising an exhaust gas turbine with a compression relief engine brake, wherein the turbocharger is an adjunct to the braking system and the braking operation is an adjunct to the improved operation of the turbocharger. With our braking system the turbocharger is controlled to maximize air flow into the engine during braking operation by diverting all of the exhaust gas through a portion of the turbine so as to increase the compression work done by the engine.

More specifically, we provide in accordance with the invention an engine braking system with improved engine performance for an internal combustion engine having intake and exhaust manifolds, characterized by the combination of a compression relief engine brake, operative on opening at least one exhaust valve of the combustion engine near the end of the compression stroke of the engine cylinder with which said exhaust valve is associated, and a turbocharger comprising an exhaust gas turbine having a divided volute and an air compressor which supplies compressed air to said engine intake manifold, said turbocharger including a diverter valve operatively connected at one side thereof with said exhaust manifold and at its opposite end with said divided volute for directing, with predetermined braking action, flow of exhaust gas from said exhaust manifold to only one of the portions of said divided volute instead of both as occurs on less than said predetermilned braking action.

By diverting the exhaust gas flow through a portion of the turbine, the gas pressure in the exhaust manifold is increased. This effect not only increases the retarding horsepower developed by the engine but also increases the temperature of the air within the engine. The increased temperature of the air, in turn, causes an increase in the energy of the exhaust gas which further increases the efficiency and, therefore, the rotational speed of the turbine. Thus the combination of an engine compression engine compression relief brake with a turbocharger having a divided volute produces a synergistic result which increases the available retarding horsepower produced by the compression relief brake. An additional advantage of this combination for the normal operation of the invention flows from its braking operation.During the braking operation a portion of the kinetic energy of the vehicle is transformed into heat which is dissipated through the engine cooling system thereby maintaining the engine at or near the normal operating temperature.

In prior systems, compression relief type brakes (see U.S. Patent 3,220,392) normally function as a brake only. Also in prior systems, turbochargers with a divided volute and diverter mechanisms (see U.S. Patents 4,008,572; 3,559,397; 3,137,477; 3,313,518 or 3,975,911) normally function to increase the mass flow of air to increase engine power during fuel feed. To our knowledge, no one has recognized that a synergistic effects could be obtained by use of a compression relief brake to improve the operation of a turbocharged engine and to use a turbocharged engine with a divided volute and diverter mechanism to improve the operation of the compression relief brake.

Additional advantages of-the novel combination according to the present invention will become apparent from the following detailed description of the invention and the accompanying drawings in which: Figure 1 is a diagrammatic view, partly in section, of an engine having a compression relief brake, an exhaust gas diverter and a turbocharger with a twin entry or divided volute turbine; Figure 2 is a schematic view, partly in section, showing the compression relief engine retarder; Figure 2A is a schematic drawing of the electrical control system for the improved en gine retarder according to the present invention; Figure 3 is a cross-sectional view of a turbocharger having a twin entry or divided volute turbine which may be employed in the present invention; Figure 4 is a plan view of a butterfly type of diverter valve which may be employed in the present invention;; Figure 5 is a sectional view taken along line 5-5 of Fig. 4; Figure 6 is a P-V indicator chart showing the pressure-volume relationships occurring with an engine cylinder during one complete cycle in accordance with prior art operation using a compression relief brake; Figure 7 is a P-V indicator chart showing the pressure-volume relationships occurring within an engine cylinder during one complete cycle in accordance with the present invention; and Figure 8 is a graph showing the retarding horsepower developed by an engine using a compressive relief engine brake alone and the increased retarding horsepower developed in accordance with the present invention.

Referring particularly to Fig. 1, an engine is indicated by 1 0. The engine 10 may be of the spark-ignition or compression-ignition type and may have any number of cylinders. The present invention will be described, however, with respect to a typical six-cylinder compression ignition engine equipped with an intake manifold 1 2 and a divided exhaust manifold comprising a front exhaust manifold 14 and a rear exhaust manifold 1 6. Exhaust ducts 1 8 and 20 lead, respectively, from the front and rear exhaust manifolds to an exhaust gas diverter valve 22. The exhaust gas diverter valve 22 is shown in Fig. 4 and 5 and will be described in more detail below.A divided exhaust gas duct 24 communicates between the outlet of the diverter valve 22 and the inlet of a twin entry or divided volute of a turbine 25 which, together with a compressor 28, form an integral turbocharger 30. The turbocharger 30 is shown in Fig. 3 and will be described in more detail below. After passing through the turbine 26, the exhaust gases pass into the engine exhaust system 32.

Air is introduced into the engine 20 through the usual engine air cleaner 34, compressor inlet duct 36, compressor 28, and the inlet manifold duct 38 which communicates between the outlet of the air compressor 28 and the intake manifold 1 2. As shown schematically in Fig. 1 and in more detail in Fig.

3, the compressor 28 is driven by the turbine 26 and typically comprises an integral turbocharger 30.

Referring now to Fig. 2, the engine 10 is fitted with a housing 40 which contains the usual compression relief braking system shown schematically in Fig. 2. Oil 42 from a sump 44 which may be, for example, the engine crankcase is pumped through a duct 46 by a low pressure pump 48 to the inlet 50 of a solenoid valve 52 mounted in the housing 40. Low pressure oil 42 is conducted from the solenoid valve 52 to a control cylinder 54 also mounted in the housing 40 by a duct 56. A control valve 58 is fitted for reciprocating movement within the control cylinder and is urged into a closed position by a compression spring 60. The control valve 58 contains an inlet duct 62 closed by a ball check valve 64 which is biased into the closed position by a compression spring 66 and an outlet duct 68.When the control valve is in the open position (as shown in Fig. 2) the outlet duct 68 registers with the control cylinder outlet duct 70 which communicates with the inlet of a slave cylinder 72 also formed in the housing 40. It will be understood that low pressure oil 42 passing through the solenoid valve 52 enters the control valve cylinder 54 and raises the control valve 58 to the open position. Thereafter, the ball check valve 64 opens against the bias of spring 66 and the oil will flow into the slave cylinder 72. From the outlet 74 of the slave cylinder cylinder 72 the oil 42 flows through a duct 76 into the master cylinder 78 formed in the housing 40.

A slave piston 80 is fitted for reciprocation within the slave cylinder 72. The slave piston 80 is biased in an upward direction (as shown in Fig. 2) against an adjustable stop 82 by a compression spring 84 which is mounted within the slave piston 80 and acts against a bracket 86 seated in the slave cylinder 72.

The lower end of the slave piston 80 acts against an exhaust valve cap 88 fitted on the stem of exhaust valve 90 which is, in turn, seated in the engine 10. An exhaust valve spring 92 normally biases the exhaust valve 90 to the closed position as shown in Fig. 2.

Normally, the adjustable stop 82 is set to provide a desired clearance between the slave piston 80 and the exhaust valve cap 88 when the exhaust valve is closed, the slave piston is seated against the adjustable stop 82 and the engine is cold. The desired clearance is provided to accommodate expansion of the parts comprising the exhaust valve train when the engine is hot without opening the exhaust valve 90 and to control the timing of the exhaust valve opening.

A master piston 94 is fitted for reciprocating movement within the master cylinder 78 and biased in an upward direction (as shown in Fig. 2) by a light leaf spring 96. The lower end of the master piston 94 contacts an adjusting screw mechanism 98 of a rocker arm 100 controlled by a pushrod 102 driven from the engine camshaft (not shown) It will be understood that when the solenoid valve 52 is opened oil 42 will raise the control valve 58 and then fill both the slave cylinder 72 and the master cylinder 78. Re verse flow of oil out of the slave cylinder 72 and master cylinder 78 is prevented by the section of the ball check valve 64. However, once the system is filled with oil, upward movement of the pushrod 102 will drive the master piston 94 upwardly and the hydraulic pressure, in turn, will drive the slave piston 80 downwardly to open the exhaust valve 90.

The valve timing is selected so that the exhaust valve 90 is opened near the end of the compression stroke of the cylinder with which exhaust valve 90 is associated. Thus the work done by the engine piston in compressing air during the compression stroke is released to the exhaust system of the engine and not recovered during the expansion stroke of the engine. In some engines it may be convenient to operate the master piston from the injector push rod associated with the cylinder with which the salve piston is in communication while in other engines it may be desirable to use a pushrod associated with an intake or exhaust valve for another cylinder. In either event, the result will be the same since the exhaust valve is opened near the end of the compression stroke.

When it is desired to deactivate the compression relief brake, the solenoid valve 52 is closed whereby the oil 42 in the control valve cylinder 54 passes through duct 56, the solenoid valve 52 and the return duct 104 to the sump 44. When the control valve 58 drops downwardly, as viewed in Fig. 2, a portion of the oil in the slave cylinder 72 and master cylinder 78 is vented past the control valve 58 and returned to the sump 44 by duct means (not shown).

The electrical control system for the present invention is shown schematically in Fig. 2A to which reference is now made. The vehicle battery 106 is connected at one terminal to ground 1 08. The opposite battery terminal is connected, in series, to a fuse 110, a dash switch 112, a clutch switch 114 and a fuel pump switch 11 6 and, preferably, through a diode 11 8 back to ground 108. A multiposition selector switch 1 20 is also connected in series to the switches 112, 114 and 116.

In order to provide varying degrees of braking power through the engine retarder and exhaust diverter system it may be desirable to utilize the selector switch 1 20 which, as shown in Fig. 2A, has three positions. In position 1 (as shown in Fig. 2A) the selector switch 1 20 activates the front engine brake solenoids 1 22 which may, for example, control the solenoid valves 52 associated with half of the cylinders of the engine (three in the case of the six-cylinder engine shown in Fig.

1). In position 2, the selector switch 120 activates the front engine solenoids 1 22 and the rear engine solenoids 1 24 so as to control the solenoid valves 52 associated with all of the cylinders of the engine thereby providing increased engine braking. In position 3, the selector switch 1 20 will activate not only all of the solenoid valves 52 but also the diverter valve 22 through solenoid 1 26 so as to provide a maximum engine braking power as described in more detail below. it will be understood that additional positions may be provided for the selector switch 1 20 so that the engine brake can be applied to one or more engine cylinders as desired.Of course, the selector switch 1 20 can also be eliminated if maximum engine braking, i.e. all engine cylinders plus the braking due to the diverter valve 22, is required at all times. The switches 112, 114 and 11 6 are provided to complete the control system and assure the safe operation of the system. Switch 11 2 is a manual control to deactivate the entire system. Switch 114 is an automatic switch connected to deactivate the system whenever the clutch is disengaged so as to prevent engine stalling. Switch 11 6 is a second automatic switch connected to the fuel system to pre- vent engine fueling when the engine brake is in operation.

Fig. 3, to which reference is now made, shows a typical turbocharger 30 which may be employed in the present invention. The turbocharger 30 comprises a twin entry turbine and a compressor 28 coaxially mounted on a shaft 1 28 journalled for rotation on bearings 1 30 in a stationary housing 1 32.

The turbine 26, here illustrated as a radial flow turbine, comprises a divided volute 1 34 having two series of nozzles 136, 1 38 directed toward the vanes of an impeller wheel 1 40 affixed to the shaft 1 28. Gas flowing in the divided volute 1 34 is accelerated as it passes through the nozzles 136, 1 38 and imparts its kinetic energy to the impeller wheel 1 40. It will be appreciated that the speed of the impeller wheel 1 40 is a function of the volume of gas flowing through the volute 1 34 which determines the velocity of flow through the nozzles 136, 1 38.It is known that at relatively low gas flow rates, the efficiency of the turbine decreases and that greater efficiency can be attained if, at low gas flow rates, all of the gas is directed into one portion of the volute 1 34.

The impeller 140 of the turbine 26 is connected to the impeller 142 of the compressor 28, shown here as a centrifugal compressor. Rotation of the impeller 1 42 draws air through the entry port 1 44 and delivers the air at increased pressure through the compressor volute 1 46 to the inlet manifold duct 38. It will be understood that while a radial flow turbocharger has been shown and described, various types of turbochargers may be utilized in the present invention provided only that the turbine is of a type in which all of the exhaust gas used as a driving fluid can be delivered to a portion of the turbine wheel when desired.

Figs. 4 and 5 illustrate a typical form of a diverter valve 22 adapted to divert the flow of exhaust gas from ducts 1 8 and 20 to one portion of the duct 24 and thence to one portion only of the volute 1 34 of the turbine 26. As shown, the diverter valve 22 comprises a pair of relatively thick plates 148, 1 50 which form a housing adapted to be placed between the ducts 18, 20 and the divided duct 24. The plates 148, 1 50 are provided with bolt holes 152 for fastening the plates to flanges on the ducts 18, 20 and 24.

An aperture 154 is formed in each plate 148, 1 50 A butterfly valve 156 is mounted within the aperture 1 54 on stub shafts 1 58, 1 6.0 journalled for rotation with respect to the plates 148, 150 from a closed position substantially parallel to the plates to an open position substantially normal to the plates.A second butterfly valve 1 62 is mounted within the aperture 154 on a shaft 164 journalled for rotation with respect to the plates 148, 1 50 from a closed position substantially normal to the plates to an open position in which the plane of the butterfly valve 162 is at an acute angle to the-plane of the plates 148, 1 50. It will be understood that when the butterfly valve 1 56 is in the open position and butterfly valve 1 62 is in the closed position, the flow of gas from the ducts 18, 20 will enter both portions of the divided duct 24 and, hence, both portions of the divided volute 1 34 of the turbine 26.However, when the butterfly valve 1 56 is in the closed position and the butterfly valve 162 is in the open position, the gas flow from the ducts 18 and 20 will be diverted to one portion of the divided duct 24 and, hence, to one portion of the divided volute 1 34 of the turbine 26. The position of the butterfly valves 1 56 and 1 62 need only be controlled as between a fully open and a fully closed position. Hence they may readily be actuated by solenoid 1 26 (Fig.

2A) through appropriate linkage systems (not shown) as will be understood by those skilled in the art. As these actuating mechanisms form no part of the present invention, they need not be described here in detail. While a specific form of a diverter valve has been shown and described, it will be appreciated that various types of diverter valves or diverting mechanisms may be employed in accordance with the present invention provided only that the device is capable of diverting all of the engine exhaust gas into a single duct directed to only a portion of the turbine whereby the turbine efficiency and velocity may be increased under low exhaust gas flow rates.

Fig. 6 is a pressure-volume diagram for a Mack 676 compression ignition engine equipped with a compression relief engine brake manufactured by the Jacobs Manufacturing Co. The portion of the diagram from points 1 to 2 represents the compression stroke of the engine, starting at bottom dead center (B DC). Before the piston reaches top dead center (TDC) the exhaust valve 90 is opened by the engine brake and the cylinder pressure begins to drop. At point 2a the compression stroke ends and the piston reverses its motion to begin what would be the "power" stroke if the engine were being fueled. Point 3 represents the end of the "power" stroke at BDC. The diagram from point 3 to point 4 represents the exhaust stroke while the diagram from point 4 to point 1 represents the intake stroke.During the compression and exhaust strokes work is being done by the engine compressing the air within the cylinder while during the "power" and intake strokes the engine is delivering the stored energy to the engine cooling system and exhaust system. The area within the diagram is therefore proportional to the retarding horsepower developed by the engine using the prior art Jacobs engine brake.

Fig. 8 (Curve A) is a graph showing the variation in retarding horsepower with engine speed for a Mack 676 compression ignition engine equipped with a Jacobs engine brake of the type shown schematically in Fig. 2.

In accordance with the present invention applicant provided a diverter valve of the type shown in Fig. 4 and 5 in the exhaust manifold of a Mack 676 engine equipped with a turbocharger and a Jacobs engine brake. The remarkable improvement in engine braking performance as well as in engine operating performance is shown insofar as braking performance is concerned in Figs. 7 and 8.

Fig. 7 is a pressure-volume indicator chart similar to Fig. 6 but showing the effect of the addition of the diverter valve. It will be noted that a considerably higher maximum pressure is attained on the compression stroke while the "power" stroke curve is relatively unchanged so that the area between the curves which is proportional to the retarding horsepower has been increased. Similarly, the maximum pressure (as well as the mean effective pressure) during the exhaust stroke has been increased so that the area between the exhaust and intake stroke curves and the retarding horsepower represented thereby has also been increased.

Curve B of Fig. 8 is a graph of the retarding horsepower developed by the apparatus of the present invention. It will be noted that at all engine speeds within the useful operating range of the engine, the retarding horsepower developed by the engine operating in accordance with the present invention is greater than that available when the engine is operated only with the standard Jacobs brake.

Moreover, at the higher engine speeds which are usually encountered during use of the engine brake the improvement in braking performance is greatly enhanced.

Applicant believes that the improvement in braking performance is due to the synergistic reaction of the Jacobs engine brake and the turbocharger having the divided volute and the diverter valve. When engine braking is required, for example, while negotiating a long decline, the engine is operating near the top of its operating speed range but the engine is not being fueled. As a result both the volume and temperature of the exhaust gases are reduced. This produces the two adverse effects earlier described. These adverse effects are reckened with by diverting all of the available exhaust gas through a portion of the turbine so that the turbine nozzle velocity is increased with a resultant increase in the compressor speed.With increased compressor speed, a greater mass of air may be charged at the engine inlet thus increasing the compression work done by the engine as shown by the curve 1 '-2' of Fig. 7 as compared with the curve 1-2 of Fig. 6. Moreover, the effect of the diverter valve is to provide a restriction in the exhaust manifold which results in increased resistance during the exhaust stroke. This latter effect is shown by a comparison of the curve 3'-4' of Fig. 7 with curve 3-4 of Fig. 6. The increased work done by the engine during the compression and exhaust strokes is reflected in an increased temperature of the exhaust gases which also increases the volume of the exhaust gas. As noted above, an increase in exhaust gas volume increases the speed of the turbine and this further increases the mass of air charged to the engine via the compressor.It thus becomes apparent that the novel combination of the compression relief engine brake and the turbocharger with its diverter valve provides a synergistic effect wherein the compression relief brake functions in an improved manner and also functions as an exhaust brake.

Moreover, not only is the braking performance improved, but also the operating performance of the engine is improved. As mentioned previously, herein, it frequently occurs that an upgrade immediately follows a long downgrade during which engine braking has been required. However, at the bottom of the decline, the engine temperature has been considerably decreased and the turbocharger has been slowed down. Under these conditions, as mentioned heretobefore, it is difficult to accelerate the engine rapidly. With the combi nation of the present invention, not only the engine temperature will be higher (because of the increased work done on the increased mass flow of the air during the engine braking operation) but also the turbocharger speed will be maintained by the combined effect of the diverter valve and the increased mass flow.

Thus, the turbocharger will operate at a speed more nearly required for the rapid acceleration of the engine. An additional performance advantage resides in the fact that upon com mencement of engine fueling the higher tem perature and higher mass flow of air will promote complete combustion and the avoidance of exhaust smoke emission with its concomitant loss of power. The maintenance of engine temperature and the mass flow of air also tends to prevent carboning while operating in the engine braking mode.

While the combination of the present invention includes the function of increasing the exhaust manifold pressure and is, in this respect somewhat analogous to an exhaust brake, it avoids one of the principal disadvantages of an exhaust brake, viz. the problem of valve floating. Ordinarily, exhaust manifold pressure is limited by the requirement that it must not exceed the force of the exhaust valve spring. However, the use of the engine brake insures that the pressure on the combustion side of the exhaust valve will be substantially greater during the intake cycle than that which occurs when an exhaust brake alone is used. With this greater pressure, the compression relief brake will operate at a higher exhaust manifold pressure without the problem of valve float.Eliminating valve float results in maintaining higher exhaust manifold pressure providing additional retarding horsepower.

Another advantage accruing to the combination of the present invention relates to the performance reliability of the turbocharger.

The effect of the higher intake manifold pressure is to reduce the pressure differential across the turbocharger from the compressor to the turbine. This means that the side thrust on the turbocharger bearings is reduced so that the reliability of the turbocharger is enhanced.

Still a further advantage of the combination of the present invention over an engine brake and exhaust brake designed to produce the same retarding horsepower is the reduction of turbine housing pressure which increases the life of the turbine and its reliability. The exhaust brake necessarily increases the exhaust manifold pressure while the combination of the present invention increases the inlet manifold pressure with only a relative small increase in exhaust manifold pressure.

The fact that the present invention produces the same retarding horsepower with a smaller increase in the exhaust manifold pressure means that the turbine housing stress is smaller and hence the life of the turbine is enhanced.

The terms and expressions which have been employed are used as terms of description and not of limitation and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible.

Claims (7)

1. An engine braking system with im proved engine performance for an internal combustion engine having intake and exhaust manifolds, comprising the combination of a compression relief engine brake, operative on opening at least one exhaust valve of the combustion engine near the end of the compression stroke of the engine cylinder with which said exhaust valve is associated, and a turbocharger comprising an exhaust gas turbine having a divided volute and an air compressor which supplies compressed air to the engine intake manifold, said turbocharger including a diverter valve operatively connected at one side thereof with the engine exhaust manifold and at its opposite end with said divided volute for directing, with predetermined braking action, flow of exhaust gas from said engine exhaust manifold to only one of the portions of said divided volute instead of both as occurs on less than said predetermined braking action.

2. The system of claim 1, wherein the exhaust gas turbine comprises a radial flow turbine.

3. The system according to claim 1 or 2, wherein the diverter valve is a solenoid actuated butterfly valve.

4. A method of braking with improved engine performance of an internal combustion engine driven vehicle, comprising equipping the vehicle with a turbocharged engine having a turbocharger equipped with a divided volute and a compression relief type engine brake, directing exhaust gases, on actuating said compression relief type engine brake a predetermined extent, from the engine exhaust manifold to one portion of said divided volute to increase the rotational speed of the turbocharger above that which it would assume if said exhaust gases were directed to both portions of the divided volute, increasing as a function of increased speed of rotation of the turbocharger the mass flow rate of air through the turbocharger with resulting inhibition of the mass flow of exhaust gases from said exhaust manifold, continuously compressing the increased mass flow of air, improved braking and engine performance resulting on releasing the increased mass of compressed air to said exhaust manifold near the end of the engine compression stroke.

5. The method of claim 4, wherein on deactivating said compression relief engine brake the mass flow of said exhaust gases is directed through both portions of the divided volute.

6. An engine braking system with improved engine performance for an internal combustion engine substantially as hereinbefore described with respect to the accompanying drawings.

7. A method of braking with improved engine performance of an internal combustion engine driven vehicle substantially as hereinbefore described.