WO2013112172A1

WO2013112172A1 - System and method for increasing effectiveness of a compression release brake of a turbocharged engine

Info

Publication number: WO2013112172A1
Application number: PCT/US2012/022849
Authority: WO
Inventors: Steven J. Dickerson; Joseph William AUGUST
Original assignee: International Engine Intellectual Property Company, Llc
Priority date: 2012-01-27
Filing date: 2012-01-27
Publication date: 2013-08-01

Abstract

A control increases braking effectiveness of a compression release brake when the compression release brake has been activated and pressure in an intake manifold is less than a first pressure by causing compressed air from a compressed air source to expand against blades on a turbocharger shaft and accelerate rotational speed of the turbocharger shaft to a speed which causes pressure in the intake manifold to become at least as great as the first pressure.

Description

SYSTEM AND METHOD FOR INCREASING EFFECTIVENESS OF A

COMPRESSION RELEASE BRAKE OF A TURBOCHARGED ENGINE

Technical Field

[0001] This disclosure relates to a motor vehicle, such as a large truck vehicle, which is propelled by a turbocharged (either single- or multiple- stage) internal combustion propulsion engine having a compression release brake.

Background

[0002] Some internal combustion propulsion engines, such as diesel

engines which typically run unthrottled, have a compression release braking mechanism, sometimes simply called a compression release brake. A compression release brake functions to release air which has been compressed by engine pistons during compression upstrokes into an exhaust manifold of the engine at or near top dead center (TDC) so that energy which has been used to compress the air is not recovered and therefore not used as a contribution to propulsion of the vehicle during ensuing downstrokes of the pistons.

[0003] When a motor vehicle is in motion after having been accelerated by its propulsion engine, and a driver of the vehicle ceases operating an accelerator control for the propulsion engine while road-engaging drive wheels of the vehicle continue to be coupled to the propulsion engine through a drivetrain, the propulsion engine begins to be driven by the road-engaging drive wheels through the drivetrain, rather than by combustion of fuel in the engine cylinders, and as a result, the load which the drivetrain and engine impose on the drive wheels begins to decelerate the vehicle. If the engine has a compression release brake, the latter can be activated by the driver's operation of a compression release brake control to decelerate the vehicle more quickly than if the compression release brake is not activated. An example of such a control comprises an on-off switch for activating and de-activating the compression release brake and possibly a selector switch for selecting which engine cylinders will be used for engine braking. A control may also provide for engine braking to occur automatically upon the driver releasing the accelerator.

[0004] In an unthrottled turbocharged propulsion engine, air from an

intake manifold enters through an open cylinder intake valve or valves of a respective engine cylinder into the engine cylinder during an intake downstroke of a piston which reciprocates within the engine cylinder and is coupled by a connecting rod to a crankshaft of the engine. The mass airflow into the respective engine cylinder is a function of pressure in the intake manifold which is created by a compressor (single- or multi-stage) of a turbocharger, i.e. is a function of boost created by a turbocharger compressor.

[0005] As the engine cycle for each engine cylinder transitions from an intake downstroke to a compression upstroke, the respective cylinder intake valve or valves operate from open to closed. Because one or more cylinder exhaust valves for each engine cylinder remain closed during the respective piston's compression upstroke, intake valve closing causes a volume of air which has entered a respective engine cylinder during the piston downstroke to be trapped in the respective engine cylinder. As the respective piston upstrokes, it compresses the trapped volume of air. Because operation of the accelerator control has ceased, kinetic energy of the moving vehicle provides the energy to compress the trapped air, thereby contributing to vehicle

deceleration.

[0006] In the absence of compression release braking, intake and exhaust valves for the respective engine cylinder would remain closed for substantially most of an ensuing downstroke of the respective piston after a compression upstroke, thereby allowing the energy of expansion of the trapped air to force the respective piston downward and return energy through the drivetrain as a contribution to vehicle acceleration.

[0007] Activation of a compression release brake opens a respective

engine cylinder to an exhaust manifold slightly in advance and/or during at least some portion of what would otherwise be an expansion power downstroke of the respective piston if combustion were occurring in the engine cylinder. Activation of the compression release brake causes energy imparted to air which was compressed during a compression upstroke to be dissipated to the exhaust manifold instead of being recovered and used as a contribution to vehicle acceleration.

[0008] The purpose of activating a compression release engine brake is therefore to essentially eliminate contributions to vehicle acceleration which would otherwise occur during an expansion downstroke if air whose compression has contributed to vehicle deceleration during a compression upstroke were allowed to expand within the engine cylinder during the downstroke. Summary

[0009] It has been observed that effectiveness of a compression release brake is a function of boost being developed by a turbocharger when the compression release brake is first activated. Above some level of boost present at compression release brake activation, a particular turbocharger will be able to build substantial boost (20 psi for example) for enabling the compression release brake to provide an acceptable level of engine braking. Below some level of boost present at compression release brake activation (less than 15 psi for example), a particular turbocharger will be unable to build boost sufficiently for enabling the compression release brake to provide acceptable engine braking.

[0010] The level of boost present at initial activation of a compression release brake depends on how the vehicle was operating immediately prior to compression release brake activation, such as whether the vehicle was coasting or was being propelled by the propulsion engine.

[0011] A variable geometry turbocharger (VGT) is capable of controlling boost during activation of a compression release brake in a way that can provide acceptable engine braking. That is not necessarily true of fixed geometry turbochargers.

[0012] According to the present disclosure, boost provided by a fixed geometry turbocharger can be built up in response to activation of the compression release brake by using a compressed gas (air for example) to rapidly spin up a turbocharger shaft. Compressed gas is communicated from a compressed gas source (such as an air tank which is kept charged to some superatmospheric pressure by an engine-driven air compressor) through a nozzle mounted in a turbocharger housing to direct the air toward blades of a wheel on a turbocharger shaft. The blades may be those of a compressor wheel and/or a turbine wheel.

[0013] Energy of expansion of the compressed air rapidly accelerates the shaft in the same manner as when a waste gate control valve closes to allow engine exhaust to act on and thereby accelerate the shaft, and consequently accelerate the compressor wheel to build boost.

[0014] The claimed subject matter relates to a motor vehicle comprising an internal combustion propulsion engine coupled to road-engaging drive wheels through a drivetrain, the propulsion engine comprising engine cylinders within which pistons reciprocate to propel the vehicle by delivering torque through the drivetrain to the drive wheels when fuel is being combusted within the engine cylinders, but when fuel is not being combusted within the engine cylinders and the vehicle is rolling on a road surface underlying the drive wheels, the drive wheels act through the drivetrain to reciprocate the pistons, the propulsion engine further comprising an intake system, an exhaust system, an intake manifold through which air which has passed through the intake system enters the engine cylinders to support combustion, and an exhaust manifold through which exhaust resulting from combustion leaves the engine cylinders for ensuing passage through the exhaust system, a fixed geometry turbocharger comprising a turbine in the exhaust system operated by exhaust from the exhaust manifold and a compressor in the intake system operated by the turbine via a turbocharger shaft to create pressure in the intake manifold exceeding ambient atmospheric pressure, and a compression release brake which, when the drive wheels act through the drivetrain to reciprocate the pistons, can be activated to dissipate energy of air which a respective piston has compressed within at least one engine cylinder by causing air which the respective piston has compressed to be released into the exhaust manifold so that energy of the released air is not recovered as a contribution to propulsion of the vehicle.

[0015] When the compression release brake has been activated and pressure in the intake manifold is less than a first pressure, braking effectiveness of the compression release brake is increased by causing compressed gas from a compressed gas source to expand against blades on the turbocharger shaft and accelerate rotational speed of the shaft to a speed which causes pressure in the intake manifold to become at least as great as the first pressure.

[0016] The foregoing summary is accompanied by further detail of the disclosure presented in the Detailed Description below with reference to the following drawings which are part of the disclosure.

Brief Description of the Drawings

[0017] Figure 1 schematically shows a truck vehicle having a turbocharged internal combustion propulsion engine which has a compression release brake.

[0018] Figure 2 is a general schematic diagram of the propulsion engine.

[0019] Figure 3 is a schematic diagram showing greater detail of the turbocharger by itself and devices associated with the turbocharger.

[0020] Figure 4 is a diagram showing greater detail of some of the turbocharger and devices of Figure 3. [0021] Figure 5 is a diagram showing greater detail of some of the turbocharger and devices of Figure 3.

Detailed Description

[0022] Figure 1 shows a truck vehicle 10 which is propelled by a multi- cylinder internal combustion propulsion engine 12 operating to deliver torque through a drivetrain 14 to drive wheels 16.

[0023] Figure 2 shows multi-cylinder internal combustion propulsion engine 12 as a diesel engine which comprises structure forming a number of engine cylinders 18 into which fuel is injected by fuel injectors 20 to combust with air which has entered engine cylinders 18 through an intake system 22. Engine 12 comprises an intake manifold 24 through which air which has passed through intake system 22 enters engine cylinders 18 when cylinder intake valves 26 for controlling admission of air from intake manifold 24 into respective engine cylinders 18 are open.

[0024] Intake system 22 comprises a compressor 28 which may comprise either a single stage or multiple stages for elevating pressure in intake manifold 24 to superatmo spheric pressure, meaning pressure greater than that of ambient air pressure, i.e. for creating boost air in intake manifold 24. Other components which may be present in intake systems of contemporary diesel engines are not shown in Figure 2.

[0025] Engine 12 further comprises cylinder exhaust valves 30 for controlling admission of exhaust from respective engine cylinders 18 into an exhaust manifold 32 for further conveyance through an exhaust system 34. Exhaust system 34 includes a turbine 36 which may comprise either a single stage or multiple stages each of which is coupled by a respective shaft to operate a respective stage of compressor 28. Other components which may be present in exhaust systems of contemporary diesel engines are not shown in Figure 2.

[0026] Collectively, compressor 28 and turbine 36 form a fixed geometry turbocharger 37 which may be either a single- or a multiple-stage type.

[0027] Engine 12 comprises mechanisms 38 for controlling the timing of opening and/or closing of cylinder intake valves 26 and cylinder exhaust valves 30 respectively during engine cycles. The mechanisms may comprise one or more camshafts (depending on engine configuration) having cams shaped to provide fixed timing of operation of the cylinder valves. If an engine has variable valve actuation (VVA) for varying timing of opening and/or closing of cylinder valves, that capability may be provided by any of a variety of mechanisms.

[0028] A processor-based engine control module (ECM) 40 controls various aspects of engine operation, such as fueling of engine cylinders 18 by fuel injectors 20. Control is accomplished by processing various input data, including accelerator position data from an accelerator position sensor 42 operated by an accelerator 44, shown schematically as a foot pedal which is depressed by a driver of the vehicle to accelerate propulsion engine 12.

[0029] Engine 12 also has a compression release brake 46 which, when activated, interacts with cylinder exhaust valves 30 in a manner which causes them to open during portions of engine cycles which are significantly different from portions of engine cycles during which they would otherwise be open if truck vehicle 10 were being propelled by combustion in engine cylinders 18. Activation and de-activation of compression release brake 46 may be controlled in any of various ways.

[0030] One type of control comprises an on-off switch 48 which can be operated by a driver of the vehicle to activate and de-activate compression release brake 46. A control may also include a selector switch (not shown) for selecting which engine cylinders 18 will be used for engine braking. A control may also provide for engine braking to occur automatically upon the driver releasing accelerator 44.

[0031] Figures 3-5 show turbocharger 37 to comprise a central housing 50 which provides bearing support of a turbocharger shaft 52, a turbine housing 54 fastened to one end of central housing 50, and a compressor housing 56 fastened to the opposite end of central housing 50. A turbine wheel 58 is disposed on an end of shaft 52 within turbine housing 54, and a compressor wheel 60 is disposed on an end of shaft 52 within compressor housing 56.

[0032] Turbine housing 54 has an exhaust gas inlet 62 and an exhaust gas outlet 64. A wastegate valve 66 and an actuator 68 (schematically shown in Figure 2) are associated with turbine 36. Actuator 68 is operable to cause wastegate valve 66 to selectively shunt exhaust gas around turbine 36 so that the shunted exhaust gas does not act on turbine wheel 58. Compressor housing 56 has an air inlet 70 and an air outlet 72.

[0033] Exhaust gas which acts on turbine wheel 58 operates turbine 36 and the coupling of turbine wheel 58 to compressor wheel 60 via turbocharger shaft 52 operates compressor 28, creating superatmo spheric pressure in intake manifold 24. The magnitude of that pressure (i.e. the amount of boost) is a function of various factors.

[0034] The braking effectiveness of compression release brake 46 depends on the amount of boost. Depending on how vehicle 10 and engine 12 have been operating before compression release brake 46 is activated, boost may not be high enough to make compression release brake 46 as effective as it could be. When such a situation occurs, as evidenced by pressure in intake manifold 24 being less than a first pressure, boost may be increased by causing compressed gas from a compressed gas source to expand against blades of either or both turbine wheel 58 and compressor wheel 60.

[0035] Figure 4 shows an injection nozzle 74 mounted on turbine housing 54 for directing compressed gas toward blades of turbine wheel 58. Nozzle 74 has an outlet 76 proximate the circular path of rotation of tips of the blades. Gas exiting outlet 76 expands toward the blades to impart acceleration to them and hence also to shaft 52. As a result compressor wheel 60 is also accelerated.

[0036] Figure 5 shows an injection nozzle 78 mounted on compressor housing 56 for directing compressed gas toward blades of compressor wheel 60. Nozzle 78 has an outlet 80 proximate the circular path of rotation of tips of the compressor wheel blades. Gas exiting outlet 78 expands toward the blades to impart acceleration to them and hence to compressor wheel 60.

[0037] Figure 3 shows a compressed air tank 82 which is on board vehicle 10 for supplying compressed air to nozzles 74, 78. A respective control valve 84, 86 controls the delivery of compressed air from tank 82 to the respective nozzle 74, 78. The control valves themselves are under the control of ECM 40.

[0038] After ECM 40 has activated compression release brake 46, ECM 40 will open one or both control valves 84, 86 whenever ECM 40 detects that pressure in intake manifold 24 is less than a first pressure. One or both control valves 84, 86 can be operated to selectively restrict the flow of compressed air to the respective nozzles74, 78, thereby controlling acceleration of turbocharger shaft 52, and consequently how boost increases.

[0039] When intake manifold pressure has increased to a magnitude which is at least as great as the first pressure and which is considered to provide acceptable braking effectiveness of compression release brake 46, further use of compressed air can be terminated by closing both valves 84, 86. Should boost decrease sufficiently enough to cease providing acceptable engine braking while compression release brake 46 continues to be activated, one or both valves control 84, 86 can be re-opened.

Claims

WHAT IS CLAIMED IS:

1. In a motor vehicle comprising:

an internal combustion propulsion engine coupled to road-engaging drive wheels through a drivetrain;

the propulsion engine comprising engine cylinders within which pistons reciprocate to propel the vehicle by delivering torque through the drivetrain to the drive wheels when fuel is being combusted within the engine cylinders, but when fuel is not being combusted within the engine cylinders and the vehicle is rolling on a road surface underlying the drive wheels, the drive wheels act through the drivetrain to reciprocate the pistons;

the propulsion engine further comprising an intake system, an exhaust system, an intake manifold through which air which has passed through the intake system enters the engine cylinders to support combustion, and an exhaust manifold through which exhaust resulting from combustion leaves the engine cylinders for ensuing passage through the exhaust system;

a fixed geometry turbocharger comprising a turbine in the exhaust system operated by exhaust from the exhaust manifold and a compressor in the intake system operated by the turbine via a turbocharger shaft to create pressure in the intake manifold exceeding ambient atmospheric pressure; and

a compression release brake which, when the drive wheels act through the drivetrain to reciprocate the pistons, can be activated to dissipate energy of air which a respective piston has compressed within at least one engine cylinder by causing air which the respective piston has compressed to be released into the exhaust manifold so that energy of the released air is not recovered as a

contribution to propulsion of the vehicle, a method of increasing the braking effectiveness of the compression release brake when the compression release brake has been activated and pressure in the intake manifold is less than a first pressure by causing compressed gas from a compressed gas source to expand against blades on the turbocharger shaft and accelerate rotational speed of the shaft to a speed which causes pressure in the intake manifold to become at least as great as the first pressure.

2. The method set forth in Claim 1 in which the step of causing compressed gas from a compressed gas source to expand against blades on the turbocharger shaft comprises causing compressed gas from a compressed gas source to expand against blades of a turbine wheel on the turbocharger shaft.

3. The method set forth in Claim 1 in which the step of causing compressed gas from a compressed gas source to expand against blades on the turbocharger shaft comprises causing compressed gas from a compressed gas source to expand against blades of a compressor wheel on the turbocharger shaft.

4. The method set forth in Claim 1 in which the step of causing compressed gas from a compressed gas source to expand against blades on the turbocharger shaft comprises opening a control valve to communicate compressed gas from the compressed gas source to a nozzle through which compressed gas is directed toward blades on the turbocharger shaft.

5. The method set forth in Claim 4 further comprising, while the

compression release brake is activated, closing the control valve to terminate communication of the compressed gas source to the nozzle when pressure in the intake manifold becomes greater than the first pressure, and then continuing activation of the compression release brake.

6. The method set forth in Claim 1 in which the step of causing compressed gas from a compressed gas source to expand against blades on the turbocharger shaft comprises causing compressed air from a compressed air source to expand against blades on the turbocharger shaft.

7. A motor vehicle comprising:

a fixed geometry turbocharger comprising a turbine in the exhaust system operated by exhaust from the exhaust manifold and a compressor in the intake system operated by the turbine via a turbocharger shaft to create pressure in the intake manifold exceeding ambient atmospheric pressure; a compression release brake which, when the drive wheels act through the drivetrain to reciprocate the pistons, can be activated to dissipate energy of air which a respective piston has compressed within at least one engine cylinder by causing air which the respective piston has compressed to be released into the exhaust manifold so that energy of the released air is not recovered as a

contribution to propulsion of the vehicle;

a source of compressed gas; and

a control which operates to increase the braking effectiveness of the compression release brake when the compression release brake has been activated and pressure in the intake manifold is less than a first pressure by causing compressed gas from the compressed gas source to expand against blades on the turbocharger shaft and accelerate rotational speed of the turbocharger shaft to a speed which causes pressure in the intake manifold to become at least as great as the first pressure.

8. The motor vehicle set forth in Claim 7 in compressed gas is directed to expand against blades of a turbine wheel on the turbocharger shaft.

9. The motor vehicle set forth in Claim 7 in compressed gas is directed to expand against blades of a compressor wheel on the turbocharger shaft.

10. The motor vehicle set forth in Claim 7 further comprising a control valve, which when operated open by the control, communicates compressed gas from the compressed gas source to a nozzle through which compressed gas is directed toward blades on the turbocharger shaft.

11. The motor vehicle set forth in Claim 10 in which, while the compression release brake is activated, the control closes the control valve to terminate communication of the compressed gas source to the nozzle when pressure in the intake manifold becomes greater than the first pressure, while thereafter continuing activation of the compression release brake.

12. The motor vehicle set forth in Claim 7 in which the compressed gas source comprises a compressed air source.