Patent Application
20220178315
The present disclosure relates generally to engine braking, and more particularly to varying engine braking power by way of intake air pressure control within a cylinder-number braking mode.
Engine compression release braking is generally understood as a practice that operates combustion cylinders in an engine to compress air without combusting fuel, effectively transforming the engine into an air compressor to retard engine speed. While a great many different hardware designs and control strategies have been proposed over the years, the basic concept of compression release braking requires modifying engine valve timings from a normal timing used in combustion cycles to an engine braking timing.
In one typical strategy, an exhaust valve is held closed during a portion of a piston's compression stroke in a combustion cylinder, and then opened just before the subject piston reaches top-dead-center instead of remaining closed as would occur during an engine cycle. No fuel is injected during the engine cycle so no combustion take place to produce a power stroke. The compressed air in the cylinder is discharged to the exhaust system, thus retarding engine speed based on the work required to compress the air. Various modifications to the opening timing, closing timing, number of opening and closing events within an engine cycle, and still other parameters have been the subject of much experimentation in the engine field.
A desire for flexibility in the relative amount or power of engine braking has led to strategies where all of the combustion cylinders in an engine are operated in a braking mode, or only some of the combustion cylinders are operated in a braking mode. While such strategies can provide greater flexibility than an all or nothing approach, there remains ample room for improvements and/or alternative strategies. U.S. Pat. No. 6,609,495 to Cornell et al. sets forth one example strategy for electronic control of an engine braking cycle.
In one aspect, a method of braking an engine includes operating an engine in a cylinder-number braking mode where exhaust valves for at least some combustion cylinders in the engine are operated in an engine braking timing pattern, and determining a control term indicative of at least one of an intake air pressure or a change to an intake air pressure that varies a braking power of the engine. The method further includes commanding varying a position of an exhaust-impinged surface in an exhaust turbine for the engine based on the determined control term, and varying a speed of an intake air compressor for the engine driven by the exhaust turbine, based on the commanded varying of a position of the exhaust-impinged surface. The method still further includes adjusting the braking power of the engine, within the cylinder-number braking mode, based on a change to intake air pressure in the engine occurring in response to the varied speed of the intake air compressor.
In another aspect, an engine braking control system includes an engine braking controller structured to couple to an engine braking control switch. The engine braking controller is further structured to receive an engine braking request from the engine braking control switch indicative of a requested cylinder-number braking mode in an engine having a plurality of combustion cylinders, and to command operation of exhaust valves for a number of the combustion cylinders that is dependent upon the requested cylinder-number braking mode in an engine braking timing pattern. The engine braking controller is still further structured to determine a control term that is indicative of at least one of an intake air pressure or a change to an intake air pressure that varies a braking power of the engine within the requested cylinder-number braking mode, and to command varying a position of an exhaust-impinged surface in an exhaust turbine coupled to the engine, based on the determined control term, to vary a speed of a compressor driven by the exhaust turbine. The engine braking controller is still further structured to adjust the braking power of the engine based on a change to a pressure of intake air supplied to the engine in response to the varied speed of the compressor.
In still another aspect, an engine braking system includes a plurality of engine braking actuators structured to adjust timings of exhaust valves for a plurality of combustion cylinders in an engine. The engine braking system further includes an exhaust turbine actuator structured to couple with an exhaust-impinged surface in an exhaust turbine, and an engine braking control system. The engine braking control system includes an engine braking control switch, an engine speed sensor, and an engine braking controller coupled to the engine braking control switch and to the engine speed sensor. The engine braking controller is structured to command, using the respective engine braking actuators, transitioning at least some of the exhaust valves from a first timing pattern to an engine braking timing pattern, based on an engine braking request from the engine braking control switch indicative of a requested cylinder-number braking mode of the engine. The engine braking controller is further structured to determine, based on an engine speed signal produced by the engine speed sensor, a control term that is indicative of at least one of an intake air pressure or a change to an intake air pressure that varies a braking power of the engine within the requested cylinder-number braking mode. The engine braking controller is still further structured to command, using the exhaust turbine actuator, varying a position of an exhaust-impinged surface in the exhaust turbine based on the determined control term, such that a speed of a compressor rotated by the exhaust turbine is varied. The engine braking controller is still further structured to adjust the braking power of the engine based on a change to intake air pressure occurring in response to the commanded varying of a position of the exhaust-impinged surface.
Referring to
Referring also now to
Internal combustion engine system 18 further includes an engine braking system 30. Engine braking system 30 includes a plurality of engine braking actuators 54 structured to adjust timings or timing patterns of a plurality of exhaust valves 56 for combustion cylinders 34 in engine 20. Engine braking actuators 54 could be electronically controlled hydraulic actuators, pneumatic actuators, or electrical actuators, that controllable open, controllably close, hold open, hold closed, or otherwise control the positions of exhaust valves 56 at desired engine timings. Each combustion cylinder 34 is shown associated with one exhaust valve 54, however, it will be appreciated that each combustion cylinder 34 may be associated with multiple exhaust valves as well as multiple intake valves (not shown) in a practical implementation. Engine braking actuators 54 may control the state of one or plural exhaust valves.
Engine braking system 30 further includes an exhaust turbine actuator 58 structured to couple with an exhaust-impinged surface 60 in exhaust turbine 50. Exhaust turbine actuator 58, or multiple exhaust turbine actuators if used, may be electronically controlled hydraulic actuators, pneumatic actuators, or electrical actuators. Exhaust-impinged surface 60 can include a surface of a turbine vane, approximately as shown, having a position that can be varied relative to a flow of exhaust through exhaust turbine 50 to vary an internal geometry of exhaust turbine 50. In other embodiments, exhaust-impinged surface 60 could include a movable turbine wall surface, or still another movable surface, having a position relative to the flow of exhaust that varies a speed of rotation of exhaust turbine 50 in a generally known manner. A change to an orientation of an exhaust-impinged surface relative to a flow of exhaust is a change to a position as contemplated herein. As noted above, intake air compressor 52 is rotated by exhaust turbine 50, and thus has a compressor speed that can be varied by varying a position of exhaust-impinged surface 60 for purposes that will be apparent from the following description.
Engine braking system 30 further includes an engine braking control system 62 including an engine braking control switch 64, an engine speed sensor 66, and an engine braking controller 68 coupled to engine braking control switch 64 and to engine speed sensor 66. In one practical implementation, engine braking control switch 64 may be positioned in cab 16 of machine 10 for manipulation by an operator. Also in a practical implementation, engine braking control switch 64 can have a plurality of different positions, finite in number, each corresponding to a requested cylinder-number braking mode of engine 20. Engine braking controller 68 can include any suitable electronic control unit, such as a microprocessor, or a microcontroller, having a central processing unit in communication with a computer readable memory structured to store program instructions for operating engine braking system 30 as further discussed herein.
Engine braking controller 68 may be structured to receive an engine braking request from engine braking control switch 64 indicative of a requested cylinder-number braking mode in engine 20. Engine braking controller 68 may be further structured to command, using respective engine braking actuators 54, transitioning at least some of exhaust valves 56 from a first timing pattern to an engine braking timing pattern, based on the engine braking request from engine braking control switch 64 indicative of a requested cylinder-number braking mode of engine 20. A cylinder-number braking mode means operation, for a given number of combustion cylinders, where at least some of exhaust valves 56 associated with the respective combustion cylinders open and/or close at appropriate timings for compression release braking. A first cylinder-number braking mode could include operating two of combustion cylinders 34 and associated exhaust valves 56 in an engine braking timing pattern to brake engine 20, while permitting four of combustion cylinders 34 and associated exhaust valves 56 to continue operating according to a normal timing pattern or a combustion timing pattern, but without combusting any fuel. A second cylinder-number braking mode could include operating four of combustion cylinders 34 and associated exhaust valves 56 to brake engine 20, whereas a third cylinder-number braking mode can include operating all of combustion cylinders 34 and associated exhaust valves 56 at engine braking timings to brake engine 20. Also in a practical implementation, engine 20 is a compression-ignition engine operated on a directly injected liquid fuel such as a diesel distillate fuel. In other embodiments, however, engine 20 could be operated on a different fuel type or otherwise according to hardware and operating methodology different from that explicitly disclosed herein.
Engine braking controller 68 may be further structured to determine, based on an engine speed signal produced by engine speed sensor 66, a control term that is indicative of at least one of an intake air pressure or a change to an intake air pressure that varies a braking power of engine 20 within the requested cylinder-number braking mode. The control term can include a numerical term, for example, that is or corresponds to an absolute intake air pressure that is desired or a change to an absolute intake air pressure that is desired, to vary braking power without changing a number of combustion cylinders and associated exhaust valves 56 presently operated to brake engine 20. In a practical implementation, the subject control term includes a desired intake manifold air pressure (IMAP). Engine braking system 30 and engine braking control system 62 may further include an IMAP sensor 70 structured to monitor an IMAP for purposes further discussed herein. Engine braking system 30 and engine braking control system 62 may also include an altitude sensor 72, structured to produce an altitude signal 72 also used by engine braking controller 68 in determining the subject control term. Any of engine speed, intake air pressure, or altitude, can be determined directly or indirectly by any suitable sensor or sensor group or even a so-called virtual sensor in some embodiments. Thus, an altitude sensor might not necessarily sense altitude directly, and an altitude signal might not explicitly encode altitude but instead a value indirectly indicative of or having a known or determinable relationship with altitude.
Also depicted in
It will be recalled that engine braking control switch 64 can be moved by an operator to vary a requested cylinder-number braking mode, such as by moving switch 64 between a finite number of switch configurations, for example, lever positions, each corresponding to one of a plurality of available cylinder-number braking modes. Accordingly, certain aspects of the present disclosure can be thought of as providing an operator with control to select a number of cylinders that will be used to brake engine 20, with second controller 28 operating to cause modulation of the actual braking power output in a manner responsive to present conditions. Various other justifications than transmission speeds or relative speeds, for example, a machine ground speed or acceleration, could serve as the basis for a braking power modulation request.
Engine braking controller 68 is further structured to command, using exhaust turbine actuator 58, varying a position of exhaust-impinged surface 60 in exhaust turbine 50 based on the determined control term, such that a speed of intake air compressor 52 rotated by exhaust turbine 50 is varied. Thus, engine braking controller 68 can be thought of as adjusting a position of exhaust-impinged surface 60 that can increase or decrease a speed of rotation of compressor 52. Engine braking controller 68 is thus further structured to adjust a braking power of engine 20 based on a change to intake air pressure occurring in response to the commanded varying of position of exhaust-impinged surface 60. In this aspect, engine braking controller 68 is thus understood to increase or decrease compressor speed to increase or decrease braking power as the resulting change to intake air pressure varies the amount of work performed by combustion cylinders currently operating to brake engine 20.
It will be recalled the intake air pressure or change to intake air pressure of interest may be IMAP. Embodiments are contemplated where the sole variable targeted for adjusting braking power within a given cylinder-number braking mode is IMAP. It will also be recalled engine braking control system 62 may include IMAP sensor 70. IMAP sensor 70 is structured to monitor IMAP, and engine braking controller 68 may be further structured to command a further change to a position of exhaust-impinged surface 60 based on monitored IMAP. In this way, engine braking controller 68 may periodically or continually adjust exhaust-impinged surface 60, such as by adjusting a position or orientation of a turbine vane, to drive IMAP towards a desired IMAP.
Referring also now to
Referring also now to
It will be recalled that braking level can be modulated within a present cylinder-number braking mode according to the present disclosure. Reference numeral 220 shows a lower braking power level at a curve 222, and a higher braking power level at a curve 224 that can be obtained according to the present disclosure where IMAP is varied within a lower-power cylinder-number braking mode, in other words a lesser number of combustion cylinders operated to brake the engine. Reference numeral 220 identifies a range of braking power that can be obtained for the lower-level cylinder number braking mode. Another range 230 including curves 232, 234, and 236 is shown illustrating braking power levels that can be obtained in a medium-power cylinder-number braking mode, in other words a mode where a greater number of combustion cylinders but less than all combustion cylinders, are used to brake the engine. Yet another range is shown at 240 for a higher power cylinder-number braking mode such as might be used where all combustion cylinders are operated to brake the engine, and includes curves 242, 244, 246, and 248 corresponding to the different braking power levels.
In view of
Referring to the drawings generally, but also now to
From block 315, flowchart 300 advances to a block 320 to receive a braking modulation request as discussed herein that is a request to vary engine braking power within a present cylinder-number braking mode, in other words, varied braking power level without changing a number of combustion cylinders used in engine braking. From block 320, flowchart 300 advances to a block 325 to determine a control term, such as a desired IMAP, as discussed herein. From block 325, flowchart 300 advances to a block 330 to command varying a position of an exhaust-impinged surface based on the determined control term. From block 330, flowchart 300 advances to a block 335 to vary compressor speed based on the commanded varying of position of the exhaust-impinged surface. From block 335, flowchart 300 advances to a block 340 to vary engine braking power within the requested cylinder-number braking mode. It will also be recalled that engine braking control, according to the present disclosure, can include closed loop control of a target intake air pressure variable such as desired IMAP. From block 340, flowchart 300 advances to a block 345 to determine IMAP error, such as by comparing monitored IMAP to desired IMAP, and thenceforth to a block 350 to command further varying of a position of exhaust-impinged surface based on the determined IMAP error.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims. As used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.
