Electro-hydraulic compression release brake

Abstract: A system and method (10) for controlling combustion engine compression braking having the variable timing of the dwell period of at least one exhaust valve (14-24) by an electronic control module (12) within each one of the engine cylinders (26-36) during a braking event as well as the variable timing of the commencement or onset of the braking event. The system and method (10) thus facilitate the proper performance of the braking event as a function of engine speed and prevents interference or physical impact with the cam driving elements used for achieving the normal or regular exhaust valve (14-24) event.

Description: Technical Field The present invention relates generally to engine compression release brakes, and more particularly to a system and a method of operating an engine compression release brake. Background Art Vehicle engine compression brakes are conventionally used to assist and supplement wheel brakes when it is desired, for example, to slow heavy vehicles, such as, tractor-trailer trucks. Engine compression brakes are desirable because they help alleviate overheating of the wheel brakes. Engine compression brakes effectively convert an internal combustion engine from a power generating unit to a power consuming air compressor. In engine compression braking systems, it is known that the later the exhaust valve is opened during the compression stroke of the engine cycle, that is, as the piston is disposed closer or closest to the top-dead-center (TDC) position, the more retarding horsepower or braking will be generated or produced. Conversely, the sooner or earlier the exhaust valve is opened during the compression stroke of the engine cycle, that is, as the piston is disposed closer or closest to the bottom-dead-center (BDC) position, the less retarding horsepower or braking will be generated or produced. When maximum engine compression braking is desired, the timed opening of the engine compression brake exhaust valve is such that the engine compression brake exhaust valve undergoes or experiences maximum lift at approximately the top-dead-center (TDC) position of the cylinder piston. In connection with vehicle engine compression braking schemes, systems, or methods of operating the same, an additional consideration to be taken into account is the duration of the valve dwell of the compression released braking event, that is, the amount of time that the engine compression release exhaust valve is maintained in its opened position. While it has been determined through analysis of various simulations, testing, and the like, that the amount or duration of the valve dwell does not significantly impact upon or influence the amount or level of engine compression braking achieved, the amount or duration of the valve dwell does significantly impact upon or influence the time required to close the compression release exhaust valve and the velocity at which the compression release exhaust valve moves toward its valve seat. More particularly, the pressure within the cylinder affects the exhaust valve closing time and the velocity at which the exhaust valve seats upon its valve seat. Accordingly, the sooner you close the exhaust valve after the top-dead-center (TDC) position, the higher the pressure within the cylinder and therefore the faster the exhaust valve closes and the greater the velocity at which the exhaust valve seats. If the exhaust valve closes too rapidly, that is, if its seating velocity is too high, damage to the exhaust valve and/or its valve seat can occur. Consequently, a need exists in the art for an engine compression braking or release system, and a method of operating the same, wherein the exhaust valves of the engine cylinders can be activated or energized in various trade-off dwell time modes of operation so as to achieve, on the one hand, the engine exhaust valves must also achieve proper closure time periods and seating velocities. A still further consideration to be taken into account in connection with vehicle engine compression braking schemes, systems, or methods of operating the same, is the fact that the exhaust valves of the engine also undergo regular or normal cam-driven-exhaust events, and that the compression release or braking event must be conducted or performed, in effect, independently of the normal or regular cam-driven exhaust event such that high velocity impact or interference between the operating or control cam for the normal or regular exhaust event, and the exhaust valve undergoing a compression braking or release event, does not occur, thereby preventing the generation of undesirable noise and potential damage to the engine components. A need therefore exists in the art for an engine compression release or braking system, and a method of operating the same, wherein the dwell of the engine compression release or braking exhaust valve can be appropriately controlled so as to achieve the engine compression or braking mode of operation while avoiding any high velocity interference with or impact upon the normal or regular exhaust valve event driving cam so as to prevent the generation of undesirable noise and potential damage to the engine components. One such system is disclosed in US-A- 5,357,926. In this patent the lash of the engine brake is adjusted to have a clearance between an engine brake slave piston and the engine exhaust valve mechanism. Thus, noise is reduced. US-A-6 082 328 discloses a method and apparatus for carrying out variable timing exhaust gas recirculation for use during both positive power and retarding operation of an internal combustion engine. Motion or energy is derived from an engine component and stored as potential energy. The stored energy is selectively applied to a valve actuator to carry out exhaust gas recirculation in an engine cylinder. The energy derived from the engine may be stored and selectively applied to the valve actuator with an electronically controlled trigger valve. The valve actuator may be a slave piston having an inner core and an outer sleeve capable of opening the valve of the cylinder in response to independent exhaust gas recirculation and compression release hydraulic systems. US-A-5 012 778 discloses an engine retarding system of a gas compression release type for an engine equipped with a high pressure hydraulic fluid supply system. The retarder comprises an hydraulically driven exhaust valve actuator, a solenoid actuated servo valve controlling the flow of high pressure hydraulic fluid from the supply to the actuator and an electronic controller which provides a signal to operate the solenoid as a function of the engine speed and crankshaft position. EP-A-0 747 576 discloses a device for use in an engine brake control to move an exhaust valve to an open position, including an actuator engageable with the exhaust valve and an electrically-operable control valve. The actuator includes a valve spool and a slave piston wherein the slave piston includes a passage and wherein the valve spool includes a high pressure annulus coupled to a source of high fluid pressure and a low pressure annulus coupled to a source of low fluid pressure. The valve spool is movable relative to the slave piston to interconnect the passage with the high pressure annulus or the low pressure annulus. The electrically-operable control valve selectively provides high fluid pressure to the valve spool and to the slave piston to cause the slave piston to oscillate about a point at which the exhaust valve is disposed in the open position and the passage is alternately connected to the low pressure annulus and the high pressure annulus. US-A-6 012 424 discloses a method and apparatus of carrying out exhaust gas recirculation and compression release retarding for use during both positive power and retarding operation of an overhead cam internal combustion engine. Energy is derived from an engine component and stored as potential energy. The stored energy is selectively applied to a valve actuator to carry out exhaust gas recirculation in an engine cylinder. The energy derived from the engine may be stored in the form of a compressed hydraulic fluid and selectively applied to the valve actuator with an electronically controlled trigger valve. The valve actuator may be a slave piston having an inner core and an outer sleeve capable of opening the valve of the cylinder in response to independent exhaust gas recirculation and compression release hydraulic systems. However, none of the prior art documents discloses to variably adjust a dwell period of the exhaust valve as a function of engine speed so as to ensure completion of the braking event prior to commencement of a cam driven regular exhaust valve event. The present invention is directed to overcome one or more of the problems as set forth above. Disclosure of the Invention In one aspect of the invention a method of achieving a compression braking event within a combustion engine is provided as set forth in claim 1. In another aspect of the invention a system for achieving a compression braking event with a combustion engine is provided as set forth in claim 7. Preferred embodiments of the present invention may be gathered from the dependent claims. Brief Description of the Drawings FIGURE 1 is a schematic view of a control system for an engine; and FIGURE 2 is a graph showing crank angle, in connection with both the regular exhaust valve event and the compression release or braking event. Best Mode for Carrying Out the Invention Referring to FIGURE 1, a control system for a six-cylinder engine is schematically disclosed and is generally indicated by the reference character 10. The control system 10 has an electronic control module (ECM) 12, and the electronic control module 12 is operatively connected to each one of a plurality of exhaust valves 14-24. The plurality of exhaust valves 14-24 are respectively disposed within each one of the engine cylinders 26-36. The electronic control module 12 can control the timing of the opening of each one of the exhaust valves 14-24 through well-known mechanisms, such as, for example, electrical, or electro-hydraulic solenoid-drives 38-48. With reference to FIGURE 2, there is illustrated a graph illustrating exhaust valve lift as a function of engine crank angle. The opening, closing, and dwell duration periods of the exhaust valves are controlled during both engine compression release or braking events and normal or regular exhaust valve events. It is to be understood that the electronic control module 12 of FIGURE 1 controls the exhaust valves 14-24 during the engine compression release or braking events while the exhaust valves 14-24 are cam controlled in a conventional manner, by conventional cam driven mechanisms, not shown, during the regular or normal exhaust valve events. It is further noted that since the vertical or y-axis of the graph is depicting exhaust valve lift, the exhaust valves are illustrated as being in their closed or seated positions or states at an exhaust valve lift level of zero both during the engine compression braking and regular or normal exhaust valve events. In addition, as the horizontal or x-axis of the graph is depicting the engine crank angle in degrees, the top-dead-center (TDC) position of the crankshaft at the end of the piston compression stroke is noted at 0°. The bottom-dead-center (BDC) position of the crankshaft at the end of the piston power stroke is noted at 180°. And, the top-dead-center (TDC) position of the crankshaft at the end of the piston exhaust stroke is noted at 360°. Still further, it is noted that the engine compression braking event is commenced when the crankshaft is at an angular position of approximately 30° before compression top-dead-center (CTDC). And, the maximum exhaust valve lift is achieved during the engine compression braking event when the crankshaft is disposed at an angular position approximately coinciding with compression top-dead-center (CTDC). Similarly, the regular or normal exhaust valve event is commenced when the crankshaft is at an angular position of approximately 100° after compression top-dead-center (CTDC). This is also equivalent to an angular position of approximately 80° before power bottom-dead-center (PBDC), that is, the normal or regular exhaust valve event. The exhaust valves are caused to commence their opening by their cam controlled mechanisms, is commenced during performance of the piston power stroke and before commencement of the piston exhaust stroke. It is therefore imperative that in order to prevent any interference or physical impact between the opened exhaust valve during performance of the engine compression braking event, and the cam mechanism for controlling the exhaust valve during the regular or normal exhaust valve event, that the engine compression braking event be completed before commencement of the regular or normal exhaust valve event. In other words, there must be provided a sufficiently long period of time subsequent to the completion of the engine compression braking event, and prior to the commencement of the regular exhaust valve event, for the exhaust valve to be fully closed and seated before again being opened by the cam driven mechanisms such that the aforenoted interference or physical impact between the exhaust valve and the cam-driven mechanisms does not occur. This is graphically illustrated by the pre-regular exhaust valve event (PREVE) time period which occurs at approximately 80° after the compression top-dead-center (CTDC) position and lasts until approximately 100° after compression top-dead-center (CTDC) at which time the regular exhaust valve event commences as has been noted hereinbefore. With reference continuing to be made to the graph of FIGURE 2, the dwell period of the exhaust valve is maintained in its maximum open or valve lift position. It is also noted as occurring at or approximately coinciding with the compression top-dead-center (CTDC) position, during performance of an engine compression braking event. It has been determined, however, that as engine speed increases, the real time available for closing the engine compression exhaust valve during, for example, performance of its braking event, decreases substantially. For example, if the exhaust valve is to be completely closed within 100° after compression top-dead-center (CTDC), then the real time period for achieving such closure is 9.26 msec at an engine speed of 1800 RPM, however, the real time period for achieving such closure at an engine speed of 3300 RPM is only 5.05. Accordingly, the entire engine compression braking event, including the opening, closing, and dwell time periods for the exhaust valve must be adjusted in a real-time based manner so as to again ensure that the braking event is completed sufficiently before commencement of the regular exhaust valve event. As has been noted hereinbefore, it must be remembered that the angular cycle time at which the braking event is commenced by opening the engine compression release exhaust valve, that is, for example, at 20° before compression top-dead-center (CTDC), will influence or impact upon the real time or rapidity required to open the compression release exhaust valve during the compression stroke, and this real-time-period or duration is graphically illustrated in FIGURE 2 by the slope of the braking event graphical plot labeled S-O which indicates the slope of the event for the opening phase thereof. In a similar manner, it is also to be remembered that the amount or duration of the valve dwell significantly impact upon or influences the real time required to close the compression release exhaust valve and the velocity at which the compression release exhaust valve moves toward its valve seat. More particularly, the valve dwell duration also determines in part the pressure within the cylinder. The sooner the exhaust valve is closed after the compression top-dead-center (CTDC) position, the higher the pressure remaining within the cylinder and therefore the faster the exhaust valve will close and the greater the velocity at which the exhaust valve will seat. Therefore, if the exhaust valve is closed too soon after compression top-dead-center (CTDC), that is, the dwell period is too short, the pressure within the cylinder remains high and the exhaust valve will close rapidly. However, the valve seating velocity is also high which can potentially damage the exhaust valve and/or its valve seat. This real-time period or duration for closure of the exhaust valve during the braking event is graphically illustrated in FIGURE 2 by the slope of the braking event graphical plot labeled S-C which indicates the slope of the event for the closing phase thereof. On the other hand, if the dwell period is too long, the real-time period for closure of the exhaust valve will be extended, the pre-regular exhaust valve event (PREVE) period will have been effectively eliminated and interference with the cam driven engine components for achieving the regular exhaust valve event may occur. Industrial Applicability In accordance with the principles and teachings of the present invention, the electronic control module 12 can be pre-programmed so as to vary the dwell period or duration as a function of, for example, engine crank angle and/or vehicle compression engine braking event is ensured to be completed prior to the commencement of the cam controlled regular exhaust valve event so as to avoid any interference or physical impact with the cam driven control mechanisms for achieving the regular exhaust valve event. Simulations and tests have shown, for example, that when the exhaust valve is closed 20° after compression top-dead-center (CTDC), the valve is closed 20° after compression top-dead-center (CTDC), the valve closing time is approximately twice as long as the closing time required for the valve when the valve is closed at compression top-dead-center (CTDC). In a similar manner, the time at which the braking event is commenced, that is, in terms of engine crank angle, also determines the rapidity at which the compression braking exhaust valve opens to its full extent during the braking event, and consequently, such commencement time can also be suitably controlled by the electronic control module 12 along with the aforenoted control of the dwell period duration. It is also to be remembered that as engine speed increases, the real time available for achieving closure of the engine compression release or braking exhaust valve drastically decreases. Thus, it may be readily appreciated that both the commencement or onset of the braking event, as well as the duration or dwell of the braking event, can be suitably controlled by the electronic control module which activates or energizes the compression release brake valve at suitable times of the braking event both from an engine crankshaft angle base reference as well as a real-time-base reference. It is to be noted that when altering or adjusting the pre-programmed modes of the electronic control module 12 so as to in turn energize or activate the compression release brake exhaust valve at the predetermined times of the braking event cycle, trade-offs in achieved results will be experienced or achieved. For example, in order to achieve completion of the braking event prior to the commencement or onset of the regular exhaust valve event, the dwell time or duration may have to be shortened if engine speed is substantially high, however, the cylinder pressures may then be somewhat high or relatively elevated which may then lead to rapid closure of the exhaust valve with relatively high seating velocities. Conversely, the dwell time or duration can be somewhat lengthened so as to permit additional cylinder pressure to exhaust whereby the exhaust valve closes somewhat more slowly and the substantially high impact forces of the exhaust valve upon its valve seat are somewhat alleviated, it nevertheless being ensured that sufficient time is still provided for completion of the braking event prior to commencement or onset of the regular exhaust valve event. While the use of an electronic control module to control the opening and closing of an engine compression release or braking exhaust valve within and engine is known, and therefore will not be discussed in detail herein, what is submitted to be new and novel is the use of an electronic control module to control the timing of the opening, closing, and dwell duration of the engine compression release or braking exhaust valves as a function of engine speed by varying the dwell time or opened duration of the exhaust valves of the engine cylinders at different predetermined times of the compression and power strokes of each piston within each cylinder such that the engine compression release or braking events can be achieved without interference with the cam control elements or components operatively associated with the normal or regular exhaust valve events. Obviously, many variations and modification of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.

Claims: A method (10) of achieving a compression braking event within a combustion engine, comprising the steps of: providing at least one exhaust valve (14-24) acting within each one of a plurality of cylinders (26-36) of a combustion engine, wherein said exhaust valve (14-24) undergoes a crank angle based, cam driven regular exhaust valve (14-24) event and a crank angle based braking event having a predetermined dwell period; connecting an electronic control module (12) to each one of said exhaust valves (14-24) such that said electronic control module (12) can respectively activate said each one of said exhaust valves (14-24) for performance of said braking event; and programming said electronic control module (12) so as to activate said exhaust valve (14-24) at a predetermined time during a compression stroke and thereby achieve said braking event, characterised in that said electronic control module is programmed to variably adjust said dwell period of said exhaust valve (14-24) as a function of engine speed so as to ensure completion of said braking event prior to commencement of said cam driven regular exhaust valve event. The method as set forth in Claim 1, wherein said electronic control module (12) is programmed so as to activate said exhaust valve (14-24) at a predetermined time during said compression stroke up to 30° before compression top-dead-center. The method as set forth in Claim 1, wherein said electronic control module (12) is programmed so as to activate said exhaust valve (14-24) at a predetermined time during said compression stroke wherein said dwell period includes an angular camshaft extent of 20°. The method as set forth in Claim 3, wherein said electronic control module (12) is programmed so as to activate said exhaust valve (14-24) wherein said dwell period commences at a camshaft angular position which coincides with compression top-dead-center. The method as set forth in Claim 1, wherein said electronic control module (12) is programmed so as to activate said exhaust valve (14-24) at a predetermined time during said compression stroke wherein said predetermined dwell time period is progressively shortened as said engine speed increases. The method as set forth in Claim 5, wherein said electronic control module (12) is programmed so as to activate said exhaust valve (14-24) at a predetermined time during said compression stroke wherein said predetermined dwell time period is sufficiently long so as to permit a sufficient amount of compression pressure to escape from said cylinder (26-36) such that said exhaust valve (14-24) does not impact upon its valve seat with an inordinately high amount of impact force so as to prevent damage to said exhaust valve (14-24) and said valve seat. A system for achieving a compression braking event within a combustion engine, comprising: at least one exhaust valve (14-24) within each one of a plurality of cylinders (26-36) of a combustion engine, wherein said exhaust valve (14-24) undergoes a crank angle based, cam driven regular exhaust valve (14-24) event and a crank angle based braking event having a predetermined dwell period; an electronic control module (12) connected to each one of said exhaust valves (24-34) and predeterminedly programmed such that said electronic control module (12) can activate said exhaust valve (14-24) at a predetermined time during a compression stroke and thereby perform said braking event, and to variably adjust said dwell period of said exhaust valve (14-24) as a function of engine speed so as to ensure completion of said braking event prior to commencement of said cam driven regular exhaust valve event. The system as set forth in Claim 7, wherein said electronic control module (12) is programmed so as to activate said exhaust valve (14-24) at a predetermined time during said compression stroke up to 20° before compression top-dead-center. The system as set forth in Claim 7, wherein said electronic control module (12) is programmed so as to activate said exhaust valve (14-24) engine cylinders (26-36) at a predetermined time during said compression stroke wherein said dwell period includes an angular camshaft extent of 20°. The system as set forth in Claim 9, wherein said electronic control module (12) is programmed so as to activate said exhaust valve (14-24) wherein said dwell period commences at a camshaft angular position which coincides with compression top-dead-center. The system as set forth in Claim 7, wherein said electronic control module (12) is programmed so as to activate said exhaust valve (14-24) at a predetermined time during said compression stroke wherein said predetermined dwell time period is progressively shortened as said engine speed increases. The system as set forth in Claim 11, wherein said electronic control module (12) is programmed so as to activate said exhaust valve (14-24) at a predetermined time during said compression stroke wherein said predetermined dwell time period is sufficiently long so as to permit a sufficient amount of compression pressure to escape from said cylinder (26-36) such that said exhaust valve (14-24) does not impact upon its valve seat with an inordinately high amount of impact force so as to prevent damage to said exhaust valve (14-24) and said valve seat. An internal combustion engine having a plurality of cylinders (26-36) and a plurality of exhaust valves (14-24); said internal combustion engine comprising: an electro-hydraulic solenoid driver (38-48) connected to a respective one of said cam driven exhaust valves (14-24) for achieving a compression braking event within said internal combustion engine ; and a system as set forth in any of claims 7 to 12.

Inventors: BHARGAVA SAMEER NMI, FUNKE STEVEN J, LEMAN SCOTT A, MICKIEWICZ MATTHEW G, RUEDIN JOSHUA C, BHARGAVA, SAMEER, FUNKE, STEVEN J., LEMAN, SCOTT A., MICKIEWICZ, MATTHEW G., RUEDIN, JOSHUA C., Bhargava, Sameer (NMI), c/o Caterpillar Inc., Funke, Steven J., c/o Caterpillar Inc., Leman, Scott A., c/o Caterpillar Inc., Mickiewicz, Matthew G., c/o Caterpillar Inc., Ruedin, Joshua C., c/o Caterpillar Inc.
Applicants: CATERPILLAR INC, CATERPILLAR INC.
Application year: 2001
Main classification: F01L13
IPC codes: F01L13