Patent Publication Number: US-6705282-B2

Title: Method and apparatus to provide engine compression braking

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a compression brake system that provides retarding horsepower in an internal combustion engine, and particularly to a compression brake system using compressed engine oil to actuate actuator pistons that open exhaust valves at predetermined times. 
     BACKGROUND OF THE INVENTION 
     Compression or decompression brake systems are commonly known and used in internal combustion engines for trucks and other vehicles. Generally, a compression brake augments the conventional vehicle brake system thereby protecting the conventional brake system from excessive wear. Two well known compression brakes are a lost motion design and an electro-mechanical design. The lost-motion brake utilizes and additional lobe on the engine&#39;s cam to open the exhaust valve when needed. The electro-mechanical brake generally uses high pressure or compressed engine oil or fluid to activate slave pistons that open the exhaust valves. 
     As is know by those of skill in the art, the basic function of the decompression brake is to open an exhaust valve of a given cylinder at the end of the compression cycle when there is compressed air in the cylinder. The opening of the exhaust valve allows the power cylinder to “decompress” and thus removes energy. By allowing the compressed gas within the cylinder to be purged prematurely through the open exhaust valve, the mechanical energy that was required to compress the gas can be wasted through the open exhaust valve, instead of being transferred back into the engine during the ensuing “power stroke.” As a result, the engine absorbs and dissipates more energy than it otherwise normally would and thus provides retarding horsepower to the vehicle. This allows the vehicle to be slowed down. Typically, this process only occurs when the brake function is armed and then activated by the driver removing their foot from the accelerator pedal. When the input signal conditions are right, the fuel injectors stop supplying fuel to the power cylinders and the brake cycle begins. 
     In prior art engine compression brakes, opening the exhaust valve at, or near, the conclusion of the compression stroke required the application of axial force to the exhaust valve thereby causing the valve to open. In at least one type of prior art engine, mechanical force required to overcome the exhaust valve spring and to open the valve was provided by an actuator piston located “above” or extant the exhaust valve stem and to which compressed engine oil was delivered, hydraulically opening the valve by pulsing the actuator piston at predetermined times. 
     These prior art hydraulic engine compression braking systems often require their own high-pressure oil systems, fast-acting actuators and precise timing in order to open the exhaust valve when the piston is at or near the top of the compression stroke. Some of these prior art engines also use pressurized engine oil to control the opening of the diesel fuel injectors, requiring two separate complex, high-pressure engine oil systems that both deliver pulses of high-pressure engine oil. Eliminating at least one of the complex, high-pressure oil control systems in such prior art engines would yield a higher-reliable engine compression braking system at a reduced cost. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for engine compression braking for an internal combustion engine that uses hydraulic-fluid-actuated fuel injectors, where the engine compression braking can be provided by diverting or re-routing hydraulic fluid that would normally open the fuel injectors, to slave engine compression brake actuator pistons which are mechanically coupled to the exhaust valves so as to cause the exhaust valves to open at the time that the fuel injectors would have been opened to inject fuel. 
     There is provided a method for compression engine braking in an internal combustion engine, having a source of pressurized fluid for a hydraulically-actuated fuel injector, comprising the steps of activating compression engine braking mode, generating a diverter valve actuation signal in an engine computer, actuating the diverter valve based on the diverter valve actuation signal thereby diverting the pressurized fluid to the fuel injector towards a slave piston, actuating the slave piston via the diverted high pressure fluid, and actuating an exhaust valve, via the slave piston, for a predetermined amount of time at or near the top of a compression stroke via translation of the slave piston movement to thereby vent compressed gases in a combustion chamber to the atmosphere. 
     In an alternate embodiment, the method for compression engine braking in an internal combustion engine further comprises actuating a diverter valve based on a diverter valve actuation signal thereby diverting the pressurized fluid from the fuel injector towards a stroke limiter piston. The stroke limiter piston is then actuated via the diverted high pressure fluid. Next, the slave piston is actuated by translating the movement of the stroke limiter piston via hydraulic coupling means between the stroke limiter and the slave piston. As before, the exhaust valve is actuated for a predetermined amount of time at or near the top of a compression stroke, by translation of the slave piston movement, to thereby vent compressed gases in a combustion chamber to the atmosphere. 
     In another embodiment, there is provided a compression engine brake for an internal combustion engine having a source of pressurized fluid for at least one hydraulically-actuated fuel injector, at least one fuel injector control valve for selectively delivering pressurized fluid to a corresponding fuel injector, at least one exhaust valve through which combustion chamber gases can travel from the combustion chamber to the atmosphere, and an engine computer for monitoring and controlling engine functions. The engine compression brake comprises a diverter control valve for diverting pressurized fluid from the fuel injector in response to a diverter control valve actuation signal from the engine computer, and a slave piston for opening the exhaust valve in response to the diverted pressurized fluid to thereby vent compressed gases in a combustion chamber to the atmosphere. 
     In another alternate embodiment, there is provided a compression engine brake for an internal combustion engine having a source of pressurized fluid for at least one hydraulically-actuated fuel injector, at least one fuel injector control valve for selectively delivering pressurized fluid to a corresponding fuel injector, at least one exhaust valve through which combustion chamber gases can travel from a combustion chamber to the atmosphere, and an engine computer for monitoring and controlling engine functions. The engine compression brake comprises a diverter control valve for diverting pressurized fluid from the fuel injector in response to a diverter control valve actuation signal from the engine computer, a stroke limiter piston having an input face for receiving the diverted pressurized fluid and an output face such that upon the diversion of the pressurized fluid to the stroke limiter piston input face, the stroke limiter piston is displaced, and a slave piston hydraulically coupled to the stroke limiter piston via the output face such that the stroke limiter piston displacement displaces the slave piston which in turn actuates and opens a corresponding exhaust valve at substantially the end of the engine&#39;s compression stroke to vent compressed gases from the combustion chamber to the atmosphere. 
     The following drawings and description set forth additional advantages and benefits of the invention. More advantages and benefits will be obvious from the description and may be learned by practice of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be better understood when read in connection with the accompanying drawings, of which: 
     FIG. 1 depicts a simplified schematic diagram of the components of an embodiment of the system and method to provide engine compression braking according to the present invention. 
     FIG. 2 shows a timing diagram that approximates the actuations of an intake valve, exhaust valve, fuel injector and the engine compressing braking apparatus shown in FIG. 1, as a function of the relative location of a piston through-out its travel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a simplified schematic representation of an apparatus to provide engine compression braking  10  according to a preferred embodiment of the present invention. Although the preferred embodiment contemplates use with a diesel-cycle internal combustion engine, those of ordinary skill in the art will readily recognize that the embodiment disclosed herein could also be used with a gasoline-fueled internal combustion engine application. 
     As is known in the art, pistons  12  (only one shown for simplicity) reciprocate in corresponding cylinders  16  (a partial one shown in cross-section) in response to rotation of a crankshaft (not shown for simplicity) to which the piston connecting rod  13  is rotatably affixed via the connecting rod journal. The piston  12  is shown in FIG. 1 as traveling in the direction indicated by the arrows  14 , however, the invention disclosed and claimed herein does not require the piston to travel in any particular direction or spatial orientation. 
     In a four-cycle internal combustion engine, the piston  12  completes four separate strokes or cycles, as is well know, during which an intake valve (not shown) opens thereby allowing outside air into the combustion chamber  18  as the piston  12  travels downward  14  away from the intake and exhaust  24  valves, which are usually located at or near the top of the cylinder  22 , e.g. in a cylinder head (not shown). In a gasoline-fueled engine, air and fuel are drawn into the combustion chamber together during the intake stroke. In a diesel-cycle engine, only air enters the combustion chamber when the intake valve opens. A compression stroke follows the intake stroke. 
     When the piston  20  approaches or reaches the bottom of its intake-stroke travel, the intake valve closes. As the crankshaft to which the piston&#39;s  12  connecting rod  13  is attached, continues it&#39;s rotation, the piston eventually stops and reverses its travel to begin moving upward beginning the combustion stroke. In the embodiment shown in FIG. 1 the piston  12  is shown as moving vertically, however alternate embodiments would include pistons moving in any spatial orientation. As the piston moves toward the top of the cylinder  22 , gas (i.e., air) within the cylinder  22  is compressed. Alternatively, in gasoline-fueled engines, air and fuel in the cylinder  22  is compressed. 
     During the compression stroke, both the intake valve and the exhaust valve  24  are held tightly closed as the piston  12  travels or rises in the cylinder  16 . The compression of the air within the combustion chamber  18  by the piston&#39;s upward travel requires a delivery of a mechanical force to the piston  12  through the crankshaft (not shown) in order to overcome the counter or opposing force exerted on the piston by the gas as it is squeezed into an increasingly-smaller volume by the upwardly traveling piston  12 . In an engine compression brake system, the “upward” piston  12  force (in the embodiment shown in FIG. 1) in the cylinder  22  is supplied or translated to the piston  12  from the momentum of a moving vehicle through the crankshaft to which the vehicle&#39;s wheels are coupled via a transmission and drive train. 
     In the preferred embodiment shown in FIG. 1, fuel is injected into the cylinder  22  for a diesel engine using a hydraulic-fluid-actuated fuel injector  26 . Unlike electrically-actuated fuel injectors that are commonly used on many engines and which are made to open by an electrical current passing through a coil of wire to create a magnetic force, the hydraulic-fluid-actuated fuel injector  26  operates under the control of a high-pressure engine fluid or oil supply  28 . The delivery of the high pressure engine fluid  28  to the fuel injector  26  is gated or controlled so as to open the injector using oil pressure. The hydraulic-fluid-actuated fuel injector  26  opens whenever the high-pressure engine oil supply  28  is “turned on” by an electronically-controlled injector control valve  30 . When the injector control valve  30  is activated at a predetermined time by an appropriate injector control valve enabling signal  58  from the engine computer  50 , the hydraulic fluid (engine oil) is introduced into the fuel injector body which thereby injects fuel into the combustion chamber  18 . The operation and control of a fuel injector control valve  30  is not shown in FIG. 1 for simplicity. The operation and control of a fuel injector control valve  30  is known in the art, but only to control a fuel injector—not to control engine compression braking. 
     The injector control valve  30  depicted in FIG. 1 is shown schematically as a single pole, single pole switch so as to model the behavior of the injector control valve only. In a first position, high-pressure engine fluid or oil  28  is disconnected or isolated from the fuel injector body  26 . In a second position, high-pressure engine fluid  28  is connected to the fuel injector  26  thereby causing the injector to open and allow fuel into the cylinder  18 . In order to effectively meter fuel into the cylinder  18 , the injector control valve  30  rapidly and controllably opens and closes the high pressure oil supply  28  to the injector body  26  through a diverter valve  32  so as to periodically activate the injector body  26  using hydraulic engine fluid  28 . 
     Controlling the amount of fuel delivered to the engine is accomplished by holding the fuel injector  26  open for different lengths of time. The “open” time of the hydraulically-actuated injector  26  is controlled by controlling the length of time that the injector control valve  30  is held “open.” The injector control valve  30  is operably coupled to a engine computer  50 , which monitors an engine throttle position sensor  52  (among other engine parameters) to sense whether to increase, decrease or maintain the engine&#39;s output power, (i.e. throttle position), and in response thereto, open, close or maintain the “open” time of the injector control valve  30 . Fuel metering can be accomplished by pulse-width modulating the enabling signal  58  delivered to the injector control valve  30  from the computer  50 . 
     In the preferred system of FIG. 1, the simplified engine compression braking system and method is achieved by using the high-pressure oil supply  28  that is provided for and used by the fuel injector  26 , to open the cylinder  18  exhaust valve  24  instead. Re-direction of the high-pressure engine oil supply  28  is accomplished by way of a high-pressure oil diverter valve  32 , which directs high-pressure engine oil to either the fuel injector  26 , or, to a slave piston  36 , mechanically coupled to the exhaust valve  24 . The high-pressure oil diverter valve  32  re-directs the high engine oil  28  from the fuel injector  26  to the slave piston  36  under the direction of appropriate compression system signals  56  from the computer  50  upon the computer&#39;s  50  detection that engine compression braking is selected by the engine compression brake control input  54 . Upon detection of the engine compression brake signal  54 , the computer  50  activates (or deactivates) the diverter valve  32  so as to re-route the high-pressure engine oil  28  to the slave piston  36 . Thereafter, the duration of the exhaust valve  24  open time can be adjusted by controlling the control signals  58  to the injector control valve  30 . 
     During normal engine operation, the diverter valve  32  allows the high pressure oil supply  28  to be delivered to the injector body  26 . The timing and control of the injector control valve  30 , thereafter (by the computer  50 ) controls opening and closing of the fuel injector body  26 . Not shown in FIG. 1 are timing circuits which sense various engine conditions or parameters, such as engine temperature, ambient temperature, engine load etc., so as to determine the optimal times at which the injector control valve  30  will open thereby determining the specific time and duration at which fuel is injected into the combustion chamber  18  for optimum control of combustion and emissions. Such devices are well known and used in prior art diesel engines, International Models DT466, DT530 and HT530, that are made and sold by the assignee of this application. 
     As is known, in a diesel-cycle engine, fuel is injected into the highly-compressed air within the cylinder  18  whereupon the air fuel mixture ignites and burns. In the embodiment shown in FIG. 1, the injector body  26  and the resulting fuel injection into the combustion chamber  18  occurs just before the piston  12  reaches the top of its travel in the cylinder  16 , the precise occurrence of which is determined by the computer  50 . 
     In the preferred embodiment of FIG. 1 there are shown, two series-connected hydraulic pistons  34  and  36 . One piston is considered to be a “stroke limiter” piston  34  and the other is the slave piston  36 . A first side or face  40 A of the stroke limiter  34  is fluidly or fluidically coupled by a high pressure hydraulic engine fluid or oil line  43  to a first outlet  41  of the two-outlet, diverter valve  32 . Another high-pressure hydraulic engine oil line  39  fluidly or fluidically couples the second side or face  40 B of the stroke limiter  36  to the top or crown  37  of the slave piston  36 . The bottom end  45  of the slave piston  36  is adjacent to and mechanically in contact with the top of the exhaust valve stem  38  of the exhaust valve  24 . The series-operated stroke limiter or stoke limiter piston  34  and the slave piston  36  operate to controllably open the exhaust valve  24  when oil pressure is applied to the first side  40 A of the stroke limiter  34 . The oil pressure that performs that task is supplied from the high-pressure engine fluid or oil supply  28  via the diverter valve  32 . 
     Inasmuch as diesel fuel injection normally occurs, at or near the top of the compression stroke, diverting the high pressure oil supply away from the fuel injector body  26  and instead to the, two series-connected control pistons  34  and  36 , the slave piston  36  preferably being axially mounted directly above the exhaust valve stem  38 , the normal timing of the injector control valve oil pressure pulse is nearly ideal to the timing at which the exhaust valve  24  should be made to open in an engine compression braking system. Stated alternatively, instead of activating the injector body and opening the fuel injector at the top of the compression stroke, the same control pulse of hydraulic fluid or oil  28  for the fuel injector  26  can be used instead to open the exhaust valve  24  thereby purging the cylinder  18  gas, which was compressed using, at least in part, the vehicle&#39;s momentum. By opening the exhaust valve  24  at or near the top of the compression stroke, the mechanical energy supplied by the vehicle and which was required to compress the air taken into the cylinder  18  during the intake stroke can be wasted to the atmosphere providing a substantially enhanced engine braking effect. 
     As shown in FIG. 1, the diverter valve  32  redirects the flow of high pressure engine fluid or oil  28  from the fuel injector body  26  to a stroke limiter piston  34 . A front surface of the stroke limiter  40 A has a surface area against which the pressure of the high pressure oil supply  28  is applied so as to hydraulically multiply, in conjunction with the slave piston  36 , the force supplied from the high pressure engine oil supply  28 , to a level sufficient to open the exhaust valve  24 . The force supplied by the high pressure oil supply  28  must open the exhaust valve against the force of the exhaust valve spring (not shown for clarity) and the force applied to the valve face from the combustion chamber compressed gases. 
     The stroke limiter  34  is hydraulically coupled to the slave piston  36 , which is mounted on and substantially coaxially with the stem  38  of the exhaust valve  24  and which also preferably has a relatively large cross-sectional area to further increase the force applied to the exhaust valve  24  from the high-pressure oil supply  28 . As shown in FIG. 1, as the stroke limiter  34  travels upward, the upward translation of the stroke limiter  34  causes a downward displacement of the slave piston  36  against the top of the stem  38  of the exhaust valve  24 . 
     In an alternate embodiment, the stroke limiter  34  has an adjustable length of travel (not shown in FIG.  1 ). By controlling the travel of the stroke limiter  34 , the travel of the slave piston  36  can also be controlled thereby avoiding overextending the exhaust valve  24  into the cylinder and risking damage to the piston crown  20 . 
     The exhaust valve  24  can be held in an open position for the duration of the pulse of high pressure engine fluid or oil  28  supplied to the slave piston  36 , which is determined by the length of time that the injector control valve  30  is held open. The length of time that the injector control valve is open is controlled by injector control valve signals  58  from the computer  50 . When engine compression is required, it may be desirable for the computer  50  to lengthen the open time of the injector control valve  30  thereby purging more of the compressed gas within the cylinder  18 . The engine computer  50  is operably coupled to the injector control valve  30  and controls or determines the length of time that the injector control valve  30  is open to provide throttle control 
     When engine compression braking is no longer required, the injector control valve  30  is switched to a purge position (not shown) by which the high-pressure oil in line  43  is dumped within the engine at an appropriate location (typically under the engine rocker arm cover.) In the absence of high-pressure oil or fluid applied to the face  40 A of the stroke limiter, a stroke limiter spring  40 C opposite the face  40 A forces the stroke limiter to return to its resting position. Also, a slave piston spring  36 B opposite face  37  causes the slave piston  36  to return to its normal position allowing the exhaust valve to operate normally. The slave piston spring  36 B is operably coupled to the slave piston  36  preferably via a slave piston retaining snap ring  36 C. 
     In the embodiment of FIG. 1, the working fluid, i.e. the hydraulic fluid is preferably engine lubricant oil. Alternate embodiments of the invention would be equally effective using non-engine-oil hydraulic fluids or gases. For claim construction purposes therefore, the term hydraulic fluid should be construed to include any liquid (as well as a gas) by which the fuel injector and slave piston can both be actuated. 
     In order to keep the volumes between the slave piston  36  and the stroke limiter  34  filled with oil at all times, a low-oil-pressure valve  42 , continuously supplies fluid to the volume between the stroke limiter  34  and the slave piston  36  so as to make up oil volume therein which might be lost to leakage. 
     FIG. 2 shows a simplified timing diagram of the travel of the piston  12  depicted in FIG.  1  and an approximation of the intake valve operation, the hydraulically actuated fuel injector  26  operation, the exhaust valve  24  action and the displacement of the slave piston/stroke limiter assembly  34  and  36  as a function of piston  12  travel during the four different cycles of a four-stroke (four-cycle) internal combustion engine. As described above, the exhaust valve  24  can be made to open using the hydraulically-operated slave piston  36 . 
     During normal operation however, i.e., when the compression brake is not operating or actuated, intake and exhaust valve operation is achieved by a camshaft (not shown in FIG. 1) as those of skill in the art will appreciate. At time t 0 , which is identified by reference numeral  202 , the piston  12  begins a first intake stroke (identified by reference numeral  204 ) traveling downward in the cylinder  18 . During this first intake stroke  204 , a typical intake valve is opened (identified by reference numeral  210 ) by the engine&#39;s camshaft for a time period substantially between to and just before t 1 . While the intake valve is open, the piston  12  draws in or sucks in outside air for subsequent use in the ensuing compression stroke, (identified by reference numeral  212 ). At the conclusion of the intake stroke the camshaft rotates with the crankshaft causing the intake valve to close. 
     As the piston travels upward in the cylinder  16  during the compression stroke  214 , the fuel injector body  26  is opened, shown at time interval  216 , for a relatively short time period during which fuel is injected into the combustion chamber  18 . At time t 2 , the piston  12  begins its downward travel as part of the power stroke (identified by reference numeral  218 ) during which the piston  12  supplies mechanical power to the engine crankshaft. 
     At time t 3 , the first exhaust stroke begins (identified by reference numeral  220 ). Exhaust valve  24  is opened by the camshaft (not shown) during the time interval depicted by reference numeral  222 . The camshaft&#39;s rotation will cause the exhaust valve to close at a time  224  just prior to t 4 , which denotes the beginning of the second intake stroke  226 . 
     The second intake stroke  226  can be considered to begin when engine compression braking is desired. However, those of skill in the art will readily recognize that engine compression braking can be selected by an operator at any time and does not necessarily have to be synchronized to any one stroke of a four-cycle engine. 
     In the second intake stroke  226 , the camshaft opens the intake valve during time interval  228  and closes just before the time interval t 5 . During the ensuing compression stroke  230 , after an operator has activated engine compression braking, the fuel injector will be inhibited (as indicated by reference numeral  232 ) and no high pressure oil  28  will be routed to the fuel injector. The computer  50  will generate a diverter valve actuation signal  56  to the diverter valve  41 . The diverter will actuate and thereby divert the high pressure oil supply  28  from the fuel injector  26  to the stroke limiter  34  which will actuate the slave piston  34  (indicated by reference numeral  240 ). 
     The engine computer  50  generates an injector control valve signal  58  that is sent to the injector control valve  30  as before, however the additional generation of the diverter valve actuation signal  56  actuates the diverter valve  41  to divert the flow of high pressure oil or fluid from the fuel injector to the stroke limiter  34 . By diverting the high pressure oil supply  28  away from the fuel injector body  26  no fuel is injected into the combustion chamber  18  during the second compression stroke  230 . Instead, the high pressure fluid or oil  28  is routed to the stroke limiter  34  which in turn actuates the slave piston  36 . The slave piston  36  then acts on the exhaust valve  24  and opens the exhaust valve  24  (indicated by reference numeral  238 ) at the precise instant when the fuel injector would have opened had the engine been in normal operation mode instead of engine compression mode. The exhaust valve  24  opens when the slave piston  34  and stroke limiter  36  respond to the high pressure oil control pulse directed to them by the diverter valve  32  (indicated by reference numeral  240 ). 
     Prior art hydraulically actuated engine compression braking systems often required a separate high pressure engine compression braking oil supply in addition to a fuel injection high pressure oil supply. In the embodiment of the present invention, the existing fuel injection high pressure oil supply is simply redirected to a slave piston by redirecting or generating a hydraulic fluid signal or pressure pulse to a diverter valve. The diverted high pressure fluid then actuates a slave piston or stroke limiter/slave piston combination which opens the exhaust valve  24  at the optimum time at which the combustion chamber pressure should be purged to waste mechanical energy required to compress the cylinder contents. 
     While the preferred embodiment disclosed herein contemplates a stroke limiter  34  as a safety or control mechanism limiting the travel of the exhaust valve  24  as a result of the slave piston  36 , those skilled in the art will recognize that in instances where the volume of high pressure oil supply  28  delivered to the slave piston  36  can be closely controlled, the stroke limiter  34  may be redundant. Accordingly, at least one alternate embodiment contemplates an engine compression brake comprised of an oil pressure supply, diverter valve and the slave piston. Such an embodiment, as mentioned above, requires a more precise control of the fluid delivered to the slave piston so as to avoid forcing the exhaust valve  24  downward in an amount exceeding the safe clearance between the piston crown  20  and the limit of the exhaust valve travel. Stated alternatively, if the slave piston  36  travels too large a distance such that the exhaust valve exceed the safe clearance, the exhaust valve would travel too far into the combustion chamber  18  possibly striking the top of the piston crown resulting in severe damage to the engine. 
     The invention has been described and illustrated with respect to certain preferred embodiments by way of example only. Those skilled in that art will recognize that the preferred embodiments may be altered or amended without departing from the true spirit and scope of the invention. Therefore, the invention is not limited to the specific details, representative devices, and illustrated examples in this description. The present invention is limited only by the following claims and equivalents.