Abstract:
An exhaust brake for an internal combustion engine is disclosed. The exhaust brake includes a main valve and a bypass valve for restricting the flow of exhaust gas. The main valve may be selectively closed, while the bypass valve is biased into a closed position with a selective biasing force. Closing the main valve may cause exhaust back pressure to build against the bypass valve until the biasing force is overcome. When the biasing force is surpassed by the exhaust back pressure, the bypass valve opens to relieve the back pressure. The bypass valve closes when back pressure falls below the biasing force. The biasing force may be varied to operate the exhaust brake at a maximum back pressure for a given engine speed and/or engine condition. A method of operating the exhaust brake is also disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to exhaust brakes and their use independently or in conjunction with engine brakes. More specifically the invention relates to control of the flow of exhaust gas through an exhaust brake. 
     BACKGROUND OF THE INVENTION 
     Presently, it is not uncommon for vehicles, such as trucks and buses, to be equipped with an exhaust brake. Fundamentally, an exhaust brake need only comprise some means for restricting the flow of exhaust gas from an internal combustion engine. Restricting the exhaust gas increases the exhaust manifold pressure, i.e. “back pressure”. The exhaust manifold pressure may be used to oppose the motion of the engine pistons, converting the kinetic energy of the pistons into thermal energy. The engine and vehicle may be slowed by dissipating the thermal energy that is generated. Selective restriction of the flow of exhaust gas from the engine may therefore be used to selectively brake or not brake a vehicle. 
     An exhaust brake may be used to complement and/or enhance the braking achieved with compression release braking systems, and more specifically compression release systems that use exhaust gas recirculation (EGR). EGR may be used to increase the braking power of a compression release braking system. EGR returns exhaust gas to a cylinder from the exhaust manifold to boost the mass of gas in the cylinder for each compression release event. In order to carry out EGR in a compression release braking system, high exhaust gas back pressure (i.e. exhaust manifold pressure) is required to charge the cylinders with exhaust gas during the intake cycle. The increase in compression release braking realized from EGR is therefore related to the amount of exhaust gas that is returned to the cylinder, which in turn is related to the exhaust manifold pressure. Thus, the increased exhaust manifold pressure produced by an exhaust brake may be particularly useful for use in compression release braking systems that employ EGR. 
     Exhaust manifold pressure produced by an exhaust brake may also be useful in warming an engine during positive power operation. A cold engine may be more quickly warmed by placing the engine under load during positive power operation. Partially closing an exhaust brake during positive power creates an engine load because it makes it more difficult for the pistons to cycle in the cylinders. The exhaust brake creates this load by backing up warm exhaust gases in the engine and exhaust manifold, which also helps to warm the engine at an accelerated pace. 
     An exhaust brake may generate exhaust back pressure in the exhaust manifold. The back pressure in the exhaust manifold may be proportional to the speed of the engine. The faster the engine runs, the more frequently exhaust gas is discharged to the exhaust manifold, and consequently the higher the exhaust manifold pressure. The increased manifold pressure produced by an exhaust brake translates into decreased removal of heat from the engine. Engines cannot withstand unlimited amounts of exhaust manifold pressure or the accompanying heat. Accordingly, exhaust brakes have been designed so that the thermal limits of an engine are not exceeded when the engine is running at maximum speed. This type of exhaust brake design optimizes engine and exhaust braking only for one engine condition; maximum speed. Very frequently, however, engine braking and exhaust braking is carried out at less than maximum engine speed. As engine speed decreases, so does exhaust manifold pressure, and as a result the level of braking realized is decreased. 
     Some exhaust brakes have been designed to provide a fixed maximum level of back pressure over a range of engine speeds. In such exhaust brakes, control of the exhaust manifold pressure may be achieved by control of the restriction of exhaust gas flow by the exhaust brake. These exhaust brakes typically allow back pressure to build to a preset limit. Back pressure which exceeds the preset limit is relieved via a bypass around the closed exhaust brake. For example, U.S. Pat. No. 5,638,926 to McCrickard discloses an exhaust brake having a main tube and a bypass tube. During exhaust braking, the main tube is blocked with a rotatable valve. Back pressure is relieved by opening a bypass valve located at the far end of the bypass tube. Also see U.S. Pat. Nos. 4,750,459 and 4,682,674 to Schmidt, and U.S. Pat. No. 5,372,109 which disclose alternative bypass arrangements for an exhaust brake. 
     One restriction of other exhaust brakes is that they may be limited to providing one level of exhaust braking. For example, an exhaust brake, such as the one disclosed in the above-referenced patent to McCrickard, does not provide a means for varying the pressure level which results in opening the bypass valve. The bypass valve must be set to open at a back pressure which will not cause the engine temperature to exceed a critical level when the engine is running at maximum speed. As it turns out, however, this preset back pressure is less than the maximum back pressure which could be used at lower engine speeds. This preset is therefore only optimal for maximum engine speed. Accordingly, there is a need for exhaust brakes which provide variable levels of exhaust back pressure. 
     The present invention improves exhaust brake performance by selective variation of the back pressure at which a bypass valve opens. Variation of this pressure in response to one or more engine conditions can optimize the back pressure for a range of engine speeds. One way of determining the optimal back pressure for a given engine speed is to sense the temperature of the engine. The critical temperature of the engine may be tracked for a range of engine speeds by varying the bypass pressure so that engine temperature is a constant safe margin below critical temperature for each engine speed. Tracking the critical temperature in this way may result in selection of a moderate back pressure at the maximum engine speed, and a gradually increasing back pressure down through the speed range to the lowest engine speed. Variable back pressure through bypass control may enable tailoring the exhaust braking effect to optimize braking in response to the variation of conditions such as engine speed, exhaust pressure, engine temperature, EGR activation, and/or compression release braking activation. Control of the bypass pressure may be particularly beneficial in combination braking systems which may require high back pressure at low engine speeds and low back pressure at high engine speeds. 
     Bypass systems should also be constructed to remain operable under the harsh conditions of an exhaust brake. Exhaust gas typically contains carbon particles, water moisture, and other contaminants within it. Exposure of the moving parts of a bypass system to exhaust gas and its contaminants can cause the moving parts to rust and become gummed up with carbon. Bypass valves, such as the one disclosed in the above-referenced Schmidt patents, have been known to become inoperable because of the build up of contaminants on the moving parts in the system. Accordingly, there is also a need for an exhaust brake bypass system that is less prone to malfunction as a result of carbon, rust, or other contaminant build up on the moving parts of the bypass. 
     Furthermore, bypass systems should preferably be designed to avoid the exposure of heat sensitive elements of the bypass from being over exposed to high temperature exhaust gas. A bypass system may use a spring and/or electronic activators to open and close the bypass. These types of elements may not operate well under fluctuating or extreme temperature conditions. Accordingly, there is a need for an exhaust brake with a bypass activator that has an acceptable exposure to high temperature exhaust gas. 
     One of the designs described herein is a bolt-on bypass circuit which may be very effective at reducing the exposure of the bypass spring and/or electronic activators to exhaust gas temperatures. A bolt-on bypass may also add the benefit of manufacturability which allows for a fixed flow area device or a variable area device with minimal manufacturing set up changes. A bolt-on bypass may be used with an exhaust brake that is pre-configured to accept the bypass. The exhaust brake may be provided originally with two or more plugged openings. The openings may be unplugged when a bolt-on bypass is added to provide exhaust gas flow to and from the bypass. 
     OBJECTS OF THE INVENTION 
     It is therefore an object of the present invention to provide an exhaust brake with a bypass around a main valve in the exhaust brake. 
     It is another object of the present invention to provide an exhaust brake which provides variable levels of exhaust back pressure. 
     It is a further object of the present invention to provide selective activation of a bypass valve in an exhaust brake. 
     It is still another object of the present invention to shield a means for operating a bypass valve in an exhaust brake from exhaust gas born contaminants. 
     It is yet another object of the present invention to provide selective activation of a bypass valve in an exhaust brake responsive to an engine condition. 
     It is still yet another object of the present invention to provide an exhaust brake that is useful as a warm up device for an engine. 
     It is yet a further object of the present invention to provide an exhaust brake that makes use of bolt-on bypass system. 
     It is still a further object of the present invention to provide a method of operating an exhaust brake that is responsive to the thermal loading of an engine. 
     Additional objects and advantages of the invention are set forth, in part, in the description which follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention. 
     SUMMARY OF THE INVENTION 
     In response to the foregoing challenge, Applicants have developed an innovative, economical exhaust brake comprising: a main exhaust passage; means for selectively blocking the flow of exhaust gas through the main exhaust passage; a bypass exhaust passage communicating with said main exhaust passage and providing for the flow of exhaust gas around the means for selectively blocking; means for selectively closing the bypass exhaust passage; means for biasing the means for selectively closing in a closed position; and means for varying a biasing force applied by the means for biasing to the means for selectively closing. 
     Applicants have also developed an innovative and economical exhaust brake comprising a housing containing a main valve, a bypass passage provided through the main valve, a bypass valve for closing the bypass passage, and the improvement comprising means for selectively opening the bypass valve responsive to an engine condition value. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated herein by reference, and which constitute a part of this specification, illustrate certain embodiments of the invention, and together with the detailed description serve to explain the principles of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view in elevation of an exhaust brake embodiment of the invention. 
     FIG. 2 is a cross-sectional view in elevation of a second exhaust brake embodiment of the invention. 
     FIG. 3 is a cross-sectional view in elevation of a third exhaust brake embodiment of the invention. 
     FIG. 4 is a view of section B—B of the exhaust brake shown in FIG.  5 . 
     FIG. 5 is a view of section A—A of the exhaust brake shown in FIG.  6 . 
     FIG. 6 is a side view in elevation of a fourth exhaust brake embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to a preferred embodiment of the present invention, an example of which is illustrated in the accompanying drawings. A preferred embodiment of the present invention is shown in FIG. 1 as exhaust brake  10 . 
     In a preferred embodiment, the exhaust brake  10  comprises a main valve  100 , a bypass valve  200 , and control system  300 . The main valve housing  110  may have a passage  112  extending therethrough, and an inlet  114  and an outlet  116 . The inlet  114  may be connected to an upstream exhaust conduit  400  leading from an engine exhaust manifold (not shown). The outlet  116  may be connected to the remainder of a vehicle exhaust system  450 , which may include a muffler and exhaust pipe (not shown). 
     The main valve  100  also includes a gate  130  which may be used to selectively block and unblock the passage  112 . The gate  130  may have an axle  140  running through a central region of the gate. The axle  140  may extend from the gate  130  through the main valve housing  110  to an actuator (not shown) outside of the housing. The actuator may comprise a solenoid, air, vacuum, hydraulic, electronic, or other type of actuation device. The actuator may be linked to the gate  130  so that it can rotate the gate in the passage  112  between blocking and unblocking positions. 
     The gate  130  is shown to be a butterfly valve in FIG.  1 . In alternative embodiments, however, the gate  130  may be provided by a sliding gate, flapper, iris type, rotary, or any other means for selectively blocking the flow of exhaust gas through the passage  112 . 
     The main valve  100  may have two ports  118  and  120  in the housing  110  at upstream and downstream locations relative to the gate  130 . The ports  118  and  120  provide communication between an inlet  212  and an outlet  214  of the bypass valve housing  210 . 
     A bypass restrictor  220  is provided in the exhaust gas passage  216  extending through the housing  210 . The bypass restrictor may include a conical shaped stopper  222  and a mating conical shaped valve seat  224  for the stopper. The stopper  222  may be biased in a closed position against the valve seat  224  by a spring  226 . The spring  226  is compressed, and as a result transmits a biasing force to the stopper  222  through plate  228  and rod  230 . A seal  232  may be provided around the rod  230  to prevent exposure of the spring  226  to exhaust gas and to provide thermal insulation of the spring. The spring  226 , the plate  228 , and the portion of the rod  230  which extends past the seal  232  may be enclosed in a separate housing or bracket  234 . 
     The spring  226  provides a means for biasing the stopper  222  in a closed position. The biasing force applied by the spring  226  to the stopper may be varied using control system  300 . The control system  300  may include an actuator  310  attached to the back of the bracket  234 . The actuator  310  may be a vacuum, air, hydraulic, or an electronic actuator. The actuator  310  may have a shaft  312  connected to the plate  228 . The actuator  310  may be controlled by controller  320  which may receive control instructions from a computer  330  used to determine the appropriate biasing force for the stopper  222 . The computer  330  may determine the appropriate biasing force based upon information received from sensors  340 . Sensors  340  may be used to sense conditions of the engine/vehicle  500 , such as engine speed, exhaust gas pressure, engine temperature, exhaust gas temperature, exhaust gas recirculation activation, exhaust brake activation, foundation brake application, compression release braking activation, vehicle speed, cylinder pressure, intake manifold pressure, fuel rate, throttle position, percent of engine load, ambient temperature, air fuel ratio, vehicle start up, and head rejection to coolant Btu/min. 
     When the exhaust brake  10  is activated, the gate  130  may be rotated into a blocking position, as shown in FIG.  1 . Exhaust gas flows into the main valve  100  through inlet  114  and is blocked by the gate  130 . The blocked exhaust gas is diverted to the bypass valve  200  and flows through port  118 , bypass inlet  212 , and bypass exhaust gas passage  216 . As exhaust gas is diverted to the bypass valve  200 , pressure builds against the stopper  222 , which is biased closed by the spring  226  against the valve seat  224 . Eventually the exhaust back pressure on the stopper  222  may build to a level sufficient to overcome the force of spring  226 . The force from spring  226  is transmitted by rod  230  which may have a length sufficient to remove the spring from excessive thermal loading. At this point the stopper  222  is pushed in, away from the valve seat  224 , such that the exhaust gas flows past the stopper to the downstream side of the main valve  100 . As exhaust gas flows to the downstream side of the main valve  100 , the exhaust back pressure asserted against the stopper  222  falls until the spring  226  can close the stopper. 
     The biasing force applied by the spring  226  to the stopper  222  may be varied to control the exhaust back pressure level at which the stopper will be opened. The biasing force may equal the maximum exhaust back pressure the engine valve train can accommodate. The biasing force may change by using the actuator  310  to provide a pushing or pulling biasing force on the plate  228  through shaft  312 . If wanted, the actuator  310  may be used to completely overcome the force of the spring  226  and open the stopper  222  on command. In this manner, the actuator  310  can be used to increase the exhaust back pressure level required to open stopper  222  with decreasing engine speed. Using sensors  340 , actuator  310  can be used to set the exhaust back pressure level that will open the stopper  222  at the maximum level it can be without exceeding the temperature and/or exhaust manifold pressure constraints of the engine  500 . 
     With regard to FIG. 2, in which like elements are identified with like reference numerals, in an alternative embodiment of the invention the biasing force on the plate  228  is controlled mechanically. This may be done by connecting passage  216  in the bypass valve housing  210  to the variable control housing  600  with passage  602 . The variable control housing can be attached to the bracket  234  or remotely mounted. Within the control housing  600  may be a plunger  604  that is used to control a variable pressure device  606 . The variable pressure device  606  regulates the supply pressure  608  to the pneumatic actuator  612  through connector  610 . The pressure supplied from supply  608  to the pneumatic actuator  612  may be proportional to the displacement of plunger  604  within control housing  600 . 
     By increasing or decreasing the pressure to the pneumatic actuator  612 , the biasing force may be increased or decreased to open the bypass valve  200 . As the exhaust back pressure increases, the plunger  604  may be pushed in and the pneumatic pressure to the actuator  612  increased. The increased pneumatic pressure acts to pull the bypass valve  200  open against the closing force of the spring  226 . If the pneumatic pressure becomes great enough, the opening force of the actuator  612  may overcome the closing force of the spring  226  and the bypass valve will open. Opening the bypass valve  200  may reduce the pressure on the plunger  604  which in turn may reduce the opening force of the actuator  612 . When the opening force is sufficiently reduced, the bypass valve  200  may close under the force of the spring  226 . 
     In alternative embodiments, the actuator  612  may be responsive to electrical, hydraulic, a or mechanical actuation as opposed to pneumatic actuation. For example, the actuator  612  may comprise a solenoid that opens the bypass valve  200  in response to a predetermined displacement of the plunger  604 . As an alternative to the linear displacement provided by a solenoid, the actuator  612  may comprise a ball screw that provides opening through an angular displacement. It is also appreciated that the predetermined displacement of the plunger that results in the bypass valve being opened may be varied as called for by operation of the engine and/or vehicle. 
     With regard to FIG. 3, in which like elements are identified with like reference numerals, an alternative bypass restrictor  220  is shown. The exhaust brake functions the same as the exhaust brake shown in FIG.  1 . The differences between the two exhaust brakes (that in FIG. 1 and that in FIG. 3) arise from the use of a different type of bypass valve. In FIG. 3, the bypass restrictor  220  is provided using a butterfly valve  223  rather than a conical stopper (shown in FIG.  1 ). The butterfly valve  223  may be rotatable on an axle  225  which extends through the butterfly valve and out of the housing  210 . The axle  225  may be connected to a means for biasing  226  the butterfly valve via a lever arm  236 . Control over the force biasing the butterfly valve  223  is realized using control system  300  which may include actuator  310 . 
     With regard to FIG. 4, in which like elements are identified with like reference numerals, an alternative embodiment of the invention is shown. In this embodiment, the bypass valve  200  is provided within the main valve  100  using a selectively opened passage  216  through the gate  130  in the main valve. The bypass valve comprises a stopper  222  which fits into passage  216  and seats against a valve seat  224  provided along the wall of passage  216 . The stopper  222  may have a conical shape so that it is less likely to jam against the mating valve seat  224 . The stopper  222  may be attached by a screw, weld, or other attachment means  250  to a flange  241  which extends from a ring  240 . 
     The ring  240  is coaxial with the axle  140  on which the gate  130  is rotated. During operation of the bypass valve  200 , the stopper  222  may be pushed out of contact with the valve seat  224  causing the flanges  241  to rotate relative to the axle  140  and the gate  130 . Contact between the flanges  241  and the gate  130  when the bypass valve is closed, cause the ring  240  to rotate with the gate  130  and the axle  140  when the main valve is opened. 
     With reference to FIG. 5, the gate  130  is viewed from a downstream location. FIG. 5 is related to FIG. 4 in that it is the source of section B—B shown in FIG.  4 . The ring  240  does not extend into the main valve passage  112 , however the flanges  241  do extend into this passage. The ring  240  extends out of the housing  110  and is connected to a bypass valve arm  244 . The axle  140  passes through a bore provided in the ring  240 . The axle  140  may be received at a boss  142  at a distal end, and connected to a main valve arm  144  at a proximal end. 
     With reference to FIG. 6, the main valve arm  144  and the bypass valve arm  244  are shown. The main valve arm  144  may be connected near its midpoint to a main valve actuator  600 . Linear motion provided by the actuator  600  is converted by means of the main valve arm into a rotational movement for application to the axle  140 . The gate  130  in the main valve may be opened by extending the actuator  600  to rotate the axle  140  in a clockwise direction. Rotation of the axle  140  and gate  130  causes the ring  240  and bypass valve arm  244  to rotate in a clockwise direction due to contact between the gate  130  and the flanges  241 . The angular separation of the main valve arm  144  and the bypass valve arm  244  is, thus, not affected by the opening and closing of the gate  130  in the main valve. 
     With reference to FIGS. 4-6, the stopper  222  may be biased in a closed position against the valve seat  224  by a tension spring  226  linking the end  146  of the main valve arm with the end  246  of the bypass valve arm. The spring  226  is under tension, and as a result transmits a force through bypass valve arm  244 , ring  240 , and flange  241  that biases the stopper  222  into a closed position against the valve seat  224 . 
     The biasing force applied by the spring  226  to the stopper may be varied using adjustment nut  248 . A control system  300  may be provided to adjust the nut  248  during exhaust braking or to activate the lever  244 . The control system  300  may include the features discussed in relation to the embodiment shown in FIG.  1 . 
     With continued reference to FIGS.  4 — 6 , when the gate  130  is closed (as shown in FIG. 4) exhaust gas flows into the main valve  100  through inlet  114  and is blocked by the gate  130 . As pressure builds against the stopper  222 , which is biased closed by the spring  226  against the valve seat  224 . Eventually the exhaust back pressure on the stopper  222  may build to a level sufficient to overcome the force of spring  226 . At this point the stopper  222  is pushed in, away from the valve seat  224 , such that the exhaust gas flows past the stopper to the downstream side of the main valve  100 . As exhaust gas flows to the downstream side of the main valve  100 , the exhaust back pressure asserted against the stopper  222  falls until the spring  226  can close the stopper. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the construction, configuration, and/or operation of the present invention without departing from the scope or spirit of the invention. For example, in the embodiments mentioned above, means other than a spring, such as hydraulic, electronic, air, vacuum, etc., may be used to bias the bypass valve stopper into a closed position, without departing from the scope of the invention. Further, various changes may be made to the shape of the main valve and bypass valve housing(s), and the type of gate used to block the main valve, without departing from the scope of the invention. The invention also should not be limited to application in aftermarket exhaust brakes. Thus, it is intended that the present invention cover the modifications and variations of the invention provided they come within the scope of the appended claims and their equivalents.