Abstract:
An exhaust brake is incorporated with an internal combustion engine. The brake comprises an exhaust rocker arm actuated by an exhaust cam for operating an exhaust valve; a brake rocker arm actuated by a brake cam; a first contacting unit held by either one of the exhaust and brake rocker arms; a second contacting unit held by the other of the exhaust and brake rocker arms. The second contacting unit is contactable with the first contacting unit when an exhaust braking is needed. Only when the brake rocker arm is actuated by the brake cam upon need of the exhaust braking, there induces the contact between the second and first contacting units, which provides an integral action of the exhaust and brake rocker arms thereby to actuate the exhaust valve for establishing the exhaust braking.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to brakes provided by automotive internal combustion engines, and more particularly to engine brakes of a compression release type, that is, usually called exhaust brakes. 
     2. Description of the Prior Art 
     The compression release type exhaust brake is a brake wherein each exhaust valve of the engine is crack opened at the end of each compression stroke when the brake is in operation. That is, when the exhaust valve is crack opened at the end of the compression stroke, part of compressed gas in the combustion chamber is exhausted. Thus, in the subsequent expansion stroke, repulsion applied to the piston is lowered due to reduction of the gas in the combustion chamber. Furthermore, since, after effecting the crack opening, the exhaust valve is kept closed during the expansion stroke, the combustion chamber produces a resistance against the movement of the piston toward a lower dead center. Thus, in the expansion stroke, the force for rotating the crankshaft in a normal direction is reduced resulting in that the engine rotation is lowered or braked. 
     In order to appropriately operate each exhaust valve in the above-mentioned manner, Japanese Patent First Provisional Publication 9-184407 proposes a mechanism including an exhaust rocker arm which is swingably actuated by an exhaust cam for operating the exhaust valve, a brake rocker arm which is swingably actuated by a brake cam and a coupling structure through which the two rocker arms are operatively coupled. That is, under normal operation of the engine, the exhaust valve is actuated by only the exhaust rocker arm, and upon need of the exhaust braking, the coupling structure couples the two rocker arms causing the exhaust valve to be actuated by the brake rocker arm as well as the exhaust rocker arm. 
     However, due to its inherent construction, the above-mentioned conventional exhaust brake fails to exhibit a satisfied function. That is, in this conventional exhaust brake, during the operation, the associated engine is subjected to a marked change in inertia mass of a valve actuating mechanism between two cases, one being a brake case wherein the brake rocker arm is in operation for effecting the exhaust braking and the other being a normal case wherein the brake rocker arm is not in operation. Such marked change tends to induce a non-smoothed movement of the exhaust valve. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an exhaust brake which is free of the above-mentioned drawback. 
     According to the present invention, there is provided an exhaust brake incorporated with an internal combustion engine. The exhaust brake comprises an exhaust rocker arm actuated by an exhaust cam for operating an exhaust valve; a brake rocker arm actuated by a brake cam; a first contacting unit held by either one of the exhaust and brake rocker arms; a second contacting unit held by the other of the exhaust and brake rocker arms, the second contacting unit being contactable with the first contacting unit when an exhaust braking is needed; and a coupling structure which, only when the brake rocker arm is actuated by the brake cam upon need of the exhaust braking, induces the contact between the second and first contacting units to provide an integral action of the exhaust and brake rocker arms thereby to actuate the exhaust valve for establishing the exhaust braking. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a plan view of an exhaust brake according to the present invention, showing a condition wherein a second contacting unit is in operation; 
     FIG. 2 is a sectional view taken along the line “A—A” of FIG. 1; 
     FIG. 3 is a view similar to FIG. 2, but showing a condition wherein the second contacting unit is not in operation; 
     FIG. 4 is a sectional view of the exhaust brake practically incorporated with a brake cam and a brake rocker arm, showing a condition wherein with the second contacting unit being in operation, an exhaust valve is slightly opened for effecting the exhaust braking; 
     FIG. 5 is a view similar to FIG. 4, but showing a condition wherein with the second contacting unit being in operation, the brake cam pivots the brake rocker arm; and 
     FIG. 6 is a view similar to FIG. 4, but showing a condition wherein with the second contacting unit being in operation, an exhaust cam pivots an exhaust rocker arm. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, the present invention will be described in detail with reference to the accompanying drawings. 
     For ease of understanding, directional terms, such as, right, left, up, down, rightward, leftward and the like are used in the description. However, these terms are to be understood with respect to the drawings on which corresponding parts or structures are illustrated. 
     Referring to the drawings, particularly FIG. 4, there is shown an exhaust brake of the present invention practically incorporated with parts of an internal combustion engine. 
     In the drawing, designated by numeral  1  is an exhaust rocker arm, and  2  is a brake rocker arm. These two arms  1  and  2  are incorporated with each combustion cylinder of an internal combustion engine. These two rocker arms  1  and  2  are pivotally supported by a rocker shaft  3 . 
     As is seen from FIG. 6, a right end la of the exhaust rocker arm  1  is formed with a cam follower  5  which contacts an exhaust cam  4 . While, a left end  1   b  of the exhaust rocker arm  1  is formed with a screw supporting portion  8  equipped with an adjusting screw  9  which contacts a valve stem  7  (see FIG. 4) of an exhaust valve  6  incorporated with an exhaust passage  36  formed in a cylinder head  35 . A nut  10  is engaged with the adjusting screw  9  for adjusting a space between the adjusting screw  9  and the valve stem  7 . 
     As is understood from FIGS. 1 and 6, the brake rocker arm  2  is identical in shape to a right portion  1   a  of the exhaust rocker arm  1 . More specifically, the brake rocker arm  2  and the right portion  1   a  of the exhaust rocker arm  1  are the same in shape. A right end  2   a  of the brake rocker arm  2  is formed with a cam follower  12  which contacts a brake cam  11 . 
     Referring back to FIG. 4, the rocker shaft  3  is formed with an axially extending oil gallery  13  and a radially extending bore  14  which extends from the oil gallery  13 . 
     The exhaust cam  4  and the brake cam  11  are formed on axially spaced portions of a common cam shaft  15  and arranged to operatively contact the respective cam followers  5  and  12  of the exhaust rocker arm  1  and the brake rocker arm  2 , as is seen from FIG.  5 . 
     In FIG. 4, designated by numeral  16  is a first contacting unit supported by the brake rocker arm  2 . As shown, the first contacting unit  16  is provided on an upwardly projected portion (no numeral) of the brake rocker arm  2 . The first contacting unit  16  comprises an adjusting screw  17  axially movably held by the projected portion and a nut  18  engaged with the adjusting screw  17 . Thus, by rotating the screw  17  about its axis, an effective length of the same can be adjusted. As shown, the adjusting screw  17  extends in a direction perpendicular to the axis of the s rocker shaft  3 . 
     Designated by numeral  19  is a second contacting unit provided on the exhaust rocker arm  1 . The second contacting unit  19  comprises a lever  20  which can contact a head of the adjusting screw  17  of the first contacting unit  16 . A hydraulic plunger  21  is operatively held in the exhaust rocker arm  1 , which actuates the lever  20 . As shown, the lever  20  is pivotally connected at its generally middle portion to the exhaust rocker arm  1  by means of a pin  22 . The hydraulic plunger  21  is axially movably received in a cylindrical bore  23  formed in the exhaust rocker arm  1 . 
     A small spherical left end  20   a  of the lever  20  is in contact with an upper end or head of the hydraulic plunger  21 , so that up-and-down movement of the plunger  21  in the cylindrical bore  23  induces a pivotal movement of the lever  20  about the pin  22 . The spherical shape of the left end  20   a  reduces or minimizes a frictional force inevitably produced when contacting the hydraulic plunger  21 . A right end  20   b  of the lever  20  is contactable with the head of the adjusting screw  17 . As shown, the right end  20   b  of the lever  20  is shaped convexly. Due to this convex shape, slipping movement of the right end  20   b  relative to the head of the adjusting screw  17  is smoothly carried out. 
     Into the cylindrical bore  23 , there is led an operation oil from the oil gallery  13  through the bore  14  formed in the rocker shaft  3  and an oil passage  24  formed in the exhaust rocker arm  1 . In an upper portion of the cylindrical bore  23 , there is slidably disposed a hollow plunger  26  whose bottom is in contact with the small spherical left end  20   a  of the lever  20 . A return spring  25  is put in the recess of the plunger  26  to press the plunger  26  against the spherical left end  20   a , so that the spherical left end  20   a  of the lever  20  is biased toward the hydraulic plunger  21 . As shown, the bottom of the plunger  26  that is in contact with the spherical left end  20   a  of the lever  20  is shaped convexly. Due to this convex shape, relative slipping movement between the plunger  26  and the left end  20   a  is smoothly achieved. 
     In FIG. 4, designated by numeral  29  is a coil spring which is disposed between the exhaust rocker arm  1  and the brake rocker arm  2  for biasing these two rocker arms  1  and  2  in opposite directions. The coil spring  29  is put in a blind bore  30  formed in the right end portion  2   a  of the brake rocker arm  2 . The blind bore  30  is communicated with the atmosphere through a small passage  33  formed in the brake rocker arm  2 . A hollow plunger  31  is put on the coil spring  29  having an upper portion of the spring  29  received in the hollow thereof. A convex head portion of the plunger  31  is in contact with a flat lower surface of an arm  32  extending from the exhaust rocker arm  1 . Due to the force of the coil spring  29 , the exhaust and brake rocker arms  1  and  2  are biased to pivot about the rocker shaft  3  in counterclockwise and clockwise directions respectively, so that the second contacting unit  19  on the exhaust rocker arm  1  and the first contacting unit  16  of the brake rocker arm  2  are biased away in opposite directions, that is, in the directions to be separated from each other. 
     Designated by numeral  37  is an oil feeding passage through which the oil is fed to the oil gallery  13  from an oil pan  38 . An oil pump  39  and a control valve  40  are arranged in the oil feeding passage  37 . The control valve  40  is controlled by a control unit  41  for adjusting the amount of oil fed to the oil gallery  13 . 
     In the following, operation will be described with reference to the drawings. 
     Under normal operation of the engine wherein the exhaust braking is not needed, the second contacting unit  19  does not operate. That is, under this condition, the second contacting unit  19  assumes a rest position as shown in FIGS. 3 and 5. Thus, even when the brake rocker arm  2  is pivoted by the brake cam  11  (see FIG.  5 ), the pivoting movement of the brake rocker arm  2  is not transmitted to the exhaust rocker arm  1 . That is, under such normal condition, the exhaust valve  6  is actuated by only the exhaust rocker arm  1  pivoted by the exhaust cam  4 . In other words, in this normal condition of the engine, the exhaust rocker arm  1  and the brake rocker arm  2  are not coupled. 
     More specifically, as is seen from FIG. 5, in such normal condition, the hydraulic plunger  21  assumes its lowermost position due to shortage of oil fed to the cylindrical bore  23 . Thus, the lever  20  is forced to assume an inclined inoperative position by the force of the return spring  25 . Thus, even if the adjusting screw  17  is moved leftward due to counterclockwise pivoting of the brake rocker arm  2 , the head of the screw  17  does not contact the right end  20   b  of the lever  20 . 
     While, under a brake condition of the engine wherein the exhaust braking is needed, the second contacting unit  19  operates. That is, under this condition, the second contacting unit  19  assumes a work position as shown in FIG. 2,  4  and  6 . Thus, when the brake rocker arm  2  is pivoted by the brake arm  11  (see FIG.  4 ), the pivoting movement of the brake rocker arm  2  is transmitted to the exhaust rocker arm  1  through the operated second contacting unit  19 . That is, under such brake condition, the exhaust valve  6  is actuated by both the exhaust rocker arm  1  and the brake rocker arm  2 . 
     More specifically, as is understood from FIG. 4, when, upon receiving an instruction signal from the control unit  41 , the control valve  40  works to increase the amount of oil fed to the oil gallery  13 , the pressure in the cylindrical bore  23  is increased and thus the hydraulic plunger  21  is moved up together with the spherical left end  20   a  of the lever  20  against the force of the return spring  25 . Thus, the lever  20  is pivoted clockwise and finally assumes the operative position as shown. 
     In this operative condition of the second contacting unit  19 , the head of the adjusting screw  17  can abut against the right end  20   b  of the lever  20  when the brake rocker arm  2  is pivoted counterclockwise by the lobe of the brake cam  11 . 
     However, as is seen from FIG. 6, while the cam follower  12  of the brake rocker arm  2  is contacting a portion other than the lobe of the brake cam  11 , the head of the adjusting screw  17  is away from the right end  20   b  of the lever  20  keeping a predetermined space therebetween. It is to be noted that the space can be adjusted by turning the adjusting screw  17 . It is further to be noted that, as has been mentioned hereinabove, due to the force of the coil spring  29 , the adjusting screw  17  on the brake rocker arm  2  is biased away from the lever  20  on the exhaust rocker arm  1 . 
     Accordingly, as is seen from FIG. 6, for a time when with the second contacting unit  19  being in operation, the head of the adjusting screw  17  is away from the right end  20   b  of the lever  20 , the exhaust rocker arm  1  is actuated by only the exhaust cam  4 . That is, for that limited time, the exhaust valve  6  is controlled by only the exhaust cam  4 . In other words, during this time, the movement of the exhaust valve  6  is the same as that achieved under normal operation of the engine wherein the exhaust braking is not needed. 
     That is, for the time when with the second contacting unit  19  being in operation for inducing the exhaust braking, the head of the adjusting screw  17  is away from the right end  20   b  of the lever  20 , the exhaust rocker arm  1  and the brake rocker arm  2  are independent from each other and thus the inertia mass of the valve actuating mechanism is substantially equal to that provided under the normal operation of the engine. 
     While, when with the second contacting unit  19  being in operation, the lobe of the brake cam  11  is brought into abutment with the cam follower  12  of brake rocker arm  2 , the head of the adjusting screw  17  abuts against the right end  20   b  of the lever  20  as is seen from FIGS. 1 and 2. Upon this, the brake rocker arm  2  and the exhaust rocker arm  1  become coupled, so that the counterclockwise pivoting of the brake rocker arm  2  by the lobe of the brake cam  11  is transmitted to the exhaust rocker arm  1 . 
     Thus, as is seen from FIG. 4, the exhaust valve  6  is forced to open slightly or instantly for effecting the exhaust braking. 
     Of course, also in the present invention, suitable measures are employed for inducing a crack or instant opening of the exhaust valve  6  at the end of the compression stroke. 
     In the following, advantages of the present invention will be briefly described. 
     First, the inertia mass of the valve actuating mechanism at a normal exhaust period when the exhaust cam  4  swings the exhaust rocker arm  1  to open the exhaust valve  6  shows substantially no change between the two cases, one being a case wherein the exhaust braking is needed and the other being a case wherein the exhaust braking is not needed. In other words, the exhaust brake of the present invention has substantially no influence on the movement of the exhaust valve  6  at the normal exhaust period. 
     Second, since the coupling of the brake rocker arm  2  and the exhaust rocker arm  1  is achieved by only contacting the adjusting screw  17  to the lever  20 , there is no need of using a complicated coupling structure. Thus, the exhaust brake of the present invention is readily and economically manufactured. 
     Third, due to usage of the adjusting screw  17 , the effective distance between the adjusting screw  17  and the lever  20  is adjustable, which can control the operation timing of the exhaust braking. 
     Fourth, due to nature of the hydraulic plunger  21 , the second contacting unit  19  can exhibit a responsive operation. 
     Fifth, due to provision of the coil spring  29  which biases the two rocker arms  1  and  2  in opposite directions, undesired play of the brake rocker arm  2 , which would occur when the coupled connection therebetween is not established, is assuredly suppressed. 
     In the following, modifications of the present invention will be described. 
     If desired, contrary to the above-mentioned arrangement, the adjusting screw  17  and the second contacting unit  19  may be mounted to the exhaust and brake rocker arms  1  and  2 , respectively. 
     Furthermore, if desired, the screw supporting portion  8  of the exhaust rocker arm  1  may be equipped with a lash controlling device for adjusting contact between the adjusting screw  9  and the valve step  7 . 
     The entire contents of Japanese Patent Application P10-367334 (filed Dec. 24, 1998) are incorporated herein by reference. 
     Although the invention has been described above with reference to a certain embodiment of the invention, the invention is not limited to the embodiment. Various modifications and variations of the embodiment will occur to those skilled in the art, in light of the above teachings.