Engine brake control system
BACKGROUND OF THE INVENTION 
     Field of the invention 
     The present invention relates to braking systems for automobiles, and more particularly to an engine brake control system of the type in which a cut-off valve is provided within an exhaust pipe of an internal combustion engine to block the exhausted gas in response to the release of an accelerator pedal to thereby increase the engine braking effect. 
     In the engine brake control system of this kind, a vacuum motor is generally provided to open and close the cut-off valve in response to operation of the accelerator pedal. Accordingly, it is required that the vacuum motor is swiftly activated in response to operation of the accelerator pedal to ensure the operation of the control system. 
     SUMMARY OF THE INVENTION 
     The primary object of the present invention is, therefore, to provide an engine brake control system wherein first and second chambers facing a spring loaded diaphragm piston in the vacuum motor are communicated with a vacuum source during depression of the accelerator pedal to open the cut-off valve in such a manner that only the second chamber is communicated with the atmospheric pressure in response to release of the accelerator pedal to swiftly operate the piston so as to close the cut-off valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more readily apparent from the following description of the preferred embodiment with reference to the accompanying drawings forming a part of the specification wherein 
     FIG. 1 is a diagrammatic view showing an engine brake control system in accordance with the present invention; 
     FIG. 2 is an enlarged vertical sectional view of a vacuum motor shown in FIG. 1; and 
     FIG. 3 is a side view of a link assembly shown in FIG. 2, looking in the direction of the arrow III. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and in particular FIG. 1, there is illustrated a portion of an exhaust pipe 10 of an internal combustion engine, a vacuum pump 11 driven by the engine, and an electrically operated switch-over valve 12. A suction port of the vacuum pump 11 is connected by way of a pipe P 1  to a first port 12a of the switch-over valve 12 through an orifice 13. Pivoted within the exhaust pipe 10 is a cut-off valve 14 in the form of a butterfly valve which is actuated by a vacuum motor 20 by way of a link assembly 15. 
     As shown in FIGS. 2 and 3, the vacuum motor 20 comprises a housing 21 and a diaphragm piston assembly 22 reciprocable within the housing 21. The housing 21 is mounted on a bracket member 25 which is secured to one side of the exhaust pipe 10. The housing 21 is provided thereon with a first port 21a and a second port 21b, the former being connected by way of a pipe P 2  to the pipe P 1  between the orifice 13 and the switch-over valve 12 and the latter being connected by way of a pipe P 3  to a second port 12b of the switch-over valve 12 (see FIG. 1). 
     The diaphragm piston assembly 22 includes a diaphragm 22a hermetically secured at its outer periphery to the inner peripheral wall of the housing 21 and an operation rod 22b fixed at its upper end with the central portion of the diaphragm 22a by way of protector plates 22c, 22d and 22e. Thus, the interior of the housing 21 is subdivided by the diaphragm 22a into an upper chamber R 1  in communication with the first port 21a and a lower chamber R 2  in communication with the second port 21b. The diaphragm piston assembly 22 is biased downwardly toward the lower chamber R 2  by means of a compression coil spring 23 interposed between the inner wall of the housing 21 and the protector plate 22c. The operation rod 22b is extended outwardly through a seal member 24 from the housing 21 and connected at its lower end with the link assembly 15. The moving stroke of the rod 22b is restricted by engagement of an arm 15a of the link assembly 15 against a pair of stoppers 26 and 27 secured to a flange of the bracket member 25. 
     The switch-over valve 12 is to be energized in response to closing of a manual switch S 1  and a normally closed accelerator switch S 2 . The manual switch S 1  is installed on a portion of a steering column assembly or an instrument panel of the vehicle. The accelerator switch S 2  is arranged to be opened by depression of an accelerator pedal and to be closed upon release of the accelerator pedal. 
     With the switch-over valve 12, the first port 12a is communicated with the second port 12b during deenergization of the valve 12 and the second port 12b is communicated with the third port 12c upon energization of the valve 12. The third port 12c is in open communication with the atmospheric air through a pipe P 4  and an air cleaner 16. Furthermore, a vacuum tank 17 for a conventional brake booster is connected through a check valve 17a to the pipe P 1  between the orifice 13 and the vacuum pump 11, and an indication lamp 18 is provided to be lighted by closing of the manual switch S 1 . 
     In operation of the engine brake control system having the above-mentioned construction, when the manual switch S 1  is in open during travelling of the vehicle, the switch-over valve 12 is deenergized regardless of the operation of the accelerator switch S 2  to connect the first port 12a with the second port 12b. Under this mode, the upper and lower chambers R 1  and R 2  in the vacuum motor 20 are respectively communicated with the vacuum pump 11 to be applied negative pressure therein. As a result, the diaphragm piston assembly 22 is in the downward stroke end due to biasing force of the coil spring 23, as shown in FIGS. 2 and 3, thereby to fully open the cut-off valve 14, as shown in FIG. 1. 
     When the manual switch S 1  is closed under the above-mentioned condition, the lamp 18 is lighted and teh switch-over valve 12 may be electrically controlled in response to the operation of the accelerator switch S 2 . Thereafter, when the accelerator pedal is released during the travelling of the vehicle to cause the engine braking operation, the accelerator switch S 2  is closed to energize the switch-over valve 12. Upon energization of the switch-over valve 12, the second port 2b is communicated with the third port 12c so that the atmospheric pressure is swiftly applied into the lower chamber R 2  of the vacuum motor 20 by way of the air cleaner 16 and the pipes P 3  and P 4 . Then, the diaphragm piston assembly 22 is moved up against the spring 23 due to a difference in pressure between the upper and lower chambers R 1  and R 2  until the arm 15a of the link assembly 15 is engaged with the stopper 26. This closes the cut-off valve 14 to block the gas exhausted from the engine. Thus, the braking effect is instantly increased by back pressure applied to the engine in response to closing of the cut-off valve 14. 
     When the accelerator pedal is depressed again to accelerate the vehicle, the accelerator switch S 2  is opened and, in turn, the switch-over valve 12 is deenergized to connect the first port 12a to the second port 12b. Then, the lower chamber R 2  of the vacuum motor 20 is communicated with the upper chamber R 1  by way of the pipe P 3 , the valve 12, the pipe P 1  and the pipe P 2  so that pressures in the two chambers R 1  and R 2  are balanced in negative valve. Thus, the diaphragm piston assembly 22 is moved down by the biasing force of the spring 23 until the arm 15a of the link assembly 15 is engaged with the stopper 27. This opens the cut-off valve 14 to open the exhaust pipe 10 so as to release the back pressure. In this mode, atmospheric air in the lower chamber R 2  is communicated or sucked through the orifice 13 into the vacuum pump 11. This means that the orifice 13 serves to reduce the instant load applied to the vacuum pump 11. 
     Although the present invention has been illustrated and described in connection with a specific embodiment, various adoptation and modifications will become apparent to those skilled in the art from the description in conjunction with the appended claims without departing from the scope and spirit of the present invention.