Abstract:
A supplementary brake for a vehicle adapted for use in a heavy duty vehicle to supplement the capacity of a main brake system for obtaining sufficient braking efficiency. The brake comprises an oil pressure supplying unit, an oil pressure control unit for controlling oil pressure, a pulsatory pressure forming unit for forming a pulsatory pressure to the oil pressure supplied from the oil pressure control unit to the profile of an engine injection cam, a valve opening and closing unit for opening an closing an exhaust valve of an engine according to the pulsatory pressure formed by the pulsatory pressure forming unit, and a controller for controlling the oil pressure supply unit according to the operating state of the engine.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a brake system used for a heavy-duty truck or bus, and more particularly, to a brake adapted to supplement the capacity of a main brake system for obtaining sufficient braking in a heavy duty vehicle.  
         BACKGROUND OF THE INVENTION  
         [0002]    Heavy duty trucks, buses or the like, being heavy in weight and load need good braking capacity for sufficient braking performance. However, there is a problem in that a main brake system alone cannot hold the heavy weight, load and vehicle itself due to oversized parts and load concentrations, such that an appropriate supplementary brake is provided in the form of an exhaust brake, retarder and the like.  
           [0003]    Among such supplementary brakes, the exhaust brake is typically mounted inside the exhaust pipe including a butterfly valve by which exhaust gas discharged from the engine is blocked to reduce engine revolutions and thereby slow down the speed of the vehicle when braking power is needed. However, in such a brake, if back pressure inside the exhaust pipe rises beyond a critical level, erroneous operation occurs in the engine exhaust valve, causing damage to the engine. Also, because the butterfly valve cannot be completely closed, it is difficult for an exhaust brake to obtain a sufficient braking performance as a supplementary brake.  
           [0004]    Furthermore, there is a problem with the butterfly valves typically employed in that the back pressure of the exhaust pipe generated when the exhaust brake is operated gradually deteriorates the exhaust brake capability.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides a supplementary brake for a vehicle adapted to be used particularly in diesel-engine, heavy-duty commercial vehicles as an improved exhaust brake for improved braking capability and durability.  
           [0006]    In accordance with an embodiment of the present invention, there is provided an oil pressure supplying means and oil pressure control means for controlling the oil pressure supplied from the oil pressure supplying means. A pulsatory pressure forming means forms a pulsatory pressure in the oil pressure supplied from the oil pressure control means in accordance with the profile of an engine injection cam. A valve opening and closing means opens and closes the exhaust valve of the engine according to pulsatory pressure formed by the pulsatory pressure forming means. A controller controls the oil pressure supply means according to the operating state of the engine. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    For fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings in which:  
         [0008]    [0008]FIG. 1 is a block diagram illustrating the construction of an engine brake according to the present invention;  
         [0009]    [0009]FIG. 2 is a schematic drawing of a control valve illustrated in FIG. 1; and  
         [0010]    FIG. 3  is a schematic drawing of the opening and closing means illustrated in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]    Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.  
         [0012]    As shown in FIG. 1, a supplementary brake for a vehicle according to the present invention comprises an oil pressure supply means  5  and oil pressure control means  21  for controlling oil pressure supplied from the oil pressure supplying means. A pulsatory pressure forming means  26  forms a pulsatory pressure in oil supplied from the oil pressure control means  21  in accordance with the profile of the engine injection cam  29 . A valve opening and closing means  48  opens and closes the exhaust valve  37  according to the pulsatory pressure formed by the pulsatory pressure forming means  26 . A controller  1  controls the oil pressure supply means  5  according to the operating state of the engine.  
         [0013]    Controller  1  receives engine brake operating instructions from the driver through switch  3 , and determines the vehicle condition as to whether the engine and drive shaft are connected by way of a released clutch pedal. The controller  1  also determines whether the driver is not stepping on the accelerator pedal. If the driver steps on the accelerator pedal to try to accelerate, the controller  1  stops the braking operation activity. The controller  1  then determines whether or not the gear shift is in neutral position. If the gear shift is in the neutral position, the controller  1  stops the braking operation promptly, and when the braking operation is in motion, stops the fuel injection.  
         [0014]    Controller  1  may comprise a processor and memory, with associated hardware and software, as may be selected and programmed by a person of ordinary skill in the art to execute the control functions described herein. In one preferred alternative embodiment, an existing engine Electronic Control Unit (ECU) may be used as controller  1  in an electronically-controlled diesel engine with added functions and programming as described herein.  
         [0015]    Oil pressure supplying means  5  can be formed as a solenoid valve such that engine oil supplied from a conventional engine oil pump is used by switching the oil-passing state of the solenoid valve by way of an electrical signal supplied by the controller  1 . The solenoid valve  5  preferably uses a bolt from the installation of the supplementary brake to form an oil passage by forming an oil passage through the bolt. A solenoid actuator is added to regulate the oil passage for more effective results in terms of space saving and reduction of the number of parts.  
         [0016]    As shown in FIG. 2, the oil pressure control means  21  which may comprise a control valve for regulating oil that has passed the solenoid valve  5  under a constant pressure state, comprises a valve body  7  equipped with a cylindrical cylinder  6 . Body  9  is inserted into the cylinder  6  to define a regulating oil passage  10  for regulating the flow of oil in the cylinder  6 . A check ball  11  is positioned at one end of regulating oil passage  10 . A check piston  15  is mounted to slide within the cylinder  6 , with a check spring for resiliently supporting the check ball  11 . A constant pressure spring  17  resiliently supports the check piston  15 . Closing cap  19  supports the constant pressure spring  17  and closes the cylinder  6 .  
         [0017]    The closing cap  19  is coupled to the valve body  7  while being resiliently acted on by closing spring  23 , in order to further solidify the mounted state as illustrated in the drawing. Closing cap  19  is further fastened by a locking nut  25 .  
         [0018]    As illustrated in FIG. 1, pulsatory pressure forming means  26  comprises a pulsatory pressure cylinder  27  and a piston  31  mounted to slide within the pulsatory pressure cylinder  27 . The piston is acted on by injection cam  29  to control the timing of the injecting oil to the engine. A cam spring  33  resiliently supports the piston  31  toward the injection cam  29 .  
         [0019]    The valve opening and closing means  48 , shown in more detail in FIG. 3, includes a valve body  35  and an actuator rod  41  reciprocatively moved by the pulsatory pressure supplied to the valve body  35 . Movement of rod  41  provides actuating force for rocker arm  39  for opening and closing exhaust valve  37 . An actuator piston  43 , and first and second springs  45  and  47 , absorb lateral forces from the rocker arm acting on the actuator rod  41 . Piston  43 , and springs  45  and  47 , also act in response to the pulsatory pressure to generate a reciprocating force in the actuator rod. A robolash valve  49  positioned opposite piston  43  comprises a robolash unit for prompting the actuator rod to contact the rocker arm with a pre-load. As used herein, “robolash” means “to regulate a gap”. The robolash unit is described in greater detail below.  
         [0020]    Actuator rod  41  is formed with a flange  51  that is accommodated in a flange groove  53  formed around the inside of actuator piston  43 , as shown in FIG. 3. Flange  51  is resiliently supported by the first spring  45  to permit actuator rod  41  to move with the actuator piston  43 . The actuator piston  43  is also resiliently supported by the second spring  47  to provide an elastic force corresponding to the pulsatory pressure provided to a floor surface of the actuator piston  43 .  
         [0021]    The peripheries of flange  51  and flange groove  53  are preferably smooth, curved surfaces to allow flange  51  to sway at a constant angle relative to the flange groove  53 , such that lateral force from rocker arm  39 , introduced from the actuator rod  41 , can be absorbed. Actuator rod  41  preferably includes a swivel boot  61  mounted over ball part  59  to compensate for angle differences generated in the course of contact with the rocker arm  39 .  
         [0022]    The robolash unit preferably includes a robolash piston  63  facing the actuator piston  43  and having a smaller floor surface area than that of the actuator piston. A part  63 a of the robolash piston  63  is detached at a constant space from a floor surface of the actuator piston  43 . Robolash spring  65  and robolash plug  67  force the robolash piston  63  toward the valve body  35 . A stroke limiting groove  69 , formed at the robolash plug  67 , limits slip of the robolash piston  63  in cooperation with a limiting ring  71  mounted at the robolash piston  63 .  
         [0023]    Hereinafter, the operation of the present invention thus constructed will be described.  
         [0024]    When a driver manipulates switch  3  to actuate the supplementary brake while a vehicle is in motion, the controller  1  checks the state of the vehicle. For example, controller  1  checks whether the clutch pedal is in released mode, whether the driver is stepping on the accelerator pedal, and whether the gear shift is placed in neutral position.  
         [0025]    When the switch  3  is turned on and the clutch pedal is in released mode and the gear shift is not in the neutral position, engine oil is supplied to the oil pressure supply means  5 , and the fuel injection of the engine is blocked, thereby affecting the braking operation. If the clutch pedal is released, if the accelerator pedal is stepped on, or if the gear shift is in the neutral position, the oil pressure supplied to oil pressure supply means  5  is blocked and the engine fuel injection is re-started to stop the supplementary brake operation and to protect the engine.  
         [0026]    When the controller  1  actuates supply means  5  to supply engine oil to the oil pressure circuit of the supplementary brake, oil pressure control means  21  allows the oil pressure to be maintained at a constant pressure state and provides a constant oil pressure.  
         [0027]    When oil from the supply means  5  is infused into the oil inlet  8  in valve body  7  of control means  21 , check ball  11  opens to allow oil to be infused so that only the pressure adjusted by the check piston  15  is discharged to the oil outlet  10  by the constant pressure spring  17 . If pressure is reversely transferred from the oil outlet side, the oil passage is blocked by the check ball  11 , to thereby supply a constant pressure into the oil pressure circuit at all times.  
         [0028]    As a result, the constant pressure thus formed is provided into the valve body  35  of the robolash valve  49  and the pulsatory cylinder  27 . The constant pressure supplied to the robolash valve  49  actuates the robolash to prompt the swivel boot  61  at the actuator rod  41  to contact the rocker arm  39  of the exhaust valve  37  at a pre-load.  
         [0029]    When constant pressure is supplied to the oil inlet  36  of the valve body  35 , the actuator piston  43  overcomes the resilience of the first and second spring  45  and  45  to move to the rocker arm  39  a constant distance. The robolash piston  63  is provided with pressure produced by oil introduced through oil passage  64 , plus resilience provided by the robolash spring  65  prompts the robolash piston  63  to move toward the actuator piston  43 . The distance moved is restricted to a constant level by the stroke limiting groove  69  and the limiting ring  71 . The swivel boot  61  mounted at an end of the actuator rod then provides a pre-load to rocker arm  39  when the robolash piston  63  contacts the bottom floor of the actuator piston  43 .  
         [0030]    The robolash mechanism prevents the exhaust valve  37  from being affected in operation by any other part during the normal movement of the vehicle and allows the opening/closing of the exhaust valve  37  to be affected by the actuator rod  41  in case auxiliary braking operation is needed. Allowing the swivel boot  61  at the actuator rod  41  to contact the rocker arm  39  with a pre-load prevents noise and durability problems from occurring when the swivel boot  61  and the rocker arm  39  are continuously contacted by rapid reciprocating operation of the actuator rod  41 .  
         [0031]    Under the conditions thus described, piston  31  in pulsatory cylinder  27  slides along the cam profile of injection cam  29  under the biasing force of the cam spring  33  to provide pulsatory pressure to the oil filled in the pulsatory cylinder  27 . The pulsatory pressure thus formed is supplied into the valve body  35  of the robolash valve  49 . When the pulsatory pressure is provided, the actuator piston  43  overcomes the first and second piston  45  and  47  to push the actuator rod  41  towards the rocker arm  39 , whereby the rocker arm  39  opens the exhaust valve  37 .  
         [0032]    The exhaust valve  37  is preferably opened near the top dead center of a compression stroke. Fuel supply through the controller  1  is thus blocked at the vicinity of the top dead center of the compression stroke and the exhaust valve  37  is opened to prevent engine power from being generated during an expansion stroke. The power to be consumed thereafter for operation of the pistons is transformed to work force needed for braking.  
         [0033]    Because the actuator rod  41  is linearly and reciprocally moved within a constant passage while the rocker arm  39  is rotated through a constant angle, the swivel boot  61  mounted at the end of the actuator rod  41  is pivoted between the actuator rod  41  and the rocker arm  39 , to thereby connect the reciprocating motion of the actuator rod  41  with the rotating motion of the rocker arm  39 . The lateral force transmitted to the swivel boot  61  and the actuator rod  41  by the operation of the rocker arm  39  is absorbed by the flange  51  at the actuator rod  41  and flange groove  53  in the actuator piston. The first piston resiliently supports flange  51  toward the flange groove  53  to allow the actuator rod  41  to maintain a stable state where a smooth operational force is provided to the actuator rod  41  from the actuator piston  43 .  
         [0034]    When a driver turns off the switch  3 , or the controller  1  detects that the clutch pedal is in released mode, the accelerator pedal is stepped on or a gear shift is in neutral position, the controller blocks the oil pressure supplied from the solenoid valve  5  and re-opens the fuel injection, thereby stopping the braking operation of the supplementary brake and transferring to the normal running state. If oil pressure supplied from the solenoid valve  5  is stopped, oil is discharged to the oil drain passage installed in the valve body  7  of the control valve  21 , and the actuator piston  43  and the actuator rod  41  retreat along with retreat of the robolash piston  53  to be spaced from the rocker arm  39  so that the exhaust valve  37  does not interrupt normal engine operation.  
         [0035]    As apparent from the foregoing, there is an advantage in the supplementary brake for a vehicle thus described according to the present invention in that fuel injection is blocked near the top dead center compression stroke and an exhaust valve is opened at the same time to allow power needed for piston operation of the engine to be consumed for braking without using power so that no parts such as a butterfly valve and the like having durability problems are needed, thereby allowing use for longer periods and obtaining sufficient braking power at least twice that of the prior-exhaust brake.