Abstract:
A volume reducer for a hydraulic system, particularly useful for low pressure hydraulic systems such as used in engine compression braking systems. The hydraulic system has an actuator and a pressurizer, with a hydraulic line interconnecting the actuator and the pressurizer. A substantially straight section of the hydraulic line is provided, and a slidable body is provided in the substantially straight section. The body slides in the hydraulic line in response to pressure changes in the hydraulic line, and occupies hydraulic line volume, to stiffen the hydraulic system and reduce system sluggishness.

Description:
TECHNICAL FIELD 
     The present invention relates to hydraulic systems, and more specifically to a low pressure hydraulic system for an engine compression braking system. 
     BACKGROUND 
     Work machines commonly use hydraulic actuators, such as hydraulic motors and hydraulic pistons, as drive and operating mechanisms to perform work. A pressurizer, such as a pump or master cylinder supplies hydraulic fluid under pressure to the actuator. Hydraulic lines, which may be tubes, hoses, pipes or the like are used to interconnect the various devices in the hydraulic system, including the pressurizer and the actuator. For proper operation, the system, including all hydraulic lines, must be full of hydraulic fluid. In some machines, the hydraulic lines may be quite long, extending between devices. Long runs of hydraulic lines are often relatively straight, and are known to encompass drilled passages through metal bodies forming part of the work machine. 
     A known application for a hydraulic system is in the actuation of an engine compression brake. When required, the engine compression brake is actuated to open cylinder valves of the engine. The hydraulic system for an engine compression brake is known to include a bridge operating one or more engine cylinder valves, with movement of the bridge accomplished through the use of a hydraulic line circuit. A slave piston in the hydraulic circuit is connected to the bridge, and is moved in response to movement of a master piston also in the circuit. Passages drilled through the engine valve cover may be used to form part of the hydraulic fluid lines for the system. A sump and pressurized fluid supply are provided, with appropriate valves for effectively turning the hydraulic system on or off. 
     It is known to use multiple pistons in a hydraulic cylinder, including one or more floating pistons, for various purposes, including the operation of multiple branch circuits from a single master cylinder. U.S. Pat. No. 3,800,538 entitled, “Master Cylinders For Hydraulic Braking Systems”, discloses a master cylinder having a main first piston and two floating pistons collectively urged by a plurality of springs disposed in the cylinder. 
     A problem of hydraulic systems, particularly those operating at low pressures, is sponginess in response upon actuation of the system. This can occur due to the low bulk modulus of the hydraulic fluid at low pressures. Hydraulic systems used for engine compression brakes have been known to experience this type of problem. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a hydraulic system is provided with a pressurizer for pressurizing hydraulic fluid, an actuator responsive to pressurized fluid to perform work and a hydraulic fluid line interconnecting the pressurizer and the actuator. A volume reducer in the hydraulic fluid line includes a substantially straight section of the hydraulic fluid line and a body slidable in the straight section in response to pressure changes in the hydraulic fluid line. 
     In another aspect of the invention, an engine compression braking system for an engine is provided with a cylinder valve, an actuator operating on the valve responsive to pressurized fluid, and a pressurizer for pressurizing hydraulic fluid. A hydraulic fluid line interconnects the pressurizer and the actuator. A volume reducer in the hydraulic fluid line includes a body slidable in the hydraulic fluid line in response to pressure changes in the hydraulic fluid line. 
     In still another aspect of the invention, a method for operating a hydraulic system with reduced hydraulic fluid volume is provided, with steps of providing a pressurizer for pressurizing hydraulic fluid and an actuator responsive to pressurized fluid to perform work; providing a hydraulic fluid line interconnecting the pressurizer and the actuator; providing a body in the hydraulic fluid line; pressurizing fluid in the hydraulic fluid line; and sliding the body in the hydraulic fluid line in response to pressure changes in the hydraulic fluid line. 
     In yet another aspect of the invention, a volume reducer for a hydraulic circuit is provided with a substantially straight hydraulic fluid line, and a body freely slidable in the hydraulic fluid line in response to pressure changes in the hydraulic fluid line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of an compression engine brake and a hydraulic system including a volume reducer in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawing, FIG. 1 illustrates an engine compression braking system  10  including an engine compression brake  12  operated by a hydraulic system  14 . Hydraulic system  14  includes a pressure generating section which shall be referred to herein as a pressurizer  16 , and an acting section referred to herein as an actuator  18 . Hydraulic system  14  further includes a hydraulic circuit  20  between pressurizer  16  and actuator  18 . Hydraulic circuit  20  has a hydraulic system volume reducer  22  in accordance with the present invention. 
     Hydraulic circuit  20  is merely one example of a hydraulic circuit in which volume reducer  22  of the present invention can be used advantageously. Volume reducer  22  can be used in types and designs of hydraulic systems different from hydraulic system  14 , and can be used for purposes other than actuation of an engine compression braking system  10 . Compression braking system  10  and hydraulic system  14 , to be described hereinafter, should not be construed as limitations on the use or application of the invention, nor on the breadth of the claims to follow. 
     Hydraulic circuit  20  extends between pressurizer  16  and actuator  18  to enable the activation or operation of pressurizer  16  to effect the required work to be performed by actuator  18 . In the example shown, the work performed by actuator  18  is the operation of an engine compression brake  12 . Those skilled in the art will recognize that FIG. 1 illustrates a simplified engine compression brake  12 . 
     Actuator  18  operates simultaneously on two combustion cylinder valves  24  and  26  of an internal combustion engine (not shown), to open the valves and create engine braking when required. Actuator  18  includes a bridge  28  and a straddle  30 . Bridge  28  extends between valves  24  and  26 , and operatively engages the valves, transferring motion of bridge  28  equally to valves  24  and  26 , so that when engine braking is required, both valve  24  and valve  26  are depressed by the operation of a single bridge  28 . The manner in which depressing valves  24  and  26  creates engine braking is known to those skilled in the art, is not relevant to an understanding of the present invention, and will not be described in greater detail herein. 
     Straddle  30  operates against bridge  28 , at one end  32  of straddle  30 , and straddles a rocker arm  34  on bridge  28 . On an end  36  of straddle  30  opposite bridge  28  and end  32 , straddle  30  is connected to a slave piston  38  operating in a slave piston cylinder  40  of hydraulic system  14 . Straddle  30  thereby transfers movement of slave piston  38  to bridge  28 . A spring  42  operates between a flange  44  on end  36  of straddle  30 , and a fixed abutment  46  to bias straddle  30  away from bridge  28 . 
     Pressurizer  18  includes a cam  48  and a cam follower  50  including a roller  52  in a yoke  54 . Roller  52  rotates about a pin  56  secured in yoke  54 , and follows the surface of cam  48 . Those skilled in the art will recognize that other types of cam and cam follower constructions can be used, include sliding or slipping surfaces, rather than the rolling surface of roller  52 . 
     Cam follower  50  is connected to a master piston  58  operating in a master piston cylinder  60  of hydraulic system  14 . Rotation of cam  48  thereby induces linear motion in master piston  58 . A spring  62  operates between an end  64  of yoke  54  and an abutment  66  of a housing  68 , to bias cam follower  50  toward cam  48 . 
     Hydraulic circuit  20  includes a hydraulic fluid line  70  extending between master piston cylinder  60  and slave piston cylinder  40 . A portion of hydraulic line  70  includes a bore  72  drilled in a valve cover  74  of the engine (not shown). Hydraulic line  70  is connected further to a hydraulic fluid sump  76  in a branch line  78 . A solenoid valve  80  is provided in hydraulic line  70 , and selectively connects hydraulic line  70  to branch line  78  and thereby sump  76 , or to a supply line  82  from a pressurized supply  84  of hydraulic fluid. Supply line  82  includes a poppet valve  86 . Pressurized supple  84  provides pressurized hydraulic fluid for hydraulic circuit  20 , in known manner. 
     To reduce the sponginess in response of hydraulic circuit  20 , volume reducer  22  is provided, and includes a sliding body  88  disposed in bore  72 . Body  88  can be provided in any straight section of hydraulic line  70 , and is used preferably in a rigid straight section, such as in a pipe or tube (not shown) or in bore  72 . Body  88  is an elongate body, in the nature of a plug or slug, and is shaped on the outer surface thereof to slide smoothly and freely in bore  72 . Body  88  may be solid, or may be hollow, but if hollow should define a sealed inner space, and must be sufficiently strong to withstand the pressure in hydraulic line  70  without collapsing or rupturing. Steel is a suitable material for body  88 . A spring  90  lightly biases body  88  toward master piston  58 . 
     INDUSTRIAL APPLICABILITY 
     In the use of compression braking system  10 , pressurizer  16  of hydraulic system  14  activates actuator  18  to cause operation of compression brake  12 . Actuator  18  opens valves  24  and  26  of the engine (not shown). 
     Pressurized supply  84  provides pressurized hydraulic fluid to hydraulic line  70 , and thereby to master piston cylinder  60 , and slave piston cylinder  40 , which are filled with pressurized hydraulic fluid above master piston  58  and slave piston  48 , respectively. Solenoid valve  82  has a “normally open” position, connecting hydraulic line  70  to sump  76  via branch line  78 , and a “normally closed” position connecting hydraulic line  70  to pressurized supply  84  via supply line  82 . 
     With solenoid valve  80  in the “normally ” open position, compression braking system  10  is off, and supply pressure from pressurized supply  84  is blocked. Access to sump  76  is open, and both slave piston  38  and master piston  58  are drawn away from the valve operating train. 
     With solenoid valve  80  in the “normally closed” position, compression braking system  10  is on, and supply pressure from pressurized supply  84  is transmitted to hydraulic line  70 . Access to sump  76  is blocked, and pressurized hydraulic fluid pushes slave piston  38  against the valve operating train, including straddle  30  and bridge  28 . 
     Master piston  58  and slave piston  38  operate in the known master/slave hydraulic system relationship, such that linear motion of master piston  58  in master piston cylinder  60  is transferred to slave piston  38  in slave piston cylinder  40 . Rotation of cam  48  builds and relieves pressure in hydraulic circuit  20 . As roller  52  rides against an outwardly extending lobe of cam  48 , master piston  58  is moved upwardly in master piston cylinder  60 . The corresponding effect, transmitted through the pressurized hydraulic fluid in hydraulic line  70 , is a downward movement of slave piston  38  in slave piston cylinder  40 . Straddle  30  is moved downwardly, against bridge  28 , the downward movement of which depresses valves  24  and  26 . Conversely, as roller  52  rides away from an outwardly extending lobe of cam  48 , master piston  58  moves downwardly in master piston cylinder  60 . The corresponding effect is an upward movement of slave piston  38  in slave piston cylinder  40 . Straddle  30  is moved upwardly, away from bridge  28 . The downward movement of master piston  58  and the upward movement of straddle  30  are assisted by spring  62  and spring  42 , respectively. 
     Body  88  displaces hydraulic fluid in hydraulic circuit  20 . As pressure builds on the master piston side of body  88 , such as when cam follower  50  encounters a lobe of cam  48  as described above, body  88  is moved toward slave piston cylinder  40 , transmitting the pressurization to the hydraulic fluid on the slave piston side of body  88 , effecting slave piston movement as described above. Conversely, the hydraulic effects occurring from the movement of a lobe of cam  48  away from cam follower  50  result in the movement of body  88  toward master piston cylinder  60 . 
     By occupying volume in hydraulic line  70 , which otherwise would have to be filled with hydraulic fluid, body  88  reduces the required volume of hydraulic fluid. Hydraulic circuit  20  is thereby made stiffer, and responds more quickly to activation from master piston  58 . Body  88  can be used in any straight section of a hydraulic circuit, to reduce the required volume of hydraulic fluid, and thereby increase hydraulic system stiffness. 
     Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.