Abstract:
An engine braking system includes an exhaust control path between an engine cylinder and an exhaust discharge path. A relief valve has a valve element located within the path, the valve element operable between a closed position to close the exhaust control path, corresponding to an engine operating condition, and an open position to open the exhaust control path, corresponding to an engine-braking condition. A spring urges the valve element toward the closed position. A retainer is arranged to be positioned in two operating positions, a first operating position which prevents opening of the valve element and a second operating position which allows opening of the valve element. An actuator wedge is operable to move between a first position and a second position to move the retainer between the first and second operating positions.

Description:
TECHNICAL FIELD 
     This disclosure relates to vehicles, particularly large tractor trailer trucks, including but not limited to apparatus, control and operation for engine braking. 
     BACKGROUND 
     Adequate and reliable braking for vehicles, particularly for large tractor-trailer trucks, is desirable. While drum or disc wheel brakes are capable of absorbing a large amount of energy over a short period of time, the absorbed energy is transformed into heat in the braking mechanism. 
     Braking systems are known which include exhaust brakes which inhibit the flow of exhaust gases through the exhaust system, and compression release systems wherein the energy required to compress the intake air during the compression stroke of the engine is dissipated by exhausting the compressed air through the exhaust system. 
     In order to achieve a high engine-braking action, a brake valve in the exhaust line may be closed during braking, and excess pressure is built up in the exhaust line upstream of the brake valve. For turbocharged engines, the built-up exhaust gas flows at high velocity into the turbine of the turbocharger and acts on the turbine rotor, whereupon the driven compressor increases pressure in the air intake duct. The cylinders are subjected to an increased charging pressure. In the exhaust system, an excess pressure develops between the cylinder outlet and the brake valve and counteracts the discharge of the air compressed in the cylinder into the exhaust tract via the exhaust valves. During braking, the piston performs compression work against the high excess pressure in the exhaust tract, with the result that a strong braking action is achieved. 
     Another engine braking method, as disclosed in U.S. Pat. No. 4,395,884, includes employing a turbocharged engine equipped with a double entry turbine and a compression release engine retarder in combination with a diverter valve. During engine braking, the diverter valve directs the flow of gas through one scroll of the divided volute of the turbine. When engine braking is employed, the turbine speed is increased, and the inlet manifold pressure is also increased, thereby increasing braking horsepower developed by the engine. 
     Other methods employ a variable geometry turbocharger (VGT). When engine braking is commanded, the variable geometry turbocharger is “clamped down” which means the turbine vanes are closed and used to generate both high exhaust manifold pressure and high turbine speeds and high turbocharger compressor speeds. Increasing the turbocharger compressor speed in turn increases the engine airflow and available engine brake power. The method disclosed in U.S. Pat. No. 6,594,996 includes controlling the geometry of the turbocharger turbine for engine braking as a function of engine speed and pressure (exhaust or intake, preferably exhaust). 
     In compression-release engine brakes, there is an exhaust valve event for engine braking operation. For example, in the “Jake” brake, such as disclosed in U.S. Pat. Nos. 4,423,712; 4,485,780; 4,706,625 and 4,572,114, during braking, a braking exhaust valve is closed during the compression stroke to accumulate the air mass in engine cylinders and is then opened at a selected valve timing somewhere before the top-dead-center (TDC) to suddenly release the in-cylinder pressure to produce negative shaft power or retarding power. 
     In “Bleeder” brake systems, during engine braking, a braking exhaust valve is held constantly open during the entire engine cycle to generate a compression-release effect. 
     According to the “EVBec” engine braking system of Man Nutzfahrzeuge AG, there is an exhaust secondary valve lift event induced by high exhaust manifold pressure pulses during intake stroke or compression stroke. The secondary lift profile is generated in each engine cycle and it can be designed to last long enough to pass TDC and high enough near TDC to generate the compression-release braking effect. Such a system is described for example in U.S. Pat. No. 4,981,119. 
     The present inventor has recognized the desirability of an alternate design solution that would deliver improved engine braking at a reduced cost. 
     SUMMARY 
     Engine braking can be improved for relatively low cost with the addition of a spring loaded valve or pressure relief valve in at least one cylinder of the engine. When the piston compresses the air in the combustion chamber, the relief valve will open at a predetermined pressure to correspond to a peak pressure associated with the engine compression ratio. Thus, the crankshaft puts power into compressing air, the valve releases this pressure, and the energy of compression is lost, thus generating the braking force. 
     According to one exemplary embodiment, the engine braking system includes an exhaust control path between an engine cylinder and an exhaust discharge path. A valve element is located within the path, the valve element operable between a closed position to close the exhaust control path and an open position to open the exhaust control path. A spring urges the valve element toward the closed position. A key or retainer is arranged to be positioned in two operating positions, a first operating position which prevents opening of the valve element and a second operating position which allows opening of the valve element. A wedge is operable to move between a first position and a second position to move the key between the first and second operating positions. 
     The key can be mounted to pivot between the first and second operating positions. The key can be urged by a spring toward the first operating position. The key can have a first inclined surface and the wedge has a second inclined surface, wherein when the wedge is moved from the first position to the second position, the second inclined surface slides on the first inclined surface. 
     According to one aspect, the at least one face comprises a first surface having a first surface area subject to cylinder pressure when the valve element is in the closed position, and the valve element comprises a second surface set back from the first surface and having a greater surface area than the first surface area, the second surface subject to cylinder pressure when the valve moves toward the open position. The valve element can include a valve spindle, an end of which forms the first surface. The valve spindle can be contiguous with a valve piston. The valve piston is slidable within the exhaust control path and forms the second surface. The spindle end closes a first valve seat when the valve element is in the closed position, and the piston opens an entry to the exhaust discharge path from the exhaust control path as the valve element moves toward the open position. The valve element configuration thus provides two valve openings, a first opening between the spindle and the first valve seat and a second opening between the valve piston and the entry between the control path and the discharge path. 
     One advantage of this braking system over a traditional compression brake is noise abatement. Traditional compression brakes open up a large valve against high pressure which creates an audible ‘pop’ each time. This valve element of the exemplary embodiment will generate a significant braking force, but the routing of gas from the valve back to the exhaust will dampen this audible ‘pop’ substantially, which will allow the use of this braking system in noise restricted areas. 
     Numerous other advantages and features of the present invention will be become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic system diagram of the present invention; 
         FIG. 2  is a schematic sectional view of an engine braking system according to the invention with the system operating in a non-braking mode; and 
         FIG. 3  is a schematic sectional view similar to  FIG. 1  but with the system operating in a braking mode. 
     
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
       FIG. 1  illustrates a simplified schematic of an engine braking control system  100 . Although the system is shown applied to one cylinder of an engine, more than one cylinder or all cylinders of an engine can be configured identically to the cylinder shown. The system acts on a spring loaded braking valve  114  that opens a cylinder  116  to an exhaust manifold  118  as shown enlarged in  FIG. 2 . A piston  117 , operatively connected to an engine crankshaft (not shown), reciprocates within the cylinder  116 . An engine braking controller  120 , such as a microprocessor or other electronic control, responsive to an engine braking command by the vehicle operator or to an otherwise generated braking signal, can be signal-connected to a control actuator  126  of a variable geometry turbocharger turbine  128  having one or more stages. The turbine  128  drives one or more stages of an intake air compressor (not shown) that charges pressurized air into the intake manifold of the engine. The engine braking control  120  can also be connected to one or more wastegates or turbine bypasses  150 . As an alternative to the variable geometry turbocharger, a conventional, non-variable geometry turbocharger can be provided. 
       FIG. 2  shows an exemplary exhaust valve control system  200  used in engine braking operation. Identical devices can be used at all cylinders or some of the cylinders, of the engine, although only the system  200  at the cylinder  116  is shown. The system  200  includes a rocker arm  212 , a valve bridge  216 , a braking valve control  214  an operating exhaust valve  220  and the braking valve  114 . The valve bridge is used when two operating exhaust valves  220  (only one shown) are operated in tandem, i.e., both open and close together, during normal operation. If only one operating exhaust valve  220  is used, the bridge can be eliminated and the rocker arm  212  can act directly on the operating exhaust valve end. The valves  220  and  114  open the cylinder  116  to the exhaust manifold  118  via exhaust gas passages  224 ,  226  provided in a cylinder head  230 . Although the gas passage  226  is shown as a separate passage from the braking valve  114  to the manifold  118 , it could also be a shorter passage wherein the passage  226  is open into the path  224  within the head  230 . 
     Each operating exhaust valve  220  includes a stem  234  having a stem end  237 , a head  235 , and a spring keeper  236 . A valve spring  238  surrounds the stem  234  and is fit between the keeper  236  and the cylinder head  230 . To move the head  235  away from valve seat  240  during normal engine operation, at the selected crankshaft angle, the rocker arm  212  presses the valve bridge  216  down to move the valve stem  234  down via force on the end  237  against the expansion force of the spring  238  as the spring is being compressed between the keeper  236  and the cylinder head  230 , and against the cylinder pressure force on the valve  220 . 
     The braking control  214  includes the braking valve  114 , a valve spring  302 , a valve key or retainer  306 , a valve retainer spring  310 , an actuator wedge  316 , and an actuator  326 . The braking control  214  is substantially held within and supported by a housing portion  317 . 
     The braking valve  114  includes a valve spindle  330  with a valve head  336  formed as a beveled tip portion of the spindle  330 . The valve head  336  is configured to close a valve seat  337  formed on the head  230 . The valve seat angle should be shallow to avoid sticking. The spindle  330  is formed with, or attached to, a valve piston  344 . The piston  344  slides within a valve cylinder  348 , and includes a piston face  352 . A valve stem  356  is attached to, or formed with, the piston  344 , opposite to the spindle  330 . The stem  356  includes a stem end  360  that is exposed outside a cylinder  348  through a hole in a top wall  357  thereof. The valve spring  302  surrounds the stem  356  and is fit within the cylinder  348  between the top wall  357  and the piston  344 . 
     The retainer  306  is mounted on a pivot pin  366  to the head  230  and can be pivoted about the pin  366  into alternate position shown in  FIG. 2  and  FIG. 3 . The position shown in  FIG. 2  corresponds to a non-engine braking condition and the position shown in  FIG. 3  corresponds to an engine braking condition. 
     Both the retainer  306  and braking valve  114  should be hardened material. 
     As shown in  FIG. 2 , the actuator  326  has caused the actuator wedge  316  to be elevated. Accordingly, the spring  310 , which as shown is a torsion spring, urges the retainer  306  clockwise to the position wherein the retainer overlies the end  360  of the stem  356 . The retainer  306  has a bottom surface  379  shaped to have a cam action so the retainer  306  wedges the braking valve  114  closed when not needed. 
     The braking valve  114  is thus held down in a closed position. The valve head  336  closes the valve seat  337  and the piston  344  closes an entry  380  of the exhaust path  226 . The valve cylinder  348  forms an exhaust control path between the valve seat  337  and the entry  380 . The valve  114  and the retainer  306  should hold closed against cylinder combustion pressures of about 3000 psi. 
     When the actuator  326  drives the actuator wedge  316  down, a first oblique surface  386  on the wedge slides over a second oblique surface  388  on the retainer  306  to force the retainer to rotate counterclockwise from the position shown in  FIG. 2  to the position shown in  FIG. 3 , against the urging of the spring  310 . 
     With the retainer  306  in the position of  FIG. 3 , the retainer bottom surface  379  clears the end  360  of the braking valve  114 . The pressure within the cylinder  116  is sufficient to displace the head  336  from the seat  337  and the pressure on the face  352  further moves the piston upward to progressively expose the entry  380  to the cylinder gas. 
     Although a wedge device is shown, other actuator types can be used to effect the locked and unlocked positions of the spring loaded device. The actuator  326  can be solenoid operated or operated by oil pressure. 
     Sufficient delay is required to keep the valve open long enough to evacuate the combustion chamber as the pressure decreases. This decreased pressure should be 50-100 psi. Opening pressure should be around 750 psi. These opening and closing pressure actuations are achieved by having two different diameters on the valve, the first diameter of the valve head  336  and the second diameter of the piston  344 . 
     The size of the first diameter must be big enough to evacuate the compressed air at the highest desired operating speed. When the valve opens, air impinges on the second diameter to keep the valve open until about 150 psi is reached. Total valve actuation motion and valve weight should be minimized to reduce kinetic forces. Valve motion in the figures is exaggerated for explanation purposes. 
     As an example, for an inline-6 cylinder, 570 cubic inch engine, with a maximum braking speed of 2500 RPM and a compression ratio of 17:1, the opening diameter at the valve seat  337  should be about 11 mm or 0.44 inches or greater. With this opening, the spring force should be 110 lbs to open at top dead center. The diameter of the valve piston  344  should be about 25 mm, or one inch or greater. 
     Bore fit between the larger bore diameter and the housing should seal enough for good actuation. Either tight tolerances or an O-ring can be used. An O-ring may require grease and tight bore tolerances may require oil. 
     The valve spring  302  should be a dual spring to avoid resonance issues which are typical during high engine speeds. An alternative to a dual spring is a shaped spring that rubs against the body, and this will require hardened materials of the spring and body, and will require more development testing. 
     The actuator will be part of the valve assembly if it is a solenoid, but will be part of the high pressure oil rail if it is hydraulic. 
     The housing portion  317  can be partially integrated into the cylinder head  230  or it can be a self contained unit fastened to the cylinder head or otherwise supported on the engine. If desired, braking valves  114  for each engine cylinder can be actuated for braking, or less than all of the braking valves  114  can be actuated to modulate the amount of braking force desired. 
     Referring to  FIG. 1 , for an enhancement to the braking effect of the valves  114 , the braking control  120  can cause the actuator  126  of the variable geometry turbine  128  to clamp down the variable geometry turbine to increase turbine speed and thus increase compressor speed and air into the engine. Also, the braking control  120  can close any wastegate  150  to also increase the turbine speed by increasing exhaust gas flow through the turbine to increase air into the engine from the compressor. 
     PARTS LIST 
     
         
           100  engine braking control system 
           114  spring loaded braking valve 
           116  cylinder 
           117  piston 
           118  exhaust manifold 
           120  engine braking control 
           126  turbine control actuator 
           128  variable geometry turbocharger turbine 
           150  turbine wastegate 
           200  engine exhaust valve control system 
           212  rocker arm 
           214  braking valve control 
           216  valve bridge 
           220  operating exhaust valve 
           224  exhaust gas passage 
           226  exhaust gas passage 
           230  cylinder head 
           234  valve stem 
           235  valve head 
           236  spring keeper 
           237  stem end 
           238  valve spring 
           240  valve seat 
           302  valve spring 
           306  key or retainer 
           310  valve retainer spring 
           316  actuator wedge 
           317  housing portion 
           326  actuator 
           330  valve spindle 
           336  valve head 
           337  valve seat 
           344  valve piston 
           348  valve cylinder 
           352  piston face 
           357  valve stem 
           360  stem end 
           366  pivot pin 
           379  bottom surface 
           380  exhaust passage entry 
           386  first oblique surface 
           388  second oblique surface 
       
    
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred.