Patent Publication Number: US-6662778-B2

Title: Engine compression release brake system and method for operating the same

Description:
TECHNICAL FIELD 
     This invention relates to a compression release brake system for an internal combustion engine and a method of operating the same to achieve desired noise emission levels. 
     BACKGROUND ART 
     Engine compression release brakes are well known for providing retarding of vehicles without activation of the vehicle&#39;s service brakes. Examples of known engine compression release brakes are shown in U.S. Pat. Nos. 5,012,778 to Pitzi and 4,741,307 to Meneeley. In general, traditional engine compression release brakes provide retarding by absorbing energy as a result of compressing intake air in the engine&#39;s combustion chamber. The engine&#39;s exhaust valves are opened near the end of the normal compression stroke, thereby preventing energy from being imputed back into the drive train. When the exhaust valves are opened, the pressure in the engine cylinder is released or “blown down”, which produces a high level of noise emissions through the engine exhaust system. 
     The aforementioned compression release brake systems are routinely used on over-the-road or on-highway vehicles, such as delivery truck and semi-tractors that regularly operate in both rural and urban regions. Many jurisdictions have instituted noise level restrictions, especially in residential areas, and traditional compression release brake systems typically produce noise levels that exceed the maximum noise levels permitted by law in many geographic regions. Consequently, vehicle operators are routinely prohibited from operating compression release brakes when operating in noise restricted regions. As a result, the operator must utilize the vehicle&#39;s services brakes to retard or slow the vehicle in cases where a compression release brake could be advantageously used to avoid wear on the service brakes. 
     Traditional engine compression release brakes, such as those commercially available from Jacobs Manufacturing Company for example, are able to modulate the applied retarding force by selectively operating brake cycles on less than all of the engine cylinders. For example, in a six cylinder engine, brake systems are typically installed such that one portion of the brake system controls braking on one cylinder, another portion of the brake system controls braking on two cylinder together, and a third portion of the system controls braking on the remaining three cylinders. As a result, the vehicle operator can select among six discrete levels of braking by activating one to six of the cylinders. However, such modulation of the brake systems does not significantly alter the noise emission level produced by brake operation, but instead only changes the frequency of noise emissions and/or the cadence the noise emissions. This is due to the fact that resulting noise emissions correspond to the cylinder pressure at the time of pressure release, which is in turn tied to the timing of the pressure release event, which is in turn tied to the fixed shape of the cam that operates a traditional compression release brake. Although de minimis noise reduction may be achieved in traditional systems because lower braking levels produce lower turbo boost and thereby reduce cylinder pressure at the time of release, significantly reduced levels of noise emissions are not achievable in traditional systems even when operating at lower levels of braking or retarding. 
     Another attempt to reduce noise is illustrated in U.S. Pat. No. 5,357,926 to Hu. In this patent, noise is reduced when the vehicle operator electrically adjusts the “lash” of the engine brake. “Lash” is the “at rest” clearance between the engine brake slave piston and the engine exhaust valve mechanism operated on by the slave piston to produce braking. By reducing the “lash”, the timing of the braking event is advanced slightly, thereby reducing the cylinder pressure at “blow down.” Unfortunately, this approach is not automatic and requires the driver to recognize that he or she is in a noise restricted area and manually change the lash. Additionally, this design only provides one level of adjustment, even though jurisdiction may have varying degrees of noise restrictions. This system also increases the number of components in the vehicle and increases cost. Finally, because the “lash” is manually changed, the braking system is not capable of automatically providing additional braking power in an emergency, when it would otherwise be desirable to “ignore” noise restrictions for overriding safety concerns. 
     This invention is directed to overcoming one or more of the problems identified above. 
     DISCLOSURE OF THE INVENTION 
     The present invention includes a method for operating a vehicle having an engine compression release brake, comprising: operating the engine compression release brake in a first mode producing a first level of noise emissions; determining that the vehicle is operating in a noise restricted geographic region; and in response to the determining step, automatically operating the engine compression release brake in a second mode producing a second level of noise emissions lower than the first level of noise emissions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 diagrammatically illustrates a vehicle having an internal combustion engine equipped with a compression release brake system in accordance with a first embodiment of this invention. 
     FIG. 2 diagrammatically illustrates a second embodiment of a portion of the compression release brake system shown in FIG.  1 . 
     FIG. 3 diagrammatically illustrates a third embodiment of a portion of the compression release brake system shown in FIG.  1 . 
     FIGS. 4 and 5 are graphs illustrating noise emission and retarding torque, respectively, based on timing of a compression release event in accordance with this invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     FIG. 1 diagrammatically illustrates a vehicle  10  having an internal combustion engine  12  equipped with a compression release brake system  14  in accordance with this invention. The vehicle  10  may be an on-highway vehicle, such as a Class 6,7 or 8 on-highway truck, or may be an off-highway vehicle, such as an earthmoving machine or other piece of construction/mining equipment. The engine  12  is a conventional reciprocating piston engine having one or more cylinders  16  in which a piston  18  reciprocates. The illustrated engine  12  includes six cylinders, although this invention is equally applicable to engines having more or less than six cylinders. 
     Each cylinder  16  and corresponding piston  18  cooperate to define a combustion chamber  20  having one or more conventional intake valves  22  and exhaust valves  24 . The valves  22  and  24  may be operated in several ways that are well known in the art. First, the valves  22  and  24  can be cam operated. Second, they could be operated in a “camless” manner, using electromagnetic or electrohydraulic actuators or the like. Third, a hybrid, cam and camless, method could be used in which the valves are actuated with a cam and alternative “camless” type actuators. One or more—and preferably all—of the cylinders  16  are provided with a brake actuator, generally designated  26 , forming part of the engine compression release brake system  14 . Each brake actuator  26  is preferably controllable to open one or more exhaust valves  24  with timing independent of engine speed. It should be noted that the system could also implement a separate, dedicated retarder valve as opposed to using one of the exhaust  24  or intake  22  valves. 
     FIG. 1 diagrammatically illustrates a compression brake system  14 . A variety of compression brake systems are known in the art and the present invention would work well with all systems capable of changing timing or otherwise selecting a mode of operation that reduces noise at blow down. Greater details on how compression brake systems are structured and operate can be found in commonly owned U.S. patent application Ser. Nos. 9/742730 and 9/441854, as well as U.S. Pat. Nos. 5,012,778 to Pitzi and 5,357,926 to HU. As generally shown in FIG. 1, the compression brake system  14  comprises a brake actuator  26 , an electronic control valve  28 , a high pressure pump  30 , and a source of hydraulic fluid  32 . The pump  30  has a fluid line that connects it to the low pressure source of hydraulic fluid, which is preferably lubricating fluid, such as oil, but could be a variety of other fluids including fuel or transmission fluid. The pump  30  then provides high pressure fluid to the electronic control valve  28 . The valve  28  is preferably a 3-way poppet or spool valve operated by solenoid or piezo actuator but could have other configurations. The electronic control valve  28  is controlled by electronic control unit (ECU)  34 . When the electronic control valve  28  is actuated, high pressure fluid actuates a piston in the brake actuator  26  which, in turn, opens the exhaust valve  24 . 
     Braking is accomplished by opening a cylinder valve, usually the exhaust valve  24 , when the piston is near top dead center (TDC) during the compression stroke. Specifically, during the compression stroke, the piston  18  works to compress air in the combustion chamber  20 . When the exhaust valve is opened near TDC, the compressed air is vented or “blown down” and thus no energy is imported back into the drive train during the subsequent turnaround stroke of the piston (i.e. the normal “power stroke”). This has a retarding effect on the engine as a whole, helping to slow the vehicle  10 . The closer the piston  18  is to TDC, the more work the piston has performed before the cylinder pressure is blown down and consequently, the more braking power that is generated. Unfortunately, the closer the exhaust valve  24  is to TDC when it is opened, the more noise emissions that are created. FIGS. 4 and 5 illustrate representative noise emissions and retarding torque based on the timing of the braking event. 
     When the desired braking event is accomplished, the electronic control valve is deactivated, stopping high pressure fluid from acting on the brake actuator  26  and venting the high pressure fluid present in the brake actuator  26 , allowing exhaust valve  24  to return to it&#39;s closed position. 
     The ECU  34  controls the timing of the braking events by actuating the electronic control valve  28 . Depending on when the ECU actuates the control valve  28 , various levels of braking can be obtained with various levels of noise. In particular, it is important to be able to control the noise level of the brakes. In many urban areas, for example, noise restrictions limit the amount of noise that can be produced by a vehicle. In order to comply with the laws in these noise restricted areas, it is desirable to be able to control the timing of the braking event to reduce noise emissions. According to one aspect of the present invention, the ECU  34  automatically recognizes that the vehicle  10  is in a noise restricted area and adjusts the brake timing accordingly. 
     The ECU  34  communicates with at least one sensor  36  to receive information that allows the ECU  34  to determine that the vehicle  10  is in a noise restricted area. The sensor can receive a variety of information to help the ECU  34  make the proper determination. In FIG. 1, the sensor  36  is illustrated receiving data from a satellite, such as global positioning data from a global positions satellite (GPS)  38 . The GPS data would allow the ECU  34  to determine that it was in an urban or other noise restricted area and then adjust the brake timing accordingly. In FIG. 2, the sensor  36  is illustrated receiving data from a land-based transmitter  40 . The transmitter  40 , could be transmitting a variety of signals including sonic (e.g. RF) and light based (e.g. 1R) signals and could be located near a city limit or wherever noise restrictions took effect. In FIG. 3, the sensor  36  is designed to monitor vehicle  10  parameters, designated as p1-p4, that would indicate that the vehicle  10  is being operated in an urban area and noise levels should be controlled. Specifically, the sensor  36  could monitor a variety of vehicle parameters including vehicle speed, gear selection, and frequency of gear selection and speed changes. 
     The system illustrated in FIG. 1 also illustrates a manual override switch  42 . This would allow the vehicle operator to decide that the ECU  34  should not reduce braking power based upon a signal from the sensor  36 . A vehicle operator may want this ability if road conditions are bad or in the case of an emergency where full retarding power is desired. The ECU  34  could also provide an automatic override function. In this case, the sensor  36  could also monitor vehicle parameters, such as brake pedal position, to determine the amount of braking power requested by the operator. The ECU  34  could then determine if an emergency stop was required and automatically provide maximum braking even if the vehicle was in a noise restricted area. The system illustrated in FIG.  1 . also illustrates a signal light,  44 . The signal light  44  would be controlled by the ECU  34  such that it would be on whenever the vehicle  10  was operating in a noise reduction mode. This would keep the operator informed about the operating conditions of the vehicle  10 . As an alternative to or an addition to this visual signal, an audible signal could also be sounded. 
     Industrial Applicability 
     The present invention automatically controls compression brake noise by determining when the vehicle  10  is in an urban area or an otherwise noise restricted area. As stated previously, the specific structure of the compression brake system  14  can take a variety of forms as long as it is controllable by the ECU  34 . The ECU  34  controls when the timing of the braking events in order to control noise emissions. In the default operating mode, the ECU  34  will provide the maximum amount of braking allowed without regard to noise emissions. However, the ECU  34  can automatically change to a reduced-mode when it receive information from the sensor  36  which indicates that the vehicle  10  is operating in a noise restricted area. 
     The sensor  36  can be designed to receive information from a variety of sources such as GPS or other satellite land-based transmitter, or vehicle systems. Once the sensor  36  receives information, the ECU  34  processes the information and determines if the vehicle  10  is operating in a noise restricted area. If the vehicle is in a noise restricted area, the ECU  34  alters the compression brake timing and activates a signal such as light  44 , to inform the operator that the vehicle is in the reduced noise mode and that less retarding is thus available. 
     The reduced retarding mode can be turned off manually by the operator by activating the override switch  42 . Further the ECU  34  can automatically override the reduced retarding mode if it senses an emergency and the immediate need for full retarding. 
     Although the presently preferred embodiments of this invention have been described, various other modifications could be made to the illustrated embodiments without operating from the scope of the claims below.