초록 ▼

A variable valve actuation system for providing discrete exhaust and intake valve lift profiles for various operating modes of an internal combustion engine. The variable valve actuation system includes exhaust and intake rocker assemblies, exhaust and intake hydraulic extension devices operatively

A variable valve actuation system for providing discrete exhaust and intake valve lift profiles for various operating modes of an internal combustion engine. The variable valve actuation system includes exhaust and intake rocker assemblies, exhaust and intake hydraulic extension devices operatively coupling corresponding rocker assemblies with respective engine valves and exhaust and intake control valves for selectively supplying the pressurized hydraulic fluid to the extension devices so as to independently switch them between a pressurized condition and a depressurized condition. The engine further includes an exhaust brake provided to initiate a small lift of the exhaust valve during the engine braking operation while the exhaust extension device maintains the exhaust valve open during a compression stroke for bleeder-compression release braking. The exhaust and intake valves can be adjusted independently to provide combinations of valve lift modes.

대표청구항 ▼

1. A variable valve actuation system for operating at least one exhaust valve of an internal combustion engine during a positive power operation and an engine braking operation, said system comprising:an exhaust rocker assembly for operating said at least one exhaust valve, said exhaust rocker assem

1. A variable valve actuation system for operating at least one exhaust valve of an internal combustion engine during a positive power operation and an engine braking operation, said system comprising:an exhaust rocker assembly for operating said at least one exhaust valve, said exhaust rocker assembly driven by an exhaust cam member; an exhaust hydraulic extension device operatively coupling said exhaust rocker assembly with one of said at least one exhaust valve and said exhaust cam member for controlling a lift and a phase angle of said at least one exhaust valve; a source of a pressurized hydraulic fluid in fluid communication with said exhaust hydraulic extension device; and an exhaust control valve provided to selectively supply the pressurized hydraulic fluid from said source to said exhaust hydraulic extension device so as to switch said exhaust hydraulic extension device between a pressurized condition when the pressurized hydraulic fluid is supplied to said exhaust hydraulic extension device and a depressurized condition when the pressurized hydraulic fluid is not supplied to said exhaust hydraulic extension device; said engine having an exhaust brake provided to generate an exhaust backpressure sufficient to cause said at least one exhaust valve to open near a bottom dead center of an intake stroke of the engine during the engine braking operation; said exhaust hydraulic extension device in said pressurized condition provided to maintain said at least one exhaust valve open during a compression stroke when said engine performs the engine braking operation. 2. The variable valve actuation system as defined in claim 1, wherein said exhaust hydraulic extension device is operatively coupled to said exhaust rocker assembly adjacent to said at least one exhaust valve.3. The variable valve actuation system as defined in claim 1, wherein said exhaust hydraulic extension device is operatively coupled to said exhaust rocker assembly adjacent to said exhaust cam member.4. The variable valve actuation system as defined in claim 1, wherein said exhaust hydraulic extension device is a hydraulically expandable linkage including a lower lifter body slidingly mounted within said exhaust rocker assembly and an upper lifter body adapted to reciprocate within said lower lifter body between an expanded position and a collapsed position; said lower lifter body and said upper lifter body define a variable volume hydraulic chamber therebetween.5. The variable valve actuation system as defined in claim 4, wherein said exhaust rocker assembly further includes a fluid channel providing the pressurized hydraulic fluid from said source to said hydraulic chamber to extend said exhaust hydraulic extension device when there is a gap between said exhaust extension device and said at least one exhaust valve.6. The variable valve actuation system as defined in claim 4, wherein said exhaust hydraulic extension device further includes a check valve provided to hydraulically lock said hydraulic chamber when a pressure of the hydraulic fluid within said hydraulic chamber exceeds the pressure of the hydraulic fluid from said source.7. The variable valve actuation system as defined in claim 4, further including means permitting controlled leakage of the pressurized hydraulic fluid from said hydraulic chamber during the compression stroke, said means permitting controlled leakage is calibrated so as to allow said at least one exhaust valve to substantially close near the completion of the compression stroke.8. The variable valve actuation system as defined in claim 7, wherein said means permitting controlled leakage of the pressurized hydraulic fluid is a radial clearance between said upper lifter body and an internal bore in said lower lifter body.9. The variable valve actuation system as defined in claim 4, further including means permitting controlled leakage of the pressurized hydraulic fluid from said hydraulic chamber during the compression stroke, said means permitting controlled leakage is calibrated so as to maintain said at least one exhaust valve substantially open throughout the entire engine cycle.10. The variable valve actuation system as defined in claim 9, wherein said means permitting controlled leakage of the pressurized hydraulic fluid is a radial clearance between said upper lifter body and an internal bore in said lower lifter body.11. The variable valve actuation system as defined in claim 1, wherein said exhaust brake includes a butterfly valve operated by an exhaust brake actuator.12. The variable valve actuation system as defined in claim 1, wherein said exhaust brake includes a variably restrictive turbocharger.13. The variable valve actuation system as defined in claim 1, wherein said exhaust hydraulic extension device maintains said at least one exhaust valve open throughout the compression stroke.14. The variable valve actuation system as defined in claim 1, further including an electronic controller operatively connected to said exhaust control valve for selectively opening thereof depending on operating demand of the engine and to said exhaust brake so as to adjust said exhaust brake during braking operation of said variable valve actuation system so that the exhaust pressure is sufficient to cause said at least one exhaust valve to open.15. The variable valve actuation system as defined in claim 14, wherein said electronic controller includes a lookup table of exhaust pressure values which are sufficient to cause said exhaust valve to open, but below a predetermined maximum value.16. The variable valve actuation system as defined in claim 14, further including a temperature sensor for sensing an exhaust gas temperature, said temperature sensor being operatively connected to said electronic controller, said electronic controller adjusting said exhaust brake so that the exhaust gas temperature remains below a predetermined maximum value.17. The variable valve actuation system as defined in claim 1, wherein said system provides an extended lift and phase angle of said at least exhaust valve when said exhaust hydraulic extension device in said pressurized condition and a reduced lift and phase angle of said at least exhaust valve when said exhaust hydraulic extension device in said depressurized condition.18. The variable valve actuation system as defined in claim 17, wherein said extended and reduced lift and phase angle of said at least exhaust valve are provided during said positive power operation.19. The variable valve actuation system as defined in claim 1, wherein said engine further includes at least one intake valve, an intake rocker assembly driven by an intake cam member for operating said at least one intake valve, an intake hydraulic extension device operatively coupling said intake rocker assembly with one of said at least one intake valve and said intake cam member for controlling a lift and a phase angle of said at least one intake valve and an intake control valve provided to selectively supply the pressurized hydraulic fluid from said source to said intake hydraulic extension device so as to selectively switch said intake hydraulic extension device between a pressurized condition when said pressurized hydraulic fluid is supplied to said intake hydraulic extension device and a depressurized condition when said pressurized hydraulic fluid is not supplied to said intake hydraulic extension device.20. The variable valve actuation system as defined in claim 19, wherein said system provides an extended lift and phase angle of said at least intake valve when said intake hydraulic extension device in said pressurized condition and a reduced lift and phase angle of said at least intake valve when said intake hydraulic extension device in said depressurized condition.21. The variable valve actuation system as defined in claim 19, wherein said intake rocker assembly and said intake hydraulic extension device are substantially identical to said exhaust rocker assembly and said exhaust hydraulic extension device.22. The variable valve actuation system as defined in claim 1, wherein said exhaust brake generates the exhaust backpressure sufficient to cause said at least one exhaust valve to open prior to the bottom dead center of an intake stroke of the engine when said exhaust hydraulic extension device is in said pressurized condition during the engine braking operation.23. The variable valve actuation system as defined in claim 1, wherein said exhaust hydraulic extension device controls said lift and said phase angle of said at least one exhaust valve during said positive power operation.24. A method for controlling a variable valve actuation system for operating at least one exhaust valve of an internal combustion engine during a positive power operation and an engine braking operation; said system comprising an exhaust rocker assembly driven by an exhaust cam member for operating said at least one exhaust valve, an exhaust hydraulic extension device operatively coupling said exhaust rocker assembly with one of said at least one exhaust valve and said exhaust cam member for controlling a lift and a phase angle of said at least one exhaust valve, a source of a pressurized hydraulic fluid and an exhaust control valve provided to selectively supplying the pressurized hydraulic fluid from said source to said exhaust hydraulic extension device so as to selectively switch said exhaust hydraulic extension device between a pressurized condition and a depressurized condition; said engine having an exhaust brake; said method comprising the steps of:a) determining an operating mode demanded; b) if the braking operation is demanded then: 1) opening said exhaust control valve to set said exhaust hydraulic extension device in said pressurized condition; 2) adjusting said exhaust brake to generate an exhaust backpressure sufficient to cause said at least one exhaust valve to open near a bottom dead center of an intake strokes of said engine; and 3) maintaining said at least one exhaust valve open during a compression stroke when said engine performs the engine braking operation; c) if the positive power operation is demanded then: 1) determining a lift and phase angle of said at least exhaust valve demanded; 2) opening said exhaust control valve to set said exhaust hydraulic extension device in said pressurized condition if an extended lift and phase angle of said at least one exhaust valve is demanded; and 3) closing said exhaust control valve to set said exhaust hydraulic extension device in said depressurized condition if a reduced lift and phase angle of said at least one exhaust valve is demanded. 25. The method for controlling said variable valve actuation system as defined in claim 24, wherein said engine further includes at least one intake valve, an intake rocker assembly driven by an intake cam member for operating said at least one intake valve, an intake hydraulic extension device operatively coupling said intake rocker assembly with one of said at least one intake valve and said intake cam member for controlling a lift and a phase angle of said at least one intake valve and an intake control valve provided to selectively supply the pressurized hydraulic fluid from said source to said intake hydraulic extension device so as to selectively switch said intake hydraulic extension device between a pressurized condition and a depressurized condition; said method further comprising the steps of:opening said intake control valve to set said intake hydraulic extension device in said pressurized condition if an extended lift and phase angle of said at least intake valve is demanded; and closing said intake control valve to set said intake hydraulic extension device in said depressurized condition if a reduced lift and phase angle of said at least intake valve is demanded.