60/065,816, filed on November 14,1997.

Field of the Invention The present invention relates to an apparatus and method for implementing a fully- hydraulic valve train on an internal combustion engine. This invention includes features that allow for the elimination of lash adjustment, elimination of mechanical valve train components, and integrated retarding function.

Background of the Invention There currently is an interest in new valve actuation systems that provide superior function at lower total system cost than comparable components available today. Many of the systems that are known today provide compression release retarding by adding components to the engine, which increases cost. Systems that eliminate the need for lash adjustment during engine assembly and field service save time and money for the customer.

Objects of the Invention It an object of the present invention to provide a method for implementing a fully hydraulic valve train on an internal combustion engine.

It is another object of the present invention to provide a system for implementing a fully hydraulic valve train on an internal combustion engine.

It is another object of the present invention to provide a system that allows the adaptation from a fixed-timed valve actuation system to a variable timed valve actuation system.

It is another object of the present invention to provide compression release retarding by means of hydraulically switching the exhaust valve train between positive power and retarding modes.

It is another object of the present invention to provide integrated lost motion compression release retarding.

It is another object of the present invention to provide engine retarding with internal exhaust gas recirculation for enhanced performance.

It is another object of the present invention to eliminate the need for lash adjustment.

It is another object of the present invention to provide a system having low total system height, weight and cost.

It is another object of the present invention to provide a system having limited accumulation of hydraulic fluid to provide a predictable back up mode.

It is another obj ect of the present invention to provide a system for implementing a fully- hydraulic valve train which eliminates mechanical valve train components.

Brief Summary of the Invention The present invention is directed to a system which will replace, rather than augment, the existing mechanical valve train (rocker arms) while eliminating the need for lash adjustment, and providing compression release retarding by means of hydraulically switching the exhaust valve train between positive power and retarding modes. This system also lends itself to adaptation from a fixed-timed valve actuation system to a variable-timed valve actuation system.

The present invention is directed to a valve actuation system for an internal combustion engine. The valve actuation system includes an intake valve actuation assembly for operating at least one intake valve in response to an intake cam. The valve actuation system further includes an exhaust valve actuation assembly for operating at least one exhaust valve in response to at least one exhaust cam to produce at least one of a main exhaust event, an engine retarding event and an exhaust gas recirculation event. The exhaust valve actuation assembly is capable of operating in two modes. In the first operating mode, the at least one exhaust valve is operated to produce the main exhaust event. In the second operating mode, the at least one exhaust valve

is operated to produce at least one of the main exhaust event, the engine retarding event and the exhaust gas recirculation event.

The intake valve actuation assembly may comprise an intake energy deriving assembly for deriving energy from the intake cam, and an intake energy transfer assembly for transferring energy derived from the intake energy deriving assembly for operating the at least one intake valve. The intake energy transfer assembly may include an intake hydraulic fluid assembly for transferring energy derived from the intake energy deriving assembly. The intake energy transfer assembly may further include an intake hydraulic fluid supply assembly.

The exhaust valve actuation assembly may comprise an exhaust energy deriving assembly for deriving energy from the exhaust cam, and an exhaust energy transfer assembly for transferring energy derived from the exhaust energy deriving assembly for operating the at least one exhaust valve. The exhaust energy transfer assembly may include a control assembly for controlling the operation of the exhaust energy transfer assembly wherein the exhaust energy transfer assembly operates in one of the first operating mode and the second operating mode in response to the control assembly. The exhaust energy transfer assembly may further include an exhaust hydraulic fluid supply assembly. The control assembly is in communication with the exhaust hydraulic fluid supply assembly.

The control assembly may include a valve assembly for switching between the first operating mode and the second operating mode, and an energy storage assembly for storing a portion of the exhaust energy from the exhaust energy deriving assembly when in the first operating mode. It is contemplated that the exhaust valve actuation assembly is capable of fixed timing valve actuation. Furthermore, it is contemplated that the exhaust valve actuation assembly is capable of variable timing valve actuation.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only. And are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated herein by reference and which constitute a part of the specification, illustrate certain embodiments of the invention and, together with the detailed description, serve to explain the principles of the present invention.

Brief Description of the Drawings The present invention will now be described in connection with the following figures in which like reference numbers refer to like elements and wherein: Fig. 1 is a schematic view of the intake configuration of the valve actuation system according to the present invention; Fig. 2 is a schematic view of the exhaust configuration of the valve actuation system according to the present invention; and Fig. 3 is a graph depicting exhaust valve lift according to the present invention.

Detailed Description of the Invention Fig. 1 depicts the intake circuit 10 of the lost motion hydraulic overhead system according to an embodiment of the present invention. The intake circuit 10 includes a master piston 110 positioned within housing 100. The master piston 110 includes a cam follower 111 that follows intake cam 1. The master piston 110 is connected to at least one slave pistons 120 through passage 130. The passage 130 preferably receives hydraulic fluid therein whereby force imparted by the master piston 110 is transferred to the at least one slave piston 120 by hydraulic pressure. The hydraulic pressure may be amplified or reduced by suitable means (such as, for example, an accumulator) if it is necessary to control the hydraulic pressure applied to the at least one slave piston 120. A fluid source 140 is connected to the passage 130. The fluid source 140 replaces fluid lost from the intake circuit 10 due to leakage. The fluid source 140 may include a suitable assembly to prevent the backflow of hydraulic fluid to the fluid source. In a preferred embodiment, a check valve 141 is used to prevent the backflow of fluid.

Fig. 2 depicts the exhaust circuit 20 of the lost motion hydraulic overhead system according to an embodiment of the present invention. The exhaust circuit 20 is a similar hydraulic motion transmitting device. The exhaust circuit 20, however, is more sophisticated than the intake circuit 10 because it can be switched between operating modes. The exhaust circuit 20 includes a master piston 210 positioned within housing 100. The master piston 210 includes a cam follower 211 that follows the profile of exhaust cam 2. It is contemplated that the exhaust cam 2 has multiple lobes 21,22 and 23 corresponding to multiple exhaust valve

operating events including, but not limited to, a main exhaust event, a retarding event and an exhaust gas recirculation event. The exhaust circuit 20 also has a high pressure circuit 250. The exhaust circuit 20 further includes a spool valve 220. The spool valve 220 controls the operating mode of the exhaust circuit 20. The operation of the spool valve 220 is controlled by working fluid, controlled by a valve assembly 230. The assembly valve 230 is preferably a solenoid valve 230. When the solenoid valve 230 is deactivated, the spool valve 220 is in a home position as shown in Fig. 2. In home state, the high pressure circuit 250 is connected with an accumulator 240. The accumulator is capable of absorbing only a portion of the oil that is displaced by the master piston 210 in a complete stroke. As the master piston 210 starts to follow any of the auxiliary lobes 22 and 23 on the cam 2, the accumulator 240 absorbs all motion. Once the master piston 210 starts to follow the main lobe 21, the accumulator 240 goes solid so that it cannot absorb any additional motion. Thus, the full exhaust motion occurs as it would without the present invention.

The operation of the system will now be described. The master piston 110 of the intake circuit 10 controls the operation of the at least one valve piston 120. The motion of the master piston 110 in response to cam 1 is transferred to the at least one slave piston 110 to operate the intake valves. The opening and closing of the valves operated by the slave pistons 120 are controlled by the profile of cam 1.

During normal exhaust operation (i. e., no retarding event or exhaust gas recirculation event), the spool valve 220 is in the position shown in Fig. 2. In this position, a portion of the hydraulic fluid displaced by the master piston 210 will travel through the high pressure circuit 250 to the accumulator 240. Accordingly, a portion of the motion located below the dashed line in Fig. 3 is absorbed by the accumulator 240. In particular, the motion of the master piston 210 in response to the cam lobes 22 and 23 for the retarding event and exhaust gas recirculation event is absorbed which prevents opening of the exhaust valve. The exhaust valve will open in response to the main lobe 21 on cam 2 for the main exhaust event because the amount of fluid displaced by the master piston 210 is greater than that which can be absorbed by the accumulator 240, as shown in Fig. 3.

When exhaust retarding and exhaust gas recirculation events are desired, the solenoid valve 230 is operated to move the spool valve 220 to an OFF position. As a result, the

accumulator 240 is excluded from the high pressure circuit 250. In this position, all motion from the master piston 210 is transferred to the slave piston 260. This permits the opening of the exhaust valves in response to the auxiliary lobes 22 and 23 on cam 2 to permit a retarding event and an exhaust gas recirculation event.

It will be apparent to those skilled in the art that various modifications and variations can be made in the construction and configuration of the present invention without departing from the scope or spirit of the invention. For example, the high pressure circuits in both the intake circuit 10 and exhaust circuit 20 may be formed from external tubing or an integral passage formed in housing 100. The present invention may be used in connection with a cam profile having braking and positive power EGR lobes. It, however, is contemplated that the present invention may be used without engine braking and/or EGR. The slave pistons 120 and 260 may include spill ports to prevent excess valve motion during braking. The followers on the master piston may comprise a suitable cam follower including, but not limited to, an oscillating follower, flat follower and/or roller follower. Additionally, it is contemplated that the spool valve 220 and valve 230 may be replaced with a single high pressure solenoid valve.

Furthermore, makeup hydraulic fluid may be supplied directly to the hydraulic circuit rather than through the accumulator, as shown in Fig. 2. The intake circuit may also have a configuration to exhaust circuit 20, described above, such that the intake circuit may be enable and/or disable selected events. Finally, it is contemplated that the present invention is capable of being used for both fixed timing and variable timing applications.

While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.