Engine valve actuation system and method using reduced pressure common rail and dedicated engine valve

Abstract

A system and method for actuating an engine valve to provide engine braking and/or exhaust gas recirculation using a common source of hydraulic fluid is disclosed. The system receives high pressure hydraulic fluid from a common rail system, such as those used to provide fuel injection. The fluid pressure is reduced before being used to actuate an engine valve for engine braking or EGR. Preferably an engine valve that is dedicated to the engine braking or EGR function is provided in the engine. The dedicated engine braking/EGR valve may be driven by an electromagnetic actuator in an alternative embodiment.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to methods and apparatus for actuating an engine valve in an internal combustion engine to achieve a compression-release braking event, a bleeder type engine braking event, and/or an internal exhaust gas recirculation (EGR) event.

BACKGROUND OF THE INVENTION

[0002] During engine braking, the exhaust valves may be selectively opened to convert, at least temporarily, a power producing internal combustion engine into a power absorbing air compressor. As a piston travels upward during its compression stroke, the gases that are trapped in the cylinder are compressed. The compressed gases oppose the upward motion of the piston. During engine braking operation, as the piston nears top dead center (TDC), at least one engine valve that communicates with the exhaust manifold may be opened to release the compressed gases, preventing the energy stored in the compressed gases from being returned to the engine on the subsequent expansion down-stroke. In doing so, the engine develops retarding power to help slow the vehicle down.

[0003] The operation of a compression-release type engine brake, as described in the preceding paragraph has long been known. One of the earliest descriptions of a system used for compression-release braking is provided in Cummins, U.S. Pat. No. 3,220,392. The system described in the Cummins '392 patent derives the motion to open a pair of exhaust valves for a compression-release event from an existing intake, exhaust, or injector pushrod or rocker arm. The compression-release motion is conveyed from a pushrod or rocker arm to a bridge joining two exhaust valves by a selectively expandable hydraulic linkage. This hydraulic linkage is expanded to convey the compression-release motion during engine braking operation, and contracted to absorb such motion during positive power operation. The contraction of the hydraulic linkage during positive power operation causes the compression-release motion to be “lost” during positive power, and accordingly, such systems are commonly referred to as “lost motion” valve actuation systems.

[0004] In the lost motion systems, such as the Cummins system, the engine valves are typically driven by fixed profile cams, more specifically, by one or more fixed lobes on each of the cams. The use of fixed profile cams makes it difficult to adjust the timing and/or magnitude of the engine valve lift needed to optimize engine performance for various engine operating conditions, such as different engine speeds during engine braking.

[0005] Over the years there have been various improvements to the systems and methods described in the Cummins '392 patent. One such improvement has been to use a common source of high pressure fluid, such as that used for fuel injection systems, to actuate one or more valves for engine braking. Such systems are often called “common rail” systems. In common rail valve actuation systems, a source of high pressure hydraulic fluid is selectively applied to an actuator piston to actuate one or more valves for the compression-release events. The valves chosen for actuation to achieve engine braking are most commonly exhaust valves. Examples of such systems are shown in Sickler, U.S. Pat. No. 4,572,114, Pitzi, U.S. Pat. No. 5,012,778, and Meistrick et al., U.S. Pat. Nos. 5,787,859, 5,809,964, and 6,082,328, each of which are hereby incorporated by reference. In some common rail systems, a dedicated auxiliary valve is provided for engine braking. Examples of such systems are shown in Korte et al., U.S. Pat. No. 5,564,386, Schmidt et al., U.S. Pat. No. 5,609,134, and Bergmann, U.S. Pat. No. 5,794,590, each of which are hereby incorporated by reference.

[0006] Common rail systems may provide virtually limitless adjustment to valve timing because the source of high pressure hydraulic fluid is constantly available for valve actuation. Because common rail systems theoretically may provide almost infinite variation in valve timing, they may be used to carry out almost any type of engine valve event, such as intake, exhaust, compression-release braking, bleeder braking, or exhaust gas recirculation (EGR), so long as the valve being actuated has communication with the appropriate manifold (i.e. the intake or exhaust manifold). Accordingly, given sophisticated and high speed control over the application of this hydraulic pressure, a common rail system should be able to deliver valve actuation on demand for a variety of valve events, as well as provide some control over lift and duration.

[0007] To date, however, common rail engine valve actuation systems used for braking and EGR have not been widely used. The necessary sophisticated control, particularly in the seating of engine valves, has not been effectively realized. Two problems in particular that tend to discourage the use of common rail actuation systems are the expense of the components required to exercise the level of control called for, and the susceptibility of the system to complete failure in the event of a loss in hydraulic pressure. Until these problems are solved, it is likely that lost motion systems will continue to be the predominate type of system used to carry out engine braking.

[0008] The foregoing problems with common rail systems stem in part from the use of very high pressure sources to open the engine valves, and in part from the reliance on the systems to carry out critical valve events, i.e. main intake and main exhaust events. The proposed use of very high pressure systems for common rail engine braking has resulted from the plan to piggy-back the engine braking system off of the common rail fuel injection system that is already installed on a vehicle. This “piggy-backing” is thought to provide significant cost savings because only one high pressure source (and set of components) may be needed for two systems, engine braking and fuel injection. Because fuel injection requires very high pressures, on the order of 3000 psi, attempts have been made to provide an engine braking common rail system that uses fluid at a similar pressure. Use of such high pressure, however, dictates the use of a very high force return spring for the actuated valve, which in turn requires complicated valve seating apparatus. Furthermore, leakage is more of a problem for high pressure systems, and component design is inherently more critical and expensive. Accordingly, there is a need for a common rail system that may be used for engine braking and EGR that does not suffer from the disadvantages that accompany the use of high pressure fluid for common rail actuation.

[0009] A second significant challenge that arises from the use of common rail systems for engine valve actuation is the potential for failure of the system. An hydraulic system suffers from vulnerability to failure as a result of fluid leakage. The greater the extent of leakage prevention measures, the more expensive the system becomes. Failure of a common rail system to deliver engine braking and/or EGR would not in and of itself be catastrophic since the vehicle could certainly be operated without these features, albeit sub-optimally. Loss of main intake or main exhaust valve events, however, cannot be tolerated because it results in the complete failure of the engine. Accordingly, there is a need for a common rail system that is responsible only for engine braking and/or EGR valve events, but is not required for main intake or main exhaust engine valve events.

[0010] Applicants have solved various of the foregoing challenges to the effective use of common rail systems for engine braking and EGR by coupling a reduced pressure common rail system, or an electromagnetically driven actuator, with a dedicated engine braking/EGR engine valve. The use of reduced pressure reduces the likelihood and effect of leakage, and reduces valve train load. Furthermore, such a system may provide near infinite timing variations for engine braking and internal EGR without jeopardizing the main intake and exhaust valve operation.

[0011] Additional objects and advantages of some, but not necessarily all, of embodiments of the present invention are set forth, in part, in the description which follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.

SUMMARY OF THE INVENTION

[0012] Responsive to the foregoing challenges, Applicants have developed an innovative engine valve actuation system for engine braking and/or exhaust gas recirculation comprising: a high pressure hydraulic fluid source; a fluid pressure reduction device connected to the high pressure hydraulic fluid source; a hydraulic fluid control valve connected to the fluid pressure reduction device; and an engine valve actuator connected to the hydraulic fluid control valve.

[0013] In one embodiment, the present invention is an engine valve actuation system comprising: a high pressure hydraulic fluid passage; a high pressure hydraulic fluid source; a fluid pressure reduction device connected to the hydraulic fluid source through the high pressure hydraulic fluid passage; a low pressure hydraulic fluid passage; a hydraulic fluid control valve connected to the fluid pressure reduction device through the low pressure hydraulic fluid passage; an actuator hydraulic fluid passage; and an engine valve actuator for producing an engine valve event, the engine valve actuator communicating with the hydraulic fluid control valve through the actuator hydraulic fluid passage.

[0014] In another embodiment, the present invention is a method for actuating an engine valve in an internal combustion engine to produce an engine valve event. The method may comprise the steps of: providing hydraulic fluid to a fluid pressure reduction device; reducing the pressure of the hydraulic fluid from a first pressure to a second pressure; selectively applying the hydraulic fluid at the second pressure to an engine valve actuator; and actuating the engine valve to produce the engine valve event.

[0015] 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 this 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

[0016] In order to assist the understanding of this invention, reference will now be made to the appended drawings, in which like reference characters refer to like elements. The drawings are exemplary only, and should not be construed as limiting the invention.

[0017] FIG. 1 is a block diagram of an engine valve actuation system according to a first embodiment of the present invention.

[0018] FIG. 2 is a block diagram of an engine valve actuation system according to a second embodiment of the present invention.

[0019] FIG. 3 is a schematic diagram of an engine valve actuation system according to a third embodiment of the present invention.

[0020] FIG. 4 is a block diagram of an engine valve actuation system according to a fourth embodiment of the invention.

[0021] FIG. 5 is a schematic diagram of an engine valve actuation system according to a fifth embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0022] Reference will now be made in detail to embodiments of the present invention, an example of which is illustrated in the accompanying drawings. With reference to FIG. 1, a valve actuation system 10 for an internal combustion engine is shown. In one embodiment, the valve actuation system 10 may comprise: a high pressure hydraulic fluid source 100; a fluid pressure reduction device 300 connected to the high pressure hydraulic fluid source 100; a hydraulic fluid control valve 400 connected to the fluid pressure reduction device 300; and an engine valve actuator 600 connected to the hydraulic fluid control valve 400 for actuating an engine valve 700. The engine valve 700 may comprise a dedicated braking valve. It is contemplated, however, that the engine valve 700 may comprise an exhaust valve, and/or an intake valve.

[0023] In another embodiment of the present invention, as shown in FIG. 2, the valve actuation system 10 may further comprise an accumulator 500 connected to the hydraulic fluid control valve 400; and a low pressure hydraulic fluid tank 200 connected to the high pressure fluid source 100.

[0024] With reference to FIG. 3, in one embodiment of the invention the valve actuation system 10 includes a high pressure fluid source 100, such as may be used to supply a common rail fuel injection system. The hydraulic electronic unit injection (HEUI) system sold by Navistar International is one example of such a common rail fuel injection system.

[0025] The high pressure fluid source 100 may include a high pressure pump 110, a pressure regulator 120, and a high pressure plenum 130. The high pressure fluid pump 110 may draw hydraulic fluid, such as diesel fuel, from a low pressure tank 200. The fluid pressure provided by pump 110 may be on the order of several thousand (e.g. 3000) psi. High pressure fluid sources 100 are known in the art for fuel injection systems. The pressure provided by the high pressure fluid source 100 may be indicated by pressure P1.

[0026] In the embodiment of the present invention shown in FIG. 3, the high pressure fluid provided by the source 100 may be used, not only to provide fuel injection, but also to provide a motivating source for engine braking operation. One advantage of using the high pressure fluid source, such as source 100, for engine braking is that it is already resident in the engine. In order to take advantage of the high pressure source 100 for engine braking purposes, pressurized fluid from the high pressure fluid source 100 may be provided through a high pressure line 140 to a pressure reducing device 300. The pressure reducing device 300 preferably may reduce the pressure of the fluid by approximately a magnitude, and more preferably to a level of approximately 300 psi. The reduced pressure fluid may be provided through line 310 to a control valve 400. The pressure provided by the pressure reducing device 300 may be indicated by pressure P2.

[0027] In one embodiment, the pressure reducing device 300 may comprise a pressure reducing valve. The pressure reducing device 300 may comprise a directly-operated pressure reducing valve, a two-way pilot-operated pressure reducing valve, and/or any other known pressure reducing valve. As will be apparent to those of ordinary skill in the art, other pressure reducing devices adapted to reduce the pressure of the fluid from the high pressure fluid source 100 are considered to be within the scope and spirit of the present invention.

[0028] With continued reference to FIG. 3, the control valve 400 may include a valve body 410 and a controller 420. The valve body 410 is preferably a 3/2 directional control valve and may include internal passages that connect a first port 412 with a second port 414, and a third port 416 with a fourth port 418. The valve body 410 may be biased into a default position by a control valve spring 430.

[0029] In the default position the internal passages in the valve body 410 may connect the brake actuator line 440 with an accumulator 500. In an alternative embodiment, as shown in FIG. 4, the accumulator 500 may be replaced with a vent or a fluid return line that connects the control valve 400 to the low pressure tank 200.

[0030] The controller 420 may be used to translate the valve body 410 so that fluid flows to and from the brake actuator line 440. In FIG. 3, the valve body 410 may be translated linearly toward the control valve spring 430. The controller 420 may be any suitable device for translating the valve body 410 at high speed. It is appreciated that the controller 420 may be a hydraulic, hydroelectric, mechanical, piezoelectric, or electromagnetic (e.g. solenoid) device. The controller 420 preferably is capable of translating the valve body 410 at least once, and preferably more than once per engine cycle.

[0031] It is further appreciated that the controller 420 is preferably controlled by an electrical signal issued by an engine control module (ECM) (not shown). As will be apparent to those of ordinary skill in the art, the ECM may include a microprocessor, and may be connected to sensors linked to other engine components, such as for example, the engine cylinder, the exhaust manifold, the intake manifold, or any other engine component, to control the controller 420.

[0032] The brake actuator line 440 provides fluid communication between the control valve 400 and the engine valve actuator 600. The engine valve actuator 600 includes a fluid chamber 610, an actuator piston 620 disposed to slide in the fluid chamber, and a return spring 630.

[0033] The return spring 630 is shown inside of the fluid chamber 610, however, it is appreciated that the return spring may be provided at any location between the engine valve actuator 600 and the engine cylinder (not shown). The return spring 630 may even be provided as a return spring for the dedicated brake valve 700 since return of the dedicated brake valve 700 to its up most position will also return the actuator piston 620 to its up most position.

[0034] The actuator piston 620 may terminate in an engine valve head, or alternatively, actuate an engine valve 700 dedicated to the braking and/or exhaust gas recirculation function. The engine valve 700 provides selective communication between an engine cylinder 720 and an exhaust manifold 710. The return spring 630 may bias the actuator piston 620 toward the upper end of the fluid chamber 610. In this position the dedicated engine valve 700 is closed.

[0035] The control valve 400 may assume two primary positions under the influence of the controller 420. A first position of the control valve 400 corresponds to the condition in which no engine braking and/or exhaust gas recirculation is desired, i.e. the dedicated engine valve 700 is closed. When the dedicated engine valve 700 is to be closed, the controller 420 maintains the valve body 410 in the position shown in FIG. 3. In this position the first port 412 of the valve body 410 communicates with the brake actuator line 440 and the second port 414 communicates with the accumulator 500. As a result, the valve body 410 provides communication between the fluid chamber 610 and the accumulator 500. Fluid pressure in the accumulator 500 is low, and, accordingly, the dedicated engine valve return spring (which may be spring 630) can displace the actuator piston 620 upward to push fluid out of the fluid chamber 610 and into the accumulator 500. No new fluid may flow into the fluid chamber 610 to displace the actuator piston 620 downward because the control valve 400 is not in a position in which it provides communication between the reduced pressure line 310 and the brake actuator line 440.

[0036] When engine braking and/or exhaust gas recirculation is desired, the actuator piston 620 may be displaced downward to actuate the dedicated engine valve 700 as a result of application of reduced pressure fluid from the control valve 400 on the actuator piston. When the actuator piston 620 is displaced downward toward the dedicated engine valve 700, the dedicated engine valve is open and gas is free to flow between the engine cylinder associated with the dedicated engine valve and the exhaust manifold.

[0037] As an initial matter, the system may be turned “on” for braking, EGR, or other valve actuation duty by applying reduced fluid pressure from the pressure reducing device 300 to the reduced pressure line 310. Once fluid pressure exists in the reduced pressure line 310, the controller 420 may be instructed to translate the valve body 410 downward. This downward translation causes the third port 416 of the valve body to align with the reduced pressure line 310, and the fourth port 418 to align with the brake actuator line 440. In this position the valve body 410 provides fluid communication between the reduced pressure line 310 and the brake actuator line 440. This communication causes the brake actuator piston 620 to translate downward and open the engine valve 700 for an engine braking or exhaust gas recirculation event.

[0038] The foregoing cycle of opening and closing the engine valve 700 may be carried out as quickly as the controller 420 can cause the fluid chamber 610 to drain and refill. It is apparent that the speed of the system will depend upon the speed and size of the control valve 400, the size and length of the brake actuator line 440 and the viscosity of the working fluid. Accordingly, it may be advantageous to locate the control valve 400 as close as possible to the fluid chamber 610 to improve the response time of the system. For some embodiments of the invention, It is desired that the system be capable of more than one engine valve event per engine cycle, and that the system provide an almost infinite variety of timing selections for the opening, closing, and duration of braking and EGR events. Although it is desirable for the system to be capable of high speed actuation, the system need not always be operated at a high speed to provide beneficial results. For example, the system 10 could be used to provide partial or full cycle bleeder braking during times that braking noise is a concern (in a town or city), and to provide compression release type braking at other times when noise is of less concern.

[0039] The use of a reduced fluid pressure (i.e., on the order of 300 psi as opposed to 3000 psi) for the actuation of the dedicated engine braking valve 700 may provide several advantages. Advantages realized during braking and/or EGR include the fact that a high-speed trigger valve used as control valve 400 may be easier to make and more reliable because it need only handle reduced pressure fluid. The use of reduced pressure fluid may also reduce the impact load and seating velocity of the braking components and make such loads and velocities more controllable. Furthermore, the use of reduced pressure fluid may reduce fluid leakage and vibration of the braking system, and make the overall system more compact. Advantages realized during positive power include near infinite variation of valve timing to provide internal EGR tailored to engine speed and/or load. The system 10 could also be modified to provide cooled internal EGR since the exit passage for the dedicated valve can be different from that for the main exhaust valves and a cooler can be provided in the dedicated passage.

[0040] An alternative embodiment of the present invention is shown in FIG. 5, in which like reference numerals refer to like elements. In the system shown in FIG. 5, the engine valve actuator 600 is provided by an electromagnetic actuator 690. In this embodiment, there is no need for a common rail system, as in the system of FIG. 3. In all other respects, the system of FIG. 5 may be operated similarly to the system shown in FIG. 3.

[0041] In one embodiment, the electromagnetic actuator 690 may comprise a high-speed solenoid valve capable of actuating the engine valve 700 at a rate of at least once per engine cycle. In another embodiment, the electromagnetic actuator 690 may comprise a low-speed solenoid valve. Other embodiments of the engine valve actuator 600, including, but not limited to, a piezoelectric actuator are considered within the scope and spirit of the present invention.

[0042] The dedicated engine valve 700 for engine braking and EGR may be smaller than the main exhaust valve and may need less force to open it. Once the valve is fully open, the flow area through the valve is controlled by the annular gap between the bore and the valve stem, and even less force may be needed to keep the valve open.

[0043] It will be apparent to those skilled in the art that variations and modifications of the present invention can be made without departing from the scope or spirit of the invention. For example, the relative pressures of the high pressure system and the reduced pressure system may be different from those referenced in the foregoing discussion without departing from the intended scope of the invention. The size and design of the individual components may vary, and some components, such as the accumulator, the pressure sensors, etc., may be eliminated without departing from the intended scope of the invention. Further, design of the control valve 400 may vary without departing from the intended scope of the invention. Furthermore, the hydraulic fluid used can vary without departing from the intended scope of the invention. In addition, embodiments of the methods and apparatus of the present invention may be adapted for two-stroke engine braking, in which the normal engine exhaust and intake valve events are modified, as well as four-stroke engine braking. Thus, it is intended that the present invention cover all such modifications and variations of the invention, provided they come within the scope of the appended claims and their equivalents.

Claims

1. An engine valve actuation system, comprising:

a high pressure hydraulic fluid passage;

a high pressure hydraulic fluid source;

a fluid pressure reduction device connected to the hydraulic fluid source through the high pressure hydraulic fluid passage;

a low pressure hydraulic fluid passage;

a hydraulic fluid control valve connected to the fluid pressure reduction device through the low pressure hydraulic fluid passage;

an actuator hydraulic fluid passage; and

an engine valve actuator for actuating an engine valve to produce an engine valve event, the engine valve actuator communicating with the hydraulic fluid control valve through the actuator hydraulic fluid passage.

2. The system of claim 1, wherein the engine valve event is selected from the group consisting of: a compression release braking event, a bleeder braking event, and an exhaust gas recirculation event.

3. The system of claim 1, wherein the hydraulic fluid source comprises a fuel injection system.

4. The system of claim 1, wherein the fluid pressure reduction device reduces the pressure of the hydraulic fluid from a first pressure to a second pressure having a pressure of approximately a magnitude lower than the first pressure.

5. The system of claim 4, wherein the second pressure is approximately 300 psi.

6. The system of claim 1, wherein the control valve comprises:

a valve body having a plurality of fluid passages formed therein, the valve body adapted to selectively translate between a first operating position and a second operating position;

a controller for translating the valve body; and

a spring for biasing the valve body into the first operating position.

7. The system of claim 6, wherein the controller translates the valve body at a rate of at least once per engine cycle.

8. The system of claim 6, further comprising an accumulator, wherein the control valve connects the actuator hydraulic fluid passage with the accumulator when the valve body is in the first operating position.

9. The system of claim 6, wherein the control valve connects the actuator hydraulic fluid passage with a low pressure hydraulic fluid tank when the valve body is in the first operating position.

10. The system of claim 6, wherein the control valve connects the actuator hydraulic fluid passage with the low pressure hydraulic fluid passage when the valve body is in the second operating position.

11. The system of claim 1, wherein the engine valve actuator comprises:

a fluid chamber for receiving hydraulic fluid from the actuator hydraulic fluid passage;

an actuator piston slidably disposed in the fluid chamber; and

a return spring in contact with the actuator piston.

12. The system of claim 1, further comprising:

a low pressure hydraulic fluid tank, and wherein the hydraulic fluid source further comprises:

a high pressure pump in communication with the low pressure fluid tank;

a pressure regulator; and

a high pressure plenum connected to the high pressure hydraulic fluid passage.

13. The system of claim 1, wherein the engine valve is a dedicated engine exhaust valve.

14. The system of claim 1, wherein the engine valve requires less force to actuate it than a main exhaust valve.

15. An engine valve actuation system, comprising:

a high pressure hydraulic fluid source for providing hydraulic fluid at a first pressure;

a fluid pressure reduction device connected to the hydraulic fluid source;

a hydraulic fluid control valve connected to the fluid pressure reduction device having a first operating position and a second operating position; and

an engine valve actuator for actuating an engine valve to produce an engine valve event adapted to receive the hydraulic fluid at a second pressure when the hydraulic fluid control valve is in the second operating position.

16. The system of claim 15, wherein the second pressure is approximately 300 psi.

17. A method of actuating an engine valve in an internal combustion engine to produce an engine valve event, the method comprising the steps of:

providing hydraulic fluid to a fluid pressure reduction device;

reducing the pressure of the hydraulic fluid from a first pressure to a second pressure;

selectively applying the hydraulic fluid at the second pressure to an engine valve actuator; and

actuating the engine valve to produce the engine valve event.

18. The method of claim 17, wherein the step of actuating the engine valve further comprises the step of producing a compression release braking event.

19. The method of claim 17, wherein the step of actuating the engine valve further comprises the step of producing a bleeder braking event.

20. The method of claim 17, wherein the step of actuating the engine valve further comprises the step of producing an exhaust gas recirculation event.