EP0548294B1

EP0548294B1 - Method of operating a valve system with recuperation

Info

Publication number: EP0548294B1
Application number: EP92900062A
Authority: EP
Inventors: J. Roger Weber
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 1991-07-12
Filing date: 1991-10-10
Publication date: 1995-11-08
Anticipated expiration: 2011-10-10
Also published as: WO1993001399A1; EP0548294A1; JPH06501081A; DE69114509D1; DE69114509T2; AU9017291A; JP3121011B2

Abstract

A recuperative engine valve system (10) for an internal combustion engine. The system (10) includes an engine valve (12) having a plunger surface (16), a first means (20) for biasing the engine valve (12) towards its closed position, a source of relatively low pressure fluid (22), a source of relatively high pressure fluid (24), and a second means (28) for selectively communicating fluid between the plunger surface (16) and one of the low pressure fluid source (22) and the high pressure fluid source (24). The timing of the selective communication of low pressure fluid and high pressure fluid to the plunger surface (16) during valve displacement is controlled so as to preserve and recuperate energy.

Description

The present invention relates generally to the method of operation of hydraulically-actuated valves, and more particularly to a method of operation which significantly reduces the energy consumption normally associated with hydraulically actuated valves by recuperating some of the energy used in pressurizing the hydraulic fluid.
Hydraulically actuated engine valves are advantageous over mechanically actuated engine valves because they are capable of varying and thereby optimizing the timing of engine valve opening and closing events in rapid response to varying engine operating conditions.
One disadvantage typically associated with hydraulic systems is the high amount of hydraulic energy necessary to quickly actuate an engine valve. High energy consumption is particularly evident when the engine valve is an exhaust poppet valve that must open against relatively high gas pressure developed in an engine combustion chamber during the compression and combustion phases. This power consumption can be seventy-five percent higher than the power required to actuate typical mechanical engine valves.
The present invention is for recuperating some of the energy used in pressurizing the hydraulic fluid so that the energy requirements for hydraulic valve systems will be comparable to mechanical valve systems.
EP-A-0520633, which belongs to the prior art according to Art. 54(3) EPC discloses a method of operating a valve system having a valve with a plunger surface and being displaceable between first and second positions, a first means for biasing the valve towards the first position, a source of relatively high pressure fluid, and a source of relatively low pressure fluid, the method comprising causing the valve to be displaced from the second position towards the first position by, during a first portion of the displacement, not communicating the high pressure fluid to the plunger surface and communicating the low pressure fluid to the plunger surface whereby the first means urges the valve towards the first position; during a second portion of the displacement of the valve from the second position towards the first position, prior to the valve reaching the first position, ceasing communication of the plunger surface with the low pressure fluid and communicating high pressure fluid to the plunger surface; whereby the momentum of the valve carries the valve towards the first position and pumps the high pressure fluid in communication with the plunger surface back to the high pressure fluid source. EP-A-0520633 does not disclose that the communication between the plunger surface and the high and low pressure fluids is controlled by a single valve.
EP-A-0520633 discloses a valve system having a valve with a plunger surface and being displaceable between first and second positions, a first means for biasing the valve towards the first position, a source of relatively high pressure fluid, and a source of relatively low pressure fluid, means for causing the valve to be displaced from the second position towards the first position by, during a first portion of the displacement, not communicating the high pressure fluid to the plunger surface and communicating the low pressure fluid to the plunger surface whereby the first means urges the valve towards the first position; and means for ceasing communication of the plunger surface with the low pressure fluid and communicating high pressure fluid to the plunger surface during a second portion of the displacement of the valve from the second position towards the first position; prior to the valve reaching the first position, whereby the momentum of the valve carries the valve towards the first position and pumps the high pressure fluid in communication with the plunger surface back to the high pressure fluid source. EP-A-0520633 does not disclose that there is a single valve for controlling the communication between the plunger surface and the high and low pressure fluids.
JP-A-60085209 discloses a method of operating a valve system, according to the preamble of claim 1, as well as a valve system according to the preamble of claim 5, for each of the countries designated.
The object of the invention is achieved by a method and a system according to claims 1 and 5 for DE, GB, FR, as well as for BE.
The present invention reduces the hydraulic power consumption normally associated with hydraulically actuated valve systems by recuperating a portion of the energy used to pressurize the hydraulic fluid. Moreover, the velocity of the valve can be controlled while it is opening so that it does not overshoot its equilibrium position when fully opened. Furthermore, the velocity of the valve can be controlled while it is closing so that the valve gently abuts against its seat. Finally, the present invention enables the valve to be opened and closed at the most appropriate times to help optimize engine performance.
In the accompanying drawings:-
Fig. 1 is a diagrammatic partial cross-sectional view of an electro-hydraulic valve system of the present invention.
Fig. 2 shows three diagrammatic exemplary graphs that illustrate an exemplary operation of the system of Fig. 1. The bottom graph shows microprocessor logic pulse in terms of voltage "v" as a function of time "t" . The middle graph shows spool valve displacement "d_sv" as a function of time "t". The top graph shows engine valve displacement "d_ev" as a function of time "t".
Referring to Fig. 1, there is shown an exemplary embodiment of an engine valve system 10 of the present invention for an internal combustion engine.
The system 10 includes one or more engine valve(s) 12 each displaceable between a first closed position (shown) and a second open position (not shown), a plunger 14 integrally formed with or separately positioned adjacent to each engine valve 12 having a plunger surface 16, first means, preferably a pair of helical compression springs 18, for biasing each engine valve 12 towards its first position, a source 20 of relatively low pressure fluid, a source 22 of relatively high pressure fluid, second means, preferably a second valve, preferably a two-way spool valve 24 for selectively communicating fluid through a rail 25 between one of the low pressure fluid source 20 or the high pressure fluid source 22 and the plunger surface 16. The spool valve 24 is biased to a first position (shown) by a helical compression spring 26 and moved against the force of the spring 26 to a second position (not shown) to the right of the first position by an actuator. In this embodiment, the actuator is a piezoelectric motor 28. Adjacent the piezoelectric motor is a relatively large diameter piston 30, and spring biased array which is in hydraulic communication with a relatively small diameter piston 32, which is adjacent the spool valve 24. The large 30 and small 32 pistons are spring biased away from each other.
The engine valves 12 are only partially shown in Fig. 1 and may, for example, be a set of conventional exhaust or intake poppet valves that are reciprocally disposed in a cylinder head 34.
The plunger 16 is reciprocally guided in a bore 36 of a valve body 38.
The fluid pressure of the fluid from the low pressure fluid source 20 is preferably less than 400 psi, and more preferably less than 200 psi. It is recommended that enough pressure be maintained in the low pressure fluid source so that there will be little if any cavitation in the rail 25 and at the plunger surface 16 when switching from high pressure fluid to low pressure fluid, as is later explained.
The fluid pressure of the fluid from the high pressure fluid source 22 is preferably greater than 1500 psi, and more preferably greater than 3000 psi.

Industrial Applicability

For clarity, the following sequence begins with the engine valve 12 at its first position, which is its closed or seated position, as shown by A₁ in the top graph of Fig. 2, and the spool valve at its first position, as shown by P_L in the middle graph of Fig. 2. To begin the valve opening sequence, at t₁ a voltage V_H is sent to the piezoelectric motor 28. The piezoelectric motor 28 expands, thus driving the large piston 30, which through hydraulic communication drives the small piston 32, which in turn drives the spool valve 24 from its first position P_L to its second position P_H.
Movement of the spool valve 24 from the first position P_L to the second position P_H closes off communication of the low pressure source 20 with the plunger surface 16 and opens communication of the high pressure source 22 with the plunger surface 16. The high pressure fluid is great enough to cause the engine valve 12 to open against the force of the compression springs 18. Communication of the high pressure source 22 with the plunger surface 16 is maintained during a first portion of displacement of the engine valve 12 from A₁ to A₂ until sufficient momentum is built up in the engine valve 12 so that it will coast to full open.
At engine valve displacement A₂, corresponding to t₂, the voltage is removed from the piezoelectric motor 28, resulting in the spool valve 24 returning under the force of the springs 26 from its second position P_H to its first position P_L cutting off communication of the high pressure fluid with the plunger surface 16 and again communicating low pressure fluid with the plunger surface 16.
From A₂, the momentum in the engine valve 12 is able to carry it to full open A₃. The increasing volume of the rail 25, created by the plunger 14 moving down with the engine valve 12, is filled with low pressure rather than high pressure fluid, thereby conserving hydraulic energy during the coasting period. In this manner, the hydraulic power required to open the engine valve 12 can be reduced by about 10 to 20%, depending upon cylinder pressure and other factors. Analytically, from A₁ to A₃, potential energy in the high pressure fluid is converted into kinetic energy of the moving engine valve 12 and potential energy in the compression springs 18.
At maximum displacement of the engine valve A₃ (full open), the kinetic energy of the engine valve 12 has been transformed into potential energy stored in the compression springs 18. Maximum designed displacement is reached when the hydraulic pressure and the force of the compression spring 18 are in equilibrium or when the plunger 14 contacts a physical stop. In the absence of a plunger stop, if the fluid supply is not switched to low pressure before full open, the engine valve 12 can overshoot its equilibrium position due to the increasing momentum of the engine valve 12 which can damage the springs 18 and cause the engine valve 12 to oscillate. Even with a stop, if the plunger 14 hits the stop at full speed, it can cause wear, breakage, and oscillation.
At t₃, corresponding to A₃ of the engine valve 12, the piezoelectric motor 28 is again energized, again forcing the spool valve 24 to its second position P_H, thus switching the fluid in communication with the plunger surface 16 from low pressure to high pressure. In this manner, the engine valve 12 is able to be maintained open against the force of the compression springs 18. Between t₃ and t₄, the velocity of the engine valve is zero. The engine valve 12 is held open in this manner until the appropriate time t₄ in the engine cycle for it to close.
At t₄, the voltage is removed from the piezoelectric motor 28 allowing the spool valve 24 to return from its second position P_H to its first position P_L thus switching the fluid in communication with the plunger surface 16 from high pressure to low pressure, thereby allowing the engine valve 12 to begin its closing stroke. At this stage, the potential energy of the compression springs 18 is turned into kinetic energy in the moving engine valve 12. The low pressure fluid supply 20 is maintained in communication with the plunger surface 16 until there is sufficient momentum to close the engine valve 12 against relatively high pressure fluid.
At engine valve displacement A₅, corresponding to t₅, the piezoelectric motor 28 is again energized, moving the spool valve 24 from its first position P_L to its second position P_H, thus switching the fluid in communication with the plunger surface 16 from low pressure to high pressure. Because enough momentum is in the engine valve 12 to carry it to its closed position A₆ against the force of the high pressure fluid, the plunger 14 now acts like a fluid pump by returning fluid under pressure to the high pressure source 22 as the valve moves from A₅ to A₆. This is the hydraulic energy recuperation portion of the cycle. Analytically, the kinetic energy of the engine valve 12 is converted into potential energy in the high pressure fluid source 22. About 30% to 50% of the hydraulic energy originally used to open the engine valve 12 can be recuperated during this phase. Pressure drops across the spool valve 24 and friction losses in the system limit the recuperation from being 100%. Of course, the velocity of the engine valve 12 at A₆ is zero since the engine valve 12 has again seated.
As soon as the valve seats, the piezoelectric motor 28 is deenergized and the spool valve 24 moves from its second position P_H to its first position P_L, thus switching the fluid in communication with the plunger surface 16 from high pressure to low pressure, otherwise the engine valve 12 would begin to open again. The cycle is now ready to be repeated.
Note that the system described herein could be reversed as a matter of design choice such that the engine valve 12 is biased towards it open position and high pressure fluid is used to urge the engine valve 12 towards its closed position.
The recuperative valve system of the present invention has several advantages. First, the system is able to selectively turn "on" or "off" fluid communication between the high pressure source 22 and the plunger surface 16 depending upon the position of the engine valve 12 so that hydraulic power consumption is minimized. Second, the displacement of the engine valve 12 in the opening direction is controlled so that the the engine valve 12 does not overshoot its equilibrium position at full open. Third, the displacement of the engine valve 12 in the closing direction is controlled so that valve seating velocity is minimized. Fourth, the system is capable of opening and closing the engine valve 12 at the most appropriate times in order to help optimize engine performance. Fifth, hydraulic energy is saved and recuperated during the coasting phases of the engine valve 12 thereby reducing the energy requirements of the system.
While the present invention has been shown and explained as used with a poppet engine valve 12 of a combustion chamber of an engine, it is to be understood that the present invention is applicable to any hydraulically actuated valve that can benefit from its advantages.

Claims

A method of operating a valve system (10) having a valve (12) with a plunger surface (16) and being displaceable between first and second positions, a first means (18) for biasing the valve (12) towards the first position, a source of relatively high pressure fluid (22), and a source of relatively low pressure fluid (20), the method comprising causing the valve (12) to be displaced from the second position towards the first position by, during a first portion of the displacement, not communicating the high pressure fluid (22) to the plunger surface (16) and communicating the low pressure fluid (20) to the plunger surface (16) whereby the first means (18) urges the valve (12) towards the first position; characterised by, during a second portion of the displacement of the valve (12) from the second position towards the first position, prior to the valve (12) reaching the first position, ceasing communication of the plunger surface with the low pressure fluid (20) and communicating high pressure fluid (22) to the plunger surface (16); whereby the momentum of the valve (12) carries the valve (12) towards the first position and pumps the high pressure fluid (22) in communication with the plunger surface (16) back to the high pressure fluid source (22).
A method according to claim 1, preceded or succeeded by the steps of communicating high pressure fluid (22) to the plunger surface (16) of the valve (12) while the valve (12) is at its first position; temporarily maintaining fluid communication between the high pressure fluid (22) and the plunger surface during a first portion of displacement of the valve (12) from its first position towards its second position and ceasing communication of the high pressure fluid (22) with the plunger surface (16) during a second portion of displacement of the valve (12) from its first position towards its second position, prior to reaching its second position, whereupon the valve continues moving towards its second position.
A method according to claim 2, wherein when the valve (12) reaches the second position the high pressure fluid (22) is again communicated with the plunger surface (16) and when the valve is to be returned to the first position, communication of the high pressure fluid (22) with the plunger surface (16) is ceased.
A method according to claim 2 or claim 3, wherein when the communication of the high pressure fluid (22) with the plunger surface (16) is ceased, during the displacement of the valve from its first position towards its second position, the plunger surface (16) is put in communication with the low pressure fluid (20).
A valve system (10) having a valve (12) with a plunger surface (16) and being displaceable between first and second positions, a first means (18) for biasing the valve (12) towards the first position, a source of relatively high pressure fluid (22), and a source of relatively low pressure fluid (20), means for causing the valve (12) to be displaced from the second position towards the first position by, during a first portion of the displacement, not communicating the high pressure fluid (22) to the plunger surface (16) and communicating the low pressure fluid (20) to the plunger surface (16) whereby the first means (18) urges the valve (12) towards the first position; characterised by means for ceasing communication of the plunger surface with the low pressure fluid (20) and communicating high pressure fluid (22) to the plunger surface (16) during a second portion of the displacement of the valve (12) from the second position towards the first position, prior to the valve (12) reaching the first position; whereby the momentum of the valve (12) carries the valve (12) towards the first position and pumps the high pressure fluid (22) in communication with the plunger surface (16) back to the high pressure fluid source (22).
A system according to claim 1, further comprising means for communicating high pressure fluid (22) to the plunger surface (16) of the valve (12) while the valve (12) is at its first position; and means for temporarily maintaining fluid communication between the high pressure fluid (22) and the plunger surface during a first portion of displacement of the valve (12) from its first position towards its second position and ceasing communication of the high pressure fluid (22) with the plunger surface (16) during a second portion of displacement of the valve (12) from its first position towards its second position, prior to reaching its second position, whereupon the valve continues moving towards its second position.
A system according to claim 6, further comprising means for communicating the high pressure fluid (22) with the plunger surface (16) when the valve (12) reaches the second position, and ceasing communication of the high pressure fluid (22) with the plunger surface (16) when the valve is to be returned to the first position.
A system according to claim 6 or claim 7, further comprising means for communicating the plunger surface (16) with the low pressure fluid (20) when the communication of the high pressure fluid (22) with the plunger surface (16) is ceased, during the displacement of the valve from its first position towards it second position.