EP1215369A2 - Variable hydraulic valve drive - Google Patents

Abstract

Fully variable valve drive comprises a hydraulic drive unit, especially a piston/cylinder unit, which is impinged upon by hydraulic fluid to open and close a valve (V), especially of an internal combustion engine. On the closing or opening stroke the drive unit bombards a temporary storage device (Z1) with pressurized hydraulic fluid. On the corresponding stroke the pressurized hydraulic fluid drives the drive unit again. Preferred Features: On the opening and/or closing stroke the valve is accelerated or braked in the form of a free oscillator, with preferably a control valve (V3) holding the valve in the open and closed state.

Description

The present invention relates to a fully variable hydraulic valve drive a hydraulic drive unit, in particular piston-cylinder unit, which for Opening and closing a valve, in particular an internal combustion engine, with Hydraulic fluid is applied, the drive unit of the valve when closing or Opening stroke an intermediate store with pressurized hydraulic fluid applied.

In today's internal combustion engines, the engine is increasingly operating actively intervened. This makes it possible to increase efficiency and thus Save fuel and reduce pollutant emissions. A step into this Direction is the influence of the exhaust gas discharge and the fresh air supply or Supply of the gas mixture. To a state of the art It is to be able to carry out far-reaching influences in this area necessary to be able to control each individual valve of an engine separately. For one Complete intervention in this part of the cycle must take the opening time Opening times and the opening strokes of the individual valves vary as desired can be. The invention is concerned with an energy efficient Realization of a fully variable valve drive in hydraulic design.

There are various methods for realizing a variable valve drive. The Individual procedures can be divided into the following groups with those related to these groups belonging to individual patent numbers:

Examples of systems without a camshaft are the electrical Functional principle of DE 330 707 070, US 4,375,793 and EP 0 390 519 call. A system without a camshaft with a pneumatic functional principle is used in DE 37 39 775 and US 5 193 495. A system without a camshaft hydraulic operating principle is in DE 20 08 668, in DE 39 09 822 A1, in DE 38 33 459, DE 38 36 725, EP 0 19 376, WO 84/01 651, in U.S. 5,272,136 and U.S. 5,829,396. On the mechanical Systems based on the principle of operation without a camshaft are described in DE 20 06 618, DE 23 63 891, DE 24 28 915, DE 368 775, US 4 231 130, DE 31 26 620, DE 33 26 096, DE 34 15 245, DE 38 00 347, DE 40 36 279, the DE 36 21 080, DE 30 15 005, US 5 103 779, DE 21 01 542 and DE 29 26 327 shown.

In addition to the systems mentioned, there are also systems with a camshaft. These are on the one hand, systems with conventional camshafts. Here are different Intervention in the variability of the valve drive by coupling hydraulics and mechanics, use of several camshafts, etc. realized. Besides there are systems with special camshafts. Here are different places the intervention in the variability of the valve drive through mechanical gears realized. In summary, there are a large number of patents dealing with systems deal with camshafts.

When implementing a variable valve drive with a magnetic drive have to put up with a high power requirement and high development costs become. In addition, the engine emergency operation in the event of a power failure must be implemented in a complex manner. The power density of electromagnets is very low compared to hydraulics, the implementation therefore takes up a lot of space.

Pneumatic drives also need a lot of power. The power density is only marginally larger compared to electromagnetic drives.

Hydraulic drives allow compact due to their high power density Realizations. Only a small part of the supplied power cached. Therefore, these switching options are required large connected loads. The patent represents the state of the art US 5,272,136 explained in the description of the figures. In this patent Embodiment of a valve drive is a partial energy recovery achieved. A major problem with this arrangement, however, is that the hydraulic valves at the greatest valve speeds and thus the greatest volume flows be opened and closed. This is due to finite Valve speeds convert energy into heat through throttling losses. In other patents do not recover the energy used at all. These valve drives therefore have a high power requirement.

DE discloses another hydraulic valve drive with a pressure accumulator 40 02 856 A1. Here can be recovered from a lock cylinder Hydraulic medium, however, only again when a certain pressure in the accumulator is reached be used for a working stroke.

The object of the invention is therefore to provide a fully variable, selectively controllable to create hydraulic valve drive, in which the valve drive once the energy used is almost completely recovered and used for the subsequent Opening or closing cycle is provided. Furthermore, it is a task of this invention to overcome the other disadvantages of the prior art.

This is achieved according to the invention in that this is stored in the buffer Pressure stored hydraulic fluid then at the opposite stroke drives the valve drive unit again.

The present invention thus describes a variant which covers the entire supplied energy (except for the friction losses of the valve tappet and the Flow losses through the open hydraulic valves) are recovered and at recycled in the next cycle. This greatly reduces energy consumption. The remaining losses are mainly determined by the size, i.e. of the Size of the nominal volume flow (unit l / min) of a fast switching valve is determined.

In the fully variable hydraulic valve drive according to the invention, the valve during the opening and / or closing stroke in the form of a free oscillator accelerated and braked, preferably a control valve in the valve holds open and closed state. This can be approximated and below Neglecting the friction losses a free swinging pendulum, which in its extreme deflections is recorded as a physical analogy become. In the sense of this analogy, it corresponds to the state of the pendulum when it is is held at maximum deflection and thus maximum potential energy in the case of the valve drive, e.g. the valve closed and so that the hydraulic fluid is stored under pressure in the intermediate store. Becomes now the control valve between the buffer and the drive unit of the Valve open, this corresponds to releasing the pendulum. After opening the Control valve flows the pressurized hydraulic fluid in via the control valve the cylinder of the drive unit of the valve and the valve is accelerated. This corresponds to the pendulum in the analogy of the pendulum. With increasing amount of Hydraulic fluid, which from the buffer into the cylinder chamber Valve drive unit has flowed, the resulting force on the drive unit of the valve. This will brake the valve. This corresponds to the pendulum, though it has swung beyond the zero position and through the corresponding forces is braked. Before the drive unit of the valve begins its direction of movement changes, the control valve is closed and thus the drive unit in the other Extreme position fixed. In analogy, this corresponds to the state when the pendulum is the has reached the second extreme position and is being held there. The control valve will now opened again, the opposite process begins.

As shown with the pendulum analogy explained above, the inventive one Valve drive an opening and / or a closing stroke of the valve in one hydraulic system closed at this time interval. This hydraulic system preferably consists of a buffer, a drive unit of the valve and a control valve.

The variable valve drive according to the invention is for driving inputs and Exhaust valves suitable. The only differences are in the dimensioning. It will therefore in the following description, when talking about valves, input or Exhaust valves of the internal combustion engine addressed. The possible area of application of the variable valve drive according to the invention is about pure use Internal combustion engines. There are other possible uses directly for active valve control in compressors and for controlling fast hydraulic valves.

In the valve drive according to the invention, the hydraulic closing forces Valve held in the closed position. It can be done easily Valve play, as it occurs due to wear and deposits on the valve, compensated become.

In one embodiment of a fully variable valve drive according to the invention the control valve (s) are only switched if the valve (s) hydraulic fluid volume flow flowing through it is less than 20% of the maximum through it (it) flowing volume flow. A particularly preferred one Embodiment provides that the control valve (s) only switched will be when the one flowing through it Hydraulic fluid volume flow less than 10% or less than 5% of the maximum through it (it) flowing volume flow. In this embodiment the switching speed of the hydraulic valves is not as critical as when the vehicle is stationary of the technique. In addition, much less energy is lost through throttle losses Heat converted.

In essence, this concept according to the invention is a positioning drive, which is characterized by the following functional features. The positioning takes place in one go. Different positions are in advance selectable. The acceleration force dominates for all forces to be overcome. This makes energy recovery significant. The time for positioning is largely independent of the selected position. It will be dynamic and dynamic extremely short positioning times achieved. Overall occur at The valve drive according to the invention has only slight losses. The when positioning overcoming forces are known in advance, otherwise large ones would Scatters occur in the position.

Fig. 1

den Stand der Technik anhand eines Patentes von Ford,

Fig. 2

eine Ausführungsform des erfindungsgemäßen vollvariablen hydraulischen Ventilantriebs,

Fig. 3

Varianten anderer bevorzugter Ausführungsformen.

Further features and details of the present invention result from the following description of the figures. It shows

Fig. 1

the state of the art based on a Ford patent,

Fig. 2

one embodiment of the fully variable hydraulic valve drive according to the invention,

Fig. 3

Variants of other preferred embodiments.

In the prior art shown in Fig. 1, the inlet and outlet valve kept in closed position by a constant system pressure. The constant pressure (port 44) acts on the annular surface of the piston 26. By Opening the control valve 64, oil is pressed into the piston chamber 25 and the valve 16 open. After closing the control valve 64, the valve 16 sucks over the Check valve 10 oil until the kinetic energy is reduced. After that persists the valve 16 in the open position. To close, the control valve 68 opened and the internal pressure to the tank released. The valve closes. The control valve 68 is closed shortly before the valve hits the valve seat and the excess kinetic energy is transferred in the form of overpressure in the fluid check valve 66 is fed back into the supply line.

In the hydraulic circuit diagram of a preferred embodiment shown in FIG. 2 the hatched parts of the valve drive according to the invention indicate the Cylinder walls, the cylinder head and the valve seat. The differential cylinder is A1 connected to the valve stem of valve V via its piston rod. The Cylinder chamber RK of the differential cylinder is through a line with the constant Pressure pS connected. The volume Z1 forms a hydraulic capacity. The three Hydraulic valves V1, V2 and V3 (= control valves) are as 2/2-way valves executed and can be controlled electrically independently. The 2/2-way valve V4 (= control valve) connects the cylinder chamber LK of the Differential cylinder with the tank line. The prevailing pressure in the supply line is pS, the pressure pT indicates the pressure prevailing in the return line (tank line).

The operating principle of the fully variable according to the invention is described below Valve drive explained. The cycle is divided into the following four sections: Start state, open valve, compensation of friction losses and close valve. At the The 2/2-way valves V1, V2 and V3 (= control valves) are closed in the initial state. In of the hydraulic capacity Z1 (= intermediate storage) there is the set pressure pZ (= Filling pressure). The piston of the differential cylinder is in the retracted state close to its mechanical end position, valve V is closed. The 2/2-way valve V4 is open so that the resulting leaks flow freely into the tank can and no unwanted pressure builds up in the left cylinder chamber LK. In the right cylinder chamber RK has the supply pressure pS. This causes a constant force F which presses the valve V against the valve seat.

To open the valve V, the 2/2-way valves V4 must be closed and V3 be opened. The piston of the differential cylinder is accelerated because one part the compressed hydraulic fluid from the hydraulic capacity Z1 in the Differential cylinder overflows. This overflow will stop when the piston of the cylinder has reached the reversal point (piston speed becomes zero). The 2/2-way valve V3 is closed again so that valve V remains open.

In the case of no friction, the piston would open when the 2/2-way valve was opened again Move V3 back to the starting position. So that the losses through Friction and leakages are compensated for when valve V is open Drain oil from volume Z1 via the 2/2-way valve V2. The pressure in Z1 will thereby reduced to the discharge pressure pZA.

So that the valve V is closed, the 2/2-way valve V3 is opened. The piston is together with the valve V according to the one acting in the cylinder chamber RK hydraulic pressure pS accelerated. This movement continues until the Distance between the valve V and the valve seat a very small predetermined Has reached value. The kinetic energy of the valve V is in the hydraulic Capacity Z1 saved again. The 2/2-way valve V3 is switched off when the Piston closed again. So that the valve V is closed completely, must the 2/2-way valve V4 can be opened. The leaks, which arise in the components used, passed into the tank, so that safe closing of the valve V is guaranteed. The pressure that is currently in the hydraulic capacity Z1 prevails, is too low for a new cycle because Losses have occurred. Therefore the 2/2-way valve V1 is opened until the desired target pressure pZ is reached again. If the 2/2-way valve V1 is closed, you have reached the start state again. The control of the stroke of valve V can be achieved by varying the pressure in the starting state pZ. If the pressure is increased, there is more stored energy in the prestressed Volume Z1 and this opens valve V further. For a small stroke only the starting pressure has to be reduced. Since it is a cyclical process pressure can be changed simply by varying the opening time of the 2/2-way valve V1 can be set.

The opening time can be easily controlled by valve V3. Will that Hydraulic valve never opened, then valve V is not opened and it can open this way every valve V and therefore every single cylinder of the engine for certain Time can be switched off (idle operation, partial load operation). If valve V is open, then valve V can be opened again at any time by opening hydraulic valve V3 again getting closed.

In addition to this preferred embodiment of the valve drive according to the invention 3 shows further possible embodiments according to the invention. When inserting a variant in the variable valve drive according to Fig. 2 must on the Nodes A, B, C, D and E are respected. Only the same names may be used Nodes are interconnected.

Variants of the memory block SP are discussed below: There is one in SP1 hydraulic capacity, i.e. a cavity filled with the hydraulic fluid with the constant volume V1 shown. The variant SP2 is made up of a common gas-filled hydraulic accumulator formed. Here are all three types (Diaphragm accumulator, bladder accumulator and piston accumulator).

The variants of the refill and drain block NA are discussed below: NA1 consists of two 2/2-way valves. They can be controlled independently of one another. Variant NA2 consists of a 2/2-way valve and a 3/2-way valve. The two Valves can be controlled separately. NA3 consists of a 3/3-way valve, which in a switch position, the connections A, B and D completely can close. NA4 consists of a 2/2-way valve connected to the Pressure connection and a throttle connected to the tank connection. NA5 consists of a 2/2-way valve connected to the tank connection and a throttle with the pressure connection. NA6 consists of a 3/3-way valve, which will be the same used in NA3. The pressures p1 and p2 in the two supply lines can can be infinitely adjusted independently of each other.

As variants of the main valve - block HV is next to HV1, which consists of a 2/2-way valve there is also variant HV2 shown in Fig. 3. Here is the block HV consisting of two 2/2-way valves and one-way valves. The control of the Valves are made independently. The task of the two check valves is described in the description of variant HV4. The variant HV3 provides that the block HV consists of a 3/2-way valve and two check valves. The The task of the two check valves is also in the description of Variant HV4 described. The variant HV4 provides that the block HV consists of one 2/2-way valve and a 3/2-way valve with two integrated check valves consists. The control spool of the 3/2-way valve is with the 2/2-way valve controlled. The check valve used closes automatically when the Piston of the differential cylinder changes its direction of movement and thereby also reverses the direction of flow through the respective check valve used. The piston remains in its position until the control slide the 3/2-way valve is switched to the other position. The for the pilot control of the Control valve required hydraulic fluid is depending on the direction of movement of the Control spool taken from node B or C. With this type of feedforward control the same amount of hydraulic fluid is at the other end of the spool ousted, which had to be fed on one side. The displaced Hydraulic fluid is fed to node C or B and stands for the Acceleration of the piston continues to be available. Before the pressure in node C or B is larger than that in node B or C (reversal point), the 2/2-way valve must getting closed. This will result in an unwanted switching of the control spool prevented. If the cycle is to be continued, the 2/2-way valve must can be opened again briefly.

The following are variants of the main valve and refill drain block HVNA discussed. This block can be used instead of the NA and HV blocks. On 5/4-way valve with two built-in check valves is replaced by a 2/2-way valve pilot. The function is the same as for valve block HV4 and was described there. The other part of the valve is the same as that of NA2 described valve concept. The control spools of the two 3/2-way valves are mechanically (or only hydraulically) coupled and through the 2/2-way valve controlled. The principle of pilot control was also used in HV4 described.

A variant to HVNA is HVNB. HVNB is made up of two different ones Directional valves formed. One is a 3/3-way valve, which Drainage in node B controls, and the other is a 3/2-way valve that the Overflow between nodes B and C allows. The control spool of the two Directional control valves described above are connected to one another Control spool united. With this one achieves a simultaneous actuation which the Control of the system significantly simplified. The pressures p1 and p2 of the two As in NA6, supply lines can be steplessly independent of each other can be set.

Variants of the leakage oil return block LR are discussed below. LR1 consists only of a 2/2-way valve. LR2 consists of only one choke with constant cross section. The throttle shown in the LR3 is the hydraulic one Resistance of the throttle depends on the piston position of the differential cylinder. The Resistance should be small when the piston is retracted. If the piston is his End position (piston is fully retracted) and a certain barrier exceeds, the throttle should be closed completely.

Variants of the cylinder with return device ZR are discussed below. In ZR, the cylinder is designed as a differential cylinder. In the cylinder room on the side the constant system pressure pS prevails in the ring surface. The cylinder is in ZR2 designed as a single-acting cylinder (plunger cylinder) with spring return. In ZR3 the cylinder is designed as a differential cylinder. Furthermore, a hydraulic Capacity Z2 and a 2/2-way valve used. The oil losses caused by Leakages can be compensated for when the 2/2-way valve is open becomes. In ZR4 the cylinder is designed as a differential cylinder. Furthermore, one hydraulic capacity Z2 and a check valve are used. The check valve opens when the pressure in the hydraulic capacity Z2 the supply pressure p1 falls below. This compensates for the leaks. The variant ZR5 is the hydraulic capacity is the same as that described for ZR4. A hydraulic accumulator Z2 is used instead of the hydraulic capacity. The Use of a hydraulic accumulator instead of the hydraulic capacity Z2 also possible in the ZR3 variant. When executing the hydraulic accumulator Z2 are generally all three types (diaphragm accumulator, bladder accumulator and piston accumulator) suitable. In the variants ZR1, ZR4 and ZR5, a gas can also be used as a medium be used. In variant ZR2, gas pressure can be used in addition to the spring be specified.

Regulation measures are discussed below. The The method presented is essentially based on a control. In principle, it is enough off, for the desired opening stroke of the valve V the correct pressure pZ in Set memory Z1. The setting values can vary depending on Influence parameters (temperature of the oil and in the cylinder head, state of charge, ...) as Characteristic curves can be saved. The accuracy that can be achieved should not can be sufficient by measuring the position of the valve V or any other an integral part of it corresponding regulation can be achieved.

The position can be measured in the following ways. A path picker MS1 continuously measures the according to a common principle (inductive, optical, capacitive, ...) current position of the valve. Alternatively, a pressure sensor (pressure sensor) in the Capacity Z1-MS2 can be used. At a given inflation pressure the hydraulic capacity Z1 is unique in both variants SP1 and SP2 Relationship between the position of valve V and the pressure in Z1. This Pressure signal can also be used for setting the filling pressure pZ or Drain pressure pZA can be used. As an alternative to MS2, MS3 can also be used become. Here is a pressure sensor (pressure sensor) in the cylinder chamber LK arranged. In the open position of valve V3, the pressure in LK is essentially equal to the pressure in Z1 and can therefore be used equally for the measurement the position of the valve V can be used. The pressure measurement for determination the position of the valve V can also be in the buffer Z1 and Memory Z2 can be measured. As an alternative to the variants mentioned above, use the variant MS4 showed a possibility to measure at certain positions of the Valve V to perform. During the positioning process, certain Valve positions V signals triggered. This allows conclusions to be drawn about the Drag the course of the movement in particular over the end position reached. Such signals can by inductive or capacitive proximity switches or by Light barriers are triggered.

In the control process, the correction of the filling pressure pZ is first in Z1 to lead. By continuously observing the end position reached, the Adjustment values for the filling pressure in Z1 are adjusted so that the desired position with the required accuracy is achieved. This can e.g. by varying the Valve V1 is opened. The correction of the discharge pressure pZA in Z1 is performed as follows. By observing the position profile of the valve V in The setting value for the discharge pressure pZA can be readjusted in the closing phase. In the variant HVNB and NA6 are the two pressures for an entire engine regulated together.

Claims (10)

Fully variable hydraulic valve drive with a hydraulic drive unit, in particular piston-cylinder unit, which is acted upon by hydraulic fluid for opening and closing a valve, in particular an internal combustion engine, the drive unit of the valve acting on a buffer store with pressurized hydraulic fluid during the closing or opening stroke, thereby characterized in that this hydraulic fluid stored under pressure in the intermediate store (Z1) then drives the drive unit of the valve (V) again in the opposite stroke. Valve drive according to claim 1, characterized in that the valve (V) accelerates and brakes in the form of a free oscillator during the opening and / or closing stroke, preferably a control valve (V3) holding the valve (V) in the open and closed state. Valve drive according to claim 1 or 2, characterized in that an opening and / or a closing stroke of the valve (V) takes place in a hydraulic system which is closed in this time interval and which preferably consists of an intermediate store (Z1) of a drive unit of the valve (V) and a Control valve (V3) exists. Valve drive according to one of claims 1 to 3, characterized in that the stroke of the valve (V) is adjustable. Valve drive according to one of claims 1 to 4, characterized in that the losses caused by friction and leakage are compensated for by supplying hydraulic fluid, which is preferably under pressure, from a supply line. Valve drive according to one of claims 1 to 5, characterized in that the opening and closing time of the valve (V) is freely controllable. Valve drive according to one of claims 1 to 6, characterized in that the stroke of the valve (V) is controlled by the filling pressure prevailing in the intermediate store (Z1) when the valve (V) is closed. Valve drive according to one of claims 1 to 7, characterized in that the opening time of a control valve (V1) regulates the filling pressure of the intermediate store (Z1) in the closed state of the valve (V). Valve drive according to one of claims 1 to 8, characterized in that the setting values, depending on various influencing parameters, preferably the temperature of the oil and / or the temperature of the cylinder head and / or the charging state, are stored as characteristic curves. Fully variable hydraulic valve drive with at least one control valve and with a hydraulic drive unit, in particular piston-cylinder unit, which is acted upon by hydraulic fluid for opening and closing a valve, in particular an internal combustion engine, the drive unit of the valve providing an intermediate store with pressure during the closing or opening stroke standing hydraulic fluid, in particular according to one of claims 1 to 9, characterized in that the control valve (s) is / are only switched when the hydraulic fluid volume flow flowing through it (it) is less than 20% of the maximum through it (it) is flowing volume flow.

Images