Patent Application
20150369093
The present invention relates to a variable electrohydraulic valve control system according to the preamble of patent claim 1.
Such valve control systems are used, for example, for controlling gas exchange valves of motor vehicles. A differentiation is in principle made between mechanical or electromechanical valve control systems and hydraulic or electrohydraulic valve control systems.
Variable valve drives or valve control systems are becoming increasingly significant. In particular for Otto or diesel internal combustion engines, increasing variability is required, in particular in order to reduce the exhaust gas emissions and the fuel consumption. Existing systems are limited in terms of variability, excessively complex and have an excessively high level of losses as a result of a poor degree of efficiency and are too imprecise in terms of control.
There is known, for example, from WO 2008/107111 A1 an electromechanical valve control system having camshaft adjustment. Since, in this valve control system, the valve stroke profiles are predetermined by means of camshaft contours, it has limited variability since a selection has to be made in this instance between two valve stroke profiles.
DE 10 2006 013 100 A1 discloses a segment motor for a valve drive, by means of which, as a result of improved adjustment possibilities of the valve stroke, the variability can be expanded, wherein each valve is controlled by means of an electromechanical segment motor with an end stage/actuator.
This is a completely variable system in which the stroke and control time can be varied. However, this solution has a relatively high weight and is comparatively expensive. Furthermore, it requires a high level of technical regulation complexity in order to ensure low placement speeds and a high level of complexity in the event of valve failure.
EP 1 691 041 A2 sets out an electrohydraulic valve control system of the type mentioned in the introduction. In this relatively simple variable valve control system, the camshaft acts on a hydraulic system. A similar system which is improved in terms of failure reliability is known from DE 10 2008 049 181 A1. In these solutions, the variability is also still limited since profiles smaller than the camshaft shape and the valve closure profiles are coupled to the camshaft profile. In addition, the control time variability (opening and closing control time angle variation) is limited. Furthermore, in these systems, there is a relatively high power requirement and an inadequate level of precision. A solution for venting the system is not provided.
An object of the invention is to improve a variable valve control system of the type mentioned in the introduction in such a manner that, with a relatively low level of complexity, complete variability (valve stroke and control times) is achieved.
This object is achieved according to the invention with the features of patent claim 1.
With the solution according to the invention, there is provided a device and a method for fully variable valve control which allows precise regulation and moreover a high level of valve control precision. The variability relates in particular to the stroke variation, wherein the valve strokes may be larger or smaller than the camshaft contour and the control time variation. For example, power increases at full load by means of stroke increase in comparison with the camshaft are possible. The variability is provided with a central, preferably electromotive plunger unit which varies the volume of the valve hydraulic chamber for valve control. This unit may be used centrally for all valve control systems (inlet and outlet valves) for internal combustion engines having four cylinders or more.
The advantages of the invention can be achieved with a small weight and structural space and low costs. Thus, for example, only four valves and one plunger drive unit are sufficient for the operation of a four cylinder motor, in which the inlet valves are constructed in a variable manner and two valves are combined with a hydraulic chamber.
Furthermore, the invention is distinguished by a low power requirement, which enables operation at 12 V (standard on-board system) and a high level of availability (emergency operation in the event of component malfunction).
Advantageous embodiments and developments of the invention are contained in the additional patent claims.
The invention or the advantageous embodiments and developments thereof further afford the following additional advantages in particular:
Embodiments of the invention and the configurations thereof, and additional features and advantages will be appreciated from the following description and the drawings, to which reference is made.
a: shows a linear actuator as an alternative to the motor screw drive;
b: shows a valve unit having two coupled valves;
a: shows a dual-circuit drive system having a pressure store;
a: shows a valve block having a valve switching-off mechanism between the camshaft and valve;
b: shows a camshaft adjustment mechanism with two contours;
a: shows a regulation method with four sequential valves;
b: shows a valve stroke variation with different control methods;
The plunger piston 14 has the zero position s0 in front of a breather hole 15a which leads via a hydraulic line to a hydraulic medium reservoir 24 so that in this position hydraulic fluid can be drawn from the reservoir. At sA, the plunger piston 14 is in an operating position (illustrated with dashed lines). The plunger piston 14 is returned by means of one or more restoring springs 16d into the zero position s0 in which it is in abutment with a stop 16c. The plunger piston 14 can be adjusted in both directions by means of the ball screw drive via a drive which is described below so that the operating chamber or the volume in the operating chamber of the piston/cylinder unit 13 can be increased or decreased accordingly.
The drive which drives the ball screw drive 16 has an electric motor 17 (stator and rotor) with a corresponding bearing 18 and angle sensor 19. In the system, there is further provided a pressure sensor 21 and an additional 2/2 switching valve 22 which connects the valve hydraulic chamber 6 to the hydraulic medium reservoir 24. This valve 22 is used for venting the system and the emergency operation control. As a replacement (illustrated in
During normal operation without valve stroke variation, the camshaft acts via the carrier 8 and the piston 9 on the valve hydraulic chamber 6 and the valve 12 is closed. In this instance, the force of the camshaft is transmitted via the hydraulic medium which is enclosed in the hydraulic chamber and the piston 5 to the gas exchange valve 2. Preferably, oil is used as the hydraulic medium so that no sealing complexity is required and motor oil can be used for the valve stroke actuation and the motor lubrication. The oil is acted on with pressure, wherein the pressure is formed and adjusted by the plunger drive unit in order to prevent compression strokes so that the valve can follow the cam contour as directly as possible without any time delay. This is necessary in order to achieve a precise valve stroke. During valve drive, leakages occur. The leakage flows in the valve drive are returned via a return line 33 to the hydraulic medium reservoir 24. Via the switching valve 22 or the non-return valve 22a, hydraulic medium which was lost as a result of leakages is guided out of the hydraulic medium reservoir 24 in the “valve closed” position.
During operation with valve stroke variation, the valve 12 is opened and closed during the camshaft stroke and a corresponding movement of the master piston 9. Volume from the hydraulic chamber 6 is taken up by corresponding movement of the plunger piston 14 from the operating chamber of the piston/cylinder unit 13 and returned to the valve hydraulic chamber 6. Should the valve stroke be reduced in comparison with the stroke predetermined by the camshaft, the piston 14 is moved backwards in the valve opening movement (the volume in the operating chamber of the piston/cylinder unit 13 is thereby increased) and moved forward again in the valve closure movement so that the original volume is returned to the hydraulic chamber 6 again when the valve is closed. If a larger valve stroke than predetermined by the camshaft is desired, additional volume can be conveyed into the hydraulic chamber 6 via the piston/cylinder unit 13 and is removed again at “valve closure”.
Via the control of the piston of the piston/cylinder unit 13, any valve opening contours, substantially limited only by the dynamics of the plunger drive unit, can be achieved. The control of the valves and the drive are carried out by means of an electronic control and regulation unit (ECU) 20. The control of the volume is carried out by means of a stroke regulation of the piston 14 of the piston/cylinder unit via an angle sensor 19 of the electric motor. In a simple variant, it is possible to dispense with the pressure sensor 21 by conclusions being drawn in relation to the drive torque and the pressure in the plunger compression chamber by means of a current measurement of the phase current. The current measurement can also be used for control in the event of a malfunction (failure of the pressure sensor).
The 2/2-way switching valve 12 is provided with a large cross-section so that the volume flow is not throttled and large volume flows can be achieved. Another switching valve 22 is arranged in a hydraulic line which leads from the hydraulic chamber 6 to the hydraulic medium reservoir 24. The second 2/2-way switching valve 22 has the function that volume missing from the hydraulic medium reservoir 24 as a result of leakage can be subsequently supplied or can be returned to the oil circuit and serves to vent the system. In the event of a failure of the drive unit, this valve 22 can additionally be used as a suction valve in order to convey the volume into the valve hydraulic chamber. The valve may also be constructed as a simple non-switchable blocking valve 22a which enables volume flow in only one direction (from the hydraulic medium reservoir 24 to the valve hydraulic chamber 6).
The pressure sensor 21 serves to control the volume flow and adjust the basic pressure in the valve hydraulic chamber and to detect variable viscosity under the influence of temperature. The control is carried out based on a model by means of pressure/volume characteristic lines. An additional valve stroke sensor 25 serves to balance the control and regulation and is preferably provided in a circuit in a valve and optionally as an insert in all valves. In particular as a result of temperature influence, the medium properties change (volume flow, leakage flow). This can be determined with the valve stroke sensor 25 and the precision of the valve stroke regulation can consequently be significantly improved since these changes can be identified during operation. In addition, the valve stroke sensor 25 can be used for the regulation and pressure fluctuations can be reduced.
During emergency operation (failure of the electric motor), the valve 12 is closed and the valve drive is operated at full stroke. Via the valve 22 or 22a, hydraulic medium is conveyed in accordance with the leakage of the system. If the power supply drops, the system is fully operational. The valve stroke can no longer be varied.
If the switching valve 12 fails in the open position in the event of a second malfunction (for example, incoming particle flow), the operation is stopped in variable valve stroke. The system is then operated only in full stroke operating mode. The motor then remains in a fixed position and is no longer controlled in the context of taking up volume and compensates only for volume flows in order to control the full stroke and the other valves 22 are closed (see in this regard also
a shows an alternative embodiment of the plunger drive unit, in which the motor gear unit is replaced by a linear actuator 26. The linear actuator comprises a stator having coils 27 and a rotor 28 having permanent magnets 29.
As an alternative to a linear actuator, it is also possible to use a segment motor comparable with the valve drive actuator of DE 10 2006 013 100 A1.
b shows an alternative embodiment of the hydraulic cap 11 in which 2 or more valves can be actuated with a common valve hydraulic chamber 6 and a camshaft, wherein the valve hydraulic chamber is connected to the plunger drive unit by means of a switching valve 12.
In
a shows a hydraulic solution for the switching between the camshaft and operation with the decoupled camshaft. The camshaft 7 is on a first camshaft hydraulic chamber 6a which is connected to the valve hydraulic chamber 6 and the hydraulic medium reservoir 24 by means of a hydraulic line 33 and a 3/2 separation switching valve 32. If the separation switching valve 32 is closed, the camshaft is decoupled from the valve hydraulic chamber. The hydraulic medium in 6a is then returned with a camshaft stroke via a hydraulic line into the hydraulic medium reservoir 24 and conveyed again via the valve. Consequently, the gas exchange valve is separated from the camshaft pressure actuation and can be controlled exclusively via the valve 12 and the plunger piston/cylinder unit 13 or the associated drive. Consequently, the energy requirement for the partial-load operation can be minimised since only small volume flows and stroke movements are required and no compression losses of the camshaft occur.
b shows an adjustable camshaft contour, as used, for example, in EP 213241881 (to which reference will also be made here for disclosure or further explanation). Via an adjustment mechanism, the camshaft can be axially displaced and the camshaft contour which acts on the hydraulic system can be varied. This has the advantage that existing mechanical valve drives can be taken over and the stroke variation is carried out on the basis of two different camshaft contours (maximum stroke contour and zero stroke). This has a positive effect on the electrical power requirement of both large and small strokes since the volume flow and consequently the power requirement can be minimised. A camshaft contour with full stroke would in particular be used for maximum load and a camshaft contour with zero stroke for small strokes and partial load operation. Consequently, the power requirement of the drive system can be minimised with low costs and the valve drive system can also be operated with a standard on-board system voltage of 12V.
In the context of a low power requirement, an electric motor with the smallest possible mass of inertia (inner rotor or inner rotors with a dual air gap) or a linear actuator with a small rotor mass or segment motor (as described, for example, in DE 102006013100 A1 of the Applicant, which will be referred to in this instance for disclosure and description of further details) is intended to be used. In addition, a hydraulic translation between the valve hydraulic chamber and plunger hydraulic chamber is advantageous in order to minimise the overall mass inertia and the torque requirement/power requirement. The hydraulic system is preferably intended to be constructed in such a manner that the entire mass inertia (valve+plunger piston/cylinder drive unit) is minimised in total.
a illustrates the control method. In the upper region of the image, the camshaft stroke sNW of sequential valves is illustrated as a function of the crankshaft angle ° kW. Below this the stroke path of the valve sV, the switching position of the switching valves (1: open/0: closed) and the piston stroke sk of the plunger drive unit are illustrated. As soon as the stroke path of the camshaft should deviate from the desired valve stroke, the valve is opened and the plunger sk is adjusted. The plunger operates based on the operating stroke position sA and during operation is always in front of the initial position s0. The volume is taken up as far as the maximum stroke and returned again afterwards. As soon as the desired valve stroke corresponds again to the camshaft valve stroke, the valve can be closed again and the remaining valve stroke is predetermined by the camshaft. In phase (1), this sequence is the same for all successive valves so that, in spite of overlapping of the camshaft paths, the plunger control can be carried out in a sequential manner since, at the beginning and at the end of the valve elevation, no control intervention is required. In phase (2), the stroke Sv is reduced and the piston movement consequently increases since more volume has to be displaced.
During real operation, a corresponding pre-control is required since both the switching valves have downtimes and the pressure is built-up and reduced in a time-delayed manner. This is intended to be taken into account in the regulation and is not precisely set out in the schematic illustration.
b shows other valve stroke variation possibilities and the corresponding control. In phase (3), a larger valve stroke Sv is desired than the camshaft profile. In order to achieve this, the valve is opened at the beginning of the valve elevation curve and increased by means of a positive piston movement sk of the valve stroke. This method is advantageous in order to achieve large valve opening cross-sections and to achieve more filling in the cylinder at maximum motor load.
In phase (4), no stroke is produced by the camshaft by camshaft decoupling according to
In phase (5), a specific feature of the multiplexing is illustrated in which two switching valves of two successive valves (for example, outlet and inlet) are temporarily opened at the same time and consequently an overlapping of the valve elevation curves is prevented. The first valve is closed early and the second valve is opened late and consequently desirable negative pressures are achieved in the cylinder. Both valve curves can be controlled at the same time by the plunger.
The embodiment of a device for variable electrohydraulic valve control illustrated in
Using the pump 42, leakage losses can be compensated for via the non-return valves 22a, 22b. If the pressure in the valve hydraulic chambers 6 falls below the pressure level of the pump, a fluid flow begins via the non-return valves. The non-return valves 22a, 22b lock in the counter-direction, that is to say, volume never flows in the direction of the pump, even when during a modulation higher pressures are produced than the pressure level of the pump 42. In particular for each valve hydraulic chamber 6a, 6b, a non-return valve 22a and 22b is provided so that no transverse flow can be produced between the valve hydraulic chambers (which, in the event of modulation on a valve in the basic circuit phase of the cam, would otherwise be possible). The pump pressure maintains a minimum pressure in the valve hydraulic chambers, whereby the “hydraulic rod assembly” is pretensioned. The higher the minimum pressure, the better the valve stroke follows the cam stroke, with a reduction of the compression losses being carried out. In a simple embodiment, the oil pump of the internal combustion engine is used as a pump and the motor oil is used as a medium for the valve drive. In order to reduce the compression losses, an oil pump with a higher pressure, for example, 10 bar is advantageous or a separate oil circuit. This leads to higher control time precision (less air in the oil, more rigid system), but also higher system costs.
With the solenoid valve 22c open, the linear actuator LA moves the piston 13a of the piston/cylinder unit 13 back and thus produces by means of differential pressure with respect to the hydraulic valve chamber 6 a volume flow in the operating chamber 13b of the piston/cylinder unit 13 or when the linear actuator is activated, back into the hydraulic valve chamber. The valve stroke is thereby controlled. A spring 44 supports the actuator movement and reduces by means of corresponding configuration taking into account the other resilient forces in the system (valve and carrier restoring spring 3, 10) the required linear actuator force and consequently reduces the power requirement. In addition, leakage losses can be compensated for directly in the piston/cylinder unit 13 by volume from the piston/cylinder unit being conveyed into the hydraulic valve chamber 6 by forward movement of the piston 13 by means of actuation of the linear actuator.
With the solenoid valve 22c open and at the same time at least one open solenoid valve 12c, 12d (control valve(s)) on the valve hydraulic chambers, there begins a volume flow which is driven by the pump 42 or alternatively by the linear actuator LA. This is advantageous when the pump is mechanically driven only by the internal combustion engine and cannot be used for venting during downtime. Via the valve hydraulic chambers 6a, 6b and the control valves 12c, 12d, the piston/cylinder unit 13 and the solenoid valve 22c which is open for this purpose in the container 24, it is thus possible to carry out an active venting routine. As a result of the venting, the control precision is improved since the hydraulic medium (oil) becomes “stiffer” or less resilient. At the same time, there is a reduction of the compression losses.
For an emergency operation or system component failure, it is advantageous to construct the valves 12c and 12d so as to be open in a current-free state. In the event of a valve failure, the volume can consequently be displaced out of the valve hydraulic chamber into the piston/cylinder unit. It is thereby ensured that there is no collision between the gas exchange valve 2 and the motor piston as a result of volume being conveyed into the hydraulic chamber of the relevant valve. With appropriate safety measures (for example, valve stroke control), the valve can still be controlled by the piston/cylinder unit by volume being conveyed via the linear actuator. The other remaining valves can still be controlled in emergency operation without limitation by the control method described without limitation.
In the event of system failure of the valve control device, all the valves 12c, 12d are then open and the volume from the valve hydraulic chamber is conveyed into the valve hydraulic chamber in the piston/cylinder unit. The hydraulic chamber then acts as a storage chamber and conveys the volume back into the hydraulic chamber again. Consequently, the motor can continue to be operated. Leakage losses are compensated for by means of the pump.
For a shutdown of the cylinder of the motor, it may be sufficient to hydraulically switch off the inlet valves of the cylinder (both at the same time). To this end, the solenoid valve 22c can be opened, together with an opened control valve 12c or 12d. The cam which is associated with the cylinder then pushes the hydraulic medium via the piston 13a into the pressure-free storage container 24. This type of switching-off is only one of other possible switching-off operations, that is to say, it is optional.
In the embodiment illustrated in
Using the pressure sensor 21, it can be established whether there is a risk of a motor valve opening. In this instance, by means of appropriate control of the electric actuator, the piston/cylinder unit of the piston can be supported in terms of its movement in such a manner that the motor valve does not open.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 100 632.9 | Jan 2013 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/050784 | 1/16/2014 | WO | 00 |
