Patent Document

The application claims priority of PCT application PCT/EP2008/009772 having a priority date of Nov. 23, 2007, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The invention relates to a fluid-operated valve drive, in particular for a gas exchange valve in a combustion cylinder of an internal combustion engine and to an internal combustion engine having such a valve drive. 
     BACKGROUND OF THE INVENTION 
     Fluid-operated valve drives, in particular for gas exchange valves in a combustion chamber of an internal combustion engine, which within the context of this invention encompass both hydraulically and also pneumatically operated valve drives, have long been known. Firstly, said valve drives were used to replace a camshaft-controlled opening of an engine valve, while the closing of the valve continued to be provided by means of a spring mechanism. Such systems are known for example from the German laid-open specification 1,944,177. However, bidirectionally controlled fluid operated valve drives for valve control arrangements have also already long been known in principle, for example from CH 417,219. Here, use is usually made of the principle that an actuating piston has two surfaces which are acted on with pressure and of which one is larger than the other. In CH 417,219, however, it is also proposed that the fluid supply—in this case the oil supply—be controlled by means of a conventional camshaft. Said principle is also inherent in the proposal according to DE 101 439 59 A1, in which however the valve control arrangement operates without a camshaft. In DE 101 439 59 A1, the surface area of at least one of the two active surfaces of the actuating piston should vary along the movement path of said actuating piston. It is also proposed therein that one of two fluid pressure chambers is in each case filled with a fluid and emptied. Said proposal has proven not to be especially advantageous since the valve control arrangement cannot be set up very precisely with a manageable amount of expenditure. 
     A significant improvement of said concept is known originally from U.S. Pat. No. 5,225,641 A, and proposed in improved form in U.S. Pat. No. 6,223,846 B1, referred to hereinafter as Schechter. It is proposed here that two oppositely arranged active surfaces be acted on in each case with a fluid which is extracted from a common reservoir and controlled by means of supply valves. The outflow valves are provided inter alia for pressure relief. Said system is however very complex and can only be used to a limited extent on account of the complex fluid supply control. 
     In relation to conventional mechanically driven valve drives, fluid-operated valve drives basically have the disadvantage or the problem of higher energy consumption, since the power of the internal combustion engine is then lost. The known fluid-operated valve drive devices—in particular also the devices known from U.S. Pat. No. 5,058,857, from U.S. Pat. No. 3,844,528, DE 199,31129, U.S. Pat. No. 6,170,524, WO-A-02/46582 and WO-A-02/066,796—have in common the fact that the problem of increased energy consumption is not solved or is only rudimentarily solved. For example, in WO-A-02/066,796, although it is provided there that a buffer store should absorb pressure fluctuations, the hydraulic fluid from the outlet of the piston for valve control is however conducted into a reservoir, from which said hydraulic fluid must be pumped back up to the working pressure of the hydraulic system by means of a high-pressure pump, which wastes energy. A typical system with increased energy consumption in which the fluid is simply returned into the reservoir is known from WO 2006/121637 A1. 
     In Schechter, it has already been proposed that not only the acceleration of the fluid-operated valves but rather also the braking for a smooth set-down onto the valve seat be carried out by means of a fluid. It is also already indicated in said document that the energy which can be recovered as a result of the braking—by means of a low-pressure rail in said document—should be used. A first approach for recuperation has thereby already been disclosed. However, in Schechter, the high-pressure rail must still be fully charged with pressure, since the low-pressure rail is connected only to the reservoir. Said inferior type of recuperation likewise has room for improvement. 
     US 2004/107699 A1 describes a fluid-operated piston drive in which first approaches for recuperation have likewise already been proposed. The type of recuperation proposed therein is entirely suitable for use for example in a forklift truck etc. but, on account of its complexity, would appear to be entirely unsuitable for use for driving an actuating piston for an internal combustion engine, and would not appear to be a model for solving the above-described problem. The rudimentary recuperation as proposed in US 2004/107699 A1 has the particular disadvantage that the recovered pressure must be used as it accumulates. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a simplified fluid-operated valve drive in which the above-described disadvantages of the prior art are eliminated. In particular, the energy consumption should not be increased by the valve control. Moreover, the most optimum possible form of recuperation should be used. 
     The object of the invention is achieved initially by means of a fluid-operated valve drive. Here, the measures of the invention firstly have the result that the energy which can be recovered by means of the braking of the engine valves is supplied to an intermediate pressure level. Said intermediate pressure level may be arranged between the valve acceleration pressure and the reservoir, which for example saves energy for charging the valve acceleration pressure and simultaneously serves to provide an optimally damped braking process. The recuperation of the second pressure reservoir P 1  may however basically also be used for the pressure conditioning for the provision of pressure for the fuel pump, and/or for the fuel conditioning, such as for example vaporization etc. If, as a special embodiment of the invention, fuel is used as a fluid, and in particular when diesel fuel is used, said pressure conditioning may be carried out directly. If the fluid is simultaneously used as fuel, this may be not only a hydraulically usable fluid but rather also a pneumatically usable gas or similar medium, for example in gas-operated engines. Furthermore, the recuperation of an engine valve or of a plurality of engine valves with a higher pressure requirement—for example the outlet valves of an internal combustion engine—may also be used for the pressure conditioning of another engine valve or a plurality of other engine valves with a lower pressure requirement—for example the inlet valves of the internal combustion engine. 
     To be able to implement the invention, it is basically possible to switch directly from the acceleration phase into the braking phase. This also produces the fastest engine valve movement with minimum fluid pressure. In energy terms, however, it may be advantageous for a non-accelerated overrunning phase to be incorporated between said two phases, if permitted by the valve movement speed. The length of the overrunning phase provides a further control or regulating parameter. 
     It is basically possible for the second fluid valve means to be designed either as proportional valves, which can then be quantity-controlled, or else—or additionally—simple valves with only one open and one closed position and time control. It would however appear to be advantageous—at least for certain applications—to make said valves controllable for fine adjustment with regard to their degree of opening. For the first fluid valve means, however, a design as fluid valves only with selective open and closed positions to P 1  and P 2  would appear to be to be adequate and advantageous. 
     For fine adjustment, it would appear—in certain cases—to be advantageous if, during the transition phase from the first to the second phase and/or from the second to the third phase, both second fluid valve means can be connected for a certain period of time to the base pressure reservoir P 0  while one of the first fluid valve means is open. It is thereby prevented—in particular in the case of a hydraulic design—that a phase occurs in which the pressure chambers are closed and the movement of an only slightly compressible fluid can lead to shocks or excess pressure. It is pointed out that corresponding problems are also possible in the case of a pneumatic design, which problems can be eliminated by means of this advantageous design. For fast control, an embodiment with solenoid valves is advantageous. Particularly advantageous is an embodiment of the invention in which a measuring sensor is provided for measuring the position of the engine valve, preferably by means of a measurement of the position of the actuating piston, by means of which measurement the opening and closing of the fluid valve means is controlled or regulated. 
     Further advantageous embodiments of the invention are described in the claims. 
     The advantages of the invention, in particular within the context of the proposed design, may be summarized as follows: with the proposed valve control, free control of the entire movement sequence for each individual valve is possible without further expenditure, for example the lift height from 0 to maximum, accelerations, braking processes and speeds. An extremely wide variety of states and demands are therefore met, such as starting without a starter, throttle-flap-free operation, optimization of the air inlet into the combustion chamber at all engine speeds, early closing of the outlet valve for NOx reduction, valve adjustment for boosting the engine braking action, cylinder shut-down at part load, unpressurized rest state with valves held closed mechanically, emergency running with partial shut-down of the engine, etc. High energy efficiency is also obtained with short and streamlined paths for the fluid, a low pressure, which can be adapted to the operating state, in the high-pressure system, low mass and therefore low energy requirement for accelerating and braking the moved masses, movable parts guided at the top and bottom without bending loading, slim valve shank and low friction resistances, small piston and hydraulic and pneumatic effective surfaces and low wear. Operational reliability is high on account of technical simplicity, without boosting of the initial acceleration (on account of a low moved mass). Also advantageous is the control on the basis of the effective movement of the engine valves with the possibilities of automatic correction of shifts of the cycle on account of thermal dilatation, changing viscosity of the fluid, gas bubbles, production tolerances and mechanical wear with attrition of the sealing between the piston and cylinder wall. With the system, low maintenance is to be expected on account of low mechanical loading of the components, of the closed system with few sealing surfaces, a simple exchange of the entire valve actuating arrangement, individual valves or components. The geometry is advantageous because no disruption of the paths for intake air and exhaust gases is to be expected, and there is little spatial requirement. 
     A further advantage of the invention is that the demands on the engine oil of engines with a mechanical valve drive are defined primarily by the camshaft drive of the valves, and necessitate the corresponding addition of additives to the engine oil. Said addition of additives is based partially on substances which are detrimental to the exhaust-gas aftertreatment (catalytic converter poisons such as phosphorous or zinc). Without measures to reduce the poisoning of the exhaust-gas aftertreatment, the high service lives which will be demanded in future in exhaust-gas legislature cannot be adhered to. To eliminate said oil-based damage to the exhaust-gas aftertreatment arrangement, complex measures (for example separate lubricating oil circuits for camshaft and valve drive on the one hand and crankshaft and pistons on the other hand) are under discussion. Hydraulically or pneumatically operated valve drives considerably reduce the demands on the engine oil in relation to mechanically operated valve drives, which ultimately also has a positive effect on the service life of the exhaust-gas aftertreatment arrangement. 
     In another embodiment, said aspect of the invention is characterized in that the movement sequence of the engine valve is monitored with regard to its movement travel by means of a sensor. At all times, the deviation of the effective location of the engine valve from its setpoint location according to specification is determined and measured by means of a control unit for said engine valve. The change in the cross section of the corresponding second fluid valve means is calculated such that the valve returns to the position according to specification. According to said aspect of the invention, the system is self-correcting by means of said function, and influences which can unfavorably vary the movement of the engine valve need not be taken into consideration. 
     According to a further aspect of the invention, the recuperation of the above-described valve drive, that is to say the conditioned pressure prevailing in the second reservoir, is used exclusively or additionally for the valve drive of a different valve drive of the internal combustion engine. Since the working pressures for the fluid pressure of the outlet valves of an internal combustion engine should conventionally be higher than the working pressures of the inlet valves—since the outlet valves must operate at most at least briefly counter to the combustion gas pressure—a design is then particularly advantageous in which, in the internal combustion engine, the valve drives of the outlet valves are designed according to the invention and the recuperation energy thereof is designed for the lower fluid pressures of the valve drives of the inlet valves. In this case, it is possible for a pressure arrangement according to the prior art to be provided for the valve drives of the inlet valves, in which only one common pressure reservoir—specifically the second pressure reservoir of the outlet valves—is provided in addition to the base reservoir. Said second pressure reservoir would then ideally not additionally need to be supplied with pressure. 
     The elements mentioned above and the elements claimed and described in the following exemplary embodiments, and which are to be used according to the invention, are not subject to any particular exceptions with regard to their size, shaping, material usage and their technical design, such that the selection criteria known from the respective application may be used without restriction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, advantages and features of the subject matter of the present invention will emerge from the following description of the associated drawings, in which devices according to the invention are explained by way of example. In the drawings: 
         FIG. 1  shows an illustration of an engine valve with a valve control arrangement according to a first exemplary embodiment of the invention; 
         FIG. 2  shows an illustration of an engine valve having a valve control arrangement according to a second exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a valve arrangement according to a first exemplary embodiment of the present invention, having an engine valve  2  and having a driving device (actuator) for said engine valve. The valve  2  comprises—in the usual way—a valve plate  3  which is adapted to a valve seat ring  7  in order to close off the engine bay. When the valve  2  is open, that is to say when the valve is lowered, the combustion chamber  4  of the engine is connected to the combustion gas duct  6 . It is said connection that is to be controlled or regulated by means of the valve drive. 
     The engine valve  2  bears, on its valve shank  5 , an actuating piston  14  which is fixedly connected thereto and which has an upper active surface, which is formed on the upper side of the actuating piston  14 , and also a lower active surface, which is formed on the underside of the actuating piston  14 . Together with the pressure chamber housing  15  in which the actuating piston  14  is arranged so as to be movable upward and downward, the actuating piston  14  forms an upper pressure chamber  10  and a lower pressure chamber  12 . The two pressure chambers  10  and  12  have in each case one first fluid valve  20  and  22  and one second fluid valve  24  and  26  for a pressure fluid, in the exemplary embodiment described here a hydraulic oil or the fuel for the engine, preferably a diesel fuel. In the present exemplary embodiment, said fluid valves are designed as solenoid valves, with in each case only one open and one closed position being provided for the first fluid valves  20  and  22  in each case via the fluid inflow line  16  to the pressure reservoir P 2  and via the fluid outflow line  18  to the pressure reservoir P 1 , while the second fluid valves  24  and  26  can be connected in each case via the fluid inflow and outflow line  19  to the base reservoir P 0 . The second fluid valves  24  and  26  can be controlled in analog or—alternatively—digital fashion into a multiplicity of positions. It is pointed out at this juncture that said analog or digital modulating design of the opening of the second fluid valves  24  and  26  is merely exemplary. 
     Other modulation methods such as intermittent opening, if necessary also with for example pulse width modulation assuming a suitable bandwidth of the opening, may likewise be used. 
     The two first fluid valves  20  and  22  can be selectively connected to a first pressure reservoir P 2  for the pressurized fluid and to a second pressure reservoir P 1 . Here, it is provided that, to accelerate the engine valve  2  in each case one direction, one of the first fluid valves  20  and  22  is opened and therefore the first pressure reservoir P 2  is connected to one of the two pressure chambers. Here, for acceleration for the purpose of opening the engine valve  2 , the upper first fluid valve  20  is opened. So as not to generate a counter pressure, the lower second fluid valve  26 , which is connected to the base reservoir P 0 , is simultaneously opened. Here, for acceleration for the purpose of closing the engine valve  2 , the lower first fluid valve  22  is opened. So as not to generate a counter pressure, the upper second fluid valve  24 , which is connected to the base reservoir P 0 , is now simultaneously opened. 
     As already mentioned, the first fluid valves  20  and  22  can also be connected to a second pressure reservoir P 1 . Here, it is provided that, to brake the engine valve  2  in each case one direction, one of the first fluid valves  20  and  22  is opened and therefore the second pressure reservoir P 1  is connected to one of the two pressure chambers. 
     Here, for braking during the opening of the engine valve  2 , the lower first fluid valve  22 , connected to the second pressure reservoir P 1 , is opened. To continue to fill the upper pressure chamber  10  with fluid, the upper second fluid valve  24  which is connected to the base reservoir P 0  is simultaneously opened. Here, the fluid flows, unpressurized, into the upper pressure chamber  10 . 
     Here, for braking during the closing of the engine valve  2 , the upper first fluid valve  20 , connected to the second pressure reservoir P 1 , is opened. To continue to fill the lower pressure chamber  12  with fluid, the lower second fluid valve  26  which is connected to the base reservoir P 0  is simultaneously opened. Here, the fluid flows, unpressurized, into the lower pressure chamber  12 . 
     In the present exemplary embodiment, it is provided, and the control arrangement is also set up in such a way, that a non-accelerated movement can be carried out in each case between the acceleration and the braking processes. Here, the two first fluid valves  20  and  22  are closed and the two second fluid valves  24  and  26  are opened, such that the engine valve  2  performs a virtually uniform movement and in each case one pressure chamber  10  or  12  is emptied and the other pressure chamber  10  or  12  is filled to the same extent. It will be clear to a person skilled in the art that, by means of the length of said non-accelerated phase, the movement of the engine valve can be regulated using measurement data regarding the present position of the engine valve  2 . This is provided in the exemplary embodiment. 
     It is also provided in the present exemplary embodiment that, for a short time, both second fluid valves  24  and  26  are open while the first fluid valve  20  or  22  are still open. This has the effect that no shocks occur as a result of the incompressible fluid. 
     The supply for the first fluid valves  20  and  22  is fed from said base reservoir P 0 —as described below. 
     Above, in each case individual fluid valves  20 ,  22 ,  24 ,  26  have been described for the fluid valve means according to the invention. In particular, the first fluid valve means  20  and  22  with the selective connections, described in the exemplary embodiment, to P 1  and P 2  may however also be designed in each case as separate fluid valves for P 1  and P 2 —without restricting the generality of the invention. Provision may also be made for the second fluid valve means  24  and  26  to be divided into in each case one merely switchable fluid valve and additionally one fluid valve which can be controlled in terms of its flow rate, if the specific design of the hydraulic or pneumatic relationships and/or the regulating bandwidth necessitate this. 
     In the present exemplary embodiment, two-stage pressure generation is carried out from the base reservoir P 0  firstly to the second pressure reservoir P 1  and from there to the first pressure reservoir P 2 , in each case by means of a pressure stage  31  and  32  which comprises a regulable high-pressure pump  33  and  35  respectively and a non-return valve  38  and  39  respectively. 
     In said exemplary embodiment, therefore, the energy recovered by means of the braking of the engine valves  2  is used in its entirety for maintaining the pressure in the first pressure reservoir P 2  in that—after a starting process—the first pump from P 0  to P 1  consumes very little energy and the high-pressure pump from P 1  to P 2  is correspondingly relieved of load. An optimal recuperation system is therefore proposed. 
     A central electronic control/regulating unit  42  determines, for each engine valve, the optimum movement sequence for each engine valve on account of the ambient and operating conditions and transmits said specification to the electronic valve control device  40 , which outputs the commands for opening the fluid valves. Each engine valve  2  has a separate electronic valve control device  40 . The position of the engine valve  2  is detected over the entire movement path and transmitted to the valve control device  40  by means of a measuring sensor  50 , and said valve control device  40 , in the event of deviations from the setpoint value, corrects the opening of the respective outlet solenoid valve  24  and  26  to P 0 . The lift of the engine valves  2  and the course of the movement over time may be determined freely. The central electronic control/regulating unit  42  determines the pressure in the high-pressure system, specifically in the pressure reservoirs P 2  and P 1 . 
     In the fluid pressure system P 2 , the same pressure prevails for all the engine valves  2  which it supplies. The pressure may be adapted to different operating conditions by controlling the regulable high-pressure pump  33 . 
     As parameters for the regulation by means of the central regulating device  42 , use is made, for example, of the following: throttle pedal position, brake actuation, gear selection, program selection of automatic transmission, temperatures of engine oil or water, position of the vehicle (ascending or descending gradient), outside air temperature. 
     Each engine valve  2  has a valve control device  40  which, by means of control commands to the fluid valves  20  and  22  and also  24  and  26 , controls the movement of the engine valve as precisely as possible according to the specifications of the central valve regulating device  42 . 
     All the valve control devices  40  of an engine transmit the parameters of the valve movement back to the central regulating device  42 , which can adapt the pressure in the high-pressure system—in particular in the first pressure reservoir P 2 . With said system of the comparison of the actual position of the engine valve  2  with the setpoint position, deviations from the specification are corrected. Such deviations may have different causes, for example for the fluid: temperature, viscosity and aging, and with regard to wear: play between the piston and cylinder chamber, production tolerances. 
     The valve shank  5  of the engine valve  2  protrudes, at the upper delimitation of the upper pressure chamber  10 , through the cover of the cylinder. A spiral spring  62  acts, in a valve spring chamber  66 , on a spring plate which is connected to the valve shank  5 . In the event of faults in a limited number of engine valves, the relevant cylinder—or else plurality of cylinders—may be partially shut down and the pistons moved passively. An emergency running program with mechanical restoration of engine valves  2  into a rest state is therefore provided. In the rest state, the fluid in the high-pressure system can be discharged by means of a brief opening of all the fluid valves. The engine valves  2  are guided by means of said springs  62  into their upper position in order that servicing and repairs can be carried out in the unpressur±zed state. The valves do not come into contact with the pistons of the engine when said pistons are in the vicinity of top dead center. The cylinder head, when removed from the engine block, may be put down in the installed position without the risk of damage. The mounting and dismounting of the valve drive are thereby considerably simplified. Fluid which passes into the valve spring chamber  66  through the upper valve guide  60  at the transition from the upper pressure chamber  10  to said valve spring chamber  66  is conducted through an opening into the unpressurized base reservoir P 0 . 
     In a second exemplary embodiment according to  FIG. 2 , the engine fuel is used as fluid, and the first pressure reservoir P 2  serves as an intermediate stage for the provision P 3  of the required fuel pressure for the fuel injection. A third pump is provided which provides the required fuel pressure. The operating conditions for the control and the movement of the engine valves  2  are otherwise unchanged. 
     It will be clear to a person skilled in the art that, within the scope of the patent claims, further modifications are possible without it being necessary to depart from the basic concept of optimum recuperation. These include for example an embodiment (not illustrated here in the figure) in which the first pressure reservoir P 2  is fed directly from the base reservoir P 0 , while the second pressure reservoir P 1  is fed either by means of an auxiliary pump or a branch from the first pressure reservoir P 2  only during the starting of the engine when no fluid pressure is yet present there, but then obtains its pressure solely from the braking of the engine valves  2 . In this case, it may be provided that the excess of energy obtained in the second pressure reservoir P 1  as a result of the braking serves—as an intermediate stage—for the above-described provision of the required fuel pressure for the fuel injection. 
     In the above description, it has been assumed that the pressures in the two pressure reservoirs P 1  and P 2  will be unequal, with the pressure in P 2  being assumed to be greater than that in P 1  if P 1  is provided as an intermediate stage for P 2 . This is however not necessary. The pressure in P 1  may basically be equal to the pressure in the first pressure reservoir. The two pressure reservoirs P 1  and P 2  may then be connected or formed together. In this case, the braking force for the engine valves  2  would then be approximately equal to their acceleration force. In one particularly simple, not specially claimed but highly advantageous design of the recuperation, only one pressure reservoir cylinder P 2  is provided, which is then preferably connected by means of in each case one fluid line  16  and  18 , which is simultaneously designed as a fluid inflow line and also as a fluid outflow line, to the upper first fluid valve  20  and to the lower first fluid valve  20  on the one hand and to the pressure reservoir P 2 . Said design with self-recuperation is particularly advantageous if the valve control is controlled by means of the length of the overrunning phase. In this case, it would also be possible for the overrunning phase to be configured such that the two first fluid valves  20  and  22  are open, if necessary also when the second fluid valves  24  and  26  are closed. 
     It would even be possible for the pressure relationships to be interchanged, such that the braking force of the engine valves  2  is greater than their acceleration force, which would then be imparted for longer than the braking force. This may be realized for example by interchanging P 2  and P 1 , with which indeed the two first fluid valves  20  and  22  are acted on. 
     List of Reference symbols 
     
         
         
           
               2  Engine valve 
               3  Valve plate 
               4  Combustion chamber 
               5  Valve shank 
               6  Combustion gas duct 
               7  Valve seat ring 
               8  Seal 
               10  Upper pressure chamber 
               12  Lower pressure chamber 
               14  Actuating piston 
               15  Pressure chamber housing 
               16  Fluid inflow line 
               17  Filter 
               18  Fluid outflow line 
               19  Fluid inflow and outflow line 
               20  Upper first fluid valve, fluid valve means 
               22  Lower first fluid valve, fluid valve means 
               24  Upper second fluid valve, fluid valve means 
               26  Lower second fluid valve, fluid valve means 
               31  Pressure stage 
               32  Pressure stage 
               33  High-pressure pump 
               35  High-pressure pump 
               38  Non-return valve 
               39  Non-return valve 
               40  Valve control device 
               42  Central control/regulating device 
               50  Measuring sensor 
               60  Valve guide 
               62  Valve spring 
               66  Valve spring chamber 
             P 0  Base reservoir for the fluid 
             P 1  Second pressure reservoir for the fluid 
             P 2  First pressure reservoir for the fluid 
             P 3  Additional pressure reservoir for fuel injection

Technology Category: 2