Abstract:
A device for controlling gas-exchange valves of an internal combustion engine is provided, which device has hydraulic valve actuators each allocated to one gas-exchange valve. Each valve actuator has an actuating piston acting on the gas-exchange valve, and two hydraulic working chambers delimited by the actuating piston, of which the first working chamber acting upon the gas-exchange valve in the closing direction is constantly filled with fluid under pressure, and the second working chamber acting upon the gas-exchange valve in the opening direction is able to be alternately filled with fluid under pressure and relieved via two electric control valves. For the purpose of cost reduction, provided for each valve-actuator pair is a single first electric control valve that is acted upon with the fluid pressure on the intake side, and is connected on the outlet side to the second working chamber of one valve actuator. The second working chamber of the other valve actuator is filled with fluid with the aid of a switchover valve and the fluid pressure in the second working chamber of the one valve actuator.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is related to a device for controlling gas-exchange valves in combustion cylinders of an internal combustion engines.  
       BACKGROUND INFORMATION  
       [0002]     In a device disclosed in German patent document 198 26 047, each valve actuator, whose actuating piston is joined in one piece with the valve tappet of the allocated gas-exchange valve, is permanently connected with its first working chamber to a fluid-pressure source delivering fluid under high pressure, and with its second working chamber is connected, on one hand, to a first electric control valve alternately closing or releasing a supply line to the fluid-pressure source, and on the other hand, is connected to a second electric control valve alternately releasing or closing a discharge line leading to a fluid reservoir. The electric control valves are designed as 2/2-way solenoid valves having spring resetting. When the gas-exchange valve is closed, because of the first working chamber connected permanently to the fluid-pressure source, and because of the second working chamber separated from the fluid-pressure source by the first electric control valve and connected to the discharge line by the second electric control valve, the actuating piston of the valve actuator takes its normal position. Both electric control valves are switched over to open the gas-exchange valve. In this manner, on the one hand, the second working chamber of the valve actuator is blocked with respect to the discharge line by the second electric control valve, and on the other hand, is connected by the first electric control valve to the supply line to the fluid-pressure source. Since the actuating-piston surface delimiting the second working chamber in the valve actuator is larger than the actuating-piston surface delimiting the first working chamber, the actuating piston moves out of its normal position, accompanied by reduction in the volume of the first working chamber, and thereby opens the gas-exchange valve. The size of the opening lift is a function of the formation of the electric control signal applied to the first electric control valve, and the opening speed is a function of the fluid pressure applied from the fluid-pressure source. To maintain the gas-exchange valve in a specific open position, the first electric control valve is subsequently switched over, so that it blocks the supply line to the second working chamber of the valve actuator. In this way, all open positions of the gas-exchange valve may be adjusted by an electric control unit for generating control signals. The gas-exchange valve is closed by resetting the second electric control valve into its open position, so that the first working chamber of the valve actuator is again connected to the discharge line. To control a gas-exchange valve, in each case two electric control valves are necessary which act upon the second working chamber of the allocated valve actuator with fluid pressure, or relieve it of pressure, accordingly.  
       SUMMARY  
       [0003]     The device of the present invention for controlling gas-exchange valves has the advantage that, by replacing the first electric control valve of one of the valve actuators in the valve-actuator pair by a simple switchover valve, via which the fluid pressure in the second working chamber is controlled with the aid of the fluid pressure at hand in the second working chamber of the other valve actuator, the number of electric control valves per valve-actuator pair is reduced. Furthermore, according to an example embodiment of the invention, a second electric control valve in the valve-actuator pair may be replaced by a simple check valve which connects the second working chamber of the one valve actuator to the second electric control valve allocated to the other valve actuator, and it is then possible to save on two solenoid valves per valve-actuator pair. Since the electric control valves, usually constructed as 2/2-way solenoid valves, must realize extremely small switching times, in practice approximately 0.3 ms given an opening cross-section of 3 mm 2 , such electric control valves are very costly, so that the reduction in the number of electric control valves in the control device is accompanied by a marked cost savings. Due to the lower number of electric control valves, the number of output stages and the expenditure on electric cabling for these control valves are also reduced, which reduction leads to a further cost savings. The smaller number of electric control valves also reduces the electric energy demand and lowers the probability of the device malfunctioning. Because of the smaller unit volume of a simple switchover valve compared to a solenoid valve, the installation space required for accommodating the device in the vehicle may also be reduced. The valve-actuator pair, controlled by a single first electric control valve and by two or only one second electric control valve, includes such valve actuators which are used for actuating two gas-exchange valves of the same kind, thus two intake valves or two exhaust valves, in the same combustion cylinder.  
         [0004]     According to one example embodiment of the invention, the switchover valve is positioned in a connecting line between the two working chambers of the two valve actuators of the valve-actuator pair. If the switchover valve, designed as a 2/2-way valve able to be actuated either electromotively, electromagnetically or hydraulically, is deblocked, then the second working chamber of the one valve actuator is supplied with fluid pressure via the second working chamber of the other valve actuator, and therefore the actuating piston of the valve actuator is shifted in the direction of opening the gas-exchange valve. By suitably selecting the instant for deblocking the switchover valve, it is possible to realize different opening times of the gas-exchange valve actuated by this valve actuator, or to keep this gas-exchange valve closed, if necessary. The single first electric control valve in the valve-actuator pair may be designed so that, in the extreme case, it is able to regulate the entire volumetric flow which both valve actuators of a valve-actuator pair need to execute a simultaneous or staggered, but always parallel, stroke. Different closing times may be realized at both gas-exchange valves via the triggering of the second electric control valves. If, as observed above, one of the two second electric control valves is replaced by a check valve, then the gas-exchange valves are closed at the same point of time.  
         [0005]     According to one example embodiment of the invention, the switchover valve is a hydraulically actuated 2/2-way valve having two hydraulic control inputs, and is designed so that a valve deblocking takes place only when both control inputs are acted upon. The one control input is linked to the second working chamber connected to the single first electric control valve, and the other control input is linked to the outlet of a further switchover valve acted upon on the input side by a fluid pressure. The second working chamber of the valve actuator connected to the switchover valve is connected via the switchover valve directly to the fluid-pressure source. As soon as the single first electric control valve is triggered, the fluid pressure input by it into the second working chamber is also available at the one control input of the switchover valve. The switchover valve may then be deblocked at any point in time by acting upon the second control input; with the switching of the switchover valve, fluid flows directly from the fluid-pressure source into the second working chamber of the other valve actuator. This example embodiment has the advantage that the single first electric control valve in the valve pair only has to be dimensioned for the supply of a single valve actuator, and does not have to switch the entire fluid quantity for triggering both valve actuators. In addition, unsteadiness in the lifting movement of the one valve actuator, which may be produced during the stroke of its actuating piston by the switching in of the other valve actuator and by the additional fluid requirement of the second working chamber of the following valve actuator thus occurring, is avoided.  
         [0006]     According to one example embodiment of the invention, all switchover valves of the existing valve pairs are deblocked by the further switchover valve, so that only a single further switchover valve is present in the device, which results in reduction in production costs and installation space.  
         [0007]     According to one example embodiment of the invention, the further switchover valve is acted upon by fluid pressure by linking its valve intake via a check valve to the second working chamber of the valve pair, the second working chamber being connected to the single first electric control valve. Alternatively, the further switchover valve may be acted upon by pressure through an external fluid-pressure source, e.g., the low-pressure circuit of the internal combustion engine. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  shows a circuit diagram of a device for controlling eight gas-exchange valves arranged in four different combustion cylinders of a four-cylinder internal combustion engine.  
         [0009]      FIG. 2  shows a circuit diagram of a modified device for controlling the gas-exchange valves.  
         [0010]      FIG. 3  shows a schematic representation of a gas-exchange valve, connected to a valve actuator, in a combustion cylinder of the internal combustion engine. 
     
    
     DETAILED DESCRIPTION  
       [0011]     The device for controlling gas-exchange valves in combustion cylinders of an internal combustion engine, as shown in  FIG. 1 , is designed for the control of a total of eight gas-exchange valves  10 , like one shown schematically in  FIG. 3 , of which two are arranged in each combustion cylinder of a four-cylinder/four-stroke internal combustion engine. Gas-exchange valves  10  may be the intake valves or the exhaust valves in the combustion cylinders. The device according to the present invention includes a plurality of hydraulic valve actuators  11 , e.g., in the exemplary embodiment a total of eight valve actuators  11 , each of which actuates one gas-exchange valve  10 . Each valve actuator  11  has a working cylinder  12  in which an actuating piston  13  is guided in an axially displaceable manner. Actuating piston  13  divides working cylinder  12  into two hydraulic pressure or working chambers  121  and  122 , and is fixedly joined to a valve tappet  14  of gas-exchange valve  10 .  FIG. 3  shows schematically in enlarged representation a valve actuator  11  in connection with an open gas-exchange valve  10 . At its end turned away from actuating piston  13 , valve tappet  14  bears a valve sealing surface  15  that cooperates with a valve seat surface that is formed in cylinder head  16  of the combustion cylinder of the internal combustion engine, for controlling an opening cross-section. Working cylinder  12  has a total of three hydraulic connections, of which two hydraulic connections  122   a  and  122   b  discharge in the upper pressure chamber or second working chamber  122 , and one hydraulic connection  121   a  discharges in the lower pressure chamber or first working chamber  121 .  
         [0012]     The device also has a pressure-supply device  20 , whose output  201  forms a fluid-pressure source for supplying valve actuators  11 . Pressure-supply device  20  includes a high-pressure pump  21  that delivers fluid from a fluid reservoir  18 , a check valve  22  positioned on the outlet side at high-pressure pump  21 , and an accumulator  23  for pulsation damping and energy storage. Output  201  of pressure-supply device  20 , which is tapped between check valve  22  and accumulator  23 , is connected via a line  24  to hydraulic connections  121   a  of first working chambers  121  in all of the total of eight valve actuators  11 , so that first working chambers  121  of valve actuators  11  are constantly acted upon by high fluid or hydraulic pressure available at output  201  of pressure-supply device  20 .  
         [0013]     Of the total of eight existing valve actuators  11 , in each case two valve actuators  11  are combined to form a valve-actuator pair, which in each instance control two intake valves or two exhaust valves in the same combustion cylinder. The allocated combustion cylinder is symbolized in  FIG. 1  by dotted edging  19  of the valve-actuator pair with the associated control means. To simplify the description, valve actuators  11  of one valve-actuator pair are designated in the following by  11   a  and  11   b , and the description is limited only to one valve-actuator pair allocated to one combustion cylinder. However, the following description holds true in the same manner for the remaining three valve-actuator pairs allocated to the remaining combustion cylinders.  
         [0014]     Fluid connection  122   a  of second working chamber  122  of valve actuator  11   a  is linked via a first electric control valve  25 , formed as a 2/2-way solenoid valve having spring resetting, to line  24  leading to output  201  of pressure-supply device  20 , while fluid connection  122   b  of second working chamber  122  of valve actuator  11   a  is connected to a second electric control valve  26  likewise formed as a 2/2-way solenoid valve with spring resetting. On the output side, second electric control valve  26  is connected to a return line  27  discharging into fluid reservoir  18 . Fluid connection  122   a  of second working chamber  122  of valve actuator  11   b  is connected to fluid connection  122   b  at valve actuator  11   a  via a connecting line  28 , in which is arranged a hydraulically deblockable switchover valve  29  having spring resetting. Fluid connection  122   b  of second working chamber  122  of valve actuator  11   b  is likewise connected via a check valve  30  to the intake of second electric control valve  26 . Switchover valve  29  has a hydraulic control input  291  that is connected via a control line  31  to the outlet of a further switchover valve  32  able to be actuated electromagnetically. On the intake side, further switchover valve  32  is connected via a check valve  33  to second working chamber  122  of valve actuator  11   a.    
         [0015]     Alternatively, however, the intake side of further switchover valve  32  may also be connected to output  201  of pressure-supply device  20  or to a low-pressure circuit of the internal combustion engine. The outlet side of further switchover valve  32  is connected via corresponding control lines  31  to all control inputs  291  of switchover valves  29  for all valve-actuator pairs. If, as in the exemplary embodiment of  FIG. 1 , switchover valve  32  is constructed as a 2/2-way solenoid valve with spring resetting, then for the relief of control line  31 , a discharge valve  35  formed as a 2/2-way solenoid valve with spring resetting must also be provided, whose one valve connection is connected to control line  31 , and whose other valve connection is connected to fluid reservoir  18 . This discharge valve  35  may be omitted if switchover valve  32  is constructed as a 3/3-way solenoid valve having spring resetting as shown in  FIG. 2 . In this case, of the three valve connections, the valve intake is linked via check valve  33  again to second working chamber  122  of valve actuator  11   a  and to output  201  of pressure-supply device  20 , respectively, and a first valve outlet is connected to control line  31 , and a second valve outlet is connected to fluid reservoir  18 .  
         [0016]     With closed gas-exchange valves  10 , valve actuators  11   a  and  11   b  of a valve-actuator pair take their normal position in which first electric control valve  25  blocks second working chamber  122  of valve actuator  11   a  from output  201  of pressure-supply device  20 , and second electric control valve  26  links second working chamber  122  of valve actuator  11   a  to return line  27 . Second working chamber  122  of valve actuator  11   b  is likewise connected to return line  27  via check valve  30  and open second electric control valve  26 . Due to the resetting action of their resetting springs, both switchover valves  29 ,  32  take their blocking position. Because of the system pressure prevailing in first working chamber  121 , actuating piston  13  is shifted maximally into its normal position and, via valve tappet  14 , holds gas-exchange valve  10  closed. In the exemplary embodiment shown, control valves  25 ,  26  are currentless, and switchover valve  29  is pressureless.  
         [0017]     To open gas-exchange valves  10 , first of all, second electric control valve  26  is transferred into its closed or shut-off position, so that the two second working chambers  122  of both valve actuators  11   a  and  11   b  are closed. Discharge valve  35  is put into its closed position. At the same time, first electric control valve  25  is put into its working or open position, so that second working chamber  122  of valve actuator  11   a  is connected to pressure-supply device  20 , and the system pressure available at output  201  of pressure-supply device  20  is now also available in second working chamber  122  of valve actuator  11   a . Since the surface of actuating piston  13  delimiting first working chamber  121  is smaller than the surface of actuating piston  13  delimiting second working chamber  122 , a displacement force develops which moves actuating piston  13  in  FIG. 1  to the right, whereby gas-exchange valve  10  is opened. The size of the opening lift of gas-exchange valve  10  is a function of the opening duration and the opening speed of first electric control valve  25 .  
         [0018]     If, at a point of time thereafter or simultaneously with first electric control valve  25 , further switchover valve  32  is triggered, it then deblocks switchover valve  29 , in that the system pressure reaching control input  291  of switchover valve  29  via check valve  33  and opened further switchover valve  32  switches over switchover valve  29  against the force of the resetting spring. Thus, fluid from second working chamber  122  of valve actuator  11   a  will flow into second working chamber  122  of valve actuator  11   b , and its actuating piston  13  is displaced in the direction of valve opening. Since the entire fluid stream is now flowing via first electric control valve  25 , it is necessary that first electric control valve  25  be designed for the maximum volumetric flow through both valve actuators  11   a  and  11   b . After second valve actuator  11   b  is switched in, gas-exchange valve  10  actuated by this valve actuator  11   b  moves in accordance with the triggering of first electric control valve  25 , so that actuating pistons  13  of both valve actuators  11   a  and  11   b —depending upon the instant of the deblocking of switchover valve  29 —execute a simultaneous or staggered, parallel stroke.  
         [0019]     To retain gas-exchange valves  10  in their open position, first electric control valve  25  is again switched over (in the exemplary embodiment of  FIG. 1 , de-energized), so that it separates second working chamber  122  of valve actuator  11   a  from line  24  to pressure-supply device  20 .  
         [0020]     If gas-exchange valves  10  are to be closed again after a certain opening time, then second electric control valve  26  is also switched over (in the exemplary embodiment of  FIG. 1 , de-energized), so that it links working chambers  122  of both valve actuators  11   a  and  11   b  to return line  27 . Due to the system pressure in first working chambers  121  of valve actuators  11   a  and  11   b , actuating pistons  13  in working cylinders  12  of both valve actuators  11   a  and  11   b  are returned to the normal position shown in  FIG. 1 , gas-exchange valves  10  thereby being closed with the same closing times.  
         [0021]     If different closing times are sought to be realized, then check valve  30  is to be replaced by a further second electric control valve  26  which is likewise constructed as a 2/2-way solenoid valve and is to be connected on the intake side to second working chamber  122  of valve actuator  11   b , and on the output side directly to return line  27 .  
         [0022]     Instead of hydraulically deblockable switchover valve  29  between the two second working chambers  122  of both valve actuators  11   a  and  11   b , a switchover valve able to be deblocked electromotively or electromagnetically may also be used. Further switchover valve  32  may also be replaced by an electric actuator which directly deblocks all switchover valves  29  electromotively or likewise hydraulically.  
         [0023]     As shown in a partial diagram in  FIG. 2 , another embodiment of the device for controlling gas-exchange valves in combustion cylinders of an internal combustion engine is modified in comparison to the device shown in  FIG. 1  insofar as switchover valve  29  in  FIG. 1 , with connecting line  28  between second working chambers  122  of both valve actuators  11   a  and  11   b , is replaced by a hydraulically controlled switchover valve  34 , via which second working chamber  122  of valve actuator  11   b  is connected directly with line  24  to output  201  of pressure-supply device  20 . Switchover valve  34 , which is designed as an “AND gate”, has two hydraulic control inputs  341 ,  342 , which must both be acted upon by a hydraulic pressure for the switching of switchover valve  34 . Switchover valve  34  also possesses a hydraulic reset input  343  to which a hydraulic pressure is applied for switching the switchover valve  34  into the closed or blocking position shown in  FIG. 2 , and to that end, is connected to line  24  to output  201  of pressure-supply device  20 . One control input  341  of switchover valve  34  is connected to fluid connection  122   b  of second working chamber  122  of valve actuator  11   a , and the other control input  342  is connected via control line  31  to electrically controlled further switchover valve  32 . Electrically controlled switchover valve  32  is constructed here as a 3/3-way solenoid valve having spring resetting, whose second valve outlet is connected to fluid reservoir  18 . Depending upon the position of the 3/3-way solenoid, valve, pressure may be built up, retained, or reduced in control line  31 . However, switchover valve  32  may also be constructed as a 2/2-way solenoid valve as in  FIG. 1 . In this case, in the same way as in  FIG. 1 , discharge valve  35  constructed as a 2/2-way solenoid valve is also to be retained. Moreover, in this case, the switching device according to  FIG. 2  is unchanged, so that the same components are provided with the same reference numerals.  
         [0024]     Given pressure at hand in second working chamber  122  of valve actuator  11   a , control input  341  is hydraulically loaded, so that at any point in time thereafter switchover valve  34  may be deblocked by the triggering of further switchover valve  32 . With the deblocking of switchover valve  34 , fluid flows directly from line  24  into second working chamber  122  of valve actuator  11   b , and actuating piston  13  in working cylinder  12  of valve actuator  11   b  is shifted in a parallel stroke with respect to actuating piston  13  in, working cylinder  12  of valve actuator  11   a , so that gas-exchange valve  10  actuated by valve actuator  11   b  is opened accordingly. In this modified control device, first electric control valve  25  only has to be dimensioned to supply valve actuator  11   a  with fluid, since valve actuator  11   b  is supplied directly by pressure-supply device  20 . At the same time, unsteadiness in the lifting movement of valve actuator  11   a , which may be produced when working with the control device according to  FIG. 1  in response to the switching in of valve actuator  11   b  during the travel of valve actuator  11   a  due to the additional fluid requirement of valve actuator  11   b , is avoided.  
         [0025]     The above description applies to the further valve pairs, (not shown in  FIG. 2 ), for the other combustion cylinders of the internal combustion engine in the case of the control device according to  FIG. 2 , as well.