DE4415524A1 - Electro-mechanically actuated valve timing system - Google Patents

Abstract

The invention relates to a hydraulic actuating device for varying and adjusting the valve timings of a camshaft of an internal combustion engine driven by a crankshaft. The rotational position of the camshaft is adjustable by a limited angle of rotation, vanes seated in a chamber being acted upon by pressure medium. The pressure medium is controlled by means of a slide valve. According to the invention the slide valve is vented and is held in a centred middle position by a spring and an electrically actuated magnet acting in the opposite direction. By varying the magnetic force, the chambers can be hydraulically actuated by way of the slide valve, thereby adjusting the rotational position.

Description

The invention relates to an electromechanically actuated Ven valve timing system (VCT) according to the preamble of the patent claims 1. The camshaft position is the extent versus crankshaft position in response to torque Reversals that changed the camshaft in normal loading drive experienced. In such a VCT system there is an electro mechanical-hydraulic system provided to the cams wave again when such torque reversals occur to defer and a tax system is provided to optionally to ensure that the hydraulic system this Make provision or not.

In particular, the invention relates to a control system that use of a variable force solenoid valve makes to directly the position of the fully ventilated slider control valve, which is a useful part of the hydrauli system.

With regard to the state of the art, reference is made to the following publications:
US 5,002,023 relates to a VCT system with two counteract the hydraulic cylinders and flow elements for the fluid exchange between the cylinders in order to change the starting position of a camshaft relative to the crankshaft in both directions of rotation. The valve has a slide which is displaceable in both directions from a central or rest position. This changes the hydraulic pressure that acts on a slide end and thus the ratio between the hydraulic force at one end and an opposing mechanical force at the other end, which comes from a spring.
US 5,107,804 explains another VCT system in which the aforementioned cylinders are replaced by a wing with cams in a housing. The wing is rotatable relative to the housing and thereby displaces liquid in the housing from one side of a cam to the other and vice versa, so that the wing is rotated in one direction or the other. The result is a corresponding rotation of the camshaft.
US 5,172,659 and 5,184,578 deal with problems of such VCT systems in order to compensate for the forces acting on the valve spool of the valve by balancing both valve ends hydraulically. This eliminates pressure changes or changes in viscosity and the middle position of the slide remains.

The disadvantage, however, is that the slide position in the up warm phase of the engine is not controllable. With the engine It takes several seconds to start before the oil pressure is attained poses. During this time, the position of the spool is unknown.

Furthermore, the dynamic response is sluggish. Even if the engine speed reaches a normal operating speed, there are different properties depending on the engine. So be a new machine sits at high speed and lower Temperature a completely different oil pressure than one much used machine in a healthy condition and idling. Want one operationally all of these different characteristics record (through larger cross sections for the hydraulic Pistons and springs too small), this leads to a sluggish Responsiveness and a corresponding interpretation of the Reg lers to maintain stability.

Such controllers with a higher gain factor, however, do the system is sensitive to tolerances and operational conditions conditions. However, this (for example in the pulse widths  control for zeroing the slide valve) leads to a deterioration in the control behavior in the overall system.

Furthermore, the moving parts lead with impulses controlled solenoid valve, as is usually the case with such Systems is used to annoying noises. Operational the solenoid valve switches the vol len stroke. The fast switching leads to a flutter of the Anchor and plunger, d. H. a high frequency hammering, that makes the noise.

The invention has for its object the system of to improve the position a vented piston in a hydraulic control valve to control. In particular, it was an improvement te control of the vented piston of a control system in a VCT system, the valve being similar to the valve, that in U.S. 5,002,023 or in U.S. 5,107,804.

According to the invention, the stated object is based on the features of claim 1 solved. Advantageous further training can be found in the subclaims.

According to the invention there is no hydraulic loading of one piston end with hydraulic fluid from the engine lubricating oil system at full hydraulic pressure P _S , as is the case with known VCT systems. The force at the other end of the vented piston comes from an electromechanical actuation, preferably a variable force magnet, which acts directly on the piston when driven by an electrical signal from an engine control unit (ECU) according to various engine parameters is supplied. The ECU receives signals from sensors for the positions of the camshaft and crankshaft and uses this information to calculate a relative phase angle. The preferred embodiment uses a closed control system, which is explained, for example, in US Pat. No. 5,184,578 in order to correct the phase angle error. The invention provides an effective and economical solution to the aforementioned problems and has other advantages.

Is the relationship between piston position and control signal (Solenoid current) independent of the engine oil pressure, so all are omitted Problems associated with oil pressure and its fluctuations me. A lack of operating oil pressure, for example errors when starting the engine because the signal of the ECU directly controls the magnet, which directly drives the col ben positioned.

The magnet with adjustable force (proportional magnet) releases also the problem of sluggish dynamic control behavior. The Magnetic devices can be as fast as mechanical ones Response behavior of the slide valve and with certainty we considerably faster than the well-known, fully hydraulic Ven tile. The higher speed enables higher amplification factors in the control loop and reduces the system temperature sensitivity to component tolerances and operating conditions gung.

Furthermore, the stroke of the proportional magnet is very small and is controlled by the current of the ECU, as opposed to the full constant switching strokes of a pulse width controlled mag nets. Because the required stroke rarely reaches the end positions enough, hammering and fluttering is avoided and the sy stem works practically noiselessly.

Probably the most important advantage over known Ven arrangement is the improved regulation of the base systems. The invention provides a device whose Properties are significantly improved to an input  signal for the phase adjustment to be quickly detected and ge to be followed exactly.

Since - as I said - the arrangement according to the invention not from Oil pressure is dependent, it can also be used there, where oilless actuation is desirable, for example for engines with belts for the valve timing.

According to another embodiment, the elec tromechanical actuation and the piston a lever arrangement voltage or equivalent arrangement is provided. The levers order acts as a lifting amplifier / damper, so that either the magnet current is reduced or the air gap stood without deteriorating the valve lift.

Exemplary embodiments of the invention are described below the drawing explained in more detail. Show it:

Figure 1 is a partial view of a valve train with a double camshaft and VCT system.

Figure 2 is a partial view of the intake camshaft in the leading position with respect to the exhaust camshaft.

Fig. 3 is a partial view taken along line 3-3 in Fig. 6 with parts omitted in the lagging position;

Fig. 4 is a partial view similar to Figure 3 with the inlet camshaft in advance position against the lass camshaft.

Fig. 5 is a partial view of the back of components in Fig. 1;

Fig. 6 is a partial view taken along line 6-6 in Fig. 4;

Fig. 7 is a partial view taken along line 7-7 in Fig. 1;

Fig. 8 is a section along the line 8-8 in Fig. 1;

Fig. 9 is a section along the line 9-9 in Fig. 1;

Fig. 10 is an end view of a camshaft with a modified version of the VCT system;

FIG. 11 is a view similar to FIG. 10 with parts omitted;

Fig. 12 is a section along the line 12-12 in Fig. 10;

Fig. 13 is a section along the line 13-13 in Fig. 10;

Fig. 14 is a section along the line 14-14 in Fig. 11;

Figure 15 is an end view of an element of the VCT system of Figures 10 to 14;

Fig. 16 is an end view of an element of Fig. 15 from the other end;

Figure 17 is an end view of the element of Figures 15 and 16;

Figure 18 is an end view of the element of Figure 17 from the other end;

FIG. 19 is a simplified schematic representation of the VCT system of Fig 10 to 18. and

Fig. 20 is a simplified schematic representation similar Lich Fig. 19 in a modified version.

In the embodiment of FIGS. 1 to 9, a sprocket 24 is keyed on a crankshaft 22 , the rotation of which is transmitted to an exhaust camshaft 26 for actuating the exhaust valves of the engine via a chain 28 , which is around the chain tenrad 24 and one on the camshaft 26th attached Ket tenrad 30 is looped. Chain tensioners can be used even if they are not shown. The sprocket 30 is twice the size of the sprocket 24 . This results in a rotation of the camshaft 26 that is half the size of that of the crankshaft 22 , which is correct for a four-stroke engine. Instead of the chain 28 , a belt can be seen easily.

The camshaft 26 has a further chain wheel 32 ( FIGS. 3, 4 and 6) which can be rotated by a certain circumferential angle with respect to the camshaft, but otherwise rotates with the camshaft 26 . The rotation of the camshaft 26 is transmitted to the camshaft 34 via a chain 36 by means of the chain wheel 32 and the chain wheel 38 . The sprockets 32 and 38 have the same diameter, so that there are corresponding rotational numbers. Instead of the chain 36 , a belt can also be provided.

Fig. 6 shows that one end of the camshafts 26 , 34 in La like 42 and 44 of the cylinder head 50 is mounted, which is only shown in parts and screwed to the engine block, namely Lich with screws 48th The other ends of the camshafts 26 and 34 , not shown, are mounted in a similar manner on the cylinder head. The sprocket 38 sits on the camshaft 34 outside of the cylinder head 50 . The sprockets 30 and 32 also lie next to one another outside the head 50 , the sprocket 32 lying opposite the sprocket 38 and the sprocket 30 somewhat outside the sprocket 32 in accordance with the position of the sprocket 24 .

The sprocket 32 has an arcuate support 52 (s. Fig. 7 and 8) which is formed thereon and which extends from the sprocket 32 through an arcuate opening 30a in the sprocket 30 to the outside. An arcuate hydraulic housing 46 is screwed to the chain wheel 30 , in which various hydraulic components of the control system are arranged, pivotably supports the housing-side end of two counter-acting, single-acting hydraulic cylinders 54 and 56 , which are located on opposite sides of the longitudinal axis of the camshaft 26 . The piston-side ends of the cylinders 54 and 56 are pivotally hinged to a bo-shaped bracket 58 , which in turn is attached to the sprocket 32 with a plurality of screws 60 . Thus, if one of the cylinders 54 , 56 extends and the other simultaneously pushes together, the circumferential position of the sprocket 32 changes with respect to the sprocket 30 , either leading the sprocket 32 when the cylinder 34 pushes out, as shown in FIG. 2 and 4, or lagging when the cylinder 56 extends, as shown in FIGS. 1, 3, 7 and 8. In any case, when hurrying or lagging the sprocket 32 against the chain tenrad 30 , which is either permitted or avoided in response to the torque direction in the camshaft 26 , as explained in US 5,002,023, leading or lagging the position of the camshaft 34th compared to that of the camshaft 26 due to the chain connection between the sprocket 32 , which is rotatably mounted on the camshaft 26 be limited and the sprocket 38 which is fixed on the camshaft 34 . This ratio can be seen from the drawing if one considers the relative position of a time stamp 30 b on the chain wheel 30 and a time stamp 38 a on the chain wheel 38 in the lagging position of the camshaft 34 , see FIG. Fig. 1 and 3, and their relative positio nen in the advanced position of the camshaft 34, s. Fig. 2 and 4.

Figs. 10 to 20 show two embodiments of the dung OF INVENTION, in which a housing in the form of a sprocket is rotatably supported on a camshaft 126,132. The camshaft 126 can be regarded as the only camshaft of an internal combustion engine with a camshaft, either as an OH camshaft or as a block.

Furthermore, the camshaft 126 can operate either the intake valves or the exhaust valves of a double camshaft engine. In any event, the sprocket 132 and the camshaft 126 are rotatable relative to one another and the rotation takes place by means of a torque which is exerted on the sprocket 132 by an endless roller chain 138 , which is shown in part and which is wound around the crankshaft and the sprocket 132, not shown. As will be explained in more detail below, the sprocket 132 is rotatably mounted on the camshaft 126 so that it can pivot about at least one circular arc with respect to the camshaft 136 when the camshaft rotates, which adjusts the phase position of the camshaft 126 with respect to the crankshaft.

An annular pump vane 160 sits firmly on the cam shaft 126 and has two diametrically opposite radially outwardly projecting cams 160 a, 160 b and is attached to a ver enlarged end portion 126 a of the camshaft 126 with screws 162 , which through the wing 160 in the Grab end part 126 a. Here, the camshaft 126 is also provided with a stop shoulder 126 b, so that the camshaft is positioned precisely relative to an engine block, not shown. The pump vane 160 is also defined relative to the end portion 126 a by means of a dowel pin 164 exactly positio. The cams 160 a, 160 b sit in radially outwardly directed chambers 132 a, 132 b of the chain wheel 132 , the circumferential length of the chambers 132 a, 132 b being somewhat greater than the circumferential length of the cams 160 a, 160 b, which in each case sit in a chamber and thus allow the sprocket 132 to rotate relative to the wing 160 . The chambers 132 a, 132 b slept around the cams 160 a, 160 b via spaced, transversely directed annular plates 166 , 168 , which are fastened to the wing 160 and thus opposite the camshaft 126 with screws 170 , which are arranged extend. Furthermore, the inner diameter 132 c of the Ket tenrades 132 is sealed against the outer diameter of the part 160 d of the wing 160 between the cams 160 a, 160 b and the tips of the cams 160 a, 160 b of the wing 160 are with slots 160 e, 160 f see to accommodate seals. The chambers 132 a, 132 b of the chain wheel 132 are thus closed hydraulically in a pressure-tight manner and this also applies to each chamber 132 a, 132 b and the section on each side of the cam 160 a, 160 b.

The operation of the embodiment according to FIGS. 10 to 18 can be understood with the aid of FIGS. 19 and 20. Of course, the hydraulic control system of FIGS. 19 and 20 can also be used in a VCT system with opposing hydraulic cylinders according to the embodiment of FIGS. 1 to 9, just as for the VCT system with wings according to FIGS. 10 to 18.

In any case, hydraulic fluid, here in the form of engine lubricating oil, flows into the chambers 132 a, 132 b via a common inlet line 182 . This ends in the middle between two check valves 184 and 186 , which are connected to the chambers 132 a, 132 b via branch lines 188 , 190 . The check valves 184 , 186 have annular seats 184 a, 186 a, so that pressure medium can flow through the check valves 184 , 186 into the chambers. The flow is interrupted by valve balls 184 b, 186 b, which are acted upon by springs 184 c, 186 c. This means that the chambers can initially be filled using the check valves and fluid can be supplied to compensate for leakage losses. The oil enters the inlet conduit 182 via a spool valve 192, which is seated in the camshaft 126 and returns from the chambers via feedback lines 194, 196 to slide back berventil 192.

The slide valve 162 consists of a cylindrical Ge housing 198 and a vented slide 200 which slides in the cavity 198 a. The spool 200 has cylindrical collars 200 a, 200 b at one end each, wherein each collar, the back flow from the conduits 194, 196 controlled via its control edge, in the central position, namely, the zero position of the spool 200, both return lines 194, 196 abge are blocked, as FIGS. 19 and 20 show.

According to the position of the slide 200 in the housing 198 is influenced by a spring 202 which acts on the end of the collar 200 a. The spring 202 thus pushes the piston 200 to the left. The inlet line 182 receives pressure medium oil (engine oil) directly from the main oil distribution 230 of the engine via a line 230 a, past the slide 200 . This oil also lubricates the bearing 232 for the camshaft 126 .

The control of the slide bearing is directly dependent on an electromechanical actuating device 201 , preferably a proportional magnet, which is shown in FIG. 19 Darge. The magnet receives current via a cable 238 , which is guided through the housing 201 d to the winding 201 a, which pushes the armature 201 b forward. The armature 201 b presses on the extension 200 c of the piston 200 and thus pushes the aerated piston 200 to the right, as shown in FIG. 19. If the force of the spring 202 matches the force exerted in opposite directions by the armature 201 b, the slide 200 remains centered in its zero position. Thus, the slider 200 can be moved in any direction by increasing or decreasing the magnetic current. Of course, the construction of the magnet 201 can also be reversed so that the force on the slide extension 200 c does not push but pull. This means a modification of the spring 202 , which in turn must act against the armature movement. However, there are cases in which the slider 200 is to move all the way to the left in the biased position. The arrangement of the spring 202 in the cavity 198 c or 198 a, as shown in Fig. 19 or 20 ge, ensures that the slide 200 returns to the pre-tensioned position when there is no current signal on the magnetic winding 201 , for example if the energy fails or the engine stops.

The displacement of the armature 201 b is dependent on the current in the winding 201 a, which is supplied by a control signal from the ECU 208 and which is shown schematically in FIG. 19. In known versions of the VCT system, the force exerted on the slide extension 200 c must be compensated for by the force of the spring 202 plus the oil pressure in the chamber 198 a, which acts on the end of the collar 200 a if the zero position of the slide 200 is desired becomes. The problem with this compensation is that the oil pressure can fluctuate greatly. The optimal solution is to make the control system independent of the fluctuating oil pressure.

According to the invention the pressure in the chamber 198a relieved so only the force needs of the armature 201 b opposite to the force of the spring 202 to be balanced to reach the zero position of the piston. The pressure relief in room 198 a can be done, for example, by providing a flow path to the wing system which is in the bypass to the slide valve over 200 , ie which does not use an internal channel for supplying oil to the inlet line 182 , as was previously the case. The bypass for the spool 200 can be a connective end bypass line 220 a directly to the inlet line 182 , with an exchange of the inlet check valve 222 a for the check valve, which has previously been arranged in the inner channel of the spool. In connection with the alternative flow path and ventilation of the valve 198 to the atmosphere via the ventilation duct 198 d completes the intention to relieve the pressure in the space 198 a, which has previously acted on the end face of the federal government 200 a.

If the oil pressure quantity is thus eliminated, only forces that are predictable are responsible for the position of the slide 200 . The force of the armature 201 b corresponds to the current signal in the winding 201 a and the force of the spring 202 can also be determined (depending on the spring position). The position of the slide 200 is thus solely dependent on the current signal.

The magnet used in the preferred embodiment has a cylindrical armature corresponding to FIG. 19. The air gap 201 c extends circumferentially around the armature 201 b and can have non-magnetic bearing material. If the armature 201 c moves axially, the cylindrical area of the gap 201 c increases, but the force and the distance from the winding remain constant. Since the force is relatively unaffected by the axial armature position, it is not necessary that the distance between the housing 201 d and the slider 200 is selected exactly.

Another embodiment of the invention is shown in FIG. 20. A proportional magnet with a flat armature or variable air gap is used. The force is inversely proportional to the square of the air gap 201 c. It is therefore advantageous to limit the air gap 201 c to a relatively small value. If you use a Hubver stronger in connection with the magnet with variable gap, then a force boost is achieved. The armature 201 b is connected to the slide extension 200 c via a lever arrangement 201 e, which provides the force amplification. You can reduce the size of the actuator 201 so that the current signal in the winding 201 a is smaller, but the valve lift remains the same.

After for the movement of the slide in each direction only the imbalance between an electrically generated force at one end of the slide 200 a and the spring force at the other end 200 b is responsible (in contrast to hydraulic forces acting on both ends from a common 19), the control systems of FIGS. 19 and 20 are completely independent of the hydraulic system pressure. This eliminates all the measures that were required for a large range of changing oil pressures and that result from certain properties of individual engines. According to the invention, it is also possible to quickly and accurately adjust the slide 200 in its zero position.

The wing 160 can be influenced alternately clockwise and counterclockwise by the torque fluctuations in the camshaft 126 and these fluctuations can cause the wing 160 and thus the camshaft 126 to oscillate with respect to the sprocket 132 . In the slide position shown in FIGS. 19 and 20, however, these rotational fluctuations are avoided by the pressure medium in the chambers 132 a, 132 b on both sides of the cams 160 a, 160 b, since the oil from none of the chambers 132 a, 132 b emanates. Both return lines 194 , 196 are blocked by the slide 200 . However, if the camshaft 126 and the wing 160 are to be rotated counterclockwise with respect to the sprocket 132 , it is only necessary to increase the current signal in the winding 201 a. This pushes the armature 201b to the right and thus also the slide 200 , so that the return line 194 opens. In this state, pump torque fluctuations in the camshaft 126 from the oil chamber 132 a and thus the cam 160 a a turn has been discharged from the oil chamber in the direction of the 132nd A reverse movement of the vane 160 does not occur because the torque fluctuations in the camshaft 126 are directed in opposite directions, although and until the slide 200 runs to the left, since the flow through the return line 196 is blocked by the collar 200 b of the slide 200 . While FIGS. 19 and 20 show a sealed passage, the scope of the vane 160 has an open passage slot 160 c, as shown in FIGS. 10, 11, 15, 16 and 17, through the oil from the chamber 132 a on the right Side of the cam 160 can enter the chamber 132 b on the right side of the cam 160 b, which are the inactive sides of the cam 160 a, 160 b. This results in a counterclockwise movement of the wing 160 with respect to the sprocket 132 when there is flow via the return line 164 and a movement in the clockwise direction when the flow takes place via the return line 196 .

Furthermore, the inlet line 182 is connected via an extension 182 a to the inactive side of each cam 160 a or 160 b, here the cam 160 b is shown, so that oil is constantly on the inactive sides of the cam 160 a, 160 b can flow in for better rotational compensation, whereby the damping of the wing movement is also improved and better lubrication of the bearing surfaces of the wing 160 is achieved. This afterflow of oil does not affect the mode of operation of the electromagnetic actuator 201 . The post-flow oil is continuously provided for the cams 160 a and 160 b.

Claims (13)

1. Electromechanically actuated valve timing system for an internal combustion engine with a crankshaft, at least one camshaft ( 126 ), which experiences torque fluctuations when rotating, with a wing ( 160 ) attached to the camshaft with two spaced cams ( 160 a, 160 b), one limited to the camshaft rotatable, sitting on the camshaft housing ( 132 ) with two spaced chambers ( 132 , 132 b), in which the cams are received, with a drive between the crankshaft and camshaft, and a device for adjusting the rotational position of the housing , depending on torque fluctuations of the crankshaft, for which purpose a valve is provided, characterized in that the valve is formed as a slide valve ( 200 ), the slide of which has two collars ( 200 a, 200 b) and is ventilated that from the slide gest the connection of return lines ( 194 , 196 ) from one chamber ( 132 a, 132 b) depending on the slide position euert is that an inlet line ( 182 a) is connected via the valve to each chamber ( 132 a, 132 b) that check valves ( 184 , 186 ) are provided in the inlet line, with which the flow from each chamber towards the valve is blocked that sensors ( 207 a, 207 b) are provided for detecting the positions of the crankshaft and camshaft, a relative phase angle between the crankshaft and camshaft being calculated by an engine control unit ( 208 ) and that the slide ( 200 ) depending on one of the motor control signal supplied by an electromechanical actuation device ( 201 ) is adjustable, the slider ( 200 ) being biased so that the slider is pressed to the full position before the actuating device is switched off. 2. System according to claim 1, characterized in that the two cams ( 160 a, 160 b) each divide a chamber ( 132 a, 132 b) into a first and second part and both parts of each chamber are pressure-sealed. 3. System according to claim 1 or 2, characterized records that the control is reversible so that flow medium from the first and second sections in each chamber exit and in the other first and second Ab cut each of the two chambers can cross. 4. System according to one of claims 1 to 3, characterized in that the engine lubricating oil is used as a fluid, and a connecting line ( 230 a) to a pressure oil pump ( 230 ) of the control is provided. 5. System according to one of claims 1 to 4, characterized in that opposite sections of the first and second chamber ( 132 a, 132 b) via a line ( 160 c) and a line ( 182 a) are connected to the inlet line for pressure medium . 6. System according to claim 5, characterized in that the inlet line ( 182 ) is connected to a bypass line ( 220 a) in which a check valve ( 222 a) is seen before, which prevents the flow from the inlet line through the valve housing. 7. System according to any one of claims 1 to 6, characterized characterized in that the electromechanical actuation direction is a magnet with adjustable force. 8. System according to claim 7, characterized in that for the magnet, a winding ( 201 a), an armature ( 201 b) within the winding, an air gap ( 201 c) and a housing ( 201 d) is provided, one of Current signal in the winding of the armature is actuated to exert a force on the slide ( 200 ). 9. System according to claim 7 or 8, characterized records that between the actuator and the Valve a lifting reinforcement is provided with which the Valve stroke is extended. 10. System according to claim 9, characterized in that the lifting amplifier is a lever arrangement ( 201 e). 11. System according to one of claims 7 to 10, characterized in that the actuating device against the end face of the slide ( 200 ) is acted upon by a spring ( 202 ) and vented ( 198 d). 12. System according to one of claims 1 to 11, characterized in that the slide valve ( 200 ) in a Boh tion ( 182 ) of the seated on the camshaft housing ( 132 ) is installed. 13. Electromechanically actuated valve timing system for an internal combustion engine with a crankshaft ( 22 ), at least one camshaft ( 26 ), which experiences torque fluctuations during rotation, with a device fastened to the camshaft with counter-actuated hydraulic piston-cylinder arrangements for rotating the angular position between two sprockets ( 30 , 32 ) seated on the camshaft ( 26 ) and with a valve for controlling the piston-cylinder arrangements with pressure medium, characterized in that the valve is designed as a slide valve ( 200 ), the slide of which has two collars ( 200 a, 200 b) and is ventilated that the connec tion of return lines is controlled from one cylinder chamber depending on the slide position that an inlet line is connected via the valve to each cylinder chamber that check valves are provided in the inlet line with de den the flow from each cylinder space shut off in the direction of the valve that sensors are provided for detecting the positions of the crankshaft and camshaft, a relative phase angle between the crankshaft and camshaft being calculated by an engine control unit ( 208 ) and that the slide of the slide valve ( 200 ) depending on one of the Motor control signal supplied by an electromechanical actuator ( 201 ) is adjustable, the slider being biased so that the slider is pressed into the full advance position when the actuating device is switched off.