DE4227001A1 - Hydraulic drive for cam setting in IC engine - has hydraulic pump driven by reversible DC motor and separated from pump by non return valves cross linked to other feed lines. - Google Patents

Abstract

The relative setting of the cam and the camshaft for each cylinder, is controlled by a hydraulic servo cylinder (15) connected to both sides of a constant output hydraulic pump (10). The pump is driven by a reversible DC motor (11) and the servo is separated from the pump by non return valves (26, 28). The motor is a permanent magnet DC motor. The non return valves are cross linked to the other feed lines for pressure control and for return feed of fluid. A control valve (35) controls the return flow to the sump (38) as well as the pump take-up from the sump. ADVANTAGE - Power saving pump only operated when required. Variable cam setting control. Reduced power loss, so reduced exhaust emissions.

Description

The invention is based on a hydraulic drive which Adjustment of the relative rotational position between a camshaft an internal combustion engine and a drive wheel for the cams shaft is used and the one with two connections Constant pump and an actuating cylinder with two pressure chambers points that can be pressurized by the constant pump are.

Devices for adjusting the camshaft relative to one Drive wheels are therefore used in modern internal combustion engines seen to achieve high specific performance and preferential have a high torque in the lower speed range to be able to ask. By adjusting the camshaft the opening time of the valves controlled with this camshaft not changed in length, but after "EARLY" or "LATE" postponed. Especially with 4-valve engines with ge separated camshafts for the intake valves and exhaust valves tile you twist the former camshaft compared to the latter cam shaft depending on load and speed, so that the overlap valve opening times vary. Ultimately, through this Technology reduces fuel consumption and emissions be improved.

DE 39 29 624 A1 discloses a device with which the described adjustment of the relative rotational position between egg ner camshaft and its drive wheel can be performed. There is a head between the drive wheel and the camshaft pellied switched on the one hand via a spur gear with the camshaft and on the other hand via an inclined or Screw teeth with a hub part of the drive wheel in one handle stands. The coupling member is by means of a hydraulic to adjustable in the axial direction. With an adjustment  it is ge due to the helical teeth relative to the drive wheel rotates and takes the camshaft through the spur gear with, so that ultimately the relative rotational position between the Drive wheel and the camshaft changes.

A hydraulic drive according to the preamble of claim 1 is already from a brochure "ATE hydraulic applications: Va riable camshaft adjustment "from Alfred Teves GmbH be knows. In this known hydraulic drive a Kon Stant pump used, which is driven by the camshaft and connected to a connection with a pressure medium container is. A differential cylinder is used as the actuating cylinder, its piston rod-side pressure chamber constantly with the other Connection of the constant pump is connected. The other came mer, which is designed so that the pressure prevailing in it a larger area is applied to the piston than that in the first pressure prevailing in the pressure chamber is proportional valve can be shut off or with the second connection of the pump or connectable to the pressure medium container. The piston of the Differenti So alzylinders is always on the rod side with pumps pressure is applied and is relieved or acted upon the piston-side, larger pressure chamber with the help of the Propor tional valve controlled. This hydraulic drive is advantageous that in the event of a failure of the electrical part of the Proportional valve a stable and defined so-called "Fail-safe" position can be reached because the valve body is from a compression spring against whose force the electromagnet of the Pro portional valve must work, is brought into a position in which the piston-side pressure chamber with a pressure medium container ter connected, that is relieved. However, the well-known hydraulic drive at rest a large power loss, because the constant pump works constantly and the flow rate over promotes a pressure relief valve in a pressure medium container.

In order to reduce the power loss, it is registered earlier DE patent application P 41 36 286 already a hydraulic to has been proposed for camshaft adjustment, which in  Principle of two radial piston pumps, each with a suction valve and contains a pressure valve. The pressure valve of a radial piston Ben pump is between the displacement chamber (s) Pump and a pressure chamber of the actuating cylinder arranged and can be unlocked by the other radial piston pump. The Both suction valves are except for the respective radial piston pump controllable by an electromagnet. To adjust the The solenoid controls the piston of the actuating cylinder Suction valve so that only the other can work normally and only the one pump pressure medium into the one pressure chamber of the Actuating cylinder promotes during the or the displacer of the push the pump without pressure. In a quiet place if the camshaft should not be adjusted, controls the solenoid on both suction valves, so that the displacer Push both radial piston pumps without pressure, so that the loss performance is low. The disadvantage, however, is that at rest still the moving parts of the pumps though are moved without pressure and the electromagnet ver care must be taken to keep both suction valves open.

The invention has for its object a hydraulic Drive according to the preamble of claim 1 weiterzuent wind that the power loss can be further reduced.

This task is solved by a hydraulic drive that in addition to the characteristics from the generic term also the characteristics has the characterizing part of claim 1. After that a constant pump used by a reversal of direction The electric motor can be driven in opposite directions and their connections depending on the direction of rotation suction or pressure are over. The electric motor and thus the pump are only switched on when the camshaft can be adjusted. There with every power loss between two adjustment processes avoided. So that the camshaft maintains its position when the pump is not running, every pressure chamber of the actuating cylinder from a different connection of the constant pump from each an unlockable non-return valve that locks to the constant pump  valve can be pressurized. When the pump is stopped the check valves closed and the piston of the actuating cylinder ders is clamped between two pressure medium cushions. While one adjustment is the check valve in the return line tion unlocked, so that from a pressure chamber of the Stellzylin pressure fluid can drain off.

Advantageous embodiments of a hydraulic system according to the invention The drive can be found in the subclaims.

One between the one connection of the constant pump and the one Pressure chamber arranged check valve is according to claim 2 preferably hydraulically unlockable and for this purpose via a tax Line connected to the other connection of the constant pump. Around To be able to compensate for any leakage oil losses that may occur is in accordance with Claim 3 at least one connection of the constant pump via a Suction valve connected to a pressure medium container. With egg Nem synchronous cylinder as an actuating cylinder is for each type close the constant pump provide such a suction valve. With a differential cylinder as an actuating cylinder, one is sufficient umzugsaugventil, through which the constant pump pressure medium can suck up a container if it is in the larger of the promotes the pressure chambers of the differential cylinder. Besides, is with a differential cylinder, because of the possible small Construction is preferably used, a controllable Ableitven til provided over which when the piston is acted upon rod-side, ie the smaller pressure chamber from pressure medium derivable from the piston-side pressure chamber to the pressure medium container is.

The design effort to open the drain valve is particularly low if, according to claim 6, the valve body of the Suction valve and the valve body of the discharge valve mecha nisch are coupled together in such a way that the discharge valve is controllable from the suction valve. Because of the moment of inertia the unit consisting of electric motor and constant pump on Any inaccuracies that may occur at the end of an adjustment process  is met in a very simple and effective way net that the electric motor short-circuited when switched off and so that it is braked dynamically. Such a short circuit brake with a permanent magnet excited DC motor, as used in automobiles today for a variety of tasks will be realized very easily. Only the two connections of the electric motor connected together. According to Claim 9 is preferably an electrical reversing switch with only two switch positions used, no neutral middle position lung and is therefore particularly easy to control. For the short-circuit brake is an electrical short-circuit switch intended. The direction of rotation is now expedient of the electric motor by a corresponding switch position of the Polarity reversal switch can be specified and only then the short circuit by a Operation of the short-circuit switch can be canceled. This is ge ensures that the electric motor immediately turns into the desired rotation direction turns. The control of the electrical switch ge expediently with the help of motor electronics that is present anyway in modern internal combustion engines and for Control of the electric motor can be easily expanded.

Two embodiments of a hydraulic drive for the cam shaft adjustment are shown in the drawings. Based the figures of these drawings, the invention will now he closer purifies:

Show it

Fig. 1 shows the first embodiment with a hydraulically on expensive cash diverter valve,

Fig. 2 shows the second embodiment in which the valve body of an anti-cavitation valve and a diverter valve are mechanically coupled to each other,

Fig. 3 shows a schematic representation of the crankshaft and two camshafts of an internal combustion engine and

Fig. 4 shows a circuit for controlling the electric motor driving the constant pump.

To the two hydraulic drives according to FIGS. 1 and 2 includes a reversible constant pump 10 , which can be driven in two opposite directions of rotation by a direction-reversible permanent magnet excited DC electric motor 11 . The constant pump has two connections 12 and 13 , wherein in one direction of rotation the connection 12 of the pressure connection and the connection 13 of the suction connection and in the other direction of rotation the connection 12 of the suction connection and the connection 13 is the pressure connection.

To the hydraulic drive also includes a Differentialzy cylinder 15 with a housing 16 , the interior of which is divided by a piston ben 17 into two pressure chambers 18 and 19 . On one side protrudes from the piston 17 a piston rod 20 , which leaves the housing 16 on one end face. The cross section of the piston rod-side, because of the piston rod annular pressure chamber 18 is smaller than the cross section of the pressure chamber 19 kolbenseiti conditions, so that the amount of pressure medium flowing into the pressure chamber during a certain path of the piston 17 differs from the amount flowing from the other pressure chamber is.

The pressure chamber 19 of the differential cylinder 15 is via a line 25 , in which there is an unlockable check valve 26 opening towards the pressure chamber 19 , with the connection 12 and the pressure chamber 18 via a line 27 , in which there is an unlockable check valve opening towards the pressure chamber 18 28 is connected to the connection 13 of the constant pump 10 . To unlock a control line 29 leads from the line 27 to the check valve 26 and a control line 30 from the Lei device 25 to the check valve 28th Pressure relief valves between the two lines 25 and 27 are not absolutely necessary, because the drive z. B. can be protected from overload by a thermal switch in the electric motor 11 .

In the embodiment of Fig. 1 a 2/2-way valve is provided with a spool 36 provided 35, which is loaded by a compression spring 37 towards a rest position to, in which the directional valve is locked and hydraulically in a switching position ge introduced in which the directional control valve is open. The input of the directional valve is connected between the connection 12 and the check valve 26 with the line 25 and the output with a Druckmit telkammer 38 .

At the connection 13 , the constant pump 10 can also suck in pressure medium from the container 38 via a suction valve 39 designed as a check valve opening towards it. This suction valve can be attached directly to the pump or integrated into it, but can also be connected to the line 27 outside the pump. A second suction valve is indicated by dashed lines, which may be present if a constant pump is used, which is equipped with two suction valves as standard. However, this replenishment valve has no function in the hydraulic drive shown.

The constant pump 10 will now be driven by the electric motor 11 so that the connection 12 is the pressure connection and the connection 13 is the suction connection. As a result, a pressure is built up in line 25 , which opens the check valve 26 and, via the control line 30, also the check valve 28 . Pressure medium is conveyed into the pressure chamber 19 , while pressure medium flows out of the pressure chamber 18 . The amount of pressure medium flowing out is less than the amount of pressure medium flowing into the pressure chamber 19 . The difference is sucked out of the container 38 via the suction valve 39 . When the electric motor 11 is switched off, the two check valves 26 and 28 close and the piston 17 is clamped between the two pressure medium cushions in the chambers 19 and 18 . He stays calm. If it is to be moved again in the other direction, the pump 10 is driven in the opposite direction, the connection 13 being the pressure connection and the connection 12 being the suction connection. In line 27 , a pressure builds up, which opens the check valves 26 and 28 . In the pressure chamber 18 , a certain amount of pressure medium is conveyed, while a larger amount flows out of the pressure chamber 19 . The difference flows through the directional control valve 35 , which is open via the control line 34 , which leads from the line 27 , to the container 38 .

In the embodiment according to FIG. 2, a suction valve 39 , which, like the embodiment according to FIG. 1, is designed as a check valve with a ball 40 as a valve body, is connected directly to line 27 , towards which it opens. A discharge valve 41 , which has the same function as the directional control valve 35 according to FIG. 1, is also a check valve with a ball 42 as the valve body and opens to the section of the line 25 located between the connection 12 of the pump and the check valve 26 . Both valves 39 and 41 block towards container 38 . Between their two valve bodies 40 and 42 extends a pin 43 , the length of which is greater than the distance between the two circular lines on which the balls 40 and 42 can rest against their valve seats. Accordingly, at least one of the two valves 39 and 41 is open.

If the pump 10 is now driven so that the connection 13 is the pressure connection, the ball 40 of the suction valve 39 is held on its valve seat by the pressure in the line 27. The valve 41 is therefore open, so that from the Pressure chamber 19 flowing excess amount of pressure medium can flow through the valve 41 in the container 38 . In the reverse direction of rotation of the pump 10 , a pressure builds up in the line 25 , by which the drain valve 41 is closed. The valve body 40 of the suction valve 39 is lifted mechanically from its valve seat by the valve body 42 and the pin 43 and possibly hydraulically by a small negative pressure in the line 27 . The amount of pressure medium that is additionally required for filling the pressure chamber 19 is sucked in from the pressure medium container 38 via the valve 39 .

To control the electric motor 11 , the position of the crankshaft 50 , which determines the position of a drive wheel driving the intake camshaft 51 , and the position of the intake camshaft are scanned via displacement sensors 52 and 53 and compared with one another in engine electronics 54 . In addition to the signals A and B from the two displacement sensors 52 and 53 , the motor electronics 54 are provided with further motor data C, D. . . . fed and calculates an optimal relative rotational position between the camshaft 51 and the drive wheel. If the instantaneous position of the camshaft coincides with the optimal position, then a signal appears at output x and at output y of the engine electronics.

The output x of the motor electronics 54 is connected to a relay 55 which controls two contact bridges 57 and 58 of a Umpolschal age 59 . The contact bridges 57 and 58 are so-called change-over contacts with two switch positions, each contact bridge being permanently connected to one of two outputs 60 and 61 of the pole-reversal switch 59 . In one switch position, which the contact bridges assume when the relay 55 is not energized, the contact bridge 57 is also connected to a positive potential-carrying fixed contact and the contact bridge 58 is connected to a negative potential-carrying contact of the pole-reversal switch 59 . In the other switching position with the relay 55 energized, the reverse is the case.

One terminal 65 of the electric motor 11 is permanently connected to the output 61 of the pole-reversal switch 59 , while at the other terminal 66 via a short-circuit switch 67 designed as a changeover contact, the contact bridge of which can be activated by a relay 68 , either with the terminal 65 of the motor or can be connected to the output 60 of the pole-reversal switch 59 . The relay 68 can be controlled via the output y of the motor electronics 54 . In the rest position when the relay is not energized, the two connections 65 and 66 of the motor 11 are short-circuited via the switch 67 .

If the motor electronics 54 based on the further motor data C, D.. . determines that the camshaft 51 is to be set in a direction that speaks the rest position of the pole-reversal switch 59 , so it gives a signal to the output y, due to which the relay 68 switches the switch 67 so that the electric motor 11 rotates in one direction and drives the pump 10 in one direction. If the engine electronics determines that an adjustment of the camshaft in the other direction is necessary, it first gives a signal to the output x, which pulls the relay 55 and brings the contact bridges 57 and 58 into the other switching position, not shown. After a short delay, a signal appears on the output x, which in turn switches 67 so that the electric motor 11 runs in the other direction. As soon as there is no signal at output y, relay 68 drops out and motor 11 is short-circuited.

Claims (9)

1. Hydraulic drive for adjusting the relative rotational position between a camshaft ( 51 ) of an internal combustion engine and a drive wheel for the camshaft ( 51 ) with a constant pump ( 10 ) provided with two connections ( 12 , 13 ) and with an actuating cylinder ( 15 ) two pressure chambers ( 18 , 19 ) which can be pressurized by the constant pump ( 10 ), characterized in that the constant pump ( 10 ) can be driven in opposite directions by a reversible electric motor ( 11 ) and that each pressure chamber ( 18th , 19 ) from another port ( 13 , 12 ) of the constant pump ( 10 ) can be pressurized via a respective check valve ( 28 , 26 ) which locks to the constant pump ( 10 ). 2. Hydraulic drive according to claim 1, characterized in that between a connection ( 12 , 13 ) of the constant pump ( 10 ) and a pressure chamber ( 19 , 18 ) arranged check valve ( 26 , 28 ) via a control line ( 29 , 30 ) with the other connection ( 13 , 12 ) of the constant pump ( 10 ) and can be hydraulically unlocked. 3. Hydraulic drive according to claim 1 or 2, characterized in that at least one connection ( 13 ) of the constant pump ( 10 ) via a suction valve ( 39 ) with a pressure medium container ( 38 ) is connected. 4. Hydraulic drive according to claim 3, characterized in that the actuating cylinder is a differential cylinder ( 15 ) that, when the piston rod-side pressure chamber ( 18 ) is acted upon, pressure medium from the piston-side pressure chamber ( 19 ) via a controllable diverter valve ( 35 , 41 ) to the Druckmit tel container ( 38 ) can be derived and that when the piston-side pressure chamber ( 19 ) is pressurized via a suction valve ( 39 ) pressure medium from the pressure medium container ( 38 ). 5. Hydraulic drive according to claim 4, characterized in that the discharge valve is a to the pressure medium container ( 38 ) blocking releasable check valve ( 41 ). 6. Hydraulic drive according to claim 4 or 5, characterized in that the valve body ( 40 ) of the suction valve ( 39 ) and the valve body ( 42 ) of the discharge valve ( 41 ) are mechanically coupled to one another such that the discharge valve ( 41 ) from the suction valve ( 39 ) is taxable. 7. Hydraulic drive according to a preceding claim, characterized in that the electric motor ( 11 ) is short-circuited when switching off. 8. Hydraulic drive according to claim 7, characterized in that the electric motor is a permanent magnet DC motor ( 11 ). 9. Hydraulic drive according to claim 7 or 8, characterized in that an electrical reversing switch ( 59 ) with two switching positions and an electrical short-circuit switch ( 67 ) are present and that first the direction of rotation of the electromotive gate ( 11 ) can be predetermined and then the short circuit by a Actuation of the short-circuit switch ( 67 ) can be canceled.