Patent Application
20100326383
The invention relates to a device for variably adjusting the control times of gas exchange valves of an internal combustion engine, having a drive input element, a drive output element, at least one pressure chamber, a pressure medium supply device and at least one pressure accumulator, with it being possible for pressure medium to be supplied to or discharged from the at least one pressure chamber by means of the pressure medium supply device, with it being possible for a phase position of the drive output element relative to the drive input element to be varied by means of the supply of pressure medium to or discharge of pressure medium out of the pressure chamber, with the pressure accumulator having a movable element which is provided with a first pressure surface which partially delimits a store chamber, with the store chamber being connected or being connectable to the pressure medium supply device, with a force store loading the movable element with a force in the direction of an initial position, and with it being possible by means of the pressurization of a the store chamber for the movable element to be moved counter to the force of the force store.
In modern internal combustion engines, use is made of devices for variably adjusting the control times of gas exchange valves in order to be able to make the phase relationship between the crankshaft and camshaft variable in a defined angle range between a maximum early position and a maximum late position. The device conventionally comprises an actuating device which is driven by a crankshaft and which transmits the torque of said crankshaft to the camshaft. Here, the actuating device has formed within it a hydraulic actuating drive which makes it possible to targetedly influence the phase position between the crankshaft and camshaft. A pressure medium supply device is provided for supplying pressure medium to the actuating device.
A device of said type is known for example from EP 1 025 343 B1. The device comprises two rotors which are rotatable relative to one another, with an outer rotor being drive-connected to the crankshaft and with the inner rotor being rotationally fixedly connected to the camshaft. The device comprises a plurality of cavities, with each of the cavities being divided by means of a vane into two oppositely-acting pressure chambers. By supplying pressure medium to and discharging pressure medium from the pressure chambers, the vanes are moved within the pressure chambers, thereby effecting a targeted rotation of the rotors relative to one another, and therefore of the camshaft relative to the crankshaft.
The pressure medium supply to the pressure chambers and the pressure medium discharge from the pressure chambers is controlled by means of a pressure medium supply device which comprises a pressure medium pump, a tank, a control valve and a plurality of pressure medium lines. Here, a pressure medium line connects the pressure medium pump to the control valve. In each case one further pressure medium line connects one of the working ports of the control valve to the pressure chambers. The pressure medium is conventionally extracted from the lubricant circuit of the internal combustion engine.
To ensure the function of the device, the pressure in the pressure medium system must exceed a certain value in all operating phases of the internal combustion engine. This is particularly critical in the idle running phases of the internal combustion engine, since the pressure medium pump is driven by the crankshaft and therefore the system pressure rises with the rotational speed of the internal combustion engine. The system pressure provided by the pressure medium pump is also dependent on the pressure medium temperature, with the system pressure falling with rising temperature. The pressure medium pump must therefore be designed so as to provide sufficient system pressure under the most unfavorable conditions, in order to ensure a sufficiently fast adjustment of the phase position of the inner rotor relative to the outer rotor. To ensure the required adjusting speed even under the most unfavorable pressure conditions, such as for example high pressure medium temperatures and/or low rotational speeds, the pressure medium pump must be designed accordingly. As a result, use is made of pressure medium pumps which are designed for the peak demands of the actuating device, and which are therefore of excessively large dimensions during most operating phases of the internal combustion engine. It is alternatively possible to use controllable pressure medium pumps which provide pressure medium according to demand. In both cases, the increased expenditure has an adverse effect on the costs, the installation space requirement and the fuel consumption of the internal combustion engine.
U.S. Pat. No. 5,775,279 A discloses a further device of said type. In said embodiment, a pressure accumulator is arranged between the pressure medium pump and the control valve, which pressure accumulator communicates with the pressure medium supply device. Said pressure accumulator is filled with pressure medium in phases of high system pressure. When the system pressure falls, then the pressure accumulator is emptied automatically, as a result of which additional pressure medium is supplied to the pressure medium supply device. The phase adjustment of the device is assisted in this way.
A disadvantage of said embodiment is the fact that the pressure accumulator is emptied even if the system pressure falls not on account of an adjustment process but rather on account of other external circumstances, for example as a result of a drop in the rotational speed. Therefore, reduced pressure assistance and a smaller pressure medium volume from the pressure accumulator are available for a subsequent phase adjustment process.
A further disadvantage is that the maximum pressure with which the pressure accumulator can assist the pressure medium supply device corresponds to the pressure which prevailed in the pressure medium supply device directly before the phase adjustment process. When the engine controller transmits an adjustment demand to the device at high temperatures and low rotational speeds, then the pressure assistance from the pressure accumulator is less pronounced, because the system pressure with which the pressure accumulator was filled was low. This may have the result that the adjustment process cannot be carried out, or that the adjustment speed is considerably reduced. It is therefore necessary in this case, too, for the pressure medium pump to be designed for the peak load, with the resulting disadvantages.
The invention is based on the object of providing a device for variably adjusting the control times of gas exchange valves of an internal combustion engine, with it being sought to ensure a functionally reliable adjustment of control times at high adjustment speeds in all operating phases of the internal combustion engine. Here, it should likewise be possible to dispense with an overdimensioning of the pressure medium pump (design for the expected peak loads), and with the use of variable pressure medium pumps.
The object is achieved according to the invention in that the movable element has a counterpressure surface which at least partially delimits a counterpressure chamber, with it being possible by means of the application of pressure medium to the counterpressure chamber for the movable element to be moved in the direction of the initial position.
The movable element may for example be designed as a pressure piston which can be moved within a pressure reservoir counter to the force of a force store which is designed for example as a spring element. In the event of a supply of pressure medium to the store chamber, the volume of the latter increases at the expense of the counterpressure chamber. When the system pressure in the pressure medium supply device falls, then the force of the force store exceeds the force on the first pressure surface caused by the system pressure. The pressure piston is thus pushed by the force store into an initial position in which the volume of the store chamber is at a minimum.
As an alternative to the spring element, use may also be made of other types of force stores, for example reversibly deformable bodies, for example composed of elastomers, or gas-filled balloons.
When the counterpressure chamber is acted on with pressure medium in those operating phases of the internal combustion engine in which the pressure accumulator is to dispense pressure medium to the pressure medium supply device, then the movable element is acted on not only by the force of the force store but also by a further force which pushes said movable element in the direction of the initial position. Said additional force results from the pressure in the counterpressure chamber, which acts on the counterpressure surface. The magnitude F of said additional force can be defined as: F=pAG, where p is the pressure acting on the counterpressure surface and AG is the surface area of the counterpressure surface.
As a result of the increase of the pressure provided by the pressure accumulator, the pressure accumulator can accommodate peak consumptions, such that the pressure medium pump can be designed for the normal operation of the internal combustion engine. No overdimensioned or controlled pressure medium pumps are required in order to ensure a functionally reliable and fast adjustment of the phase position. The adjustment speed of the actuating device is additionally increased. Alternatively, for the same adjustment speed, the actuating device may be dimensioned to be smaller. The mass, mass moment of inertia and costs can be reduced in this way.
In one refinement of the invention, it may be provided that the movable element have at least one second pressure surface which partially delimits a control chamber, with it being possible by means of the pressurization of the control chamber for the movable element to be moved counter to the force of the force store, and with a pressure medium flow within the pressure accumulator from the store chamber into the control chamber being prevented. Furthermore, it may be provided that the store chamber and the control chamber do not communicate with one another within the pressure accumulator. An application of pressure medium to the store chamber advantageously moves the movable element in the same direction as an application of pressure medium to the control chamber, advantageously away from the initial position of the movable element.
By forming the pressure accumulator with a movable element, which partially delimits pressure chambers, which are isolated from one another within the pressure accumulator, said two pressure chambers can be activated, that is to say filled and/or emptied, separately from one another. Aside from leakage, there is no connection between the pressure chambers. It is thus possible, for example, to use different pressure sources for filling the store chamber and the control chamber.
It is alternatively also possible for a pressure medium connection to be provided within the pressure accumulator between the store chamber and the control chamber. Pressure medium which is supplied to the control chamber can pass via said pressure medium connection into the store chamber. Here, however, it should be ensured that a reversed pressure medium flow, from the store chamber into the control chamber, is prevented. This may be realized for example by means of a pressure medium duct in the pressure piston or in the pressure reservoir of the pressure accumulator, in which pressure medium duct a check valve is arranged. In said case, the filling of the store chamber and of the control chamber may take place solely by means of the filling of the control chamber. When the pressure accumulator is to be emptied, then the control chamber is connected to the tank. The store chamber empties into the pressure medium supply device, and the control chamber empties, unpressurized, into the tank. A passage of pressure medium from the store chamber into the control chamber is prevented by the check valve.
If it is provided that an application of pressure medium to the store chamber moves the movable element in the same direction as an application of pressure medium to the control chamber, then the control chamber can assist the filling of the store chamber. For this purpose, the control chamber is likewise filled with pressure medium during the filling process of the store chamber. In this way, a force is exerted on both pressure surfaces of the pressure piston, as a result of which a higher force is stored in the force store (the spring element is compressed to a greater extent). When the filled pressure accumulator receives the command from the engine controller to assist the phase adjustment process, then the control chamber can be emptied independently of the store chamber. That is to say, while the store chamber is emptied into the pressure medium supply device and thereby assists the phase adjustment process, the control chamber can be ventilated to atmospheric pressure into a tank. With suitable design, the ventilation of the control chamber can take place more quickly than the emptying of the store chamber into the pressure medium supply device. The entire force which has been stored in the force store therefore acts on the store chamber via the first pressure surface. As a result, the pressure at the start of the assistance process can increase by a factor of:
as a function of the load acting on the force store at said time. Here, A1 corresponds to the surface area of the first pressure surface and A2 corresponds to the surface area of the second pressure surface. If use is made, for example, of a spring element as a force store, then the pressure at the start of the assistance process is increased by the full factor
for as long as the spring has not yet reached its maximally compressed state.
In one refinement of the invention, the counter-pressure chamber may be selectively connected to a pressure source or to a tank.
Control means may be provided, with it being possible for the counterpressure chamber to be selectively connected to a tank or to a pressure source by the control means.
Here, the counterpressure chamber may be connected to the pressure medium pump of the internal combustion engine. The counterpressure chamber may be connected to the tank of the internal combustion engine.
The pressure source may for example be the pressure medium supply device or the pressure medium pump thereof, or a source separate from these, for example the pressure source of a servo consumer (for example the servo steering system). In the second case, it is possible for the pressure accumulator to be completely filled even in operating phases with low system pressure. The selective connection to a pressure source or to the tank is produced via control means, for example a 3/2 directional valve in the form of a switching valve (for example seat valve) or a proportional valve (for example slide valve). Consideration may alternatively be given to two control means, with one of the control means blocking or opening up the connection from the pressure source to the counterpressure chamber and with the other control means blocking or opening up the connection from the counterpressure chamber to the tank. The control means may for example be electromagnetically actuated hydraulic valves such as directional valves (for example switching or proportional valves), double check valves or the like. Said control means receive control signals from an engine control unit of the internal combustion engine, according to which control signals the counterpressure chamber is filled or emptied, that is to say whether the pressure accumulator should be filled or the emptying process should be assisted.
It is likewise conceivable to use hydraulically actuated control means. Here, it may be provided that the hydraulic actuating device of the control means communicates with the pressure medium supply device. The control means are thus automatically switched when the pressure in the pressure medium supply device falls below a defined value. This considerably reduces the regulating expenditure.
If the tank and/or the pressure medium pump of the internal combustion engine are/is used for filling and ventilating the counterpressure chamber, then no further components beyond those already present in the internal combustion engine in any case are required. Furthermore, the demands on the seal between the pressue medium reservoir and pressure piston are lower, since a mixing of the pressure medium in the store chamber and in the counterpressure chamber is admissible. It is therefore possible to dispense with a sealing element which acts between the pressure piston and the pressure reservoir.
Furthermore, it may be provided that a directional valve is provided as a control means, which directional valve has one port each connected to the pressure source, the tank, and the counterpressure chamber. In a development of the invention, a further port may be provided, which port is connected to the store chamber or the control chamber.
The pressure assistance of the pressure accumulator can thus be activated by simply switching one or more control means. Here, the pressure medium volume is provided which is collected in the store chamber in those operating phases of the internal combustion engine in which the phase position is held constant.
The pressure assistance of the pressure accumulator can be utilized during every phase adjustment process. For this purpose, the control means (directional valves and/or double check valves) are placed into the position in which the store chamber is emptied whenever a phase adjustment is demanded. In the operating phases between the phase adjustment demands, the pressure accumulator can be filled.
A further possibility is for the pressure assistance of the pressure accumulator to be activated according to demand. When the engine controller detects that the pressure or volume flow provided by the pressure medium pump is not sufficient for the phase adjustment, then said engine controller enables the pressure assistance by the pressure accumulator. This approach lengthens the times in which the pressure accumulator can be filled, and therefore the performance of the pressure accumulator during the pressure assistance.
It may alternatively be provided that the pressure assistance of the pressure accumulator be utilized merely as a “boost” function for critical adjustment processes which require for example a high volume flow or a high adjustment speed. When the engine controller detects that a critical adjustment process of said type should be initiated, then said engine controller enables the pressure assistance by means of suitable setting of the control means.
It is likewise conceivable for the control means to be formed in one piece with the control valve which controls the pressure medium flow to and from the pressure chambers of the actuating device.
The maximum volume of the store chamber advantageously corresponds to at least two times the volume required for a phase adjustment from a maximum late position to a maximum early position.
The pressure accumulator may for example open out into the pressure medium line between the pressure medium pump and the control valve.
It may alternatively be provided that the pressure accumulator open out into one of the pressure medium lines which connects one of the working ports of the control valve to one group of pressure chambers. It is additionally possible in said embodiment for a second pressure accumulator to be provided which opens out into the pressure medium line which connects the other working port of the control valve to the other group of pressure chambers.
Further features of the invention emerge from the following description and from the drawings, which illustrate exemplary embodiments of the invention in simplified form. In the drawings:
a shows a longitudinal section through the actuating device;
b shows a cross section through an actuating device;
The actuating device 10a,b has a drive input element designed as an outer rotor 22 and a drive output element designed as an inner rotor 23. The outer rotor 22 has a housing 22a and two side covers 24, 25 which are arranged on the axial side surfaces of the housing 22a. The inner rotor 23 is formed in the manner of an impeller and has a substantially cylindrical hub element 26, from the outer cylindrical lateral surface of which five vanes 27 extend in the radially outward direction in the illustrated embodiment. The vanes 27 are formed separately from the inner rotor 23 and are arranged in vane grooves 28 which are formed on the hub element 26. The vanes 27 are loaded in the radially outward direction with a force by means of vane springs 27a which are arranged between the groove bases of the vane grooves 28 and the vanes 27.
Proceeding from an outer circumferential wall 29 of the housing 22a, a plurality of projections 30 extend in the radially inward direction. In the illustrated embodiment, the projections 30 are formed in one piece with the circumferential wall 29. The outer rotor 22 is mounted on the inner rotor 23, so as to be rotatable relative thereto, by means of radially inner circumferential walls of the projections 30.
A sprocket 21 is arranged on an outer lateral surface of the circumferential wall 29, by means of which sprocket 21 torque is transmittable from the crankshaft 2 to the outer rotor 22 via a chain drive (not illustrated).
In each case one of the side covers 24, 25 is arranged on one of the axial side surfaces of the housing 22a and rotationally fixedly connected to the latter. For this purpose, an axial opening is provided in each projection 30, through which axial opening extends a fastening element 32, for example a screw, which serves for rotationally fixedly fastening the side cover 24, 25 to the housing 22a.
Within the actuating device 10a,b, a cavity 33 is formed between in each case two projections 30 which are adjacent in the circumferential direction. Each of the cavities 33 is delimited in the circumferential direction by opposite, substantially radially extending delimiting walls 34 of adjacent projections 30, in the axial direction by the side covers 24, 25, in the radially inward direction by the hub element 26, and in the radially outward direction by the circumferential wall 29. A vane 27 projects into each of the cavities 33, with the vanes 27 being designed so as to bear both against the side covers 24, 25 and also against the circumferential wall 29. Each vane 27 thereby divides the respective cavity 33 into two oppositely acting pressure chambers 35, 36.
The inner rotor 23 is rotatable relative to the outer rotor 22 in a defined angle range. The angle range is limited in one rotational direction of the inner rotor 23 in that the vanes 27 come to bear against in each case one corresponding delimiting wall 34 (early stop 34a) of the cavities 33. Similarly, the angle range is delimited in the other rotational direction in that the vanes 27 come to bear against the other delimiting walls 34, which serve as a late stop 34b, of the cavities 33.
The phase position of the outer rotor 22 relative to the inner rotor 23 can be varied by pressurizing one group of pressure chambers 35, 36 and relieving the other group of pressure. The phase position of the two rotors 22, 23 relative to one another can be held constant by pressurizing both groups of pressure chambers 35, 36. Alternatively, it may be provided that none of the pressure chambers 35, 36 are acted on with pressure medium during phases of constant phase position. As hydraulic pressure medium, use is conventionally made of the lubricating oil of the internal combustion engine 1.
To supply pressure medium to and discharge pressure medium from the pressure chambers 35, 36, a pressure medium supply device 37 is provided which is illustrated in
In a first position of the control valve 40, the inlet port P is connected to the first pressure chambers 35, while the second pressure chambers 36 are connected to the tank 39.
In a second position of the control valve 40, it is provided that none of the pressure chambers 35, 36 communicate with the tank 39 and the inlet port P.
In a third position of the control valve 40, the inlet port P is connected to the second pressure chambers 36, while the first pressure chambers 35 are connected to the tank 39.
During the operation of the internal combustion engine 1, an alternating torque acts on the camshaft 6, 7, which alternating torque is caused by the rolling of the cams 8 on cam followers. Here, the force of valve springs acts on the camshaft 6, 7 with a braking action until the gas exchange valve is fully open. The camshaft 6, 7 is subsequently accelerated by the force of the valve springs. Consequently, pressure peaks are generated within the actuating device 10a,b, which pressure peaks cause the pressure chambers 35, 36 which are connected to the inlet port P to be emptied counter to the pressure medium pump 38, which leads to a considerable reduction in the adjustment speed. To prevent this, a check valve 42a is provided in the pressure medium line 41 which connects the pressure medium pump 38 to the control valve 40. The check valve 42a prevents the pressure medium from flowing back from the pressure chambers 35, 36 to the pressure medium pump 38 via the control valve 40. The pressure peaks are supported on the check valve 42a, as a result of which an inadvertent emptying of the pressure chambers 35, 36 is effectively prevented and the rigidity of the torque transmission and the adjustment speed are increased.
The adjustment speed of the actuating devices 10a,b is dependent on the provided pressure or the provided pressure medium volume flow of the pressure medium pump 38. The provided pressure, or the provided pressure medium volume flow, are in turn dependent on numerous factors, for example the rotational speed of the internal combustion engine 1 and the pressure medium temperature. To ensure the demanded adjustment speed even under the most unfavorable conditions, such as for example high pressure medium temperatures and/or low rotational speeds, the pressure medium pump 38 must be designed accordingly. As a result, use is made of pressure medium pumps 38 which are designed for the peak demands of the actuating device 10a,b, and which are therefore of excessively large dimensions during most operating phases of the internal combustion engine 1. It is alternatively possible to use controllable pressure medium pumps 38 which provide pressure medium according to demand. In both cases, the increased expenditure has an adverse effect on the costs and the fuel consumption of the internal combustion engine 1.
To avoid said disadvantages, a pressure accumulator 43 is provided in the device 10 according to the invention. The pressure accumulator 43 comprises a movable element which is designed as a pressure piston 45 and which can be moved within a pressure reservoir 44 counter to the force of a force store. In the illustrated embodiment, the force store is designed as a spring element 46. However, other types of force store, such as, for example suitably shaped elastomer bodies or gas-filled balloons, are also conceivable.
The pressure piston 45 has two pressure surfaces 47, 48. Together with the pressure reservoir 44, the first pressure surface 47 delimits a store chamber 49, with the first pressure surface 47 delimiting the store chamber 49 in the movement direction of the pressure piston 45. The pressure reservoir 44 and the pressure piston 45 delimit a control chamber 50, with the second pressure surface 48 delimiting the control chamber 50 likewise in the movement direction of the pressure piston 45. Here, the pressure piston 45 and the pressure reservoir 44 are designed such that there is no connection between the two pressure chambers 49 and 50 within the pressure accumulator 43. Aside from leakage, no exchange of pressure medium takes place between said pressure chambers 49, 50 in this embodiment. In the illustrated embodiment, the pressure surfaces 47, 48 are arranged offset relative to one another in the movement direction of the pressure piston 45, with the first pressure surface 47 being surrounded by the second pressure surface 48 in the plane intersected perpendicularly by the movement direction of the pressure piston 45. The first pressure surface 47 is of circular design and the second pressure surface 48 is of annular design. By means of an application of pressure medium to the pressure chambers 49, 50, the pressure piston 45 is moved counter to the force of the spring element 46, as a result of which the volume of the pressure chambers 49, 50 increases. The distance by which the pressure piston 45 can be moved counter to the spring element 46 is delimited by stops 54 formed within the pressure reservoir 44. The stops 54 are arranged such that a connection of the store chamber 49 to the control chamber 50 is prevented.
The spring element 46 is supported at one side on that side of the pressure piston 45 which faces away from the pressure chambers 49, 50, and at the other side on that side of the pressure reservoir 44 which faces away from the pressure chambers 49, 50. Here, the spring element 46 is mounted in the pressure accumulator 43 with preload, such that the volume of the pressure chambers 49, 50 at low system pressure is minimal. In this initial position, the pressure piston 45 bears, at its side facing away from the spring element 46, against the pressure reservoir 44.
That region of the pressure reservoir 44 which faces away from the pressure surfaces 47, 48 is designed as a pressure chamber (counterpressure chamber 58). Here, that surface of the pressure piston 45 which faces toward the counterpressure chamber 58 acts as a counterpressure surface 59. By means of an application of pressure medium to the counterpressure chamber 58, a force acts on the pressure piston 45 via the counterpressure surface 59, which force is aligned parallel to the force of the spring element 46. In the illustrated embodiment, the counterpressure surface 59 is of planar design and is aligned perpendicular to the movement direction of the pressure piston 45. It is likewise conceivable for inclined surfaces to be provided, or for the counterpressure surface 59 to have further functional elements such that it differs from the planar form. For example, retainers for the spring element 46 could be formed on the counterpressure surface 59.
The store chamber 49 is connected by means of a store line 51 to the pressure medium supply device 37. The store line 51 opens out on the one hand into the pressure medium supply device 37 downstream of the check valve 42a and on the other hand via a port 56 into the store chamber 49. A check valve 42c is arranged in the store line, which check valve 42c permits a pressure medium flow from the store chamber 49 to the pressure medium supply device 37 and prevents a pressure medium flow in the opposite direction. In this way, it is achieved that pressure peaks which are generated in the actuating devices 10a,b cannot penetrate to the store chamber 49 of the pressure accumulator 43, but rather are supported on the check valve 42c. The hydraulic rigidity of the device 10 is therefore increased.
The control chamber 50 may be selectively connected to a tank 39 or via a control line 52 to a pressure source. In the illustrated embodiment, the pressure medium pump 38 of the pressure medium supply device 37 serves as a pressure source. It is however likewise conceivable to use some other pressure source, for example the pressure medium pump 38 of a servo consumer, for example the servo steering system. In said case, the pressure medium flowing out of the control chamber 50 is conducted not into the tank 39 of the lubricating oil circuit of the internal combustion engine 1 but rather to the corresponding tank 39 of the servo consumer.
A further check valve 42b is provided in the control line 52 and prevents a return flow of pressure medium from the control chamber 50 to the pressure medium supply device 37.
To control the pressure medium flow to and from the control chamber 50 and the counterpressure chamber 58, a control means 60 in the form of a directional valve 53 is provided. The directional valve 53 is designed as a 4/2 directional valve and has a pressure port P1, two working ports A1, B1 and a tank port T1. The pressure port P1 is connected to the pressure source, in the illustrated embodiment via the control line 52 to the pressure medium supply device 37. The third working port A1 is connected to the control chamber 50, the fourth working port B1 is connected to the counterpressure chamber 58 and the tank port T1 is connected to the tank 39. In a first control position of the directional valve 53, the third working port A1 is connected to the pressure port P1, while the fourth working port B1 communicates with the tank ports T1.
In a second control position of the directional valve 53, the third working port A1 is connected to the tank port T1, while the pressure port P1 communicates with the fourth port B1.
The control line opens out into the control chamber 50 via a second port 56 downstream of the directional valve 53. Furthermore, a connecting line 55 is provided which connects the control line 52 to the store line 51. The connecting line 55 opens out firstly into the store line 51 between the check valve 42c and the first port 56 of the store chamber 49, and secondly into the control line 52 between the directional valve 53 and the second port 56 of the control chamber 50. A further check valve 42d is arranged in the connecting line 55, which further check valve 42d permits a pressure medium flow from the control line 52 to the store line 51 and prevents a pressure medium flow in the opposite direction.
When no adjustment demand is transmitted from the engine controller to the device 10 during the operation of the internal combustion engine 1, then the control valve 40 is situated in the second (central) position and the first directional valve 53 is situated in the first position. Consequently, no pressure medium flows to or from the actuating device 10a. A pressure medium flow from the pressure medium supply device 37 via the store line 51 to the store chamber 49 is prevented by the check valve 42d. The control chamber 50 is acted on with pressure medium via the control line 52 and the directional valve 53. At the same time, pressure medium passes via the control line 52, the connecting line 55 and the store line 51 into the store chamber 49. At the same time, the counterpressure chamber 58 is connected to the tank 39 via the directional valve 53. The pressure medium introduced into the store chamber 49 or the control chamber 50, respectively, acts on the first or second pressure surface 47, 48 respectively, as a result of which the pressure piston 45 is moved in the direction of the stops 54 counter to the force of the spring element 46, such that the volume both of the control chamber 50 and also of the store chamber 49 increases. At the same time, the counterpressure chamber 58 is vented into the tank 39.
When a phase angle adjustment is demanded by the engine control unit, the control valve 40 is moved into its first or third position. Pressure medium therefore passes from the pressure medium pump 38 to the first or second pressure chambers 35, 36 respectively, as a result of which a phase adjustment is effected by the actuating device 10a,b. When the volume flow fed by the pressure medium pump 38 is too low to ensure the adjustment, or when a higher adjustment speed is to be obtained, then the first directional valve 53 is moved into its second control position. In said control position, the control chamber 50 is connected to a tank 39. The pressure medium which is under pressure in the control chamber 50 is thereby connected to atmospheric pressure, as a result of which a rapid emptying of the control chamber 50 takes place. At the same time, the store chamber 49 is emptied into the pressure medium supply device 37. When the emptying of pressure medium out of the control chamber 50 takes place so quickly that the pressure piston 45 is supported solely by means of the first pressure surface 47 with respect to the store chamber 49, then the entire force of the spring element 46 acts only on the store chamber 49. The pressure p in the store chamber 49 at the start of the emptying process can therefore be defined as follows:
plus the pressure which is generated by the filling of the counterpressure chamber 58. This applies when the pressure piston 45 has not yet been fully deflected, that is to say is not bearing against the stops 54. Here, psys corresponds to the system pressure of the pressure medium supply device 37 which prevailed at the start of the emptying of the pressure accumulator 43.
Since the check valve 42a is arranged in the pressure medium line 41 upstream of the store line 51, it is ensured that the entire pressure p and the entire volume of the store chamber 49 is available to the actuating device 10a, and does not flow out into the oil gallery of the internal combustion engine 1. Therefore, not only is the present system pressure available, as is the case in applications with conventional pressure accumulators, but rather a pressure increased by the factor 1+A2/A1 is available.
Pressure medium is additionally conducted by the control line 52 into the counterpressure chamber 58. Said pressure medium loads the counterpressure surface 59 of the pressure piston 45 with a force which acts in the same direction as that of the spring element 46. The pressure in the store chamber 49 is additionally increased in this way.
The pressure medium supply device 37 can therefore be provided with pressure assistance, which exceeds that of the conventional pressure accumulator, by setting the second control position in the first directional valve 53. It is thus possible for the adjustment speed of the actuating device 10a to be significantly increased for the same dimensioning, or for the actuating device 10a to be designed to be smaller for the same adjustment speed, without having to accept the disadvantages of an overdimensioned or a regulated pressure medium pump 38.
Embodiments are also conceivable in which the connecting line 55 and the arrangement of a check valve 42c in the store line 53 can be dispensed with. In operating phases of the internal combustion engine 1 in which the phase position is held constant, the pressure accumulator 43 is filled via the store chamber 51 and the control line 52.
When the system pressure falls, then no pressure medium flows out of the control chamber 50. As a result, the volume of the control chamber 50 and of the store chamber 49 remains constant despite the pressure drop in the pressure medium supply device 37. Here, the travel x by which the pressure piston 45 has been deflected out of its initial position is defined as follows:
where A1 corresponds to the surface area of the first pressure surface 47, A2 corresponds to the surface area of the second pressure surface 48, pmax corresponds to the maximum system pressure occurring during the filling phase, and D corresponds to the spring constant of the spring element 46. Here, the maximum movement travel is limited by the stops 54.
When the directional valve 53 is moved into the second switching position, then the pressure p provided by the pressure accumulator 43 when the pressure piston 45 is not yet fully deflected can be defined as follows:
plus the pressure which is generated by the filling of the counterpressure chamber 58.
In order to implement the pressure increase, the ratio QD/V of the pressure medium flow out of the control chamber 50 to the pressure medium flow out of the store chamber 49 must satisfy the following relationship:
To achieve this, it is provided that the minimum throughflow cross section AD between the control chamber 50 and the tank 39 satisfies the following relationship:
where AV corresponds to the minimum throughflow cross section between the store chamber 49 and the actuating device 10a, or the actuating device 10a and the tank 39.
It is likewise conceivable for one or more further actuating devices 10b, 10c in addition to the first actuating device 10a to be controllable by means of the pressure medium supply device 37 via further pressure medium lines 41 and further control valves 40. Here, the further actuating device 10b can likewise profit from the pressure accumulator 43. For this purpose, the branch which leads to said actuating device 10b is situated downstream of the check valve 42a in the flow direction.
If the pressure accumulator 43 is to assist only the first actuating device 10a, then the branch to the further actuating device 10c should be arranged upstream of the check valve 42a in the flow direction.
It is likewise conceivable for the check valve 42a to be arranged downstream of the branch to the store line 51. In this case, the pressure peaks are supported between the actuating device 10a,b and the branch to the store line 51. The pressure peaks therefore cannot reach the pressure accumulator 43, as a result of which more rigid torque transmission by the actuating device 10a,b is obtained.
It is likewise conceivable for in each case one check valve 42a to be used in the pressure medium line 41 upstream and downstream of the branch to the store line 51. Here, rigid torque transmission by means of the actuating device 10a,b is achieved, and the pressure or the pressure medium volume of the store chamber 49 is also prevented from being discharged into the oil gallery of the internal combustion engine 1.
In a slight modification of the embodiment, the check valve 42b and/or the entire pressure medium line 41, in which the check valve 42a is arranged between the opening-out points of the pressure accumulator 43, could be omitted.
The store chamber 49 can be acted on with pressure medium from the pressure medium supply device 37 via the store line 51. The counterpressure chamber 58 is connectable to a pressure source via the control line 52. In the illustrated embodiment, the control line opens out into the pressure medium supply device 37.
The control line 52 is therefore connected to the pressure medium pump 38 of the internal combustion engine 1. Other pressure sources such as the pressure medium pump of a servo consumer may alternatively also be used.
A directional valve 53 designed as a 3/2 switching valve is provided in the control line 51. The directional valve 53 has a pressure port P1, a working port B1 and a tank port T1. The pressure port P1 is connected to the pressure medium pump 38, the working port B1 is connected to the counterpressure chamber 58 and the tank port T1 is connected to the tank 39.
In the first control position of the directional valve 53, the working port B1 is connected to the tank port T1, while the pressure port P1 does not communicate with any of the other ports B1, T1. If the directional valve 53 is situated in said control position, then the counterpressure chamber 58 is connected to the tank 39.
In the second control position of the directional valve 53, the working port B1 is connected to the pressure port P1, while the tank port T1 does not communicate with any of the other ports B1, P1. If the directional valve 53 is situated in said control position, then the counterpressure chamber 58 is acted on with pressure medium by the pressure medium pump 38.
During the filling phases of the pressure accumulator 43, the directional valve 53 is situated in the first control position. Pressure medium is supplied to the store chamber 49. As a result, the pressure piston 45 is moved counter to the force of the spring element 46. The volume of the store chamber 49 increases at the expense of the volume of the counterpressure chamber 58.
In the pressure assistance phases, the directional valve is situated in the second control position. In said position, pressure medium is supplied to the counterpressure chamber 58, which pressure medium acts on the counterpressure surface 59. The resulting pressure force increases the force exerted by the spring element 46 on the pressure piston 45. The assistance pressure provided by the pressure accumulator 43 from the store chamber 49 is therefore increased.
Embodiments are also conceivable in which the surface area of the counterpressure surface 59 is greater than the surface area of the first pressure surface 47. This provides a pressure boost which has a positive effect on the pressure value which can be provided.
In said embodiment, pressure medium can pass from the pressure medium pump 38 via the control line 52 and the directional valve 53 into the store chamber 49 for as long as the directional valve is situated in the first control position. At the same time, the counterpressure chamber 58 is ventilated to the tank 39.
When the directional valve 53 is situated in the second control position, the working port A1 is closed and the counterpressure chamber 58 is acted on with pressure medium by the pressure medium pump 38. At the same time, the store chamber 49 is emptied into the pressure medium supply device 37.
The check valve 42c shields the pressure accumulator 43 from pressure peaks generated in the actuating devices 10a, b.
In all of the illustrated embodiments, the pressure accumulator 43 opens out into the pressure medium line 41 which connects the pressure medium pump 38 to the one or more control valves 40. Embodiments are likewise conceivable in which the one or more pressure accumulators 43 open out into the pressure medium lines 41 which connect the one or more control valves 40 to the actuating devices 10a,b.
In addition to the use of the pressure accumulator 43 in applications for variably adjusting the control times of an internal combustion engine 1, the pressure accumulator 43 may also be used in other vehicle applications, for example in switchable cam followers or in applications in automatic transmissions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 056 685.0 | Nov 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/064942 | 11/4/2008 | WO | 00 | 9/8/2010 |
