Abstract:
A pressure control valve, in particular for an automatic transmission in a motor vehicle, including a housing and including a control piston situated in the housing, the control piston being actuatable by an armature situated in a magnet chamber of a pole tube, the magnet chamber being hydraulically connected to a compensating chamber provided in the housing, which is delimited, in particular by a lateral surface of a solenoid coil and the housing.

Description:
RELATED APPLICATION INFORMATION 
     The present application claims priority to and the benefit of German patent application No. 10 2013 226 615.4, which was filed in Germany on Dec. 19, 2013, the disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a pressure control valve, in particular for an automatic transmission in a motor vehicle. 
     BACKGROUND INFORMATION 
     In modern automobile automatic transmissions, hydraulically actuated clutches are used to change gears. In order for these shift operations to occur smoothly and unnoticed by the driver, it is necessary to adjust the hydraulic pressure on the clutches according to predefined pressure ramps with the maximum possible pressure precision. For this purpose, electromagnetically actuated pressure control valves are used. These may be configured as either seat valves or slide valves. Both configurations normally include three hydraulic connections, for intake, control pressure and return flow. In the case of slide valves, an axially displaceable control piston connects openings, for example, situated radially in a sliding sleeve, which are fluidically, in particular, hydraulically, connected, to an intake connection, to a control pressure connection and to a return flow connection. In this arrangement, the control pressure connection may be axially situated, for example, whereas the intake connection and the return flow connection are radially situated. In order to ensure the pressure regulating function of slide valves, it is necessary for the control piston to be able to carry out its axial movement largely undamped. 
     In particular, if the end faces of a control piston come into contact with hydraulic oil, the axial movement of the control piston may result in a so-called “pumping” of hydraulic oil through the control piston. Consequently, oil is displaced by the movement of the control piston or, in turn, oil is drawn in due to a resulting vacuum. Pressure control valves in automatic transmissions are normally installed in the hydraulic oil reservoir or in the so-called “oil sump” of the automatic transmission. During the operation of automatic transmissions, in particular, ferromagnetic particles form in conjunction with the friction of the transmission gears as a result of the abrasion of the gears. In the hydraulic oil reservoir, such ferromagnetic particles and other dirt particles may lead to functional impairments or malfunctions. Thus, for example, the guidance of the control piston or the electromagnetic actuation of the control piston may be adversely affected due to the contaminants. In particular, ferromagnetic particles may accumulate in this case in the area of the magnetic poles. 
     Various approaches are known for ensuring the pressure regulating function of slide valves and for minimizing the entry of dirt into a pressure control valve. A slide valve is believed to be understood from DE 10 2010 039 917 A1, whereby a push rod of the pressure control valve is sealingly, but axially displaceably, guided in a bearing bush. A slide valve, in which a diaphragm is provided between an actuating rod and the valve slide in order to ensure a flow medium sealing between two housing halves, is discussed in DE 103 25 070 A1. 
     SUMMARY OF THE INVENTION 
     The problem underlying the present invention is solved by a pressure control valve having the features of claim  1 . Advantageous refinements are specified in the subclaims. Features important to the present invention are also found in the following description and in the drawings, whereby the features, when taken alone and in different combinations, may be important for the present invention, without further explicit reference being made thereto. 
     A pressure control valve according to the present invention includes a housing and a control piston situated in the housing, the control piston being actuatable by an armature situated in a magnet chamber of a pole tube. According to the present invention, it is provided that the magnet chamber is hydraulically connected via a compensating channel to a compensating chamber in the housing, which is delimited by a solenoid coil and the housing, in particular, by a lateral surface of the solenoid coil and the housing. The lateral surface in this case is formed, in particular, by an outer winding layer of the solenoid coil. The housing has advantageously a pot-shaped configuration in the area of the compensating chamber. A pole tube is understood to mean a closed arrangement in the interior of a winding carrier of the solenoid coil, in which the magnetic poles generating the axial force and, respectively, the armature are situated. A filtering effect in the pressure control valve may be provided in the compensating chamber, whereby on the one hand particles are able to settle due to gravity, and whereby ferromagnetic particles may adhere in the area of the magnetized inner wall of the housing. Thus, with the present invention, a pressure control valve having a slide configuration is obtained, which is able to prevent dirt particles from adversely affecting the function of the pressure control valve in a simple and cost-effective manner. 
     One advantageous embodiment of the present invention provides that an end face on the armature side of the control piston is hydraulically connected to the magnet chamber. Due to the connection of the magnet chamber with the compensating chamber, the end face of the control piston on the armature side is consequently also hydraulically connected to the compensating chamber. The result in this case is a pumping of the control piston, which may be in the direction of the compensating chamber. 
     It is also provided that the housing has a multi-part configuration, in particular, a two-part configuration and, in particular, is composed of a hydraulic housing and a magnet housing. Here, the hydraulic components of the pressure control valve such as, for example, the supply connection, the return flow connection to the hydraulic oil reservoir, the working connection, the control piston and the sliding sleeve may be situated in the hydraulic housing. In contrast, the electromagnetic components such as, for example, the pole tube, the armature, the solenoid coil, etc., may be situated in the magnet housing. The magnet housing in this case has, in particular, a pot-shaped configuration. 
     In order to ensure a ventilation of the magnet chamber and the compensating chamber, the compensating chamber is hydraulically connected via an opening to an outer housing side. A simple manufacturing approach has proven to be that of providing as an opening a breakthrough of the electrical connecting plug of the pressure control valve. The opening in this case may be provided on the side of the compensating chamber which faces away from the compensating channel. Consequently, hydraulic oil is able to flow via the compensating channel and the compensating chamber through the opening into the hydraulic oil reservoir. Due to the connection of the end face of the control piston on the armature side to the magnet chamber, which, in turn, is connected via the compensating channel to the compensating chamber, which via the opening, is fluidically, in particular, hydraulically, connected to the hydraulic oil reservoir, a largely undamped movement of the control piston and of the armature may be ensured. Thus, an impact on the pressure control function by so-called “pumping” may be largely avoided. 
     The pressure control function is implemented in that the control piston of the valve in an open position hydraulically connects a working connection or control pressure connection to the supply connection and separates it hydraulically from a return flow connection. In the non-activated state, i.e., when the coil of an electromagnetic actuation device is de-energized, the armature thereof moves through the coil spring installed on the magnet side in the direction of the opening and moves the control piston in the direction of an opened end position of the pressure control valve. In this way, the first section of the control piston unblocks the supply pressure opening and the pressure medium flows into an annulus space delimited by the sliding sleeve and the control piston. Since, at the same time, the third section of the control piston separates the return flow opening from the annulus space, the pressure prevailing at the supply connection is also present at the working connection. 
     When the coil is energized, the electromagnetic force acts against the restoring force of the coil spring on the magnet side, which has deflected the control piston toward the end face. The control piston is moved by the control pressure present at the piston end face back into the closed end position. The control piston in the closed end position seals the supply pressure opening and at the same time unblocks the return flow opening. Because tank pressure is present in the return flow opening which is lower than the working pressure prevailing in the annulus space, pressure medium flows via the return flow opening to the return flow connection. 
     Another advantageous embodiment of the pressure control valve provides that the compensating channel is delimited, at least in sections, by a groove in the hydraulic housing and in the pole tube. 
     In this case, in particular the groove may extend in an L-shape, at least in sections, in parallel to a median longitudinal axis of the control piston and on an end face of the hydraulic housing on the armature side at least in sections radially, perpendicularly to the median longitudinal axis of the control piston. The groove may be configured to have a U-shaped or a semi-circular cross section. The pole tube may then include an annular flange facing the control piston. The compensating channel in this case is formed by the L-shaped groove and the annular flange, as well as an end face of the pole tube on the control piston side. 
     It is also beneficial if the groove is cast or injection molded into the hydraulic housing. In this case, the groove may be particularly advantageously manufactured in conjunction with an injection molding process. 
     Another advantageous embodiment of the present invention provides that the compensating channel is configured as a radial transverse bore in the pole tube. In this case, a groove need not be provided in the hydraulic housing. A radial transverse bore in the pole tube, which connects the magnet chamber to the compensating chamber, is very simple to manufacture. 
     It is particularly helpful if the compensating channel is situated radially upwardly during operation. A radially upward arrangement of the compensating channel may ensure that air, which has accumulated in the pole tube or in the magnet chamber, is able to escape upwardly. Thus, a ventilating function of the magnet chamber may be provided by the compensating channel, and it may be ensured that the magnet chamber is filled with oil. This is particularly advantageous for a constant dynamic behavior of the pressure control valve. 
     It has also proven advantageous if the cross section of the channel is selected to be not too large, so that no additional larger particles are able to pass into the magnet chamber as a result of the residual movement of oil. It is also advantageous if the cross section of the compensating channel is selected to be not too small, so that the ventilating function of the compensating channel is not adversely affected. In particular, in this case the compensating channel may have a hydraulic diameter of 0.3 mm to 2 mm. The hydraulic diameter in this case is defined as d h =4 A/U. A is the cross sectional surface of the compensating channel, U representing the size of the cross section of the compensating channel. 
     Additional details and advantageous embodiments of the present invention result from the following description, with reference to which the specific embodiment shown in the figures is described and explained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows a representation of a hydraulic circuit, in which a pressure control valve according to the present invention is used. 
         FIG. 2  shows a partial section through a pressure control valve according to the present invention. 
         FIG. 3  shows a section along the line A-A in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     To control automatic transmissions, as they are used, for example, in passenger cars, a hydraulic circuit  10 , among other things, is used, of which a pressureless hydraulic oil reservoir  12  and a hydraulic pump  14  are a part. An outlet of the hydraulic pump  14  forms a supply connection  16 , to which a pressure control valve  18  is connected. 
     A return flow from pressure control valve  18  leads to a return flow connection  20 , which leads back to hydraulic reservoir  12 . Pressure control valve  18  is also connected to a working connection  22 , at which the pressure to be controlled by pressure control valve  18  is present. In addition, pressure control valve  18  includes an electromagnetic actuation device  24 . 
       FIG. 2  depicts the structure of a pressure control valve  18  according to the present invention. Pressure control valve  18  includes a valve connection element  26 , which is slid on to a hydraulic housing  28  and is sealingly connected to hydraulic housing  28 . Valve connection element  26 , or, respectively, hydraulic housing  28 , has a recess (with no reference numeral) situated concentrically to a median longitudinal axis  30  of pressure control valve  18 , in which a fastening section  32  is situated. Provided in fastening section  32  is an annulus space  34 . Fastening section  32  is mechanically connected at at least one point via its outer circumference to hydraulic housing  28 . In the area of this connection, annulus space  34  is also hydraulically connected to supply connection  16 . A sliding sleeve  36  is inserted into the concentric recess of hydraulic housing  28 . Sliding sleeve  36  has a continuous guide bore  38 , which serves to accommodate a control piston  40 . Sliding sleeve  36  is inserted into the hydraulic housing up to the area of hydraulic housing  28  facing away from valve connection element  26 . 
     Openings  42 ,  44  and  46  are located on the circumference of sliding sleeve  36  situated next to one another in the axial direction. The first opening in sliding sleeve  36 , referred to hereinafter as supply pressure opening  42 , opens guide bore  38  to annulus space  34  and, therefore, to supply connection  16  when control piston  40  is actuated accordingly. 
       FIG. 2  depicts pressure control valve  18  in the equilibrium position, such that no hydraulic connection exists between annulus space  34  and guide bore  38 . This equilibrium position is an intermediate position between the open and the closed end position. 
     The second transverse bore of sliding sleeve  36 , referred to hereinafter as control pressure opening  44 , connects guide bore  38  to control pressure connection  22 . In particular, during operation of pressure control valve  18 , fluid is able to flow via the control pressure opening on fastening section  32 , which is not fastened about its entire outer circumference in hydraulic housing  28 , in the direction of control pressure connection  22 . The third transverse bore, hereinafter called return flow opening  46 , establishes a hydraulic connection between guide bore  38  and return flow connection  20 . Return flow opening  46  in this case communicates, in particular, with an annulus space  48  situated in hydraulic housing  28 , which is hydraulically connected to return flow connection  20 . 
     Two O-rings  50 ,  52  are provided on the outer circumference of valve connection element  26 , which seal control pressure connection  22  outwardly during operation of pressure control valve  18 . 
     Control piston  40  is divided in the axial direction into four adjoining sections  54 ,  56 ,  58  and  60 . First section  54 , to the extreme left in the figure, has a first diameter D 1 . With this first diameter D 1 , control piston  40  is guided in guide bore  38 . 
     Second section  56  situated in  FIG. 2  approximately centrically in sliding sleeve  36 , which is connected to first section  54 , has a second diameter D 2 , which is smaller than first diameter D 1  and, thus, is also smaller than the diameter of guide bore  38  in the area of second section  56 . This creates an annulus space  62  between sliding sleeve  36  and second section  56  of control piston  40 . 
     Third section  58  connected to second section  56  also has diameter D 1  and is guided sealingly, but axially displaceably, in guide bore  38  of sliding sleeve  36 . As a result, annulus space  62  is delimited in the axial direction by first section  54  and third section  58 . 
     In fourth and last section  60 , control piston  40  has a smaller diameter and tapers conically toward an end face  64 . 
     In the equilibrium position shown in  FIG. 2 , control piston  40  is situated axially in sliding sleeve  36  in such a way that annulus space  62  communicates with control pressure opening  44 . The rim of first section  54  facing second section  56  forms a control edge (with no reference numeral). In addition, the front rim of third section  58  facing second section  56  also forms a control edge (with no reference numeral). 
     Electromagnetic actuation device  24  is situated in  FIG. 2  on the right side of pressure control valve  18 . It includes, among other things, an annular coil  66 , which is wound around a winding carrier  68 . 
     Coil  66  is surrounded by a magnet housing  70  which contains actuation device  24 . Situated inside coil  66  is a pole tube  72 . Pole tube  72  includes a first bore  74  having a diameter D 3 . Bore  74  forms a magnet chamber  76 . A sleeve-like magnet armature  78  is inserted within magnet chamber  76  from an open side into bore  74 , on the right in  FIG. 2 . Magnet armature  78  includes an armature bolt  80 , which together with magnet armature  78  is connected at at least one point on its outer circumference of magnet armature  78 . Also inserted into magnet chamber  76  of pole tube  72  is a pole disk  82  having a sleeve-like section (with no reference numeral) in magnet chamber  76 , or, respectively, in bore  74 . A coil spring  86  is situated between armature bolt  80  and a support section  84  in the interior of sleeve-like magnet armature  78  and of the sleeve-like section of pole disk  82 . Coil spring  86  is supported on the one hand on armature bolt  80  and on the other hand on support section  84 . The side of pole tube  72  facing hydraulic housing  28  includes an annular flange section  88 , which has a significantly smaller diameter than pole tube  72 . In the area of the annular flange section  88 , the pole tube includes a second bore  90  having a diameter D 4 . This bore  90 , together with bore  74 , forms a stepped through-bore in pole tube  72 . A sleeve  92  is inserted from magnet chamber  76  within bore  90 . An end face of sleeve  92  facing hydraulic housing  28  forms a stop for control piston  40 . A step in control piston  40 , which is formed between third section  58  and fourth section  60 , cannot be moved further to the right past this stop of sleeve  92 , i.e., in the direction of actuation device  24 . 
     Sleeve  92  has an inner diameter, which is larger than the outer diameter of control piston  40  in fourth section  60 . Consequently, the magnet chamber is fluidically connected to an annulus space  94  on the magnet side in hydraulic housing  28  via an annulus space formed by fourth section  60  of control piston  40  and sleeve  92 . 
       FIG. 3  shows a section along the line A-A in  FIG. 2  as viewed in the direction of arrow  96 . Here, an annulus space  94  in hydraulic housing  28  shown in  FIG. 2  is clearly apparent. It is also apparent in  FIG. 3  that sliding sleeve  36  protrudes in sections into annulus space  94 . Control piston  40  also extends through annulus space  94 . Hydraulic housing  28 , as is apparent in the section according to  FIG. 3 , is non-rotatably connected by pins  98  to magnet housing  70 . 
     As shown in  FIG. 2 , an outer winding layer of coil  66 , together with magnet housing  70 , delimits a compensating chamber  102 . This compensating chamber  102  is fluidically connected to annulus space  94  via a compensating channel  104 . Compensating channel  104  in this case is formed by a semi-open groove  106  clearly apparent in  FIG. 3 , cast in hydraulic housing  28 , the cross section of which is approximately semi-circular, and by annular flange  88  of pole tube  72  and an end face of pole tube  72  on the hydraulic side extending perpendicularly to median longitudinal axis  30 . The side of compensating chamber  102  facing away from compensating channel  104  includes an opening  112 , for example, in the area of a plug breakthrough for an electric plug  114 . This opening  112  also communicates with return flow connection  20 . 
     Groove  106 , as shown in  FIG. 3 , extends in sections in an L-shaped configuration in parallel to median longitudinal axis  30  in a section  108 , and radially perpendicularly to median longitudinal axis  30  to radially upwardly in a section  110 . Thus, compensating channel  104  is formed, in particular, by section  108  and annular flange  88 , as well as by section  110  and the end face of pole tube  72 . 
     During operation of the pressure control valve, i.e., when control piston  40  is moved by electromagnetic actuation device  24  into the open position (to the left in  FIG. 2 , not depicted), then hydraulic oil flows under high pressure from supply connection  16  and via supply pressure opening  42  into annulus space  62 , and from there via control pressure opening  44  to working connection  22 . Return flow opening  46  in this case is essentially concealed by third section  58  of control piston  40 . 
     If, on the other hand, control piston  40  is situated in a position more to the right, for example, when coil  66  is energized, supply pressure opening  42  is covered by first section  54 , and annulus space  62  is therefore essentially separated from supply connection  16 . Instead, return flow opening  46  is now connected by annulus space  62  to the control pressure opening, so that working connection  22  communicates with return flow connection  20  via control pressure opening  44 , annulus space  62  and return flow opening  46 . In this way, the pressure prevailing at working connection  22  may be reduced via return flow connection  20 , because ambient pressure prevails there in a first approximation. 
     If during operation the control piston  40  is now moved from its opened, left position into its closed, right position, a so-called “pumping” of control piston  40  may occur. In this case, movement of the end face  64  of control piston  40  displaces hydraulic oil. The resultant flow may then be diverted via compensating channel  104  into compensating chamber  102 . Since compensating chamber  102  is connected to return flow connection  20  via opening  112 , flows caused by the movement of control piston  40  may be reduced via compensating chamber  102  in the direction of return flow connection  20 . Compensating chamber  102  in this case has a filtering effect. Dirt particles may settle in compensating chamber  102  due to gravity, whereas ferromagnetic particles, which form, for example, due to gear abrasion in an automatic transmission, magnetically adhere to outer winding layer  100  of coil  66 . Since compensating channel  104  is, in particular, upwardly oriented during operation, a ventilation of magnet chamber  76  may be ensured, whereby air is able to escape upwardly. In particular, in this case compensating channel  104  may have a hydraulic diameter d h =4 A/U of approximately 0.3 mm to 2 mm. On the one hand, this may then prevent particles which are too large from passing into magnet chamber  76 , while on the other hand the ventilating function is not impaired. 
     Since the fluid displaced from end face  64  of control piston  40  via compensating channel  104  and compensating chamber  102  may flow into return flow connection  20  unpressurized to the greatest possible extent, control piston  40  may carry out its axial movement largely undamped. This results in a particularly configuration of a pressure control valve  18 , with which, on the one hand, the ingress of dirt into pressure control valve  18  may be reduced, and on the other hand a largely undamped axial movement of control piston  40  may be ensured.