Abstract:
A hydraulic bearing device that supports a rotating shaft comprises a bearing metal. On a surface of the bearing metal, a hydrostatic pocket and a land portion are formed. The land portion is defined by the hydrostatic pocket and generates hydrodynamic pressure. The hydraulic bearing device further comprises a pressure fluid supplying source and an oil-supplying hole. The oil-supplying hole is opened in the hydrostatic pocket and provides pressure fluid from the pressure fluid supplying source to the hydrostatic pocket. On the land portion, a drain hole that drains the fluid is formed. Since the fluid is drained through the drain hole, thermal expansion of the bearing metal due to heat generation of the fluid is restrained. Moreover, since the drain hole does not separate the land portion, deterioration of bearing rigidity is restrained.

Description:
INCORPORATION BY REFERENCE  
         [0001]    The entire disclosure of Japanese Patent Applications Nos.  2000-289889  filed on Sept.  25, 2000, 2001-100989  filed on Mar. 30, 2001 and  2001-280095  filed on Sep. 14, 2001 including specification, drawings and abstract is herein by reference in its entirety.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to a hydraulic bearing device that supports a rotating shaft or the like.  
           [0004]    2. Description of the Related Art  
           [0005]    [0005]FIG. 1 shows three partially developments of inner surfaces of bearing metals which constitute radial hydraulic bearing devices according to the related arts. Plural hydrostatic pockets  1 ,  2  that are quadrilateral grooves such as shown by FIGS.  1 (A) and  1 (C) or U-shaped grooves such as shown by FIG. 1(B) are formed on inner surface of the bearing metals along a rotational direction of a rotating shaft. An oil-supplying hole  3  is formed in each hydrostatic pocket. Inner surface of the bearing metal except the hydrostatic pockets are land portions  4  for generating hydrodynamic pressure. FIG. 2 shows three plane views of bearing metals which constitute thrust hydraulic bearing devices according to the related arts. A hydrostatic pocket  5  that is a ring shape groove such as shown by FIG. 2 (A) or plural hydrostatic pockets  6  that are partially ring-shape grooves such as shown by FIGS.  2 (B) and  2 (C) are formed on a surface of the bearing metals. Plural oil-supplying holes  3  are formed in the ring shape hydrostatic pocket  5 , and a oil-supplying hole  3  is formed in the each partly ring shape hydrostatic pocket  6 . The surface of the bearing metal except the hydrostatic pockets  5 ,  6  are land portions  4  for generating hydrodynamic pressure. Here, hydraulic bearing devices are distinguished two types that are a separated type such as shown by FIG. 1 (C) or FIG. 2(C), and a non-separated type such as shown by FIGS.  1 (A),  1 (B) or FIGS.  2 (A),  2 (B) according to a shape of the land portion  4 . The land portion  4  of the non-separated type is continuously all around of the surface of the bearing metal. On the other hand, the land portions  4  of the separated type are separated to rotational direction by drain grooves  7  that are formed between each hydrostatic pocket. At aforementioned hydraulic bearings, when pressure adjusted lubricant oil is supplied to the hydrostatic pockets  1 ,  2 ,  5 ,  6  through the oil-supplying hole  3 , the hydraulic bearing functions as a hydrostatic bearing by filled lubricant oil between the hydrostatic pockets  1 ,  2 ,  5 ,  6  of the bearing metal and an outer surface of a rotating shaft. Simultaneously, since the lubricant oil is filled between the land portion  4  and the rotating shaft, when the rotating shaft is rotated for the bearing metal, the hydraulic bearing functions as a hydrodynamic bearing by wedge effect that is generated between the land portions  4  and the outer surface of the rotating shaft.  
           [0006]    Then, at the non-separated type bearing, especially in a case of U-shaped hydrostatic pockets  2  such as shown by FIG. 1(B), since area of the land portion  4  is large and continuously, a large amount of hydrodynamic pressure is generated. Therefore, the non-separated type bearing is effective in high rigidity and high damping effect. However, in a case of high rotating speed, a great heat due to fluid friction is generated at the land portion  4 . The great heat causes thermal expansion of the bearing metal, and a clearance between the bearing metal and the rotating shaft decreases. As the result, calorific value by fluid friction increases, and thermal expansion of the bearing metal increases. This is in a vicious circle that causes to deteriorate the performance of the bearing.  
           [0007]    On the other hand, at the separated type bearing, heat generating at the land portion  4  is restrained because it is easy to be drained the lubricant oil by existence of the drain grooves  7 . However, existence of the drain grooves  7  causes deterioration of the rigidity because the land portion  4  is separated and small. Moreover, the separated type bearing tends to cause cavitation.  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide an improved hydraulic bearing device.  
           [0009]    A hydraulic bearing device that supports a rotating shaft comprises a bearing metal. On a surface of the bearing metal, a hydrostatic pocket and a land portion are formed. The land portion is defined by the hydrostatic pocket and generates hydrodynamic pressure. The hydraulic bearing device further comprises a pressure fluid supplying source and an oil-supplying hole. The oil-supplying hole is opened in the hydrostatic pocket and provides pressure fluid from the pressure fluid supplying source to the hydrostatic pocket. On the land portion, a drain hole that drains the fluid is formed.  
           [0010]    Because the hydraulic bearing device is provided with the hydrostatic pocket and the land portion, it functions not only as a hydrostatic bearing but also as a hydrodynamic bearing. Then, since the fluid is drained through the drain hole, thermal expansion of the bearing metal due to heat generation of the fluid is restrained. Moreover, since the drain hole does not separate the land portion, deterioration of bearing rigidity is restrained. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the accompanying drawings, wherein:  
         [0012]    FIGS.  1 (A),  1 (B) and  1 (C) are partially developments of inner surfaces of bearing metals that constitute radial hydraulic bearing devices according to the related arts;  
         [0013]    FIGS.  2 (A),  2 (B) and  2 (C) are plane views of bearing metals that constitute thrust hydraulic bearing devices according to the related arts;  
         [0014]    [0014]FIG. 3 is a schematic illustration of a wheel spindle apparatus of a grinding machine according to the first embodiment of the present invention;  
         [0015]    [0015]FIG. 4 is a sectional perspective view of a bearing metal according to the first embodiment of the present invention;  
         [0016]    FIGS.  5 (A),  5 (B) and  5 (C) are partially developments of inner surfaces of the bearing metals according to the first embodiment of the present invention;  
         [0017]    FIGS.  6 (A),  6 (B), and  6 (C) are partially developments of inner surfaces of other bearing metals according to the first embodiment of the present invention;  
         [0018]    [0018]FIG. 7 is a graph showing relations between rotational speed of a wheel spindle and static rigidity of radial hydraulic bearings;  
         [0019]    [0019]FIG. 8 is a graph showing relations between rotational speed of a wheel spindle and temperature of bearing metals of radial hydraulic bearings;  
         [0020]    [0020]FIG. 9 is graph showing pressure distribution on an inner surface of a bearing metal according to the first embodiment of the present invention;  
         [0021]    [0021]FIG. 10(A) is a sectional view of a wheel spindle showing a direction of grinding force, and FIG. 10(B) is a graph showing a relation between pressure distribution on an inner surface of a bearing metal and a position of a hydraulic pocket relative to the direction of grinding force according to the first embodiment of the present invention;  
         [0022]    [0022]FIG. 11 is a schematic illustration of a wheel spindle apparatus of a grinding machine according to the second embodiment of the present invention;  
         [0023]    [0023]FIG. 12 is a graph showing a relation between rotational speed of a wheel spindle and static rigidity of a hydraulic bearing according to the second embodiment of the present invention;  
         [0024]    [0024]FIG. 13 is a graph showing a relation between rotational speed of a wheel spindle and temperature of a bearing metal according to the second embodiment of the present invention;  
         [0025]    [0025]FIG. 14 is a graph showing a relation between rotational speed of a wheel spindle and opening of a metering orifice according to the second embodiment of the present invention;  
         [0026]    [0026]FIG. 15 is a graph showing a relation between temperature of lubricant oil and opening of a metering orifice according to the second embodiment of the present invention;  
         [0027]    [0027]FIG. 16 is a time chart to explain a relation between load acting to a wheel spindle and opening of a metering orifice according to the second embodiment of the present invention;  
         [0028]    [0028]FIG. 17 is a schematic illustration of a wheel spindle apparatus of a grinding machine according to the third embodiment of the present invention;  
         [0029]    [0029]FIG. 18 is a plain view of a bearing metal of a thrust bearing device according to the third embodiment of the present embodiment;  
         [0030]    [0030]FIG. 19 is a graph showing relations between rotational speed of a wheel spindle and static rigidity of thrust hydraulic bearings; and  
         [0031]    [0031]FIG. 20 is a graph showing relations between rotational speed of a wheel spindle and temperature of bearing metals of thrust hydraulic bearings. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0032]    [First Embodiment] 
         [0033]    Preferred embodiments of a hydraulic bearing device according to the invention will be described hereinafter with reference to the accompanying drawings. A radial hydraulic bearing device of according to the present invention is employed, for instance, in a wheel spindle apparatus of a grinding machine as illustrated in FIG. 3. The radial hydraulic bearing devices  11  are arranged to support a wheel spindle S at inner surfaces thereof. At one end of the wheel spindle S, a grinding wheel G is attached. A driving belt B is strung between another end of the wheel spindle S and a motor M 1 , and the wheel spindle S is rotated by the motor M 1 . Referring to FIG. 4, the radial hydraulic bearing device  11  comprises a ring shape inner sleeve  12  as a bearing metal and a bearing case  13  that the inner sleeve  12  is fixed therein by such as manners of a shrinkage fit or a press fit. Plural hydrostatic pockets  14  are formed on an internal circumference surface of the inner sleeve  12  in a circumference direction and are equally distant from each other. As a shape of the hydraulic pockets  14 , for example, quadrilateral groove shown by FIG. 5(A), U-shape groove which has leg portions extended in rotational direction of the wheel spindle S shown by FIG. 5(B) or quadrangular ring shape groove that a land portion is formed at a center thereof shown by FIG. 5(C) are applicable. A land portion  15  for generating hydrodynamic pressure is defined as a portion or portions except hydrostatic pockets  14  from the internal circumference surface of the inner sleeve  12 . At a center of the each hydrostatic pocket  14 , one end of an oil-supplying hole  17  which has a throttle nozzle (not shown in Figures) is opened. The other end of the oil supplying hole  17  is connected with a oil supplying pass  16  that is defined by a circumference groove formed on a outer surface of the inner sleeve  12  and an inner surface of the bearing case  13 . The oil-supplying pass  16  is connected with a pump P. which is driven by a motor M, via an outside supplying pipe L. At an inside of the inner sleeve  12 , plural drain holes  18  are formed. One end of the each drain hole  18  is opened on the land portion  15 , and the other end of the each drain hole  18  is connected with a tank  43  via an outside drain pipe  42 . As a disposition of the drain hole  18 , for example, single drain hole  18  disposed between each hydrostatic pocket  14  such as shown by FIGS.  5 (A),  5 (B) and  5 (C), or double drain holes  18  disposed between each hydrostatic pocket  14  shown by FIGS.  6 (A),  6 (B) and  6 (C) are applicable. In a case of the quadrangular ring shape groove shown by FIG. 5(C) or FIG. 6(C), it is preferable that another drain hole  18  is disposed in the center land portion that is surrounded with the quadrangular ring shape groove. A metering orifice  41  such as an electromagnetic variable valve is disposed on a way of the outside drainpipe  42 .  
         [0034]    At above described radial hydraulic bearing device  11 , when lubricant oil is supplied to the supplying pass  16  by the pump P through the outside supplying pipe L, pressure of the lubricant oil is adjusted by the throttle nozzle. The pressure adjusted lubricant oil is filled in the hydrostatic pockets  14 . Therefore, the hydrostatic pockets  14  generate hydrostatic pressure and the wheel spindle S is supported for the bearing metal by the hydrostatic pressure. That is, the hydraulic bearing device  11  functions as a hydrostatic bearing. Besides, the lubricant oil filled in the hydrostatic pockets  14  flows out between the land portion  15  and an outer surface of the wheel spindle S. When the wheel spindle S is rotated relative to the bearing metal, hydrodynamic pressure is generated by edge effect of the lubricant oil that is between the land portion  15  and the outer surface of the wheel spindle S. That is, the hydraulic bearing device  11  functions as a hydrodynamic bearing. Then, the lubricant oil is drained to each side of the bearing metal. In addition, the lubricant oil is drained from the drain hole  18  to the tank  43  through the outside drainpipe  42  and metering orifice  41 .  
         [0035]    According to the hydraulic bearing device  11  of the first embodiment, since the lubricant oil is drained with not only each side of the bearing metal but also through the drain holes  18 , drainage efficiency of the lubricant oil is improved. As the result, thermal expansion of the bearing metal due to heat generating at the land portion  15  is restrained. Then, since the drain holes  18  do not interrupt continuation of the land portion  15  like the drain grooves  7  of the related art, deterioration of bearing rigidity is restrained. That is, the hydraulic bearing device  11  of the first embodiment has a capacity of static rigidity that is close to the same of the non-separated type bearing as shown by FIG. 7, and has temperature rise that is close to the same of the separated type bearing as shown by FIG. 8.  
         [0036]    Further, according to the hydraulic bearing device of the first embodiment, since the metering orifice  41  is disposed in the outside drainpipe  42 , it is possible that bearing rigidity is controlled to adjust an opening of the metering orifice  42 . That is, as shown FIG. 10, since pressure distribution at the bearing metal changes according to opening of the metering orifice  42 , it is possible to control as follows: when high rigidity is required such as machining time by the grinding wheel G. bearing rigidity is increased by closing the metering orifice  42 ; when high rigidity is not require such as an idle time of the machining, thermal expansion of the bearing metal is decreased by opening the metering orifice  42 .  
         [0037]    Moreover, since a capacity of static rigidity and thermal expansion can be controlled by the metering orifice  41 , a range of specification of the bearing device spreads. In the result, a freedom of a design for the bearing device increases.  
         [0038]    Furthermore, in a case of that the metering orifice  42  is installed relative to each drain hole  18 , opening of each metering orifice  42  is adjustable individually. For example, at the wheel spindle apparatus of the grinding machine, the wheel spindle S receives a load, which is grinding resistance, in constant direction as shown by an arrow of FIG. O(A). Therefore, it is possible that bearing rigidity relative to load acting direction is increased to close the metering orifices V 2  relative to load receiving direction, thermal expansion of the bearing metal is decreased to open another valves V 1 , V 3 , V 4  as shown by FIGS.  10 (A) and  10 (B).  
         [0039]    In addition, since pressure in the drain hole  18  dose not become negative pressure by existence of the metering orifice  42 , generating cavitation at the drain hole  18  is prevented.  
         [0040]    [Second Embodiment] 
         [0041]    Explanation for the second embodiment that is same constitution as the first embodiment is omitted. Referring to FIG. 11, sensors are prepared for a wheel spindle apparatus of the second embodiment in addition to the constitution of the first embodiment. An encoder  22  is attached on an end face of the wheel spindle S to measure rotating speed of the wheel spindle S. A temperature sensor  23  is attached on a way of the outside drainpipe  42  to measure temperature of the drained lubricant oil. A pressure gauge  24  is attached in the hydrostatic pocket  14  to measure pressure therein. A displacement sensor  25  is disposed between the inner sleeve  12  and wheel spindle S to measure a clearance therebetween. Each of sensors  22 ,  23 ,  24  and  25  is connected electrically to a controller  21 , and output therefrom is input to the controller  21 . The controller  21  is connected electrically to the metering orifice  41  to control opening of the metering orifice  41 . Here, all sensors are not required to be installed, it is possible that one or some sensors is/are installed selectively.  
         [0042]    At above described second embodiment, controller  21  controls opening of the metering orifice  41  according to the output of the sensors  22 ,  23 ,  24  and  25 . As shown by FIG. 7, static rigidities of the first embodiment increase according to increasing of rotational speed of the wheel spindle S, because hydrodynamic pressure increase according to increasing of rotational speed. Simultaneously, temperature of the bearing metal increases according to rotational speed as shown by FIG. 8. Then, in the second embodiment, the controller  21  controls opening of the metering orifice  41  according to rotational speed of the wheel spindle S as a relationship of opening of the metering orifice  41  with rotational speed of the wheel spindle S shown by FIG. 14. Therefore, increase of the rigidity more than necessity is restrained shown by FIG. 12, and increase of the temperature of the bearing metal is restrained shown by FIG. 13. Similarly, as shown by FIG. 15, opening of the metering orifice  41  can be controlled according to temperature of the lubricant oil that is measured by the temperature sensor  23 . As another control mode of the metering orifice  41 , it is possible that the metering orifice  41  is controlled according to pressure in the hydrostatic pockets  14  that is measured by the pressure gauge  24 , or a clearance between the inner sleeve  12  and wheel spindle S that is measured by the displacement sensor  25 . For example, at the wheel spindle S of the grinding machine, machining resistance that acts to the wheel spindle S changes intermittently to repeat machining cycles as shown by FIG. 16(A). Then, at the bearing device of the related art, temperature of the bearing metal rises constantly regardless of load fluctuation as shown by FIG. 16(B). However, temperature rise more than necessity is restrained as shown by FIG. 16(D) by controlling opening of the metering orifice  41  as shown by FIG. 16(C) according to pressure in the hydrostatic pockets  14  measured by the pressure gauge  24 .  
         [0043]    According to the hydraulic bearing device of the second embodiment, in addition to the effects of the first embodiment, a balance with bearing rigidity and temperature rise can be adjusted suitably to control opening of the metering orifice  41  according to rotational speed of the wheel spindle S, temperature of the lubricant oil, pressure in the hydrostatic pockets or clearance between the wheel spindle S and the land portion  15 .  
         [0044]    [Third Embodiment] 
         [0045]    At third embodiment, the present invention is applied to a thrust hydraulic bearing device. As shown FIG. 17, a flange portion F is formed in a center of a wheel spindle S. A front and a rear thrust bearing metals  31  are arranged to oppose to end surfaces of the flange portion F each other. Each thrust beating metal  31  is ring shape formed a center hole  32  that the wheel spindle S penetrates therein, and fixed on a bearing case C. It is possible to form directly a bearing metal on end surfaces of the bearing case C. As shown FIG. 18, four hydrostatic pockets  34  that are separated ring shape grooves are formed on a surface of the bearing metal  31  which is opposed to the end surface of the flange portion F. Portions of the surface of the bearing metal  31  except the hydrostatic pockets  34  are land portions  35  to generate hydrodynamic pressure. The land portions  35  are consist of an outer land portion  35   a , an inner land portions  35   b  and spoke land portions  35   c  that are formed between each hydrostatic pockets  34 . An oil-supplying hole  17  which has a throttle nozzle (not shown in Figures) is opened into each hydrostatic pocket  34 . The other end of the oil-supplying hole  17  is connected with a pump P through an inner portion of the bearing case C. On the spoke land portion  35   c , drain holes  36  like the drain holes  18  in the first and second embodiment are formed. Similarly with the first embodiment and the second embodiment, the other end of the drain holes  36  is connected with a tank  43  through a metering orifice  41  such as a an electromagnetic variable valve.  
         [0046]    At above described thrust hydraulic bearing device, when lubricant oil whose pressure is adjusted by the throttle nozzle is supplied to the hydrostatic pockets  34  through the oil-supplying hole pass  17 , the pressure adjusted lubricant oil is filled in the hydrostatic pockets  34 . Therefore, the hydrostatic pockets  34  generate hydrostatic pressure and the wheel spindle S is supported for the bearing metal  31  by the hydrostatic pressure. That is, the hydraulic bearing device functions as a hydrostatic bearing. Besides, the lubricant oil filled in the hydrostatic pockets  34  flows out between the land portion  15  and the end surface of the flange portion F. When the wheel spindle S is rotated relative to the bearing metal  31 , hydrodynamic pressure generated by edge effect of the lubricant oil that is between the land portion  35  and the end surface of the flange portion F. That is, the hydraulic bearing device functions as a hydrodynamic bearing. Then, the lubricant oil is drained to inner and outer sides of the bearing metal  31 . In addition, the lubricant oil is drained from the drain hole  36  to the tank  43  through metering orifice  41 .  
         [0047]    According to the third embodiment, since the lubricant oil is drained with not only each side of the bearing metal but also through the drain holes  36 , drainage efficiency of the lubricant oil is improved. As the result, thermal expansion of the bearing metal  31  due to heat generating at the land portion  35  is restrained. Then, since the drain holes  36  do not interrupt continuation of the land portion  36  like the drain grooves  7  of the related art, deterioration of bearing rigidity is restrained. That is, the hydraulic bearing device of the third embodiment has a capacity of static rigidity that is close to the same of the non-separated type bearing as shown by FIG. 19, and has temperature rise that is close to the same of the separated type bearing as shown by FIG. 20.  
         [0048]    Further, according to the hydraulic bearing device of the third embodiment, since the metering orifice  41  is disposed in the outside drainpipe  42 , it is possible that bearing rigidity is controlled to adjust an opening of the metering orifice  42 .  
         [0049]    Moreover, since a capacity of static rigidity and thermal expansion can be controlled by the metering orifice  41 , a range of specification of the bearing device spreads. In the result, a freedom of a design for the bearing device increases.  
         [0050]    Furthermore, in a case of that the metering orifice  42  is installed relative to each drain hole  36 , opening of each metering orifice  42  is adjustable individually.  
         [0051]    In addition, since pressure in the drain hole  36  dose not become negative pressure by existence of the metering orifice  42 , generating cavitation at the drain hole  36  is prevented.  
         [0052]    It is possible that the sensors like the second embodiment are installed to the third embodiment. Then, the thrust bearing device of third embodiment provides same effects with the second embodiment.  
         [0053]    Obviously, numerous modifications and variations of the present invention are possible in light of the above teaching. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.