Abstract:
A two-speed gerotor motor ( 10 ) including motor valve means ( 19,43 ) to communicate fluid to and from expanding ( 33 E) and contracting ( 33   c ) fluid volume chambers. The motor includes a shift valve spool ( 61 ) to cause the motor to operate either in the normal, low-speed, high-torque (LSHT) mode (FIG.  3 ) or in a high-speed, low-torque (HSLT) mode (FIG.  4 ). When the motor operates in HSLT mode, certain of the volume chambers comprise recirculating volume chambers ( 33 R). The motor ( 10 ) defines a supplemental fluid passage ( 89 ) through which fluid is communicated from a system charge pump ( 73 ) to each of the recirculating volume chambers ( 33 R). A control valve ( 83 ) is operable, in a shift mode (S) to permit fluid communication from the charge pump ( 73 ) to the supplemental fluid passage ( 89 ), thus preventing cavitation during shifting of the motor ( 10 ), especially when shifting from the HSLT mode to the LSHT mode.

Description:
BACKGROUND OF THE DISCLOSURE 
     The present invention relates to rotary fluid pressure devices of the type in which a gerotor gear set typically serves as the fluid displacement mechanism, and more particularly, to such devices which are provided with multiple-speed (multiple-displacement) capability. Furthermore, the present invention relates to an improved method for controlling the shifting (between different speeds) of such a multiple-speed device. 
     Although the teachings of the present invention can be applied advantageously to devices having fluid displacement mechanisms other than gerotor gear sets (such as radial piston and cam lobe type devices), the present invention is especially adapted for use with devices utilizing gerotor gear sets, and will be described in connection therewith. Furthermore, the present invention is especially adapted for devices to be utilized as motors, and will be described in connection therewith. 
     Motors utilizing gerotor gear sets can be used in a variety of applications, one of the more common applications being vehicle propulsion, wherein the vehicle includes an engine driven pump which provides pressurized fluid to a vehicle hydraulic propel circuit, including a pair of gerotor motors, with each motor being associated with one of the drive wheels. Those skilled in the art will understand that many gerotor motors utilize a roller gerotor gear set, especially on larger, higher torque motors of the type typically used in propel applications, and subsequent references hereinafter to a “gerotor” will be understood to mean and include both a conventional gerotor as well as a roller gerotor, and for purposes of this invention, “gerotor” can include either an IGR (internally-generated rotor) or and EGR (externally-generated rotor), both of which are now generally well known to those skilled in the art. 
     Multiple-speed gerotor motors are known from U.S. Pat. Nos. 4,480,971; 6,068,460; and 6,099,280, all of which are assigned to the assignee of the present invention and incorporated herein by reference. The device of the &#39;971 patent has been in widespread commercial use and has performed in a generally satisfactory manner, and more recently, the devices of the &#39;460 and &#39;280 patents have also come into commercial usage. As is now well know to those skilled in the art, a gerotor motor may be operated as a multiple-speed (multiple displacement) device by providing valving which can effectively “recirculate” fluid between expanding and contracting fluid volume chambers of the gerotor gear set. If the inlet port communicates with all of the expanding volume chambers, and all of the contracting volume chambers communicate with the outlet port, the motor operates in the normal, low-speed, high-torque (LSHT) mode. If some of the fluid from certain of the contracting volume chambers (the “recirculating” chambers) is recirculated back to the expanding volume chambers, the result will be operation in a high-speed, low-torque (HSLT) mode. The HSLT mode yields the same result as if the displacement of the gerotor were decreased, but with the same fluid flow rate through the gerotor. 
     The multiple-speed gerotor motors, made in accordance with the above-incorporated patents, and sold commercially by the assignee of the present invention, operate very satisfactorily in both the LSHT and the HSLT modes. It has been observed, however, that when the motor is shifted from one mode to the other (and especially, from the HSLT mode to the LSHT mode), there is a tendency for cavitation to occur in the gerotor gear set just as the shift is occurring from one mode to the other. During the shift from HSLT to LSHT, the “displacement” of the motor increases, while the speed of the vehicle and the pump flow remain, at least in the short term, generally constant. Thus, the gerotor gear set is suddenly being “displaced” at a speed corresponding to an instantaneous fluid flow rate which is greater than what the pump can immediately provide. 
     The recirculating fluid volume chambers have the greatest tendency to cavitate because of greater restriction in the recirculation flow path than in the flow paths to and from those volume chambers which don&#39;t recirculate. As is well know to those skilled in the art, cavitation occurring within a fluid displacement element, such as a gerotor, causes a substantial amount of undesirable noise, and can also eventually result in damage to the displacement mechanism. Typically, the cavitation will continue until the vehicle slows down to a speed at which the pump flow “catches up with” the speed (displacement) of the gerotor gear set in the motor. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved fluid pressure operated device having multiple-speed capability, in which shifting from one mode to another does not result in any substantial amount of cavitation and noise. 
     It is a more specific object of the present invention to provide an improved method for controlling the shifting of a multiple-speed fluid pressure operated device, wherein the shifting occurs without any substantial amount of cavitation and noise. 
     The above and other objects of the invention are accomplished by the provision of an improved fluid pressure operated device comprising housing means defining a fluid inlet port and a fluid outlet port. A fluid pressure displacement mechanism is associated with the housing means and includes an internally toothed ring member and an externally toothed star member eccentrically disposed within the ring member, the ring member and the star member having relative orbital and rotational movement, and interengaging to define a plurality N of expanding and contracting fluid volume chambers in response to the orbital and rotational movement. A motor valve means cooperates with the housing means to provide fluid communication between the fluid inlet port and the expanding volume chambers, and between the contracting volume chambers and the fluid outlet port in a normal, low-speed, high-torque mode of operation. A shift valve means is operable, in a first condition, to permit the normal low-speed, high-torque mode of operation and, in a second condition, to interconnect a plurality M of the volume chambers, the plurality M comprising recirculating volume chambers. 
     The improved fluid pressure operated device is characterized by the device defining a supplemental fluid passage operable to provide fluid communication from a source of pressurized fluid to each of the plurality M of recirculating volume chambers. A control valve means is operable, in a normal mode, to block fluid communication from the source of pressurized fluid to the supplemental fluid passage and in a shift mode, to permit fluid communication from the source of pressurized fluid to the supplemental fluid passage. 
     In accordance with another aspect of the present invention, there is provided an improved method of controlling the shifting of a multiple-speed fluid pressure operated device from a first speed ratio to a second speed ratio, the device comprising housing means and a fluid pressure displacement mechanism as described previously. A motor valve means cooperates with the housing means to provide fluid communication in the normal manner in the first speed ratio. A shift valve means is operable in a first condition to achieve the first speed ratio, and in a second condition, to achieve the second speed ratio by interconnecting a plurality M of the volume chambers as recirculating volume chambers. 
     The improved method of controlling the shifting comprises the steps of providing a source of pressurized fluid and a supplemental fluid passage, operable to provide fluid communication from the source to each of the plurality M of recirculating volume chambers. The next step is changing the shift valve means from the first condition to the second condition, and then sensing the changing of the shift valve means and only while the changing is being sensed, generating a change sense signal. The final step is detecting the change sense signal, and in response thereto, permitting fluid communication from the source of pressurized fluid, through the supplemental fluid passage, to the plurality M of recirculating volume chambers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an axial cross-section of a low-speed, high-torque gerotor motor made in accordance with the teachings of the present invention. 
     FIG. 2 is a hydraulic schematic of the entire control system for shifting the gerotor motor illustrated in FIG.  1 . 
     FIG. 3 is a somewhat schematic view, illustrating the gerotor motor of the present invention in the LSHT mode. 
     FIG. 4 is a somewhat schematic view, similar to FIG. 3, but illustrating the gerotor motor of the present invention in the HSLT mode. 
     FIG. 5 is a greatly enlarged, fragmentary, axial cross-section, similar to FIG. 1, illustrating in greater detail one important aspect of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, which are not intended to limit the invention, FIG. 1 illustrates a valve-in-star (VIS) type of low-speed, high-torque (LSHT) gerotor motor, generally designated  10 , made generally in accordance with the teachings of U.S. Pat. No. 5,211,551, assigned to the assignee of the present invention and incorporated herein by reference. More specifically, the gerotor motor shown in FIG. 1 is a multiple-speed motor made in accordance with the teachings of the above-incorporated U.S. Pat. Nos. 6,068,460 and 6,099,280. However, it should be understood that the present invention is not limited to a VIS type of gerotor motor, and as was mentioned in the BACKGROUND OF THE DISCLOSURE, the invention is not even limited to only gerotor type devices, but is limited only to the extent specifically set forth in the appended claims. 
     The VIS motor  10  shown in FIG. 1 comprises a plurality of sections secured together such as by a plurality of bolts  11 , only one of which is shown in FIG. 1, but all of which are shown in FIGS. 3 and 4. The motor includes an end cap  13 , a spacer plate  15 , a shifter plate  17  (which may also be referred to as a “selector plate”), a stationary valve plate  19 , a gerotor gear set, generally designated  21 , and a forward bearing housing  23 , rotatably supporting an output shaft  25 . The end cap  13  defines a fluid inlet port  13   a  and a fluid outlet port  13   b  (which are not shown in FIG. 1, for ease of illustration, but which are shown in the schematics of FIGS. 2,  3  and  4 ). As is well known to those skilled in the motor art, if the port  13   a  becomes the outlet port and the port  13   b becomes the inlet port, the direction of rotation of the output shaft  25  is reversed. 
     The gerotor gear set  21 , also seen in FIGS. 3 and 4, is well known in the art, is shown and described in greater detail in the above-incorporated patents, and therefore will be described only briefly herein. The gerotor gear set  21  comprises an internally toothed ring member  27 , defining a plurality of generally semi-cylindrical openings, with a cylindrical roller member  29  disposed in each of the openings, and serving as the internal teeth of the ring member  27 . Eccentrically disposed within the ring member  27  is an externally toothed star member  31 , typically having one less external tooth than the number of internal teeth or rollers  29 , thus permitting the star member  31  to orbit and rotate relative to the ring member  27 . The orbital and rotational movement of the star  31  within the ring  27  defines a plurality of fluid volume chambers  33 , each of which, at any given instant in time, is either an expanding volume chamber  33 E, or a contacting volume chamber  33 C. As is well know to those skilled in the gerotor art, there is also, at any given instant in time, one of the volume chambers which is in a state of “transition” between expanding and contracting. In the subject embodiment, and by way of example only, there is a total of nine volume chambers  33 . 
     Referring still primarily to FIG. 1, the star  31  defines a plurality of straight, internal splines which are in engagement with a set of external, crowned splines  35 , formed about one end of a main drive shaft  37 . Disposed at the opposite end of the shaft  37  is another set of external, crowned splines  39 , adapted to be in engagement with a plurality of straight, internal splines, defined by the output shaft  25 . 
     Referring still primarily to FIG. 1, but now in conjunction with FIGS. 3 and 4, the star member  31  will be described in some additional detail. In the subject embodiment, and by way of example only, the star  31  comprises an assembly of two separate parts including a main star portion  41 , which includes the external teeth of the star, and an insert or plug  43 . The main portion  41  and the insert  43  cooperate to define the various fluid zones, passages and ports which are described in detail in the above-incorporated patents, and therefore, will not be described in detail hereinafter. The star member  31  defines a central manifold zone  45 , defined by an end surface  47  disposed in sliding, sealing engagement with an adjacent surface  49  of the stationary valve plate  19 . 
     The end surface  47  of the star  31  defines a set of fluid ports  51 , each of which is in continuous fluid communication with the manifold zone  45  by means of a fluid passage  53  defined by the insert  43 . The end surface  47  further defines a set of fluid ports  55  which are arranged alternately with the fluid ports  51 , each of the fluid ports  55  extending radially inward and opening into an outer manifold zone  57  (shown only in FIGS.  3  and  4 ), surrounding the central manifold zone  45 . The stationary valve plate  19  defines a plurality of stationary valve passages  59 , only one of which is shown in FIG.  1 . As the star member  31  orbits and rotates, each of the fluid ports  51  and  55  defined by the insert  43  engages in commutating fluid communication with each of the stationary valve passages  59 , thus porting, alternately, high pressure fluid to each volume chamber  33  while it is an expanding volume chamber  33 E, and then receiving low pressure fluid from each volume chamber  33 , while it is a contracting volume chamber  33 C. The valving arrangement just described is well known to those skilled in the gerotor motor art, is illustrated and described in greater detail in the incorporated patents, and is referenced hereinafter in the appended claims as the “motor valve means”, i.e., the valving which achieves the basic operation of the motor. 
     Referring now primarily to FIGS. 3 and 4, but also somewhat to FIGS. 1 and 2, the means by which the motor  10  of the present invention achieves multiple speed operation will be described. The motor  10  includes a shift valve spool  61  which, as is shown schematically in FIG. 2, is biased by a compression spring  63  toward a first condition, as shown in FIG. 3, in which the motor  10  is in its normal low-speed, high-torque (“LSHT”) mode of operation. As is shown schematically in FIG. 2, and as may be seen in FIG. 1, each volume chamber of the motor which is to recirculate (and therefore is referred to also as a “recirculating volume chamber  33 R”) is connected, through its respective stationary valve passage  59 , by means of a fluid passage  65 , to the shift valve spool  61 . It should be noted that in FIGS. 3 and 4, each “passage”  65  actually appears, schematically, as two separate passages, one between the shift valve spool  61  and the star port ( 51  or  55 ), and the other between the shift valve spool  61  and the recirculating volume chamber  33 R. However, for the purposes of the subsequent description and the appended claims, each such “pair” will be referenced as the passage  65 . 
     In the LSHT mode of FIG. 3, the shift valve spool  61  is in a position which isolates each of the passages  65  from the other passages  65 , and also isolates each fluid passage  65  from a “source” of recirculation fluid, the source being designated  67 . As is now well know to those skilled in the art, the source  67  may simply be the inlet port  13   a  (see FIG.  3 ), and in the case of a bi-directional motor, the source  67  could also be connected to the other port  13   b  (when the port  13   b  is serving as the inlet port). Therefore, some sort of shuttle valve arrangement, generally designated  69 , is positioned such that whichever of the ports  13   a  or  13   b  is at the higher pressure will be in fluid communication with the fluid passage comprising the source  67 . The structural and operational details associated with the source  67  and the shift valve spool  61  are now well know to those skilled in the art, are not essential to the present invention, and therefore will not be described further herein. 
     Referring now primarily to FIGS. 2 and 4, the shift valve spool  61  may be shifted, in opposition to the force of the compression spring  63 , by a pressure signal  71  which is communicated from a source of pressurized fluid, such as a system charge pump  73 . The flow of fluid from the charge pump  73  to the shift valve spool  61  is controlled by a pressure reducing valve  75 , the construction and operational details of which are not essential to the present invention, and are beyond the scope of the present invention, and therefore, will not be described further herein. Suffice it to say that the pressure reducing valve  75  is able to control the pressure communicated as the pressure signal  71  to control the shifting of the shift valve spool  61  from the position shown schematically in FIG. 2 (and in FIG. 3) to the position shown in FIG.  4 . The position of the shift valve spool  61  in FIG. 4 comprises a second condition, corresponding to a high-speed, low-torque (“HSLT”) mode of operation. In the HSLT mode of operation, the shift valve spool  61  is in a position such that each of the fluid passages  65  is in open communication with the source  67 , and therefore, is in communication with each of the other passages  65 . As the three recirculating volume chambers  33 R expand and contract, the fluid merely flows back and forth among the volume chambers  33 R, and through the fluid passages  65  and the source  67 . What has been described thus far is in commercial usage and therefore is now generally well known. 
     Referring now primarily to FIG. 2, in conjunction with FIG. 1, one important aspect of the present invention will now be described. In fluid communication with the output of the charge pump  73  is a fluid conduit  81  which is in communication with the fluid inlet of a solenoid operated control valve  83 . The control valve  83  is biased by a compression spring  85  toward a “normal” mode or position (“N”) in which the control valve  83  connects the fluid conduit  81  to a system reservoir R. The control valve  83  can be shifted from its normal mode “N” shown in FIG. 2 to a shift mode or position (“S”) by an electromagnetic solenoid portion  87 , in a manner to be described subsequently. When the control valve  83  is in the shift mode “S”, pressurized fluid is communicated from the fluid conduit  81  to a fluid passage  89  (also shown in FIG. 1) which is in fluid communication with the motor  10  at a fitting  91  (shown only in FIG.  1 ). 
     Referring now to FIGS. 1,  2  and  5 , it may be seen that the forward bearing housing  23  defines an annular chamber  93 , and in open communication with the chamber  93  is a plurality of axial fluid passages  95 , there being one of the fluid passages  95  for each recirculating volume chamber  33 R. Therefore, in the subject embodiment, there are three of the axial passages  95  (as is shown schematically in FIG.  2 ). 
     Although, in the schematic of FIG. 2, each of the axial fluid passages  95  is shown as being connected to its respective fluid passage  65  (and, if such were literally true, the desired result would be achieved), the actual construction of the preferred embodiment is somewhat different, although fully equivalent, functionally. 
     As may best be seen in FIGS. 1 and 5, whereas each of the fluid passages  65  communicates with a recirculating volume chamber  33 R through one of the stationary valve passages  59 , as was described previously, the axial fluid passages  95  are disposed on the opposite axial side of the gerotor gear set  21 . It may be seen that, disposed between the gerotor gear set  21  and the forward bearing housing  23 , is a balance plate  97  which, in the subject embodiment, and by way of example only, is made in accordance with the teachings of U.S. Pat. No. 6,086,345, assigned to the assignee of the present invention and incorporated herein by reference. Disposed adjacent the balance plate  97  is a Belleville washer  99 . It should be understood that the balance plate  97  and the Belleville washer  99  do not form any essential part of the present invention. 
     However, in accordance with one aspect of the invention, the balance plate  97  (which in and of itself is not essential to the invention) does define a stepped fluid opening  101 . A radially inner portion of the opening  101  is in communication with the adjacent recirculating volume chamber  33 R, whereas, a radially outer portion of the opening  101  is in open communication with an enlarged axial bore  103 . Disposed in the bore  103  is a check valve which, in the subject embodiment, comprises a check ball  105 . 
     The intersection of the axial fluid passage  95  and the enlarged axial bore  103  forms a check valve seat  107 , and those skilled in the valve art will understand that whenever the motor  10  is operating in its LSHT mode, and the adjacent volume chamber is either an expanding or contracting volume chamber  33 E or  33 C, respectively, the check ball  105  is in engagement with the seat  107 , and there is no substantial fluid communication between the volume chamber and the passage  95 . 
     However, in accordance with one important aspect of the present invention, when the control valve  83  is in the shift mode “S”, pressurized fluid is communicated from the charge pump  73  through the fluid passage  89 , to supplement the fluid in the recirculating volume chambers  33 R, such that the passage  89  is also referred to hereinafter, and in the appended claims, as a “supplemental” fluid passage. Therefore, the pressurized fluid in the supplemental fluid passage  89  flows through the annular chamber  93  and into each of the axial fluid passages  95 , unseating the check ball  105  and providing additional fluid to the adjacent recirculating volume chamber  33 R. It is important to note that the supplemental fluid passage  89 , and the chamber  93  and passages  95 , are all separate from, and in addition to, the “normal” motor valving as defined by the stationary valve plate  19  and the fluid ports  51  and  55 . 
     In accordance with another aspect of the invention, the control valve  83  is in the shift mode “S” only when there is a need for supplemental fluid to be communicated to those volume chambers which had been recirculating volume chambers  33 R, until the motor was shifted from HSLT mode to LSHT mode. In order to provide the supplemental fluid only when it is truly needed and beneficial, a position sensor  109  is operably associated with the shift valve spool  61  and provides a signal  111  which may be referred to as a “change sense” signal because it indicates a change in state or sense from the LSHT mode to the HSLT mode (or vice versa). The signal  111  is transmitted to motor control logic, schematically designated  113  in FIG.  2 . The control logic  113  receives the change sense signal  111 , and when the condition of the signal  111  (e.g., current, duty cycle, etc.) indicates that the shift valve spool  61  is shifting modes (especially if it is shifting from HSLT to LSHT), then the control logic  113  transmits an appropriate command signal  115  to the solenoid portion  87  of the control valve  83 , shifting it from its normal mode “N” to its shift mode “S”. Therefore, in accordance with one aspect of the invention, the control valve  83  is in the shift mode “S” only while the shift valve spool  61  is changing between the HSLT and LSHT modes of operation. 
     The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those skilled in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims.