Patent Publication Number: US-2011048224-A1

Title: Hydraulic pump or hydraulic motor having a rotation speed sensor

Description:
TECHNICAL FIELD 
     The invention relates to a hydraulic pump or hydraulic motor having an orbiting cardan shaft and, more particularly, to a speed sensor for a hydraulic pump or hydraulic motor having an orbiting cardan shaft. 
     BACKGROUND OF THE INVENTION 
     Many hydraulic pumps and hydraulic motors include speed sensors to detect or monitor rotational speed of the hydraulic pump or hydraulic motor. 
     One such embodiment of a rotation speed sensor for a hydraulic pump or hydraulic motor is known from US 2006/0257268 A1. 
     In hydraulic pumps and hydraulic motors for which speed is to be sensed, the rotational speed is tapped off from one of the rotating parts via a sensor. To do so, annular gears or magnet rings are fitted to the rotating parts to produce pulses for the sensor to detect. This means additional complexity in terms of parts, production, assembly and complexity. 
     Therefore, there is a need for a less complex mechanism for sensing rotational motor speed. 
     SUMMARY OF THE INVENTION 
     The present invention provides a hydraulic pump or a hydraulic motor having improved rotational speed sensing. 
     The hydraulic pump or hydraulic motor has an orbiting cardan shaft that is mounted in a housing. A piston is in contact with the cardan shaft and moving forward and back. The hydraulic pump or motor includes a rotation speed sensor associated with the piston to detect the rotational speed of the hydraulic pump or hydraulic motor. The rotation speed sensor may be built in to a port plate of the hydraulic pump or hydraulic motor and includes a sensor probe associated with the piston. The sensor probe can also be associated directly with the orbiting cardan shaft. 
     The sensor probe according to the present invention receives signals directly from the orbiting cardan shaft, eliminating the need for a gear wheel with teeth for impulses for a sensor probe fixed to the housing. 
     The sensor probe is preferably in the form of a Hall-effect probe of an L-shaped built in part intended for installation in the port plate between the housing and end plate, and a plug element, for electrically connecting the sensor probe to electronics fitted outside the hydraulic motor or hydraulic pump. 
     Inductive sensor probes, giant magneto resistive (GMR) sensors or anisotropic magneto resistive (AMR) sensors can advantageously be used. 
     The Hall-effect probe sensor recognizes changes in the magnetic field around the tip of the sensor probe. It contains a seal ring to avoid leaking of hydraulic oil. 
     One embodiment of the invention is to mount the sensor probe fixedly in the port plate of the hydraulic pump or hydraulic motor and the sensor probe having its signal directly from the orbiting cardan shaft. 
     Another embodiment is to mount the sensor probe in the port plate of the hydraulic pump or hydraulic motor and in the axial direction of the sensor probe extend with a mechanism of a spring and a piston in touch with the cardan shaft. As the piston follows the movement of the cardan shaft, this movement will take it in and out of the range of the Hall-effect sensor. The spring will apply enough force to maintain constant contact between the piston and cardan shaft. The output of the hall-effect sensor can be calibrated based on the reduction in the gear set and/or gearbox to provide the speed of the machine. 
     The spring will see e.g. fifty (50) compression cycles for every revolution of the motor output shaft so the spring needs to have a high fatigue limit and also able to apply the correct force. 
     An advantage compared with the prior art systems with gear wheels for signals is that the present invention provides a simple design with fewer components, meaning a cheaper solution which can be applied to almost any hydraulic motor or hydraulic pump and is ideal for an application in which the output shaft/cardan shaft is inserted into a gearbox and/or mechanism. Because the sensor probe is taking information off of the cardan shaft, which rotates forty-two to forty-eight (42-48) times per shaft revolution, the resolution will be very high. 
     The solution will not have the same interference as typical systems because the sensor is located clear of the hydraulic housing structure. Further the sensor is not near to the mounting flange, which means easier access for mounting tools e.g. by service. 
     One further advantage is that the rotation speed sensor can be combined with a temperature sensor, with the result that only one built-in part is required for both measurements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a front view of a hydraulic motor according to an embodiment of the present invention with a cardan shaft in its orbital position closest to a speed sensor; 
         FIG. 2  is a cross-sectional view of the hydraulic motor of  FIG. 1 ; 
         FIG. 3  is a front view of the hydraulic motor of  FIG. 1  with the cardan shaft in its orbital position most distant from the speed sensor; 
         FIG. 4  is a cross-sectional view of the hydraulic motor of  FIG. 3 ; 
         FIG. 5  is a graphical representation showing the motion of the cardan shaft of  FIGS. 1-4 ; 
         FIG. 6  is a partially exploded front view of another embodiment of the hydraulic motor according to the present invention; and 
         FIG. 7  is a cross-sectional view of the hydraulic motor of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1 and 2 , a hydraulic motor  10  includes a housing  12  having an end cover  14  and a port plate  16  adjacent to one another. The hydraulic motor  10  also includes a disk valve  18  sandwiched between the end cover  14  and the port plate  16  within a cavity  20  formed in the end cover  14 . The disk valve  18  includes an inner gear tooth ring (no shown) for interfacing with gear teeth  22 . The gear teeth  22  are disposed on an outer diameter of a first end  26  of a cardan shaft  24  and accommodated within the cavity  20 . The cardan shaft  24  extends outwardly from the end cover  14  through an opening  28  in the port plate  16 . The port plate  16  may also include bores  30 , shown in  FIG. 1 , for hydraulic oil passage. The port plate  16  includes a radial bore  32  that accommodates a rotation sensor  34  having a sensor probe  36  for evaluating the speed of the hydraulic motor  10 . The rotation sensor  34  is fixed to the port plate  16  by fastening means, which will depend on the specific type of rotation sensor  34  used. For example, the rotation sensor may be bolted, screwed or press fit into the port plate  16 . Additionally, the rotation sensor  34  may include a sealing ring  38  to prevent leakage of hydraulic oil. Preferably, the rotation sensor  34  is a Hall-effect sensor and more preferably is a standard ON/OFF Hall-effect sensor that detects the presence of any metallic material nearby. Suitable Hall-effect sensors are manufactured by Honeywell International Inc. of 101 Columbia Road, Morristown, N.J. Alternatively, the rotation sensor may include inductive sensor probes, giant magneto resistive (GMR) sensors or anisotropic magneto resistive (AMR) sensors. 
     The disk valve  18  generates rotational movement of the first end  26  of the cardan shaft  24  around a disk center axis  40  of the disk valve  18 . A second end  42  of the cardan shaft  24 , having gear teeth  44 , is in communication with a gear set (not shown) accommodated within a gear housing (not shown) adjacent to the port plate  16 . Thus, the port plate  16  is sandwiched between the gear housing (not shown) and the end cover  14 . The gear set (not shown) in communication with the second end  42  of the cardan shaft  24  generates an orbital movement of the second end  42  about the disk center axis  40  when the disk valve  18  causes the cardan shaft  24  to rotate. Thus, the disk valve  18  and the gear set (not shown) assure eccentric movement of the valve cardan shaft  24  such that a cardan center axis  46  of the valve cardan shaft  24  moves on a right circular cone path about the disk center axis  40  of the disk valve  18 . The orbital movement of the second end  42  of the cardan shaft  24 , in connection with the gear set (not shown), causes a motor output shaft (not shown) driven by through the gear set (not shown) to rotate. Through gear reduction, the motor output shaft (not shown) rotates at a lower rotational speed than the rotational speed of the cardan shaft  24 . For example, the cardan shaft  24  may rotate forty-two to forty-eight (42-48) times per revolution of the motor output shaft (not shown). Thus, the hydraulic motor  10  is ideal for low speed, high torque applications. 
     As seen in  FIGS. 1 and 2 , the cardan shaft  24  is in a top position, such that the cardan shaft  24  is located at its closest proximity to the rotation sensor  34 . In this situation, the rotation sensor  34  detects the presence of the cardan shaft  24  and is in an ON state, generating an ON signal. 
     Referring to  FIGS. 3 and 4 , the cardan shaft  24  is in a bottom position, such that the cardan shaft  24  is located at its farthest proximity to the rotation sensor  34 . In this situation, the rotation sensor  34  is in an OFF state and, therefore, not generating an ON signal. 
     Referring to  FIG. 5 , as the cardan shaft  24  orbits around the disk center axis  40 , an amplitude of position  48  of the cardan shaft  24  with respect to the rotation sensor  34  follows a sine curve due to the orbital movement of the second end  42  of the cardan shaft  24 . The amplitude of position  48  is at a maximum of positive one (+1) when the cardan shaft  24  is closest to the rotation sensor  34  and at a minimum of negative one (−1) when the cardan shaft  24  is farthest from the rotation sensor  34 . The rotation sensor  34  may be configured with a defined amplitude  50  to control switching between the ON and OFF signals of the rotation sensor  34 . When the amplitude of position  48  of the cardan shaft  24  is greater than the defined amplitude  50 , the rotation sensor  34  will generate and ON signal and when the amplitude of position  48  of the cardan shaft  24  is less than the defined amplitude  50 , the rotation sensor  34  will be OFF and not generate a signal. Thus, as the cardan shaft  24  orbits over time, the rotation sensor  34  will generate a position curve  52 , where all values above the defined amplitude  50 , indicated by a dotted line in  FIG. 5 , will be considered as logical 1 (one) or ON and all other values as logical 0 (zero) or OFF. Thus, the rotation sensor  34  detects the cardan shaft  24  each time the cardan shaft  24  approaches the top position closest to the rotation sensor  34 . Additionally, the defined amplitude  50  may be adjusted to configure the ON/OFF signal for the rotation sensor  34  in any hydraulic motor or pump with an orbiting cardan shaft. 
     Referring to  FIGS. 6 and 7 , an alternate embodiment of the hydraulic motor  110  is shown wherein like numerals represent like elements. Hydraulic motor  110  has an L-shaped rotation sensor  134  including a sensor probe  136 . The L-shaped rotation sensor  134  is preferably fabricated from plastic. The hydraulic motor  110  has a piston  154  with a circular tip  156  that contacts the cardan shaft  124 . A bore  132 , shown in  FIG. 7 , is formed in the port plate  116  to accommodate the piston  154  and the rotation sensor  134 . A spring  158  is disposed within the bore  132  between the piston  154  and the sensor probe  136  of the rotation sensor  134  to ensure physical contact between the piston  154  and the cardan shaft  124 . The L-shaped rotation sensor  134  is mounted in the bore  132  and fixed to the port plate  116  by a bolt (not shown) in a threaded bore  160 . The port plate  116  may also include bores  130  for hydraulic oil passage. 
     As the cardan shaft  124  rotates in orbital motion, as discussed above, the piston  154  reciprocates in bore  132 , shown in  FIG. 7 . The sensor probe  136  of the rotation sensor  134  detects the movement of the piston  154 , which corresponds to the motion of the cardan shaft  124 . The amplitude of reciprocal motion of the piston  154  follows a sine curve similar to that shown in  FIG. 5 . Thus, the rotation sensor  134  generates its ON/OFF signal through the detection of the piston  154  in the same manner discussed above in connection with  FIG. 5 . In addition to ensuring contact between the piston  154  and the cardan shaft  124 , the spring will need a high fatigue limit because it will experience approximately fifty (50) compression cycles for every revolution of the motor output shaft. 
     An advantage of the present invention is that the sensor probe  36 ,  136  receives signals directly from the orbiting cardan shaft  24 ,  124 , eliminating the need for a gear wheel having teeth to generate impulses to be read by a sensor probe fixed to the housing. Thus, the present invention provides a simple design with fewer components when compared to the prior art, resulting in a less expensive design. Additionally, the gear wheel and sensor configuration for detecting rotational speed in prior art motor assemblies is largely dependent upon available internal housing space to accommodate the gear wheel and sensor and the available external housing space to accommodate the sensor&#39;s plug element  162 , seen in  FIGS. 6 and 7 . Therefore, the prior art configuration will vary with different housing shapes, housing sizes, and internal components. The present invention overcomes the deficiencies of the prior art by eliminating the gear wheel, which allows the sensor of the present invention to advantageously be applied to almost any hydraulic motor or hydraulic pump. Thus, the present invention is ideal for an application in which the output shaft/ cardan shaft is inserted into a gearbox and/or mechanism. 
     A further advantage of the present invention is that it provides a high resolution signal because the sensor probe  36 ,  136  is taking information off of the cardan shaft  24 ,  124 . As discussed above, the cardan shaft  24 ,  124  is rotating at a greater speed than the motor output shaft (not shown). Thus, the valve cardan shaft  24 ,  124  will orbit about disk center axis  40  approximately forty-two to forty-eight (42-48) times per motor output shaft rotation. The rotation sensor  34 ,  134  will, in turn, generate forty-two to forty-eight ON signals for every rotation of the motor output shaft (not shown), allowing for frequent motor speed sampling, which will provide for a high resolution signal. Additionally, the present invention will not have the same interference with the magnetic field as typical sensor systems because the sensor is located clear of the hydraulic housing structure. 
     Another advantage of the present invention is that it provides easier access for mounting tools since the sensor is not near to the mounting flange. 
     One further advantage is that the rotation speed sensor can be combined with a temperature sensor, resulting in a single built-in part for both measurements. Hall-effect sensors suitable for both speed sensing and temperature sensing are manufactured by Honeywell International Inc. of 101 Columbia Road, Morristown, N.J. 
     Since certain changes may be made in the above-described hydraulic motor, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention. For example, those skilled in the art will recognize that the hydraulic motor  10 ,  110  can be operated as either a hydraulic pump or a hydraulic motor. However, for simplicity the invention has been described throughout this application as a hydraulic motor.