Patent Application
20110048224
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.
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.
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.
The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which:
Referring to
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
Referring to
Referring to
Referring to
As the cardan shaft 124 rotates in orbital motion, as discussed above, the piston 154 reciprocates in bore 132, shown in
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's plug element 162, seen in
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.
