Patent Application
20170015201
The present disclosure relates to a system for monitoring operation of a retarding grid associated with a traction motor of a machine. More particularly, the present disclosure relates to a system for generating a warning signal based on a performance of the retarding grid in a given environmental condition.
Earth moving machines have long been known to employ retarding grids for their traction motors. These retarding grids typically contain several sets or banks of resistors that are configured for regulating an amount of power supplied to the traction motors. However, these resistors also have a propensity for heating up during operation i.e., when regulating the power or voltage to be supplied to the traction motors. Although the resistors may be cooled down by drafts of atmospheric air, for e.g., as the machine moves in a worksite or by directing air from a high-speed blower fan, fluctuations in air density can nevertheless still impact an amount of cooling to the resistors.
U.S. Pat. No. 6,847,187 (hereinafter referred to as “the '187 patent”) discloses a thermal protection apparatus for AC traction motors. The apparatus includes a stator, a rotor, a blower fan, and an inverter. The apparatus is configured to predict the motor temperature assuming that the blower is operational. The apparatus further determines an estimated motor temperature by measuring the motor resistance or the rotor slip. The apparatus then compares the estimated motor temperatures with the predicted motor temperature to determine the condition of the motor cooling system.
However, the '187 patent does not account for changes in air density and its impact on resistors of the retarding grid.
In one aspect of the present disclosure, a system for monitoring operation of a retarding grid associated with a traction motor of a machine includes a pressure sensor, a temperature sensor, and a controller. The pressure sensor and the temperature sensor are configured to measure atmospheric pressure and atmospheric temperature respectively. The controller is communicably coupled to each of the traction motor, the pressure sensor, and the temperature sensor. The controller is configured to receive the atmospheric pressure and the atmospheric temperature from the pressure sensor and the temperature sensor respectively.
The controller determines a current air density on the basis of the received atmospheric pressure and temperature. The controller then determines a threshold retarding power limit for the retarding grid on the basis of the current air density. The controller further determines a threshold torque limit for the traction motor on the basis of the determined threshold retarding power limit and a current wheel speed of the machine. The controller also determines a current retarding torque at the traction motor, and selectively generates a warning signal to an operator of the machine on the basis of the threshold torque limit determined for the traction motor and the current retarding torque at the traction motor.
In another aspect of the present disclosure, a method for monitoring operation of the retarding grid includes measuring atmospheric pressure and atmospheric temperature. The method further includes receiving, by a controller, the measured atmospheric pressure and atmospheric temperature from the pressure sensor and the temperature sensor respectively. The method further includes determining a current air density on the basis of the received atmospheric pressure and temperature. The method further includes determining a threshold retarding power limit for the retarding grid on the basis of the current air density. The method further includes determining a threshold torque limit for the traction motor on the basis of the determined threshold retarding power limit and a current wheel speed of the machine. The method further includes determining a current retarding torque at the traction motor; and selectively generating a warning signal to an operator of the machine on the basis of the threshold torque limit determined for the traction motor and the current retarding torque at the traction motor.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to same or like parts. Moreover, references to various elements described herein are made collectively or individually when there may be more than one element of the same type. However, such references are merely exemplary in nature. It may be noted that any reference to elements in the singular may also be construed to relate to the plural and vice-versa without limiting the scope of the disclosure to the exact number or type of such elements unless set forth explicitly in the appended claims.
In alternative embodiments of the present disclosure, the machine 100 can optionally be embodied in the form of a tracked vehicle. Further, the machine 100 may be a manually-operated machine, an autonomous machine, or a machine that is operable in both manual and autonomous mode. Therefore, notwithstanding any particular type or configuration of machine disclosed in this document, it will be appreciated by one skilled in the art that systems and methods disclosed herein can be similarly applied to other types of machines known in the art without deviating from the spirit of the present disclosure.
Referring to
The electric drive system 104, disclosed herein, may include for e.g., a series electric drive system, a parallel electric drive system, a series or parallel hybrid electric drive system, or any other type of system that uses electric power for propulsion. As shown in the embodiment of
However, in an alternative embodiment, the electric drive system 104 may, additionally or optionally, be powered with the help of a pantograph 110 and an overhead catenary 112 (shown in
Generator 202, disclosed herein, may embody an electric power generator suitable for converting mechanical torque into electric power. More particularly, a rotor (not shown) of generator 202 may be coupled to the shaft 108 associated with engine 102. Upon rotation of the shaft 108 by the engine 102, the shaft 108 may rotate the rotor relative to a stator (not shown) of the generator 202, thereby generating a current in the stator coils. According to one exemplary embodiment, the generator 202 may be a three-phase AC generator.
Rectifier 204, disclosed herein, may be electrically coupled to the generator 202 and configured to convert the AC power produced by the generator 202 into DC power. Any type of rectifier may be used. According to one embodiment, the rectifier 204 may be a three-phase bridge full-wave rectifier that includes a plurality of power diodes (not shown) that are arranged in diode pairs around each phase of the output of the generator 202. Each diode pair includes two power diodes that may be connected in series to each other, with a connection to each phased output of the generator 202 between each pair. The three pairs of power diodes are connected in parallel to each other and produce DC power at the output.
Inverter 208 may be connected in parallel with the rectifier 204 and configured to transform the DC power into variable frequency sinusoidal or non-sinusoidal AC power that drives each of the traction motors 212a, 212b. The inverter 208 of the present disclosure may embody any suitable type of inverter circuit. For example, the inverter 208 may include three phase arrays of insulated gate bipolar transistors (IGBT) that are arranged in transistor pairs and that are configured to supply a 3-phase AC output to each of the traction motors 212a, 212b. In this manner, the inverter 208 can control a rotational speed of the motors 212a, 212b by controlling the frequency and/or the pulse width of the AC power output.
The traction motors 212a, 212b may include any type of motor suitable to convert electric power to mechanical torque. According to the exemplary embodiment described above, traction motors 212a, 212b may be three-phase AC motors configured to receive three-phase AC power from the inverter 208 and provide a torque output based on the frequency of the received AC power. According to one embodiment, a first traction motor i.e., 212a may be coupled to a first wheel for e.g., wheel 106b i.e. at the left side and a second traction motor 212b may be coupled to a second wheel for e.g., wheel 106b i.e. at the right side.
As shown, the wheels 106a, 106b are mechanically coupled to the traction motors 212a, 212b and hence, configured to rotate in response to a rotation of an output shaft 214 of the respective traction motor 212a, 212b. For example, in the exemplary embodiment illustrated in
Although some components pertaining to the electric drive system 104 have been disclosed herein, it is hereby contemplated that electric drive system 104 could, additionally or optionally, include other components than those illustrated in
Alternatively, the retarding grids 206 can also be configured to dissipate heat generated by the traction motors 212a, 212b when the electric drive system 104 is operating for e.g., in a retarding mode. Retarding mode, disclosed herein, may occur when the machine 100 is to be decelerated or its motion is otherwise to be retarded, for example, to prevent acceleration of the machine 100 when travelling down an incline. As known to one skilled in the art, traction motors 212a, 212b can behave like generators when kinetic energy is applied at the output shafts 214 of the traction motors 212a, 212b. For example, when the machine 100 is traveling down a steep incline, the force of gravity can cause the wheels 106a, 106b to drive the traction motors 212a, 212b in a manner similar to driving a generator, thereby supplying power back into the electric drive system 104. In order to effectively dissipate this power, some or all of the power can be supplied into the retarding grids 206. However, as the retarding grids 206 typically include numerous resistive elements (not shown) therein, the resistive elements tend to convert this excess electrical energy into heat thereby causing the retarding grids 206 to heat up during operation.
The present disclosure relates to a system 216 for monitoring an operation of the retarding grids 206. With continued reference to
The controller 222 then determines air density D on the basis of the received atmospheric pressure P and atmospheric temperature T. In an embodiment, the pressure sensor 218 and the temperature sensor 220 can be beneficially configured to measure the atmospheric pressure P and the atmospheric temperature T in real-time. In the preceding embodiment, it may be noted that the air density D measured using such real-time values of atmospheric pressure P and atmospheric temperature T can be regarded as being representative of current air density. For the sake of convenience and simplicity in this document, the air density D measured using real-time values of atmospheric pressure P and atmospheric temperature T may hereinafter be referred to as “the current air density” and designated with identical reference alphabet “D”.
In various embodiments of this disclosure, this real-time may lie in a range of few milliseconds (ms) to a few seconds (s). For example, in one application, the real-time can be 5 ms. In another example, the real-time can be set to 10 ms. In yet another example, the real-time at which the pressure sensor 218 and the temperature sensor 220 are configured to measure the atmospheric pressure P and the atmospheric temperature T can be set to 10 seconds. Therefore, notwithstanding anything contained in this document, the real-time disclosed herein can set at a value that is configured to suit specific requirements of an application and hence, may be varied from one application to another.
The controller 222 then determines a threshold retarding power limit Plimit for the retarding grid 206 on the basis of the current air density D. The controller 222 further determines a threshold torque limit To-limit for the traction motor/s 212a, 212b on the basis of the determined threshold retarding power limit Plimit and a current wheel speed S of the machine 100. As such, the system 216 can further include a wheel speed sensor 210, as shown in
In an embodiment as illustrated in
As disclosed earlier herein, the controller 222 is configured to selectively generate the warning signal W on the basis of the threshold torque limit To-limit determined for the traction motor/s 212a, 212b and the current retarding torque To-current at the traction motor/s 212a, 212b. In one embodiment, the controller 222 may be configured to generate the warning signal W at the interface 224 if the current retarding torque To-current at the traction motor/s 212a, 212b approaches the threshold torque limit To-limit determined for the traction motor/s 212a, 212b. For example, the controller 222 may be configured to generate the warning signal W when the current retarding torque To-current at the traction motor/s 212a, 212b is 0.9 times that of the threshold torque limit To-limit determined for the traction motor/s 212a, 212b. In another example, the controller 222 may be configured to generate the warning signal W when the current retarding torque To-current at the traction motor/s 212a, 212b is 0.8 times that of the threshold torque limit To-limit determined for the traction motor/s 212a, 212b. However, in various embodiments of the present disclosure, the controller 222 could be beneficially configured to generate the warning signal W at the interface 224 when the current retarding torque To-current at the traction motor/s 212a, 212b reaches any value that is between 0.7 and 0.99 times the threshold torque limit To-limit determined for the traction motor/s 212a, 212b.
In another embodiment of this disclosure, the controller 222 may be configured to generate the warning signal W at the interface 224 if the current retarding torque To-current at the traction motor/s 212a, 212b exceeds the threshold torque limit To-limit determined for the traction motor/s 212a, 212b. Additionally or optionally, the controller 222 can be further configured to reduce a maximum retarding power Pmax available from the retarding grid 206 to the traction motor/s 212a, 212b if the current retarding torque To-current at the traction motor/s 212a, 212b exceeds the threshold torque limit To-limit determined for the traction motor/s 212a, 212b. In an example, if the threshold torque limit To-limit determined for the traction motor/s 212a, 212b is 4000 N-m, and the current retarding torque To-current at the traction motor/s 212a, 212b is 4100 N-m, then the controller 222 generates the warning signal W and may, additionally or optionally, reduce the maximum retarding power Pmax available in the retarding grid 206. For example, the controller 222 may reduce the maximum retarding power Pmax from 4.5 megawatt (MW) to 4.0 MW.
However, in an alternative embodiment, the controller 222 may allow the maximum retarding power Pmax from the retarding grid 206 to be available to the traction motor/s 212a, 212b for a pre-determined period of time t even after the current retarding torque To-current at the traction motor/s 212a, 212b exceeds the threshold torque limit To-limit determined for the traction motor/s 212a, 212b. This pre-determined period of time t for which the maximum retarding power Pmax continues to be available from the retarding grid 206 to the traction motor/s 212a, 212b corresponds to a time taken by a current temperature Tcurrent of the retarding grid 206 to exceed a maximum allowable operating temperature Tmax pre-defined for the retarding grid 206. For example, if the maximum allowable temperature Tmax for the retarding grid 206 is 500 degree centigrade (C), and the retarding grid 206 is operating at a state i.e., temperature Tcurrent that is beyond the cooling capabilities i.e., the maximum allowable temperature Tmax of the retarding grid 206, then the controller 222 may allow the retarding grid 206 to continue supplying power to the traction motor/s 212a, 212b. However, this supply of power may be allowed by the controller 222 until the current operating temperature Tcurrent of the retarding grid 206 exceeds the maximum allowable temperature Tmax of 500° C. for the retarding grid 206.
In one embodiment as shown in
Furthermore, the controller 222 may be provided with suitable hardware and/or software to perform an estimation of the current temperature Tcurrent at the retarding grid 206. For example, the controller 222 can be programmed to include various pre-defined routines, algorithms, protocols, formulae, or mathematical models to perform the estimation of the current temperature Tcurrent of the retarding grid 206. However, it is to be noted that in various other embodiments of the present disclosure, the controller 222 can also be configured to compute the current temperature Tcurrent of the retarding grid 206 from theoretical models, statistical models, simulation models, or experimental test data pertaining to previous trial runs of the electric drive system 104 or the retarding grids 206 alone.
The maximum allowable operating temperature Tmax, disclosed herein, is generally constant or fixed for a given configuration/size/type of retarding grid 206. However, it may be noted that the maximum allowable operating temperature Tmax could vary depending on the configuration/size/type of the retarding grid 206 employed by the electric drive system 104. This maximum allowable operating temperature Tmax for the retarding grid 206 disclosed herein may be made known to the controller 222 beforehand. For example, if known beforehand, the maximum allowable operating temperature Tmax of the retarding grid 206 could beneficially be set as an upper limit in the controller 222 for performing functions consistent with the present disclosure.
It may be noted that in various embodiments of the present disclosure, the warning signal W generated via the interface 224 is triggered so as to notify the operator of the machine 100 of an imminent overheating of the retarding grids 206 in relative comparison with the maximum allowable operating temperature Tmax for the retarding grids 206. Based on the warning signal W, the operator of the machine 100 can slow down the machine 100 and avoid overheating of the retarding grids 206 by allowing sufficient time for the retarding grids 206 to cool as the retarding grids 206 continue to supply power to the traction motor/s 212a, 212b.
Various embodiments disclosed herein are to be taken in the illustrative and explanatory sense, and should in no way be construed as limiting of the present disclosure. All joinder references (e.g., attached, affixed, coupled, engaged, connected, and the like) are only used to aid the reader's understanding of the present disclosure, and may not create limitations, particularly as to the position, orientation, or use of the systems and/or methods disclosed herein. Therefore, joinder references, if any, are to be construed broadly. Moreover, such joinder references do not necessarily infer that two elements are directly connected to each other.
Additionally, all numerical terms, such as, but not limited to, “first”, “second”, “third”, or any other ordinary and/or numerical terms, should also be taken only as identifiers, to assist the reader's understanding of the various elements, embodiments, variations and/or modifications of the present disclosure, and may not create any limitations, particularly as to the order, or preference, of any element, embodiment, variation and/or modification relative to, or over, another element, embodiment, variation and/or modification.
It is to be understood that individual features shown or described for one embodiment may be combined with individual features shown or described for another embodiment. The above described implementation does not in any way limit the scope of the present disclosure. Therefore, it is to be understood although some features are shown or described to illustrate the use of the present disclosure in the context of functional segments, such features may be omitted from the scope of the present disclosure without departing from the spirit of the present disclosure as defined in the appended claims.
Referring to
At block 408, the controller 222 determines the threshold retarding power limit Plimit for the retarding grid 206 on the basis of the current air density D. At block 410, the controller 222 determines the threshold torque limit To-limit for the traction motor/s 212a, 212b on the basis of the determined threshold retarding power limit Plimit and the current wheel speed S of the machine 100. At block 412, the controller 222 determines the current retarding torque To-current at the traction motor/s 212a, 212b.
Thereafter, as shown at block 414 of
In another embodiment as shown at block 414b of
Moreover, in an embodiment as shown at block 418 of
However, in an alternative embodiment as shown at block 420 of
Embodiments of the present disclosure have applicability for use and implementation in monitoring an operation of the retarding grids 206 present on a machine 100. When implemented in a machine 100, the system 216 of the present disclosure can help protect the retarding grids 206 from overheating during operation. As disclosed earlier herein, in one embodiment, the system 216 can generate a warning signal W if the current retarding torque To-current at the traction motor/s 212a, 212b approaches, i.e., is substantially close to, the threshold torque limit To-limit determined for the traction motor/s 212a, 212b. In another embodiment, the system 216 can be optionally configured to generate the warning signal W if the current retarding torque To-current at the traction motor/s 212a, 212b exceeds the threshold torque limit To-limit determined for the traction motor/s 212a, 212b. Additionally, the system 216 can reduce the maximum retarding power Pmax available from the retarding grid 206 when the current retarding torque To-current at the traction motor/s 212a, 212b exceeds the threshold torque limit To-limit determined for the traction motor/s 212a, 212b.
In yet an other embodiment, the system 216 can be configured to allow the allow the maximum retarding power Pmax from the retarding grid 206 to be available to the traction motor/s 212a, 212b for the pre-determined period of time t in which the current operating temperature Tcurrent may reach the maximum allowable operating temperature Tmax pre-defined for the retarding grid 206. Thereafter, the system 216 can beneficially reduce the maximum retarding power Pmax available from the retarding grid 206 to the traction motor/s 212a, 212b.
By way of embodiments disclosed herein, the controller 222 can be configured to reduce the maximum retarding power Pmax available from the retarding grid 206 at various points of operating conditions of the retarding grid 206. By reducing the maximum retarding power Pmax available from the retarding grid 206, the controller 222 can beneficially prevent the retarding grids 206 from overheating during operation. Moreover, as the controller 222 triggers warning signals W at the interface 224, the controller 222 can assist operators in knowing when to slow down the machine 100 i.e., lower a wheel speed S of the machine 100 and/or reduce power demands from the machine 100 during operation. This way, the operators can prolong an operating time of the retarding grids 206 with the maximum retarding power Pmax from the retarding grids 206 before such maximum retarding power Pmax is reduced.
With implementation of embodiments disclosed herein, manufacturers can prolong an operational or service life of the retarding grids 206 thereby mitigating costs, time, and effort previously incurred with repair and/or replacement of retarding grids 206 that have overheated and hence, operated beyond their maximum allowable operating temperature Tmax.
While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems, methods and processes without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.
