Abstract:
Hydraulically actuated aerial lift trucks typically have a primary hydraulic pump system driven by the vehicle&#39;s engine and a backup pump system driven by a direct current motor. Due to infrequent use of such motors, they are vulnerable to failure due to corrosion of the brush/commutator interface or seizing of the motor bearings. A remote power unit is provided to periodically run the back up motor for brief periods to maintain the motor in running condition. Voltage levels across the motor terminals are monitored for correspondence to failure indicating levels.

Description:
REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Application 60/477,908 filed Jun. 12, 2003. 

   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The invention relates to the control and monitoring of electric motors and more particularly to a system providing exercising of and failure indicating for a direct current motor. 
   2. Description of the Problem 
   Utility vehicles are often advantageously supplied with auxiliary equipment, the operation of which is supported by the vehicle. Such auxiliary equipment can include hydraulically powered, aerial lift platforms as are often used for the repair of electrical power distribution lines. Typically, a hydraulic lift platform will be driven by a primary pump which is in turn driven by the vehicle&#39;s engine. In some applications, a back up hydraulic system is provided having a pump powered by a direct current motor energized by the vehicle&#39;s battery. 
   Back up direct current motors fail more often than they should due to harsh,operating environments and infrequent use. Failures of the motors can stem from corrosion between the motor brushes and commutator or from motor bearings seizing. It would be desirable to provide operators of utility vehicles indication of the status of these motors and improve the reliability by limiting the problems caused by lack of regular use. 
   SUMMARY OF THE INVENTION 
   According to the invention there is provided a motor vehicle having an engine and a direct current electrical power system. Vehicle accessory control is provided by a first controller area network including a remote power module. The remote power module includes a three state input and a control signal output. A direct current motor is connectable to the direct current electrical system for energization. A motor control switch connected by one terminal to the direct current electrical power system provides the usual method for energizing the direct current motor through the agency of an energization relay. This energization relay is exploited to provide for automated testing and exercise of the motor by the remote power module. The energization relay has an input terminal connected both to the control signal output of the remote power module and to a second terminal for the motor control switch. The power output terminal for the relay is connected to the direct current motor and to the three state input of the remote power module. Voltage levels appearing on the three state input (which is biased to first elevated voltage) indicate normal operation or failure. Periodic, momentary application of a control signal by the remote power module exercises the motor to prevent bearing seizure and to clean brushes and commutators. 
   Additional effects, features and advantages will be apparent in the written description that follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention,,are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a simplified illustration of a truck mounted aerial lift assembly for locating an operator in various raised positions. 
       FIG. 2  is a high level schematic of a vehicle electrical and hydraulic control system incorporating the invention for the truck of FIG.  1 . 
       FIG. 3  is a schematic of a remote power module and an emergency pump motor energization relay used in a preferred embodiment of the invention. 
       FIG. 4  is a flow chart of a program executed by a vehicle body controller to implement the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the drawings, and particularly to  FIG. 1 , an example of a mobile aerial lift unit is illustrated in simplified presentation for clarity of illustration. The mobile aerial lift apparatus includes a truck:  1  with an aerial lift unit  2  mounted to the bed thereof. The aerial lift unit  2  includes a lower boom  3  and an upper boom  4  pivotally interconnected to each other and to the truck bed through support  6  and rotatable support bracket  7 . A basket  5  is shown secured to the outer end of, the upper boom  4  within which the operating personnel are located during the lifting to and locating within a selected work area in accordance with known practice. Basket  5  is typically pivotally attached to the out end of the boom  4  to maintain a horizontal (level) orientation at all times. The aerial lift unit is mounted to the truck bed through support  6 . A rotatable support bracket  7  is secured to the support  6  and projects upwardly. The lower boom  3  is pivotally connected as at pivot  8 , to the rotatable support bracket  7 . A lifting lower boom cylinder unit  9  is interconnected between bracket  7  and the lower boom  3 . In the illustrated embodiment, a pivot connection  10  connects the lower boom cylinder  11  of unit  9  to the bracket  7 . A cylinder rod  12  extends from the cylinder  11  and is pivotally connected to the boom  3  through a pivot  13 . Lower boom cylinder unit  9  is connected to either of two supplies of a suitable pressurized hydraulic fluid, to lift and lower the assembly as desired. 
   The outer end of the lower boom  3  is interconnected to the lower and pivot end of the upper boom  4 . A pivot  116  interconnects the outer end of the lower boom  3  to the pivot end of upper boom. An upper boom/compensating cylinder unit or assembly  117  is connected between the lower boom  3  and the upper boom for pivoting the upper boom about pivot  116  for positioning of the upper boom relative to the lower boom. The upper boom/compensating cylinder unit  117  is constructed to permit independent movement of the upper boom  4  relative to lower boom  3  and to provide a compensating motion between the booms to maintain the upper boom raising with the lower boom and is similarly connected to the sources of pressurized hydraulic fluid. Conventionally, aerial lift unit  2  requires positive hydraulic pressure to support operation of lower boom cylinder  11  or the upper boom cylinder  117  for lifting or lowering. 
     FIG. 2  is a block diagram schematic illustrating electronic control of truck  1 , based on a controller area network technology and a body controller/computer  24 . Collectively, bus/data link  18  and the various nodes attached thereto form a public controller area network (CAN) conforming to the SAE J1939 standard. A second data link  19  also conforms to the SAE J1939 standard but is used for specialized signals relating to vehicle manufacturer specific accessories. Controller area networks are networks which do not have destination addresses for nodes attached to the networks, but rather provide for transmission of data in packets, identified as to the source, message type and priority. The nodes are programmed as to whether to respond to a packet based on one or more of the three identifiers. Many message types are predefined by the SAE J1939 standard. However, the SAE J1939 standard allows the definition of proprietary messages which conform in structure to the standard. 
   Active vehicle components are typically controlled by one of a group of autonomous, vocational controllers. The vocational controllers include a gauge cluster controller  14 , an engine controller  20 , a transmission controller  16 , and an antilock brake system (ABS) controller  22 . These controllers have publicly defined message types and are coupled to one another and with body controller/computer  24  by serial data bus  18 . The autonomous controllers communicating over serial data bus  18  include local data processing and programming and are typically supplied by the manufacturer of the controlled component. For each autonomous controller there is a defined set of variables used for communications between the autonomous controller and other data processing components coupled to the network. A body of warning lights  45 , under the direct control of gauge controller  14 , may be assigned to respond to as programmed into body controller  24 . This includes assigning a warning light to be activated upon a failure indication from remote power module  36 . Body controller  24  is programmed in certain circumstances to translate signals from one network to the other. 
   Remote power module (RPM)  36  is programmed to respond to body computer  24  commands relating to systems, typically electrical accessories, located on truck  1 . In the present, preferred embodiment, RPM  36  is used to trip a relay  46  used to power a direct current motor  48  from the vehicle&#39;s battery  21 . Control of an RPM  36  is then implemented in the body controller  24  and communicated to the RPM over a private data link  19 . Remote power module  36  includes minimal processing power and operates essentially as a slave device to body computer  24 . RPM  36  can be made independent. 
   The preferred application of the present invention is to monitor the condition of, and to exercise, an electrical motor  54  which provides a power to a back up/emergency pump  56  which in turn provides pressurized hydraulic fluid to an hydraulic system  58  such as may be used to lift and lower aerial lift unit  2 . The primary system for energizing hydraulic system  58  is primary hydraulic pump  60 , driven by engine  30 . Should engine  30  fail, for example as a result of running out of fuel, stranding a suspended worker in an elevated basket  5 , the vehicle&#39;s battery power may be used to power motor  54  and provide hydraulic drive fluid under pressure from pump  56  to hydraulic system  58  allowing the basket to be lowered. Electrical power for vehicle  11 , and for the motor supported by RPM  36 , can be supplied by one or more lead acid batteries  21 , or by an alternator, which is part of charging system  47 . Electrical power system  51  is supplied from batteries  21  upon moving a key switch (starter  53 ) from an off position to an accessory or on position, without cranking the vehicle engine  30 , or from charging system  47  when the engine is running and driving the charging system  47 . 
   The preferred application of the present invention is to monitor the condition of, and to exercise, an electrical motor  54  which provides a power source to a back up/emergency pump  56  which in turn provides pressurized hydraulic fluid to an hydraulic system  58  such as may be used to lift and lower aerial lift unit  2 . The primary system for energizing hydraulic system  58  is primary hydraulic pump  60 , driven by engine  30 . Should engine  30  fall, for example as a result of running out of fuel, stranding a suspended worker in an elevated basket  5 , the vehicle&#39;s battery power may be used to power motor  54  and provide hydraulic drive fluid under pressure from pump  56  hydraulic system  58  allowing the basket to be lowered. Electrical power for vehicle  11 , and for the motor supported by RPM  36 , can be supplied by one or more lead acid batteries  21 , or by an alternator, which is part of charging system  47 . Electrical power system  51  is supplied from batteries  21  upon moving a key switch (starter  53  ) from an off position to an accessory or on position, without cranking the vehicle engine  30 , or from charging system  47  when the engine is running and driving the charging system  47 . 
   Referring to  FIG. 3 , a remote power module  36  and its application to providing condition monitoring and exercising of an emergency electrical motor  54  is illustrated in greater detail. Remote power module  36  comprises a CAN transceiver circuit  68  and a microcontroller  66 . Microcontroller  66  controls the switching state of a plurality of FET switches, one of which (FET switch  64 ) is shown, which may be used to provide 12 volt control signals on an output port. FET  64  cannot handle sufficient current to drive motor  54 , so the FET is used instead to control the switching of a pump energization relay  46 . The gate of FET switch  64  is controlled by microcontroller  66  and the output of FET switch  64  is coupled to a DIN  86  input of relay  46 . RPM  36  has a 3 state input  84  coupled to one terminal of motor  54 . Input  84  corresponds to node  71 , the midpoint of a voltage divider circuit formed by resistors  70  and  72 . Microcontroller  66  is coupled by an input terminal  186  to node  71  between resistors  70  and  72 , which have relatively high resistances. Microcontroller  66  monitors the voltage at node  71  which provides an indication of the states of motor  54  brushes. Resistor  70  is connected between node  71  and an external source of accessory voltage suitable for establishing a first logic voltage level on, node  71  for RPM  36 . If motor  54  is not running, the voltage on node  71  will be pulled to ground by a short circuit drop through the (non-rotating) motor to ground. Insufficient current is supplied through resistor  70  to overcome the inertia of motor  54 , with the result that the motor does not rotate.. If the brush to commutator contacts are good, the motor will exhibit a negligible resistance. The current drawn through resistor  70  is a negligible drain on vehicle battery power. When motor  54  is not running microcontroller  66  should see a zero voltage on node  71 . If the brushes or commutators of motor  54  are corroded and not conductive to electricity, the voltage on node  71  rises to a six volt drop across resistor  72  to ground, which is detected by microcontroller  66  and reported over data link  19  to body computer  24  using CAN controllers  68  and  76 . Microcontroller  74  in body computer  24  interprets a six volt voltage on motor  54  as a failure indication, and instructs electronic gauge controller  14  over the public data link  18  using CAN controllers, 78  and  80  to instruct microcontroller  82  to illuminate a light  45 A designated to serve as a failure indicator. 
   Emergency pump motor  54  is normally energized by closure of a hard wired emergency pump control switch  62 , which in turn applies 12 volts to the DIN  86  input of relay  46 , closing the relay to close, and the motor to be energized directly from battery  21 . Emergency pump relay is alternatively closed by sourcing the 12 volt control signal for DIN  86  from FET  64 . This is effected by microcontroller  66  under instruction from microcontroller  74 . In effect body computer  24  and remote power module  36  combine to provide a relay controller and motor input terminal voltage sensor. Energization of direct current motor  54  is done periodically and briefly to exercise motor  54 . This helps keep brushes and commutator contacts clean and helps prevent bearings from seizing. When relay  46  is closed, the voltage on node  71  should rise to 12 volts, allowing for a momentary drop in battery voltage when the load of turning motor  54  on is first imposed. The voltages occurring on node  71  are reported by microcontroller  66  to microcontroller  74 , and if they do not track expected values, microcontroller  74  issues the appropriate instruction to the electronic gauge cluster  14  to illuminate failure LED (light)  45 A. Failure of microcontroller  66  to see a rise in voltage or three state input  84  indicates failure, as may be associated with seized bearings. 
   Referring to  FIG. 4 , a flow chart illustrates the tests executed by microcontroller  74  for monitoring motor  54 . First, with the initial condition that motor  54  is not energized, the voltage on the 3 state input is read and compared to nominal values at step  90 . If the voltage is high, that is in the range of 6 volts, the program executes step  91  and instructs the gauge controller to illuminate a failure indicator light. If the voltage level is nominal, that is close to zero volts, it is determined if the time is appropriate to exercise (run) the motor. If not, the program loops back to sample the voltage level appearing on 3 state input  84  (after an appropriate delay). If yes, a gate control signal is applied to FET  64  (step  93 ) for a brief period of time to briefly run motor  54 . Again the voltage appearing on the 3 state input is monitored and compared to expected values (step  94 ). If the voltage fails to increase, typically to about the range of 12 volts, a failure is indicated and step  95  is executed to generate an instruction to indicate failure. If voltage does rise, operation is likely nominal and the program loops back to begin again. 
   The invention provides for monitoring and maintaining a brush DC motor. By applying a low power, operating voltage signal to the motor, problems with the brushes and commutators may be detected and indicated when the blocked rotor, short circuit path through the motor is interrupted and the trickle current supported by the voltage source is interrupted. A back up relay activation circuit allows the motor to be periodically exercised to prevent seizure of the motor bearings. 
   While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.