The present invention relates generally to motor circuits, and more particularly, to motor circuits that involve multiple brush-type motors.
Convection air cooling is widely used in many industries, including the automotive industry. In automobiles, for example, heat from the internal combustion engine is transferred via coolant fluid to a radiator element. The radiator element then employs air cooling to dissipate the heat from the heated coolant fluid. Other devices, such as computers and other electronic circuits, often employ direct air cooling.
In any event, the quantity of heat transferred by air cooling is related to the size of the fan, as well as other factors, including fan speed and blade shape. However, fan size is often limited by the environment in which the fan is used. For example, the fan size in an automobile is limited by the amount of available space in the engine compartment of the automobile. Because fans rotate, any increase in fan size requires additional space in every radial direction.
One way to increase the effective cooling without requiring additional space in every radial direction is to employ multiple fans. For example, employing two identical, adjacent fans increases air flow while only requiring additional space in one direction. As a result, two smaller fans may fit more conveniently than one large fan in an application that has excess room in the horizontal direction but little or no excess room in the vertical direction.
An application that benefits from a multiple fan arrangement is the cooling system of an automobile. In many automotive designs, the use of two adjacent fans is more easily accommodated than a single large fan. One prior art automotive fan system employed two electrically commutated (xe2x80x9cECxe2x80x9d) motors which rotated the fans blades. Associated with each motor in such a system was a driver circuit that included one or more drive switches, a snubber, and other elements typically associated with EC motors.
One drawback to the above system involved the necessity of various wiring elements and harnesses to deliver the DC power to the driver circuits and motors, as well as control information to the driver circuits. In particular, EC motors typically require signals that turn the various driver circuit switches on and off at appropriate times during the rotation of the motor. Such control signals may be used to control the speed of the motors. In general, the source of the control signals is the engine control unit (ECU) of the automobile, and the source of DC power is the vehicle battery. Accordingly, multiple wires must be run to each of the two EC motors to allow control thereof. In addition, the EC motors require high frequency operation of the driver circuit switches to allow effective operation of the fan motor. Such high frequency switching undesirably creates electromagnetic interference issues that require mitigation.
Accordingly, there is a need for a dual motor system that avoids one or more of the shortcomings associated with the use of dual EC motors described above. Such need exists particularly in the automotive field for use of the dual motors for cooling fan purposes.
The present invention addresses the above need, as well as others, by providing a motor circuit and associated method that employs multiple brush-type motors that are controlled through a single switching device. The use of single switch control reduces the amount of wires that must be run from a control signal generator and/or DC power supply to a shroud or other fixture in which the motors are mounted. In another aspect of the invention, the use of brush-type motors allows for the use of low frequency switching signals, thereby eliminating or reducing electromagnetic interference issues.
A first embodiment of the present invention is a motor circuit that includes a first brush-type motor, a second brush-type motor, a switch, and a pulse width modulation circuit. The first brush-type motor has a first voltage connection and a second voltage connection, the second voltage connection adapted to be coupled to a source of DC voltage. The second brush-type motor has a third voltage connection and a fourth voltage connection, the fourth voltage connection adapted to be coupled to the source of DC voltage. The switch has a control input, a first contact and a second contact, the first contact coupled to the source of DC voltage, and the second contact coupled to the first voltage connection and the third voltage connection. The switch is operable to selectively connect the first contact to the second contact based on a voltage at the control input. The pulse width modulation circuit is operable to generate a pulse width modulated (PWM) signal. The pulse width modulation circuit is operably coupled to provide the PWM signal to the control input of the switch.
Another embodiment of the present invention is a fan assembly that includes a first fan blade set, a second fan blade set, a first brush-type motor, a second brush-type motor, a shroud, a switch and a wiring harness. The first brush-type motor has a first voltage connection and a second voltage connection and is operably coupled to rotate the first fan blade set. The second brush-type motor has a third voltage connection and a fourth voltage connection and is operably coupled to rotate the second fan blade set. The shroud supports the first brush-type motor and the second brush-type motor. The switch is secured to the shroud. The switch has a control input, a first contact and a second contact, the second contact operably coupled to the first voltage connection and the third voltage connection. The switch is operable to selectively connect the first contact to the second contact based on a voltage at the control input. The conductor harness includes a first DC conductor, a second DC conductor, and a control signal conductor. The conductor harness is affixed at a first end to the shroud. The first DC conductor is operably coupled to the second voltage connection and the fourth voltage connection, the second DC conductor is operably coupled to the first contact of the switch, and the control signal conductor is coupled to the control input.
In a preferred implementation the first DC conductor and the second DC conductor are coupled to positive and negative terminals of a DC power source, such as a battery. The control signal conductor is preferably coupled to a source of PWM signals.
The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings.