Electricity: motive power systems – Battery-fed motor systems
Reexamination Certificate
2000-11-07
2002-01-29
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Battery-fed motor systems
C318S269000, C180S205200, C310S06800R
Reexamination Certificate
active
06342769
ABSTRACT:
BACKGROUND OF THE INVENTION
This application relates to an electronic control system. It relates especially to a throttle/brake control system for a motorized wheel hub.
There are numerous vehicles in use today which have battery-powered electric motors to drive the wheels of the vehicle. These include bicycles, adult tricycles, wheel-chairs, motor scooters, golf carts, all terrain vehicles, etc. In many such vehicles, the electric motor is mounted to the vehicle frame with the motor output being coupled to the wheels by way of a chain drive, gear train or the like. More preferably, the motor is incorporated right into the wheel hub thereby minimizing the size, weight, complexity and cost of the drive system. Examples of such in-hub motors are disclosed in U.S. Pat. Nos. 572,036; 2,514,460 and 3,921,741.
A particularly desirable, modular motorized wheel hub assembly for vehicles of this type is disclosed in U.S. Pat No. 6,100,615, the contents of which is hereby incorporated herein by reference.
With modular motorized wheels of the type of interest here, it is essential that suitable control means be provided which are capable of applying the appropriate control voltages to the wheel motor to enable the wheel motor to operate in a reliable fashion. Invariably, such control means include a hand or foot-operated throttle or throttle/brake control which the vehicle operator may manipulate to accelerate the decelerate the associated vehicle. For the most part, conventional electric motor controllers, particularly those used to control electric bicycles, golf carts and other electric vehicles operate satisfactorily. However, they do have certain disadvantages which limit their wider use and application. More particularly, some such controllers are complex and costly. Others require a large number of moving, contacting parts or brushes which are prone to wear thereby limiting the useful life of the controller. Others are not suitable for all-weather outdoor applications, such as required on bicycles and other vehicles.
Also, those prior controllers used to control brushless motors of the type disclosed in the above patents often do not allow the motor to operate in a regenerative braking mode or if they do, they require the use of the Hall sensors or the like to sense the angular position of the motor rotor to effect communication of the motor in all four operating quadrants. That is, since, synchronous DC motors and other permanent magnet machines are frequently used in applications where direct control of the torque applied to the load is required, it is desirable to provide four quadrant operation, with both positive and negative torque and speed in such applications; see FIG.
10
.
When the machine is operating in quadrants one and three in
FIG. 10
, it is operating as a motor and energy is being transferred from the DC source to the load. During operation in quadrants two and four the machine is used as a generator, and energy is transferred from the mechanical load to the DC voltage source. The motor shaft torque for a rotary machine (or force for a linear machine) is proportional to the winding currents applied to the motor and the torque constant of the motor, assuming that the motor is properly commutated. Proper commutation is required to generate a magnetic field in the motor stator windings that produce the desired force when acting against the permanent magnet field of the rotor. This is normally accomplished by utilizing a rotor position sensor or sensors to tell inverter circuitry driving the motor when to commutate the current from winding to winding to maintain this relationship.
The most common implementation of this principle is with a three phase brushless DC motor such, as shown at M in
FIG. 11
, wherein the rotor position is detected with Hall effect devices H placed to indicate the angular position of the magnetic field produced by the rotor. In such a system, the commutation logic L switches the drive current to three high side switches S and three low side switches S′ in an inverter I to maintain the proper-field relationship. The rotating field of the rotor produces a back electromotive field (EMF) or voltage in the motor stator windings W. The applied voltage must overcome this back EMF for current to flow in the direction to produce motoring torque. The back EMF is proportional to the speed of the rotor and when the back EMF is equal to the applied voltage, motoring current cannot be generated. This speed is referred to as “base speed”. Operation is normally limited to speeds below base speed. With operation below base speed, the back EMF produced is, by definition, less than the applied DC voltage. Operation of the machine as a generator, where mechanical energy is supplied to the DC source, requires that the back EMF voltage be boosted to a value at least equal to the applied voltage. This is normally accomplished by applying a voltage to the motor in the inverse polarity to the direction of rotation. This inverse commutation causes the stator current to increase rapidly. The increased current stores energy in the leakage inductance of the stator windings that, when the commutation is returned, adds to the back EMF to produce a voltage, thereby allowing current to flow in the stator. The
FIG. 11
circuit produces this effect and generates a torque in the motor M that is independent of the direction of rotor rotation, and it works in all four quadrants shown in FIG.
10
. The commutation logic for the six switches S′, of that circuit is shown in FIG.
12
. An example of such a brushless DC motor control is described, for example, in U.S. Pat. No. 6,034,493.
The motor M in
FIG. 11
is thus driven in a six step per cycle sequence. This sequence is reversed to produce torque in the opposite direction. When the machine is operated in quadrants two and four (FIG.
10
), the current produced by conduction of the switches S in the direction opposite to the rotation produces a current ramp up in the leakage inductance required to boost the back EMF to the source voltage level. The source current is measured by a current sensor C and the polarity of it is reversed by a switchable 1/−1 amplifier A as a function of the direction of commutation. This arrangement maintains a unidirectional current in a hysteretic comparator H. The hysteresis in that comparator determines the frequency at which the commutation will be switched. The motor current is thus completely controlled, with the maximum and minimum being set by the hysteretic comparator H.
The circuit in
FIG. 11
requires that the position of the rotor field be known to the commutation logic L. The rotating field of the rotor induces a voltage in the stator windings W that can be detected and used to determine the rotor position as well. However, such a position sensing system has a problem with operation at stall and low speeds where the back EMF voltage produced by the motor rotor is insufficient. There are several known methods of sensing the back EMF to produce the commutation logic. These methods require sensing the field in the stator winding W that is not being driven to determine the rotor position. However, when the commutation field is reversed for second and fourth quadrant operation, this logic does not produce the required results. Thus, conventional motor drive circuits based on such sensorless commutation methods do not allow operation in the second and fourth quadrant shown in FIG.
10
. Rather, sensorless braking is normally accomplished by shorting out the stator windings and allowing the motor current produced to dissipate in the winding resistance. This can produce excessive currents which cannot be controlled as they do not flow through the current sensor C, but circulate within the stator windings W. Additionally, energy input from a mechanical source, such as a pedal crank in the case of a bicycle is not recovered, but is dissipated in the motor, potentially producing excessive motor temperatures.
Alternate methods of producing braking torque have been explored and
Birkestrand Orville J.
Peterson William A.
Cesari and McKenn
Dang Khanh
LandOfFree
Electronic throttle/brake control system for monitorized... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electronic throttle/brake control system for monitorized..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electronic throttle/brake control system for monitorized... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2856000