CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 12/896,967 filed Oct. 4, 2010 as a continuation of U.S. patent application Ser. No. 12/487,695 filed on Jun. 19, 2009 as a continuation of U.S. patent application Ser. No. 11/966,289 filed on Dec. 28, 2007 as a continuation of U.S. patent application Ser. No. 11/260,867 filed on Oct. 27, 2005. This application claims the benefit of U.S. Provisional Application No. 60/623,149, filed on Oct. 28, 2004. The specifications of the above application are incorporated herein by reference in their entirety.
The present disclosure relates generally to a brushless, alternating current (AC) drive system for providing motive power to drive wheels of an electrically operated vehicle.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
All electric motors, such as alternating current (AC) motors or direct current (DC) function on a principle that two magnetic fields in proximity to one another have a tendency to align. One way to induce a magnetic field is to pass current through a coil of wire. If two coils with current passing through them are in proximity to each other, the respective magnetic fields that are generated have a tendency to align themselves. If the two coils are between 0 and 180 degrees out of alignment, this tendency may create a torque between the two coils. An arrangement where one of these coils is mechanically fixed to a shaft and the other is fixed to an outer housing is known as an electric motor. The torque produced between these coils may vary with the current through the coils.
AC motors may encompass a wide class of motors, including single/multiphase, universal, servo, induction, synchronous, and gear motor types, for example. The magnetic field generated by AC motors may be produced by an electromagnet powered by the same AC voltage as the motor coil. The coils that produce the magnetic field are traditionally called the “field coils” while the coils and the solid core that rotates is called the armature coils.
AC motors may have some advantages over DC motors. Some types of DC motors include a device known as a commutator. The commutator ensures that there is always an angle between the two coils, so as to continue to produce torque as the motor shaft rotates through in excess of 180 degrees. The commutator disconnects the current from the armature coil, and reconnects it to a second armature coil before the angle between the armature coil and field coil connected to a motor housing reaches zero.
The ends of each of the armature coils may have contact surfaces known as commutator bars. Contacts made of carbon, called brushes, are fixed to the motor housing. A DC motor with a commutator and brushes may be known as a ‘brushed’ DC motor, for example. As the DC motor shaft rotates, the brushes lose contact with one set of bars and make contact with the next set of bars. This process maintains a relatively constant angle between the armature coil and the field coil, which in turn maintains a constant torque throughout the DC motor's rotation.
Some types of AC motors, known as brushless AC motors, do not use brushes or commutator bars. Brushed DC motors typically are subject to periodic maintenance to inspect and replace worn brushes and to remove carbon dust, which represents a potential sparking hazard, from various motor surfaces. Accordingly, use of a brushless AC motor instead of the brushed DC motor may eliminate problems related to maintenance and wear, and may also eliminate the problem of dangerous sparking. AC motors may also be well suited for constant-speed applications. This is because, unlike a DC motor, motor speed in an AC motor is determined by the frequency of the AC voltage applied to the motor terminals.
There are two distinct types of AC motors, AC synchronous motors and AC induction motors. A synchronous motor consists of a series of windings in the stator section with a simple rotating area. A current is passed through the coil, generating torque on the coil. Since the current is alternating, the motor typically runs smoothly in accordance with the frequency of the sine wave. This allows for constant, unvarying speed from no load to full load with no slip.
AC induction motors are generally the more common of the two AC motor types. AC induction motors use electric current to induce rotation in the coils, rather than supplying the rotation directly. Additionally, AC induction motors use shorted wire loops on a rotating armature and obtain the motor torque from currents induced in these loops by the changing magnetic fields produced in the field coils.
Conventional electric motor driven vehicles such as golf cars and small utility vehicles are DC powered, and primarily powered by a shunt-type DC drive system. The shunt-type DC motor has replaced many of the older series wound DC motors for powering vehicles such as golf cars. A shunt-type DC motor has armature and field windings connected in parallel to a common voltage source, a configuration which offers greater flexibility in controlling motor performance than series wound DC motors. However, these shunt type motors still present maintenance and potential spark hazard problems. It is not heretofore believed that a brushless AC drive system has been developed which provides the motive force for driving wheels of a vehicle such as a golf car.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. Throughout the disclosure, like elements are represented by like reference numerals, which are given by way of illustration only and thus are not limitative of the various embodiments.
FIG. 1 is a block diagram an AC drive system in accordance with various embodiments.
FIG. 2 is a block diagram of an instrument panel in accordance with an various embodiments.
FIG. 3 is a block diagram illustrating an arrangement of CAN communication chips in accordance with various embodiments.
FIG. 4 is a block diagram illustrating a front wheel speed sensor in accordance with various embodiments.
FIG. 5 is a block diagram illustrating a multiple or all wheel drive arrangement in accordance with various embodiments.
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FIG. 1 is an exemplary block diagram of an AC drive system in accordance with various embodiments. In FIG. 1, there is shown an AC drive system 100, which may include a three-phase (3φ) AC motor 110, such as an induction motor or permanent magnet motor, and a matched AC drive motor controller 120 to be used in conjunction with an electrically operated vehicle 190 such as a golf car and/or a small utility vehicle. As will be described in more detail below, AC drive system 100 may provide tractive power, service brake functionality, and recovery and conversion of kinetic energy from vehicle 190 motion to potential energy in the form of electromotive force (EMF).
Referring to FIG. 1, in response to motor controller 120, motor 110 may provide motive force to drive wheels 198 imparting motive force or tractive energy via axle 192 through locking differential 194 and shafts 196 to rear wheels 198. Motor 110 may be operatively connected to an electrically actuated brake 180 under the control of motor controller 120 via signal line 185 and/or motor 110. Additionally, throttle control for a throttle (accelerator pedal) 170 may be provided via a throttle position sensor 175 and a throttle enable sensor 177, based on signals received over lines 126 from motor controller 120. Further, AC drive system 100 may include a service brake pedal 160 to operatively control braking by motor 110 in accordance with signals from motor controller 120. Movement of service brake pedal 160 is detected by one or both of sensors which generate control signals sent to motor controller 120 via communication lines 122. Sensors associated with brake pedal 160 may include a brake position sensor 163 and a full stroke sensor 165, to be described in further detail below.
Motor controller 120 may be in operative communication with one or more of a portable battery pack 130, charger 140, an external network 150, and other external devices or outputs 155 such as a reverse alarm sensor via a direct connection or a controller area network (CAN) bus 145 and associated connector interfaces, as shown in FIG. 1. Operative control and data exchange between motor controller 120, charger 140 and external network 150 are described in further detail below.
The AC system logic for AC drive system 100 may include a series of drive inputs and drive outputs. The following describes exemplary inputs to and outputs from the system logic as implemented in intelligent devices such as motor controller 120. It will be understood by one skilled in the art that input and output parameters or signals other than described below may be implemented with the exemplary AC drive system.
FIG. 2 is a block diagram of an exemplary instrument panel in accordance with various embodiments. Referring to FIG. 2, a suitable instrument panel 200 may include a key switch 220, forward, neutral and reverse (FNR) switch 230, low battery indicator 235, amp-hour meter 240, LED 245, controller indicator 248, and reverse alarm indicator 250. Controller indicator 248 may indicate a condition, such as normal status, warning, and the like, for AC controller 120 or other components of the AC motor control system. LED 245 may be embodied as a single LED or multiple LEDs and may be configured to display suitable numeric or alphanumeric error codes. The error codes may include, but are not limited to error codes related approaching threshold or warning conditions of AC motor 110, motor controller 120, battery pack 130, service brake pedal 160, electrically actuated brake 180, or the like.
Vehicle 190 may also include a suitable run/tow switch 210 provided at a desired location for actuation by an operator of vehicle 190. The run/tow switch 210 may be located on the vehicle 190 at a place that is convenient for towing, yet a location where the switch may not be easily activated from the operator's (or passenger's) position, so as to avoid a purposefully or inadvertently cycling of switch 210 during normal driving evolutions of the vehicle 190.
When the run/tow switch 210 is selected to RUN, motive power may be provided via motor controller 120 and motor 110 to drive vehicle 190. When the run/tow switch 210 is switched to TOW, the electric brake 180 may be de-energized for a time period sufficient to actuate electric brake 180 and motor controller 120, such as one (1) second, and may apply a given pulse width modulated (PWM) percentage, such as a 40% by way of example hold on the electric brake 180 thereafter. As will be described in greater detail herein, this may allow the vehicle 190 to be towed at speeds up to or slightly above rated motor speed, which may be approximately 4650 RPM for an exemplary golf car application. With the run/tow switch 210 in TOW, a towing mode may be enabled that provides zero wheel torque.
Another input to the system logic may be provided via a key switch 220 having ON/OFF switch positions. With the key switch 220 set to the ON position, drive logic power may be enabled to motor controller 120 and power may be enabled to the electric brake 180. Setting the key switch 220 to OFF position may disable the logic power to the motor controller 120 and de-energize the electric brake 180.
Actuation of the FNR switch 230 to FWD may enable drive logic power for selecting a forward drive direction. Forward speed may be up to rated motor speed, or a vehicle speed in accordance with the rated motor speed. Actuation of the FNR switch 230 to NEUTRAL may disable drive logic power for selecting either a forward drive direction or reverse drive direction, so as to place AC motor 110 in a free-wheeling mode at a relatively constant RPM (i.e., idle). Actuation of the FNR switch 230 to REV may enable drive logic power for selecting a reverse drive direction. This switch position may optionally sound a reverse alarm. Reverse direction speed may be desirably limited to less than the rated speed, such as 60% of maximum motor speed, or a vehicle speed of approximately 10 MPH.
Another drive input to the system logic may include a throttle position sensor 175, as shown in FIG. 1. The throttle position sensor 175 may be located in signal line 126 between the accelerator pedal or throttle 170 and motor controller 120 and may be configured to output an analog voltage that may be converted to a digital signal in the A/D converter of controller 120. The voltage may vary between about 0 to 5.0 volts in accordance with the position or depression of throttle 170. In an exemplary configuration, 0-0.5 volts may indicate a 0 RPM commanded speed and 4.5 volts or greater may indicate a maximum commanded motor speed In other words, a 0.5 volt output corresponds to 0% commanded motor speed or zero RPM. A 4.5 or greater volt output corresponds to 100% commanded motor speed in the forward direction (4650 RPM) and approximately 60% commanded motor speed in the reverse direction (2790 RPM). The throttle position sensor 175 may be embodied as a suitable potentiometer or Hall Effect sensor, and may thus provide a limitation on actual speed to 100% of motor speed in either the forward or reverse directions.
Another drive input to the system logic may be via throttle enable sensor 177. The throttle enable sensor 177, also occasionally referred to as a pedal-up sensor, may sense one of a drive mode and a pedal-up mode, based on the position of the accelerator pedal or throttle 170. When sensing the drive mode (at any point the pedal is depressed) the throttle enable sensor 177 energizes a main contactor to enable operation of AC motor 110 and to energize the electric brake 180 so as to enable drive power, via motor controller 120 and motor 110, to wheels 198. If the pedal-up mode is sensed (indicating that the accelerator pedal is fully ‘up’ and not depressed, the main contactor may be de-energized to disable drive.
Accordingly, exemplary input conditions that may be met to provide motive power to wheels 198 could include the key switch 220 placed in ON and the FNR switch 230 selected to either the FWD or REV position, the run/tow switch 210 selected to RUN, brake position sensor 163 receiving a 0% braking command from motor controller 120, and a battery 130 state of charge (SOC) of at least 20%. These are merely exemplary conditions to provide motive power, other conditions may be set within the ordinary skill of the art.
Another drive input to system logic may be provided via brake position sensor 163. Similar to the throttle position sensor 175, the brake position sensor 163 is located in a signal line 122 between the brake pedal 160 and motor controller 120 and outputs an analog value (voltage) that is converted to a digital signal in the A/D converter of motor controller 120. For example, sensing of less than 0.5 volt output from brake position sensor 163 may represent 0% braking and the enabling of motive power to the wheels 198. Between 0.51 to 1.0 volts output, actual speed may be maintained via regenerative braking and no motive power may be applied to wheels 198, for example. Between 1.01 to 4.0 volt output, a proportional deceleration speed ramp may increase with increasing input voltage. The start and finish conditions may be adjustable, for example. For a 4.1 to 4.5 or greater volt output from brake position sensor 163, commanded motor speed may be 0% and the electric brake 180 may be de-energized (such as via a control signal sent by motor controller 120 over signal line 185, as shown in FIG. 1, for example) to enable electric brake 180 to apply a braking torque or braking pressure upon motor 110. The braking function may be tunable in accordance with course conditions, such as wet, dry, hilly, and flat terrain, and vehicle performance to provide a consistent feel to the braking operation.
The logic functions of the brake position sensor 163 may override and maintain priority over any throttle input to throttle 170, for example. The logic function for the brake position sensor 163 may operate with the key switch 220 to ON, the FNR switch 230 to either FWD or REV, and the run/tow switch 210 in either RUN or TOW, the throttle enable sensor 177 sensing either drive mode or pedal-up mode and the throttle position sensor 175 sensing commanded motor speed anywhere between 0 to 100%. A further condition may be any battery SOC value above 0%.
Another input to the system logic may be battery voltage. Motor controller 120 may monitor the battery pack 130 voltage under load or may monitor the internal resistance (impedance) of the battery pack 130 in order to determine the battery pack 130 state of charge (SOC). With the SOC between about 100% to 25%, controller 120 may enable motive power to drive the vehicle 190. With an SOC between about 24% and 20%, the logic in motor controller 120 may limit commanded speed to 40% maximum drive speed, or approximately 1860 RPM, or approximately 6 MPH to provide a limp-home capability. For a SOC less than 20%, no motive power is supplied to power vehicle 190. The logic may thus limit commanded speed to zero RPM, the electric brake 180 may be de-energized, and motor braking via motor 110 may be enabled to protect battery pack 130 from being too deeply discharged. The electric brake 180 may be energized by the run/tow switch being selected to TOW at this latter SOC range.
Table 1 summarizes exemplary drive inputs to the logic of motor controller 120.
Run/Tow Switch 210
Must be selected to enable motive
power to drive the vehicle.
Energizes Electric brake 180 for 1
second and then applies 40% PWM