Technical Field

The present subject matter, in general, relates to a traction control system and in particular relates to a controller unit for brushless direct current motors.

Background

Generally, in order to limit tire slip while in motion or moving the vehicle from its state at rest, vehicles employ a traction control system (TRAC). The TRAC controls the acceleration of the vehicle by regulating the power delivered to the wheels. The TRAC employed by hybrid and electric vehicles, typically includes a battery, an electric traction motor, and wheel speed sensors. The battery provides power to the electric traction motor, which in turn drives the wheels of the vehicle. The electric traction motor is generally implemented using a brushless direct-current motor due to its ability to render high starting torque, precise speed control, and linear torque-speed characteristics. The wheel speed sensors measure the rotational speed of the wheels and control the power input to the drive wheel(s) of the vehicle.

The electric traction motor draws varying amounts of current from the battery based on the operating conditions of the vehicle. Generally, maximum current is drawn by the electric traction motor when it is stalled. An uncontrolled drawing of current could cause overheating and damage not just the electric traction motor but also the associated circuitry. To prevent the damage associated with excess current drawn by the electric traction motor, many TRAC-implemented vehicles employ an electronic controller within the TRAC.

The electronic controller limits the maximum current, which is drawn by the motor from the battery, to a value less than a pre-defined current limit. The current limit is set based on motor characteristics and remains the same at all speeds of the TRAC in the high-load region
and also for all throttle actuator inputs or percentage speed actuation. The high-load region corresponds to the maximum power speed, i.e. when the speed of the electric traction motor is less than that at which the power supplied is maximum. By limiting the current, the electronic controller also controls the torque provided to the wheels, thereby helping the driver accelerate under control.

The motor torque is thus limited by the controller at motor speeds below the maximum power speed, even though the electric traction motor can generate more torque. Consequently, speed-torque characteristics remain constant for low motor speeds, which results in similar acceleration performance at low speeds for any throttle actuator input, and as a result the drivability feel is adversely affected.

Summary

This summary is provided to introduce a system and a method for current control in an electric traction system, which is further described below in the detailed description
According to one embodiment of the present subject matter, the electric traction system (TRAC) includes a controller unit having a processing unit, a logic circuitry, and a regulating unit. The processing unit receives input signals, hereinafter referred to as throttle position signals, from a throttle actuator; and power signals from a source such as a battery. Using any of the known modulation techniques, the power signals are modulated in accordance with the throttle position signals. The logic circuitry sets a current limit for the power signals based upon the throttle position signals. The regulating unit senses the modulated power signals and compares them with the current limit set by the logic circuitry. If the modulated power signals exceed the set current limit, then the regulating unit sends the modulated power signals back, to the processing unit to reduce the modulation of the power signals. The current-limited power signals, which are modulated as per the throttle position signals, are then transferred to a brushless direct-current motor of the TRAC.
Thus, the maximum current limit is varied based upon the throttle position signals or the percentage of speed actuation. As a result, the motor torque generated at low speeds also varies with changing throttle position signals. As the vehicle acceleration performance is proportional to the torque characteristic of the motor, the described controller unit provides higher acceleration performance and better drive-ability feel. In addition, the capacity and performance of the power source, such as a battery, also improves significantly.

The aforementioned features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

Brief Description of Drawings

The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference number in different figures indicates similar or identical items. The features, aspects, and advantages of the subject matter will be better understood with regard to the following description, appended claims, and accompanying drawings where:

Fig 1 illustrates an exemplary vehicle traction control system with a controller unit according to an embodiment of the present subject matter.

Fig. 2 illustrates a block diagram of a controller unit for the vehicle traction control system of Fig. 1.

Fig. 3 illustrates a graph showing current characteristics for the vehicle traction control system of Fig. 1.

Fig. 4 illustrates a graph showing torque characteristics for the vehicle traction control system of Fig. 1.

Fig. 5 illustrates an exemplary method diagram for controlling current in the vehicle traction control system of Fig. 1.

Detailed Description

The subject matter disclosed herein relates to an electric traction system that provides for variable current limit control in two-wheeled vehicles.

In one implementation, a brushless DC motor, hereinafter referred to as motor, receives power signals from a power source, such as a battery, and converts it into mechanical energy to drive the wheels of the vehicle. The power delivered by the battery to the motor is regulated by an electronic controller based on throttle position signals, which are received from a throttle actuator, and current limit settings. This electronic controller, hereinafter referred to as variable current limit controller, results in varied current-speed and torque-speed characteristics for different throttle actuator signals based on different percentage positions of the throttle actuator or percentage of speed actuations. Therefore, better acceleration performance is achieved, which is in accordance with the throttle position signals..

Due to the use of the variable current limit controller, the discharge current during acceleration for partial speed actuation is less than the discharge current obtained using conventional control logic. The reduced discharge current results in a significant improvement in the battery capacity and performance of the power source. Thus, the described system and method provide for improved capacity and higher range-per-charge of the vehicle as well.

The following disclosure describes a system and a method for implementing variable current limit control in an electric traction system. While aspects of the described system and method can be implemented in any number of different sensors, microcontrollers, and/or microprocessor configurations, embodiments for the variable current limit control are described in the context of the following exemplary system(s) and method(s).

Fig. 1 illustrates an exemplary vehicle traction control system (TRAC) 100 with a controller unit 102 according to an embodiment of the present subject matter. The TRAC 100 includes a controller unit 102, a throttle actuator 104, a source 106, and a motor 108. The controller unit 102 receives throttle position signals 110 from the throttle actuator 104, and power signals 112 from the source 106. The source 106 may be a single power source or a combination of power sources including current sources, power sources etc., and accordingly the power signals 112 can include current signals, voltage signals, etc.
The controller unit 102 includes a logic circuitry 114 configured to set a current limit on the current drawn by the motor 108 from the source 106 through the controller unit 102. The current limit is assigned based on the throttle position signals 110 and can be done using various techniques known in the art such as by comparing the two inputs , namely the throttle position signals 110 and the power signals 112. Further, a look up table can be used for assigning a value corresponding to the combination of the aforementioned throttle position signals 110 and the power signals 112. In one embodiment, the logic circuitry 114 can be located outside the controller unit 102.
In operation, for driving the motor 108, the controller unit 102 modulates the power signals 112 received from the source 106 based on the received throttle position signals 110. In an implementation, the speed of the motor 108 is controlled by varying the width of voltage pulses supplied to the motor 108 so that the resulting output voltage supplied to the motor 108 establishes the operational speed of the vehicle. For modulating the power signals 112, the controller unit 102 uses one of the several techniques known in the art, for example, pulse width modulation (PWM).

In said implementation, based on the received throttle position signals 110, the logic circuitry 114, in the controller unit 102, provides a signal to set a current limit for the modulated power signals to be delivered to the motor 108. The current limit is set according to the percentage of speed actuation that is calculated based on the throttle position signals 110. The controller unit 102 compares the modulated power signals with the current limit and, based on the comparison, reduces the modulation of the power signals if the modulated power signals exceed the set current limit. As a result, the maximum current that can be drawn from the source 106 is reduced at a lower percentage of speed actuation. On the other hand, the maximum current that can be drawn from the source 106 is increased at higher percentages of speed actuation.

Fig. 2 illustrates an exemplary block diagram 200 of the controller unit 102 within the traction control system 100. The controller unit 102 includes a logic circuitry 114 that receives the throttle position signals 110 from the throttle actuator 104 and sets a current limit for the power signals 112 from the source 106 based on the throttle position signals 110. The controller unit 102 also includes a processing unit 202, which receives the power signals 112 and the throttle position signals 110. The processing unit 202 modulates the power signals 112 based on the throttle position signals 110 using a variety of techniques known in the art. The processing unit 202 sends the modulated power signals to a regulating unit 204 included in the controller unit 102.

In one implementation, the regulating unit 204 includes a comparator 206 for comparing the current limit, set by the logic circuitry 114, with the modulated power signals received from the processing unit 202. Based on the comparison, the comparator 206 sends a signal to the processing unit 202 to reduce the modulation of the modulated power signals if the modulated power signals exceed the set current limit. In another implementation, the regulating unit 204 includes one or more of microprocessors, microcontrollers, digital switches, analog switches, memory, current sensors, power sensors, voltage sensors, etc., interacting with each other for processing and modulating the power signal.

Fig. 3 illustrates a graph 300 illustrating current-speed characteristics for the vehicle traction control system of Fig. 1 at different values of throttle position signals (TPS) 110 or calculated values of percentage speed actuation. In the graph 300, motor current is plotted against motor speed for different values of the TPS 110 in the TRAC 100. The graph 300 illustrates change in current limits set by the logic circuitry 114 for different values of the TPS 110.

The graph 300 shows that the current limit decreases with decreasing values of the TPS 110 or percentage speed actuation.

Curve 302 depicts current characteristics of the TRAC 100 at eighty percent speed actuation. Curve 304 depicts current characteristics of the TRAC 100 at sixty percent speed actuation. Curve 306 depicts current characteristics of the TRAC 100 at fifty percent speed actuation.

Further, the graph 300 shows the relationship between current and motor speed obtained by using variable current limits. For example, if the TPS 110 reduces from eighty to fifty speed actuation, the motor current decreases due to a decrease in the current limit. In response to a decrease in the motor current, the motor speed also decreases. Thus, when the TPS 110 is actuated to lower percentage of speed actuation, the maximum current that can be drawn by the motor is much less and as a result, the battery capacity can be utilized in a better way. On the other hand, when the TPS 110 is actuated to higher percentage of speed actuation the current drawn also increases thereby providing better drivability feel. The drawn current aiding in better drivability feel is explained later with reference to torque characteristics.

Also note that the slopes of the curves 302, 304, and 306 by the motor 108 does not get affected by a signal provided by the logic circuitry 114 to set the current limit. Essentially, the no-load speed at different values of TPS 110 is not affected by the controller unit 102. Rather, only the maximum current drawn by the motor at low speed or high-load conditions changes at different values of TPS 110.

Fig. 4 illustrates a graph 400 illustrating torque characteristics for the TRAC 100 of Fig.l for different throttle position signals (TPS) 110.

In the graph 400,the torque characteristics are plotted against motor speed for different percentage speed actuations or throttle positions. The graph 400 shows variations in torque when the current limit is reduced based upon the reduction in the percentage of speed actuation through the TPS 110. Curve 402 depicts torque characteristics of the TRAC 100 at eighty percent TPS. Curve 404 depicts torque characteristics of the TRAC 100 at sixty percent TPS. Similarly, Curve 406 depicts torque characteristics of the TRAC 100 at fifty percent TPS.

The graph 400 shows the relationship between torque and motor speed characteristics of the motor 108 obtained due to variable current limits. For example, if the TPS 110 increases from fifty to eighty percent, then the current limit increases in proportion to the TPS 110 received. Hence, the motor torque and the motor speed increase. Thus, when TPS 110 is actuated to higher degrees, the maximum torque that a motor can generate is much more than when the TPS 110 is actuated to lower degrees. The acceleration performance of the vehicle is proportional to the torque characteristics of the motor 108 in the high load region, i.e. at low speeds. The increasing torque characteristic with increasing values of TPS 110 results in acceleration performance that is proportionate to the percentage speed actuation or throttle positions, thereby providing better drivability feel. Additionally, similar to the current characteristics, the no-load speed at different values of TPS 110 is not affected by the controller unit 102. Rather, only the maximum torque generated by the motor at low speed or high-load conditions changes at different values of TPS 110.

Fig. 5 illustrates a flow diagram 500 for controlling the current in a vehicle traction control system such as TRAC 100 with a controller unit 102.

At block 502, throttle position signals 110 and power signals 112 are received. A controller unit 102 receives the throttle position signals 110 from a throttle actuator 104 and power signals 112 from a power source 106.

At block 504, a current limit is set according to the throttle position signals 110. A logic circuitry 114 receives the throttle position signals 110 and sets a current limit for modulated power signals based on the throttle position signals 110.

At block 506, the power signals 112 are modulated in accordance with the throttle position signals 110. The controller unit 102 includes the processing unit 202 for modulating the power signal 112 in proportion to the throttle position signals 110.

At block 508, the modulated power signals are compared with the set current limit. The controller unit 102 includes a regulating unit 204 that utilizes a comparator 206 for comparing the power signals 112 against the set current limit.

At block 510, it is determined if the power signals received after modulation exceed the set current limit. If the power signals are found to exceed the current limit, then at block 512 the modulation of the power signals 112 is reduced by the processing unit 202 and sent back to the regulating unit 204 for comparison. On the other hand, if the modulated power signals do not exceed the set current limit, then at block 514, the modulated power signals limited by the set current limh are sent to the motor 108.

It will be understood that the controller unit 102 continues to receive throttle position signals 110 and power signals 112 and modulate the power signals in proportion to the throttle position signals by following the process outlined by the flow diagram 500.

Therefore, controller unit 102 facilitates the assignment of maximum current limit depending on the value of TPS 110 or percentage speed actuation controlled by the driver of the vehicle. Further, controller unit 102 helps in utilizing the capacity of the battery in a better way and effectively, improves the range per charge of the vehicle.

Although the subject matter has been considered in considerable details with reference to certain preferred embodiment thereof, other embodiments are possible. As such the scope of appended claims should not be limited to the description of preferred embodiments contained therein.

Claims:

1. A controller unit (102) comprising:
a processing unit (202) that receives throttle position signals (110) from a throttle actuator (104) and power signals (112) from a source (106), wherein said processing unit (202) is configured to modulate said power signals based on said throttle position signals (110) to generate modulated power signals;characterized in that:a logic circuitry (114) receives said throttle position signals (110) from said throttle actuator (104), wherein said logic circuitry (114) is configured to set a current limit for said modulated power signals based on said throttle position signals (110).

2. The controller unit (102) as claimed in claim 1, wherein said throttle position signals (110) correspond to a position of said throttle actuator (104).

3. The controller unit (102) as claimed in claim 1, wherein said processing unit (202) modulates said power signals (112) by Pulse Width Modulation.

4. The controller unit (102) as claimed in claim 1, wherein said power signal (112) is a current signal or a voltage signal or a combination of the two.

5. The controller unit (102) as claimed in claim 1, wherein said source (106) is a voltage source or a current source or a combination of the two.

6. The controller unit (102) as claimed in claim 1, wherein a regulating unit (204) compares said modulated power signals with said current limit and signals said processing unit (202) for reducing the modulation of said power signals (112) if the modulated power signals exceed said set current limit.

7. The controller unit (102) as claimed in claim 6, wherein said regulating unit (204) includes one or more of current sensors, power sensors, switches, microprocessors, and microcontrollers.

8. The controller unit (102) as claimed in claim 6, wherein said regulating unit (204) comprises a comparator (206) for comparing average motor current with said set current limit.

9. A method for controlling current in a vehicle traction control system (100), the method comprising;receiving throttle position signals (110) and power signals (112);modulating said power signals (112) based on said throttle position signals (110);setting a current limit for said modulated power signals based on said throttle position signals (110); and controlling modulation of said power signals (112) based on said set current limit.

10. The method as claimed in claim 9, wherein the controlling modulation of said power
signals (112) comprising:comparing an average motor current with the set current limit; and
reducing said modulation of said power signals (112) when said modulated power signals exceed said set current limit.