Description:
Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed

Field of the invention
[0001] The present disclosure relates to a method and a system to obtain a rotor position and more specifically to an electric power steering (EPS) system to obtain a rotor position in an event of failure of a rotor position sensor (RPS) and a method thereof.

Background of the invention
[0002] The electric power steering (EPS) systems assist in reducing the steering force required to turn the vehicle by generating an auxiliary steering force.
[0003] The EPS system comprises of motors, torque position sensors and motor position sensors. The position and angular velocity of the motor may be detected through the rotor position sensor (RPS) and the torque sensor. The position, speed, torque, and the like of the motor may be controlled based on the detected sensing values. In cases where the reliability of a rotor position (also referred to as fallback/remote RPS) is not guaranteed due to a failure of the rotor position sensor, the steering control may be performed erroneously or not at all. To overcome this, dual channel EPS systems comprise two channels with two RPS.
[0004] In dual channel Electric Power steering systems, in case of failure of one of the Rotor position sensors (RPS) of one of the channels, the torque generation is shut down in the unhealthy channel so formed. In such a scenario, whenever the demanded torque is higher than the torque available in a single channel, a torque deficit occurs.
[0005] The prior art US2018229761AA discloses a rotation detecting apparatus. A switch is in an on state so that electrical power is supplied from a power source to a controller via the switch, the controller receives, as a first output signal, an output signal output from an output unit of a first rotation sensor, and receives, as a second output signal, an output signal output from an output unit of the second rotation sensor. The first output signal includes at least the first rotational information and the second rotational information based on the first rotation sensor, and the second output signal includes at least the first rotational information and the second rotational information based on the second rotation sensor. The controller determines whether there is a malfunction in each of the first and second rotation sensors as a function of the first output signal and the second output signal.

Brief description of the accompanying drawings
An embodiment of the invention is described with reference to the following accompanying drawings:
[0006] Figure 1 depicts an electric power steering (EPS) system to obtain a rotor position in an event of failure of a rotor position sensor (RPS).
[0007] Figure 2 depicts the process of linear extrapolation to predict a rotor position.
[0008] Figure 3 depicts a flowchart for the method to obtain a rotor position in an event of failure of a rotor position sensor (RPS).
Detailed description of the drawings

[0009] Referring to Figure 1, the same depicts an electric power steering (EPS) system to obtain a rotor position in an event of failure of a rotor position sensor (RPS).
[0010] The EPS system(10) described herein is a dual channel EPS system, however, it is to be understood that the present disclosure also holds true for multiple channel EPS systems and the described embodiment should not be construed as a limitation to the scope of the invention. The EPS system (10) comprises a first channel (1) comprising a first rotor position sensor (RPS) (1a) and a first microcontroller (1b) in connection with the first RPS (1a). The EPS system (10) further comprises a second channel (2) comprising a second RPS (2a) and a second microcontroller (2b) in connection with the second RPS.
[0011] Typically, the RPS (rotor position sensors) are integrated in an electric control unit (ECU) of the vehicle which is mounted on top of a motor. However, the RPS can also be directly mounted on top of the motor. A person skilled in the art will appreciate that the RPS indicate the position of the rotors inside the motor based on a change in magnetic flux. Both the RPS (1a , 2a) may have a magneto resistive element used as a sensor element and a hall element may also be used. Further, the RPS (1a,2a) maybe connected to invertors, power supply relays, torque sensors (all not shown) to form an integrated EPS system.
[0012] The first and second RPS are respectively connected to a first and second microcontroller (1b, 2b). Said microcontroller (1b, 2b) may have inbuilt processing capacity and an associated memory to store and execute a program. Each of the microcontrollers are capable of calculating the rotation position of the rotor based on the signals/outputs received from the RPS (1a, 2a). The first and second microcontrollers (1b, 2b) can share pieces of information obtained, such as the rotor position using microcomputer-to-microcomputer communications. In an example, the microcontroller (1b, 2b) may be configured to perform monitoring for mal-function and an inbuilt diagnosis. In an example communication means between the first microcontroller and the second microcontroller may be established by an IPC (inter-processor communication) system.
[0013] The system(10) includes a motor (4) in connection with the said first and second channel to provide a torque on the basis of a torque requested by the first and second microcontroller (1b, 2b). According to an aspect of the embodiment in the present disclosure, the motor may be a permanent magnet synchronous motor. The motor may be a brushless three phase or a six phase motor along with stators, rotors and shaft.
[0014] The rotor position is calculated by the first and second microcontroller (1b, 2b) based on the output of first and second RPS (1a, 2a). Once the RPS is obtained, an armature coil on the motor’s stator is excited to rotate the rotor and provide the necessary torque to the drive. Therefore, precise rotor position is necessary to generate appropriate amount of torque. In case of failure of one of the Rotor position sensors of one of the channels (herein referred to as the unhealthy channel), the torque generation is shut down in the entire unhealthy channel. In such a situation, the rotor position across certain phases of motor is not intelligible. This leads to a torque deficit which itself leads to lack of efficiency of the EPS. Therefore, appropriate torque assistance is not provided to the driver.
[0015] In order to solve the aforementioned problem, the first and second microcontrollers (1b, 2b) exchange a information about a first rotor position obtained from the first RPS (1a) and a second rotor position obtained from the second RPS (2a), wherein, each of said first and second microcontrollers (1b, 2b) are configured to predict the rotor position in an event of failure of either the first RPS or the second RPS.
[0016] Referring to figure 2, The first and second microcontrollers (1b, 2b) can predict the readings of the failed RPS. In an example, when in the first channel (1) , the first RPS (1a) fails to function, the second microcontroller can compute the first rotor position based on a gradient calculated by linear extrapolation of the previously exchanged RPS values between first and second microcontroller and the readily available second rotor position obtained from the second RPS (2a). This predicted first rotor position can now be exchanged with the first microcontroller of the first channel. Thus, both the first and second microcontrollers are able to request torque as the rotor positions across phases of motor are known. In figure 2, the x-axis represents time (in milliseconds (ms) or microseconds) and the y axis represents the rotor position in degrees. The curve (11) represents the readings of healthy RPS (say RPS 2a) and curve (13) represents the readings of unhealthy RPS (say RPS 1a). In the 0th µs, the first RPS fails to function, the microcontroller 2b predicts the readings of first RPS on the 2nd microseond based on a gradient obtained from the readings exchanged between the two microcontrollers. From Fig 3, the -1th and 0th value gradient is calculated and added to the base value of the healthy RPS at 0. The gradient added value is forecasted as the 1st value for the unhealthy channel. Thus, both the first and second microcontrollers are able to request torque as the rotor positions across all phases of motor are now known. It is to be understood, that irrespective of failure, the microcontrollers are continuously calculating and predicting and forcasting the added the gradient values for each other’s channels.

[0017] The best method to perform the disclosure is further described. In situations where the vehicle is speeding, say 70kmph or more (in an example), the sensitivity of steering wheel increases, more rotation of the vehicle is provided with a lesser steering input as opposed to situations where vehicle is in a low speed, say 10kmph or less (in an example). In an example, a situation can be when the driver is parking the vehicle. In such a situation, torque assistance is required to be provided to the driver by EPS, however, if one of the channels are unhealthy, a torque deficit occurs (as explained above). Therefore, the a forementioned EPS system may be subjected to a threshold speed check to comply with the safety of the passenger. The microcontrollers (1b, 2b) may be configured to implement the present disclosure based on the threshold speed check. The same can be provided by providing the microcontrollers (1b,2b) readings from a speed sensor (5) of the vehicle as input.

[0018] Further, there may be situations where the magnitude of torque requested by the microcontrollers (1b,2b) may not be feasible with respect to current condition of the vehicle. Such situations can be frequent voltage drops in the supply to motor or a situation where the vehicle is in limp home mode (where engine/transmission control is at fault) or overheating of circuits etc. Typically, the vehicles have Safety Limits that have a known safe operating envelope, which can be described by the values of the vehicle’s properties. The value of a property at which the system is no longer safe is its safety limit (e.g., a safety limit on the engine of 7500rpm might be set because the engine cannot operate above that speed without violent failure, or a top vehicle speed might be set based on the maximum speed rating of tires).

[0019] Safety-critical systems often have both a normal control system and a simple and reliable emergency backup system which has independent actuators whose express purpose is to bring a faulty system to a safe state as quickly as possible. The emergency control system may be known as the hard limit system. At the hard limit (6) the vehicle is about to become unsafe and must immediately be returned to a safe state, using a hard shutdown to avoid exceeding the safety limit. A hard shutdown for autonomous ground vehicles may include opening an electric vehicle safety relay under high current load (which causes significant wear to the relay).

[0020] Hard shutdowns are typically avoided at all practical cost due to the expense and disruption of system shutdown and recovery. Many embedded control systems in the vehicle also use a soft limit (7). The soft limit serves as a warning for the control system to attempt to transition the system to a safe state via a soft stop, which is an orderly shutdown that avoids the worst of the consequences of an emergency control system activation. For example, a soft stop might be a command to vehicle autonomy software to stop the vehicle without activating the vehicle safety relay.

[0021] Based on these hard and soft limits the capacity (8) of the disclosed EPS system to provide the requested torque can be assessed wherein the torque provided may be limited (less than the torque requested) or maximum torque (equal to the requested torque) may be provided when the capacity to provide torque is not limited by these hard/soft limit. Under hard limit, maximum torque cannot be provided to the motor by the EPS system (10). Under soft limit, maximum torque can be provided by the system, however, the necessity of it has to be assessed. Only when the need to provide the torque outweighs the possible damage while breaching the soft limit, the torque can be provided.

[0022] Referring again to Figure 1, disclosed is an electric power steering (EPS) system (10) to obtain a rotor position in an event of failure of a rotor position sensor (RPS). Said EPS system comprises a first channel (1) comprising a first RPS(1a) and a first microcontroller (1b) in connection with the first RPS and a second channel (2) comprising a second RPS (2a) and a second microcontroller (2b) in connection with the second RPS. There is a communication means (3) between the first microcontroller (1b) and the second microcontroller (2b) such that, the first and second microcontrollers (1b,2b) exchange an information about a first rotor position obtained from the first RPS (1a) and a second rotor position obtained from the second RPS (2a), wherein, each of said first and second microcontrollers (1b,2b) are configured to predict the rotor position in an event of failure of either the first RPS (1a) or the second RPS (2a).

[0023] In an event of failure of the first RPS(1a), a torque is provided by a motor (4) connected with the said first and second channels(1,2) based on- the second rotor position obtained from the second RPS (2a) and the first rotor position predicted by the second microcontroller (2b). In an event of failure of the second, a torque is provided by the motor connected with the said first and second channels based on-the second rotor position obtained from the first RPS (1a) and the second rotor position predicted by the first microcontroller (1b). The torque is provided when a speed of a vehicle comprising said EPS system is below a threshold speed. The torque is provided when said EPS system is not limited by a capacity to provide more than a threshold torque.

[0024] Referring to Figure 3, disclosed is a method (100) to obtain a rotor position in an event of failure of a rotor position sensor (RPS) the method is implemented by an electric power steering (EPS) system (10). Said system (as explained above) comprises a first channel comprising, a first RPS and a first microcontroller in connection with the first RPS and a second channel comprising a second RPS and a second microcontroller in connection with the second RPS.

[0025] The method step (101) is exchanging through a communication means, an information between the first microcontroller and the second microcontroller, about the first rotor position obtained from the first RPS and the second rotor position obtained from the second RPS . The next method step (102) is predicting by either the first microcontroller or the second microcontroller, the second rotor position or the first rotor position, in an event of failure of either the first RPS or the second RPS . It is to be understood, that irrespective of failure of the RPS, the microcontrollers are continuously calculating, predicting and forecasting the gradient added values for each of other’s channels.

[0026] In an event of failure of the first RPS, the next method step (103) is providing a torque, by a motor connected with said first and second channels, based on the second rotor position obtained from the second RPS and the first rotor position predicted by the second microcontroller.

[0027] In an event of failure of the second RPS to function, the next step (104) is providing a torque, by a motor connected with said first and second channels, based on the first rotor position obtained from the second RPS and the second rotor position predicted by the second microcontroller, the torque provided by at least one motor connected with said first and second channels. Further the torque is provided when a speed of a vehicle comprising said EPS system is below a threshold speed and when said EPS system is not limited by a capacity to provide more than a threshold torque.
[0028] The present disclosure advantageously provides enhanced torque assistance to the driver in cases of failure of the rotor position sensor in one of the channels of the Electric power steering system.
, Claims:We Claim:
1. An electric power steering (EPS) system (10) to obtain a rotor position in an event of failure of a rotor position sensor (RPS), said EPS system comprises:
-a first channel (1) comprising:
a first RPS(1a) and a first microcontroller (1b) in connection with the first RPS;
-a second channel (2) comprising:
a second RPS (2a) and a second microcontroller (2b) in connection with the second RPS;
-a communication means (3) between the first microcontroller (1b) and the second microcontroller (2b) such that,
the first and second microcontrollers (1b,2b) exchange an information about a first rotor position obtained from the first RPS (1a) and a second rotor position obtained from the second RPS (2a), wherein,
each of said first and second microcontrollers (1b,2b) are configured to predict the rotor position in an event of failure of either the first RPS (1a) or the second RPS (2a).

2. The EPS system(10) as claimed in Claim 1 , wherein, in an event of failure of the first RPS(1a), a torque is provided by a motor (4) connected with the said first and second channels(1,2) based on-
the second rotor position obtained from the second RPS (2a) and the first rotor position predicted by the second microcontroller (2b).
3. The EPS system as claimed in Claim 1, wherein, in an event of failure of the second, a torque is provided by the motor connected with the said first and second channels based on-
the second rotor position obtained from the first RPS (1a) and the second rotor position predicted by the first microcontroller (1b).

4. The EPS system(10) as claimed in Claim 2, wherein, the torque is provided when a speed of a vehicle comprising said EPS system is below a threshold speed.

5. The EPS system(10) as claimed in Claim 2, wherein, the torque is provided when said EPS system is not limited by a capacity to provide more than a threshold torque.

6. A method (100) to obtain a rotor position in an event of failure of a rotor position sensor (RPS), the method implemented by an electric power steering (EPS) system, said system comprises:
a first channel comprising :
a first RPS and a first microcontroller in connection with the first RPS;
a second channel comprising:
a second RPS and a second microcontroller in connection with the second RPS;
the method characterized by the steps of:
- exchanging through a communication means, an information between the first microcontroller and the second microcontroller, about the first rotor position obtained from the first RPS and the second rotor position obtained from the second RPS (101) ; and
- predicting by either the first microcontroller or the second microcontroller, the second rotor position or the first rotor position, in an event of failure of either the first RPS or the second RPS (102).

7. The method (100) as claimed in claim 6, wherein, in an event of failure of the first RPS, providing a torque, by a motor connected with said first and second channels, based on -
the second rotor position obtained from the second RPS and the first rotor position predicted by the second microcontroller (103).

8. The method (100) as claimed in claim 6, wherein, in an event of failure of the second RPS to function, providing a torque, by a motor connected with said first and second channels, based on
the first rotor position obtained from the second RPS and the second rotor position predicted by the second microcontroller, the torque provided by at least one motor connected with said first and second channels (104).

9. The method (100) as claimed in Claim 8, wherein, providing the torque when a speed of a vehicle comprising said EPS system is below a threshold speed.

10. The method (100) as claimed in Claim 8, wherein, providing the torque when said EPS system is not limited by a capacity to provide more than a threshold torque.