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 field of automotive steering systems. In particular, the invention discloses a method to operate an Electronic Power Steering (EPS) system.

Background of the invention
[0002] Modern vehicles use power steering or an Electronic Power Steering (EPS) system that reduce a driver's effort to turn a steering wheel of a motor vehicle. Commonly used EPS systems control and assist the steering system with the support of an intelligent electric motor. Based on the signal from a torque sensor, a control unit calculates an optimal steering support and sends the information to the electric motor to provide the necessary assistance.

[0003] In conventional EPS system safety goals are identified to prevent hazards. The identified faults must be prevented with an acceptable time limit before the occurrence of a hazard. This time limit is called as Fault Tolerant Time Interval (FTTI). According to ISO26262 Part 1 the FTTI (Fault Tolerant Time Interval) is defined as the "minimum time-span from the occurrence of a fault in an item to a possible occurrence of a hazardous event, if the safety mechanisms are not activated". The EPS system reaches a safe state if the identified fault is not cured within the FTTI.
[0004] In state-of-the-art EPS systems, reaching the safe state implies restricting or in worst case scenario sacrifice of some of the comfort or non-essential functions. For example, in case of the EPS system, the function of the electric motor that assists driver's effort to turn a steering wheel is restricted upon detection of a fault in the system. In state-of-the-art systems, FTTI is uniform and doesn’t depend upon the severity of the fault. There is a possibility that some systematic software faults or deviation in the system may self-heal. However, since the FTTI is constant, despite the intrinsic healing of the fault in the system, the system still goes into the safe state. Hence there is a need for an optimized FTTI that prevents the system from going into a safe state quickly, thereby preventing loss of comfort functions and basic functions.

[0005] Patent Application CN116279544A titled “Vehicle electronic power assisted steering control fault tolerance time interval determination method and apparatus” discloses a fault tolerance time interval determination method, apparatus and computer readable medium for an electronic power-assisted steering control system of a vehicle. The method comprising: Establishing a vehicle model based on vehicle-wide basic parameters, steering system parameters, brake system parameters, tire parameters; Road surface lateral slope, circle radius parameter and road surface adhesion coefficient parameter; road model based on design travel speed, The driving direction, the look-ahead time parameter and the maneuvering mode setting parameter establish a vehicle driving model, acquire a first duration for which the vehicle model travels from entering a curved road segment, inject a response fault parameter of the vehicle electronic power steering control system at the moment when the vehicle model travels into the curved road segment for the first duration, And obtain the time point at which the vehicle model is shifted out of the current driving lane and the second time period from entering the curved section; based on the second time period and the first time period value, obtain the fault tolerance interval for the electronic power steering control system of the vehicle.

Brief description of the accompanying drawings
[0006] An embodiment of the invention is described with reference to the following accompanying drawings:
[0007] Figure 1 depicts an Electronic Power Steering (EPS) system (100);
[0008] Figure 2 illustrates method steps (200) to operate the EPS system (100).

Detailed description of the drawings
[0009] Figure 1 depicts an Electronic Power Steering (EPS) system (100) within an automobile. The EPS system (100) comprises a motor (108), a sensor (112) and at least a control unit (102) amongst other components known to a person skilled in the art such as a steering wheel (104) coupled to a rack (114) through a steering column (106). The presently disclosed EPS system (100) in characterized by the functionality executed by the control unit (102) with help of the motor (108) and the sensor (112).

[0010] The motor (108) is configured to execute at least one non-essential or comfort function or basic function. In the present invention, the motor (108) is an electric/electronic motor (108) that assists vehicle steering and provides an optimal and enjoying steering feel (comfort function). Further, the motor (108) is coupled to the rack (114) through a pinion (118) or other mechanical means (such as gears) known in the art. The motor (108) is in communication with the control and the sensor (112). The operation of the motor (108) is regulated by the control unit (102) based on the EPS system (100) operating conditions.

[0011] The sensor (112) is configured to measure at least one motor operating parameters such as current, voltage, rotor position, motor torque and the like. In the exemplary embodiment of this invention, the motor operating parameters is the motor torque and sensor (112) is the motor torque sensor (112). The motor torque sensor (112) the motor operating parameters is motor torque. The sensor (112) communicates the instantaneous value of the measured motor torque with the control unit (102).

[0012] The control unit (102) is logic circuitry and software programs that respond to and processes logical instructions to get a meaningful result. Modern day vehicles may contain a plurality of control unit s like the Airbag control unit, Transmission control unit, Glow time control unit, Heating control unit, Vehicle charge communication unit, Engine control unit, Vehicle control unit, Steering control unit and the like. Each control unit coordinates the components specific to them for example an Engine control unit can provide torque coordination, operation, and gearshift strategies, on board diagnosis, monitoring, thermal management and much more for electrified and connected powertrains.

[0013] The control unit (102) referred here in accordance with the exemplary embodiment is the steering control unit (102). The control unit (102) may be implemented in the system (100) as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, and/or any component that operates on signals based on operational instructions.

[0014] The control unit (102) is configured to retrieve a pre-determined fault tolerance time interval (FTTI) for a critical safety goal of the EPS system (100) by means of the control unit (102); receive a value of the instantaneous motor operating parameters from the sensor (112); calculate deviation between the instantaneous value of motor operating parameters and a pre-determined ideal value of motor operating parameters by means of the control unit (102); adapt the pre-determined FTTI in dependance of the calculated magnitude of deviation; restrict the non-essential function in dependance of the adapted FTTI by means of the control unit (102). The control unit (102) adapts the pre-determined FTTI by linearly increasing the value of FTTI with respect to decreasing value of the magnitude of deviation.

[0015] It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.

[0016] Figure 2 illustrates method steps (200) to operate the EPS system (100). The EPS system (100) and its components have been described in accordance with figure 1. For clarity, it is reiterated that the EPS system (100) comprises a motor (108), a sensor (112) and at least a control unit (102) amongst other components known to a person skilled in the art.

[0017] Method step 201 comprises retrieving a pre-determined fault tolerance time interval (FTTI) for a critical safety goal of the EPS system (100) by means of the control unit (102). The pre-determined FTTI is calculated for the particular system (100) specifications in accordance with numerous methods known in state of the art such as Hazard analysis and risk assessment (HARA) and Controllability investigation.
[0018] Method step 202 comprises receiving a value of the instantaneous motor operating parameters from the sensor (112). For most critical safety goals such as the unintended actuator functionality, in the EPS system (100), the motor operating parameters is motor torque. The sensor (112) communicates it’s instantaneous readings of motor torque to the control unit (102)

[0019] Method step 203 comprises calculating deviation between the instantaneous value of motor operating parameters and an ideal value of motor operating parameters by means of the control unit (102). For every system (100) operating an ideal value of the motor torque value is calibrated. The difference between this ideal motor torque value and the instantaneous value of motor torque is calculated to determine deviation from an ideal/expected behavior and thereby a fault. The magnitude of deviation indicates the severity of the fault.

Torque Deviation
0-1Nm 2Nm 3Nm 4Nm 5Nm 6Nm 7Nm
Current FTTI 20ms 20ms 20ms 20ms 20ms 20ms 20ms
Adapted FTTI 180ms 150ms 120ms 90ms 60ms 40ms 20ms
[0020] Method step 204 comprises adapting the pre-determined FTTI in dependance of the calculated magnitude of deviation. Adapting the pre-determined FTTI comprises linearly increasing the value of FTTI with respect to decreasing value of the magnitude of deviation. Table 1 below gives an example of how the FTTI is adapted in accordance with the magnitude of deviation.

Table 1.

[0021] Method step 205 comprises restricting the non-essential function in dependance of the adapted FTTI by means of the control unit (102). The non-essential or the comfort function is restricted by the control unit (102) if the fault is not rectified within the adapted FTTI. The adapted FTTI increases the availability of the comfort features and also provides a possibility for healing of the faults.

[0022] For example, the critical safety goal here is the “Unintended Actuator Functionality (UAF)”. It describes a vehicle speed depending faulty rack (114) force, resulting from a wrong motor torque characteristics of more than safety limit which results in an unintended movement of the steering rack (114) that causes a sudden non controllable lateral displacement of the vehicle. To steer a vehicle, the driver initiates the steering maneuver with a change of the input shaft motion. A change of the input shaft motion in the vehicle causes a change of the rack (114) force. The EPS system (100) function is amplify steering motion assists the driver with the provision of a pleasant steering wheel torque. High steering torque for comfortable parking at low vehicle speed and Low steering torque for stabilization of the vehicle at higher vehicle speed. A 0.5Nm deviation of Motor torque is acceptable, if the deviation is above 0.5Nm (It might be 0.6Nm or 6.0Nm) in the conventional EPS systems, the EPS goes into the safe state. This means the comfort function or the basic function i.e. the pleasant steering wheel assistance provided by the motor (108) has to be turned off within 20ms.

[0023] But it is assumed that, even for the slight deviation of motor torque the vehicle can’t be controllable more than 20ms. As represented in Table 1, the FTTI (i.e. the adapted FTTI) can be increased inversely to the motor torque deviation. As per the current method, referred in the table 1, when the deviation is very less (0.6 Nm) it is controllable by the driver for a longer time (180 ms) and if the deviation is very high (6Nm) it is not controllable by the driver for a longer time (40 ms). This is the reason why there is a need for adaptive FTTI dependent upon magnitude of deviation which provides extra time leading to increased possibility of healing the system fault.

[0024] A person skilled in the art will appreciate that while these method steps describes only a series of steps to accomplish the objectives, these methodologies may be implemented with adaptation and modifications to the EPS system (100).

[0025] This idea to develop an optimized FTTI reduces unwarranted loss of comfort or basic features while also fulfilling the stringent safety goals. It must be understood that the embodiments explained in the above detailed description are only illustrative and do not limit the scope of this invention. Any modification to the proposed EPS system (100) and the method (200) of operating the EPS system (100) are envisaged and form a part of this invention. The scope of this invention is limited only by the claims.

, Claims:We Claim:
1. An Electronic Power Steering (EPS) system (100), said EPS system (100) comprising a motor (108), a sensor (112) configured to measure at least one motor operating parameters, a control unit (102) in communication with the sensor (112) and the motor (108), said motor (108) configured to execute at least one non-essential function, characterized in that EPS system (100): the control unit (102) configured to:
retrieve a pre-determined fault tolerance time interval (FTTI) for a critical safety goal of the EPS system (100) by means of the control unit (102);
receive a value of the instantaneous motor operating parameters from the sensor (112);
calculate deviation between the instantaneous value of motor operating parameters and an ideal value of motor operating parameters by means of the control unit (102);
adapt the pre-determined FTTI in dependance of the calculated magnitude of deviation;
restrict the non-essential function in dependance of the adapted FTTI by means of the control unit (102).

2. The Electronic Power Steering (EPS) system (100) as claimed in claim 1, wherein the motor operating parameters is motor torque.

3. The Electronic Power Steering (EPS) system (100) as claimed in claim 1, wherein the control unit (102) adapts the pre-determined FTTI by linearly increasing the value of FTTI with respect to decreasing value of the magnitude of deviation.

4. A method (200) to operate an Electronic Power Steering (EPS) system (100), said system (100) comprising a motor (108), a sensor (112) configured to measure at least one motor operating parameters, a control unit (102) in communication with the sensor (112) and the motor (108), said motor (108) configured to execute at least one non-essential function, the method steps comprising:
retrieving a pre-determined fault tolerance time interval (FTTI) for a critical safety goal of the EPS system (100) by means of the control unit (102);
receiving a value of the instantaneous motor operating parameters from the sensor (112);
calculating deviation between the instantaneous value of motor operating parameters and a ideal value of motor operating parameters by means of the control unit (102);
adapting the pre-determined FTTI in dependance of the calculated magnitude of deviation;
restricting the non-essential function in dependance of the adapted FTTI by means of the control unit (102).

5. The method (200) to operate an Electronic Power Steering (EPS) system (100) as claimed in claim 2, wherein the motor operating parameters is motor torque.

6. The method (200) to operate an automotive system (100) as claimed in claim 1, wherein adapting the pre-determined FTTI comprises linearly increasing the value of FTTI with respect to decreasing value of the magnitude of deviation.