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:
The present invention relates to a controller and method to operate an electrically powered steering motor of a vehicle.

Background of the invention:
In conventional Electric Power Steering (EPS) system, safety goals are identified to prevent hazards. The identified faults must be prevented with an acceptable time limit before the occurrence of the hazard. This time limit is called as Fault Tolerant Time Interval (FTTI). Every fault occurring in an item must be detected and reacted to reach the safe state within the identified FTTI of the safety goal. Each functionality is identified with a “safety limit threshold” which is the controllable torque value of the functionality. If the functionality is within the prescribed safety threshold the functionality is controllable forever and if the safety limit threshold is breached in the functionality should mandatorily reach the safe state within the FTTI. Currently to check whether the functionality has breached the safety threshold, the torque output interface of the functionality is compared against the safety limit threshold of the functionality. If the torque output interface of the functionality has already breached by the safety limit threshold of the functionality, the functionality violates the safety goals and to prevent the safety goal violation the functionality should reach the safe state within the FTTI.

According to a prior art US2011276230 a method for operating a power steering mechanism is disclosed. A method is disclosed for operating a power steering system in which a motor torque is computed by an electronic processor and established by suitable motor actuation, wherein a plausibility check is carried out for the computed motor torque as part of a 3-level design, wherein integration of a part above a motor torque limit curve and decrementation of an integrator with a part below the motor torque limit curve are performed, the target motor torque being limited to a first integration threshold in level 1, and the limitation is monitored in level 2, with an intrinsically safe motor torque limit curve being used as a function of an actual motor torque.

Brief description of the accompanying drawings:
An embodiment of the disclosure is described with reference to the following accompanying drawings,
Fig. 1 illustrates a block diagram of a controller to operate an electrically powered steering motor of a vehicle, according to an embodiment of the present invention, and
Fig. 2 illustrates a method for operating an electrically powered steering motor of a vehicle, according to the present invention.

Detailed description of the embodiments:
Fig. 1 illustrates a block diagram of a controller to operate an electrically powered steering motor of a vehicle, according to an embodiment of the present invention. The vehicle 102 comprises an Electric Power Steering (EPS) system 120 shown separately and coupled to drive wheels 116 of the vehicle 102. The EPS system 120 comprises a steering wheel 104 coupled to a rack 114 through a steering column 106. The steering wheel 104 is rotatable in both directions. The rack 114 is electrically steerable by a steering motor 108. The steering motor 108 is controlled by the controller 110 for operating as per the request from the driver. The controller 110 is either internal to the EPS system 120 or externally interfaced with the EPS system 120. Further, the steering motor 108 is coupled to the rack 116 through a pinion 118 or other mechanical means (such as gears) known in the art. There are circuits through which the controller 110 drives the steering motor 108 along with sensors 122 which measures the parameters of the steering motor 108 such as current sensor, voltage sensor, rotor position sensor and the like. The input from the sensors 122 is given to the controller 110 along with other signals 112 as known in the art for required operation of the steering motor 108. The above construction is provided to explain the general construction of the EPS system 120. Any other type of steer-by-wire system is also applicable which is known in the art.

According to an embodiment of the present invention, the controller 110 operates the steering motor 108 based on a steering functionality which is currently active or activated by the Electrical Power Steering (EPS) system of the vehicle 102 or by a service engineer. The controller 110 configured to calculate/estimate a desired/requested motor torque to drive the steering motor 108 as per the active functionality, characterized in that, the controller 110 determines an actual motor torque imparted by the steering motor 108 for the same functionality, compare the actual motor torque with a safe threshold torque, and activate a safe state of operation for the steering motor 108 based on the comparison. The controller 110 compares and determines if the actual motor torque is greater than the safety threshold torque. The comparison is performed continuously from the moment the functionality is called or activated. The calculation/estimation of the requested motor torque is based on the preconfigured values during calibration of the active functionality.

According to another embodiment of the present invention, the controller 110 operates the steering motor 108 based on a steering functionality which is currently active or activated by the Electrical Power Steering (EPS) system of the vehicle 102 or by a service engineer. The controller 110 configured to calculate/estimate a desired/requested motor torque to drive the steering motor 108 as per the active functionality, compare the requested motor torque with safety threshold torque, and activate safe state based on the comparison, characterized in that, the controller 110 configured to consider the actual motor torque instead of the requested motor torque for comparison. The actual motor torque is the real physical torque (or provided motor torque) imparted by the steering motor 108 for the same functionality. The controller 110 compares and determines if the actual motor torque is greater than the safety threshold torque. The calculation/estimation of the requested motor torque is based on the preconfigured values during calibration of the active functionality.

According to an embodiment of the present invention, the actual motor torque is imparted by the steering motor 108 and calculated/determined based on values of the static parameters and dynamic parameters of the steering motor 108. The static parameter are selected from group comprising number of rotor pole pairs (Zp), inductance of torque production (Lq) and inductance for field weaking (Ld), and said dynamic parameter are selected from a group comprising flux of a permanent magnet (Ψ), current for torque production (Iq), and current for field weaking (Id). Further, the static parameters are predetermined and stored in the memory element, and the dynamic parameters are determined measured/estimated during operation of the steering motor 108 using the sensors 122 or derived using existing values within the EPS system 120.

According to an embodiment of the present invention, the controller 110 is configured to determine the actual motor torque based on the model formed using the static parameters and dynamic parameters as below:
M=3/2*Z_p*(Ψ_pm*I_q+(L_d-L_q )*I_d*I_q
Where,
M – Actual motor torque
Zp – Number of rotor Pole pairs
Ψpm– Flux of the Permanent Magnet
Iq – Current for Torque production
Id – Current for Field weakening
Lq – Inductance for Torque production
Ld – Inductance for Field weakening

According to an embodiment of the present invention, the controller 110 uses the physical (Hwlib), i.e. actual motor torque (also known as “Provided Motor Torque”), which is calculated as feedback from the signals such as phase currents and the rotor positions etc. The controller 110 uses the physical motor torque or the actual motor torque instead of the requested motor torque and therefore provides the technical advantage over the existing solution. The actual motor torque is the real torque which must be considered instead of the requested motor torque.

According to an embodiment of the present invention, the functionality is selected from but not limited to basic steering assist where steering motion is amplified, an active return of the steering wheel once rotated, an end stop, a block detection, a level two autonomous driving and a level three autonomous driving etc., and the like. The functionality is either activated by the EPS system 120 or the controller 110 as per predefined routines or trigger conditions or is activated by the service engineer in a service stations/garage.

According to the present invention, the controller 110 is provided with necessary signal detection, acquisition, and processing circuits. The controller 110 is a control unit which comprises memory element (not shown) such as Random Access Memory (RAM) and/or Read Only Memory (ROM), Analog-to-Digital Converter (ADC) and a Digital-to-Analog Convertor (DAC), clocks, timers, counters and at least one processor (capable of implementing machine learning) connected with each other and to other components through communication bus channels. The memory element is pre-stored with logics or instructions or programs or applications or modules/models and/or threshold values, safety threshold torque, safe threshold limit, which is/are accessed by the at least one processor as per the defined routines. The internal components of the controller 110 are not explained for being state of the art, and the same must not be understood in a limiting manner. The controller 110 is implementable in the form of System-in-Package (SiP) or System-on-Chip (SOC) or any other known types.

According to the present invention, a working of the controller 110 is provided to operate the electrically controlled steering motor 108 of the vehicle 102. Consider the steering functionality comprising detection of blocked steering is activated. The activation is done automatically as per requirements within the vehicle 102 or manually by a technician or driver. Consider below table which assumes safety threshold torque limit, requested motor torque and actual motor torque for three cases/scenarios.
Function Safety threshold torque Requested motor torque Actual Motor torque
Case I Actual Motor torque
Case II Actual Motor torque
case III
Detect blocked steering/Any function 1 Nm 1.1 Nm 1.1 Nm 0.9 Nm Nm

As per the case I, the actual motor torque calculated by the controller 110 through the model is 1.1 Nm. Here the actual motor torque is equal to the requested motor torque i.e. the actual motor torque is higher than the safety threshold torque. Now, as per conventional system, if the requested motor torque is greater than the safety threshold torque, the controller 110 operates the steering motor in safe state. However, as per the present invention, the controller 110 now compares the actual motor torque, instead of the required motor torque, with the safety threshold torque, which in this case is greater than the safety threshold torque, and thereby operates the steering motor 108 in safe state. However, since in case I, both the requested motor torque and actual motor torque are same, the effect of present invention is not visible.

In brief, as per conventional solution, it was requested motor torque > safety threshold torque > Go to “safe state”.
Now as per present invention, actual motor torque > Safety threshold torque –> Go to “Safe State”
Therefore, in case I since the requested motor torque (1.1 Nm) = actual motor torque (1.1 Nm) > safety threshold torque (1 Nm), the safety threshold torque is violated and therefore the controller 110 operates the functionality of the steering motor 108 in safe state.

As per case II, the actual motor torque calculated by the controller 110 is 0.9 Nm. The actual motor torque is lesser than the requested motor torque. Here, the requested motor torque is higher than the safety threshold torque whereas the actual motor torque is lesser than the safety threshold torque. Now, as per conventional solution, if requested motor torque was considered, the safe state would be activated by the controller 110. However, since as per the present invention, since the actual motor torque is compared, the controller 110 waits for some more time to before moving to safe state.

In brief, as per conventional solution, the requested motor torque > safety threshold torque –> Go to “Safe State”.
Now as per the present invention, actual motor torque < safety threshold torque –> No “Safe State”
Therefore, in case II, the requested motor torque (1.1 Nm) > safety threshold torque (1 Nm) > actual motor torque (0.9 Nm). The controller 110 gets an additional wait time before going to the safe state, which provides a possibility for the healing of the error (systematic software failure) in the functionality.

As per Case III, the actual motor torque calculated by the controller 110 is higher than the requested motor torque i.e. both the calculated (ASW) and actual motor torque (Hwlib) are higher than the safety threshold torque. As per both, i.e. the conventional solution and the present invention, the controller 110 activates the safe state.

In brief, as per conventional solution, the requested motor torque > safety threshold torque –> Go to “Safe State”.
Now as per the present invention, the actual motor torque > safety threshold torque –> Go to “Safe State”
In the case III, the actual motor torque (1.3 Nm) > requested motor torque (1.1 Nm) > safety threshold torque (1 Nm), hence the safe state is activated by the controller 110 instantly.

Thus, in view of the three cases, the technical effect of using the actual motor torque rather than the requested motor torque is brought out in Case II and Case III.

Fig. 2 illustrates a method for operating an electrically powered steering motor of a vehicle, according to the present invention. The method comprises plurality of steps of which a step 202 comprises estimating, by the controller 110, the desired/requested motor torque to drive the steering motor 108 as per the active functionality of the steering motor 108. The method is characterized by a step 204 which comprises determining, by the controller 110, the actual motor torque imparted by the steering motor 108 for the same functionality. A step 206 comprises comparing, by the controller 110, the actual motor torque with the safe threshold torque. A step 208 comprises activating, by the controller 110, the safe state of operation for the steering motor 108 based on the comparison.

In an alternative and according to the present invention, the method comprises plurality of steps of which a step 210 comprises estimating, by the controller 110, the desired/requested motor torque to drive the steering motor 108 as per the active functionality of the steering motor 108. A step 212 comprises comparing, by the controller 110, the requested motor torque with the safety threshold torque stored in the memory element. A step 206 comprises activating, by the controller 110, the safe state of the steering motor 108 based on the comparison. The method is characterized by the step 212 where the comparison of the actual motor torque (instead of the requested motor torque) with the safety threshold torque is performed. The actual motor torque is the real physical torque imparted by the steering motor 108 for the same functionality.

According to the present invention, the comparison comprises checking if the actual motor torque is greater than the safety threshold torque.

According to the present invention, the actual motor torque is imparted by the steering motor 108 and determined by measuring static parameters and dynamic parameters. The static parameter are selected from group comprising number of rotor pole pairs (Zp), inductance of torque production (Lq) and inductance for field weaking (Ld), and said dynamic parameter are selected from a group comprising flux of said permanent magnet (Ψ), current for torque production (Iq), and current for field weaking (Id). Further, the static parameters are predetermined and stored in the memory element, and the dynamic parameters are determined by measuring/estimating during operation of the steering motor 108. The model used by the method is same as described above and repetition is avoided here.

According to the present invention, the controller 110 and method is provided to use the actual motor torque instead of the requested motor torque to decide the activation of safe state of the steering motor 108. The steering functionality gets benefitted, i.e. increased availability and possible healing of error (excessive torque). The present invention is applicable for the EPS system 120 in the manually driven vehicle 102 and autonomous vehicles 102 having autonomous functions where “Steer by Wire” mandates the increase of availability of the steering motor 108.

It should be understood that the embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.
 
, Claims:We claim:
1. A controller (110) to operate an electrically powered steering motor (108) of a vehicle (102), said controller (110) operates said steering motor (108) based on a steering functionality, said controller (110) configured to,
estimate a requested motor torque to drive said steering motor (108), characterized in that,
determine an actual motor torque imparted by said steering motor (108);
compare said actual motor torque with a safe threshold torque, and
activate a safe state of operation for said steering motor (108) based on said comparison.

2. The controller (110) as claimed in claim 1, wherein said comparison is done to check if said actual motor torque is greater than said safety threshold torque.

3. The controller (110) as claimed in claim 1, wherein said actual motor torque is imparted by said steering motor (108) and determined based on static parameter and dynamic parameters of said steering motor (108).

4. The controller (110) as claimed in claim 3, wherein said static parameter are selected from group comprising number of rotor pole pairs (Zp), inductance of torque production (Lq) and inductance for field weaking (Ld), and said dynamic parameter are selected from a group comprising flux of said permanent magnet (Ψ), current for torque production (Iq), and current for field weaking (Id).

5. The controller (110) as claimed in claim 4, wherein said static parameters are predetermined and stored in a memory element, and said dynamic parameters are determined measured/estimated during operation of said steering motor (108).

6. A method for operating an electrically powered steering motor (108) of a vehicle (102), said method comprising the steps of:
estimating a requested motor torque to drive said steering motor (108), characterized by,
determining an actual motor torque imparted by said steering motor (108);
comparing said actual motor torque with a safe threshold torque, and
activating a safe state of operation for said steering motor (108) based on said comparison.

7. The method as claimed in claim 6, wherein said comparison comprises checking if said actual motor torque is greater than said safety threshold torque.

8. The method as claimed in claim 6, wherein said actual motor torque is imparted by said steering motor (108) and determined by measuring static parameters and dynamic parameters.

9. The method as claimed in claim 8, wherein said static parameter are selected from group comprising number of rotor pole pairs (Zp), inductance of torque production (Lq) and inductance for field weaking (Ld), and said dynamic parameter are selected from a group comprising flux of said permanent magnet (Ψ), current for torque production (Iq), and current for field weaking (Id).

10. The method as claimed in claim 9, wherein said static parameters are predetermined and stored in a memory element, and said dynamic parameters are determined by measuring/estimating during operation of said steering motor (108).