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 the field of automotive steering. In particular the invention discloses a method to calculate a rack position of a steering rack in an automotive steering system and a Steering Control Unit (SCU) configured to do the same.

Background of the invention
[0002] The steering angle measurement determines where the driver wants to steer, and vehicle systems match the steering wheel with the vehicle's wheels. Modern day vehicles equipped with features such as the Electronic Stability Program (ESP), Adaptive cruise control (ACC), Park assist etc. require steering-angle information. Conventional steering angle sensors are mounted on steering column, the steering column is mechanically coupled to a steering rack by means of a rack and pinion arrangement. A separate rack position sensor (RPS) is mounted on the steering rack. Conventional system currently calculate the rack position and steering angle by synchronization of the RPS with either the steering angle sensor at startup or during resynchronization if needed.

[0003] Since the RPS is mounted on the steering rack proximate to a motor and gear assembly that is prone to slipping, the RPS is prone to errors caused by the internal oscillation of the motor. This translates to inaccuracy of the calculated outputs like rack position and steering angle. Further since the RPS is physically distant from the steering column that houses the input shaft of the steering wheel due to stiffness and elasticity it may again give inaccurate values of the steering angle. The current idea proposes calculation of steering angle and rack position based on information only from an inductive torque and angle sensor (a type of steering angle sensor) mounted on the steering column and thereby dispensing with the need of information from the RPS.

[0004] Patent application US2022306192 AA titled “Torque sensor, steering angle sensor and corresponding integrated sensor and monitoring system” discloses a torque sensor that includes an input rotation component, which rotates with a steering column input shaft and is provided with a first conducting part, an output rotation component which rotates with a steering column output shaft and is provided with a second conducting part, and an electromagnetic carrier positioned in a positionally fixed manner and provided with a magnetic field generating component and a magnetic field detection component. The magnetic field generating component generates a magnetic field penetrating the first conducting part and the second conducting part, the magnetic field detection component detects a change in the magnetic field caused by a change in the positions of the first and second conducting parts in the magnetic field when the steering column is under torsional stress, and the steering torque is determined on the basis of the detected change in the magnetic field.

Brief description of the accompanying drawings
[0005] An embodiment of the invention is described with reference to the following accompanying drawings:
[0006] Figure 1 depicts an automotive steering system (100);
[0007] Figure 2 depicts a steering column (104) of the automotive steering system (100);
[0008] Figure 3 illustrates method steps to calculate a rack position of steering rack (106) in the automotive steering (AS) system (100);
[0009] Figure 4 (4a, 4b, 4c, 4d, 4e, 4f) are graphs illustrating calculation of steering angle.

Detailed description of the drawings
[0010] Figure 1 depicts an automotive steering system (100). The automotive steering system (100) comprises an input shaft (141) and an output shaft (142) connected to each other by a torsion bar (143) and a gear system, an inductive torque and angle sensor (ITAS (120)) mechanically coupled to the input shaft (141) and the output shaft (142), the output shaft (142) mechanically coupled to the steering rack (106) by means of a rack and pinion arrangement. A steering control unit (SCU (130)) in communication with the ITAS (120) and other components of the AS system. The input shaft (141), output shaft (142), torsion bar (143) and gear system are collectively known as the steering column (104). The steering column (104) mechanically connects the steering wheel (102) to the steering rack (106).

[0011] Figure 2 depicts the steering column (104) of the automotive steering system (100). The input shaft (141) translates the rotational motion on the steering wheel (102) to a telescopic movement of the torsion bar (143) and a gear system. The gear system comprises a centre gear (145) and a satellite gear (144). Due to this arrangement, there is greater difference between effort and resistance that results in greater degree of twist that exists between input and output shaft (142) as these rotate during steering. The output shaft (142) is connected to the steering rack (106) by means of a rack and pinion arrangement.

[0012] The ITAS (120) is mounted on the steering column (104) such that it is mechanically coupled to the input shaft (141) and the output shaft (142). Such sensors use the basic principle of the underlying inductive, eddy current technology. There is a transmitting coil embedded in a PCT which incurs a magnetic field. The magnetic field is influenced by the gaps in the blades of a rotor mechanically coupled to the output shaft (142). A receiving coil measures the difference between the transmitted and the measured magnetics, and uses it calculate the input shaft (141) angle (ISA) and output shaft (142) angle (OSA). The value of the Input Shaft Angle and Output Shaft Angle is calculated using the following formula. Input Shaft Angle (ISA) = (360 deg/9 (no of rotors in Input Shaft)) = 40 deg (maximum value of Input Shaft Angle). Output Shaft Angle (OSA) = (360 deg/ 6 (no of rotors in Output Shaft) = 60 deg (maximum value of Shaft Angle).

[0013] The steering rack (106) further comprises a motor (108) and rack position sensor (110) (RPS). The RPS detects a linear position of a steering rack (106). Modern vehicles use power steering or an Electronic Power Steering (EPS) system that reduce a driver's effort to turn a steering wheel (102) of a motor (108) vehicle. Commonly used EPS systems control and assist the steering system with the support of this intelligent electric motor (108). Based on the signal from the ITAS (120), the SCU (130) calculates an optimal steering support and sends the information to the electric motor (108) to provide the necessary assistance.

[0014] The steering control unit (SCU (130)) is logic circuitry and software programs that respond to and processes logical instructions to get a meaningful result. The SCU (130) may be implemented in the system as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, one or more microchips or integrated circuits interconnected using a parent board, hardwired logic, software stored by a memory device and executed by a microprocessor, firmware, an application specific integrated circuit (ASIC), and/or a field programmable gate array (FPGA), and/or any component that operates on signals based on operational instructions.

[0015] The SCU (130) receives values of an input shaft (141) angle (ISA) and an output shaft (142) angle (OSA) from the ITAS (120) sensor. It then computes a true power on angle based on ISA, OSA and a predefined satellite gear (144) angle for the gear system. The pre-defined satellite gear (144) angle is determined based on the ratio of the number of tooth in the satellite gear (144) and the centre gear (145). While computing the true power on angle the ECU is configured to calculate an index angle based on the ISA and OSA. It is further configured to perform nonious calculations on the index angle in dependance of the satellite gear (144) angle to compute the true power on angle.

[0016] It then determines a steering angle based on the OSA and a calibrated value of the true power on angle for the vehicle centre. The calibrated value of the power on angle for vehicle centre takes into account any system offset. Finally, it calculates the value of rack position based on the value of steering angle and AS system design parameters. AS design parameters are automotive steering design parameters that include but are not limited to a gear ratio and a rotor to rack ratio. The functionality of the SCU (130) is further elucidated in accordance with figure 3 and method steps 200.

[0017] 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.

[0018] Figure 3 illustrates method steps to calculate a rack position of steering rack (106) in the automotive steering (AS) system (100). The AS system and its major components have been elucidated in accordance with figure 1. For the purposes of clarity, it is reiterated that automotive steering system (100) comprises an input shaft (141) and an output shaft (142) connected to each other by a torsion bar (143) and a gear system, an inductive torque and angle sensor (ITAS (120)) mechanically coupled to the input shaft (141) and the output shaft (142), the output shaft (142) mechanically coupled to the steering rack (106) by means of a rack and pinion arrangement. A steering control unit (SCU (130)) in communication with the ITAS (120).

[0019] Method step 201 comprises receiving values of an input shaft (141) angle (ISA) and an output shaft (142) angle (OSA) from the ITAS (120) sensor. Method step 202 comprises computing a true power on angle based on ISA, OSA and a predefined satellite gear (144) angle for the gear system by means of SCU (130). The true power on angle refers to total amount angular rotation permissible in the steering wheel (102). For example - vehicle with electronic power steering have possibility of turning the steering wheel (102) 2 times in either side hence the true power on angle here can range between -720 degrees to + 720 degrees. The true power on angle is computed using the following method steps. First an index angle is calculated based on the ISA and OSA. Index angle is the calculated using the nonious calculation of ISA and OSA. The Index Angle can be anywhere between 0 to 120 deg. The Gear Angle is calculated is using the following formula, Gear Angle = Satellite Gear (16 no of teeth)/Centre Gear (51- no of teeth) = 16/51 *360 = 112.94 (maximum value of the Gear Angle). The TPO (True Power On Angle) is calculated using the nonious calculation formula where the inputs are Index Angle and Gear Angle. This is followed by performing nonious calculations on the index angle in dependance of the satellite gear (144) angle to compute the true power on angle.

[0020] Method step 203 comprises determining a steering angle based on the OSA and a calibrated value of the true power on angle for the vehicle centre. The calibrated value of the true power on angle for the vehicle centre takes into account an offset in the system. Usually for vehicle centre the true power on angle would be zero but due to some offset in the system it can for example show vehicle centre at +20 degrees.

[0021] The steering angle is determined by integrating the OSA onto the true power on angle for the vehicle centre. This is explained in figure 4. Fig 4a depicts the OSA and ISA. OSA can have values from 0 to 60 deg and ISA can have values from 0 to 40 deg depending upon the number of rotor blades. Figure 4b depicts an Index Angle which is based on the nonious calculation based on the OSA and ISA. Gear Angle or the satellite gear angle is calculated using the Main and satellite gear angle - Formula = (Satellite Gear Angle)/ (Main Gear Angle) * 360. For example (assuming there are 16 and 51 teeths in the gears), thus 16/51 * 360 = 112.94. The Gear Angle can be anywhere between 0 to 112.94. Figure 4c depicts the true power on angle which is based on the nonious calculation of gear angle and index angle. The true power on angle adjusted and synchronized to vehicle centre is also shown. Figure 4d shows the OSA. Figure 4e shows the integrated OSA i.e. OSA accumulated in respect of the vehicle centre. Figure 4f depicts the synchronization of Integrated OSA with true power on angle.

[0022] Method step 204 comprises calculating the rack position based on the value of steering angle and AS system design parameters. AS system design parameters include but are not limited to at least a gear ratio and a rotor to rack ratio. The gear ratio is the ratio to covert Steering Angle to Rotor Angle, it is dependent upon the design of the gear and its value ranges between 18 to 30. The Rotor to Rack is a ratio factor which converts the Rotor Angle to Rack Position, it is usually anywhere between 1.8 to 3.5.The rack position is determined by following formulae:

Rack Position = ((Steering Angle/Gear Ratio) * (Rotor_2_Rack))/360

[0023] 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 modification and customizations to the automotive steering system (100). This idea to develop a method to calculate steering angle and rack position without input information from the rack position sensor (110) or the motor (108) on the steering rack (106) gives a more accurate value of the steering angle and rack position. Since no input is taken from the rack position sensor (110) which is proximate to the motor (108), internal oscillations and noise of the motor (108) are avoided.

[0024] 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 method to calculate rack position of steering rack (106) in the automotive steering (AS) system (100) and the SCU (130) thereof are envisaged and form a part of this invention. The scope of this invention is limited only by the claims.
, Claims:We Claim:
1. A method (200) to calculate a rack position of steering rack (106) in an automotive steering (AS) system (100), said system comprising an input shaft (141) and an output shaft (142) connected to each other by a torsion bar (143) and a gear system, an inductive torque and angle sensor (ITAS (120)) mechanically coupled to the input shaft (141) and the output shaft (142), the output shaft (142) mechanically coupled to the steering rack (106) by means of a rack and pinion arrangement, a steering control unit in communication with the ITAS (120) sensor, the method comprising:
receiving (201) values of an input shaft (141) angle (ISA) and an output shaft (142) angle (OSA) from the ITAS (120) sensor;
computing (202) a true power on angle based on ISA, OSA and a predefined satellite gear (144) angle for the gear system by means of SCU (130);
determining (203) a steering angle based on the OSA and a calibrated value of the true power on angle for the vehicle centre;
calculating (204) the rack position based on the value of steering angle and AS system design parameters.

2. The method (200) to calculate a rack position of steering rack (106) as claimed in claim 1, wherein true power on angle is computed using the following method steps:
calculating an index angle based on the ISA and OSA;
performing nonious calculations on the index angle in dependance of the satellite gear (144) angle to compute the true power on angle.

3. The method (200) to calculate a rack position of steering rack (106) as claimed in claim 1, wherein the AS system design parameters include at least a gear ratio and rotor to rack ratio.

4. A Steering Control Unit (SCU (130)) adapted to calculate a rack position of steering rack (106) in an automotive steering (AS) system (100), said system comprising an input shaft (141) and an output shaft (142) connected to each other by a torsion bar (143) and a gear system, an inductive torque and angle sensor (ITAS (120)) mechanically coupled to the input shaft (141) and the output shaft (142), the output shaft (142) mechanically coupled to the steering rack (106) by means of a rack and pinion arrangement, the SCU (130) in communication with the ITAS (120) sensor, the SCU (130) configured to:
receive values of an input shaft (141) angle (ISA) and an output shaft (142) angle (OSA) from the ITAS (120) sensor;
compute a true power on angle based on ISA, OSA and a predefined satellite gear (144) angle for the gear system;
determine a steering angle based on the OSA and a calibrated value of the true power on angle for the vehicle centre;
calculate the rack position based on the value of steering angle and AS system design parameters.

5. The Steering Control Unit (SCU (130)) adapted to calculate a rack position as claimed in claim 4, wherein the SCU (130) is configured to compute true power on angle is computed by:
calculating an index angle based on the ISA and OSA;
performing nonious calculations on the index angle in dependance of the satellite gear (144) angle to compute the true power on angle.

6. The Steering Control Unit (SCU (130)) adapted to calculate a rack position as claimed in claim 4, wherein the AS system design parameters include at least a gear ratio and a rotor to rack ratio.