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 steering systems and more specifically to steer by wire systems.

[0002] Background of the invention
[0003] The steer by wire (SBW) systems electrically connects the steering wheel with the road wheel , without any mechanical linkages between the two. A road wheel motor drive provides the transmission of the driver’s input steering request to the vehicle wheels and a steering wheel motor drive provides the feel of steering to the driver. The SBW comprises steering wheel (SW) and road wheel (RW) modules. The SW module receives the driver’s commands and converts the demanded angle or torque to an electronic signal using appropriate sensors located on steering wheel motor shaft. The electronic signal are transmitted to a RW electronic control unit (ECU) in order to determine a relevant command for the vehicle wheels motor drive. The RW ECU also receives other information from speed sensors, accelerometers, angle sensors, and yaw rate sensors to determine corresponding commands to be sent to the HW actuator.
[0004] In the present vehicles equipped with SBW functionality, typically when the vehicle is being parked or taking a U-turn, more rotations of the steering wheel are required to take shorter turns. Parking the vehicle becomes cumbersome, when multiple rotations of steering wheel are required to move the road wheels from left to right. The maneuvers become more tiring when the vehicle has to be reversed whilst parking.
[0005] The present invention solves the problem aforementioned by increasing sensitivity of the steering wheel with respect to the vehicle wheel while the vehicle runs on a speed lower than a threshold safety speed limit. The presents invention discloses a technique to increase the steering wheel rotation sensitivity such the ratio of the steering wheel rotation angle to the vehicle wheel rotation angle is one or close to one.

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 a steer by wire system with a controller to improve a steering sensitivity
[0008] Figure 2 depicts a flowchart for a method to improve a steering sensitivity

[0009] Detailed description of the drawings

[0010] The present invention discloses a system and a method to improve a steering sensitivity in a steer by wire system of a vehicle.
[0011] The present invention will now be described by way of example, with reference to accompanying drawings. Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In predetermined instances, details which are not necessary for an understanding of the present invention, or which render other details difficult to perceive may have been omitted.
[0012] The steer by wire system comprises a steering wheel mounted on a steering shaft. Sensors are mounted on the steering shaft to detect a torque applied by the driver on the steering wheel and the rotation angle of the steering wheel. In an embodiment, at least one of the sensors mounted on the steering is a torque sensor and a steering wheel angle sensor. The steering wheel further comprises a feedback motor to transmit a reaction force to the steering wheel. The reaction force is a force in a direction opposite to the direction in which the driver steers the steering wheel. The feedback motor receives command from a feedback motor control unit. The feedback motor control unit computes a feedback motor drive current based on the torque applied by the driver on the steering wheel, the steering wheel rotation angle and based on the input signals received from a steering motor control unit.
[0013] The steer by wire system comprises a steering shaft comprising the road wheels mounted on it. The steering shaft further comprises a steering motor that actuates the turning of the road wheels according to the torque applied on the steering wheel in the steering coloumn. The steering motor is driven based on the commands from the steering motor control unit. The steering motor control unit drives the steering motor based on a steering motor drive current output. The steering motor drive current output is computed by the steering motor control unit based on input from plurality of sensors. The steering motor control unit is in communication with plurality of sensors. In an example, these plurality of sensors include (non exhaustively) speed sensors, accelerometers, angle sensors, yaw rate sensors and the torque sensor.
[0014] The steering motor comprises a steering motor angle sensor to detect a rotational angle of the steering motor. Based on this rotational angle of the steering motor, the steering motor control unit computes a signal for the feedback motor control unit, which in turn computes the feedback motor drive current. It is to be understood that all the in vehicle communications between sensors, motors and controllers may be made based on controller area network (CAN) bus operation which may be an event-trigged or time triggered such as in CAN (TTCAN), Byteflight, and Flexray.

[0015] Referring now to Figure 1, the same depicts a controller(1) to improve a steering sensitivity in a steer by wire system (10) of a vehicle. The controller (1) may be an electric control unit (ECU) of a vehicle. Said controller may comprise an inbuilt processor with an associated memory. The controller may further comprise input/output interface, communication links, embedded softwares and the electronic circuitry to perform the function further described. According to an aspect of the present embodiment in this disclosure, the controller may comprise the steering motor control unit(1a) and the feedback motor control unit(1b) as described above. According to another aspect of the present invention, the steering motor control unit(1a), the feedback motor control unit (1b) and the proposed controller(1) may be separate components so as to form a combined controlling system (10).

[0016] Said controller(1) is in communication with at least one torque sensor (3) adapted to measure an input torque applied to a steering wheel (2). Said controller is further in communication with at least one steering sensor(4) adapted to measure a steering wheel rotation angle, at least one vehicle wheel rotation sensor (5) adapted to measure a vehicle wheel rotation angle and at least one speed sensor(6) adapted to measure a speed of the vehicle.

[0017] Said controller is adopted to obtain a gain factor in accordance with a pre-defined value, from the steering wheel rotation angle with the vehicle wheel rotation angle. The gain factor is a ratio of the steering wheel rotation angle with the vehicle wheel rotation angle. The same indicates the steering sensitivity, that is, for every unit angle of rotation of steering wheel, the corresponding unit angle of the road wheel turned indicates the steering sensitivity.

[0018] The controller is adapted to maintain said obtained gain factor in accordance with a pre-defined value. An objective of the present disclosure is to improve this steering sensitivity when the vehicle is below a threshold speed. Therefore, the pre-defined value of the gain factor under ideal parameters should be one (or closest to one). The gain factor value is maintained based on the speed of the vehicle, the steering wheel rotation angle, the vehicle wheel rotation angle and the input torque.

[0019] The controller(1) is in communication with at least one steering motor(7) to actuate a turning of at least one wheel (8) of the vehicle, and at least one feedback motor(8) to transmit a reaction force to the steering wheel of the vehicle. The controller(1) is adapted to compute a feedback motor drive current to drive the feedback motor(8), and a steering motor drive current to drive the steering motor(7). The feedback motor drive current and the steering motor drive current is computed based on the speed of the vehicle, the steering wheel rotation angle, the vehicle wheel rotation angle (of vehicle wheel (9)) and the input torque. The controller maintains the gain factor in accordance with the pre-defined value when the speed of the vehicle is below a threshold speed.

[0020] In an example, when the speed of the vehicle is below a threshold speed, as detected by the speed sensor, the output steering motor drive current is computed by the controller (by the steering motor control unit as a part of the controller) such that the steering wheel rotation angle and the vehicle wheel rotation angle are equal or nearing to equal. The threshold speed may be calibrated based on the speed generally adapted by a driver in parking scenarios or the scenarios when the driver is taking a U-turn.
[0021] Referring to figure 2, the same depicts a method (100) to improve a steering sensitivity in a steer by wire system(see Fig 1) of a vehicle by a controller. Said controller (See Fig 1) in is communication with at least one torque sensor adapted to measure an input torque applied to a steering wheel, at least one steering sensor adapted to measure a steering wheel rotation angle, at least one vehicle wheel sensor adapted to measure a vehicle wheel rotation angle and at least one speed sensor adapted to measure a speed of the vehicle. It is to be understood that a system to implement the method (100) is described in Fig 1 as explained above. The method (100) comprises the step (101) of obtaining a gain factor value, by the controller, from the steering wheel rotation angle and the vehicle wheel rotation angle. The method step (102) is maintaining the gain factor in accordance with a pre-defined value, by the controller, based on the speed of the vehicle, the steering wheel rotation angle, the vehicle wheel rotation angle and the input torque. The controller in communication with at least one steering motor to actuate a turning of at least one wheel of the vehicle at least one feedback motor to transmit a reaction force to the steering wheel of the vehicle. The method (103) is computing by the controller a feedback motor drive current to drive the feedback motor, and a steering motor drive current to drive the steering motor based on the speed of the vehicle, the steering wheel rotation angle, the vehicle wheel rotation angle and the input torque. The gain factor is maintained by the controller when the speed of the vehicle is below a threshold speed.

[0022] In an example, when the speed of the vehicle is below a threshold speed, as detected by the speed sensor, the output steering motor drive current is computed by the controller (by the steering motor control unit as a part of the controller) such that the steering wheel rotation angle and the vehicle wheel rotation angle are equal or nearing to equal. The threshold speed may be calibrated based on the speed generally adapted by a driver in parking scenarios or the scenarios when the driver is taking a U-turn.
[0023] The present invention thus provides improved steering sensitivity in the scenarios when steering sensitivity is needed to minimize the input effort by the driver.
, Claims:We Claim:
1. A controller (1) to improve a steering sensitivity in a steer by wire system(10) of a vehicle, said controller in communication with:
- at least one torque sensor(2) adapted to measure an input torque applied to a steering wheel(3),
- at least one steering sensor(4) adapted to measure a steering wheel rotation angle,
-at least one vehicle wheel rotation sensor(5) adapted to measure a vehicle wheel rotation angle,
-at least one speed sensor (6) adapted to measure a speed of the vehicle,

characterized in that,

said controller(1) adapted to obtain a gain factor value from the steering wheel rotation angle and the vehicle wheel rotation angle.

2. The controller(1) as claimed in Claim 1, wherein, said controller adapted to maintain said obtained gain factor in accordance with a pre-defined value, based on :
the speed of the vehicle,
the steering wheel rotation angle,
the vehicle wheel rotation angle and
the input torque.

3. The controller (1) as claimed in Claim 1, the controller in communication with:

-at least one steering motor (7) to actuate a turning of at least one wheel of the vehicle,
-at least one feedback motor (8) to transmit a reaction force to the steering wheel of the vehicle,

said controller adapted to compute:
- a feedback motor drive current to drive the feedback motor (7), and
-a steering motor drive current to drive the steering motor(8),

based on the speed of the vehicle, the steering wheel rotation angle, the vehicle wheel rotation angle and the input torque.

4. The controller (1) as claimed in Claim 1, wherein the controller maintains the gain factor in accordance with the pre-defined value when the speed of the vehicle is below a threshold speed.

5. A method(100) to improve a steering sensitivity in a steer by wire system of a vehicle by a controller, said controller in communication with:
- at least one torque sensor adapted to measure an input torque applied to a steering wheel,
- at least one steering sensor adapted to measure a steering wheel rotation angle,
-at least one vehicle wheel sensor adapted to measure a vehicle wheel rotation angle,
-at least one speed sensor adapted to measure a speed of the vehicle,

characterized in that method,

obtaining a gain factor value, by the controller, from the steering wheel rotation angle and the vehicle wheel rotation angle (101).

6. The method (100) as claimed in Claim 5, wherein, maintaining the gain factor in accordance with a pre-defined value, by the controller, based on the speed of the vehicle, the steering wheel rotation angle, the vehicle wheel rotation angle and the input torque (102).

7. The method (100) as claimed in Claim 5, the controller in communication with:

-at least one steering motor to actuate a turning of at least one wheel of the vehicle,
-at least one feedback motor to transmit a reaction force to the steering wheel of the vehicle,
wherein,

computing by the controller:
-a feedback motor drive current to drive the feedback motor, and
-a steering motor drive current to drive the steering motor,
based on the speed of the vehicle, the steering wheel rotation angle, the vehicle wheel rotation angle and the input torque (103).

8. The method (100) as claimed in Claim 5, wherein regulating the gain factor, by the controller when the speed of the vehicle is below a threshold speed.