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 systems are steering systems without mechanical linkages (pinions and gears) between the steering wheel and the road wheel. The steer by wire system uses electric signals to control the steering angle. The steering wheel angle sensors sense the driver’s input which in turn is sent as a signal input to a control unit. These signals are then sent to the steering rack actuator in order to physically turn the vehicle. The steering rack actuator then uses electric motors to adjust the angle and direction of wheel.
[0004] The steer by wire system mainly comprise of the steering wheel actuator (SWA) and the steering rack actuator (SRA). Whilst the SWA acts as the connection point with the driver, the SRA acts as the connection point with front wheel. Both the SWA and SRA comprise position sensors, electric motors and control units to electrically send signals across each other.
[0005] These steer by wire systems have no physical connection between the steering wheel and road wheels due to absence of intermediate shaft connecting the SWA and SRA. Considering the safety, the steer-by-wire system requires redundant hardware such as backup ECU, motor, and sensors. And additional software safety measures require to achieve redundancy. All of it increases the cost of the steering system.

[0006] The prior art US2023032374 AA proposes A steer-by-wire device for controlling a vehicle includes a housing; an input shaft that is rotatable relative to the housing and is configured to receive a rotary input from an operator of the vehicle at a first end of the input shaft, the first end being located external to the housing; a rotor attached to the input shaft at a second, opposite, end of the input shaft, the second end being located internal to the housing; a sensor for detecting an angular position, an angular velocity, and/or an angular acceleration of the input shaft relative to the housing; and a coil for generating a magnetic field to generate a rotary force or torque in the rotor to resist rotation of the rotor. The rotor is attached to the input shaft to allow a relative movement between at least a portion of the rotor and the input shaft.

[0007] An objective of the present invention is to obtain a cost effective and safe steer-by-wire system that eliminates the redundant hardware & software required by the SWA in order to establish a connection between Steering Wheel Actuator (SWA) and Steering Rack Actuator (SRA). The same is achieved by using a flexible shaft for torque transfer, only when primary hardware of the steer by wire system fails.

Brief description of the accompanying drawings
[0008] An embodiment of the invention is described with reference to the following accompanying drawings:
[0009] Figure 1 depicts a system a system to transmit a torque supplied to a steering wheel of a vehicle to at least one road wheel of the vehicle.
[0010] Figure 2 depicts a flow chart for a method to transmit a torque from a steering wheel of the vehicle to at least one road wheel of the vehicle.

Detailed description of the drawings

[0011] The steer by wire system comprises a steering wheel actuator (SWA) and a steering rack actuator (SRA). Unlike the conventional steering system, the steer by wire systems do not have a physical connection between the steering wheel actuator and the steering rack actuator. This physical connection in the conventional steering systems is replaced by wires in the steer by wire systems which serve the purpose of communication between the steering wheel actuator and the steering rack actuator.
[0012] The steering wheel actuator (SWA) acts as a connection point with the driver. The same comprises steering wheel angles sensors, position sensors, an electrically adjustable stowable steering column, gears (or electrically run gear box), a steering control unit (which may be an ECU), a motor and the encoded software to send and receive signals. The steering control unit receives signals from steering wheel sensors and translates them into commands for gears to convert the high speed output of the motor into the slower and higher torque output needed to turn the wheels.

[0013] The steering rack actuator (SRA) acts as the connection point for wheels for the driver to turn the vehicle. It comprises the steering rack, gears , tie rods and the control unit. The control unit or the control circuitry of the steering rack actuator comprises of motor, ECU and the encoded software to receive signals from the steering wheel actuator and translate them into commands for gears.

[0014] Due to the complexity of the steer by wire system and lack of any physical connection between the steering wheel actuator and steering rack actuator, backup motors, ECU and additional hardware has to be installed in the steer by wire system.

[0015] In the present disclosure, this gap is filled by a flexible shaft installed between the SRA and SWA that functions only when the SWA is unable to transfer the torque to SRA. A controller is adapted to detect this failure to transfer the torque and actuate the flexible shaft to transfer the said torque.

[0016] A flexible shaft transmits rotary motion much like a solid steel shaft, but it can be routed over, under, and around obstacles that would make using a solid shaft impractical. A "Flexible Shaft Assembly" consists of a rotating shaft (sometimes called a core) with end fittings for attachment to the driving and driven mating parts. A protective outer casing is used when necessary. This casing has its own fittings, called ferrules, which keep it stationary during use. Flexible Shafts are often the preferred choice for rotary motion transmission over Gear boxes, Universal joints, and Belts-and-pulleys. It is a highly effective means of transmitting rotary motion and is more efficient than universal joints, gears, sprockets and chains, or belts and pulleys and can be used for bi-direction rotation application. Flexible shaft are typically used in Aerospace and medical fields.

[0017] In addition, they pose the advantages of eliminating alignment problems, being light weight, easy to install, providing greater degree of freedom, having lower installation cost amongst the others.

[0018] 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.

[0019] Referring to Figure 1 , the same depicts a system a system to transmit a torque supplied to a steering wheel of a vehicle to at least one road wheel of the vehicle.

[0020] The system(10) comprises a steer-by-wire unit {(1) represented by dotted box} adapted to transmit the torque from the steering wheel (2) to said at least one road wheel (3). The steer-by-wire unit comprises a steering wheel actuator (SWA) (4) in connection with the steering wheel (2). It further comprises a steering rack actuator (SRA) (5) in connection with said at least one road wheel (3). At least one Engine control unit (ECU) (9) is in connection with the Steering Wheel Actuator(SWA) and the steering rack actuator (SRA).

[0021] It is to be noted that the SRA and SWA may have individual ECUs each as control units comprising the control circuitry and the software to send across signals. The same is not to be construed as limiting the scope of the invention.

[0022] The system is further characterized by a controller(6) adapted to detect a failure of the steer by wire unit (1) to transmit the torque from steering wheel to said at least one road wheel and a flexible-shaft (7) connecting the SWA (4) with the SRA (5) to transmit the torque from the SWA to SRA when the steer-by-wire unit (1) fails to transmit the torque from the steering wheel (2) to said at least one road wheel (3).
[0023] The controller(6) is adapted to detect actuate a flexible shaft (7) to transmit the torque from the steering wheel actuator (SWA)(6) to the steering rack actuator (SRA)(5) upon the failure of the steer-by-wire unit to transmit the torque from steering wheel to said at least one road wheel.
[0024] In an example the controller(6) may be the at least one ECU (9) as explained above.
[0025] The flexible shaft(7) forms an electromechanical connection between the SWA and SRA and is actuated by the controller.
[0026] In an example, when a driver applies a certain torque on the steering wheel. Due to reasons such as malfunction in the electronic or software components of the steer by wire system, malfunction of gearbox and motors or power supply issues, the steer by wire system may fail to transfer the torque from the steering wheel actuator to steering rack actuator. This failure is detected by controller by means of sensor and electrical signals. Upon detection of the failure, the controller activates the flexible shaft between the SWA and SRA, thereby making an electromechanical linkage between the two and successfully transferring the torque from steering wheel and the road wheel.

[0027] Referring to figure 2, the same depicts a method to transmit a torque from a steering wheel of the vehicle to at least one road wheel of the vehicle. The method (100) described herein is implemented by the system (10) described in Figure 2 above. The first step (101) of the method includes transmitting the torque from the steering wheel to the at least one road wheel by a steer by a wire unit. The steer by wire unit comprises the steering wheel actuator (SWA) in connection with the steering wheel ; the steering rack actuator (SRA) in connection with said at least one road wheel and at least one Engine control unit (ECU) in a wired connection with the SWA and the SRA ( See Figure 1). The method is followed by the charachterizing step (102) of detecting, by a controller, a failure of steer-by-wire unit to transmit the torque from the steering wheel to said at least one road wheel and the step (103) of transmitting the torque from the steering wheel actuator (SWA) to the steering rack actuator (SRA) through a flexible shaft when the steer-by-wire unit fails to transmit the torque from the SWA to SRA. The flexible shaft is actuated by the said controller
, Claims:We Claim:

1. A system (10) to transmit a torque supplied to a steering wheel(2) of a vehicle to at least one road wheel of the vehicle(3), the system comprising:
-a steer-by-wire unit(1) adapted to transmit the torque from the steering wheel(2) to said at least one road wheel (3), the steer-by-wire unit(1) comprising:
-a steering wheel actuator (SWA)(4) in connection with the steering wheel ;
-a steering rack actuator (SRA)(5) in connection with said at least one road wheel;
- at least one Engine control unit (ECU)(9) in connection with the Steering Wheel Actuator(SWA) and the steering rack actuator (SRA);
characterized in the system:
-a controller (6) adapted to detect a failure of the steer by wire unit (1) to transmit the torque from steering wheel (2) to said at least one road wheel (3); and
-a flexible-shaft (7)connecting the SWA with the SRA to transmit the torque from the SWA to SRA when the steer-by-wire unit (1) fails to transmit the torque from the steering wheel (2) to said at least one road wheel (3).

2. The system (10) as claimed in Claim 1, wherein, the controller is further adapted to :
-actuate the flexible shaft (7) to transmit the torque from the steering wheel actuator (SWA) (4) to the steering rack actuator (SRA) (5) upon the failure of the steer-by-wire unit to transmit the torque from steering wheel to said at least one road wheel.

3. The system(10) as claimed in Claim 1, wherein, the controller(6) is the at least one ECU (9).

4. A method (100) to transmit a torque from a steering wheel of a vehicle to at least one road wheel of the vehicle, the method comprising the steps of:
- transmitting the torque from the steering to the at least one road wheel by a steer by wire unit (101) comprising :
a steering wheel actuator (SWA) in connection with the steering wheel ;
a steering rack actuator (SRA) in connection with said at least one road wheel;
at least one Engine control unit (ECU) in a wired connection with the SWA and the SRA;
the method characterized by the step of:
-detecting, by a controller, a failure of steer-by-wire unit to transmit the torque from the steering wheel to said at least one road wheel (102).

- transmitting the torque from the steering wheel actuator (SWA) to the steering rack actuator (SRA) through a flexible shaft when the steer-by-wire unit fails to transmit the torque from the SWA to SRA (103).

5. The method (100) as claimed in Claim 4, wherein, the method comprises the further step of:
- actuating, by the controller, the flexible-shaft to transmit the torque from the steering wheel to the said at least one road wheel upon the failure of the steer-by-wire unit to transmit the torque from steering wheel to said at least one road wheel.