System for modification of the steering ratio for a vehicle provided with a steering wheel, and corresponding vehicle

1. A modification system for modifying the steering ratio for a vehicle having steered wheels, a steering wheel, and a steering transmission device serving to transmit steering movement between the steering wheel and the steered wheels with a steering ratio R=Alpha/Beta, where Alpha is the turning angle of the steering wheel, and Beta is the steering angle of the wheels;

said system comprising a device for determining the angular speed of the steering wheel, and

a control module for controlling the steering ratio R that is configured to calculate the steering ratio as a function of the angular speed of the steering wheel,

wherein said control module is configured to reduce the steering ratio R when the angular speed of the steering wheel increases, and

wherein said module for controlling the steering ratio R is configured to calculate the steering ratio as a function of the angular speed of the steering wheel when the speed of the vehicle is in a given speed range, referred to as a “low” speed range, the steering ratio being independent of the angular speed of the steering wheel above this low speed range, or with the influence of the angular speed of the steering wheel on the steering ratio being reduced for a vehicle speed above this low speed range.

2. A system according to claim 1 , wherein the module for controlling the steering ratio is configured in such a manner as to calculate the steering ratio also as a function of the travel speed of the vehicle.

3. A system according to claim 1 , wherein said module for controlling the steering ratio R is configured to calculate the steering ratio as a function of the angular speed of the steering wheel when the speed of the vehicle is in a speed range in the range 0 km/h to 10 km/h, preferably in the range 0 km/h to 8 km/h, e.g. in the range 0 km/h to 5 km/h.

4. A system according to claim 1 , wherein, said vehicle includes a tiltable telescopic boom arm, the system includes an angle sensor (Af) for sensing the angle formed between the telescopic arm and the bearing plane of the wheels of the vehicle on the ground, and the module for controlling the steering ratio (R) is configured in such a manner as to calculate the steering ratio also as a function of the value of the angle, referred to as the boom angle, formed between the telescopic arm and the bearing plane of the wheels of the vehicle on the ground, in such a manner as to increase the steering ratio when the boom angle increases.

5. A system according to claim 4 , wherein, said system includes a load sensor configured to determine the load at, or in the vicinity of, the end of the telescopic arm, and the module for controlling the steering ratio is configured to modify the steering ratio R as a function of said determined load.

6. A wheeled vehicle including:

steered wheels;

a steering wheel; and

a steering transmission device serving to transmit steering movement between the steering wheel and the steered wheels with a steering ratio R=Alpha/Beta, where Beta is the steering angle of the wheels, and Alpha is the turning angle of the steering wheel;

said vehicle being wherein said wheeled vehicle also includes a system for modifying the steering ratio in accordance with claim 1 .

7. A vehicle according to claim 6 , wherein the module for controlling the steering ratio is configured in such a manner as to modify the steering ratio also as a function of accelerator pedal depression.

8. A vehicle according to claim 6 or claim 7 , wherein the steering transmission device comprises a hydraulic circuit.

9. A vehicle according to claim 8 , wherein the hydraulic circuit comprises:

a pump, also referred to as an “integral pump”, making it possible to pressurize the hydraulic circuit;

a hydraulic valve system coupled to the steered wheels;

a steering pump making it possible to direct the steering fluid towards one side or the other of the or each valve of the hydraulic valve system as a function of the turning of the steering wheel; and

a system for increasing flow rate, preferably a proportional solenoid valve, that can be controlled by the control module for causing additional steering fluid flow to be added into the hydraulic circuit as a function of the steering ratio defined by the control module.