Method for controlling a steering assist system of a vehicle

Abstract

The present disclosure relates to a method for controlling a steering assist system of a vehicle. Based on a signal indicative of a road characteristics of a road segment, a flow of fluid supplied by a fluid pump is controlled to generate a steering assist force to a wheel of the vehicle.

Claims

1. A method for controlling a steering assist system of a vehicle, comprising: obtaining a signal indicative of road characteristics of a road segment operable by a vehicle; determining a required wheel angle for operating the vehicle during the road segment; determining a desired steering assist force to be applied to a wheel based on the required wheel angle; and controlling flow of fluid supplied by a fluid pump of the steering assist system based on the steering assist force when operating the vehicle at the road segment to generate the steering assist force to the wheel of the vehicle during operation, the fluid pump connected to a steering system of the vehicle.

2. The method of claim 1, wherein the flow of fluid supplied by the fluid pump is controlled proportionally to the desired steering assist force.

3. The method of claim 1, further comprising: obtaining a signal indicative of a parameter value relating to a lateral acceleration of the vehicle; and controlling the flow of fluid supplied by the fluid pump based on the steering assist force and the lateral acceleration.

4. The method of claim 3, wherein the signal indicative of the parameter value relating to the lateral acceleration is received from an acceleration sensor when operating the vehicle during the road segment.

5. The method of claim 1, further comprising: obtaining a signal indicative of an applied steering wheel torque applied by a vehicle operator; and controlling the flow of fluid supplied by the fluid pump based on the steering assist force and the applied steering wheel torque.

6. The method of claim 1, further comprising: comparing the required wheel angle with a predetermined threshold angle; and reducing the flow of fluid supplied by the fluid pump to a lower steering assist force limit when the required wheel angle is below the predetermined threshold wheel angle.

7. The method of claim 6, wherein the lower steering assist force limit is between 20%-40% of a maximum steering assist force capacity of the fluid pump.

8. The method of claim 6, wherein the predetermined threshold wheel angle is between 0-2 degrees.

9. The method of claim 1, wherein the fluid pump is a hydraulic fluid pump arranged to supply a flow of a hydraulic fluid for generating the steering assist force.

10. The method of claim 1, wherein the steering assist system further comprises a positioning system, the positioning system being arranged to determine the road characteristics of the road segment.

11. The method of claim 1, wherein the fluid pump is connected to an internal combustion engine of the vehicle for operation of the fluid pump, the fluid pump comprising a valve for controlling the supply of fluid flow, wherein the method further comprises: controlling the flow of fluid supplied by the fluid pump by controlling an openness degree of the valve.

12. The method of claim 1, wherein the fluid pump is connected to an electric machine of the vehicle for controlling operation of the fluid pump, the method further comprising: controlling the flow of fluid supplied by the fluid pump by electrically controlling a rotational velocity of the electric machine.

13. A steering assist system of a vehicle, the steering assist system comprising: a positioning system; a fluid pump connected to a steering system of the vehicle, wherein the fluid pump is arranged to supply a flow of fluid for generating a steering assist force to a wheel of the vehicle during operation; and a control unit arranged to communicate with the positioning system, wherein the control unit is configured to: obtain a signal from the positioning system, the signal being indicative of road characteristics of a road segment operable by the vehicle; determine a required wheel angle for operating the vehicle during the road segment; determine a desired steering assist force to be applied to the wheel based on the required steering angle; and control the fluid pump to supply a flow of fluid based on the steering assist force when operating the vehicle at the road segment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above, as well as additional objects, features and advantages, will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments, wherein:

(2) FIG. 1 is a lateral side view illustrating a vehicle in the form of a truck, which is arranged to utilize a steering assist system according to an example embodiment;

(3) FIG. 2 is a schematic illustration of a steering assist system according to an example embodiment; and

(4) FIG. 3 is a flow chart of a method for controlling the steering assist system according to an example embodiment.

DETAILED DESCRIPTION

(5) The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. Like reference character refer to like elements throughout the description.

(6) With particular reference to FIG. 1, there is provided a vehicle 100 in the form of a truck. The vehicle 100 comprises a pair of steerable wheels 102 connected to a steering wheel 104 of the vehicle 100. The vehicle also comprises a steering assist system 150 for steering assist during operation of the vehicle 100. In the exemplified embodiment, the steering assist system 150 comprises a steering system 300 connected to the wheels 102 as well as to the steering wheel 104. The steering assist system 150 further comprises a positioning system 200, 400, in the following also exemplified as a GPS 200 and a camera 400 arranged to visually determine the characteristics of the road ahead of the vehicle 100. Although FIG. 1 illustrates a positioning system comprising both a camera 400 and a GPS 200, the present disclosure is not limited to the use of both of these devices, it is equally applicable with the use of only one of them.

(7) In order to describe the steering system 150 and its functionalities in further detail, reference is made to FIG. 2, which is a schematic illustration of the steering assist system 150 according to an example embodiment. As can be seen, and as briefly described above, the steering assist system 150 comprises the positioning system 200, 400, a fluid pump 500 connected to the steering system 300 of the vehicle, and a control unit 450 arranged in communication with the positioning system 200, 400 and the fluid pump 500. As will also be described in further detail below, the control unit 450 is arranged to receive control signal(s) from the positioning system and to control the fluid pump 500 based on this/these signals.

(8) The control unit may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the control unit includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device.

(9) In the exemplified embodiment depicted in FIG. 2, the steering system comprises a steering gear 600 and a cardan joint 700 connecting the fluid pump 500 to the steerable wheels 102. The fluid pump 500 is thus arranged to supply a flow of fluid for generating a steering assist force to the steerable wheels 102 of the vehicle during e.g. a turning maneuver.

(10) The fluid pump is preferably arranged as a hydraulic fluid pump 500 configured to generate the steering assist force to the steerable wheels 102 by supplying a flow of hydraulic fluid for operation of the fluid pump 500. According to an example embodiment, the fluid pump can be connected to a prime mover 550, in the form of an internal combustion engine, of the vehicle for controlling operation thereof. In such a case, the flow of fluid supplied by the fluid pump can be controlled by means of a valve (not shown). In further detail, the operational capacity, and thus in turn the steering assist force generated to the steerable wheels, is controlled by controlling the openness degree of the valve. When reducing the flow of fluid through the valve, the operational capacity of the fluid pump will be reduced, whereby a reduced steering assist force is generated.

(11) According to another example embodiment, the fluid pump can instead be connected to, and controlled by, a prime mover 550 in the form of an electric machine. In such a case, the flow of fluid supplied by the fluid pump 500 is controlled by controlling the rotational velocity of the electric machine. Thus, an increased rotational velocity generates an increased supply of fluid flow, and in turn an increased steering assist force.

(12) In order to describe the functionality of controlling the steering assist system 150 in further detail, reference is made to FIG. 3, in combination with the features illustrated in FIG. 2.

(13) During operation of the vehicle, a signal indicative of the road characteristics of a road segment operable by the vehicle is obtained S1 by the control unit 450. Preferably, and as described above, the signal is received from the positioning system 200, 400. Hereby, the control unit 450 receives data indicative of the upcoming road characteristics, e.g. the curvature of the road. Based on the road characteristics, the control unit 450 determines S2 a required steering angle of the steerable wheels 102, whereby the determined required steering angle is sufficient for operating the vehicle during the road segment.

(14) The control unit 450 further determines S3, based on the required steering angle, a desired steering assist force to be applied to the steerable wheels 102 of the vehicle. When the vehicle 100 is operated at the road segment, the control unit 450 controls S4 the flow of fluid supplied by the fluid pump 500 based on the determined steering assist force. As described above, the flow of fluid can be controlled by a valve or by the rotational velocity of an electric machine depending on the current application and type of vehicle.

(15) By means of the above described control functionality of the fluid pump 500, the fluid pump 500 is not operated at its full capacity if not needed to. Preferably, the flow of fluid supplied by the fluid pump is controlled proportionally to the desired steering assist force. According to a non-limiting example, if the desired steering assist force is determined to be 70% of its full capacity, the fluid pump 500 is controlled to supply a flow of fluid of approximately 70% of its full flow capacity.

(16) Preferably, the fluid pump is controlled to always maintain a minimum steering assist force. If the road segment is substantially straight, i.e. comprising no curvature, the fluid pump 500 is preferably controlled to supply a flow of fluid to generate a lower steering assist force. The lower steering assist force is preferably between 20-40% of a maximum steering assist force capacity of the fluid pump 500. The steering assist force is thus preferably increased proportionally from the lower steering assist force level up to its full capacity.

(17) The above described fluid pump 500 may also be controlled based on a signal received from an acceleration sensor (not shown). The acceleration sensor is in such a case arranged to obtain a current lateral acceleration of the vehicle. The lateral acceleration signal is transmitted to the control unit 450, whereby the control unit 450 controls the fluid pump 500 to supply a flow of fluid also based on the determined lateral acceleration. As a further option, the control unit 450 can receive a signal indicative of a current steering wheel torque applied by an operator of the vehicle. In such a case, the control unit controls the flow of fluid supplied by the fluid pump 500 also based on the applied steering wheel torque.

(18) It is to be understood that the present disclosure is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.