Power-assisted steering system of an automobile

• US 20030150665A1
• Filed: 02/10/2003
• Published: 08/14/2003
• Est. Priority Date: 03/20/2000
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Weeber, Kai, Muenz, Rainer
• Granted Patent: US 7,168,520 B2
• Time in Patent Office: Days
• US Class Current: 180/421
• CPC Class Codes: B62D 5/008 Changing the transfer ratio between the steering wheel and the steering gear by variable supply of energy, e.g. by using a superposition gear
• CPC Class Codes: B62D 6/003 in order to control vehicle yaw movement, i.e. around a vertical axis B62D6/007 takes precedence
• CPC Class Codes: B62D 6/008 Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications

Abstract

The invention concerns a servo-assisted steering system (1) for a motor vehicle, in which the steering system (1) comprises a steering wheel (2) for presetting a desired steering angle for the wheels (3) of the motor vehicle, driving-dynamics means (4) for superimposing a correction angle on the steering angle, said correction angle being determined with a view toward increasing the driving stability and/or the driving comfort of the motor vehicle, and a servo drive (6). To keep the efficiency of the driving-dynamics means (4) nearly constant over the entire road-speed range of the vehicle, it is proposed that the servo drive (6) be implemented as a variable torque assistance system, the degree of torque assistance (M) being dependent on the road speed (V) of the vehicle and on at least one variable of the driving-dynamics means (4) that characterizes the correction angle.

Claims

1. A servo-assisted steering system (1) for a motor vehicle, said steering system (1) comprising a steering wheel (2) for presetting a desired steering angle for the wheels (3) of said motor vehicle, driving-dynamics means (4) for superimposing a correction angle on said steering angle, said correction angle being determined with a view toward increasing the driving stability and/or the driving comfort of said motor vehicle, and a servo drive (6), characterized in that said servo drive (6) is implemented as a variable torque assistance system, the degree of torque assistance (M) being dependent on the road speed (V) of said motor vehicle and on at least one variable of said driving-dynamics means (4) that characterizes said correction angle.

2. The steering system (1) as recited in claim 1, characterized in that said driving-dynamics means (4) comprise a motor (5) for eliciting said correction angle, the variables of said driving-dynamics means (4) that characterize said correction angle being implemented as the actual acceleration (a_actual) of said motor (5) and/or as the nominal acceleration (a_nominal) of said motor (5).

3. The steering system (1) as recited in claim 1 or 2, characterized in that said servo drive (6) is implemented as a hydraulic torque assistance system.

4. The steering system (1) as recited in claim 2 or 3, characterized in that said servo drive (6) comprises a converter (7) that can be acted upon by a converter flow (I_w) and that serves as a control device for the steering angle of said wheels (3) of said motor vehicle, and means (9) for determining said converter flow (I_w) as a function of the road speed (V) of said motor vehicle, said actual acceleration (a_actual) of said motor (5) and said nominal acceleration (a_nominal) of said motor (5).

5. The steering system (1) as recited in claim 4, characterized in that said means (9) for determining said converter flow (I_w) comprise first means (10) for constructing a first converter current (I_V) dependent on road speed, second means (13) for constructing a second converter flow (I_a) dependent on said actual acceleration (a_actual) of said motor (5) and said nominal acceleration (a_nominal) of said motor (5), and third means (17) for constructing said converter flow (I_w) from said first converter flow (I_V) and said second converter flow (I_a).

6. The steering system (1) as recited in claim 5, characterized in that said first means (10) comprise a lowpass filter (11) for filtering the road-speed values (V) of said motor vehicle and a characteristic curve (12) from which the relationship between the filtered road speed values (V_f) and values for said first converter flow (I_V) may be obtained.

7. The steering system (1) as recited in claim 5 or 6, characterized in that said second means (13) comprise a differentiator (14) for constructing a differential acceleration (a_diff) from the difference between said actual acceleration (a_actual) of said motor (5) and said nominal acceleration (a_nominal) of said motor (5), a quantity former (15) for constructing the quantity of said differential acceleration (a_diff), a multiplier (15) for multiplying said differential acceleration (a_diff) by a presettable factor (k), and a delay unit (16) for constructing said second converter flow (I_a) by applying a presettable dead time (T_t) to said quantity (I′

_a) of said differential acceleration (a_diff), multiplied by said factor (k).

8. The steering system as recited in any of claims 5 to 7, characterized in that said third means (17) comprise an adder for constructing said converter flow (I_w) by adding said first converter flow (I_V) and said second converter flow (I_a).

9. A servo drive (6) for a motor-vehicle servo-assisted steering system (1), implemented as a variable torque assistance system and comprising a converter (7) that can be acted upon by a converter flow (I_w) and that serves as a control device for the steering angle of the wheels (3) of said motor vehicle, and means (9) for determining the converter flow (I_w) as a function of at least the road speed (V) of said motor vehicle, characterized in that the steering system (1) comprises driving-dynamics means (4) for superimposing a correction angle on said steering angle, said correction angle being determined with a view toward increasing the driving stability and/or the driving comfort of said motor vehicle, and in that said means (9) for determining said converter flow (I_w) do so as a function of at least one variable of said driving-dynamics means (4) that characterizes said correction angle.

10. A method for determining the converter flow (I_w) of a servo drive (6), implemented as a variable torque assistance system, of a servo-assisted steering system (1) for a motor vehicle, said servo drive (6) comprising a converter (7) that can be acted upon by said converter flow (I_w) and that serves as a control device for the steering angle of the wheels (3) of said motor vehicle, and said converter flow (I_w) being determined as a function of at least the road speed (V) of said motor vehicle, characterized in that the steering system (1) comprises driving-dynamics means (4) for superimposing a correction angle on said steering angle, said correction angle being determined with a view toward increasing the driving stability and/or the driving comfort of said motor vehicle, and in that said converter flow (I_w) is determined as a function of at least one variable of said driving-dynamics means (4) that characterizes said correction angle.