STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
Varying the toe angle of the rear wheels on an automotive vehicle during the operation of the vehicle improves the vehicle's handling and maneuverability. The following rear wheel reactions result in better vehicle dynamics under the respective operating conditions:
- a. braking or deceleration: toe-in
- b. acceleration: toe-in
- c. cornering: initial toe-out of the outer wheel that changes to toe-in at a lateral force of 0.4 to 0.5 g.
An optimized rear wheel alignment can also impact favorably the vehicle fuel efficiency, by minimizing the drag and spin on the rear tires.
Two major approaches have been used:
- (1) to actively orient the wheels by an input from the car's steering wheel; and
- (2) to let road forces and suspension geometry realign the toe and camber angles as generally shown in U.S. Pat. No. 4,740,012. The first approach can be called an active design, and the second is called a passive design. Both of these systems add more moving parts, complexity, weight and cost to the rear suspension.
The present invention involves an Active Toe Control System that is a cost effective and efficient alternative to the two previous approaches as described above.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
In the drawings, wherein like numerals and letters refer to like parts wherever they occur.
FIG. 1 is a perspective view of a standard rear suspension system for an automotive vehicle;
FIG. 2 is section view of one embodiment of the present invention; and
FIG. 3 is section view of another embodiment of the present invention.
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.
While one embodiment of the present invention is illustrated in the above referenced drawings and in the following description, it is understood that the embodiment shown is merely for purpose of illustration and that various changes in construction may be resorted to in the course of manufacture in order that the present invention may be utilized to the best advantage according to circumstances which may arise, without in any way departing from the spirit and intention of the present invention, which is to be limited only in accordance with the claims contained herein.
DETAILED DESCRIPTION
As shown in FIG. 1, the majority of the current rear suspension designs include means for manually adjusting the length of a trailing arm or control arm for the rear wheel suspension in order to modify the toe angle of the corresponding wheel. That configuration includes a rear upper arm 1, a forward link 2, and a toe link 3, both of which are connected to the spindle assemblies 4 of each of the two rear wheels on an automotive vehicle 5.
Referring to FIG. 2, the present invention of an active toe control system A resides in a control arm or link 6, usually in a trailing position, with a built-in linear actuator that can meet the travel, force, response time and packaging requirements to realize a continuously variable toe angle that can address specifically the various vehicle-operating conditions to obtain significant benefits related to safety, handling and fuel-efficiency. The control arm or link 6 has a continuously adjustable length that can be used to directly replace an existing control arm or link such as the toe link 3 of FIG. 1, without other modifications of the rear suspension design. The optimum toe angle is achieved by relying on the suspension compliance.
An electronic control unit 10 (not shown) receives and processes the signals from a wide variety of sensors placed in the automotive vehicle 5 (FIG. 1). For example, one group of typical sensors would include a yaw sensor, a wheel speed sensor, a lateral acceleration sensor, a longitudinal acceleration sensor, and a steering angle sensor. It is appreciated that other sensors may also be included depending upon the application. The electronic control unit 10 makes the final decision on the modifications to be made to the overall length of the control arm or link 6 modifications resulting to make the any necessary adjustments to the toe angle.
FIG. 2 also shows a cross section of one embodiment of the present invention. In FIG. 2, the control arm or link 6 contains an integrated linear actuator 15 comprising an electric motor 16, a ball screw or trapezoidal screw mechanism 17, and a hydraulic system 18 that reduces the axial travel between the connecting points 18 and 19 while amplifying the axial force within the control arm or link 6. The rotor 20 of the electric motor 16 is integral with the screw mechanism 17 that controls the axial displacement of the nut 23 and integrated small piston 24 of the small cylinder 25. The small piston 24 pushes a fluid into the small cylinder 25 and transmits the axial displacement of the small piston 24 to the large cylinder 26 that is connected to the connecting point 19 that is itself connected to the joint of the suspension arm (not shown) on the automotive vehicle 5.
The ratio between the axial displacement of the small cylinder 25 and the axial displacement of the large cylinder 26, controls the ratio between the axial force applied on the small cylinder 25 and the axial cross-sections. Together, the small cylinder 25 and the large cylinder 26 act as a hydraulic system to function as a force amplifier and displacement reducer, thereby replacing the more costly and less reliable planetary gear mechanisms used as torque amplifiers/speed reducers in some linear actuator designs.
In order to reduce the length of the control arm or link 6, the rotor 20 of the electric motor 16 rotates the screw mechanism 17 to retract the small piston 24 by drawing the nut 23 toward the electric motor 21. This action will push the fluid 30 behind the small piston 24 of the small cylinder 25 to the cavity 32 behind the large piston 34 of the large cylinder 26, through the channels 33 situated between the actuator housing 36 and the outer diameter of the actuator housing cylinder 36 in which the pistons 24 and 34 operate.
An alternative design of the present invention is presented in FIG. 4. Here, the arm length reduction is realized just by retracting the small cylinder 40 and using a spring 41 behind the large piston 42 to provide additional axial force. All other components and operation of the embodiment of FIG. 4 are generally the same as the embodiment shown in FIG. 3.
In yet another embodiment of the invention, the hydraulic force/displacement generated by the small piston 24 is sufficient and the large piston 34 can be eliminated, provided that an electric motor 21 with the sufficient required torque capacity and rotary positioning capability is used.
While the above description describes various embodiments of the present invention, it will be clear that the present invention may be otherwise easily adapted to fit any configuration where an active toe control system for an automotive vehicle is required. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
Patent Application
20050051988
