AUTOMATIC ROAD WHEEL STEERING SYSTEM

Abstract: An automatic road wheel steering system (1) utilizes a strut-type suspension (2) including a cylinder (3) connected at one end to a steering knuckle (5) and a piston/piston rod assembly (33, 25) slidable within the cylinder (3). An actuator (35) is mounted to a vehicle body (39) and operatively connected to the piston rod (25) so as to rotate the same (25). The piston rod (25) is also operatively connected through a suitable connection to the cylinder (3) so that rotary motion of the piston rod (25) is carried to the cylinder (3). This causes swing motion of the steering knuckle (5) and thus a road wheel (17). The actuator (35) is disposed in surrounding relation to the cylidner (3) to bring the system into a compact arrangement.

Description: The invention relates to a system for automatically steering a road wheel, comprising: a strut-type suspension including a cylinder, a piston rod reciprocable within the cylinder, a piston attached to one end of the piston rod a steering knuckle fixed to the cylinder and rotatably supporting the road wheel thereon, an actuator to rotate the piston rod about its axis, the actuator being mounted to a vehicle body and operatively connected to the other end of said piston rod, a mechanism to axially guide said piston rod within the cylinder and operatively connect the piston rod with the cylinder so that rotary motion of the piston rod may be carried to the cylinder. A strut-type suspension, better known as MacPherson-strut suspension is light in weight and simple in structure and has, thus, been used in many compact cars. A typical strut-type suspension includes a strut with its upper end fixed to a vehicle body. The strut has at its lower end a ball joint through which a control arm is attached to a spindle. A shock absorber is built into the upper section of the strut, and a coil spring fits around the shock absorber. See "6th edition, Brakes, Suspension and Steering" by William H. Crouse and Donald L. Anglin (McGraw-Hill Book Company). Japanese utility model publication No. 59-94976 discloses a strut-type suspension having a shock strut with its upper end rotatably attached to a vehicle body through a suitable bearing assembly, and its lower end having an integral spindle on which a wheel is mounted. A system is provided to automatically turn each steerable wheel. This system generally includes an electric motor attached to the lower side of the vehicle body adjacent to the strut. The output shaft of the motor is connected to the strut through a flexible long shaft by which torque is transmitted to assist turning of the steerable wheel. In this prior system, the motor is provided separately from the strut-type suspension. This results in an increase in the size of the overall system. A system for automatically steering a road wheel as initially described is known from DE-A-2 452 066. In this system a lever arm fixed to the upper end of the piston rod is moved by a gear unit which in turn is connected to a driving gear unit by a flexible driving shaft. The driving gear unit which drives both turning road wheels is in turn mechanically driven by a steering wheel. Due to the mechanical connection between steering wheel and road wheels, the possibilities of changing the steering characteristics, for example as a function of the vehicle speed, are reduced as compared to the use of an electric motor to turn the road wheels. The object of the invention is to provide a system for automatically steering a road wheel with reduced size of the overall system. To solve this object, an electric motor is provided as actuator disposed in surrounding and coaxial relation to the upper section of the cylinder. The electric motor provides for automatical steering independent of the steering wheel. Since the electric motor is disposed in surrounding and coaxial relation to the upper section of the cylinder, rather than being separately from the strut-type suspension, the system is brought into a compact arrangement. One way of carrying out the invention is described in detail below with reference to the drawings which illustrate only one specific embodiment, in which: Figure 1 is a perspective view of an automatic road wheel steering system constructed according to the teaching of the invention; Figure 2 is a sectional view of the system as shown in Figure 2, and Figure 3 is an enlarged sectional view taken along the line III-III of Figure 2. With reference to Figures 1 and 2, there is shown an automatic road wheel steering system generally indicated at 1 and including a strut-type suspension 2. The struttype suspension 2 has a shock strut 3 in the form of a cylinder. A spring (not shown) is separately provided, instead of being mounted directly on the strut 3. It may be disposed between a lower control arm and a vehicle body. The illustrated suspension is designed for the left rear road wheel. It will be understood that the form and arrangement of the suspension for the right rear wheel is reversely similar. It will also be understood that the system may be used for each driven front wheel. The shock strut 3 is fixedly attached at its lower end to the upper end of a steering knuckle 5 by a bolt/nut assembly 6. The lower end of the steering knuckle 5 is connected through a ball joint (not shown) to the outer end of a lower control arm 7. The inner end of the lower control arm 7 is, in turn, pivotably connected to a crossmember 9 through a pivot connection 11. When the vehicle moves over the road, the steering knuckle 5 pivots up and down slightly. This causes the control arm 7 to swing up and down. The steering knuckle 5 receives a spindle or axis 13 through a bearing assembly 15. The spindle 13 is fixedly connected at its one end to a wheel 17 and is drivingly connected at its other end to a drive shaft 19 though a universal joint 21. In the illustrated embodiment, a piston/piston rod assembly is slidably and rotatably received within the cylinder 3. More specifically, a piston rod 25 has three radial vanes 27 on its outer peripheral surface. Each of the vanes 27 has opposite side wings 29 which are slidably received within corresponding three axial guides 31 formed at the inner peripheral surface of the cylinder 3. The piston rod 25 is attached at its lower end to a piston 33 and at its upper end to an actuator 35. As best seen in Figure 2, the actuator 35 generally includes a cylindrical stator 37 mounted to a vehicle body 39 through a mount assembly 41. Specifically, the mount assembly 41 has a flanged inner plate 43 fixed to the stator 37, a flanged outer plate 45 bolted at 47 to the vehicle body 39, and an isolator 49 sandwiched between the flanges of the inner and outer plates. The stator 37 has a plurality of permanent magnets 50 on its inner peripheral surface. Rotatably supported by the stator 37 through a bearing assembly 51 is a coaxial rotor sleeve 53 which surrounds the cylinder 3 and having a coil 55. This rotor sleeve 53 is connected to a drive member 57 through a planetary-gear system or speed reducer 59 of a conventional construction. The drive member 57 has a cylindrical upper section 57a rotatably supported on the inner peripheral surface of the stator 37 through a bearing assembly 61 and connected to the upper end of the piston rod 25, and a cylindrical lower section or internal gear 57b connected to the upper section 57a through a ledge 57c and having a diameter greater than that of the upper section 57a. The speed reducer 59 generally includes a sun gear 63 fixedly mounted onto the upper end of the rotor sleeve 53, and a plurality of planet pinions 65, disposed in mesh with both the sun gear 63 and the internal or ring gear 57b. In operation, as the rotor sleeve 53 is rotated with respect to the stator 37, the rotary motion is first carried through the speed reducer 59 to the drive member 57. This causes rotation of the piston rod 25. As the piston rod 25 is in engagement with the cylinder 3, the cylinder 3 is rotated together with the piston rod 25. The rotary motion of the piston rod 25 then causes the steering knuckle 5 to swing either forwards or backwards. The wheel 4 is finally turned in response to the swing motion of the steering knuckle 5.

Claims: 1. A system for steering a road wheel, comprising: a strut-type suspension (2) including a cylinder (3), a piston rod (25) reciprocable within the cylinder (3), a piston (33) attached to one end of the piston rod (25), a steering knuckle (5) fixed to the cylinder (3) and rotatably supporting the road wheel (17) thereon, an actuator (35) to rotate the piston rod (25) about its axis, the actuator (35) being mounted to a vehicle body (39) and operatively connected to the other end of said piston rod (25), a mechanism to axially guide said piston rod (25) within the cylinder (3) and operatively connect the piston rod (25) with the cylinder (3) so that rotary motion of the piston rod (25) may be carried to the cylinder (3), characterized in that for automatical steering an electric motor is provided as actuator (35) disposed in surrounding and coaxial relation to the upper section of the cylinder (3). 2. A system as claimed in claim 1, wherein the actuator (35) comprises a cylindrical stator (37) having a plurality of permanent magnets (50), a rotor sleeve (53) rotatably supported on the stator (37) in coaxial relation and having a coil (55), and a drive member (57) operatively connected to the rotor sleeve (53) and fixed to the upper end of the piston rod (25). 3. A system as claimed in claim 2, wherein said mechanism comprises a plurality of guides (31) formed on the inner peripheral surface of the cylinder (3), and a plurality of corresponding inserts (27, 29) formed on the outer periphery of the piston rod (25) and fitted within the guides (31).

Inventors: ASANUMA, NOBUYOSHI
Applicants: HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1988
Main classification: B62D5
IPC codes: B60G13, B62D5, B60G3, B60G17, B62D7