GB2199618A

GB2199618A - Hydraulic actuator

Info

Publication number: GB2199618A
Application number: GB08729046A
Authority: GB
Inventors: Charles Brashears Steger; Kenneth Robert Meloche
Original assignee: General Motors Corp
Current assignee: Motors Liquidation Co
Priority date: 1987-01-08
Filing date: 1987-12-11
Publication date: 1988-07-13
Anticipated expiration: 2007-12-11
Also published as: JPH0628969B2; CA1299207C; JPS63170114A; GB8729046D0; GB2199618B; DE3800246A1; DE3800246C2

Description

5, t:

2 19 9 6.1 (G -I- HYDRAULIC ACTUATOR This invention relates to a hydraulically powered telescopic.actuator suitable for use in an active vehicle suspension.

The invention is particularly concerned with an actuator of this type having an involuted cylinder tube configuration to shorten the overall length of the actuator.

Accordingly, by the present invention there is provided a hydraulically powered telescopic actuator for an active suspension system of a wheeled vehicle, operatively connecting a road wheel assembly to support structure of the vehicle, comprising concentric inner and outer cylinder tubes forming an involuted cylinder tube assembly and defining a- cylindrical space therebetween, a piston mounted for reciprocatory movement in the cylindrical space, a piston rod guide secured to the upper end of the outer cylinder tube, piston rod means operatively connected to the piston and extending upwardly therefrom through the rod guide for connection to the support structure of the vehicle, the piston having an annular inner seal for sealing contact with the inner cylinder tube and an annular outer seal for sealing contact with the outer cylinder tube so that a first variable-volume chamber is formed above the piston, the piston rod means having a hydraulic passage operatively connected to the first variable-volume chamber, control means for supplying a pressurised hydraulic fluid to the first chamber to cause expansion thereof with consequent contraction of the actuator, the piston rod means being mounted for telescopic movement with respect to the inner cylinder tube and the sealing contact of the piston with the inner cylinder tube thereby defining a second variable-volume chamber, the control means being effective to supply a pressurised fluid to the second chamber to cause expansion thereof with consequent expansion of the actuator.

Dual-acting hydraulically powered dual-acting actuators in accordance with the present invention are telescopically adjustable to effect roll movement of the vehicle to selected roll angles for stabilised cambering turns over a wide range of vehicle speeds and road curvatures. In addition to maintaining co- ordinated vehicle turns under steady-state conditions for an indefinite number of vehicle operating speeds, such an actuator, in the context of an appropriate control system, has the capability of making fast transient responses to steering commands to change from one roll angle to another, and to erect the vehicle for straight-ahead driving or when stationary.

The present invention thus makes available a new and improved dual-acting hydraulically-powered telescopic actuator usable for each road wheel of a vehicle to provide control of suspension loads and deflection, such as (but not limited to) powered leaning of the vehicle, and for damping ride motions of the vehicle, in a manner that is not possible with conventional suspension elements.

The dual-acting hydraulically-powered telescopic actuator in accordance with the present invention potentially has a shorter overall length for a given amount of stroke, such that it can be effectively employed as an active suspension unit in a vehicle.

In a dual-acting hydraulically-powered telescopic actuator in accordance with the present invention, the substantially concentric cylinder 0 1- r0 1 tubes can form a power cylinder proportioned to provide the same pressure force relationship in both elongation and contraction, with the piston mounted for telescopic movement within an involuted cylinder tube construction and having equal pressure areas to provide a wide range of positions and to provide an indefinite number of adjusted positions from a full jounce (collapsed) position to a full rebound (extended) position.

An advantageous further feature is that a dual-acting hydraulicallypowered telescopic actuator in accordance with the present invention may include a trapped air volume separate from the hydraulic (oil) volumes of the hydraulic actuator, with the-air volume sized so that an air spring, integrated within the actuator, is created by the moving piston. With this air spring, the requirement for carrying the static load is removed from the hydraulic portion of the actuator, thereby substantially reducing power consumption. This eliminates the requirement for coil springs around the actuator, or other mechanical spring means, to carry the static load and provide a sufficient suspension effect-in the event that the hydraulic system is damaged so that its lifting force is reduced.

Figure 16 of US-A-3 277 840 discloses a vehicle stabilisation system utilising hydraulically-powered piston-and-cylinder type telescopic actuators subject to pressure control.

In the drawings:

Figure 1 is a longitudinal sectional view of a preferred embodiment of a hydraulic actuator in asccordance with the present invention, shown in a powered collapsed position; Figure 2 is a view similar to Figure'l, but showing the hydraulic actuator in a powered extended position; and Figure 3 is a diagrammatic view of part of a control system for an active suspension system incorporating hydraulic actuators in accordance with the present invention.

With reference now to the drawings in grea ter detail, there is shown in Figures 1 and 2 a dual-acting active suspension unit 10 for a vehicle, designed to replace passive conventional struts such as the well-known MacPherson type of suspension strut. The suspension unit 10 is effectively made shorter by the use of an involuted cylinder tube assembly formed from an outer cylinder tube 12 and an inner cylinder tube 14 interconnected at their lower ends by a base cup 16. As is diagrammatically shown in Figure 3, one such unit 10 is located at each corner of a vehicle, and is adapted to be connected to an associated road wheel assembly 17.

Such inversion represents an important feature in shortening the suspension units 10 for optimum space utilisation, so that these units can be readily employed in place of conventional strut configurations, and be selectively powered and elongated for achieving co-ordinated vehicle roll.

Each suspension unit 10 has a piston assembly 18 reciprocably mounted with respect to the cylinder tube assembly 12,14 and has concentric inner and outer annular piston rods 22 and 24 connected at their lower ends to a cylindrical piston 26. The concentric piston rods 22 and 24 define between them an oil passage 27, and extend upwardly through a cylindrical rod guide 28 into an upper connector block 30. The rod guide has an annular seal 31 for k 1 -5 41 k, sliding sealed contact with the outer piston rod 24 as it strokes in jounce and rebound action. A nut 32 threaded on to the upper end of the piston rod 24 fastens the Piston rods 22 and 24 to the connector block 30 and to the vehicle body, here represented by a portion of a conventional mounting tower 34 trapped between a lower surface 35 of the connector block 30 and an upper shoulder 36 of the outer piston rod 24. The vehicle body is thus rigidly connected to the piston of the suspension unit 10 and moves therewith.

The piston 26 is mounted for reciprocatory movement in a cylindrical space between the'outer and inner cylinder tubes 12 and 14 and carries inner and outer 0- ring seals 40 and 42 to hydraulically and pneumatically seal this cylindrical space to form expansible and contractible upper and lower chambers 44 and 46 respectively. The upper chamber 44 is an oil chamber that is supplied with pressurised oil from a control system 48, basically illustrated in Figure 3, that incorporates a separate servo valve 50 for each of the suspension units 10. Pressure oil for the servo valves 10 is supplied from a pump 52 through pressure lines 56 and 58, as is schematically shown in Figure 3. Fluid exhausted from the servo valves 50 is transmitted by lines 62 to a reservoir 64. The pump 52 draws oil from the reservoir 64 through lines 66 and 68 via an oil cooler 69, as is shown diagrammatically.

In a downwardly shifted position of the spool of the valve 50., pressure oil is fed from the pressure line 56 by a passage 59 into an annular chamber 70 in the connector block 30, and thence -through a radial pass4ge 72 in the upper end of th-e outer piston rod 24. Pressure oil accordingly fills the space between the inner and outer piston rods 22 and 24, and through openings 74 and 76 fills the space between the outer piston rod 24 and the cylinder tube 12. The upper chamber 44 is accordingly filled with pressure oil, that exerts a downward force on the piston 26. When this pressure exerts a force of sufficient magnitude, the upper chamber 44 expands to shorten the actuator unit. In the position shown in Figure 1, the chamber 44 is fully expanded and the actuator unit is in its telescopically collapsed position.

In addition to supplying pressure oil to the upper chamber 44, the servo valve 50 is shiftable upwardly to supply pressure oil to the inner chamber 80 formed between the inner cylinder tube 14 and the inner piston rod 22. As in the case of the upper chamber 44, this pressure oil is routed by the servo valve 50 through a line 73 into the opening 74, which in form comprises an annular chamber, in the connector block 30. This pressure oil is then fed through a radial passage 78 in the neck of the outer piston rod into the inner chamber 80. When pressure in the inner chamber 80 is raised above a predetermined pressure, the resulting force in the inner chamber 80 acts on the walls thereof and on the end of the inner cylinder tube 14 to linearly expand the inner chamber 80 to a predetermined length. Figure 2 shows the inner chamber 80 fully expanded, although an indefinite number of positions in between those shown in Figures 1 and 2 can be obtained by force equilibrium in the expansion and contraction chambers.

An elongate cylindrical ferrous rod 81 fixed to the top of the outer piston rod 24 extends into a coil 82 that is mounted within the confines of the inner piston rod 22 and is retained in position -1 1 It 1 1 by a helical spring 85. A load sensor is operatively mounted at the upper end of each piston rod assembly and is connected in a circuit 86. The rod 81 and the coil 82 co-operate to form a linear variable differential transformer 83 which provides a displacement signal that.is transmitted to a computer 84 by means of the circuit 86. The computer 84 receives continuous signals during vehicle operation, indicative for example of vehicle loading, speed, bank angle, road curvature, lateral acceleration and road undulations. These signals are processed by the computer, which provides a control signal to the servo valves 50. The servo valves 50 are actuated by torque motors 90. Signals from the computer 84 are is supplied through circuits 92, 94, 96 and 98 to the torque motors 90 for the respective actuators. In dependence on the input signals 86 entering the Compu ter, the torque motors thereby adjust the servo valves so that the dual-acting actuators are adjusted to actively lean the vehicle into turns to provide... co-ordinated steady- state turning for a wide range of operating conditions and to erect the vehicle for straight-ahead driving and for standing still. Damping is provided by the restriction in theservo valve as provided by spool adjustment. Different sensors, and different control algorithms in the controller, can cause this or any other control mode to theoretically exist. Thus roll and pitch control, damping and spring rate control can be synthesised by the system.

The described preferred embodiment of a hydraulic actuator in accordance with the present invention also provides air suspensi on of the vehicle, utilising an outer support tube 100 that is threaded or otherwise fixed to the bas(. cup 16. This outer support tube 100 extends upwardly from the base cup 16 to an inwardly turned and air-sealed connection 102 to the rod guide 28. The support tube 100 is spaced from the outer cylinder tube 12 to form a cylindrical space 104 therebetween that is connected to the lower chamber 46 by a radial passage 106 in the lower end of the cylinder tube 14. Pressurised suspension air from a control system 108 is supplied to the cylindrical space 104 and the lower chamber 46 via a line 110. Pressure air acting in the lower chamber 46 provides the air suspension force for the suspension unit. This trapped air volume is separate from the oil volumes, and is appropriately sized such that an air spring is created by the moving piston, the size of the air spring being appropriate to provide approximately the correct load and rate for the vehicle.

This removes the requirement for static vehicle load to be carried by the hydraulic portion of the device, and thereby substantially reduces power consumption. It also eliminates any requirement for a coil spring to surround the actuator or other suspension device to carry these static loads, and further provides a "limp-home" capability in the event that the hydraulic system is damaged and does not work.

Thus the embodiment of the hydraulically powered telescopic actuator which has been described in the foregoing forms a high-pressure actuator for actively positioning the body of the vehicle relative to the running gear of the vehicle and the road surface. When the chamber 44 is pressurised, the unit contracts (telescopically collapses), whereas when the chamber 80 is pressurised, the unit expands (telescopically extends). By this means, the four 11 p 7 Q I 4 1 corners of the vehicle may be positioned in accordance with requirements, and the involuted cylinder tube design provides the concentric and separate hydraulic (oil) pressure chambers which permit the desirable overall shortening of the unit.

1

Claims

Claims:

1. A hydraulically powered telescopic actuator for an active suspension system of a wheeled vehicle, operatively connecting a road wheel assembly to support structure of the vehicle, comprising concentric inner and outer cylinder tubes forming an involuted cylinder tube assembly and defining a cylindrical space therebetween, a piston mounted for reciprocatory movement in the cylindrical space, a piston rod guide secured to the upper end of the outer cylinder tube, piston rod means operatively connected to the piston and extending upwardly therefrom through the rod guide for connection to the support structure of the vehicle, the piston having an annular inner seal for sealing contact with the inner cylinder tube and an annular outer seal for sealing contact with the outer cylinder tube so that a first variable-volume chamber is formed above the piston, the piston rod means having a hydraulic passage operatively connected to the first variable-volume chamber, control means for supplying a pressurised hydraulic fluid to the first chamber to cause expansion thereof with consequent contraction of the actuator, the piston rod means being mounted for telescopic movement with respect to the inner cylinder tube and the sealing contact of the piston with the inner cylinder tube thereby defining a second variable-volume chamber, the control means being effective to supply a pressurised fluid to the second chamber to cause expansion thereof with consequent expansion of the actuator.

2. A hydraulically powered telescopic actuator according to claim 1, in which the actuator further incorporates an outer support tube that C1.1 Q 9 extends around the outer cylinder tube in sealing relation thereto and forms an air chamber therebetween, means is provided for supplying pressure air to the air chamber at a predetermined pneumatic pressure effective to support the weight of the vehicle, and means is provided for varying the pneumatic pressure to cause the actuator to act as a variable suspension spring system.

-

3. A hydraulically powered telescopic actuator according to claim 1 or 2t in which the piston rod means comprises radially spaced inner and outer piston rods both operatively connected to the piston, the hydraulic passage is defined between the inner and outer piston rods, and the inner and outer piston rods are mounted for telescopic movement over the inner cylinder tube.

Published 1988 ax The Patent Office, State House. 8671 High Holborn, London WC1R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by MWtiplex techniques ltd, St Mary Cray, Kent. Con. 1/87.