Patent Application
20060185949
The present invention relates to a suspension system, and more particularly to an active suspension system that utilizes a compressible fluid.
Conventional suspension systems isolate a vehicle frame or chassis from impacts and vibrations resulting from vehicle wheels traversing uneven terrain. Vehicle ride characteristics have complex dynamics. Excess vibration can have detrimental consequences on suspension components, often resulting in premature wear or failure.
Current passive suspension systems employ springs, struts, rubber elements, torsion bars, or the like to maintain a centered suspension. Perturbations from a normal condition initiates a harmonic motion that would continue indefinitely but for the addition of damping mechanisms such as shocks, or other hysteresis or coulomb damping devices. Current suspension technologies are defined in frequency domains with natural frequencies and damping coefficients to define suspension characteristics. Such passive suspension systems offer a compromise between spring and dampening coefficients of fixed rates.
Current active suspension systems provide powered components that isolate the vehicle chassis from vibrations induced by uneven terrain. In active vehicle suspension systems, actuators are provided to actively apply forces, which counteract and balance forces applied to the chassis of the motor vehicle. Such active systems utilize relatively complicated control schemes to determine an amount of force that the actuators should apply to the vehicle chassis to provide a smoother ride. As examples, known schemes include some schemes based on balancing the forces acting on the vehicle chassis, and some schemes based on supporting the vehicle chassis at a selected ride height. Active suspension systems require relatively large power inputs so that the actuator will be quick enough to compensate for impacts and vibrations that occur at desired traveling velocities over rough terrain. The power requirements for such fully active suspension systems are generally prohibitively demanding.
Another type of active suspension system utilizes an incompressible fluid. An example of such a system is disclosed in U.S. application Ser. No. 10,785,880, filed Feb. 24, 2004 and which is assigned to the assignee of the subject invention. This type of center seeking suspension uses a fluid strut, an accumulator that is in fluid communication with the fluid strut via an accumulator valve, and a reservoir that is in fluid communication with the fluid strut via a reservoir valve. A fluid pump pressurizes the accumulator with an incompressible fluid stored in the reservoir. A controller operates each valve and the fluid pump to control flow of the incompressible fluid within the strut. The controller operates each valve and the fluid pump to exploit the incompressible properties of the incompressible fluid to obtain an infinitely variable suspension system.
One of the advantages with this type of suspension system is that the suspension system responds rapidly and uses relatively minimal power inputs and damping elements. However, one disadvantage is that a significant number of fluid connections are required to interconnect various valves, the fluid strut, and the reservoir. This increases assembly time and overall system cost. Further, these fluid connections, the accumulator, and the reservoir take up valuable packaging space underneath the vehicle chassis.
Accordingly, it is desirable to provide an active center seeking suspension system that can respond rapidly using minimal power inputs and damping elements, and which is more compact and easily installed on a vehicle.
The suspension system according to the present invention includes a fluid strut between a sprung load such as a vehicle chassis and an unsprung load such as a vehicle axle assembly. The fluid strut includes an outer cylinder defining a first fluid chamber and an inner cylinder defining a second fluid chamber, wherein the inner cylinder is at least partially received within the outer cylinder. A rod is mounted for movement relative to the inner and outer cylinders and has one rod end extending into the second fluid chamber. A compressible fluid, such as silicon oil for example, is contained within the first and second fluid chambers. A valve and controller cooperate to control flow of the compressible fluid between the first and second fluid chambers to provide a desired suspension rate and ride height.
In one example, a plate is received within the outer cylinder and surrounds the inner cylinder. The plate separates the first fluid chamber into a main chamber and an auxiliary chamber. A first valve directs fluid flow between the main chamber and the second fluid chamber. A second valve directs flow between the auxiliary chamber and the second fluid chamber. Preferably, the first valve is a two-way valve and the second valve is a three-way valve. A transfer pump is positioned within the inner cylinder between the second valve and the end of the rod. The controller controls the two-way valve to adjust suspension rate by controlling a total volume of the compressible fluid. The controller controls the three-way valve and transfer pump to increase ride height as needed, and/or to maintain ride height as the compressible fluid exits the fluid strut over time.
The present invention therefore provides an active center seeking suspension system that responds rapidly while utilizing minimal power inputs and damping elements, and which is compact and easy to install.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
The fluid strut 12 has an outer cylinder 20 defining a first fluid chamber 22 and an inner cylinder 24 defining a second fluid chamber 26. The inner cylinder 24 is at least partially received within said first fluid chamber 22, which extends at least in part, between an outer wall 28 of the inner cylinder 24 and an inner wall 30 of the outer cylinder 20.
The first 22 and second 26 fluid chambers are at least partially filled with a compressible fluid 32. Compressible fluids have densities that can vary in response to changes in pressures exerted on the compressible fluid. One example of a compressible fluid that could be used in the fluid strut 12 is silicon oil, however, other compressible fluids could also be used. The specific properties of compressible fluids are generally well-known and will not be discussed in further detail.
A rod 34 has a first rod end 36 and a second rod end 38 that extends into the second fluid chamber 26. The rod 34 moves back-and-forth within the inner cylinder 24 along an axis A as the vehicle and suspension system 10 travels over a ground surface. Seals 46 are installed between the rod 34 and inner cylinder 24 to seal the second fluid chamber 26. The rod 34 and the compressible fluid 32 within the first 22 and second 26 fluid chambers cooperate to provide a desired suspension rate and ride height. This will be discussed in greater detail below.
A damper plate 40 is mounted to the rod 34 adjacent to the second rod end 38. The damper plate 40 has a greater diameter than the rod 34 but does not touch an inner surface 42 of the inner cylinder 24. The damper plate 40 moves with the rod 34 along the axis A. The damper plate 40 may include openings 44 that extend through the damper plate 40 such that the compressible fluid 32 can flow through the damper plate 40. The damper plate 40 provides additional damping as needed, however, the suspension system 10 may not require a damper plate 40.
In the example shown, the outer cylinder 20 is mounted to the sprung load 14 and the first rod end 36 is mounted to the unsprung load 16, however, other mounting configurations could also be used. A rigid plate 50 separates the first fluid chamber 22 into a main chamber 52 and an auxiliary chamber 54. The auxiliary chamber 54 is a low pressure volume and the main chamber 52 is a high pressure volume. The second fluid chamber 26 is also a high pressure volume that is in fluid communication with main chamber 52 through a first valve 60. The rigid plate 50 abuts against the outer wall 28 of the inner cylinder 24 and the inner wall 30 of the outer cylinder 20. The rigid plate 50 can be fixedly mounted to either or both of the inner 24 and outer 20 cylinders. Respective positions of the outer cylinder 20, the inner cylinder 24, and the rigid plate 50 remain fixed relative to each other and remain fixed relative to the sprung load 14.
The first valve 60 controls fluid flow between the main chamber 52 and the second fluid chamber 26 to adjust an instantaneous rate of the suspension system 10. Preferably, the first valve 60 is an ON/OFF, i.e., open/closed, two-way valve that provides extremely rapid reaction times. This type of valve is also often referred to as a bang-bang valve. The first valve 60 is normally open or ON during vehicle operation. In this position, the compressible fluid 32 flows back and forth between the main chamber 52 and second fluid chamber 26 to increase compressible fluid volume. To increase stiffness, the first valve 60 is closed or turned OFF.
A controller 62 determines when the first valve 60 should be closed and generates a control signal 64 that is communicated to the first valve 60. Suspension rate is adjusted by effectively controlling a total fluid volume of the compressible fluid 32. When the first valve 60 is open the fluid strut 12 has a first predefined operational fluid volume. When the first valve 60 is closed, the fluid strut 12 has a second predefined operational fluid volume that is less than the first predefined operational fluid volume. In other words, when the first valve 60 is open, the first predefined operational fluid volume is defined by at least an amount of compressible fluid 32 within the second fluid chamber 26 and within the main chamber 52. When the first valve 60 is closed the second predefined operation fluid volume does not include compressible fluid 32 within the main chamber 52, thus the overall fluid volume is reduced when the first valve 60 is closed.
The controller 62 determines when the first valve 60 should be opened or closed based on a desired suspension rate and in response to suspension inputs exerted on the rod 34. Thus, the controller 62 automatically adjusts suspension rate as needed by adjusting the stiffness of the fluid strut 12 by opening and closing the first valve 60.
The fluid strut 12 also includes a transfer pump 70 that is mounted within the inner cylinder 24. The transfer pump 70 is positioned between a bottom wall 72 of the inner cylinder and the second rod 38. The transfer pump 70 includes a pump body 74 that is fixed to the bottom wall 72 of the inner cylinder 24 and a pump needle 76 that is mounted for movement with the rod 34 along the axis A. The pump needle 76 moves back and forth within the pump body 74 and is coupled to the second rod end 38.
The transfer pump 70 pumps the compressible fluid 32 within the second fluid chamber 26 and cooperates with a second valve 80. The second valve 80 controls fluid flow between the auxiliary chamber 54 and the second fluid chamber 26. The transfer pump 70 and second valve 80 utilize road perturbations to pump fluid into the high pressure volume of the main chamber 52 via the second fluid chamber 26 and first valve 60. This provides adjustment to achieve desired ride height variations while the vehicle is operating.
The second valve 80 is preferably a three-way valve that allows for adjustment of ride height by transferring compressible fluid 32 into or out of the auxiliary chamber 54. The second valve 80 responds to a control signal 82 generated by the controller 62. The second valve 80 is normally closed during vehicle operation. The second valve 80 is selectively opened in response to receipt of the control signal 82 to adjust ride height as needed. The second valve 80 allows either two-way flow of the compressible fluid 32 back-and-forth between the auxiliary chamber 54 and the second fluid chamber 26 during vehicle operation or one-way flow from the auxiliary chamber 54 to the second fluid chamber 26 or vice-versa to adjust ride height when the vehicle is stationary.
Thus, the controller 62 operates the first 60 and second 80 valves to control flow of the compressible fluid 32 as needed to adjust right height and suspension rate. The controller 62 is also in communication with at least one sensor 84 that monitors a position of the pump needle 76 and/or rod 34 relative to at least one of the inner 24 and outer 20 cylinders. The sensor 84, which is shown schematically, can be incorporated within the fluid strut 12 or can be externally positioned relative to the fluid strut 12. The suspension system 10 may also include other sensors, such as pressure sensors, as needed.
The controller 62 operates the first 60 and second 80 valves to exploit the compressible properties of the compressible fluid 32 to obtain an infinitely variable suspension system. In response to operating requirements, the controller 62 selects a stiffness range to provide sufficient centering forces to return the suspension system 10 to a desired center without overshoot. The controller 62 preferably minimizes any bouncing and therefore minimizes the requirement for energy wasting damping. It should be understood that various well-known control algorithms would benefit from the present invention.
Referring to
Additionally, the suspension system 10 can automatically adjust ride height in response to leakage of compressible fluid 32 from the seals 46. Over time, the seals 46 are subjected to wear, which decreases a sealing force of the seals 46 against the rod 34. Some compressible fluid 32 may leak out of the fluid strut 12 through the seals 46 in such a situation. The controller 62 can automatically add compressible fluid 32 from the auxiliary chamber 54 to the main chamber 52, via the second fluid chamber 26, to maintain a generally constant desired ride height over time.
Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.
The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.
