Brakes – Internal-resistance motion retarder – Motion damped from condition detected outside of retarder
Reexamination Certificate
1999-12-23
2001-10-16
Butler, Douglas C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Motion damped from condition detected outside of retarder
C188S322130, C188S318000
Reexamination Certificate
active
06302248
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a damping force control type hydraulic shock absorber attached to a suspension system of a vehicle, for example, an automobile.
Hydraulic shock absorbers attached to suspension systems of automobiles or other vehicles include damping force control type hydraulic shock absorbers which are designed so that the level of damping force can be appropriately controlled in accordance with the road surface conditions, vehicle running conditions, etc. with a view to improving the ride quality and the steering stability.
In general, this type of hydraulic shock absorber includes a cylinder having a hydraulic fluid sealed therein. A piston, which has a piston rod connected thereto to constitute a piston assembly, is slidably fitted in the cylinder to divide the inside of the cylinder into two chambers. The piston assembly is provided with a main hydraulic fluid passage and a bypass passage, which provide communication between the two chambers in the cylinder. The main hydraulic fluid passage is provided with a damping force generating mechanism including an orifice and a disk valve. The bypass passage is provided with a damping force control valve for controlling the flow path area of the bypass passage.
When the bypass passage is opened through the damping force control valve, the flow resistance to the hydraulic fluid flowing between the two chambers in the cylinder is reduced, thereby reducing damping force. When the bypass passage is closed, the flow resistance between the two chambers is increased, thereby increasing damping force. Thus, damping force characteristics can be appropriately controlled by opening and closing the damping force control valve.
In the above-described damping force control type hydraulic shock absorber, in which damping force is controlled by changing the flow path area of the bypass passage, the damping force characteristics can be changed to a considerable extent in the low piston speed region because damping force depends on the restriction by the orifice in the hydraulic fluid passage. However, the damping force characteristics cannot greatly be changed in the intermediate and high piston speed regions because in these regions damping force depends on the degree of opening of the damping force generating mechanism (disk valve, etc.) in the main hydraulic fluid passage.
To solve the above-described problem, Japanese Patent Application Unexamined Publication (KOKAI) No. 62-220728, for example, discloses a damping force control type hydraulic shock absorber in which a pressure chamber (pilot chamber) is formed at the back of a disk valve serving as a damping force generating mechanism in a main hydraulic fluid passage common to the extension and contraction sides, and the pressure chamber is communicated with a cylinder chamber on the upstream side of the disk valve through a fixed orifice and also communicated with a cylinder chamber on the downstream side of the disk valve through a variable orifice (flow control valve).
According to the above damping force control type hydraulic shock absorber, the flow path area of the passage between the two chambers in the cylinder is controlled by opening and closing the variable orifice. Moreover, the valve opening initial pressure of the disk valve can be varied by changing the pressure in the pressure chamber by the pressure loss in the variable orifice. Thus, it is possible to control orifice characteristics (in which damping force is approximately proportional to the square of the piston speed) and valve characteristics (in which damping force is approximately proportional to the piston speed), and hence possible to widen the control range for damping force characteristics.
However, the above-described conventional damping force control type hydraulic shock absorber suffers from the following problems.
In general, the above described conventional damping force control type hydraulic shock absorber uses a spool valve or the like as the variable orifice. In this regard, variations in size of the sleeve, spool, ports, etc. attributable to machining accuracy cause variations in flow path area of a small flow path formed when the damping force characteristics are controlled to the “hard” side, i.e. when the variable orifice is closed. For this reason, it is difficult to obtain stable “hard” damping force characteristics.
SUMMARY OF THE INVENTION
In view of the above-described circumstances, an object of the present invention is to provide a damping force control type hydraulic shock absorber capable of obtaining stable damping force characteristic at all times.
To attain the above-described object, the present invention provides a damping force control type hydraulic shock absorber including a cylinder having a hydraulic fluid sealed therein. A piston is slidably fitted in the cylinder. A piston rod is connected at one end thereof to the piston. The other end of the piston rod extends to the outside of the cylinder. A main hydraulic fluid passage passes the hydraulic fluid in response to sliding movement of the piston. A sub-hydraulic fluid passage is provided in parallel to the main hydraulic fluid passage. A pilot-type damping valve is provided in the main hydraulic fluid passage. A fixed orifice and a variable orifice are provided in the sub-hydraulic fluid passage. The pressure between the fixed orifice and the variable orifice in the sub-hydraulic fluid passage is used as a pilot pressure of the pilot-type damping valve. An orifice passage is provided in parallel to the variable orifice.
With the above-described arrangement, by controlling the degree of opening of the variable orifice, damping force generated before the pilot-type damping valve opens is directly controlled, and at the same time, the pilot pressure is changed to control the valve opening pressure of the pilot-type damping valve. When the flow path area of the variable orifice is restricted, the flow rate of the hydraulic fluid flowing through the sub-hydraulic fluid passage is substantially determined by the orifice passage and hence unlikely to be affected by variations in flow path area of the variable orifice.
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patent: 5655633 (1997-08-01), Nakadate et al.
patent: 5934421 (1999-08-01), Nakadate et al.
patent: 5996748 (1999-12-01), Nezu et al.
patent: 6079526 (2000-06-01), Nezu et al.
patent: 6119829 (2000-09-01), Nakadate
patent: 6155391 (2000-12-01), Kashiwagi et al.
patent: 6182805 (2001-02-01), Kashiwagi et al.
Butler Douglas C.
Tokico Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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