Patent Description:
A piston assembly is a key component of a hydraulic damper and its construction and configuration has a major influence on a damper force vs. piston velocity characteristic during the damper compression and rebound stroke. It is therefore desirable to enable for shaping and tuning this force-velocity relation for each piston velocity range (low speed, medium speed, high speed) independently for each range and independently for the compression and for the rebound stroke, in order to improve safety and vehicle handling properties, reduce unwanted vibrations, improve passengers comfort, etc..

In deflectable-disc valves, a plurality of deflectable discs with predefined geometry and thickness are used to tune the damping characteristic in all piston velocity ranges. In a blow-off valve, a deflectable or displaceable closing element, usually in a form of a flat disc, is biased by a spring to keep the flow passages closed. After a certain pressure threshold is reached, the closing element compresses the spring, opening the flow passages. Various spring preloads are used to adjust damping characteristics of such a valve. The main advantage of a blow-off valve is its flat and digressive characteristic, so that driving a vehicle over curbs is smother.

Dampers having piston assemblies provided both with deflectable-disc type valves and blow-off valves are known e.g. from patent publications <CIT>, <CIT>, <CIT>, <CIT>, <CIT> or <CIT>.

Certain disadvantage in the process of manufacturing a piston assembly is a necessity of angular positioning of its components, which causes production and operation issues. Another disadvantage is the necessity of providing distinct components for the rebound and compression sides of a piston assembly.

It has been the object of the present invention to provide a hydraulic damper of a simple construction, which would be cost efficient, simple to manufacture, provide versatile damper tuning capabilities for different piston velocities, and would be devoid of the aforementioned disadvantages.

A damper of the kind mentioned in the outset, according to the present invention is characterised in that the piston assembly is provided with an internal chamber and comprises two sleeve-shaped members closing each side of said internal chamber, wherein each sleeve-shaped member is provided with a number blow-off valve flow passages, which are radially proximal, a plurality of deflectable-disc valve flow passages, which are radially distal, and a central opening, wherein the piston rod passes through said central openings in said sleeve-shaped members to secure the piston assembly, a plurality of deflectable disc(s) of the deflectable-disc valve cover(s) said radially distal flow passages of each sleeve-shaped member at its external side, wherein said deflectable disc(s) is/are provided with a plurality of radially proximal flow passages corresponding to said radially proximal flow passages of said sleeve-shaped member, and is/are axially fixed at the piston rod, a plurality of disc(s) of the blow-off valve adjoin(s) said radially proximal flow passages of each sleeve-shaped member at its internal side, wherein a flow channel fluidly connects said internal chamber with said radially proximal flow passages of each sleeve-shaped member, and the piston assembly further comprises two spring seats abutting said disc(s) of the blow-off valve, and at least one spring disposed within said internal chamber that biases said spring seats towards said number of disc(s).

Preferably, said sleeve-shaped members each include a cylindrical section that extends annularly around said internal chamber of the piston assembly, and wherein said piston assembly further includes an annular seal configured to seal between the cylindrical sections and the tube.

Alternatively preferably, the piston assembly further comprises a body defining said internal chamber of the piston assembly and is provided with an annular seal configured to seal against the tube.

Preferably, said at least one disc of the blow-off valve is deflectable or displaceable.

Preferably, said piston assembly further comprises at least one internal flange and said at least one spring disposed within said internal chamber is compressed between said internal flange and one of said spring seats and biases this seat towards said at least one number of disc.

In this case, preferably the piston assembly further comprises at least one insert disposed within said internal chamber and provided with said radially internal flange.

Also in this case, preferably the piston assembly further comprises at least one second spring disposed within said internal chamber and compressed between said internal flange and one of said spring seats, and biases this seat towards said number of disc(s).

Preferably, said internal chamber is cylindrical.

Preferably, said rebound valve assemblies and said compression valve assemblies are made of identical parts.

Preferably, said flow channel is defined by a plurality of radially external notches of at least one disc of the blow-off valve.

Alternatively or additionally, preferably said flow channel is defined by a space separating the at least one disc and said radially proximal flow passages of the blow-off valve.

If said cylindrical sections of said sleeve-shaped members define an annular gap therebetween, preferably the piston assembly further comprises an internal sleeve disposed within said internal chamber abutting an internal wall of each of said cylindrical sections and covering said annular gap.

Alternatively preferably, said annular seal includes a narrowed section defining an annular chamber between said annular seal and the main tube, said annular seal defining a plurality of radial openings that fluidly join said internal chamber of the piston assembly with said annular chamber to balance hydraulic pressure therebetween.

The invention shall be described and explained below in connection with the attached drawings on which:.

<FIG> schematically illustrates a fragment of an exemplary vehicle suspension comprising a damper <NUM> of the present invention attached to a vehicle chassis <NUM> by means of a top mount <NUM> and a plurality of screws <NUM> disposed on the periphery of the upper surface of the top mount <NUM>. The top mount <NUM> is connected to a coil spring <NUM> and a piston rod <NUM> of the damper <NUM>. The external tube <NUM> of the damper <NUM> is connected to the steering knuckle <NUM> supporting the vehicle wheel <NUM>.

<FIG> presents an embodiment of a twin-tube damper <NUM> according to the present invention that may be employed in a typical motor vehicle suspension. The damper <NUM> comprises an external tube <NUM> and a main tube <NUM> filled with viscous working liquid inside of which a piston assembly 4a is attached to a piston rod <NUM>. The piston rod <NUM> extends outside the main tube <NUM> through a sealed piston rod guide <NUM> is movably disposed along an axis A. The damper <NUM> is also provided with a base valve assembly <NUM> fixed at the other end of the main tube <NUM>. The piston assembly 4a makes a sliding fit with the inner surface of the main tube <NUM> and divides the tube <NUM> into a rebound chamber <NUM> (between the piston rod guide <NUM> and the piston assembly 4a) and a compression chamber <NUM> (between the piston assembly 4a and the base valve assembly <NUM>). An additional compensation chamber <NUM> is located at the other side of the base valve assembly <NUM>.

The base valve assembly <NUM> is provided with compression <NUM> and rebound <NUM> valve assemblies to control the flow of working liquid passing between the compression chamber <NUM> and the compensation chamber <NUM> while the piston assembly 4a is in motion. Nonetheless, as shall be recognised by those skilled in the art from the following description, the invention is also applicable other damper constructions, including mono-tube dampers provided with a gas compensation chamber separated with a slidable diaphragm from the compression chamber <NUM>.

The term "compression" as used herein with reference to particular elements of the damper refers to these elements or parts of elements which are adjacent to or face the compression chamber <NUM> or, in a case of working liquid flow direction, it refers to this flow direction that takes place during the compression stroke of the damper. Similarly the term "rebound" as used in this specification with reference to particular elements of the damper refers to these elements or these parts of particular elements which are adjacent to or face the rebound chamber <NUM> or, in a case of working liquid flow direction, it refers to this flow direction that takes place during the rebound stroke of the damper. Where appropriate suffixes "c" and "r" were added to numerical references in order to distinguish respectively compression and rebound side components of the piston assemblies according to the present invention. Otherwise numerical references to the same functional elements are the same throughout the drawings. Where appropriate, they are supplemented with additional suffixes ("a", "b",. ) to differentiate elements of the same functionality but different construction.

The piston assembly according to the present invention is provided with compression valve assemblies 41c, 42c and rebound valve assemblies 41r, 42r to control the flow of working liquid passing between the rebound chamber <NUM> and the compression chamber <NUM> while the piston assembly 4a is in motion. Each valve assembly <NUM>, <NUM> includes a deflectable-disc valve <NUM> and a blow-off valve <NUM>.

The embodiment of the piston assembly 4a, shown in <FIG>, <FIG>, and 5a and 3b, is symmetric with respect to the plane perpendicular to the axis A; compression valve assemblies 41c, 42c are mirror images of the rebound valve assemblies 41r, 42r and are made of the same components. This significantly simplifies the construction of the piston assembly 4a.

In this embodiment, the piston assembly 4a comprises two sleeve-shaped members 44a provided with central openings <NUM>. A narrowed section <NUM> of the piston rod <NUM> passes through these openings <NUM> and a nut <NUM> is screwed on a threaded end of this narrowed section <NUM> securing the piston assembly 4a tightly to the piston rod <NUM>. Each sleeve-shaped member 44a has a cylindrical section <NUM> and the cylindrical sections <NUM> of both sleeve-shaped members 44a face each other with a certain annular gap <NUM> (cf. <FIG>) in between. A sleeve <NUM> adjoining the narrowed section <NUM> of the piston rod <NUM> provides support for the sleeve-shaped members 44a. An annular seal <NUM> is disposed radially outside of the sleeve-shaped member 44a and disposed within two adjoining annular groves <NUM> formed in the cylindrical sections <NUM>, closing this annular gap and sealing against the main tube <NUM> with a sliding fit. Sleeve-shaped members 44a and the sleeve <NUM> of the piston rod <NUM> define an internal, substantially cylindrical chamber <NUM>.

Each sleeve-shaped member 44a is provided with a plurality of blow-off valve flow passages <NUM> spaced at equal angular intervals, which are radially proximal, and a plurality of deflectable-disc valve flow passages <NUM> spaced at equal angular intervals, and which are radially distal.

The deflectable-disc valve <NUM> comprises a deflectable disc <NUM> that covers the radially distal flow passages <NUM> at the external side of the sleeve-shaped member 44a and is provided with a plurality of radially proximal flow passages <NUM> corresponding to the blow-off valve flow passages <NUM> of the sleeve-shaped member 44a. The deflectable disc <NUM> is axially fixed at the narrowed section <NUM> of the piston rod <NUM> by means of a spacer <NUM> and a retainer <NUM>.

The blow-off valve <NUM> comprises stack of discs formed by a spacer <NUM> adjoining the sleeve-shaped member 44a at its internal side, followed by a notched disc <NUM> provided with a plurality of radially external notches <NUM> spaced at equal angular intervals, three discs <NUM> and a spacer <NUM>. In this embodiment radially internal sides of the stacks of discs <NUM>, <NUM> are clamped by the sleeve <NUM> to the sleeve-shaped members 44a. Each blow-off valve <NUM> further comprises a spring seat <NUM>, also slidably disposed about the sleeve <NUM>, which abuts the axially internal disc <NUM>. A spring 47a disposed within the internal chamber <NUM> biases the spring seats <NUM> towards the discs <NUM> and <NUM> to cover the blow-off valve flow passages <NUM> in the sleeve-shaped member 44a.

During the piston assembly 4a operation the working liquid flows into the chamber <NUM> through radially proximal flow passages <NUM> of the disc <NUM>, blow-off valve flow passages <NUM> of the sleeve-shaped member 44a, and through a flow channel defined by the external notches <NUM> in the notched disc <NUM> inside the chamber <NUM>. Flowing out of the chamber <NUM> the working liquid enters into the deflectable-disc valve flow passages <NUM> of the sleeve-shaped member 44a on the opposite side of the chamber <NUM> and forces the disc <NUM> of the deflectable-disc valve <NUM> outside the chamber to deflect creating an annular gap restricting the flow and having the width increasing along with the pressure of the working liquid, until the point when the disc <NUM> abuts the retainer <NUM> and its further deflection is impossible.

After a certain piston velocity threshold is reached the pressure of the working liquid flowing into the chamber <NUM> will be higher than the pressure of the spring 47a and preload of the deflectable discs <NUM> and <NUM>. At this point the spring seat <NUM> of the blow-off valve <NUM> will displace and the discs <NUM> and <NUM> will deflect toward the interior of the chamber creating an annular gap allowing more unrestricted flow of the working liquid. Therefore this velocity threshold is defined by the spring 47a constant and the elasticity of the stack of deflectable discs <NUM> and <NUM>. This allows to control the characteristics of the blow-off valve to a much greater extent than it could be achieved with a blow-off valve with displaceable discs. Geometry of blow-off valve flow passages <NUM> in the sleeve-shaped member 44a determines the valve characteristics at the highest speeds of the piston rod <NUM>.

Another embodiment of a piston assembly 4b is shown in <FIG> and <FIG>. This embodiment is also symmetric, similarly as in the embodiment of the piston assembly 4a, and the compression valve assemblies 41c, 42c are mirror images of the rebound valve assemblies 41r, 42r and are made of the same components.

The piston assembly 4b comprises a piston body <NUM> defining a cylindrical chamber <NUM>. The piston body <NUM> is provided with an annular grove <NUM> in which an external annular seal <NUM> is disposed to seal against the main tube <NUM> with a sliding fit. The piston assembly 4b comprises two sleeve-shaped members 44b of a construction similar to sleeve-shaped members 44a of the piston assembly 4a. A narrowed section <NUM> of the piston rod <NUM> passes through central openings <NUM> of the sleeve-shaped members 44b and a nut <NUM> is screwed on a threaded end of this narrowed section <NUM> securing the piston assembly 4b to the piston rod <NUM>. Each sleeve-shaped member 44b is disposed in an annular recess <NUM> provided in the piston body <NUM> at the end of the cylindrical chamber <NUM> and this connection is sealed with an annular o-ring seal <NUM>. The deflectable disc valve <NUM> has the construction similar to the one discussed above with regard to the piston assembly 4a. The blow-off valve <NUM> comprises a spacer <NUM> adjoining the sleeve-shaped member 44b at its internal side, followed by a deflectable disc <NUM> and a spring seat <NUM> disposed slidably about the narrowed section <NUM> of the piston rod <NUM> and abutting the disc <NUM>. A spring 47b disposed within the internal chamber <NUM> biases both spring seats <NUM> towards the disc <NUM> to cover the blow-off valve flow passages <NUM> in the sleeve-shaped members 44b. Spring seats <NUM> comprise cylindrical sections <NUM> providing guidance for the spring 47b.

The piston assembly 4b operation is similar to the operation of the piston assembly 4a discussed above. In this embodiment, however, the working liquid flows into the chamber <NUM> through radially proximal flow passages <NUM> of the disc <NUM>, blow-off valve flow passages <NUM> of the sleeve-shaped member 44b, and through a flow channel <NUM> defined by the spacer <NUM> between the blow-off valve flow passages <NUM> and the disc <NUM>.

Yet another embodiment of a piston assembly 4d is shown in <FIG>. Similarly as in the embodiment of the piston assembly 4b the piston assembly 4d comprises a piston body <NUM> defining a cylindrical chamber <NUM> which is closed at the compression and at the rebound side with sleeve-shaped members 44b. In this embodiment the piston assembly 4d comprises an insert <NUM> disposed within an annular recess 482r of the piston assembly 4d at the rebound side of the cylindrical chamber <NUM> and at the rebound side of the cylindrical chamber <NUM> the sleeve-shaped member 44b is disposed within an annular recess 492r provided in the insert <NUM>. The insert <NUM> has a radially internal flange <NUM> within the cylindrical chamber <NUM> that provides an abutment surface for an additional second spring 47d biasing a spring seat <NUM> of the rebound blow-off valve 42r along with a main spring 47b which is compressed between the spring seats <NUM> of the blow-off valves 42c and 42r. As shall be recognised by those skilled in the art another embodiment of the piston assembly (not shown) could be provided with two inserts <NUM> or without insert but with an internal flange by the piston assembly <NUM> itself (cf.

<FIG> illustrates the functionality of the piston assembly 4d during the compression stroke.

As shown in <FIG> (left side of the drawing), during the compression stroke, at low velocity of the piston assembly 4d, the working liquid flows via pathway C1 from the compression chamber <NUM> to the rebound chamber <NUM> through flow passages <NUM> in the deflectable-disc <NUM>, through blow-off valve flow passages <NUM> of the sleeve-shaped member 44b, through an annular gap between the blow-off valve disc <NUM> and the rebound side of the blow-off valve flow passages <NUM>; through the cylindrical chamber <NUM>; through the deflectable-disc valve flow passages <NUM> of the sleeve-shaped member 44b and its pressure forces the deflectable-disc <NUM> of the compression deflectable-disc valve 41c to deflect. Above a predefined velocity threshold, as shown in <FIG> (right side of the drawing), increased pressure of the working liquid in the compression chamber <NUM> lifts the spring seat <NUM> of the compression blow-off valve 42c against the pressure of the spring 47b opening additional pathway C2. This lowers the reaction force and provides digressive force vs. velocity characteristic of the damper.

As shown in <FIG> (left side of the drawing), during the rebound stroke, at low velocity of the piston assembly 4d, the working liquid flows via pathway R1 from the rebound chamber <NUM> to the compression chamber <NUM> through flow passages <NUM> in the deflectable-disc <NUM>, through blow-off valve flow passages <NUM> of the sleeve-shaped member 44b, through an annular gap between the blow-off valve disc <NUM> and the compression side of the blow-off valve flow passages <NUM>; through the cylindrical chamber <NUM>; through the deflectable-disc valve flow passages <NUM> of the sleeve-shaped member 44b and its pressure forces the deflectable-disc <NUM> of the rebound deflectable-disc valve 41r to deflect. Above a predefined velocity threshold, as shown in <FIG> (right side of the drawing), increased pressure of the working liquid in the rebound chamber <NUM> lifts the spring seat <NUM> of the rebound blow-off valve 42r against the pressure of both springs 47b and 47d opening additional pathway R2. This lowers the reaction force and provides digressive force vs. velocity characteristic of the damper. In this case the resultant spring constant of these two parallel springs 47b and 47d is the sum of their spring constants.

Yet another embodiment of a piston assembly 4e, shown in <FIG>, has a construction similar to the piston assemblies 4b and 4d, wherein a piston body <NUM> is provided in a chamber <NUM> with a radially internal flange <NUM>. A spring 47e is compressed between this internal flange <NUM> and a spring seat <NUM> of a rebound blow-off valve 42r. Another spring 47f is compressed between this internal flange <NUM> and a spring seat <NUM> of a compression blow-off valve 42c.

As shown in <FIG> an annular gap <NUM> present between facing each other cylindrical sections <NUM> of both sleeve-shaped members 44a creates an opportunity for the working liquid to flow through this gap <NUM> and act with its pressure on an external annular seal <NUM> of the piston assembly 4a, leading to disadvantageous increase of friction.

To suppress this effect a sealing arrangement is provided in a form of a thin-walled internal sleeve <NUM> disposed within an internal chamber <NUM>. The internal sleeve <NUM> abuts the internal wall of the cylindrical sections <NUM> of the sleeve-shaped members 44a and with a certain axial clearance covers the annular gap <NUM>.

Another form of a sealing arrangement is shown in <FIG>. Here an annular seal <NUM> is provided with a narrowed section <NUM> in the middle defining an annular chamber <NUM> between the sealing <NUM> and the main tube <NUM>. This narrowed section <NUM> is provided with a plurality of radial openings <NUM> spaced at equal angular intervals and which fluidly join an internal chamber <NUM> of the piston assembly 4a with the annular chamber <NUM> and balance hydraulic pressure therebetween.

Claim 1:
A hydraulic damper (<NUM>), in particular a motor vehicle hydraulic suspension damper, comprising:
a tube (<NUM>) filled with working liquid;
a piston assembly (<NUM>) disposed slidably inside the tube (<NUM>), dividing the tube (<NUM>) into a rebound chamber (<NUM>) and a compression chamber (<NUM>), characterized in that the piston assembly includes two sleeve-shaped members (<NUM>), a rebound valve assembly (41r, 42r), and a compression valve assembly (41c, 42c), wherein each of the rebound valve assembly (41r, 42r) and the compression valve assembly (41c, 42c) includes a deflectable-disc valve (<NUM>) and a blow-off valve (<NUM>);
an internal chamber (<NUM>) extending between the two sleeve-shaped members (<NUM>);
a piston rod (<NUM>) attached to the piston assembly (<NUM>) and extending outside the tube (<NUM>) through a sealed piston rod guide (<NUM>);
wherein each of the sleeve-shaped members (<NUM>) defines a plurality of blow-off valve flow passages (<NUM>), which are radially proximal, a plurality of deflectable-disc valve flow passages (<NUM>), which are radially distal, and a central opening (<NUM>),
wherein the piston rod (<NUM>) passes through said central openings (<NUM>) in each of said sleeve-shaped members (<NUM>);
each of the deflectable-disc valves (<NUM>) including at least one deflectable disc (<NUM>) covering an external end of said deflectable-disc valve flow passages (<NUM>) of a corresponding one of said sleeve-shaped members (<NUM>);
wherein each of said at least one deflectable disc (<NUM>) is axially fixed at said piston rod and defines a plurality of radially proximal flow passages (<NUM>) corresponding to said blow-off valve flow passages (<NUM>) of a corresponding one of said sleeve-shaped members (<NUM>);
each of the blow-off valves (<NUM>) including at least one disc (<NUM>, <NUM>) adjoining an internal end of said blow-off valve flow passages (<NUM>) of a corresponding one of said sleeve-shaped members (<NUM>);
wherein a flow channel (<NUM>, <NUM>) fluidly connects said internal chamber (<NUM>) with said blow-off valve flow passages (<NUM>) of each sleeve-shaped members (<NUM>); and
wherein the piston assembly (<NUM>) further comprises a spring seat (<NUM>) abutting said at least one disc (<NUM>, <NUM>) of each of the blow-off valves (<NUM>), and at least one spring (<NUM>) disposed within said internal chamber (<NUM>) and configured to bias said spring seats (<NUM>) towards said at least one disc (<NUM>, <NUM>).