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Technical field

The present invention relates to a pressurized hydraulic two-way acting damper embodied according to claim 1, in which a rotary motion is translated via an arm rotating about its one end into a linear motion of the piston, which operates in a damping hydraulic medium. The rotating arm is arranged in a space which is pressurized by a pressurizing member to a pressure in excess of atmospheric pressure. The piston divides a damping volume in two damping chambers, which are connected together by a duct, through which an adjustable flow runs. Also arranged in the piston are piston passages, through which a damping medium is allowed to flow at low piston speeds. The damper is intended for use as a steering damper on a vehicle having handlebars, preferably a motor cycle, snow scooter or ATV.

Background of the invention

A steering damper is fitted between the handlebars of a vehicle and its frame or chassis, in order to damp impacts and severe movements that are transmitted from the front wheel (s) to the handlebars, or in order to solve the problem of wobbling, which can occur on a motorcycle at high speeds. Wobbling means that the front wheel of the motor cycle is beginning to oscillate with increasing amplitude.

Damping oscillations or other movements in the handlebars of a vehicle by means of hydraulic dampers is generally known. Modern steering dampers are mainly manufactured according to two different principles; linear damping or rotational damping. Embodiments of these principles are demonstrated in US 4,558,878, EP 1477397 and US 2004211632, for example.

US 4,558,878 describes a simple hydraulic damper in which a piston with a piston rod operates in a cylinder filled with a damping medium. The ends of the damper are fixed to the handlebars and the frame respectively. This design is simple but takes up a lot of space and can impart an unsymmetrical steering sensation.

EP 1477397 demonstrates a damper enclosed in a cylindrical housing, in which a piston fixed to a piston rod passing through it functions in a damping medium. The piston rod is coupled via an end eye to the handlebars, whilst the housing is fixed to the frame of the vehicle. The piston rod passing through means that the same quantity of damping medium is displaced in both expansion and compression. This design is not ideal either, since it is relatively large and unwieldy and moreover affords no pressurization of the damping medium. Pressurizing the damper reduces the risk of cavitation in the damping medium.

US 2004211632 shows a rotational damper in the form of a vane damper, in which the damper consists of a housing having a cut-out sector in which a vane-shaped arm is made to rotate in a damping medium. In the housing there are also ducts, which can be adjusted in order to regulate the flow between the two chambers formed by the housing and the vane-shaped arm. The housing is fitted to the handlebars and the center of rotation of the vane-shaped arm is fixed in the steering stem. A vane damper of this type requires close tolerances, especially in the milling operation, which means that it is expensive and difficult to manufacture. Pressurizing this damper whilst minimizing the external dimensions makes for an even more costly manufacturing process.

There is therefore a demand for a hydraulic damper for damping steering movements, which will solve the aforementioned problems such as the need for close milling tolerances, expensive and complicated manufacture, large overall dimensions, a high level of friction and the risk of cavitation.

There is another known type of damper that solves elements of these problems. This damper, however, is intended for use in damping the movement between the wheel and the chassis in a vehicle. The damper is designed with a two-way acting piston, which moves linearly in a cylinder, in which the movement is induced by an arm rotating about a first end, the other end of the arm being centered in the piston, see US 1,819,523, DE 907018, FR 1550091 and FR 1003856, for example .

FR 1550091 demonstrates a linear two-way acting piston damper, in which the damping chambers are connected to a space, which is separated off from the damping medium and pressurized to atmospheric pressure, so as to be flexible and capable of absorbing volume changes of the damping medium.

None of the aforementioned linear piston dampers is used to damp movements between the handlebars of a vehicle and its frame or chassis, that is to say these dampers are designed to absorb all the large forces acting between the road and the chassis. A steering damper is only intended to operate in the event of large impacts or forces acting on the handlebars. In the case of small, slow movements, which are initiated by a rider turning the handlebars, the damper must not have any effect on the steering sensitivity. It is therefore important that the damper should have a controlled leakage flow over the piston throughout the entire stroke when the damper is subjected to small impacts. In order to prevent cavitation, it is also essential that both damping chambers of the damper be pressurized to a pressure considerably greater than atmospheric pressure.

Summary of the invention

The design of the damper described in the application comprises a housing, which encloses a damping chamber filled with a damping medium and a pressurization chamber arranged parallel to the damping chamber. The damping medium is preferably an ordinary hydraulic oil, containing well-known additives. The rotational movement about a steering axis from a vehicle steering arrangement is translated by a second arm rotating about its one end into a linear movement of the piston.

The rotating second arm is arranged in a space which is pressurized to a certain basic pressure considerably greater than atmospheric pressure, the pressure preferably being between 6 and 10 bar. The pressurization is achieved by means of a pressurizing member arranged in the pressurization chamber. The pressurizing member may take the form of a piston, on which a pressure created by a gas, a liquid or a spring acts, or may take the form of an internally gas-pressurized rubber bladder. The function of the pressurization chamber is to accumulate the volume changes that occur as a result of temperature changes in the damping medium and to ensure at all times that a certain pressure always prevails in the space in which the rotating arm is arranged.

The piston has internal piston passages, through which the damping medium is allowed to flow in a controlled leakage flow. The pressurized area is connected, via the piston passages defined by a leaf valve, to the chamber which at that precise instant has the lowest pressure. Thus even the pressure in the chamber having the lowest pressure will not be less than the basic pressure .

The flow over the leaf valve is controlled by arranging a thin, flexible washer at a predefined distance from the valve seat. When the leaf valve is subjected to lower pressures, that is to say when the piston only performs small movements or is moving at low speed, the damping medium can flow between the chambers through the gap that is formed between the washer and the seat, but when a certain pressure prevails, the washer is deflected and prevents any further flow through the piston ducts. The damping medium then flows only through the first duct with adjustable damping medium flow.

The damper can also easily be adapted to different types of vehicle intended for use in different driving situations that require different maximum steering angles between the handlebars and the frame/chassis. Adjustment is achieved by varying the length of the rotating arm without changing the stroke length of the damper. In addition to the arms of different length, the same design details can then be used in many different applications, thereby simplifying the manufacturing process.

Brief description of the drawings

The invention will be described in more detail below with reference to the drawings attached, in which:

Fig. 1 shows the outside of the damper,
Fig. 2 shows a front part of a vehicle frame with the damper fitted,
Fig. 3 shows a side view of the damper with section lines drawn in,
Fig. 4a shows the section A-A in Fig. 3 through the piston and the damping chamber, Fig 4b shows a simplified section through the piston and the damping chamber,
Fig. 5 shows the section B-B in Fig. 3 through the reservoir,
Fig. 6a shows a cross section through the piston,
Fig. 6b shows an enlarged, detailed view of Fig. 6a.

Detailed description of the invention

Fig. 1 shows the damper 1. The damper 1 has an outer housing Ia separated from the surroundings by covers Ib, Ic and two valves 2, 3. The holes 4a, 4b are intended for fasteners allowing the damper to be fitted to the vehicle. A first arm 11 coupled to the movement-damping arrangement, which is fitted to the inside of the damper, is also shown as a part projecting from the damper .

Fig. 2 shows how the damper 1 is fitted to the handlebars 5 of a vehicle, in this embodiment a motorcycle. A handlebar 5 and a fork leg 8 (only one drawn in) are fixed to an upper fork crown 6 by spring clamps 7a, 7b. A lower fork crown stabilizes the fork legs and the front wheel is fixed to the bottom end of the fork legs (not shown) . The fork crown 6 rotates around a steering axis 10a against a bearing 10b, the steering axis 18a being centered in the head tube 10 in the front, non-rotating part of a frame 9. The front wheel is therefore steered through rotation of the handlebars 5 in relation to the non-rotating frame 9.

The damper 1 is fitted on top of the fork crown 6 and secured by two screws in the holes 4a, 4b, so that the steering axis 10a around which the front wheel rotates coincides with the axis 10' around which the damper rotates. The first arm 11 extends from the damper 1 and is fixed to a first pin 15 which extends basically outwards at right angles from the longitudinal direction of the damper housing (Ia) . The first arm 11 couples the damper 1 rotating with the handlebars 5 to the fixed, non-rotating frame 9 via a second pin 28.

Because the damper is pressurized and thereby independent of the rotational position in the space, there are also alternative placings of the steering damper that are not shown in the figure. For example, the steering damper 1 can instead be fixed directly to the frame 9, preferably between or immediately behind the fork legs 8a, and the first arm 11 can then be fixed to the one fork leg 8a. The following description, however, relates to the first embodiment, in which the steering damper is fitted on top of the fork crown.

Fig. 3 shows the damper from the side and, as can be seen, the outer damper housing Ia is designed in such a way that it can easily be produced from an extruded piece of metal, for example, or by machining a piece of metal. A number of holes are arranged parallel in the piece, these being hidden in Fig. 3 by the cover Ib and by the valve heads of the valves 2 and 3. These holes may be circular or may take some other suitable shape. They may also be through-holes and/or bored a certain distance from one or more directions. The first pin 15 protrudes from the lower part of the housing and in Fig. 1 is coupled via the first arm 11 to the frame 9 of the vehicle.

A cross section through the damper can be seen from the section A-A in Fig. 4a. The section runs through the bored hole that is used as damping chamber 12 and through a bored duct 13, which conveys the damping medium between two separated chambers 12a, 12b of the damping chamber. Fig. 4 also shows the piston 14, which divides the two sub-chambers 12a, 12b in the damping chamber and which functions in the damping medium, so that a damping force is generated.

Movements of the piston 14 are initiated by a rotating second arm 16, preferably in the form of a truncated figure of eight, coupled to the frame 5 of the vehicle via the first pin 15 protruding from the housing and the first arm 11. The second arm 16 rotates about the axis of rotation 10' , which passes through the rotation point RP in the first end part 16a of the second arm. The axis of rotation 10' coincides with the steering axis 10a of the steering arrangement as a whole. The second end part 16b of the rotating second arm 16 rotates in a space 17 in the middle of the piston, so that the rotational movement of the second arm 16 imparts a linear motion to the piston 14 in the damping chamber 12. The rotating second arm 16 has a length L, which is measured between the rotation point RP and the center of the second end part 16b.

Fig. 4b shows a simplified sectional view of a damper when the piston 14 is in its limit position, that is to say when the handlebars 5 of the vehicle have reached their maximum steering angle α relative to the frame/chassis 9. In order to adapt the damper for different types of vehicle intended for different driving conditions, this length L may be varied. For example, a shorter arm length Ll can be used for those applications that require a larger possible steering angle α, for example on MX motorcycles or ATVs and a longer arm length L2 may be used for road and racing motorcycles .

The length of the second arm 16 is determined by the following formula:
L = S / 2* sinα
where α is the maximum steering angle and S is the largest possible stroke of the piston.

Ll may be 12 mm, for example, and L2 16 mm. With a steering angle of approx. 50 and approx. 35 degrees respectively, these arm lengths give the same overall damper stroke. The same damper housing Ia and piston 14 can then be used for different applications. This then serves to reduce the complexity of the product manufacturing process.

The chambers 12a, 12b are connected via the duct 13 to openings 13a, 13b to the damping chamber 12. The flow through the duct 13 can be adjusted, for example, by the valve 2 shown in the figure. The valve 2 consists of a head 2a serving to adjust the position of the valve needle 2b. In this embodiment the damping chamber 12 is closed at both ends by sealed covers Ib, Ic. The valve 2 may be of a known, so-called bleed needle type, which is adjusted by turning the valve head 2a so that the conical needle 2b covers a larger or smaller area of the duct 13.

In Fig. 5 the section is taken through the cut-out 19 which is used as pressure reservoir and which is arranged parallel to the damping chamber 12. Pressurization of the pressure reservoir 19 can be achieved via a piston and spring or gas pressure, or via excess gas pressure in a rubber bladder. The figure shows the embodiment with a piston 20 and excess gas pressure. The gas filling is done via a self-sealing rubber part 21 in the cover 3. A duct 22 for ducting the pressurized damping medium extends from the reservoir 19 to the space 17, cf. Fig. 4. The function of the reservoir is to accumulate the volume changes that occur as a result of temperature changes in the damping medium and to ensure at all times that a certain pressure always prevails in the space 17.

Fig. 6a shows a sectional view of the piston 14, which also includes an enlarged detailed view 6b of an outer end of the piston. The piston comprises a piston housing 14a, which is defined at its ends by two piston parts 14b 14c. The space 17 is formed between the piston parts 14b 14c. The piston parts 14b 14c are held pressed against the piston housing 14a by a screwed connection 23, preferably in the form of a rod passing through the piston with nuts fitted at either end of the rod. The second end part 16b of the rotating second arm 16 rests against two wearing elements 24 also held fast by the screwed connection 23. The wearing elements 24 are spring-loaded by a spring arrangement 25, such as a disk spring, a coil spring or the like, so that the piston parts 14a, 14b are pressed together with a certain force. The fit between the wearing elements 24 and the second end part 16b is then kept constant even after a long operating life when any wearing down of the material in the piston 14 and the second arm 16 has occurred.

Ducts 14d are arranged in each of the piston parts 14b, 14c and connect the sub-chambers 12a and 12b to one another via the space 17 between the piston parts 14b, 14c. There may be two, three or more ducts 14d and they are placed in a circle around the center line of the piston inside an outer diameter dy. A leaf valve in the form of a thin, flexible washer 26 is designed to extend over the ducts on the outer area of the piston. The term outer relates to the area on which the higher pressure acts when the damper is in operation. The leaf valve 26 preferably has an outside diameter Dy that substantially coincides with or exceeds the outer diameter dy within which the ducts 14d are located. The leaf valve 26 is arranged at a distance from the piston 14, so that a gap x is formed between the valve 26 and the piston part 14b and 14c respectively. This distance is preferably defined by the thickness of a rigid washer 27 located tight against a seat 28 on the outer area of each piston part 14b 14c. The leaf valve 26 and the washer 27 are kept pressed against the piston parts 14b 14c by the screwed connection 23.

When the leaf valve 26 is subjected to lower pressures, that is to say when the piston 14 only performs small movements or is moving at low speed, the damping medium can flow between the chambers 12a, 12b through the gap x that is formed between the leaf valve 26 and the seat 28, but when a certain pressure prevails, or at high piston speeds, the leaf valve 26 is deflected and prevents any further flow through the piston ducts 14b, 14c. The damping medium then flows only through the first duct 13 with adjustable damping medium flow. High speeds of the piston 14 occur, for example, due to impacts in the handlebars 5 caused by uneven ground, whilst ordinary steering movements may be regarded as a movement that imparts a low speed to the piston 14.

Since the space 17 is connected to each damping chamber 12a, 12b via the gap x, the pressure in the damping chambers will always be at least equal to the pressure in the pressurized space 17. Pressurization also on the low-pressure side of the piston means that the risk of cavitation in the damper is reduced, since when the direction of the piston is reversed there is then always an opposing pressure acting on the piston.

The tolerance between the piston 14 and the outside diameter of the cut-out 12 in the damper housing Ia is selected so that the gap between them is so slight that no oil can pass. This means that the precise fit, in the order of a couple of hundredths of a millimeter, preferably between 0.01 and 0.03 mm, between the piston 14 and the housing Ia functions as a separator between the high and low pressure sides. Since these close tolerances are used in a circular geometry, it is a relatively inexpensive operation to manufacture the piston 14 and the damper housing Ia with these tolerances. Due to these close tolerances, no separate sealing is required between the chambers, which means that the friction in the system can be minimized.

The invention is not limited to the embodiment shown above by way of example, but lends itself to modifications without departing from the scope of the following claims and the idea of the invention.