Dashpot for damping a closing movement of a hinged closure member
A dashpot comprising a housing; a closed cylinder cavity filled with hydraulic fluid; a slideable piston within the housing and dividing the closed cylinder cavity into a high pressure compartment and a low pressure compartment; a one-way fluid passage allowing fluid flow from the low pressure compartment to the high pressure compartment when the dashpot is being opened; a first restricted fluid passage determining a closing speed of the dashpot; and a mechanism for compensating temperature-induced viscosity changes of the hydraulic fluid. The compensation mechanism comprises: a second restricted fluid passage and a needle valve comprising: an elongated body whose a length is temperature dependent. The tip of the needle valve has a shape so that fluid flow along the second restricted fluid passage is always possible.
1 . A dashpot for damping a closing movement of a closure system having a support and a closure member that are hingedly connected to each other, the dashpot comprising:
a housing;
a closed cylinder cavity formed within the housing and being filled with hydraulic fluid;
a piston within said housing so as to divide the closed cylinder cavity into a high pressure compartment and a low pressure compartment, the piston being slideable with respect to the housing between two extreme positions in a sliding direction;
a one-way fluid passage provided in the piston and allowing fluid flow from the low pressure compartment to the high pressure compartment when said closure member is being opened;
a first restricted fluid passage provided in the housing and connecting the high pressure compartment and the low pressure compartment and determining a closing speed of the closing movement of the closure system; and
a compensation mechanism configured for compensating temperature-induced viscosity changes in said hydraulic fluid, the compensation mechanism comprising:
a second restricted fluid passage provided in the housing connecting the high pressure compartment and the low pressure compartment and having a narrowest cross-sectional area, wherein a location at which the second restricted fluid passage has its narrowest cross-sectional area determines a hypothetical plane, which hypothetical plane has a normal direction; and
a needle valve positioned at least partially inside the second restricted fluid passage and comprising:
an elongated body extending between a first end fixed to the housing and a second end opposite the first end, wherein a length of the elongated body is temperature dependent; and
a tip positioned at the second end of the elongated body near said location at which the second restricted fluid passage has its narrowest cross-sectional area, wherein a projection of the tip onto said hypothetical plane along said normal direction forms a two-dimensional shape which does not fully cover said narrowest cross-sectional area.
2 . The dashpot according to claim 1 , wherein the hydraulic fluid has a kinematic viscosity which is variable in a first temperature range and which is stable in a second temperature range.
3 . The dashpot according to claim 2 , wherein the first temperature range extends between a lower temperature value and a critical temperature value and the second temperature range extends between said critical temperature value and an upper temperature, said critical temperature being comprised between 0° C. and 40° C.
4 . The dashpot according to claim 3 , wherein said critical temperature is comprised between 10° C. and 30° C.
5 . The dashpot according to claim 2 , wherein, in said second temperature range, a surface area of the part of the narrowest cross-sectional area that is not covered by the projection stays substantially constant.
6 . The dashpot according to claim 1 , wherein the needle valve is adjustable to adjust a position of the tip with respect to the narrowest cross-sectional area.
7 . The dashpot according to claim 1 , wherein the needle valve comprises a base on which the first end of the elongated body is mounted, the base having a threaded outer area which engages a corresponding threaded area of the housing to mount the base on the housing.
8 . The dashpot according to claim 1 , wherein the hydraulic fluid has a viscosity index of at least 100 determined in accordance with ISO 2909:2002.
9 . The dashpot according to claim 1 , wherein the elongated body is made of a material having a first coefficient of thermal expansion and the housing is made of a material having a second coefficient of thermal expansion, a difference between the first and second coefficient of thermal expansion being at least 50 μm/m° C.
10 . The dashpot according to claim 1 , wherein the elongated body extends substantially along said normal direction, the tip comprising a tapered free end and a tip body which fits inside the narrowest cross-sectional area.
11 . The dashpot according to claim 10 , wherein the tip body is cylindrical with the two-dimensional shape formed by the projection being a circle which is smaller than the narrowest cross-sectional area.
12 . The dashpot according to claim 1 , wherein the elongated body extends substantially in a direction parallel to said hypothetical plane with the tip being adjacent the narrowest cross-sectional area.
13 . The dashpot according to claim 1 , wherein the elongated body has a length of at least 20 mm.
14 . The dashpot according to claim 1 , wherein the elongated body has a length of at least 30 mm.
15 . The dashpot according to claim 1 , wherein the dashpot comprises a first adjustable needle valve which cooperates with a valve seat formed in the first restricted fluid passage to allow adjusting said closing speed.
16 . A hydraulically damped actuator for damping a closing movement of a closure system having a support and a closure member that are hingedly connected to each other, wherein the hydraulically damped actuator comprises a dashpot comprising:
a housing;
a closed cylinder cavity formed within the housing and being filled with hydraulic fluid;
a piston within said housing so as to divide the closed cylinder cavity into a high pressure compartment and a low pressure compartment, the piston being slideable with respect to the housing between two extreme positions in a sliding direction;
a one-way fluid passage provided in the piston and allowing fluid flow from the low pressure compartment to the high pressure compartment when said closure member is being opened;
a first restricted fluid passage provided in the housing and connecting the high pressure compartment and the low pressure compartment and determining a closing speed of the closing movement of the closure system; and
a compensation mechanism configured for compensating temperature-induced viscosity changes in said hydraulic fluid, the compensation mechanism comprising:
a second restricted fluid passage provided in the housing and connecting the high pressure compartment and the low pressure compartment and having a narrowest cross-sectional area, wherein a location at which the second restricted fluid passage has its narrowest cross-sectional area determines a hypothetical plane, which hypothetical planes has a normal direction; and
a needle valve positioned at least partially inside the second restricted fluid passage and comprising:
an elongated body extending between a first end fixed to the housing and a second end opposite the first end, wherein a length of the elongated body is temperature dependent; and
a tip positioned at the second end of the elongated body near said location at which the second restricted fluid passage has its narrowest cross-sectional area, wherein a projection of the tip onto said hypothetical plane along said normal direction forms a two-dimensional shape which does not fully cover said narrowest cross-sectional area.
17 . The hydraulically damped actuator according to claim 16 , wherein the hydraulic fluid has a kinematic viscosity which is variable in a first temperature range and which is stable in a second temperature range.
18 . The hydraulically damped actuator according to claim 17 , wherein, in said second temperature range, a surface area of the part of the narrowest cross-sectional area that is not covered by the projection stays substantially constant.
19 . The hydraulically damped actuator according to claim 16 , wherein the needle valve is adjustable to adjust a position of the tip with respect to the narrowest cross-sectional area.