Long life vibration canceller having a gas spring

A linearly driven, counterbalanced machine comprising

• a cylinder enclosing at least a portion of a space,
• a piston arranged to be driven linearly within said cylinder to perform a thermodynamic function,
• means for driving said piston linearly at a given frequency which is variable over a range,
• an elongated chamber arranged coaxially with and rigidly connected to said cylinder, having a central region surrounded by a cylindrical wall coaxial with said axis, a buffer region and a compression region communicating with respective opposite ends of said central region,
• a counterbalance mass disposed within said central region, having a cylindrical surface arranged to have a small clearance space between said surface and said cylindrical wall,
• means for centering said mass about said axis,
• means for applying a biasing axial force to said mass in either axial direction, and
• a gas filling which occupies the space within said buffer region, compression region and clearance space;
• the mass of the counterbalance, the volume of the compression region and the gas pressure being selected such that the gas in at least the compression region acts as a spring opposing oscillatory movement of the counterbalance mass in the axial direction, and defines a spring-mass system resonant at substantially said given frequency,
• whereby the resonant frequency of the counterbalance system is changeable over said range upon application of a biasing force by said means for applying, said application of a biasing force causing the central position of the mass with respect to oscillatory movement to be changed as a result of net gas flow through the clearance space to or from the compression space.

A hermetically sealed Stirling cycle refrigeration machine, comprising

• a hermetically sealed case enclosing a space, at least a portion of the space being a cylinder having an axis,
• a piston movable axially within said cylinder,
• means for driving said piston linearly at a given frequency which is variable over a range,
• a displacer arranged to be movable linearly within said space in cooperation with said piston to perform a refrigerating thermodynamic function,
• an elongated chamber arranged coaxially with and rigidly connected to said cylinder, having a central region surrounded by a cylindrical wall coaxial with said axis, and a buffer region and a compression region communicating with respective opposite ends of said central region,
• a counterbalance mass disposed within said central region, having a cylindrical surface arranged to have a small clearance space between said surface and said cylindrical wall,
• means for centering said mass about said axis,
• means for applying a biasing axial force to said mass in either axial direction, and
• a gas filling which occupies the space within said buffer region, compression region and clearance space;
• the mass of the counterbalance, the volume of the compression region and the gas pressure being selected such that the gas in at least the compression region acts as a spring opposing oscillatory movement of the counterbalance mass in the axial direction, and defines a spring-mass system resonant at substantially said given frequency,
• whereby the resonant frequency of the counterbalance system is changeable over said range upon application of a biasing force by said means for applying, said application of a biasing force causing the central position of the mass with respect to oscillatory movement to be changed as a result of net gas flow through the clearance space to or from the compression space.