Shock absorber with sonar position sensor

A method of determining the relative displacement between a piston and a stationary surface within a pressure cylinder of a direct acting shock absorber, said method comprising the steps of:

• delivering an electrical signal generated by a wave generation circuit to an ultrasonic transmitter through a first electrical path including at least a two-position switch when said switch is in a first position, said ultrasonic transmitter operable to emit pulsed ultrasonic waves of fixed and controlled frequency in response to said electrical signal generated by said wave generation circuit, said switch being operable to allow electric current to flow in a second electrical path when said switch is in a second position;
• changing the position of said switch from said first position to said second position so as to allow electric current to flow through said second electrical path;
• reflecting said ultrasonic waves emitted by said ultrasonic transmitter against a fixed inner surface of said pressure cylinder;
• receiving said ultrasonic wave reflected by said fixed inner surface by an ultrasonic receiver through said second electrical path;
• changing the position of said switch from said second position to said first position so as to allow electrical current to flow through said first electrical path;
• providing timing means for determining the time an emitted ultrasonic wave takes to be reflected back to said receiver, and generating an output signal in response thereto;
• and
• calculating the relative distance between said piston and said fixed inner surface in response to said output signal from said timing means.

A direct acting hydraulic shock absorber operable to selectively vary a suspension characteristic thereof in response to the relative displacement between a movable and a stationary component, said shock absorber comprising:

• a pressure cylinder forming a working chamber operable to store damping fluid;
• a piston disposed within said pressure cylinder defining a first and second portion of said working chamber, said piston being movable with respect to said pressure cylinder and comprising valve means for metering the flow of damping fluid between said first and second portions of said working chamber during movement of said piston within said pressure cylinder;
• transducer means for emitting and receiving sound waves propagating through said damping fluid contained within said second portion of said working chamber, said transducer means being mounted to said piston;
• means for driving said transducer means being operable to cause said transducer means to emit sound waves upon generation of a first electrical signal;
• a base valve operable mounted to an end surface of said second portion of said working chamber, said base valve operable to reflect sound waves emitted by said transducer means, said base valve having means for compensating for variations in the speed of propagation of said sound waves through said damping fluid;
• a timing circuit for measuring the difference in time of said sound wave emitted by said transducer means and said sound waves received by said transducer means, and generating an output in response thereto, said timing circuit including switch means for electrically connecting said transducer means to said means for driving upon receipt of said first electrical signal, said switch means being further operable to electrically connect said transducer means to said timing means in the absence of said first electrical signal;
• a computer for calculating the distance between said piston and said base valve from said output of said timing circuit;
• and
• a piston control circuit for selectively controlling said valve means so as to change the flow of damping fluid in said shock absorber in response to the distance between said piston and said base valve.