A control valve in a brake booster that supplies pressurized fluid to a brake system, said control valve having first bearing member and a second bearing member located in a first axial bore of a housing, said first bearing member having a second axial bore connected to a source of pressurized hydraulic fluid, a stem located in said second axial bore and having a ball retained on a first end;
- a cylindrical member connected to first bearing member to define a supply chamber within said second axial bore for receiving fluid from said source;
- said cylindrical member having a seat surrounding an axial orifice therein, a first spring located in said supply chamber for urging said ball toward said cylindrical member and into engagement with said seat to closed said supply chamber and retain fluid therein;
- said second bearing member being separated from said first bearing member to define an operational chamber within said first axial bore that is connected to said brake system, said second bearing member having a third axial bore therein, a plunger located in said third axial bore having a flange on a first end located in said operational chamber and a spherical head on a second end that extends into a relief chamber, said plunger having a passage that extends from said first end to a cross bore adjacent said second end;
- a tube extending from said first end of said plunger;
- a second spring located in said operational chamber and acting on said plunger to urge said flange into engagement with said second bearing to establish a position of rest for said plunger wherein said actuation chamber wherein said actuation chamber is in communication with said relief chamber by way of said passage and cross bore;
- an actuation assembly fixed to said housing including linkage assembly connected to said second end of said plunger for moving said tube into engagement with said ball in response to an input force being communicated from an operator to effect a brake application, said plunger initially moving to terminate communication from said operational chamber to said relief chamber and thereafter moving said ball away from said seat to allow pressurized fluid from said supply chamber to flow into said actuation chamber that is communicated to said brake system to effect said brake application, said pressurized fluid in said actuation chamber under certain operational condition being subjected to an oscillation in the fluid pressure such that said second spring acts on said flange and moves said tube away from said ball such that pressurized fluid from said supply chamber is communicated to said relief chamber by way of said passage even though said input force remains applied to said second end of said plunger;
- the improvement wherein said plunger is defined by a cylindrical body having a first diameter defined by said flange and located in a first diameter of said third axial bore and a second diameter that is sealingly located in a second diameter of said third axial bore, a space between said first diameter of said plunger and said first diameter of said third bore in said second bearing member defining a dampening chamber such that on initial movement of said plunger by said input force fluid is drawn into said dampening chamber and when pressurized fluid from said supply chamber is communicated into said actuation chamber additional fluid is communicated to said dampening chamber such that if oscillation should occur in the fluid pressure of the said actuation chamber said fluid in said dampening chamber acts as a lock to retain said plunger in a substantially stationary position corresponding to said input force applied to said second end of said plunger.