Pressure sensor having reduced hysteresis and enhanced electrical performance at low pressures

A pressure sensor adapted for sensing pressures near and below atmospheric pressure, the pressure sensor comprising:

• a housing formed from a first material having a coefficient of thermal expansion;
• a piezoresistive sensing element enclosed within the housing, the sensing element having an integrally-formed diaphragm with a first surface, the sensing element being formed from a second material whose electrical resistance changes in response to a pressure exerted on the first surface of the diaphragm by a surrounding environment, the second material having a coefficient of thermal expansion that is less than the coefficient of thermal expansion of the housing;
• a constraint member with which the sensing element is interconnected to the housing such that the sensing element is spaced apart from the housing, the constraint member being formed from a third material having a coefficient of thermal expansion that is approximately equal to the coefficient of thermal expansion of the sensing element;
• an insert disposed in the housing so as to be intermediate the constraint member and the housing, the insert having a peripheral surface of which at least a portion contacts the housing, the insert having a coefficient of thermal expansion that is approximately equal to the coefficient of thermal expansion of the sensing element, such that the sensing element and the constraint member are substantially isolated from stresses transmitted through the housing;
• and
• an adhesive bonding the constraint member to the insert;
• wherein electrical performance of the sensing element to near-atmospheric and lower pressures is promoted by the sensing element being isolated from stresses transmitted through the housing.

A fuel vapor pressure sensor comprising:

• a housing formed from a plastic material having a coefficient of thermal expansion;
• a piezoresistive sensing element enclosed within the housing, the sensing element having an integrally-formed diaphragm with a first surface and an oppositely-disposed second surface, the sensing element being formed from a piezoresistive material whose electrical resistance changes in response to a pressure exerted on the first surface of the diaphragm by a surrounding environment, the piezoresistive material having a coefficient of thermal expansion that is less than the coefficient of thermal expansion of the housing;
• a constraint member with which the sensing element is interconnected to the housing such that the sensing element is spaced apart from the housing, the constraint member including a passage in fluidic communication with the second surface of the diaphragm, the constraint member being formed from a glass material having a coefficient of thermal expansion that is approximately equal to the coefficient of thermal expansion of the sensing element;
• an insert molded into the housing so as to be intermediate the constraint member and the housing, the insert having a peripheral surface entirely contacting the housing and an axial passage in fluidic communication with the passage of the constraint member and the second surface of the diaphragm, the insert being formed from a glass material having a coefficient of thermal expansion that is approximately equal to the coefficient of thermal expansion of the sensing element, such that the sensing element and the constraint member are substantially isolated from stresses transmitted through the housing;
• and
• an adhesive bonding the constraint member to the insert;
• wherein the electrical performance of the sensing element to fuel vapor pressures is promoted by the sensing element being isolated from stresses transmitted through the housing.