Systems and methods for pressure sensor assembly including improved encapsulation material

1. A pressure sensor assembly for measuring pressure of air in a compression ignition internal combustion engine, the pressure sensor assembly comprising:

an external housing unit;

a sensor unit received within the external housing unit, the sensor unit comprising an external surface including a mounting surface;

a sensing element mounted within the sensor unit and comprising a pressure-sensing surface;

a substrate upon which the mounting surface is mounted;

an air passage which enables impingement of air on the sensing element, in use; and

a filling passage, separate from the air passage, which introduces an encapsulation material onto the sensor unit, during assembly;

wherein the encapsulation material covers at least a part of the external surface of the sensor unit but does not cover the pressure-sensing surface of the sensing element which remains directly exposed to air within the air passage.

2. The pressure sensor assembly as claimed in claim 1 , wherein the pressure sensor assembly is a manifold absolute pressure sensor assembly which measures the pressure of air in the intake manifold of the engine.

3. The pressure sensor assembly as claimed in claim 1 , wherein at least one of the filling passage and the air passage is provided in the external housing unit.

4. The pressure sensor assembly as claimed in claim 3 , wherein the air passage and the filling passage are adjacent to one another in the external housing unit.

5. The pressure sensor assembly as claimed in claim 1 , wherein the pressure-sensing surface is defined in an upper surface of the sensor unit opposed to the mounting surface.

6. The pressure sensor assembly as claimed in claim 5 , wherein a region of the external surface of the sensor unit surrounds the sensing element and wherein the region surrounding the sensing element is not covered with the encapsulation material.

7. The pressure sensor assembly as claimed in claim 5 , wherein the external housing unit defines, together with the upper surface of the sensor unit, a clearance.

8. The pressure sensor assembly as claimed in claim 7 , wherein the clearance is at least partly filled with the encapsulation material.

9. The pressure sensor assembly as claimed in claim 7 , wherein the clearance is between 0.2 and 0.3 mm.

10. The pressure sensor assembly as claimed in claim 1 , wherein the encapsulation material has a viscosity in a range of 70,000 to 90,000 cP.

11. The pressure sensor assembly as claimed in claim 1 , wherein the encapsulation material is a self-levelling adhesive.

12. A method of encapsulating a sensor unit in a pressure sensor assembly for a compression ignition internal combustion engine, the pressure sensor assembly comprising an external housing unit for the sensor unit, the sensor unit comprising a sensing element defining a pressure-sensing surface, the method comprising;

providing an air passage for the sensor unit which enables an airflow to be applied to the pressure-sensing surface, in use;

mounting a mounting surface of the sensor unit on a substrate to leave at least a part of an external surface of the sensor unit exposed including a pressure-sensing surface of a sensing element of the sensor unit;

providing a filling passage, separate from the air flow passage; and

introducing an encapsulation material through the filling passage so that the encapsulation material surrounds the external surface of the sensor unit which is exposed but excluding the pressure-sensing surface of the sensing element which remains directly exposed to air within an air passage.

13. The method as claimed in claim 12 , further comprising curing the encapsulation material after it has been introduced through the filling passage.

14. The method as claimed in claim 12 , further comprising introducing the encapsulation material into a clearance between the external housing unit and the sensor unit, so that the encapsulation material surrounds an exposed external surface of the sensor unit but excluding the pressure-sensing surface of the sensing element which remains directly exposed to air within the air passage, in use.

15. The method as claimed in claim 12 , further comprising selecting the viscosity of the encapsulation material so that the introduced encapsulation material does not extend so far into the clearance as to cover the pressure-sensing surface when it is introduced into the filling passage.

16. The method as claimed in claim 15 , wherein the encapsulation material has a viscosity in a range of 70,000 to 90,000 cP.