WAX-PELLET THERMOSTAT VALVE FOR AUTOMOTIVE COOLING SYSTEM

PATENTS ACT 1952 COMPLETE SPECIFICATION (ORIGINAL) FOR OFFICE USE ji***' Form Short Title; Int. CI: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: Priority* Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: Actual Inventor: Address fo£ Services Yoshikazu KUZE 31-3, HIGASHIMAGOME 1-CHOME OHTA-KU TOKYO JAPAN Yoshikazu KUZE GRIFFITH HACK & CO., 601 St, Kilda Road, Melbourne, Victoria 3004, Australia. Complete Specification for the invention entitled: WAX-PELLET THERMOSTAT The following statement is a full description of this invention Including the best method of performing it known to me:- TITLE OF THE INVENTION WAX-PELLET THERMOSTAT < * • t • a * • • a • • a • at • * a • a « BACKGROUND OF THE INVENTION The present invention relates to a wax-pellet termo- atat for automotive engines. The conventional wax-pellet thermostat comprises a thermo-sensitive device and a valve device. The thermo- sensitive device includes a steel piston, a guide member slidably engaged with the piston, a rubber seal spool around the piston, and a wax. The piston is sealed by a sealing device provided in the guide member. However, if the sealing device deteriorates, a space in the seal spool is Communi¬ cated with a coolant passage. Under such a condition, when the temperature of coolant rapidly decreases from high temperature (about 100oG) to low temperature(below 40oC), the space in the seal spool becomes a vacuum. Accord¬ ingly, the coolant is inducted into the space. Since the seal spool tightly grips the piston, the coolant in the space cannot be discharged* As described hereinafter, the valve is slightly raised by the coolant in the space, which causes the opening temperature of the valve to decrease. As a result, the engine is overcooled, thereby reducing the thermal efficiency Of the engine and increasing the amount of emissions. The amount of the coolanfc in the space increases with time, so that the valve lift increases, which Causes engine trouble. - 1A - \ i \ '- " i t « * « • * a # * t * a 4 « • • i • * Aceordifcg to the present invention there is provided a thermostat comprising: a housing having a valve seat, a piston disposed within said housing, a guide member slidably mounted around said piston, a valve secured to said guide member for moving into and out of said valve seat, a coil spring for biasing said valve against said housing, a diaphragm secured to said guide member at a lower portion thereof, said diaphragm having an axial pocket for slidably receiving the lower portion of said piston, a heat conductive cylinder secured to said guide member and surrounding said diaphragm with a cavity> wax disposed in said cavity of said cylinder, said wax expanding when heated so as to cause said diaphragm and said guide member to slidably move upwards along said piston thereby moving said valve into said valve seat against the bias of said coil, spring, and a seal device provided in said guide member at a top 2,0 portion thereof around said piston, said seal device comprising a movable separator plate slidably mounted on said piston, a pair of O-rings provided adjacent to opposite sides of said *« movable separator plate, and a fixed cqver for compressing the O-rings, each 0-ring having a circular cross section and being deformable so that when deformed, the O-rings provide a reliable sealing effect, whereby said seal device prevents the entrance of coolant or foreign materials between said guide member and said piston. These and other features of the present invention will become more apparent from the following description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWING? Figs, 1 and 2 are sectional views of the thermostat Of the present invention; Pigs. 3 and 4 are sectional views of a conventional thermostat; Fig. 5 is a graph shoning valve lifts of the thermostat of the present invention and conventional one with respect of temperature; and. Fig. 6 shows the operation of the thermostat of the present invention. - 2a I I Xe. • ff * 4 * * DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figa. 1 and 2. the thermostat of the present invention comprises a housing 2 forming a valve seat 1, a frame 3 secured to the housing 2. A thermo- sensitive device 5 comprises a steel piston 8 secured to the housing 2 at a top 12, guide member 6 slidably engaged with the piston 8, primary valve 4 secured to the guide member 6, heat conductive cylinder 11 secured to the guide member 6, rubber seal spool 9 secured to the guide member 6. wax pellet 10 provided in the cylinder 11, and seal packing 15 for preventing counter flow of coolant. A return coil spring 7 disposed surrounding the cylinder 11 is provided between the primary valve 4 and the bottom of the frame 3. Fig. 2 shows a valve in a closed state. When the temperature of the coolant rises in excess of a predetermined value of the thermostat, the wax 10 expands. This forces the rubber seal spool 9 against the steel piston 8. As the wax squeezes the rubber seal spool 9 around the piston 8, the wax 10 overcomes the coil spring 7 and the thermo~sensitive device 5 moves downward, thereby openirg the valve 4. When the thermostat cools, the wax 10 eontracts. Then the coil spring 7 returns the valve to the closed position as shown in Fig. 2. Since a space 13 is formed in the seal spool 9 at the bottom thereof, the valve 4 is securely pressed against the seat l* Referring to Fig. 6 showing a main part of the present invention, the seal packing 15 is a double "Sf/ F V? _--l O-ring seal device. The seal device comprises an annular separator 20 slidably provided in a recess formed in the guide member 6 and mounted on the piston 8. a pair of O-rings 21 disposed on opposite sides of the separator 20, a fixed cover 22, and a peripheral flange 23 inwardly deformed by a predetermined oil pressure to fix the cover 22. By adjusting the thickness of the annular separator 20, an optimum compression state of each O-ring can be provided. By such a double O-ring seal device, entrances of coolant and foreign materials can be perfectly prevented. Figs* 3 and 4 show a conventional thermostat. A .. coolant is inducted in space 13 in the seal spool 9. Fig. shows a valve lift curve A of the thermostat of tlhe present invention shown in Figs. 1 and 2 and a valve lift curve B of the thermostat shown in Figs. 3 and 4* The valve 4 of the thermostat of Fig. 2 begins to open at 880c and fully opens at 100oC (point D) .where the valve lift is 8.5 mm. Thereafter the valve is lifted by a small increment (0.07 mm per 10C) until 130 G by thermal expansion of the wax 10. On the other hand, the valve 4 of the thermostat of Fig. 3 in which the coolant is inducted in the diaphragm * * t 4) 9 4 9 is fully opened at about 84 C lower than that of the thermostat ot the present invention by 40C« The full open valve lift becomes 10.1 mm. Further, in the elosing state* the valve 4 is not engaged with the valve seat 1# maintaining a gap of about 0.5 mm between the valve and the seat. Accordingly, the engine is percooled. - 4 ~ t.-t+v*<. •imm- In accordance with the present invention, the valve lift ia constant. Accordingly, the axial length of the sealspoolcan be reduced. Referring to Fig. 6, the length 11 of the axial hole of the seal spool ia expressed as follows. II = L + oC where L is the full open valve lift. In the thermostat of the present invention, the value oC can be set to a small value, for example about 1.4 times as large as the diameter of the piston 8. thereby reducing the axial length of seal spool. Further, it is possible to set the full open valve lift to a higher point than the point Q (Fig. 5), such as for example at a point E where the »• ** valve lift change is very small, sd that reliable operation is expected. While the invention has been described in conjunction with preferred specific embodiments thereof, it will be understood that this description is intended to illustrate and not limit the scope of the invention, which is defined by the following claims. TvrsljMW-' THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: X. A thermostat comprising: a. housing having a valve seat, a piston disposed within said housing, a guide member slidably mounted around said piston, a valve secured to said guide member for moving into and out of said valve seat, a coil spring for biasing said valve against said housing, a diaphragm secured to said g1'' de member at a lower portion thereof, said diaphragm having an axial pocket for slidably receiving the lower portion of sal<\ piston, a heat conductive cylinder secured to said guide member and surrounding said diaphragm with a cavity, wax disposed in said cavity of said cylinder, said wax expanding when heated so as to cause said diaphragm and said guide member to slidably move upwards along said piston thereby moving said valve into said valve seat against the bias of said coil spring, and ** a seal device provided in said guide member at a top portion thereof around said piston, said seal device comprising a movable separator plate slidably mounted on said piston, a pair of 0-rings provided adjacent to opposite sides of said .. - movable separator plate, and a fixed cover for compressing the 0-rings, each 0-ring having a circular Cross section and being deformable so that when deformed, the O-rings provide a reliable sealing effect, whereby said seal device prevents the entrance of coolant, or foreign materials between said guide member and said piston. * • * 4 2. A thermOtStat substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 and Figures 5 and 6 inclusive. Dated this 21st day of March 1991. YOSHIKAZU KIJZE By Their Patent Attorneys GRIFFITH HACK & CO, Fellbws Institute of Patent Attorneys of Australia.