EP2141347A1

EP2141347A1 - Thermal compensation arrangement

Info

Publication number: EP2141347A1
Application number: EP08012066A
Authority: EP
Inventors: Marco Maragliulo
Original assignee: Continental Automotive Technologies GmbH
Current assignee: Aumovio Germany GmbH
Priority date: 2008-07-03
Filing date: 2008-07-03
Publication date: 2010-01-06

Abstract

A Thermal compensation arrangement (6) comprises a housing (4) including a central longitudinal axis (A). The housing (4) comprises a cavity (14) and a solid state actuator unit (10) being arranged in the cavity (14) and having a first axial end (10a) and a second axial end (10b). The second axial end (10b) acts as a drive side of the solid state actuator unit (10). A thermal compensation unit (8) is arranged at least partially in the cavity (14) and is coupled to the first axial end (10a) of the solid state actuator unit (10). The thermal compensation unit (8) comprises a casing (32) being mechanically coupled to the housing (4) and comprising a recess (34). A piston (36) is axially movable in the recess (34) and is designed to be coupled to the solid state actuator unit (10). The recess (34) is filled with a fluid (MRF) of a viscosity (v) being influenceable by a magnetic field (B). An electromagnet (39) is arranged in the thermal compensation unit (8) and is designed to influence the viscosity (v) of the fluid (MRF) by its magnetic field (B).

Description

The invention relates to a thermal compensation arrangement.
Thermal compensation arrangements are in widespread use, in particular in combination with injection valves for combustion engines. Injection valves may be arranged in order to dose fluid into an intake manifold of the combustion engine or directly into the combustion chamber of a cylinder of the combustion engine.
Injection valves comprise length-changing electromechanical solid state actuators such as electro-restrictive, magneto-restrictive or solid state actuators. In order to inject fuel, the solid state actuator unit is energized so that a fluid flow through a fluid outlet portion of the injection valve is enabled.
During an operation of the combustion engine the components of the combustion engine, for example, the injection valves experience significant thermal fluctuations that result in thermal expansion or contraction of the components. If a solid state actuator is used for the opening and closing of the injection valve, the thermal fluctuations can result in valve element movements that can be characterized as an insufficient opening stroke, or an insufficient sealing stroke. This is due to the low thermal expansion characteristics of the solid state actuator as compared to the thermal expansion characteristics of other fuel injector or combustion engine components. Any thermal contractions or expansions of the injection valve can have a significant effect on fuel injector operation.
The object of the invention is to create a thermal compensation arrangement which facilitates a reliable and precise function of the injection valve.
The object of the invention is achieved by the features of the independent claim. Advantageous embodiments of the invention are given in the subclaims.
The invention is distinguished by a thermal compensation arrangement comprising a housing including a central longitudinal axis. The Housing comprises a cavity and a solid state actuator unit being arranged in the cavity and having a first axial end and a second axial end. The second axial end acts as a drive side of the solid state actuator unit. A thermal compensation unit is arranged at least partially in the cavity and is coupled to the first axial end of the solid state actuator unit. The thermal compensation unit comprises a casing being mechanically coupled to the housing and a recess. A piston is axially moveable in the recess and is designed to be coupled to the solid state actuator unit. The recess is filled with a fluid of a viscosity which can be influenced by a magnetic field. An electromagnet is arranged in the thermal compensation unit and is designed to influence the viscosity of the fluid by its magnetic field.
An influence on the viscosity of the fluid enables to dynamically impose the damping coefficient of the thermal compensation unit which allows to sustain a linear behavior concerning the stack activation energy with respect to the displacement of the solid state actuator unit.
In an advantageous embodiment of the invention, the fluid is a magnetorheological fluid.
This enables a simple and reproducible possibility to influence the viscosity of the fluid in order to vary the damping coefficient of the thermal compensation unit.
In a further advantageous embodiment of the invention, an injection valve comprises the thermal compensation arrangement.
By this, a reliable and precise function of the injection valve is enabled.
Exemplary embodiments of the invention are explained in the following with the help of schematic drawings. These are as follows:

Figure 1: an injection valve in a longitudinal section view, and
Figure 2: an enlarged view of a part of the injection valve according to Figure 1 with a thermal compensation arrangement.

Elements of the same design and function that appear in different illustrations are identified by the same reference characters.
Figure 1 shows an injection valve 2 that is used as a fuel injection valve for a combustion engine. The injection valve 2 comprises a thermal compensation arrangement 4 and a valve body 6.
The thermal compensation arrangement 4 comprises a housing 8, a solid state actuator unit 10 with a first axial end 10a, a second axial end 10b and a thermal compensation unit 12.
The housing 8 has a tubular shape and the solid state actuator unit 10 is inserted into the housing. The solid state actuator unit 10 changes its axial length when it is energized or de-energized. The solid state actuator unit 10 can comprise a piezo actuator, but it may, however, also comprise another type of solid state actuator, which is known to a person skilled in the art for that purpose. Such a solid state actuator may be, for example, an electro-restrictive or magneto-restrictive actuator.
The valve body 6 has a longitudinal axis A. The housing 8 has a cavity 14 which is axially led through the valve body 6. On one of the free ends of the cavity 14, a fluid outlet portion 16 is formed which is closed or open depending on the axial position of a valve needle 18. The injection valve 2 further comprises a fluid inlet portion 20 which is arranged in the housing 8 and which is hydraulically coupled to the cavity 14 and a fuel connector which is not shown. This fuel connector is designed to be connected to a high pressure fuel chamber of the combustion engine, the fuel is stored under pressure, for example, above 200 bar.
The valve body 6 comprises a valve body spring rest 22 and the valve needle 18 comprises a valve needle spring rest 24, both spring rests 22 and 24 supporting a main spring 26 which is arranged between the valve body 6 and the valve needle 18.
The injection valve 2 is of an outward opening type. In an alternative embodiment the injection valve 2 may be of an inward opening type. Between the valve needle 18 and the valve body 6 a bellow 28 is arranged which is sealingly coupling the valve body 6 to the valve needle 18. By this the fluid flow between the cavity 14 and the chamber 30 is prevented.
Furthermore, the bellow 28 is formed and arranged in a way that the valve needle 18 is actuable by the solid state actuator unit 10.
In the following, the function of the injection valve 2 will be described:

The fuel is led from the fluid inlet portion 20 in the housing 8 towards the valve body 6 and then towards the fluid outlet portion 16.

The valve needle 18 prevents a fluid flow through the fluid outlet portion 16 and the valve body 6 in a closing position of the valve needle 18. Outside of the closing position of the valve needle 18, the valve needle 18 enables the fluid flow through the fluid outlet portion 16.
The solid state actuator unit 10 changes its axial length if it is energized. By changing this length the solid state actuator unit 10 may affect a force on the valve needle 18. Due to the elasticity of the bellow 28 the valve needle 18 is able to move in axial direction out of its closing position. Outside the closing position of the valve needle 18, there is a gap between the valve body 6 and the valve needle 18 at an axial end of the injection valve 2 facing away from the solid state actuator unit 10. The gap is forming a valve nozzle 31.
The main spring 26 can force the valve needle 18 via the valve needle spring rest 24 towards the solid state actuator unit 10. In the case that the solid state actuator unit 10 is de-energized the solid state actuator unit 10 shortens its length. Due to the elasticity of the bellow 28 the main spring 26 can force the valve needle 18 to move in axial direction in a closing position. It is depending on the force balance between the force of the valve needle 18 caused by the solid state actuator unit 10 and the force on the valve needle 18 caused by the main spring 26 whether the valve needle 18 is in its closing position or not. If the valve needle 18 is not in its closing position a fuel flow is enabled through the valve nozzle 31.
If the temperature of the injection valve 2 increases during its operation, the injection valve 2, especially the housing 8, expands its axial length. In general, the housing 8, which is preferably made of stainless steel, expands more with the increasing temperature than the solid state actuator unit 10. The thermal compensation arrangement 4 is arranged in order to compensate that thermal expansion of the housing 8.
Figure 2 shows a longitudinal sectional view of the thermal compensation arrangement 4 arranged in the housing 8 and coupled to the solid state actuator unit 10.
The thermal compensation unit 12 comprises a casing 32 of a cylindrical shape which has a recess 34, in which a piston 36 is arranged. The recess is filled with a fluid MRF, preferably with a magnetorheological fluid. The viscosity v of the fluid MRF can be influenced by a magnetic field. The higher the magnetic field acting on the fluid MRF, the more viscous becomes the fluid MRF. An electromagnet 39 is arranged in the casing 32. The electromagnet 39 can, for example, also be arranged in the piston 36. The electromagnet 39 can be a solenoid and is designed to influence the viscosity v of the fluid MRF by its magnetic field B. The piston 36 is of a cylindrical shape and extends in the axial direction of the casing 32 and is coupled to the solid state actuator unit 10 by a connecting bar 38. The thermal compensation unit 12 comprises a sealing element 40 arranged in a piston rest 42 being part of the casing 32 and supporting the piston 36 in an initial state of the thermal compensation unit 12 as described below.
A spring retaining element 44 is mechanically coupled to the thermal compensation unit 12 by the connecting bar 38. A compensation spring 46 is arranged between the sealing element 40 of the thermal compensation unit 12 and the spring retaining element 44 comprising a spring rest 48. The thermal compensation arrangement 4 is rigidly coupled to the housing 8 of the injection valve 2, for example by a welding seam 50 extending circumferentially over a side surface 52 of the casing 32 of the thermal compensation arrangement 6.
The piston 36 of the thermal compensation arrangement 4 has a first front surface 54 pointing in axial direction away from the actuator unit 10 and a second front surface 56 pointing in axial direction and facing the actuator unit 10 thereby pointing away from the first front surface 54. The cylindrical shaped piston 36 furthermore has a lateral surface 58 extending between the first front surface 54 and the second front surface 56. Between the lateral surface 58 of the piston 36 and the casing 32 of the thermal compensation arrangement 6, a gap 60 is formed being a part of the recess 34 in the casing 32. Between the first front surface 54 of the piston 36 and the casing 32 a recess section 62 is extending in axial direction. Between the second front surface 56 of the piston 36 and the sealing element 40 a bottom recess section 64 is arranged. The recess section 62 and the bottom recess section 64 are part of the recess 34 of the casing 32.
In the following the function of the thermal compensation unit 12 concerning the compensation of the thermal expansion of the housing 8 will be described in detail:

During the operation of the thermal compensation unit 12, the recess section 62 and the bottom recess section 64 are filled with the fluid MRF. The fluid MRF in the recess section 62 and in the bottom recess section 64 is pressurized. The fluid MRF may be pressurized by the compensation spring 46. In a static condition, there is the same pressure of the fluid MRF in the recess section 62 and the bottom recess section 64 because of the gap 60. The first front surface 54 of the piston 36 has a larger surface than the second front surface 56 of the piston 36 because of the connecting bar 38. Therefore, the pressure acting on the first front surface 54 of the piston 36 causes a bigger force on the piston 36 than the pressure acting on the second front surface 56 of the piston 36. So, there is a drift force F1 originating in the piston 36 acting on the connecting bar 38 in axial direction towards the solid state actuator unit 10.

The thermal compensation unit 12 is arranged in the injection valve 2 such that it is preloaded by the mechanical coupling to the compensation spring 46 such that a spring force F2 acts on the piston 32 in an axial direction away from the solid state actuator unit 10 and on the solid state actuator unit 10 towards the valve needle 18. The piston 32 moves in an axial direction in the casing 32 until there is a force balance between the drift force F1 and the spring force F2.
If, for example, the housing 8 expands with an increasing temperature, the length of the compensation spring 46 increases due to its preload. This decreases the spring force F2 acting on the piston 32 and the solid state actuator unit 10. The piston 36 in the casing 32 moves in an axial direction towards the solid state actuator unit 10. This decreases the length of the compensation spring 46 and increases the spring force F2 until there is a new force balance between the drift force F1 and the spring force F2. As a result, the spring force F2 ensures that the valve needle 18 can reliably be actuated by the solid state actuator unit 10. By this, the thermal expansion of the housing 8 can be compensated.
When the solid state actuator unit 10 is energized it expands in an axial direction of the longitudinal axis A so that the valve needle 18 opens the fluid outlet portion 16 and fuel is injected through the injection nozzle 31. Preferably, any expansion of the solid state actuator unit 10 is directed towards its second axial end 10b, the direction of the valve needle 18. This enables a linear dependence between the energy provided to the solid state actuator unit 10 and the movement of the valve needle 18 along the longitudinal axis A. An expansion of the solid state actuator 10 solely in the direction of its second axial end 10b takes place if the first axial end 10a remains static.
Due to the piston 36 which is axially moveable in the casing 32 for the compensation of thermal expansions of the injection valve 2, the first axial end 10a can also move very slightly along the longitudinal axis A when the solid state actuator unit 10 is energized or de-energized. Such movements may be small in comparison to an actuation of the valve needle 18 by the solid state actuator unit 10 and the design of the thermal compensation unit 12 counteracts them. Nevertheless, the result is a non-linear dependence between the energy provided to the solid state actuator unit 10 and the movement of the valve needle 18 along the longitudinal axis A towards the fluid outlet portion 16.
For the compensation of thermal expansions of the injection valve 2 the piston 36 in the casing 32 has to be moveable in an axial direction in the casing 32. For the actuation of the valve needle 18 by the solid state actuator 10, however, the piston 36 has to be rather rigid in the casing 32.
In the following the function of the electromagnet 39 and the fluid MRF will be described in detail:

The electromagnet 39 which is arranged in the thermal compensation unit 12 is designed to influence the viscosity v of the fluid MRF by its magnetic field B. A change of the viscosity v of the fluid MRF has a direct influence on the damping coefficient of the thermal compensation unit 12. This directly influences the rigidity of the piston 36 in the casing 32. If the magnetic field B radiated by the electromagnet 39 shows, for example, a maximum value, the viscosity v of the fluid MRF is at a maximum. As a result, the rigidity of the piston 36 inside the casing 32 is maximal.

In the case the solid state actuator is energized or de-energized the magnetic field B can be given such that the viscosity v is rather high so that the damping coefficient of the thermal compensation unit 12 is rather high which results in a rigid behavior of the piston 36 so that the piston 36 is rather static in the casing 32. In case of temperature changes, the magnetic field B can be switched off such that the viscosity v of the fluid MRF is rather low in order to allow a movement of the piston 36 in the casing 32 and thus to allow a thermal compensation of the injection valve 2.
Close to the start of the combustion engine, for example, the viscosity v and thus the damping coefficient of the thermal compensation unit 12 can be kept small in order to allow a thermal compensation of the injection valve 2. During a normal operation of the injection valve 2, for example when the combustion engine runs at its operation temperature, the viscosity v of the fluid MRF can be increased or set to a maximum value in order to allow the preferred rigid behavior of the thermal compensation unit 12 when the solid state actuator 10 is energized or de-energized.

Claims

Thermal compensation arrangement (6) comprising
- a housing (4) including a central longitudinal axis (A), the housing (4) comprising a cavity (14),

- a solid state actuator unit (10) being arranged in the cavity (14) and having a first axial end (10a) and a second axial end (10b), and the second axial end (10b) acting as a drive side of the solid state actuator unit (10),

- a thermal compensation unit (8) being arranged at least partially in the cavity (14) and being coupled to the first axial end (10a) of the solid state actuator unit (10), the thermal compensation unit (8) comprising
-- a casing (32) being mechanically coupled to the housing (4) and comprising a recess (34),

-- a piston (36) being axially movable in the recess (34) and being designed to be coupled to the solid state actuator unit (10),

-- the recess (34) being filled with a fluid (MRF) of a viscosity (v) being influenceable by a magnetic field (B), and

-- an electromagnet (39) being arranged in the thermal compensation unit (8) and being designed to influence the viscosity (v) of the fluid (MRF) by its magnetic field (B).
Thermal compensation arrangement (6) in accordance with claim 1 with the fluid (MRF) being a magnetorheological fluid.
Injection valve (2) comprising the thermal compensation arrangement (6) in accordance with one of the preceding claims.