TECHNICAL FIELD OF THE INVENTION

The present invention relates to a directional valve configured to be arranged in a fluid channel at a site of connection of a branch channel thereto, the valve comprising: a valve body configured to be movable when the valve is arranged in a said fluid channel and configured to in a first position close the connection of the fluid channel to the branch channel and connect an upstream part of the fluid channel with a downstream part thereof so as to allow fluid to pass from the upstream part to the downstream part and configured to in an second position open a connection of said upstream part of the fluid channel to the branch channel and close the connection of the upstream part of the fluid channel to the downstream part thereof to prevent fluid to reach the downstream part of the fluid channel, a member configured to urge the valve body towards said first position, and an arrangement configured to control the movement of the valve body between the first and second position by applying power to the valve body counteracting power applied thereto by said member.

Such a directional valve may be arranged anywhere in a fluid channel, such as being a part of a fluid circuit, where it is desired to be able to shift between two states, to either divert fluid flowing in the fluid channel to flow into said branch channel or let the fluid flowing in the fluid channel bypassing the connection of the branch channel thereto without flowing into the branch channel. However, the invention is particularly directed to a fluid channel being a part of a circuit for circulation of fluid in a motor vehicle and especially to a directional valve arranged to divert fluid from such a fluid circuit to a retarder unit when braking a heavy motor vehicle, such as a truck or a bus, which is the reason for hereinafter mainly disclosing that application of the invention without in any way restrict the invention thereto.

When the valve body is in said first position and the branch channel is sealed with respect to the fluid channel the pressure prevailing in the branch channel and that in the fluid channel may differ a lot, which is often especially the case when the fluid channel is a part of a vehicle cooling circuit and the branch channel is connected to the working space of a retarder unit. Such pressure differences may result in irregularities and bumps or punches of components when regulating the directional valve to a change from said first to said second position. This does then also result in an inexact determination of the position of the valve body and by that the state of the directional valve. The same problem may occur when changing from said second to the first position of the valve body due to the pressure difference then built up between said upstream part and downstream part of the fluid channel.

BACKGROUND OF THE INVENTION

DE 102007055604 and EP 0972916 disclose directional valves of the type defined in the introduction arranged to divert cooling liquid from a cooling circuit in a motor vehicle to a retarder unit and facing the problem of regulating such a directional valve discussed above.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a directional valve of the type defined in the introduction being improved in at least some aspect with respect to such directional valves already known.

This object is according to the invention obtained by providing such a directional valve with the features listed in the characterizing part of appended patent claim 1.

Thus, the invention is based on connecting a piston to the valve body through a piston rod and designing the piston displaceable in a housing while sealingly dividing the housing into two chambers on opposite sides of the piston and providing means controllable to apply a pressurized medium into a first of the chambers of the housing for applying power to the piston exceeding the urging power of said member for moving the piston inside the housing and by that the valve body from the first to the second position. By then providing the piston rod with an internal channel connecting the second chamber of the housing to the branch channel the same pressure will prevail in said second chamber as in the branch channel irrespectively of the position of the piston, so that the power of the pressurized medium, such as compressed air, applied to the first chamber for moving the piston has only to exceed the power of said member urging the valve body towards the first position for moving it to the second position. Thus, the valve will be "self- regulating" and the regulation thereof will be independent of any difference of the pressures in the fluid channel and the branch channel. A more exact determination of the position of the directional valve in each situation by using a lower pressure of said controlling pressurized medium will by that be obtained. It is pointed out that these advantages are also achieved when controlling the valve body to return to the first position from the second position while letting said pressurized medium out of the first chamber of the housing.

According to an embodiment of the invention said member is a compression spring, which will then reliably define a certain power by which the valve body is urged towards the first position and which is to be overcome for moving the valve body from that position.

According to another embodiment of the invention said arrangement is configured to control the movement of the valve body by supplying compressed air to said first chamber of the housing. Such a control by supplying compressed air is simple and easy to accomplish.

The invention also relates to a circuit for circulation of a fluid channel and having a branch channel connected to the fluid channel for diverting fluid flowing in said circuit being provided with a directional valve according to the invention at the site of connection of the branch channel to the fluid channel. The advantages of such a circuit provided with a directional valve according to the invention appear from the above discussion of the valve according to the invention.

The invention also relates to a circuit for circulation of fluid in a fluid channel in a motor vehicle having a branch channel connected to the fluid channel for diverting fluid from the circuit, which circuit is provided with a directional valve according to the invention arranged at the site of connection of the branch channel to the fluid channel, and the branch channel is configured to conduct fluid diverted from the circuit to a retarder unit used to brake the vehicle. Such a circuit will benefit from the well-defined and smooth regulation of the directional valve in that circuit, and when the branch channel according to another embodiment of the invention is integrated with a working space of the retarder unit substantial pressure variations may occur but thanks to the design of the directional valve not influence the regulation of the valve body for changing the direction of the flow of fluid at the site of the directional valve.

According to another embodiment of the invention the fluid circuit is a vehicle cooling circuit and the retarder unit is a hydrodynamic retarder.

The invention also relates to a motor vehicle, especially a heavy motor vehicle, such as a truck or a bus, provided with a circuit for circulation of fluid according to the invention.

Other advantageous features as well as advantages of the present invention appear from the description following below.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a specific description of an embodiment of the invention cited as an example. In the drawings:

Fig. 1 is a schematic view illustrating how a directional valve according to the present invention may be a part of a fluid circuit including a vehicle cooling circuit and a retarder unit of a heavy motor vehicle, and

Figs.2 and 3 are cross-section views illustrating a directional valve according to an embodiment of the present invention arranged in a fluid channel at a site of connection of a branch channel thereto with a valve body in said first position and said second position, respectively. DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION Fig. 1 illustrates very schematically a possible application of a directional valve according to the present invention in a cooling circuit in a heavy motor vehicle 1, such as a truck or a bus. It is pointed out that a number of components of said cooling circuit have been omitted, since they have nothing to do with the present invention directed to the directional valve and the way it influences the behavior of the circuit. It is shown how the vehicle has a cooling circuit 2 conducting a cooling fluid fed through a fluid channel 3 of the circuit by a cooling liquid pump 4 driven by an internal combustion engine 5 of the vehicle which said cooling liquid passes for cooling thereof. The cooling circuit also includes a cooler 6.

The vehicle has a retarder unit 7 with a rotor vane wheel and a stator vane wheel not shown used to assist the ordinary brakes of the vehicle to brake the vehicle, possibly also together with an exhaust gas brake not shown. It is indicated how the retarder unit for this sake may be connected to and disconnected from a gear box 8 of the vehicle by means of a coupling member 9. The retarder unit 7 is connected to the fluid channel 3 of the cooling circuit 2 at a site 10 through a branch channel 11, and a directional valve 12 according to the present invention is arranged at said site. When cooling liquid is diverted to the retarder unit it will leave the retarder unit and return to the cooling liquid pump 4 either without passing the cooler 6 by being diverted through a thermostat 30 or by passing through the cooler 6. Thus, the directional valve 12 may be controlled to let the cooling liquid pass the branch channel 11 without being diverted to the retarder unit and then pass the cooler 6 or when braking flowing through the retarder unit 7 without passing the cooler 6.

The construction and operation of a directional valve 12 according to an embodiment of the invention will now be described while making reference to Figs. 2 and 3 showing this valve in cross-section arranged at said site 10 in the fluid channel 3 of the connection of a branch channel 11 opening directly into a working space 13 of a retarder unit 7. The valve has a valve body 14 configured to be movable when the valve is secured to the fluid channel 3. The valve body has means, such as an O-ring 15, configured to sealingly bear circumferentially around an opening 16 in the fluid channel 3 to the branch channel 11 in a first position of the valve body shown in Fig. 2. A member 17 in the form of a compression spring is configured to urge the valve body 14 towards this first position to press said O-ring 15 to bear tightly upon the internal wall of the fluid channel 3.

The valve further comprises an arrangement configured to control the movement of the valve body 14 between the first position shown in Fig.2 and a second position shown in Fig. 3 by applying power to the valve body counteracting the power applied through the compression spring 17. This arrangement comprises a piston 18 connected to the valve body 14 through a piston rod 19 and displaceable in a housing 20, through which the valve is secured to the fluid channel 3, while sealingly dividing the housing into two chambers 21, 22 on opposite sides of the piston 18. The valve further comprises means 23 in the form of a source of compressed medium schematically indicated controllable to apply a pressurized medium, here compressed air, to a first 21 of the chambers of the housing for applying a power to the piston 18 exceeding the power of the compression spring 17 acting upon the valve body, for lifting the valve body 14 from the position shown in Fig.2.

The piston rod 19 is provided with an internal channel 24 connecting the second chamber 22 of the housing 20 to the branch channel 11. This means that the same pressure always will prevail in the second chamber 22 of the housing as in the branch channel 11 and by that in the working space 13 of the retarder unit 7. The pressure may for instance be 1-2 bars in the fluid channel 3 and at the same time 8 bars in the working space 13 of the retarder unit, but thanks to the connection of said working space 13 with the second chamber 22 of the housing 20 through the piston rod channel 24 the same power will be needed to compress the spring 17 and move the valve body 14 irrespectively of the pressure inside said working space. The valve body is movable to a second position shown in Fig . 3 by applying compressed air into the f irst chamber 21 and valve body parts 25 will in this position connect to flu id chan nel parts 26 and parts 27 of the housing 20 to close the con nection of an upstream part 28 of the f luid channel 3 to a downstream part 29 thereof with respect to the directional valve 1 2. It is shown in Fig . 3 how f luid arriving to the directional valve with the valve body in the first position of Fig . 2 wil l pass the directional valve from the upstream part 28 to said downstream part 29 and how it wil l with the valve body 1 4 in the second position of Fig . 3 be diverted into the branch chan nel 1 1 and by that the working space 1 3 of the retarder un it 7.

The invention is of cou rse in no way restricted to the embodiment described above, si nce many possibilities for modif ications thereof are likely to be obvious to one skilled in the art without having to deviate from the scope of invention def ined in the appended claims.

The directional valve may j ust as well be arranged at a site for diverting a fluid in the form of oil to an oil retarder i nstead of to a water retarder as described above.