FIELD OF THE INVENTION:
The invention relates to a device for dosing of liquids.
Particularly it relates to a device for dosing of reducing agent in the exhaust path.
BACKGROUND OF THE INVENTION:
Systems using the Water-hammer effect for controlled injection tasks are already known. The fluid being pumped is suddenly stopped by closing the valve in the path. This results in a pressure impulse being generated in the fluid being pumped. The resulting pressure impulse is transferred to a spring loaded needle. When the opening pressure for the needle is exceeded, then the injection occurs. Such systems are also known for dosing of reducing agent in Selective Catalytic Reduction (SCR) applications.
Patent publication DE102008018945 discloses a device for dosing of urea solution in the exhaust path. This device requires two actuators for operation in form of a motor for the pumping of urea solution and a second actuator for controlling the opening and closing of a valve to generate the pressure impulse in the fluid flow.
DESCRIPTION OF THE INVENTION:
The present invention discloses a device for dosing liquids. The device comprises a pump driven by a motor to pump the liquid from a liquid storage tank to a first port of a t-joint. A normally closed dosing valve is connected to a second port of the t-joint and receives the liquid being pumped. A motion converter to converts the rotary motion of the motor to translation motion which is used to actuate a normally open second valve connected to a third port of the t-joint. The actuation of the second valve causes a pressure impulse to build in the liquid flow path which results in the actuation of the dosing valve and results in dosing of the liquid. A backflow path is provided from said second valve to the pump or the tank. The use of motion converter eliminates the need for two separate actuators for pump and for the second valve. This reduces overall cost of the system.

In case of SCR systems the path through which the urea solution is being pumped passes near the exhaust gas path which increases the temperature of the urea. When a .small amount of the heated urea flows back to the tank, the temperature of the urea in the tank also increases. This is not desirable as the urea solution may deteriorate. Thus, heat dissipating means are provided in the backflow path from the second valve to the pump or the tank. This prevents the heating of the urea in the tank.
BRIEF DESCRIPTION OF THE DRAWING:
The invention is now described in reference to the accompanying drawing
Fig. 1 shows a block diagram illustrating the device for dosing of liquids in accordance with
this invention; and
Fig. 2 illustrates a flowchart showing the steps in the operation of the device in accordance
with this invention.
DETAILED DESCRIPTION OF THE DRAWING:
Fig. 1 of the accompanying drawing illustrates a device for dosing liquids comprising a pump (12) driven by a motor (10) to pump the liquid from a liquid storage tank to a first port of a t-joint (14). A normally closed dosing valve (16) is connected to a second port of the t-joint (14) and receives the liquid being pumped. A motion converter (18) converts the rotary motion of the motor (10) to translation motion. A normally open second valve (20) is connected to a third port of the t-joint (14). The second valve (20) is adapted to be operated by the translation motion of the motion converter (18). A backflow path (22) is provided from the second valve (20) to the pump or the tank.
Fig. 2 illustrates a flowchart showing the steps in the operation of the device in accordance with this invention. Initially the liquid is pumped from the tank by a pump and motor assembly to a dosing valve (SO). Converting the rotary motion of the motor to a linear translation motion is achieved by a motion converter (SI). Intermittently closing the second valve is achieved by the linear motion of the motion converter (S2). The closing of second valve results in a pressure impulse being generated in said liquid being pumped (S3). The

pressure impulse on reaching the dosing valve causes the dosing to occur (S4). The urea solution when the second valve is in open state is returned to the tank or the pump (S5).
The devices currently used for dosing of urea solution in the exhaust path use at least two actuators in form of an electric motor for driving the pump and another actuator for operating the valve for generating a pressure impulse in the urea flow. Use of multiple actuators increases the cost of the device.
In the present invention the device uses only a single actuator in form of an electric motor (10). The electric motor (10) drives a pump (12) and a motion converter (18). The urea solution is pumped via a t-joint (14) to the dosing valve (16). The motion converter (18) converts the rotary motion of the motor (10) to linear translation motion. Typically an axial cam or radial cam is used as the motion converter (18). The cam is positioned in contact with the second valve (20). The second valve is connected to a third port of the t-joint (14). The second valve (20) is a hollow cylinder type valve which is actuated by pressing of a membrane. The second valve (20) is normally open and hence there is a small backflow from the second valve (20) which is directed back to the pump (12) or the tank. This backflow volume is very small compared to the volume being pumped.
As the cam rotates, the lobe of the cam causes the membrane to be pressed and thus results in the actuation of the second valve (20). The backflow path is closed momentarily for the duration when the cam is pressing the membrane. This results in a pressure impulse to build in the flow path of urea solution. As the cam rotates further, the membrane is released and the second valve opens again and the backflow is restored. The pressure impulse is transferred to the dosing valve (16) and causes the needle of the dosing valve (16) to lift. This results in dosing of the urea in the exhaust flow path.
In case of SCR systems the urea has to be dosed continually. Thus, by the proposed device this can be achieved with least number of components. The rotating cam ensures that the urea dosing happens continually and in same amount for each instance. This system requires minimum or no control for dosing of urea.

The backflow path returns a small volume of the urea solution from the normally open second valve to the pump or the urea tank. The backflow path is provided with a heat dissipation means (22). The flow path of urea from the tank to the second valve (20) passes close to the exhaust gas path. This causes the urea in the line to get heated up. As the heated urea goes back to the tank from the second valve (20), the temperature of urea in the tank increases which is not desirable. Thus, there is provided a means for heat dissipation in the back flow path to dissipate the heat before the urea solution is sent back to the tank. The backflow path may also include means for removing of the air from the urea dosing path.
It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.

WE CLAIM:
1. A device for dosing liquids, said device comprising
a pump (12) driven by a motor (10) to pump the liquid from a liquid storage tank to a first port of at-joint (14);
a normally closed dosing valve (16) connected to a second port of the t-joint (14) and receiving the liquid being pumped;
a motion converter (18) to convert the rotary motion of the motor (10) to translation motion;
a normally open second valve (20) connected to a third port of the t-joint (14), said second valve (20) adapted to be operated by the translation motion of the converter (18); and a backflow path (22) from said second valve (20) to the pump or the tank.
2. A device for dosing liquids as claimed in claim (1) wherein said motion converter is an axial cam.
3. A device for dosing liquids as claimed in claim (1) wherein said motion converter is a radial cam.
4. A device for dosing liquids as claimed in claim (1) wherein said second valve is a hollow piston type valve.
5. A device for dosing liquids as claimed in claim (1) wherein the rotating cam is placed in contact with the membrane of the hollow piston type valve.
6. A device for dosing liquids as claimed in claim (1) wherein a heat dissipating means are provided in the backflow path from the second valve and the pump or the tank.
7. A device for dosing liquids as claimed in claim (1) wherein means for removing the air from the liquid flow path is provided in the backflow path.
8. A method for dosing liquids, said method comprising the following steps

pumping the liquid from tank by a pump and motor assembly to a dosing valve; converting the rotary motion of the motor to a linear motion by a motion converter; intermittent closing of a second valve by the linear motion of the motion converter; said closing of second valve resulting in a pressure impulse in said liquid being pumped; dosing of said liquid by opening of the dosing valve due to the pressure impulse; and returning a part of the pumped fluid to the tank or the pump from said second valve when it is in open position.