Description
Apparatus for Hydraulically Adjusting the Blades of an Impeller of an
Axial-Flow Fan
The present invention relates to an apparatus for hydraulically adjusting the blades of an impeller of an axial-flow fan having the features of the introductory portion of claim 1..
Modern axial-flow fans are regulatable work machines that convert mechanical energy into kinetic energy. The regulation of the axial-flow fans is effected via the speed or the angle of inclination of the blades. If during operation the blade position is to be able to be varied, the blades must be secured to a supported shaft, the spindle. The alteration of the blade position is generally undertaken hydraulically. For this purpose, a hydraulic adjustment or displacement mechanism is mounted on the impeller of the axial-flow fan. Such an adjustment mechanism is essentially comprised of a hydraulic adjustment cylinder, which rotates at the fan speed, and of a stationary oil manifold element, to which the oil supply lines are connected.
Due to the centrifugal forces of the blade caused by the rotation, enhanced by the geometrical shape of the blade profile, a torque,

which acts as a restoring torque, results about the longitudinal axis of the spindle. If the adjustment mechanism fails during the operation, then the blade, due to this restoring torque, changes position in an abrupt manner, and the fan can no longer maintain pressure and conveying quantity. To prevent a change in position of the blades, counterweights can be mounted on each blade, generally however on the spindles, that more or less precisely compensate for the restoring torque. The drawback of such an approach is that the additional counterweights, due to the centrifugal force, effect a considerable overloading of the spindle mounting and make the impeller significantly heavier.
It is an object of the present invention to embody an apparatus of the aforementioned general type for the adjustment of blades during operation of the fan in such a way that even where there is a power failure the blade position can be maintained in the last position prior to such power failure until, by switching over the power, another control unit can take over the position regulation of the adjustment device.
The object is inventively realized with an apparatus of the aforementioned general type by the characterizing features of claim 1.

Advantageous embodiments of the invention are the subject matter of the dependent claims.
As a result of the present invention, a redundant control of the adjustment device is made available. The arrangement of the seat valves upstream of the pertaining four-way valves ensures that always only one four-way valve carries out the control of the hydraulic adjustment device, and a hydraulic short circuit between the parallel arranged redundant four-way valves is precluded. By embodying the seat valves as valves that close by spring force there is additionally ensured that if the respective power supply of the parallel control units fails, a shutting off of the feed and return line not only to the hydraulic adjustment device but also to the respective four-way valves is effected, as a result of which the respective blade position is maintained until the power supply is again applied.
Various embodiments of the in ention are explained in greater detail in the following and are illustrated in the drawings, in which:
Fig. 1a is a longitudinal section through an impeller of an axial-
flow fan having an adjustment mechanism pursuant to the invention,

Fig. 1b is a longitudinal section through an impeller of an axial-
flow fan having an adjustment mechanism pursuant to another embodiment,
Fig. 2a is a circuit diagram for the control of the adjustment
mechanism of Fig. 1a, and
Fig. 2b is a circuit diagram for the control of the adjustment
mechanism of Fig. 1b.
Fig. 1 shows an impeller 1 of an axial-flow fan, wherein the impeller is provided with a plurality of blades 2 that are disposed on its periphery, with one of the blades being indicated. The impeller is secured to a shaft 18 that can be installed not only in a separate main bearing arrangement but also in a drive motor. For the adaptation of the axial-flow fan to various operating conditions, the blades 2 are adjustable about their longitudinal axes. For this purpose, a spindle 3 that supports the blades 2 is rotatably mounted in a bearing or support ring 4 of the impeller 1.
The impeller 1 is provided with a displacement mechanism for the adjustment of the blades 2. For this purpose, secured to each spindle 3 is an offset displacement or adjustment lever 5 that is guided in a

groove provided on the periphery of a displacement or adjustment disk 17 shown in Fig. 1a and 1b.
The displacement disk 17 is connected to a piston rod 8 that is secured to a piston 7. The piston 7 is disposed within an adjustment cylinder 6. The piston rod 8 along with the piston 7 and the displacement disk 17 are displaceably disposed along the axis of the axial-flow fan, and rotate at the same speed as do the impeller 1 and the adjustment cylinder 6.
The rearward end of the piston rod 8 is surrounded by an oil manifold element 13. With the embodiment illustrated in Fig. 1b, a check or nonreturn valve 16 is additionally disposed in the oil manifold element, the significance of which will be discussed subsequently.
Two axial control channels 9, 10 are guided through the piston rod 8 and respectively open out into a chamber 11, 12 provided on opposite sides of the piston 7. Depending upon which of the chambers 11 or 12 is supplied with pressure oil, the piston 7, together with the piston rod 8 and the displacement disk 17, are shifted toward the right or toward the left, hence rotating the spindle 3, together with the blade 2, into the one or other direction.

The control for the adjustment cylinder 6 is effected via a redundant control mechanism illustrated in Figs. 2a and 2b. Not shown in Figs. 2a and 2b is the oil station, which is comprised of oil pump, oil tank and accessories including instrumentation. The control mechanism is essentially configured as follows:
- a feed line P connects a non-illustrated oil pump to two four-way valves 23, 33 via two branch lines P1 and P2.
- a return line T connects the two four-way valves 23, 33 via two branch lines T1 and T2 to the non-illustrated oil tank.
- two control oil lines A, B, which are branched into branch lines A1 and A2 as well as into branch lines B1 and B2, connect the two four-way valves 23, 33 to the oil manifold element 13 via connections 14 and 15.
Installed in the feed line P is a test connection 20. By means of a quick-release coupling having a seat valve, the test connection 20 permits the connection of testing means to the feed line P. On the fan side of the test connection 20, the feed line P is equally divided into two parallel branch lines P1 and P2.

In Figs. 2a and 2b, the flow direction of the control oil is indicated by arrows. In the direction of flow of the control oil, a respective manual shutoff valve 21, 31, which is preferably embodied as a ball valve, is installed in the two branch lines P1 and P2 of the feed line P. The purpose of the shutoff valves 21, 31 is, in the event that further valves that are disposed downstream are to be replaced, to be able to shut off the feed line P to these valves that conveys appropriate pressure. For the control of the flow in the branch lines P1, P2 of the feed line P, a respective test connection 22, 32 is provided on the fan side of the shutoff valves 21, 31.
The electromagnetically actuated four-way valve 23, 33 is respectively redundantly installed in one of the branch lines P1 or P2 of the feed line P and one of the branch lines T1 or T2 of the return line T.
Proceeding from the two four-way valves 23, 33 are two discharge lines T1 and T2 that are joined together to form the return line T. The return line T is connected to the non-illustrated oil tank.
The four-way valves 23, 33 are preferably embodied- as 4/3-way proportional regulating valves. On the fan side, the branch lines A1 and B1 of the control oil lines A, B are connected to the four-way valve

23, while the branch lines A2 and B2 of the control oil lines A, B are guided on the fan side to the four-way valve 33.
Furthermore, on the fan side ahead of the four-way valves 23, 33, installed in each branch line A1, B1, A2, B2 is an electromagnetically actuated seat valve 24, 25, 34, 35, which is held in a closed position by spring force. The seat valves 24, 25, 34 25 are preferably embodied as 2/2-way conical seat valves. The seat valves 24, 25 serve as shutoff devices for the four-way valve 23 and the seat valves 34, 35 serve as shutoff devices for the four-way valve 33. The seat valves 24, 25, 34, 35 are respectively electrically coupled with the pertaining four-way valves 23, 33. The valves installed in the branch lines P1/A1 and T1/B1, namely four-way valve 23 and seat valves 24, 25, and the valves installed in the branch lines P2/A2 and T2/B2, namely four-way valves 33 and seat valves 34, 35, are connected to different power sources.
The four-way valves 23, 33 and the seat valves 24, 25, 34, 35 are each provided with a light-emitting diode that is connected in such a way that it lights up as long as the pertaining valve is in operation.

To enable replacement of the seat valves 24, 25, 34, 35 during operation, a respective manual shutoff valve 27, 28, 37, 38 is installed downstream thereof that is preferably embodied as a ball valve; thus, replacement during operation with the redundant unit is possible without fluid pressure losses.
In order to realize the desired adjustment, the adjustment cylinder 6 can be supplied with the prescribed fluid quantities via the branch lines P1/A1/T1/B1 or via the branch lines P2/A2/T2/B2. The redundant control of the adjustment cylinder 6 is thus possible via either the one four-way valve 23 or the other four-way valve 33. If power is interrupted, the seat valves 24, 25, 34, 35 close in a spring-actuated manner. Therefore, without interrupting operation, it is possible to switch between the two four-way valves 23, 33 by changing the power supply. During the switching time, no fluid flows to or away from the adjustment cylinder 6. The position of the piston 7, and hence the position of the blades 2 that are adjustable by the adjustment cylinder 6, are maintained until the switching over is concluded and the power supply is again applied to one of the two four-way valves 23, 33. After one of the manually actuated shutoff valves 21, 31 has been closed, the respectively pertaining four-way valve 23, 33 that is not operating can be replaced. Should one of the seat valves 24, 25, 34, 35 be

defective, after the manual shutoff by means of the respective shutoff valve 27, 28, 37, 38, the appropriately pertaining seat valve that is not operating can be replaced.
As shown in Fig, 2b, a pressure relief valve 29, 39 can be installed in the return lines T1, T2 that lead to the tank connection. Such a pressure relief valve 29, 39 is advantageous if a nonreturn valve 16 is disposed in the control oil line B immediately ahead of the connection 15 of the oil manifold element of the second chamber 12 of the adjustment cylinder 6. The nonreturn valve 16 is kept in the open position by the pressure in the control oil line A. If the pressure oil supply fails or is interrupted, the nonreturn valve 16 moves into the closed position. In the closed position of the nonreturn valve 16, the adjustment cylinder 6 remains in its previously assumed position. Thus, the blade 2, which is connected via the piston rod 8 and the displacement disk 17 and the spindle 3, cannot change its position, but rather remains in the assumed position.

Patent Claims
1. Apparatus for the hydraulic adjustment of the blades (2) of an impeller (1) of an axial-flow fan, comprising an adjustment cylinder (6) that is provided with a first chamber (11) and a second chamber (12) on both sides of a piston (7) that is displaceable in the adjustment cylinder (6), each of the chambers being provided with a connection (14), (15) to control oil lines (A, B), whereby the control oil lines (A, B) are respectively connected to a four-way valve, characterized in that not only a feed line (P) that leads to a control oil line (A), but also a return line (T) that is connected to the other control oil line (B), is divided into two parallel branch lines (P1/A1, P2/A2, T1/B1, T2/B2), in that two redundant four-way valves (23), (33) are provided, of which each is disposed in one of the parallel branch lines (P1/A1 or P2/B2) and (T1/B1 or T2/B2), and in that a seat valve (24), (25), (34), (35) is disposed in each branch line (A1, A2) of the one control oil line (A) and in each branch line (B1, B2) of the other control oil line (B) between the respective connection (14), (15) and the respective four-way valve (23), (33).

2. Apparatus according to claim 1, characterized in that the seat valve (24), (25), (34), (35) is embodied as a seat valve that closes by spring force.
3. Apparatus according to claim 1, characterized in that a manually actuatabie shutoff valve (21, 31) is disposed in each of the two branch lines (P1, P2) of the feed line (P) upstream of the respective four-way valve (23, 33) in the direction of flow of the control oil.
4. Apparatus according to claim 1, characterized in that a manually actuatabie shutoff valve (27, 28, 37, 38) is disposed in each of the branch lines (A1, B1, A2, B2) of the control lines (A, B) downstream of the respective seat valve (24, 25, 34, 35) in the direction of flow of the control oil.
5. Apparatus according to claim 1, characterized in that the four-way valves (23, 33) are embodied as 4/3-way proportion regulation valves.

Apparatus according to claim 1, characterized in that the seat valves (24, 25, 34; 35) are embodied as 2/2-way conical seat valves.
Apparatus according to claim 1, characterized in that a common test connection (20) is disposed in the feed line (P) prior to its division into two branch lines (P1), (P2).
Apparatus according to claim 1, characterized in that the four-way valves (23), (33) and the seat valves (24), (25), (34), (35) are provided with a light-emitting diode (26).
Apparatus according to claim 1, characterized in that the four-way valves (23), (33) are electrically coupled with the seat valves (24), (25), (34), (35).
Apparatus according to claim 1, characterized in that the four-way valves (23), (33) and the seat valves (24), (25), (34), (35) are combined.
Apparatus according to claim 1, characterized in that a respective pressure relief valve (29, 39) is disposed in the return

lines (T1, T2), and disposed in the connection (15) of an oil manifold element (13) is a nonreturn valve (16) that is held in the open position by the pressure in the feed line (P).