GB2159228A

GB2159228A - Attenuation valve for the clutch of the power take-off shaft of a tractor

Info

Publication number: GB2159228A
Application number: GB08512789A
Authority: GB
Inventors: Tapio Vainiomaki; Pekka Kalevi Mailas
Original assignee: Valmet Oy
Current assignee: Valmet Oy
Priority date: 1984-05-22
Filing date: 1985-05-21
Publication date: 1985-11-27
Also published as: NO159842B; GB8512789D0; FI842051A0; DK159383B; SE8502395L; BR8502401A; DK225885A; FI72931B; SE8502395D0; FI842051A; DK159383C; DK225885D0; FI72931C; NO852019L; NO159842C; SE458298B; GB2159228B; FR2564922B1; FR2564922A1

Abstract

The valve is fitted in the pressure pipe passing from a hydraulic pump operated by the tractor engine to a clutch of the power take-off shaft to avoid shock on clutch engagement. The valve is provided with an inlet opening (A), an outlet opening (B), which are in direct connection with each other, and a leakage opening (C), which communicates with the inlet and outlet openings (A and B) of the attenuation valve via a bleed valve (20) placed inside the body (10) of the attenuation valve (4). The bleed valve (20) automatically regulates the ratio of the flows passing through the outlet opening (B) of the attenuation valve (4) and through the leakage opening (C) as well as the pressure of the flow passing from the outlet opening (B) to the clutch (5), and thereby the engagement time of the power take off shaft (9). The valve also contains a choke channel (11) in which a floating piston (12) is located with clearance to provide throttled flow into an annular space (14) to act on a piston (16) influencing the opening of bleed valve (20). <IMAGE>

Description

SPECIFICATION Attenuation valve for the clutch of the power take-off shaft of a tractor The invention is concerned with an attenuation valve for the clutch of the power take-off shaft of a tractor, which said attenuation valve is fitted in the pressure pipe passing from the hydraulic pump operated by the tractor engine to the clutch of the power take-off shaft, between the connecting valve and the clutch.

For the purpose of switching on the power take-off shaft of the tractor, the hydraulic system of the tractor is commonly used. The power take-off shaft is normally connected to the shaft coming from the tractor engine by means of a wet clutch, which may be, e.g., a multiple-disc clutch, whereby the power takeoff shaft is engaged when the presure in the wet clutch has reached the level of normal working pressure. In this system, the working pressure is, as a rule, of the order of 1 6 bars.

If the power take-off shaft is engaged without in any way retarding the increase in pressure, the time of increase in pressure is of the order of 0.2 seconds. Such a rapid connecting produces a sudden jerk in the power take-off, which may cause damage either on the working machine connected to the power take-off shaft, on the power take-off shaft itself, or on the cardan shaft. This problem is particularly difficult when the viscosity of the oil is low.

In order to solve this problem and, consequently, to slow down the engagement of the power take-off shaft, so far, manually controlled valves have been used, by means of which the connecting pressure of the system can be raised gradually by manual control. By means of such devices, damage to the machines and equipment is avoided in the situation of engagement. This, however, results in one extra working step for the operator of the equipment, and the operator must always remember to control the pressure increase time appropriately, depending on the situation. If the pressure increase time is too short, a consequence may be mechanical damage to the power transmission equipment. If this time is too long, the clutch may be burnt.

The object of the present invention is to provide an attenuation valve of new type for the clutch of the power take-off shaft of a tractor, which said attenuation valve does not involve the drawbacks stated above. It may be considered the most important advantage of the invention that the pressure in the clutch is increased automatically, whereby an electric control valve may be used as the connecting valve. The invention is characterized in that the attenuation valve regulates the engagement time of the power take-off shaft automatically by adjusting the pressure of the flow to the clutch.

In the following, the invention will be described in detail with reference to the attached drawings, wherein Figure 1 shows a diagram of operation of the power take-off shaft of a tractor, Figure 2 is a sectional side view of the construction of an attenuation valve, and Figure 3 shows an engagement time diagram of the attenuation valve.

Fig. 1 shows a diagram of operation of the power take-off shaft. The Figure shows the shaft 1 rotated by the engine of the tractor, which shaft rotates the hydraulic pump 2. The hydraulic pump 2 supplies the pressure into the hydraulic system. On the shaft 1, there is also the clutch of the power take-off shaft, which clutch is here illustrated as a multipledisk clutch 5. In fact, the clutch may also be a wet clutch of some other type. On the shaft 1, a tubular shaft 6 is mounted, which is, on the other hand, connected with the multipledisk clutch 5 and on which a gear wheel 7 is mounted. The gear wheel 7 is in gear contact with a second gear wheel 8, which is connected with the power take-off shaft 9. From the Figure, it is also seen that the pump 2 supplies the pressure to the valve 3, by means of which the power take-off shaft 9 of the tractor is operated.The valve 3 does, however, not feed the pressure straight to the clutch 5, but the attenuation valve 4, illustrated schematically, is mounted between the valve 3 and the clutch 5, by means of which attenuation valve 4 the increase in the engagement pressure is retarded.

Fig. 2 shows the attenuation valve. The valve is an oblong piece, in whose body 10, at one end, a hole is provided that passes through the body in the transverse direction.

One end A of the hole constitutes the inlet opening, through which the oil is passed into the valve, and the other end B is the outlet opening, through which the oil is passed out of the valve into the oil space of the clutch chamber in the clutch. Into the valve body 10, in its middle, a longitudinal bore 22 communicates, via an opening 21 at the bottom of the bore, with the transverse hole passing through the body. Into the body 10, at the side of the bore 22, a second longitudinal bore 11 is also in direct connection with the transverse hole. The bore 11 is a so-called choke channel, in which there is a freely moving choke piston 1 2. At the opposite end, opposite relative the transverse hole in the body 10, there is a threading, onto which a nut cap 1 5 is threaded.The nut cap 1 5 close the end of the valve body 10 tightly, so that the longitudinal bores 11 and 22 in the body are not connected with the space outside the valve that way. In the wall of the longitudinal bore 22 provided in the middle of the valve there is a radial bore 1 3 through which the bores 11 and 22 communicate with each other. The nut cap 1 5 covers the radial bore 1 3 so that it is not in diret contact with the space outside the valve. Moreover, in the body 10 of the valve, a radial bore C communicates with the bore 22 alongside the hole 21 placed at the bottom of the bore. On the bottom of the bore 22, there is a ball 20 covering the opening 21.At the opposite end of the bore 22, there is a piston 1 6 moving back and forth in the bore, which piston is provided with a piston rod 1 7 facing the ball 20 and with a peg 1 8 directed in the opposite direction. Between the ball 20 and the piston 16, there is a spiral spring 19, which presses the ball and the piston apart from each other.

Between the peg 1 8 and the walls of the bore 22, there remains an annular space 14, which communicates with the choke channel 11 via the radial bore 13.

When the connecting valve 3 shown in Fig.

1 is opened, the oil passes through this valve to the inlet opening A of the attenuaton valve shown in Fig. 2. The oil passes straight through the transverse opening and through the outlet opening B into the clutch of the power take-off shaft, whereby the resistance caused by the clutch produces an increase in pressure in the attenuation valve, by whose effect the ball 20 placed on the opening 21 is shifted to the right in Fig. 2, whereby a direct connection is opened from the inlet opening A to the leakage opening C. The spring 1 9 placed behind the ball 20 determines at which initial pressure p0 this opening of the leakage opening C takes place. When the pressure becomes higher, oil also flows into the choke channel 11.Between the choke piston 1 2 placed in the channel 11 and the walls of the channel 11, there is a certain gap, so-called choke gap, whose magnitude may be, e.g., 0.2 mm. The oil flowing into the channel 11 pushes the piston 1 2 to the right in Fig. 2, but, at the same time, oil also leaks through the choke gap beyond the piston 1 2 and through the radial bore 1 3 into the annular space 14 at the rear of the working piston 16. Thereby, an increase in pressure takes place behind the piston, by whose effect the piston 1 6 tends to be pushed to the left in the Figure, against the compression force of the spring 19, and to press the ball 20 back onto the opening 21.

As the piston 1 6 pushes the ball 20 towards the closed position by the intermediate of the spring 19, the gap between the ball 20 and the opening 21 becomes smaller, whereby the pressure becomes higher in the system. The pressure increase in the system also increases the pressure in the space 14, whereby the piston 1 6 is pushed further to the left, and finally the piston 1 6 has moved so far that the piston rod 1 7 forcibly presses the ball 20 to the side, whereby the opening 21 is closed completely and the leakage stops. In this way, full engagement pressure has been reached, and the engagement has been completed.

After engagement has taken place, the same pressure prevails in the entire system. Thereby the spring 1 9 pushes the piston 1 6 back to the right and, by the effect of the oil displaced by the piston, the choke piston 1 2 is shifted back to its initial position. The valve shown in Fig. 2 and pressed by the spring 1 9 does not have to be expressly a ball valve 20, but it may be a bleed valve in general, e.g., a cone.

Fig. 3 shows an engagement time diagram of the attenuation valve. In the diagram, the vertical axis denotes the engagement pressure, and the horizontal axis denotes the engagement time. It is seen from the figure that the pressure initially rises rapidly to the value p,, which is the so-called initial pressure. The magnitude of this initial pressure p0 is determined by the stiffness of the spring 1 9 acting upon the bleed valve 20. The stiffness of the spring 1 9 may be chosen advantageously, e.g., so that this initial pressure p0 is of the order of 5 bars. After the initial pressure p0 has been reached, the bleed valve 20 starts opening, whereby the increase in the pressure becomes considerably slower, as is shown in the Figure.The increase in pressure goes on as retarded to the value p1, which is the full engagement pressure. The magnitude of the engagement pressure is about 1 6 bars. The time T taken by the increase in pressure from p0 to p1 is called the attenuation time. This attenuation time can be selected within the range of 0.5 to 30 seconds, but it is preferably of the order of 1 to 2 seconds. The magnitude of the attenuation time T can be affected in several different ways. The choke gap between the choke piston 1 2 and the channel 11 may be selected so that the desired attenuation time T is obtained. The smaller this gap is, the longer becomes the attenuation time.The diameter of the working piston 1 6 also acts upon the attenuation time T so that, the larger this diameter is, the longer is the attenuation time. Constructing the valve longer also affects the attenuation time, because, in such a case, the lengths of movement of the pistons become longer.

Thus, thereby a longer attenuation time is obtained by means of a longer valve. Stiffness of the spring 1 9 does not affect the attenuation time itself, but only the initial pressure p,, as was explained above.

By means of the attenuation valve described, the advantage is obtained over priorart technology that the attenuation of the increase in the engagement pressure is accomplished automatically. Thereby, for example, an electric control valve may be used as the power take-off connecting valve 3.

The invention is not confined to the embodiment described in the description and drawing, but it may be varied in the scope of the attached patent claims.

Claims

1. An attenuation valve for the clutch of the power take-off shaft of a tractor, for fitting in the pressure pipe passing from the hydraulic pump operated by the tractor engine to the clutch of the power take-off shaft, between the connecting valve and the clutch, to regulate the engagement time of the power takeoff shaft automatically by adjusting the pressure of the flow to the clutch.

2. An attenuation valve as claimed in claim 1, wherein the valve is provided with an inlet opening and an outlet opening which are in direct connection with each other, and with a leakage opening which communicates with the inlet and outlet openings of the attenuation valve via a bleed valve placed inside the body of the attenuation valve, whereby, by means of actuating means, the bleed valve automatically regulates the ratio of the flows passing through the outlet opening and through the leakage opening, and the pressure of the flow passing from the outlet opening to the clutch.

3. An attenuation valve as claimed in claim 2, wherein the bleed valve consists of a spindle in a bore and an opening at the bottom of the bore which communicates directly with the inlet and outlet openings of the attenuation valve and whose diameter is smaller than the diameter of the bore and of the spindle, whereby the edge of the opening that faces the bore acts as the seat face of the spindle.

4. An attenuation valve as claimed in claim 3, wherein the actuating means of the bleed valve comprise a bore-like choke channel in which there is a mobile choke piston, and a working piston placed in the bore in which the bleed valve is also located, which piston acts by the intermediate of the spring of the bleed valve, whereby the choke channel and the bore communicate with each other.

5. An attenuation valve as claimed in claim 4, wherein the choke channel communicates with the inlet opening of the attenuation valve, and the the choke channel communicates with the first-mentioned bore via a further bore passing radially through the wall of the first-mentioned bore at the opposite end of this bore relative to the opening provided in this bore,

6. An attenuation valve as claimed in claim 5, wherein the diameter of the choke piston is smaller than the diameter of the choke channel so that there is a choke gap between this channel and this piston through which the oil can flow and by-pass this piston.

7.An attenuation valve as claimed in claim 5 or 6, wherein the working piston is provided with a piston rod directed towards the bleed valve and on which said spring, which is a spiral spring, is fitted between this piston and the bleed valve to push them apart, whereby, when the spring is in the compressed form, the piston rod presses directly on the spindle of the bleed valve; and wherein the working piston is provided with a peg extending in a direction opposite to the piston rod, whereby there is an annular space between the wall of the bore and the peg, with which annular space the choke channel communictes via the bore.

8. An attenuation valve as claimed in claim 7, wherein, when the power take-off shaft (9) of the tractor is operating, the oil coming through the inlet opening into the attenuation valve flows through the outlet opening directly into the clutch, whereby the resistance of the clutch causes an increase in pressure in the valve, whereby, after the pressure has reached a certain initial value (pro) the bleed valve is opened and causes a leakage flow from the inlet opening through the leakage opening back into the tank, whereby, at the same time, oil flows through the choke channel via the choke gap, by-passing the choke piston, to behind the working piston into the annular space to move the piston towards the bleed valve and, by the intermediate of the spring, to press the bleed valve towards the closed position to cause an increase in pressure in the attenuation valve, whereby, after the spring has been compressed fully, the piston rod pushes the bleed valve to the fully closed position, whereby an engagement pressure (p,) is reached.

9. An attenuation valve as claimed in claim 8, wherein the stiffness of the spring determines the initial pressure.

1 0. An attenuation valve as claimed in claim 9, wherein the initial pressure is 5 bars.

11. An attenuation valve as claimed in claims 8, 9 or 10, wherein the engagement time taken from the initial pressure pO) to full engagement pressure (put) is within the range of 0.5 to 30 seconds.

1 2. An attenuation valve as claimed in claim 11, wherein said engagement time is within the range of 1 to 2 seconds.

1 3. An attenuation valve substantially as hereinbefore described with reference to the accompanying drawings.