GB1562518A - Power takeoff units agricultural tractors - Google Patents

Description

(54) IMPROVEMENTS RELATING TO POWER TAKE-OFF UNITS FOR AGRICULTURAL TRACTORS.

(71) We, FERRANTI LIMPED a Company registered under the Laws of Great Britain of Hollinwood in the County of Lancaster, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to agricultural tractors, and in particular to power take-off units for such vehicles.

Agricultural tractors are frequently used with implements which require the application of power to drive parts of the mechanism.

Accordingly many tractors are provided with power take-off units mounted at the rear and controlled by a lever-operated clutch to engage and disengage the drive. Some tractors, generally older ones, are provided with a wheel which rotates whenever the engine is running, and which is intended to carry a belt for driving stationary machinery.

If tractors of these types are to be modified by the addition of a power take-off unit driven by the engine, it may be difficult to provide a simple mechanism for operating the clutch.

Long levers and mechanical linkages suffer from the usual problems of wear and damage.

Many tractors are provided with hydraulic systems intended to power rams for raising and lowering an implement which is secured to the tractor. It may, however, be difficult and expensive to modify this existing system to enable it to operate the clutch of an additional power take-off unit. This is because of the need to provide a number of hydraulic components to control the system.

It is an object of the invention to provide a power take-off unit for an agricultural tractor having a simple clutch actuating mechanism.

According to the present invention there is provided a power take-off unit for an agricultural tractor which includes an input shaft arranged to be coupled to the engine of the tractor, a hydraulically-actuated clutch and a gearbox connected to one another between the input shaft and a power take-off shaft, the gearbox being arranged to contain a quantity of lubricating oil, a hydraulic pump coupled to the input shaft so as to rotate therewith and operable to apply said lubricating oil under pressure to the clutch actuating mechanism, a pressure relief valve connected between the output of the pump and the gearbox, and an electricallyoperated bypass valve operable to bypass the pressure relief valve.

Preferably the gearbox is connected directly to the input shaft and the hydraulic pump is driven by the gearbox, the clutch being connected between the gearbox and the power take-off shaft.

The hydraulic pump may be formed integrally with the gearoox.

In this specification the term "coupled to" is used to indicate that two parts are interconnected, directly or indirectly, so that both are driven together when the power take-off unit is in operation. The term "connected" is used to indicate a direct mechanical connection between the parts in question.

The invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a schematic view of a power take-off unit for mounting on the front of a tractor; Figure 2 shows a similar view of an alternative embodiment; and Figure 3 is a schematic diagram of an alternative hydraulic circuit.

Referring now to Figure 1, the speed-reducing gearbox, shown in section, comprises a casing 10 within which are a pair of gears in constant mesh. The input shaft 11 is coupled through a suitable flexible coupling 12 to the crankshaft of the tractor engine, and therefore rotates whenever the engine is running. On the input shaft 11 is carried a driving pinion 13, which is in constant mesh with a larger driven pinion 14. This latter pinion is carried on the gearbox output shaft 15. This shaft 15 is connected to the input side of a clutch 16, which may be a multiple-plate dry clutch. The output side of the clutch is connected to a power take-off shaft 17, shown as carrying splines.

The output shaft 15 of the gearbox also carries a hydraulic pump 18 which draws lubricating oil from the gearbox casing 10.

The pump applies oil to the actuating cylinder 19 of the clutch 17 via hydraulic line 20. A pressure relief valve 21 is connected between the hydraulic line 20 and a line 22 returning oil to the gearbox casing. Also connected between the lines 20 and 22 is an electromagnetic bypass valve 23. This is controlled from a supply 24 by way of a switch 25.

Whenever the engine of the tractor is running, the input shaft of the gear-box is rotating, as is its output shaft. The pump 18 therefore develops hydraulic pressure in the line 20. The clutch actuating mechanism is such that when pressure is developed in the line 20, and hence applied to the actuating cylinder, the clutch is engaged, applying power to the takeoff shaft 17. Conversely, when no pressure is developed in line 20, the clutch is disengaged.

This provides a fail-safe arrangement in the case of loss of oil pressure. For the same reason the solenoid valve 23 is arranged so that the valve solenoid has to be energised to close the valve and prevent the passage of oil through it to bypass the pressure relief valve 21.

When the solenoid of bypass valve 23 is energised by the closing of switch 25, pressure is built-up in line 20 and actuates the clutch cylinder 19, allowing the clutch to engage and transmit power to the power take-off shaft 17.

Pressure in the line 20 increases to the operating pressure of pressure relief valve 21, and then that valve allows oil under pressure to return along line 22 to the gearbox casing which acts as the oil reservoir. This circulation through valve 21 is necessary to prevent damage to the hydraulic system. The pressure-relief valve 21 may in fact be built into the body of the pump 18.

When the switch 25 is opened, valve 23 also opens, and allows oil from line 20 to return via line 22 to the gearbox, causing a loss of pressure in line 20. The clutch actuating cylinder 19 thus causes clutch 16 to disengage, removing the drive from the take-off shaft 17.

The unit described with reference to Figure 1 requires that the gearbox is driven continuously when the unit is in use, even if no power is being transmitted. Figure 2 shows an alternative embodiment in which the positions of clutch and gearbox are interchanged so that the gearbox is disconnected when no power is being transmitted. The same references are used as in Figure 1.

As before, the input shaft 11 is coupled to the engine crankshaft through a flexible coupling 12. The input shaft 11 drives the clutch 16, the output shaft of which is connected to the drive pinion 13 of the gearbox. The driven pinion 14 is connected to the power take-off shaft 17. The hydraulic pump 18 is driven from the input shaft 11 by suitable gearing 26 so that it operates whenever the input shaft rotates. The pump uses the lubricating oil in the gearbox casing 10 as before, and the hydraulic circuit is unchanged.

When clutch 16 is disengaged, the hydraulic pump is still operative, but the gearbox is no longer driven. A further advantage is that, since the clutch is in the higher-speed input shaft, it transmits less torque than when connected in the lower-speed output shaft.

However, the pump drive gearing takes up extra space, and this may be a disadvantage.

In both of the embodiments described above it may be necessary to provide an arrangement for preventing the hydraulic pressure from being applied to the clutch too rapidly.

Obviously a sudden operating of the clutch could damage the power take-off unit or the tractor engine. Some of the shock may be absorbed by the flexible coupling already referred to, but additional safeguards may be necessary. Devices such as progressive pressurerelief valves, slow-operating solenoid valves or clutches, and hydraulic accumulators are examples of known devices which will enable the clutch to engage over, say, a second or two.

The hydraulic arrangements described above may not allow the clutch to disengage as quickly as is required, since disengagement is dependent upon the loss in pressure in the hydraulic lines. This may be avoided by the use of a three-way solenoid valve which, in the "disengage" position connects the clutch actuating cylinder directly to the return line 22. Figure 3 illustrates such a hydraulic circuit. In practice it is preferable to provide the pressure relief valve 21 and the solenoid valve 23 with separate return lines to the gearbox, as shown in Figure 3.

The power take-off units described above are completely self-contained, having their own hydraulic systems. The only external connections necessary are the drive from the tractor engine and the electrical supply from the tractor battery to operate the bypass valve 23.

Hence the installation of either unit on an existing tractor is very simple. The tractor hydraulic system, if there is one, does not need to be modified, and there are no mechanical linkages necessary to operate the clutch.

The hydraulic line 22 returning oil to the gearbox may be arranged so that oil passing along it is directed at the mating surfaces of the gears 13 and 14 to assist in their lubrication.

The level of oil in the gearbox casing need not cover the pump. Different types of pump may be used, and the pump need not be integral with the gearbox, though this leads to a simpler arrangement. Similarly the pump need not be driven through gearing, and may be driven either directly from the input shaft or through other drive means such as a belt.

When transmitting power to an implement a considerable amount of heat may be developed in the gearbox. It is therefore possible to divert line 22 through an oil cooler before returning it to the gearbox, as shown at 28 in Figure 3.

The power take-off unit need not be mounted on the front of the tractor and coupled directly to the crankshaft, though this is the most probable arrangement since the front end of the engine crankshaft is the most convenient point for obtaining the necessary engine output.

A mechanically operated clutch 27, shown in broken outline in Figures 1 and 2, may be included between the engine and the input shaft 11 for disconnecting the unit when it is not required for use. Such a clutch is not suitable for disconnecting the drive to an implement since it will probably be inaccessible to the driver when in his driving position.

WHAT WE CLAIM IS: 1. A power take-off unit for an agricultural tractor which includes an input shaft arranged to be coupled to the engine of the tractor, a hydraulically-actuated clutch and a gearbox connected to one another between the input shaft and a power take-off shaft, the gearbox being arranged to contain a quantity of lubricating oil, a hydraulic pump coupled to the input shaft so as to rotate therewith and operable to apply said lubricating oil under pressure to the clutch actuating mechanism, a pressure relief valve connected between the output of the pump and the gearbox, and an electricallyoperated bypass valve operable to bypass the pressure relief valve.

2. A unit as claimed in Claim 1 in which the gearbox is connected directly to the input shaft and the clutch is connected between the gearbox and the power take-off shaft.

3. A unit as claimed in Claim 2 in which the hydraulic pump is driven by the gearbox.

4. A unit as claimed in Claim 3 in which the hydraulic pump is formed integral with the gearbox.

5. A unit as claimed in any one of the preceding claims in which the input shaft is coupled to the crankshaft of the tractor engine by way of a flexible coupling.

6. A unit as claimed in Claim 5 in which a mechanically-operated clutch is connected between the tractor engine and the flexible coupling.

7. A power take-off unit for an agricultural tractor substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. The hydraulic line 22 returning oil to the gearbox may be arranged so that oil passing along it is directed at the mating surfaces of the gears 13 and 14 to assist in their lubrication. The level of oil in the gearbox casing need not cover the pump. Different types of pump may be used, and the pump need not be integral with the gearbox, though this leads to a simpler arrangement. Similarly the pump need not be driven through gearing, and may be driven either directly from the input shaft or through other drive means such as a belt. When transmitting power to an implement a considerable amount of heat may be developed in the gearbox. It is therefore possible to divert line 22 through an oil cooler before returning it to the gearbox, as shown at 28 in Figure 3. The power take-off unit need not be mounted on the front of the tractor and coupled directly to the crankshaft, though this is the most probable arrangement since the front end of the engine crankshaft is the most convenient point for obtaining the necessary engine output. A mechanically operated clutch 27, shown in broken outline in Figures 1 and 2, may be included between the engine and the input shaft 11 for disconnecting the unit when it is not required for use. Such a clutch is not suitable for disconnecting the drive to an implement since it will probably be inaccessible to the driver when in his driving position. WHAT WE CLAIM IS:

1. A power take-off unit for an agricultural tractor which includes an input shaft arranged to be coupled to the engine of the tractor, a hydraulically-actuated clutch and a gearbox connected to one another between the input shaft and a power take-off shaft, the gearbox being arranged to contain a quantity of lubricating oil, a hydraulic pump coupled to the input shaft so as to rotate therewith and operable to apply said lubricating oil under pressure to the clutch actuating mechanism, a pressure relief valve connected between the output of the pump and the gearbox, and an electricallyoperated bypass valve operable to bypass the pressure relief valve.

2. A unit as claimed in Claim 1 in which the gearbox is connected directly to the input shaft and the clutch is connected between the gearbox and the power take-off shaft.

3. A unit as claimed in Claim 2 in which the hydraulic pump is driven by the gearbox.

4. A unit as claimed in Claim 3 in which the hydraulic pump is formed integral with the gearbox.

5. A unit as claimed in any one of the preceding claims in which the input shaft is coupled to the crankshaft of the tractor engine by way of a flexible coupling.

6. A unit as claimed in Claim 5 in which a mechanically-operated clutch is connected between the tractor engine and the flexible coupling.

7. A power take-off unit for an agricultural tractor substantially as herein described with reference to the accompanying drawings.