GB1590461A

GB1590461A - Agricultural tractors

Info

Publication number: GB1590461A
Application number: GB1924677A
Authority: GB
Original assignee: Ferranti PLC
Current assignee: Ferranti International PLC
Priority date: 1977-05-07
Filing date: 1977-05-07
Publication date: 1981-06-03

Description

(54) IMPROVEMENTS RELATING TO AGRICULTURAL TRACTORS (71) We, FERRANTI LIMITED, 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 leveroperated clutch to engage and disengage the drive.

If tractors of this type 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 an additional power take-off unit. This is because of the need to provide a number of hydraulic components to control the system.

It has become desirable in some instances to carry powered implements on the front of the tractor, and hence it is necessary to provide some form of front power take-off on the tractor. In some instances this has been provided by a shaft extending to the front of the tractor from the main or a subsidiary gearbox. Such a facility must, of course, be provided by the tractor manufacturer.

There is a requirement for a front power take-off system which may readily be added to existing tractors with little or no modification to existing mechanical and hydraulic arrangements, and it is an object of the invention to provide a tractor having such a system.

According to the invention there is provided an agricultural tractor which includes an engine, a rear power take-off shaft coupled to the engine, a speed-increasing gearbox driven by the rear power take-off shaft, a hydraulic pump driven by the speedincreasing gearbox, a hydraulic motor mounted on the front of the tractor, a speed-reducing gearbox driven by the hydraulic motor and driving a front power take off shaft, hydraulic lines interconnecting the hydraulic pump and the hydraulic motor, and a hydraulic valve arranged to control the application of hydraulic fluid from the hydraulic pump to the hydraulic motor.

The invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of the hydraulic and mechanical arrangement of the system; and Figure 2 is a schematic plan view of a tractor fitted with the front power take-off system.

Referring now to Figure 1, a rear power take-off shaft 20 on a tractor is coupled to a gearbox G1 which in turn drives a hydraulic pump P. So that the rear power take-off facility is not destroyed, the gearbox G1 has a splined output shaft T rotating at the same speed and in the same direction as the tractor power take-off shaft 20.

The hydraulic pump P draws hydraulic fluid from a reservoir R and has an output line L1 connected to a two-position spool-type control valve CV. In the position shown, which is the normal inoperative position, the pump output line is connected to a drain line L2 which returns the fluid to the reservoir R through an oil cooler OC. A spring-loaded pressure relief valve RV is connected to the pump output line L1 and also drains to the reservoir R. Two hydraulic lines are connected between the control valve CV and a hydraulic motor M which is mounted on the front of the tractor. The motor M drives a second gearbox G2 having a splined output shaft. The two gearboxes have inverse gear ratios, the gearbox G1 being a speed-increasing gearbox, and gearbox G2 being a speed-reducing gearbox.

With the control valve CV in the position shown the lines from the motor M are connected together. As shown in Figure 1 the valve is operated by an electromagnetic actuator EM drawing power from a battery B under the control of a switch SW, say the tractor battery.

In operation the pump P is operating whenever the rear power take-off shaft 20 is running, but the valve in its inoperative position prevents fluid from being applied to the motor M. If the valve CV is operated so as to raise the valve spool shown in Figure 1, the pump output will be applied to the motor M, which will rotate the output shaft S.

The control valve CV should be operated in such a manner as to apply hydraulic fluid to the motor M in a gradual manner to prevent damage to the motor, the pump, or to any equipment driven by the output shafts. The pressure relief valve RV will prevent any excessive pressure from building up. The reservoir R, as well as enabling the hydraulic system to be topped-up should leakage occur, also provides an expansion chamber in which the velocity of the fluid is reduced, thus enabling trapped bubbles of air to leave the system.

The use of gearboxes has two main advantages. The usual speed of rotation of a power take-off shaft when powering an implement is of the order of 500-1000 r.p.m.

However, the size of a hydraulic pump for a particular rate of flow is inversely proportional to its speed of operation. Hence a higher driven speed leads to a smaller pump. In addition, many commerciallyavailable pumps are designed to operate most efficiently at speeds of the order of 3000 r.p.m. Hence, for these reasons at least, the gearboxes G1 and G2 could have a ratio of the order of 5 or 6 to 1.

Figure 2 shows a plan view of a tractor fitted with the front power take-off equipment just described with reference to Figure 1. The tractor has an engine 10 which drives the rear power take-off shaft 20. The motor M, pump P and gearboxes G1 and G2 are shown in Figure 2, motor M and gearbox G2 with splined output shaft S shown mounted on the front of the tractor.

The power take-off unit described is compact and self-contained, and hence is readily fitted to existing tractors. If the tractor already has a hydraulic system fitted then it might be possible to use the existing reservoir for the power take-off unit. The power output available at the front power take-off shaft is determined purely by the ratings of the pump P and motor M. As already stated the pump and motor should preferably be of the gear type, though other types may be used. The pump will usually be of a type which delivers fluid at a constant rate when driven at constant speed, though the use of variable delivery pumps is not excluded.

Many variations are possible in the hydraulic circuit arrangement. The valve CV need not be a spool valve; for example a three-position rotary valve could be used.

WHAT WE CLAIM IS: 1. An agricultural tractor which includes an engine, a rear power take-off shaft coupled to the engine, a speed-increasing gearbox driven by the rear power take-off shaft, a hydraulic pump driven by the speedincreasing gearbox, a hydraulic motor mounted on the front of the tractor, a speed-reducing gearbox driven by the hydraulic motor and driving a front power take-off shaft, hydraulic lines interconnecting the hydraulic pump and the hydraulic motor, and a hydraulic valve arranged to control the application of hydraulic fluid from the hydraulic pump to the hydraulic motor.

2. A tractor as claimed in Claim 1 in which the speed-reducing gearbox has a ratio which is the inverse of that of the speed-increasing gearbox.

3. A tractor as claimed in either of Claims 1 or 2 in which the speed-increasing gearbox carries an output shaft which rotates in the same direction and at the same speed as said rear power take-off shaft.

4. A tractor as claimed in any one of Claims 1 to 3 in which the hydraulic valve is operable to cause the hydraulic fluid to bypass the motor.

5. A tractor as claimed in any one of Claims 1 to 4 in which the hydraulic valve is operable to reverse the direction of rotation of the motor.

6. A tractor as claimed in any one of Claims 1 to 5 in which a pressure-relief valve is connected in parallel with the hydraulic valve.

7. A tractor as claimed in any one of Claims 1 to 6 in which includes an expansion chamber in the hydraulic line returning hydraulic fluid from the motor to the pump.

8. A tractor as claimed in Claim 7

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. motor M drives a second gearbox G2 having a splined output shaft. The two gearboxes have inverse gear ratios, the gearbox G1 being a speed-increasing gearbox, and gearbox G2 being a speed-reducing gearbox. With the control valve CV in the position shown the lines from the motor M are connected together. As shown in Figure 1 the valve is operated by an electromagnetic actuator EM drawing power from a battery B under the control of a switch SW, say the tractor battery. In operation the pump P is operating whenever the rear power take-off shaft 20 is running, but the valve in its inoperative position prevents fluid from being applied to the motor M. If the valve CV is operated so as to raise the valve spool shown in Figure 1, the pump output will be applied to the motor M, which will rotate the output shaft S. The control valve CV should be operated in such a manner as to apply hydraulic fluid to the motor M in a gradual manner to prevent damage to the motor, the pump, or to any equipment driven by the output shafts. The pressure relief valve RV will prevent any excessive pressure from building up. The reservoir R, as well as enabling the hydraulic system to be topped-up should leakage occur, also provides an expansion chamber in which the velocity of the fluid is reduced, thus enabling trapped bubbles of air to leave the system. The use of gearboxes has two main advantages. The usual speed of rotation of a power take-off shaft when powering an implement is of the order of 500-1000 r.p.m. However, the size of a hydraulic pump for a particular rate of flow is inversely proportional to its speed of operation. Hence a higher driven speed leads to a smaller pump. In addition, many commerciallyavailable pumps are designed to operate most efficiently at speeds of the order of 3000 r.p.m. Hence, for these reasons at least, the gearboxes G1 and G2 could have a ratio of the order of 5 or 6 to 1. Figure 2 shows a plan view of a tractor fitted with the front power take-off equipment just described with reference to Figure 1. The tractor has an engine 10 which drives the rear power take-off shaft 20. The motor M, pump P and gearboxes G1 and G2 are shown in Figure 2, motor M and gearbox G2 with splined output shaft S shown mounted on the front of the tractor. The power take-off unit described is compact and self-contained, and hence is readily fitted to existing tractors. If the tractor already has a hydraulic system fitted then it might be possible to use the existing reservoir for the power take-off unit. The power output available at the front power take-off shaft is determined purely by the ratings of the pump P and motor M. As already stated the pump and motor should preferably be of the gear type, though other types may be used. The pump will usually be of a type which delivers fluid at a constant rate when driven at constant speed, though the use of variable delivery pumps is not excluded. Many variations are possible in the hydraulic circuit arrangement. The valve CV need not be a spool valve; for example a three-position rotary valve could be used. WHAT WE CLAIM IS:

1. An agricultural tractor which includes an engine, a rear power take-off shaft coupled to the engine, a speed-increasing gearbox driven by the rear power take-off shaft, a hydraulic pump driven by the speedincreasing gearbox, a hydraulic motor mounted on the front of the tractor, a speed-reducing gearbox driven by the hydraulic motor and driving a front power take-off shaft, hydraulic lines interconnecting the hydraulic pump and the hydraulic motor, and a hydraulic valve arranged to control the application of hydraulic fluid from the hydraulic pump to the hydraulic motor.

8. A tractor as claimed in Claim 7

which includes a hydraulic reservoir connected to the expansion chamber.

9. A tractor as claimed in any one of the preceding claims which includes a cooler connected in the hydraulic line returning hydraulic fluid from the motor to the pump.

10. An agricultural tractor substantially as herein described with reference to the accompanying drawings.