GB2043565A

GB2043565A - Hydrostatic transmission device

Info

Publication number: GB2043565A
Application number: GB8004923A
Authority: GB
Original assignee: LE DEV de la SECURITE SOC IND
Current assignee: LE DEV de la SECURITE SOC IND
Priority date: 1979-02-14
Filing date: 1980-02-14
Publication date: 1980-10-08
Also published as: FR2448995A1; FR2448995B1; DE3005224A1

Abstract

A wheeled vehicle has an engine 1 driving at least some wheels through a clutch 5, a gear-box 6, and a transmission box 8. A hydrostatic transmission comprising a pump 2 driven by the engine 1 and a motor 4 connected to a second input of the transmission box 8 enables the vehicle to be driven at low speeds with the engine 1 running continuously at full speed to power, for example, a fire-fighting pump 20. <IMAGE>

Description

SPECIFICATION Hydrostatic transmission device The present invention relates to a hydrostatic transmission device intended especially, but not exclusively, for fire-fighting vehicles.

A fire-fighting vehicle must fulfil precise requirements, including those of mobility and speed when fire breaks out on an aircraft. The vehicle must be able to proceed to the site of the incident at its maximum speed and then manoeuvre slowly around th'e scene of the incident whilst at the same time the fire pump operates with a regular, optimum delivery rate. These requirements may be fulfilled by using two engines, one providing traction for the vehicle and the other driving the pump, but this solution is not in general an economic one.

French Patent Application No. 77.36127 describes a hydraulic device for driving a utility vehicle suitable for all types of terrain, comprising a pump driven by the heat engine and a hydraulic motor, with the output shaft of the hydraulic motor driving the gear-box by way of a gear-change control. Under these conditions the speed of advance of the vehicle is always dependent on the gear ratios of the said gear-box.

The present invention relates to a hydrostatic transmission device which eliminates the fixed relationship, brought about by the ratios of the gear-box, between the speed of advance of the vehicle and the rotation speed of the engine which propels the vehicle.

The invention provides a hydrostatic transmission device, for a vehicle comprising a wheeled chassis on which is mounted a heat engine driving at least some of the wheels by way of a kinetic chain comprising a clutch, a gear-box and an intermediate shaft connecting the gear-box to one inlet of a transmission box on which are mounted drive shafts for the wheels, the hydrostatic transmission device being composed of a hydraulic pump arranged to be driven by the heat engine and a hydraulic motor which is connected by pipes to the pump, and is directly coupled by means of a clutch to another inlet of the transmission box.

The invention also provides a vehicle, especially a fire-fighting vehicle, fitted with a device according to the invention.

When the vehicle arrives at the site of an incident the conventional transmission system is suppressed and the vehicle can be driven at slow speed by way of the hydrostatic device.

By means of this hydraulic connection it is possible to keep the engine running at a high speed to ensure that the fire pump is driven under the best possible conditions while the vehicle may be driven forwards or backwards at a low speed by means of the hydrostatic device. In addition, this hydrostatic device, can be designed to absorb only part of the power of the engine (approximately 25%, say,) and is restored at the input of the transmission box with a high torque, thus ensuring a maximum traction effort which allows the vehicle to manoeuvre no matter what the terrain.

One form of fire-fighting vehicle constructed in accordance with the invention will now be described by way of example with reference to the accompanying drawing, the single Figure of which shows the chassis of the vehicle.

In the drawing, fine lines indicate the conventional parts of the vehicle, and thicker lines show the components which constitute the device according to the invention.

The conventional kinetic chain is arranged as follows: the heat engine 1 of the vehicle, by way of a clutch 5, drives the gear-box 6.

An intermediate shaft 7 transmits the drive, geared down by the selected gear ratio, to a transmission box 8. This box 8 transmits the movement to the rear axles 11 by way of the shaft 9 and the shaft 10, and to the front axle 13 by means of the shaft 12. In addition a shaft 1 9 drives the fire pump 20 direct from the engine 1 by means of a power take-off 22. It is obvious that the working rate of the pump 20 is a direct function of the running speed of the engine 1. It is therefore desirable for the engine to be able to turn at its maximum rate during fire-fighting, while the vehicle when it is moved should be able to manoeuvre at slow speed.

This result can be obtained by using a device which comprises a hydraulic pump 2 driven by the heat engine 1 and connected by pipes 3 to a hydraulic motor 4 coupled to the transmission box 8 through a clutch 21. The device also comprises a reservoir 14 containing the reserves of hydraulic fluid necessary for operation, a selector 1 5 which allows the starting-up and the reversal of the output of the pump 2, thus causing the vehicle to be driven forwards or backwards by the action of the motor 4 on the gearing of the transmission box 8, and also allowing the speed of advance to be regulated. The reservoir 14 is connected by a pipe 1 7 to a radiator 1 6? allowing the liquid to be cooled.The radiator 1 6 is itself connected to the pump by means of a pipe 1 8. The device is of course equipped with all the conventional hydraulic accessories such as a filter, a distributor, a discharge valve, and so on. An automatic device prevents the simultaneous use of both methods of transmission, that is to say, the movement of the vehicle is produced either by the conventional direct drive through the gearbox or by the hydraulic drive, with the conventional transmission being disconnected in the latter case.

By actuating the selector 15, the operator determines the rate and direction of output of the pump 2 which drives the hydraulic motor 4 and the latter, by way of a clutch 21, drives the gearing of the transmission box and thus the shafts 9 and 1 2 and the wheels of the vehicle.

The operation of the device is as follows: The vehicle reaches the site of a fire by using its conventional means of propulsion.

After the vehicle has been slowed down, the driver puts the gear-box 6 into neutral, lets in the power take-off 22, causing the fire pump 20 to be operated, and thus brings the firefighting equipment into the operational state.

Through control of the clutch 21 and operation of the selector 15, the hydraulic motor 4 can drive the vehicle at a low speed (0 to 4 kph) while the heat engine can provide the required fire pump output by running at high speed, without affecting the movement of the vehicle.

Claims

1. A hydrostatic transmission device, for a vehicle comprising a wheeled chassis on which is mounted a heat engine driving at least some of the wheels by way of a kinetic chain comprising a clutch, a gear-box, and an intermediate shaft connecting the gear-box to one inlet of a transmission box on which are mounted drive shafts for the wheels, the hydrostatic transmission device being composed of a hydraulic pump arranged to be driven by the heat engine and a hydraulic motor which is connected by pipes to the pump, and is directly coupled by means of a clutch to another inlet of the transmission box.

2. A device as claimed in claim 1, which comprises a fluid reservoir a selector acting on the said pump, cooling means for the fluid and at least two pipes connecting the hydraulic pump which is arranged in the vicinity of the heat engine and the hydraulic motor which is mounted on the transmission box substantially in the middle of the chassis.

3. A vehicle which is fitted with a hydrostatic transmission device as claimed in claim 1 or claim 2.

4. A vehicle as claimed in claim 3, which comprises a wheeled chassis on which is mounted a heat engine driving at least some of the wheels by way'of a kinetic chain comprising a clutch, a gear-box, an intermediate shaft and a transmission box on which are mounted drive shafts for the wheels.

5. A vehicle as claimed in claim 4, which is a fire-fighting vehicle.

6. A vehicle substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

7. A fire-fighting vehicle, equipped with a device as claimed in claim 1 or claim 2, wherein a power take-off prvtided on the engine drives the fire pump mounted on the vehicle at the rotation speed of the engine.