GB2149492A

GB2149492A - Cooling means for a hydraulic system

Info

Publication number: GB2149492A
Application number: GB08324290A
Authority: GB
Inventors: Edward Sharp
Original assignee: JESPRO Ltd
Current assignee: JESPRO Ltd
Priority date: 1983-09-10
Filing date: 1983-09-10
Publication date: 1985-06-12
Also published as: GB8324290D0

Abstract

A cooler module for a hydraulic system for commercial motor vehicles provides a closed loop system connecting a pump P to equipment A driven thereby and operating at pressure greater than atmospheric giving positive feed of fluid to the pump P. Fluid from the pump P passes via a control valve 9 and pipe 5 to the equipment A and is returned via pipe 4 to a heat exchanger 7 cooled by a thermostatically controlled fan 8 and thence via pipe 13 to a circulation booster 10, from which part of the fluid passes via pipe 1 to the pump P and the rest (about 10%) passes via a filter 15 to a closed pressure tank 6. Fluid re- enters the booster 10 from the pressure tank 6 via a pipe 17. <IMAGE>

Description

SPECIFICATION Hydraulic cooler module The invention relates to a hydraulic cooler module for use particularly but not exclusively in commercial motor vehicles.

As is well known, the fluid, generally oil, used in hydraulic systems in commercial motor vehicles tends to increase in temperature when it performs hydraulic functions and it is desirable therefore to provide cooling means. However, in the arrangement used hitherto, the cooling has been in some circumstances excessive, resulting in an unwanted increase in viscosity in the oil or at the very least unnecessary, resulting in a waste of energy in the cooling system. Moreover, the open loop system of hydraulic fluid re-circulation previously used has tended in some circumstances to lead to an insufficient oil return to the oil pump resulting in excessive wear and shorter life in the pump.

To mitigate these problems, we provide according to our invention, a hydraulic cooler module for a hydraulic system including a hydraulic pump having high and low pressure ports connected or for connection to a closed hydraulic circuit including auxiliary equipment as hereinafter defined to provide fluid flow therethrough, said module comprising a closed fluid container, a heat exchanger for fluid connection to the downstream side of said auxiliary equipment, thermostatically controlled fan means adjacent the heat exchanger, and circulation means for fluid connection with the low pressure port of the pump and in fluid connection with the heat exchanger and the said container, whereby in use a proportion of fluid returning to the pump from the heat exchanger is diverted to the container and is replaced by fluid taken from the container, and the fluid re-enters the low pressure port of the pump at a pressure above atmospheric.

Preferably the diverted proportion of fluid is passed through a filter before entering the container, and preferably again said filter is arranged to receive fluid from conventional drain lines from said auxiliary equipment.

The container is preferably a pressure tank provided with a relief valve. The heat exchanger may take the form of a radiator and the fan means may be driven by an electric motor. The module mayfurthercomprise a second filter connected upstream of the heat exchanger.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, of which the single figure is a schematic representation of a hydraulic cooler module connected to a hydraulic pump and auxiliary equipment.

As shown in the drawing, a hydraulic cooler module M is connected by conventional piping 1,2, 3,4,5 to a conventional hydraulic pump B and auxiliary equipment A. The auxiliary equipment A may, in practice, itself comprise one or more hydraulic devices such as hydraulic motors and cylinders, but for the sake of simplicity will be referred to hereinafter as auxiliary equipment.

The module is contained in a compact framework and comprises a pressure tank 6, a radiator 7, an electric fan 8, a control valve 9 and a boost unit 10 acting as a circulating means.

In use of the module, the pump P forces fluid, conventionally oil, through pipe 2 to the control valve 9 by which, at will, the pressurised fluid can be directed to a chosen piece of auxiliary equipment, schematically represented in the drawings by block A. A system relief valve (not shown) is incorporated in the control valve 9 to safeguard the auxiliary equipment.The rate of flow of fluid is typically of the order of 20 gallons per minute.

From the auxiliary equipment the main return flow through pipe 4 enters the bottom of the radiator 7 via the control valve 9 and a filter 11.

The fluid passing through the radiator 7 is cooled by air driven by fan 8 which is controlled by thermostat 12 located in the pipe 13 so that the fan operates only when and so long as the temperature of the fluid being removed from the radiator by the pipe 13 exceeds a predetermined value. In this way, the fluid in the radiator is not "frozen" or rendered highly viscous by a blast of cold air when the system is started up in cold environmental conditions, and power for driving the fan is not wasted by running it when the auxiliary equipment is not producing excessive quantities of heat.

The pipe 13 is in fluid connection, internally within the boost unit 10, to the pipe 1 so that fluid flowing from the radiator 7 returns to the pump P. However, in passing from the pipe 13 to the pipe 1, a proportion of the fluid, typically 10%, is diverted and passes through pipe 14 into filter 15 from whence it enters the pressuretank6through pipe 16. Drain lines 3, conventionally provided with auxiliary equipment, are arranged in this embodiment also to be connected into the filter 15 so that fluid draining from the auxiliary equipment also passes through pipe 16 into tank 6.

Sufficient fluid, at least to compensate for the quantity diverted through pipe 14 and possibly also to compensate for losses in the system, is drawn by the boost unit 10 from the tank by pipe 17, and this compensating fluid is added to the fluid flowing to pump P through pipe 1. It is understood that internally of the boost unit 10 there is a constriction between pipes 13 and 1, and the withdrawal of fluid from the tank through pipe 17 may result from a reduction of pressure in the fluid on the downstream side of the constriction, or alternatively the flow of fluid from the tank may be as the result of displacement by the fluid entering the tank through pipe 16.Whatever the explanation for the operation of the boost unit 10, the fact is that fluid returns to the pump P through pipe 1 under a slight but positive pressure, typically in the order of 10 to 20 p.s.i. which contrasts with systems in which the flow back to the pump is merely under gravity. The higher pressure of the fluid in pipe 1 makes possible the use of a narrower diameter bore for pipe 1 than is the case with open systems.

In operation the tank 6 will normally be largely but not completely full of fluid. The tank is provided with a cap 18 for the introduction of fluid, and the cap has a pressure relief valve incorporated in it, the valve enabling air to enter the tank in the event that the pressure therein drops below atmospheric but primarily to release air from the tank if the pressure inside exceeds a predetermined value, say 5 p.s.i. In order that the level of fluid in the tank may be readily observed, a gauge 19 is connected externally of the tank.

Claims

1. A hydraulic cooler module for a hydraulic system including a hydraulic pump having high and low pressure ports connected or for connection to a closed hydraulic circuit including auxiliary equipment to provide fluid flow therethrough, said module comprising a closed fluid container, a heat exchanger for fluid connection to the downstream side of said auxiliary equipment, thermostatically controlled fan means adjacent the heat exchanger, and circulation means for fluid connection with the low pressure port of the pump and in fluid connection with the heat exchanger and the said container, whereby in use a proportion of fluid returning to the pump from the heat exchanger is diverted to the container and is replaced by fluid taken from the container, and the fluid re-enters the low pressure port of the pump at a pressure above atmospheric.

2. A hydraulic cooler module as claimed in Claim 1 wherein the diverted proportion of fluid is passed through a filter before entering the container.

3. A cooler module as claimed in Claim 2 wherein said filter is arranged to receive fluid from conventional drain lines from said auxiliary equipment.

4. A cooler module as claimed in any one of the preceding claims wherein the container is a pressure tank provided with a relief valve.

5. A hydraulic cooler module substantially as herein described with reference to the drawings.