FR2477083A1 - HYDRAULIC CIRCUIT EQUIPPING A TRACTOR FOR ACTUATING CYLINDERS - Google Patents

Abstract

THE CIRCUIT INCLUDES TWO VOLUMETRIC PUMPS WITH FIXED FLOW, A MAIN PUMP 10 WHICH IS ALWAYS IN SERVICE, AND AN AUXILIARY PUMP 30 WHICH IS COMMISSIONED ONLY WHEN A SIGNIFICANT FLOW IS NECESSARY, FOR EXAMPLE TO LIFT A TOOL . THE COMMISSIONING OF THE AUXILIARY PUMP 30 IS CARRIED OUT EITHER BY MEANS OF A BYPASS VALVE 33 OR BY A RELEASABLE COUPLING OF THE TWO PUMPS. APPLICATION: AGRICULTURAL TRACTORS WITH LIFT DOOR TOOLS.

Description

The invention relates to. a hydraulic circuit intended to be installed on

  a tractor, in particular on an agricultural tractor, to provide the hydraulic power necessary to actuate receiving members

  such as jacks acting on tools associated with the tractor.

  It is known that on modern agricultural tractors it is necessary to provide hydraulic drive units, such as cylinders, capable of

  provide a maximum of power to operate the associated tools.

  tractor to perform various agricultural work.

  Tools usually mounted on a tractor require power

  extreme motive force: for example, a tool focused on a trac-

  a three-point attachment system requires significant power when it is raised, whereas a relatively low oil flow, and therefore a moderate power, of

  cnomander this tool while in working position.

  The precariousness caused by the wide variations in the power required

  The fact that the hydraulic power demanded by the hydraulic circuit of the machine represents a very considerable fraction of the power supplied by the tractor engine is sufficiently important for the operation of the tool associated with the tractor; in modern tractors,

  this fraction can reach about 40% of the total power of the engine.

  In these hydraulic circuits, the source of liquid under pressure is necessarily constituted by a volumetric palp, and the control of the

  Flow control presents serious difficulties.

  The theoretically ideal solution to this problem could be to adopt a volumetric flow rate chart of known types; but this solution is fraught with various disadvantages, first and foremost at the high cost of

  these kinds of ponpes, their relative complexity and, consequently, their

  interview. In addition, it is not easy to find on the market

  variable flow pumps well adapted to the needs of their application.

  for the driving of machines of variable power as

  currently exist. Nor can we consider a solution

  genuinely acceptable that which uses indirect flow control systems, such as those proposed and which affect the flow of admission of a volumetric zone: these systems are indeed too limited as regards the regulation response time, dimensions, rotational speed and volumetric efficiency, without ocrpter that their operation is noisy. As a result, these systems are only suitable for hydraulic circuits whose flow rate

maximum is relatively low.

  On the other hand, the fractionation of the flow rate of a fixed flow volumetric pump, by external means, leads to a significant loss of power, which results not only in an increase in the operating cost of the machine, but raises also other related problems such as that of the evacuation of the heat released by the transformation of the lost power and the overheating of the liquid of the hydraulic circuit. In the specific case of the tractors to which the present invention relates, it should also be noted that the loss of power in

  the hydraulic circuit leads to an unjustifiable decrease in the

  available on the transmission of the tractor, if it is considered that it is the engine which provides the power required for traction and

  the one that drives the hydraulic circuit pump.

  The applicant observed that the flow to be supplied by the hydraulic circuit

  A tractor for the operation of a cylinder actuating a tool varies essentially between two main levels: a certain maximum flow is required, for example for the lifting of the tool (or for services external to the tractor), while only a smaller flow rate, for example of the order of the maximum flow rate, or even less, for the maneuvers of the tool once it is in the position of

work, engaged in the ground.

  These considerations are at the origin of the present invention which has for object the realization of a hydraulic circuit associated with a tractor for operating tools, this circuit comprising a source of pressurized liquid actuated by the engine used for the propulsion of the tractor this liquid being directed through a distributor member to at least one hydraulic jack or other receiving member; according to the invention, this circuit is characterized in that the hydraulic pressure source consists of a main pump and an auxiliary pump, the main pump permanently discharging into the circuit, and the auxiliary pump being connected to the circuit in order to output in parallel with the main pump, means being provided to control the intervention of the

  auxiliary pump depending on the flow required by the hydraulic cylinder (s).

  To further explain the scope and characteristics

  of the invention, an embodiment of the hydraulic circuit

  The subject of the invention will be described hereinafter with reference to the accompanying drawings in which: FIG. 1 is a diagram of a hydraulic circuit according to the invention, and

  FIG. 2 shows a variant of the circuit of FIG. 1.

3 2477083

  Fig. 1 shows a hydraulic circuit associated with a tractor, not shown. This circuit consists essentially of a first source of pressurized fluid, consisting for example of a volumetric pumape 10, the discharge pipe 11 leads to a distributor 12 allowing

  controlling the flow of liquid directed by line 13 to one or more

  sors jacks to the other receiving members shown schematically in 14. The part of the circuit described so far is to be considered as a diagram

  element of the hydraulic circuit usually installed on the trac-

  to actuate hydraulic servo motors, which can be mounted for example on the tractor itself to commaxnder tools worn or semi-worn. The pump 10 is actuated by the propulsion apparatus of the tractor, to which it is mechanically connected, as shown diagrammatically

  and partially at 20, by means of a kinematic connection 21.

  Other components necessary or useful for the proper functioning of the hydraulic circuit are part of the usual equipment of the tractors, such as for example a pressure limiting valve 16 on the delivery line 11 of the displacement pump 10. However, these The members will not need to be described here in greater detail since they are schematically shown in FIG. 1 and are otherwise

  well known technicians competent in the field.

  According to the main characteristic of the invention, the hydraulic circuit

  It comprises a second pump or auxiliary pump 30, the discharge line 31 of which is connected in parallel with the discharge pipe 11 of the main pump 10 via a nonreturn valve 32.

  The auxiliary pump 30 has been shown to be cam-related

  to the main pump 10 so as to be driven together therewith; on the discharge line 31 of the auxiliary pump 30 is placed a valve 33 which can be controlled between two positions, namely a closed position and an open position in which the pipe 31 debits

to a recovery tank 34.

  The operation of the circuit according to the invention appears clearly in FIG. 1: if the jack or the cylinders 14 require a large flow, for example to quickly raise a tool carried by the tractor, the valve of

  discharge 33 is closed, and the sum of the flows of the pumps 10 and 30 is direc-

  by the discharge line 11 to the distributor 12 and from there

to the cylinders 14.

  If, on the contrary, the discharge valve 33 is opened, the flow rate of the auxiliary pump 30 flows towards the discharge tank 34 with a negligible resistance, and the available flow rate for the cylinder is only that which can be supplied by the main pump 10 ; mechanical power

  necessary to vacuum drive the auxiliary phantom 30 is then neglected.

  geable. The size of the pacules 10 and 30 is easily deduced from what

  just described. The sum of the flow rates of these two packages must corre-

  lay at the maximum predictable flow that may be required by the cylinders.

  The flow rate of the one of the two pampers, which is in permanent operation, ie the main pamp 10, will be determined by a judicious compromise between two contrary requirements: on the one hand, this flow must be sufficiently reduced to limit the power lost when the pump is rotated without having to supply hydraulic power to the circuit for controlling the cylinders; and on the other hand, this flow must be high enough not to require an excessively frequent commissioning of the auxiliary pump 30, when the hydraulic power demanded by

  the cylinders exceed the power supplied by the main pump 10.

  The advantages of the hydraulic circuit according to the invention will become clear when calculating the dimensions of the main ramp 10, in

  assuming that this pampel should easily provide the power of

  necessary for the operation of a tool control cylinder when the tool is in the working position and is to be

  the effort and position of this tool.

  Most of the control work of the tool is therefore performed by the main scaffold 10 operating alone, so that there is little lost power and that most of the power of the engine remains

  noticeable for the propulsion units of the tractor.

  The intervention of the auxiliary gate 30, by closing the valve 33,

  is then limited to the lifting of the tool at the end of each phase of

  vail, that is to say, where the tractor requires only a power of

Relatively reduced traction.

  This allows to consider without problem the possibility of bringing the maximum hydraulic power of the circuit that can be installed on a tractor to a value representing a fairly large fraction of the total power of the engine, thanks to the possibility of leaving out of service, during

  the working phases of the tool, part of this power,

  activating the auxiliary pumice 30. This avoids any excessive loss of

Sire of power.

  The commissioning of the commissioning or decommissioning of the auxiliary pOEpe

  area 30, by means of the valve 33 shown in FIG. 1 may be achieved in various ways, including combining the operation of this valve to that of other manual requests of the circuit, so that it can easily be operated by the driver when needed

  mentally poor hydraulic power.

  While FIG. 1 shows an embodiment in which the commissioning commissioning or out of service of the blade 30 uses hydraulic means, it can be envisaged to use other means, for example mechanical, such as those represented as example in FIG. 2, which is a partial schematic view of a hydraulic circuit

similar to that of FIG. 1.

  FIG. 2 the auxiliary pmarpe 30 connected to the engine 20 by a transmission 21 with the interposition of a disengageable seal 36. When this seal is engaged, the pump 30 is driven by the motor, and delivers liquid to the discharge pipe 11, while 'in the disengaged position, the ramp 30 is inactive and the main parnpe 10 is alone in use. The proposed solution according to the invention makes it possible, for the equipment of the tractors, a hydraulic circuit capable of operating both hydraulic devices mounted on the tractor, such as a lift cylinder for a tool carried with three-fold attachment points, that

  external hydraulic devices. This solution brings together

  the availability of a high maximum hydraulic power with a power loss system, while being an acceptable cost, and easily adapting to various power ganmes

  encountered on vehicles; easy to install, the circuit according to the in-

  The invention provides an excellent solution to the problem of rationalizing the power draw on the engine of a tractor, when the engine must simultaneously provide the power required for the propulsion of the tractor and the power required to drive the source of liquid under the tractor.

hydraulic system pressure.

R EV E N D I CA T IO N S

  A hydraulic circuit associated with a tractor for operating tools, this circuit comprising a source of pressurized liquid actuated by the engine used to propel the tractor, this liquid being directed through a distributor member to at least one receiving member such as a hydraulic cylinder, characterized in that the hydraulic pressure source is constituted by a main beam (10) and an auxiliary beam (30), the main parp permanently discharging into the circuit and the auxiliary beam being connected to the circuit in order to output in parallel with the main screen, means (33 or 36) being provided for carrying the interventicn of the auxiliary poode according to the flow required by the

or hydraulic cylinders.

  2. Hydraulic circuit according to claim 1, characterized in that said means (33) for oarmnander the commissioning of the parpe auxiliary (30) consist of a member capable of interrupting the connection between the pipe repouleent (31) ) of said poarpe and the hydraulic circuit, in

  connecting said conduit (31) to a discharge conduit (34).

  3. Hydraulic circuit according to claim 1, characterized in that the toyen (36) for com- manding the commissioning of the auxiliary pump (30) consists of a mechanical coupling member disengageable between said

  (30) and the tractor engine.