CONTROL DEVICE OF the CIRCUITS OF LUBRICATION AND LOAD Of a TRANSMISSION

ΐ.

A system comprising first and second fluid supply networks of hydraulically controlled mechanisms. In particular, a system of the type described above comprising a priority valve for passing the pressurized fluid from one of the circuits in the other under certain operating conditions.

The patent of the United States of America no. 3,385 312 circuit regulator fluid in which first and second pumps circulate a fluid under pressure from a source to two separate circuits. A directional control priorities mounted between the two circuits₅ communicates a holding pressure to one of the circuitsj from the other circuit? when this pressure is necessary.

In a transmission comprising a hydrostatic device it is desirable to implement circuits lubrication and comprising means to alter the operation of the transmission to prevent it from deteriorating in the case of malfunction of certain components which may affect the pressure of one or the other of the lubricating circuits and load.

The invention relates to a system comprising first and second valves at priorities for preventing the pressure of the lubrication circuit from descending below a security level; to reduce the control pressure of the hydrostatic device to operate the latter to idle in the case where the pressure of the load circuit drops below a certain level; increasing the pressure in accordance with the control pressure? to adjust the displacement of the hydrostatic device for the suitable pressure in one or more clutches used in the transmission; and to raise the pressure of the load circuit when an overspeed condition of the hydrostatic device appear to avoid damaging the device.

Furthermore? first and second displacement pumps associated with these-circuits are connected in series? the displacement of the first pump being greater than that of the second pump. The lubrication circuit and the second pump are connected to the output of the first pump and the load circuit is connected to the output of the second pump. A conduit is mounted between the lubricating circuit *' and the load circuit " and the first distributor to distributor priority or priority of the lubrication circuit is mounted within a duct to prevent flow in the inlet channel. The dispenser causes "under the effect of a predetermined drop of pressure in the lubricating circuit" the opening of said conduit to permit fluid flow of the load circuit to the lubrication circuit to maintain a desired pressure of fluid therethrough. Furthermore " priority the dispenser of the lubrication circuit assumes the function of a relief valve responsive to the pressure in the lubricating circuit to limit the value.

Further "in a transmission comprising a hydrostatic device having a buttress member to variable displacement and a control element of the displacement", the load circuit includes two branch conduits which a first is connected to the displacement setting and the other feeds hydraulic elements containing a quantity of fluid for hydrostatic device. The second distributor or distributor priority to priority of the load circuit is mounted in the first branch conduit and is operable to reduce the pressure in the conduit while maintaining the pressure in the second branch conduit. At this time " the reduced pressure can be used to control the displacement of the hydrostatic device has the effect of operating the same at idle speed, and thereby indicating the existence of a problem in the transmission. Furthermore "the dispenser to priority of the load circuit is responsive to a control pressure existing in a servo controller unit of the displacement" so that "when the setting pressure increases and indicates an increase in the output torque of the hydrostatic device" pressure adjustment changes 1' action of the distributor to priority of the load circuit to increase the pressure in the second branch conduit poyr ensure application of a suitable pressure to hydraulic elements such as clutches connected to said second branch conduit.

Furthermore? the dispenser to priority of the load circuit is subjected to pressures respectively corresponding to the speed of the hydrostatic device and to a speed of a motor j for example the engine of a vehicle connected to the transmission and applying force to the hydrostatic device j such that_} when the device reaches a speed equal to its nominal value overspeed_s priority the dispenser operates to increase the pressure in the second branch conduit and meet the criterion according to which a rise of the load pressure is required when the speed of the hydrostatic device increases.

The invention will be described in more detail in opposite the accompanying drawings as not limiting example and on which:

-figure 1 is a schematic partial cutting

of the transmission to which the control system of the invention is applied;

-figure 2A is a graph indicating the pressure in accordance with the control pressure;

-figure 2B is a graph indicating the load pressure as a function of the rate of nominal input speed;

and

-figure 2C is a graph indicating the pressure of the lubrication circuit according to the flow rate of the coolant pump? decreased flow rate of the charge pump.

Figure 1 represents a transmission including a hydrostatic device 10 and two elements 11 and 12 connected to each other via lines 15 and 16 for hydraulic fluid.. The elements 11 and 12 are positive displacement devices? such as reciprocating axial movement? the variable displacement element 11 with several pistons 17 mounted in a rotary cylinder which is suitably fixed to a shaft 18 which can be connected to a source of motive power? for example a vehicle engine. The stroke of the pistons 17 is controlled by a swash plate 19 connected by links 20 and 21 to a servo-control 22. The element 12 is a fixed displacement with several pistons 25 rotatably mounted in a cylinder block which is fixed to a shaft 26 connected to a controlled mechanism. The stroke of the pistons 25 is controlled by a swash plate 27 fixed. When the hydrostatic device operates " one of the conduits 15 and 16 is normally at a relatively high pressure and the other line is at low pressure. Of extra Fluid can be introduced into the low pressure conduit by means of one or the other of two retaining valves 30 and 31 whose inlet ports are connected to a line 35. The outlet port of the valve 30 is connected to the conduit 16 and the outlet port of the valve 31 is connected to the conduit 15.

The hydrostatic mounting the device is well known in the prior art and can be used independently as hydrostatic transmission "or in a hydro-mechanical transmission in which the shaft 26 of the hydrostatic device is connected directly" or indirectly by a clutch selectively controlled " to one or more elements of a planetary gear. In a hydromechanical transmission "the shaft drive" for example the output shaft of an engine "may also be connected directly" could indirectly by one or more clutches " to other elements of the planetary gear. In such a hydromechanical transmission "the or the clutches can be hydraulically actuated" the hydraulic control " the clutches and their control are represented generally in the form of a control device 40. This structure is well known to those skilled in the art and described "in one of its embodiments" in the application of the United States of America no. 825,844 " 18 August 1977 Pollman and deposited by collaborators.

A conduit 45 "connectable to a source of fluid" provides fluid to a first pump 46 connected in series with a second pump 47 by means of an intermediate conduit 48. These pumps are displacement type " the first pump 46 is a coolant pump that circulates a hydraulic fluid in a lubrication circuit having a conduit 50. The lubrication circuit is passed through by a cooling fluid and lubricant the hydraulic elements of the transmission. The second pump 47 is a charge pump and the displacement or its volume is smaller than that of the cooling pump 46 so that, in normal operation, the cooling pump 46 provides a proper amount of fluid to satisfy full-custom of the pump 47 and that of the lubrication circuit. It is well known that the pumps 46 and 47 and cooling can be controlled by the main motor and thus rotated at a speed proportional to that of the engine.

In a hydrostatic transmission or hydromechanical, significant damages may be caused by certain elements if such a transmission continues to operate while the pressure of the lubrication circuit is not suitable. In the event that the flow rate of the lubrication circuit decreases, as may occur under conditions of a malfunction of the lubrication pump 46, for example, an obstruction of the pipe 45 input or gasification of the fluid, elements complete the flow of the lubricating fluid using the fluid discharged from the charge pump 47. The output of the pump 47 is connected to a load circuit comprising two branch conduits which a first is represented in the second 55 and 56.

To complete the flow of the lubrication circuit, a conduit, having portions 60 and 61, connects the charging circuit to the lubrication circuit. The flow of fluid in this conduit is controlled by a distributor with priority and discharge of the lubrication circuit, represented generally 65. Priority The dispenser comprises a casing 66 having ports communicating with the conduit sections 60 and 61, and a discharge port 67 and a vent port 68. A shutter 70 is mounted so as to be movable in the housing and is normally urged toward the left, in the orientation of Figure 1, by a spring 71.

The pressure in the lubrication circuit acts on an end face 72 of the shutter and on the bottom a longitudinal bore 73, open at one end and formed in the shutter. The bottom of the bore 73 communicates via at least one radial channel 75 with an annular groove 74 formed in the outer surface of the shutter.

During normal operation₉ while the pressure in the lubrication circuit is at a desired value) the shutter is located as shown in Figure L_s to close the conduit sections 60 and 61) and an orifice 67 discharge is blocked by a bearing 76 of the shutter. When the pressure of the lubrication circuit falls below a predetermined value) for example established by the force of the spring 71) the shutter 70 moves to the left to a position in which the annular groove 74 is aligned with the conduit section 60 so that the fluid from the charging circuit may flow through the radial channel 75 and the longitudinal bore 73 in the section conduit 61. Thus) an amount of the fluid of the charging circuit is introduced into the lubrication circuit.

The dispenser 65 apriorité discharge and exerts a control function to holding a minimum pressure (Jans the lubricating circuit) this pressure being determined by the load of the spring 71. When excessive pressure appears) the shutter 70 moves to the right and the fluid flows through the bore 73 and the radial channel 75 to the discharge port 67.

The graph of Figure 2C shows the above-described operation. On this graph) the lubricant pressure) i.e. the pressure in the lubrication circuit) is given according to the flow rate of the cooling pump 46) decreased the flow rate of the charge pump 47. The indicated values are passed only example. The pressure curve as a function of the flow rate comprenc a vertical segment 80 corresponding to the inaction of the dispenser priority 65 and at a pressure of the lubrication circuit substantially between 1.05 and 2.1 bar. A the maximum value of approximately 2.1 bar, a segment 81 is obtained which shows that, when the lubricant pressure increases, some of the fluid delivered by the pump 46 cooling Ssfe discharged to the port 67. The segment 82 of the curve shows cjue , when the pressure of the lubrication circuit falls below about 1 "05 bar" priority the dispenser 65 acts to increase-the rate of flow from the load circuit by moving the shutter 70 to the gauchej in the orientation of Figure 1. The ordered 83 indicates the maximum flow rate of the fluid can flow from the load circuit " while the vertical dotted line 84 indicates the maximum quantity to be obtained from the difference of displacement pumps 46 and 47 and cooling load.

On a graph in Fig. 2C "the point" 0 "indicated in abscissa corresponds to the situation in which" for example "the pump 46 cooling delivers a quantity of fluid equivalent to twice its displacement while the pump 47 of-charge employs an amount of fluid equivalent to a displacement times its" the fluid resulting from the difference in volume supplied to the lubrication circuit. When the lubricant pressure rises to a value greater than about 2 "1 bar" the fluid is then discharged by the distributor and discharge priority. Conversely "when the lubricant pressure becomes less than about 1" 05 bar " the device operates in the area where a portion of the fluid delivered by the charge pump is returned to the lubrication circuit.

The charge pump 47 supplies fluid to the conduits 55 and 56 for bypassing the charging circuit "the conduit 56 being connected to the pipe 35 fluid supply of make-up of the hydrostatic device" in a manner well known " to the device 40 and that provides the hydraulic drives other than those regarding the positioning of the swash plate 19.

The charging circuit includes a distributor to priority "represented generally 100" and connected to the conduit 55 of bypass that receives the fluid discharged from the charge pump 47. The dispenser priority 100 controls the flow of the charge fluid in a conduit 101 to a device 102 for adjusting the position of the swash plate 19. The device 102 displacement control is conventional and well known to those skilled in the art "and it is connected by two conduits 103 and 104 at opposite ends of the servo control 22 which may be in the form of a cylinder-piston unit and the piston being centered by springs; in such a way that pressure in one or the other of the conduits 103 and 104 acts on the position of the piston in the booster and" thus on the position of the swash plate 19.

Furthermore " the dispenser 100 is operable to give priority to the pressure in the conduit 56 bypass. load circuit.

The priority of the load circuit has a housing 110 in which a shutter 111 is mounted for movement. The shutter 111 has a central land 112 which normally cooperates with a discharge port 115 to control s away from the orifice, and maintaining a desired pressure in the load circuit. Such regulation is obtained by the combined action of a spring 116 at a first end of said envelope and carrying end against a member 117 of the shutter, and by the pressure in. the conduit bypass 55. This pressure acts in a longitudinal channel formed in the shutter 120 and 121 on a piston mounted for movement in the channel and bears at one end against a casing end wall 110. The pressure of the load circuit, which is applied to the inside of the channel 120 of the shutter, provided a certain surface of the shutter to urge it to the right, in the orientation of Figure 1, and the resultant force acts in opposition to the previously established load of the spring 116, so that the position of the range 112 relative to the port 115 discharge is adjusted to maintain a predetermined pressure in the load circuit, upstream of the priority valve. Another variable is used to control the valve position priority, the other-variable being constituted by the control pressure present in the servo commandè 22 of the. swash plate 19.

The adjusting pressure is directly proportional to the pressure in the hydrostatic unit 10 and, therefore, the output torque. The adjusting pressure is detected, the location of the device 102 to displacement control, by a conduit 130 which terminates at an orifice of the dispenser 131 y.

100 to priority. The adjusting pressure is applied to the seal for said distributor and acts in a direction such that it tends to move the shutter to the left due to a differential effect produced by the range of 132 1' shutters whose diameter is greater than that of the member end 117 of the same shutter. When the pressure in the charge circuit upstream of the distributor to priorities is held the position of the shutter 111 and 112 of its range is dependent on the pressure prevailing in the channel 120 and acting in opposition to the preset load of the spring 116s and to the adjustment pressure acting on the differential area of the shutter.

The graph of Figure 2A shows the relationship between the load pressure and the pressure of settings the values indicated on the graphical as illustrative.

On the figure 2As the dotted line 139 indicates the maximum pressure of settings while a line 140 indicates the upper limit of normal operation of the systems and more particularly an upper limit of the load pressure on the basis of the adjustment. In the case where the rate of flow in the load circuit drops as may be occasioned due to a malfunction of the excessive leakage or pumps operation of the priority circuit and lubrication the pressure in the charge circuit for example in the conduit 56 leads decreases. As a result, the surface of the discharge port 115 112 closed by the range and further movement of the shutter 111 to the left so that the piston 121 gradually reduces the opening of a port 141 communicating the radial channel 120 with the conduit 101s and decreases the flow rate of flow to the displacement control device 102. This reduction rate ' ccoulement causes a reduction in the pressure which can be applied to the servo control 22 and the possibility of hydrostatic device 10 maintain the pressure. If the load pressure falls to a certain magnetic hydrodynamic methods the flow to the conduit 101 is fully cut and the hydrostatic transmission 10 ceases to operate. It does not risk to be damaged after repair. The figure 2A shows the pressure effects of decreased load on the actuating pressure? the segment 142 showing the relationship between a drop in the load pressure and the set pressure? maintaining this relationship is to a section 143 which indicates the lower limit of pressure causing a malfunction of the hydrostatic transmission 10. When the transmission 10 does not maintain the pressure? it is idling and this indicates to an operator or a driver that there is a problem? before excessive damage appear.

A additional function of the reaction of the control pressure transmitted by the conduit 130 to the dispenser priority 100 is to increase the load pressure in the conduit 56 of branch according to the control pressure applied to the servo control 22. The adjusting pressure is directly proportional to the pressure in the hydrostatic circuit of the device 10 and? therefore? the output torque. This increase in the load pressure in response to an increase of the pressure setting obtaining pressures suitable for maintaining the engagement of the clutches or when the hydraulic torque output increases.

In the case of over-speed of the engine? for example the engine of a vehicle? the load pressure is to be greater than normal in order to prevent a damage of elements of the hydrostatic device 10. A valve 150? responsive to engine speed? is a member well known to those skilled in the art which converts the speed of the motor into a pressure signal supplied through a duct ' 151 to a chamber 152 located at one end of the envelope of the dispenser 110? so that the pressure to act on a plunger 153 movable in that chamber.

The plunger has a head 154 which is in contact with the spring 116 and which limits the movement of the plunger to the right bearing against a shoulder 155 the casing of the dispenser. The pressure in the chamber 152 increases as a function of increasing engine speed. The preset spring 116 exerts a force which opposes the pressure corresponding to the engine speed at the over-rated speed of the hydrostatic device 10" the pressure acting on the area of the cross-section of the plunger 153. It is evident that during this time) the left end of the spring 116, bears against the shutter 111 which controls the pressures as previously described.

Accordingly "variations in the pressure corresponding to the engine speed" to the over-rated speed " does not cause an increase in pressure in the conduit 56 for bypassing the charging circuit. When the engine speed exceeds the nominal value of boost " the load pressure should be increased in order to prevent damage to the hydrostatic device 10 by over-speed. An increase in the pressure corresponding to the engine speed and exerted on the plunger 153 "above a certain value" on the plunger causes the application of a force greater than that of the spring 116 and begins to increase the force exerted by the spring which thereby alters the regulatory action to raise the load pressure. The increase in such pressure continues until the shutter 111 returns to an equilibrium position.

The figure 2B is a graph showing the load pressure as a function of the nominal speed of the hydrostatic unit 10, the digital values being indicated that illustrative. On this graph, the curve 160 shows an increase in the load pressure which begins when the level of the nominal speed slightly exceeds 100%.

It should be noted that the lubrication pressure is maintained over a security value and that the pressure of load can be increased if this is required for, in a transmission, of the lubricating circuits and load " provided with discharge manifolds and to priority as described above. Furthermore, the transmission operates at idle if the load pressure falls below a predetermined level.

Of course, many modifications may be made to the control system described and shown without departing from the scope of the invention.