FR2605076A1 - Automatic transmission for a carriage - Google Patents

Abstract

Hydrostatic automatic transmission for a vehicle, including a dual-displacement member 8, 24 displaced in a longitudinal direction 9 by the accelerator pedal 11 and the tranverse direction 12 by the select lever 14, a member 15 for actuating the gases, a member 18, for actuating the positive cylinder capacities, driven by the dual-displacement member when the latter is in its transverse forward-running position, a member 19 for actuating the negative cylinder capacities driven by the dual-displacement member when the latter is in its transverse backwards-running position, the two members 18, 19 for actuating the cylinder capacity actuating the member 4, 5 for controlling the cylinder capacity by means of an elastic device 23.

Description

AUTOMATIC CAR TRASMISSION
The invention relates to transmission in vehicles, in particular of small displacement, for which a conventional automatic, hydrokinetic or hydrostatic transmission cannot be envisaged, in particular because of its high cost, and for which a conventional mechanical transmission constitutes an important limitation to their distribution, especially for carts that can. be driven without a driver's license, due in particular. the clutch control which worries many potential users of this type of vehicle.

 A conventional hydrostatic transmission usually uses. one or more hydraulic motors with fixed displacement, driving the driving wheels of the vehicle, and a variable displacement pump mechanically driven. by the internal combustion engine of the vehicle and hydraulically connected in a closed circuit to the hydraulic motor (s). By varying the displacement of the pump, the transmission ratio is therefore adjusted. If the displacement of the pump is controlled manually. from zero, this avoids the clutch but does not constitute a real automatic transmission since the displacement control must be actuated in relation to the throttle control according to the operating circumstances. In addition, to avoid any danger of destruction of the hydraulic circuit, it is necessary to provide a certain number of auxiliary protection devices, in particular discharge valves on the various parts of the circuit. If, on the contrary, the variable displacement of the pump is controlled automatically, this requires a whole complex hydraulic regulation to subject this displacement to the operating circumstances according to a defined program. It is for this reason that hydrostatic automatic transmissions reach a relatively high cost, little in relation to the cost of a small displacement cart.

 the object of the invention is to eliminate the preceding drawback by producing a hydrostatic automatic transmission - particularly simple and economical.

 the invention uses above all a variable displacement positive displacement pump comprising a drive shaft, permanently driven by the engine shaft of the vehicle, and a variable displacement control member having a neutral rest position with zero displacement , corresponding to the neutral point of the transmission, on either side of which there is an adjustment range for increasing positive displacement corresponding to the forward movement of the vehicle, and a negative displacement range corresponding to reverse movement. As usual, this pump is hydraulically connected in a closed circuit to one or more fixed displacement hydraulic motors driving the drive wheels of the vehicle. When this control member for the displacement of the pump is biased in one direction or in the other from its neutral position, it is subjected to a reaction (force or torque) tending to bring it back to its neutral position, this reaction being proportional to the hydraulic backpressure, that is to say consequently to the resisting torque encountered by the hydraulic motor (s).

 The invention also uses a selector lever having neutral, forward, and reverse positions, but which is not directly connected to the variable displacement control member.

 The invention consists in combining the above elements with an intermediate mechanism comprising a double-displacement member capable of being moved in a longitudinal direction under the effect of an appropriate control coming from the accelerator pedal, and of being moved in the transverse direction under the effect of an appropriate remote control from the selector lever to take three successive transverse positions corresponding respectively to the forward, neutral and reverse positions of the selector lever; a throttle valve actuating member, movable in the abovementioned longitudinal direction, driven by the double displacement member in its three transverse positions, and in turn actuating by remote control the throttle valve control of the heat engine of the vehicle; an actuator for positive displacements for forward travel, capable of being driven in said longitudinal direction by the double displacement member only when the latter is in its transverse forward travel position; a negative displacement actuation member for reverse gear capable of being driven in said longitudinal direction by the double displacement member only when the latter is in its transverse reverse position; the two aforementioned displacement actuators being connected remotely by appropriate transmissions and in an antagonistic manner to a receiving member, which in turn actuates the control member of the variable displacement of the pump by means of a elastic device allowing a position difference between the receiving member and the displacement control member proportional to the aforementioned reaction.

Other features of the invention will appear in the following description of an embodiment taken as an example and shown in the accompanying drawing, in which
Figure 1 is a general diagram of the transmission;
2 shows a top view of the part of the mechanism close to the conductor;
Figure 3 is a vertical longitudinal section along III-III of Figure 2;
Figure 4 is a vertical cross section along IV-IV of Figure 3;
Figure 5 is an elevational view of the part of the mechanism integral with the pump; and
Figure 6 is a horizontal section along
VI-VI of figure 5.

 FIG. 1 shows the volumetric hydraulic motors 1 with constant displacement, here two in number, for actuating for example the two rear wheels of the vehicle, not shown, in order to avoid any differential. These two motors 1 are connected in parallel and in a closed circuit to the positive displacement pump 2 with variable displacement and two flow directions, which is for example a barrel pump and a tilting plate, or a roller pump and with variable eccentricity , whose displacement, that is to say the hydraulic fluid flow rate per revolution of the input shaft 3, is controlled by a control shaft 4 secured to the displacement control member constituted here by a lever 5.This displacement has a zero value for a middle position of the lever 5, and has an adjustment range by increasing positive values for one direction of movement of the lever 5, and another adjustment range by increasing negative values for the other direction. of displacement. The power input shaft 3 of the pump 2 is coupled by any suitable mechanical means with the output shaft of the heat engine 6 that the vehicle has. The pump housing 2 is supplied with hydraulic fluid under a slight load from a hydraulic fluid reservoir 7.

 Naturally, the heat engine 6 always rotates in the same direction, and the hydraulic motors 1 rotate in the forward or reverse direction depending on whether the lever 5 is tilted in one direction or another, the ratio forward or reverse transmission being a function of the angular deviation of the lever 5 relative to its median position.

 On the right-hand side of FIG. 1, we also see the double-displacement member 8 capable of being driven in the longitudinal direction 9 by an appropriate transmission 10 from the accelerator pedal 11, and of being driven transversely , in the direction 12 or the opposite direction, by an appropriate transmission 13 from the selector lever 14 comprising, like the double-displacement member 8, a forward operating position AV and a rear reversing position AR located on either side other from a neutral position PM. We see, on the other hand, the gas actuator 15 which is capable of moving in the longitudinal direction 9 when it is pushed by the double displacement member 8 in its three transverse positions, this member 15 in turn driving, via an appropriate remote transmission 16, the lever 17 for controlling the throttle valve of the heat engine 6.

 Finally, we see the member 18 for actuating positive displacements for forward travel which is capable of being driven in the longitudinal direction 9 by the action of the double-displacement member 8 only when the latter is in the position of forward. There is likewise a member 19 for actuating negative displacements for reverse gear arranged symmetrically with respect to the previous one and driven in the longitudinal direction 9 by the double-displacement member 8 only in its transverse reverse position. These last two members 18 and 19 actuate in turn remotely, via the appropriate transmission 20 and 21, a receiving member 22, which is acted in an antagonistic manner by the two transmissions 20 and 21. Finally, according to the invention, the receiving member 22 in turn drives the displacement control lever 5 by means of an elastic device shown diagrammatically by the springs 23.

 We will now examine in more detail an embodiment of these various mechanisms.

 It can be seen, for example, in FIGS. 2 to 4, that the double displacement member consists of a pallet 8 carried by the end of a lever 24, which is articulated at 25, for lateral displacement, on a part 26 pivoting about a horizontal axis 27 carried by a support 28 substantially U-shaped and fixed to the vehicle. This support 28 also includes another axis 29 around which the lever 30 of the accelerator pedal 11 is articulated, the other end 31 of this lever 30 pulling on a cable 10, the other end 32 of which is fixed at a point lever 24.

 The gas actuating member 15 is constituted by the upper cross member of a stirrup-shaped part, the lateral branches 33 of which are articulated on the two ends of the axis 27, on either side of the faces. vertical of the support 28. This bracket has a lateral tab 34, visible in FIGS. 2 and 4 and on which a return spring 35 is hooked hooked at its other end to a tab 36 of the support 28, and another tab 37 on which hooks the gas control cable 16.

 Indeed, apart from the simple cable 10 which has just been examined, all the other transmissions 13, 16, 20, 21, examined previously, are constituted by a single target under sheath of the Bowden type or the like, the sheaths being referenced respectively 13a, 16a, 20a and 21a.

 the stirrup 15 also includes another tab 38 on which the sheath 13a of the cable 13 examined previously and coming from the selector lever 14 is fixed.

The end of this cable 13 hooks to the end 39 of a movable finger 40 rigidly secured to the lever 24, a spring 41 being further interposed around the cable 13 between the tab 38 and the end 39 so that the cable 13 always works under tension. An opposing spring of equivalent force can be arranged at the other end controlled by the selector lever 14.

 the two organs 18 and 19 for actuating the displacement of the pump are also constituted by simple levers articulated around the same axis 27, on either side of the part 26 carrying the lever 24. On these levers hang the control cables 20 and 21 respectively, and also two return springs 42 and 43 intended to keep the cables 20 and 21 under tension.

 It can thus be seen that in this embodiment the longitudinal displacements of the members 8 or 24, 15, 18 and 19, are in reality movements in an arc of a circle by pivoting around the axis 27, while the transverse displacements of the member 8 with double displacement, its lever 24 and the movable finger 40, are pivoting movements about the axis 25.

 We see that, in the middle position of the pallet 8 corresponding to the neutral position of the selector lever 14, this pallet is capable of passing between the levers 18 and 19 without actuating them, while in the tilted position of forward or reverse gear controlled by the cable 13, this pallet hooks one or the other of the levers 18 and 19. It can however be seen, in particular in FIG. 2, that a boss 44, provided in the center of the stirrup 15, housed between the pallet 8 and the rectilinear lateral edges of the stirrup a place greater than that required by the thickness of the levers 18 and 19, in such a way that the encounter between the pallet 8 and that of these levers which is selected does not take place only after the throttle valve has opened sufficiently to pass from idling to a suitable speed.

 It can also be seen in the figures that the levers 18 and 19 are extended internally by parallel cheeks and facing 45 and 46 preventing the transverse movement of the pallet 8 as long as the accelerator pedal has not substantially returned to its position of rest.

 We see in Figures 5 and 6 the pump 2 and its shaft 4 of variable displacement control on which is fixed the lever 5 indicated above. On the face of this pump 2 perpendicular to the axis 4 is fixed by means of screws a T-shaped plate 47, the two lateral branches of which include lugs 48 on which the ends of the sheaths 20a and 21a are fixed using conventional adjustment means 49.

 Furthermore, the receiving member 22 indicated above is constituted here by another lever 50, also in the shape of a T, provided with lateral branches 51 on which are fixed, for example by welding, two tubular parts 52 located substantially in the extension one from the other, each part comprising, at its end opposite the other part, a bottom 53 and a. slot 54 cutting both the bottom 53 and the side wall of the tubular part over a certain length from the center.

 Each of these tubular parts 52 contains a return spring 23, kept compressed by means of a plug 55, and each spring comes to press both on the bottom 53 and on the corresponding side of the lever 5 in the rest position.

 The plugs 55 serve to adjust the initial prestress tension of these springs 23, and are themselves held in the adjustment position by needle screws 56 and 57 which can also be used to hang the cables 20 and 21 in the crossed position as seen in Figure 5.

 The action of these cables being, as we have seen, antagonistic, it is clear that, via the cables 20 and 21 and the receiver 22, constituted here by the tilting assembly 50, 51, 52, all tilting movement of one of the levers 18 or 19 around the axis 27 necessarily causes the tilting of the other lever in the opposite direction and by the same amount. Under the effect of the return spring 35, the stirrup 15 therefore tilts until it rests on the two levers 18 and 19 at the same time, and the rest position of this stirrup can be adjusted by the action on the adjustments 49. It may however be preferable to further provide a stop lug 58 on the support 28 to better define the rest position of the stirrup and facilitate the adjustments.

 It is therefore understood that, as long as the selector lever 14 is in the neutral position PM, the paddle 8 being in the middle position as shown in the figures, an action on the accelerator pedal 11 will only have the effect of act on the caliper 15 and control the opening of the gases, without driving the vehicle, as it should.

 If, on the contrary, the selector lever 14 is in the forward operating position AV, the pallet 8 and the lever 14 are offset transversely, downwards in FIGS. 1 and 2, so as to be straddled between the boss 44 of the caliper 15 and the lever 18 for actuating positive displacements. In this case, when the accelerator pedal 11 is actuated, one begins by slightly opening the gases by action on the boss 44, as explained above, then, after this slight delay, one continues to actuate the opening of the gases by the caliper 15, and simultaneously the cable 20 is pulled by the lever 18, which causes the progressive tilting to the right of FIG. 5 of the receiving member 22, which in turn acts on the lever 5 controlling the displacement of the pump for increasing speed in forward.

 However, this last action occurs via the springs 23, so that, if the load on the wheels and the hydraulic motors 1 of the vehicle is too great, the hydraulic back pressure causes an increase in the reaction on the lever 5, as explained above, which has the effect of causing the compression of the spring 23 on the left side of FIGS. 5 and 6, as soon as this reaction exceeds the prestressing value of this spring, this compression being proportional to the importance of this reaction. This therefore has the effect both of reducing the hydraulic pressure in the connecting pipes of the motors 1 to a non-dangerous value, and on the other hand of reducing the torque taken from the motor shaft 3 so that this torque does not never exceeds the maximum value that this engine can provide under the present conditions of gas opening.

 Naturally, when the selector lever 14 is switched to the reverse AR position, the same phenomenon occurs with the lever 19 and the negative displacements.

 It can therefore be seen that, without any expensive hydraulic device, the invention makes it possible, using a mechanism which is very simple to produce and very economical, to ensure both safety and fully automatic operation of the vehicle.

Claims (5)

 1. Hydrostatic automatic transmission for a vehicle, comprising a displacement pump (2) with variable displacement comprising a drive shaft (3), permanently driven by the engine shaft (6) of the vehicle, and a member (4, 5) variable displacement control having a neutral rest position with zero displacement, corresponding to the neutral point of the transmission, on either side of which there is an adjustment range for increasing positive displacements corresponding to the forward movement of the vehicle, and a negative displacement range corresponding to reverse gear, this pump being hydraulically connected in closed circuit on one or more hydraulic motors (1) with fixed displacement, driving the driving wheels of the vehicle, this pump being of such a type that when said displacement control member (4,5) is biased in one direction or the other from its neutral position, it is subjected to a reaction tending to bring it towards its neutral position, this reaction being proportional to the resistant torque encountered at the wheels, the control of this transmission including an accelerator pedal (11) and a selector lever (14) having neutral (PM), forward ( AV) and reverse (AR),  characterized by the fact that it further comprises  a double displacement member (8,24) capable of being displaced in a longitudinal direction (9) from a rest position under the effect of an appropriate control (10) coming from the accelerator pedal ( 11), and to be moved in the transverse direction (12) under the effect of an appropriate remote control (13) from the selector lever (14) to take three successive transverse positions corresponding respectively to the forward travel positions , neutral and reverse gear of the selector lever ;;  a member (15) for actuating the throttle valve, movable in the abovementioned longitudinal direction, driven at the same time as the double-displacement member (8,24) in its three transverse positions, and actuating in turn by a transmission remotely (16) the control (17) of the throttle valve of the vehicle heat engine;  a member (18) for actuating positive displacements for forward travel, capable of being driven in said longitudinal direction (9) by the double-displacement member (8,24) only when the latter is in its transverse position forward;  a negative displacement actuation member (19) capable of being driven in said longitudinal direction (9) by the double displacement member (8,24) only when the latter is in its transverse position reverse;  the two aforementioned displacement actuating members (18,19) being connected remotely by appropriate transmissions (20,21) and in an antagonistic manner to a receiving member (22), which in turn actuates the member (4, 5) for controlling the variable displacement of the pump by means of an elastic device (23) allowing a position difference between the receiving member (22) and the proportional displacement control member (4,5) to the above reaction.  2. Transmission according to claim 1,  characterized by the fact that said longitudinal displacements of the double displacement member (8,24,26), of the gas actuation member (15), and of the two displacement control members (18,19) are pivoting movements around a common axis (27), and that the transverse movement of said double-displacement member (8,24) is a pivoting movement around an axis (25) perpendicular to the previous one.  3. Transmission according to one of the preceding claims,  characterized in that in the rest position of the accelerator pedal (11), the double displacement member (8,24), in each of its forward and reverse positions, is at a certain distance from the corresponding displacement actuator (18,19) by virtue of a boss (44) provided on the gas actuation member (15), so that the displacement control only intervenes '' after a minimum opening of the throttle valve.  4. Transmission according to one of the preceding claims,  characterized by the fact that it comprises a locking means (45, 46) preventing said transverse displacement of the double displacement member (8) as long as the longitudinal displacement (9) has not returned to the vicinity of its position of rest.  5. Transmission according to one of the preceding claims,  characterized in that said elastic device interposed between the receiving member (22) and the displacement control member (5) comprises two adjustable preload springs (23) mounted in opposition, so that said position deviation cannot take a non-zero value only when said reaction exceeds the prestressing value of said springs (23).