VEHICLE WITH HYDROSTATIC TRANSMISSION AND STEERING ELEMENT BY GUIDABLE WHEELS AND SLIDE STEERING ELEMENT

The invention concerns motor vehicles with independent wheels, driven via hydrostatic transmissions of power.

It is known to use hydrostatic transmissions (pumps displacement volumes variables and internal displacements fixed, variable or stepped) for advancing straight vehicles; the direction used is performed using a mechanism, assisted or not, which acts mechanically on the orientation of one or more pairs of steerable wheels. On vehicles to non-steering wheels, it is also known to provide steer loader or "skid 1996b", [...] i.e. by generating differential velocities of wheels, from one side to the other of the vehicle, via means for braking or steering devices that may authorize a recycling of the cornering power and minimize energy losses.

On road, the vehicles with steerable wheels have the advantage, especially in a configuration at high speed, good progress cornering and stability that provides a good level of security. A drawback of these embodiments lies in difficult terrain and maneuverability is manifested by insufficient, due to the not pivot on site or describe turns close tightly. Conversely vehicles with steerable wheels, the vehicles to turn skidsteer have the advantage of a very good off-road but the disadvantage of a poor in skidsteer (or "skid 1996b") at high speed, particularly on road.

The invention aims at providing motor vehicles with independent wheels driven by hydrostatic transmissions, which can be directed optimally in all configurations (off-road, all-path and road) and marry therefor the advantages steering systems with steerable wheels and steer loader, including the ability to pivot at least approximately about the center of gravity of the vehicle, without a disadvantages.

To this end, the invention concerns a vehicle whose wheel drive of each of at least two pairs is driven by at least one hydraulic motor of a hydrostatic transmission power, the inlet and the outlet of each hydraulic motor being connected respectively to a hydraulic fluid supply line at high pressure and a return line in a low pressure hydraulic fluid, vehicle in which pipe supply and return hydraulic motors associated with the wheels mounted on a first side of the vehicle (left side for example) form a first closed-loop while the supply lines and return that are associated with the hydraulic motors in the wheels located on the second side of the vehicle (right side, in the chosen example) form a second closed circuit loop, and wherein the hydrostatic transmission comprises power in each coil of the at least one variable displacement hydraulic pump having an inlet and discharge are respectively connected to the return line and the supply line of the loop considered; characterized in that the vehicle comprises at least a pair of steering wheels and means for connecting, by passages of respective sections adjustable, or isolate from each other on the one hand the supply lines of the two loops and the return lines of the two loops and the vehicle further comprises means for adjusting the vertical displacements of the respective hydraulic pumps identically for configuration of progress in a straight line or cornering by steering wheels and the differentially configuration progress turning by skidding, by mixing two types of steering, or for the pin arrangement about the center of gravity of the vehicle.

In this connection, there is designated by "feed line" and "return" the pipes that play actually this role when the vehicle is powered by the power generation and running straight. The respective roles of said ducts may naturally be interchangeably known manner when the vehicle is decelerating (the transmission working then holding) or cornering (the respective roles of the pipelines are then interchanged on the loop that connects the hydraulic motors arranged on the inner side).

In this way, the invention makes possible the steer loader for the pivoting of the vehicle about its center of gravity and corner radii for the low off-road, by isolating the two loops of the transmission and varying, in known manner and differential, of swept volumes of their respective pumps. The invention allows use of steering wheels on road, e.g. high speed, after full opening by from this lubricating passageway. The present invention allows for the mixing of the two direction types simultaneously or in succession in intermediate zones of operation, by steered wheels and by opening of the abovementioned passages sections adjusted, simultaneous to the differential variation of displacement volumes of the pumps to meet the requirement of a complementary force turning by skidding.

Note that has already been proposed to associate, on a motor vehicle to drive wheels not independent by side, the two principles of direction by mixing a limited steering and a skid but the proposed solution (see EP-A 0 413,206) uses a mechanical differential and is not transposable to hydrostatic transmissions on the layout plan and involves the use of advantages and disadvantages.

Another object of the invention, in a vehicle thus arranged, authorize operation modes in the driving reduced automatically by isolating the motor of the hydrostatic transmission or the motors of the wheel by disengaging deficient mechanically and hydraulically isolating one or more pairs of wheels intentionally and selectively to optimize the operating conditions of the transmission (yields, reliability, and so on) in accordance with the configurations encountered.

To this end, the vehicle according to the invention is further characterized in that the driven wheels are mechanically and hydraulically disengageable, each wheel which can be separated from the rest of the transmission by mechanical devices internal or external to the hydraulic motor which is preceded and followed by a fluid isolator so as to isolate it automatically when the wheel driven by this motor or engine itself becomes impaired or during an intent to reduce the number of pairs of driving wheels. The freewheeling of the wheel is performed by any disengagement device placed on the mechanical connection of the transmission to the wheel or made directly in the hydraulic motor itself.

The invention also seek to reduce the width of the vehicle or increasing the volume available in the vehicle body.

To this end, the angular deflection of the steered wheels, from the longitudinal axis of the vehicle, is limited in relation to what is usually encountered for standard vehicles having the same requirements of maneuverability and the integration of the hydraulic motors in the wheels releases a large volume commonly occupied by mechanical instruments of conventional transmissions.

The invention also aims at reducing lost organs ancillary functions for force feeding the hydrostatic transmission.

To this end, the vehicle is further characterized in that a supplement boost is provided by a second pump and operates under pressure as when the need booster is large, the pressure level of the pump being [...] the rest of the time, or else the supplement boost is fed by a pump already installed on the vehicle for another function, the feed pump of the drive motors or fans for example.

Preferably also, the control of the complete transmission, operation of the above means and steered wheels is managed and controlled by at least one micro-processor using one or more adapted software.

The invention will be better understood in light of the following description, in connection with the accompanying drawings, illustrating but not limited to various embodiments of the invention.

The drawings represent schematically:

• figure 1, a vehicle according to a first embodiment of the invention, the hydraulic motors which are accommodated in the wheels;
• figure 2, a vehicle according to a second embodiment of the invention, whose hydraulic motors provided with disengageable reducers are housed in the body of the vehicle;
• figure 3, a vehicle according to a third embodiment of the invention, whose four rear wheels are arranged according to the first embodiment of the invention and whose four front wheels are driven through a wheel drive by a hydraulic actuator formed by the mechanical and hydraulic coupling a first disengageable gear motor and a second hydraulic motor fast, itself represented in Figure 7;
• in Figure 4, the essential components of the vehicle transmission of Figure 1 in general configuration or particular mixed steering;
• in Figure 5, the representation of Figure 4 in a configuration to steered wheels that allows distribution rates on each hydraulic motor taking account of differences in rates of each steering wheel caused by wheel orientation;
• in Figure 6, the representation of Figure 4 in a configuration during turning by skidding or "skid 1996b";
• figures 7 to 9, schemes various variations or additions made to one of the preceding embodiments.

With reference to Figures 1 and 4, a vehicle powertrain comprises two pumps or two groups of pump 1 and 1a continuously variable displacement flow in both directions, driven by distribution means to drawers-tracking 2 and 2a, moved by electric actuators and assisted hydraulically by servo cylinders. To simplify the description, will be designated by "pump" 1 or 1a a pump as well as a pump unit. By loops 3 and 3a hydraulic closed circuit, these pumps 1 and 1a distributes hydraulic fluid flow rates n 4 hydraulic motors each driving wheel 4a and 5 or 5a (not shown in Figure 4). The pumps 1, 1a, the motors 4, 4a and the loops 3 and 3a constitute mirror circuits associated respectively with left side and right side of the vehicle. The features on the right side are distinguished elements located on the left side in that they are accompanied by the letter "has". The pressures established are the result of requirements at the hydraulic motors. Single-as an example, it was assumed that n was equal to 2 x 4 in Figure 1 and Figure 2 x 5 to 4.

6 and pumps 7 (fig. 4) respectively the [...] (the) circuitry (e) and supply flow rates and pressure control required to operate different systems: displacement control pumps and hydraulic motors, control and separation circuits, control brakes c... the pumps 1, 1a, 6 and 7 are driven by a power generation such as an internal combustion engine or a gas turbine 8.

With reference to Figure 8, the booster pump 6 is replaced by a kit of at least two pumps 6b and 6c which reduces the excess flow rate boost by the return of the flow rate of a pump of directly to a reservoir 26. In the case of Figure 8 wherein there would be suppressed the hydraulic motor 43 ventilation and the thermostatic valve 42 which will be described hereinafter. The pump 6b debits permanently towards selectors cramming 37a and 37 under the boost pressure set by the amount of preload on the pressure relief device. The pump 6c debits upstream of a check valve 50 disposed immediately prior to a selector member 45. Depending on the level of the boost pressure, the selector 45 is manned or unmanned and pump flow rate 6c is either directed to the tank 26 with a reduced pressure level to the load losses of this circuit, is directed the booster circuit at boost pressure. The pump shown in Figure 6c may be a pump already installed on the vehicle for another function and does serve as a supplement boost that as the need dictated. In this case, the pump 6c is the feed pump of the drive motors or cooling fans. The pump 6c supplies full rate, in partial delivery, or not supplied by the hydraulic motor 43 fan drive according to the position of the thermostatic valve 42, itself controlled by the temperature of the circuit. Its flow rate, either after the driving of the motor 43, either directly by passing them through the thermostatic valve 42, either from the sum of the outputs derived arrives upstream of the check valve placed just before the selector 45, and is directed to the booster or to the reservoir 26 as previously.

Each loop 3, 3a (Figure 1 and 4) is formed of a high forming pressure supply line 9, 9a and a low pressure return line 10, 10a (the respective roles of these ducts being interchanged in deceleration of the vehicle and thereby retained on the transmission and on the loop inside the turn in "skid 1996b" or cornering by superimposed steering system. The inlet 11 or 11a of each motor 4, 4a is connected to the supply pipe 9, 9a of the loop 3, 3a located on the same side of the vehicle. The output of each motor 12 or 12a 4, 4a is connected to the return pipe 10, 10a of the loop 3, 3a located on the same side of the vehicle. The pumps 1 and 1a will not accept respectively in the supply lines 9 and 9a and aspirations of these pumps 1 and 1a are connected respectively to the return lines 10 and 10a.

The loops 3 left and right 3a defined above can be selectively connected or separated by two members 13, 14 respectively connected to opposite sides of the pumps 1 and 1a symmetrical to one another. More specifically, the member 13 is connected between the supply lines 9, 9a and the member 14 between the return lines 10, 10a. These members 13, 14 which, when open, provide passages of respective sections adjustable, are electrically driven and managed by a micro-processor (not shown) center and they provide, as well as it will be explained hereinafter, items in the "off-road" turning by skidding to a configuration "road" turning by [...] wheels. The combination of both, which leads to a direction hybrid, will be possible in the case of steering angles intermediate wheels with further aid the turn by skid by reduced orientation of the wheels. The members 13, 14 are thus in intermediate position of closure. The closure will be progressive and managed in proportion to complementary torque requirement.

Regulators 15 and 15a, associated with each of the motors 4 and 4a respectively, have three main functions: a function of coupler, an isolator function of the circuit and a governor function to manage the torque on each independent wheel 5, 5a and to prevent the slip, in view of the adherence of each wheel and its torque requirement. These regulators 15, 15a must have a characteristic pressure drops very low in the open position. Isolators 46, of technology more ordinary, represented exemplary detail in fig. 9, will be mounted on the drains to isolate the hydraulic motors of the leakage circuit in case of deficiency of wheels or removal thereof.

The n hydraulic motors 4, 4a (a motor by wheel for the example of Figures 1 and 4) to more displacement volumes are stepped and have means of selecting the displacement volumes (not shown). They are characterized by means for freewheeling, [...] i.e. disengaging mechanical for maintaining the pistons in their cylinders are retracted, and also have low inertia characteristics, particularly with respect to the hydraulic components which, associated with reducing agents, are placed further upstream on the driveline.

The pumps 1, 1a are continuously variable displacement and allow the continuity of the speed of the vehicle at each step change of displacement motors 4, 4a, by rapid readjustment rate, by moving, into its proper position, the tray pumps (since this is, in the example selected, technology pumps tray).

An exchange unit and relief consists of elements 16 and 16a as drawers exchange excess loading, high pressure selectors 17 and 17a, 18a and 18 members for connecting the HP (high pressure) to the BP (low pressure) and a high pressure limiting member 19, unique for the two circuits.

Limitations are ensured over the excess pressure loading by a member 20, on cramming by limiting means 21 and on the steering system by driving the pump 22.7 takes its suction from the output of the booster pump 6.

23 and 24 members, provided or not with means pass-through rate and indicator systems of clogging, filter the circuits. The element 24 receives in particular pollution due to the braking system which is preferably scanned by the oil of the hydraulic circuit. The braking device preferred system is a multi-plate oil-immersed the inwheel. Its cooling is provided by the general circuit of the transmission, itself cooled by its own device 25. The device 25 serves for cooling the circuit and maintains a temperature threshold while dissipating heat.

A plurality of locations is shown in Figure 4, the hydraulic fluid reservoir 26.

Finally, the vehicle includes at least a pair of steering wheels. 1 to Figure, it is assumed that the first, second and fourth pairs of wheels 5, 5a (from the front of the vehicle, which is the top of the Figure) were steered and actuated for example by means of a flywheel and a linkage 27 28 conventional in directions of such or any other device.

According to the embodiment of Figure 1, each drive wheel 5, 5a is equipped with a hydraulic motor 4, 4a housed in this wheel.

The embodiment of Figure 2 differs from that of Figure 1 by the fact that the motor 4, 4a of each drive wheel 5, 5a is provided with a reducer disengageable 29, 29a and is housed therewith in the body 30 of the vehicle.

The embodiment of Figure 3 differs from that of Figure 1 in that only two pairs of wheels 5, 5a are arranged according to the invention, the other two pairs of wheels 35, 35a being entrained in an original way through a wheel drive 36, 36a by coupling a disengageable hydraulic geared to a second hydraulic motor.

The operation of the entire hydrostatic transmission just-described, will be exposed using a clear example of embodiment.

In this example, the swept volume maximum respective main pumps 1, 1a is 285 cm³ / Tr and that of each of the hydraulic motors 4, 4a of 3,600 cm³ / rpm. The displacement of the hydraulic motors 4, 4a varies stepwise and takes the following values: 3,600 cm³[...] tr - 1 800 cm³ tr - 876 [...] cm³ tr - 438 [...] cm³[...] rpm.

In operation at maximum torque, the displacement of the hydraulic motors 4, 4a is 3,600 cm³ / rpm and the pressure is maximum. In advance of the vehicle straight, the speed is limited, in view of the installed power; the displacement pumps 1, 1a is reduced. The increase of the vehicle speed is changed by increasing displacement volumes of the pumps 1, 1a up to their maximum displacement. To provide again the increase in speed of the vehicle, must first reduce the displacement of the hydraulic motors 4, 4a to head 1 800 cm³ / rpm. This first reduction in displacement of the motors 4, 4a will match a halving of the displacement pumps 1, 1a, to the differences in yield near, if the driving speed by the power generation 8 remains constant. Thus to this change of displacement pumps 1, 1a, simultaneous to that of the motors 4 and 4a, the vehicle speed is constant. For continuing the increase in speed of the vehicle, is increased displacement pumps 1, 1a again until the next bearing which corresponds to the maximum displacement of these pumps. Following the bearings will be passed in the same manner up to the maximum speed of the vehicle for which the displacement of the hydraulic motors 4, 4a is minimal (438 cm³ / rpm) and the displacement pumps 1, 1a maximum (285 cm³ / rpm). The role of separation members 13, 14 is disclosed herein.

In the numerical example considered, the maximum torque on each wheel 5, 5a can reach 2,500 [...] and the maximum speed of 500 rpm is reached wheels/minutes.

The regulators 15 and 15a serve:

• couplers in case of removal of one or more hydraulic motors 4, 4a and allow, by providing a system [...]-coring, not flush the (e) (e) during this circuit is deposited;
• of insulators if [...] a (or more) hydraulic motor (e) (e) 4, 4a (mechanical failure or for any other cause [...]); this same device closes the circuit and isolates the hydraulic motor deficient, allowing the vehicle to travel in an emergency mode or reduce the number of driving wheels and the choose to best fit the configuration; this is what was shown schematically in Figures 4, 5 and 6 by the dotted representation of two motors 4, 4a so isolated and regulators 15, 15a associated therewith; another coupler insulator 46, shown in Figure 9, the size of which is smaller and optionally be technology easier because it does not have the same requirements of pressure losses low and regulation, is on the pipeline leaks and supplements to the means 15 and 15a for removal or isolation of motors 4, 4a;
• regulators for improved management of torque on each wheel in particular in the event of slippage, the component 15 or 15a limits the flow by partial obstruction of the passage opening in order to restore the pressure on the main circuit and install the torque on each of the idler wheel 5, 5a according to their own needs.

These members 15, 15a, or even 46, regulating, couple-decoupling and isolation are through-path, thereby avoiding losses when fully closed.

Figure 6 is given in illustration of this example in a turn configuration by skid (off-road for example) or pivot about its center of gravity. The members 13, 14 of Figures 1 and 4 are then fully locked and the transmission operates on two hydraulic circuits identical, independent and symmetrical, crammed, piloted, cooled, filtered and protected by means common service pack. According to the representation of Figure 6, all will pass as if the members 13, 14 and the hydraulic connections connecting the main loops 3 and 3a had disappeared and therefore these organs have been omitted on the character.

To change direction, it will instruct the pumps 1, 1a a displacement varying progressive and differential, in addition on the circuit connected to the exterior side of the curve and in less on the circuit connected to the inner side, to increase and reduce the rates over the hydraulic motors 4, 4a which are respectively disposed to the outside and the inside of the bend. In fact, at each operating point of straight line advancement, may be a corresponding operating point in turn created a gap of displacement pumps, equivalent or not, around the displayed value of the displacement volumes in a straight line.

Figure 5 represents the same transmission in turn configuration by steering wheels. The curve is obtained by a subsequent activation of the control member 27 (Figure 1 to 3) connected itself mechanically to the direction which is preferably hydraulically assisted. The pumps 1, 1a flood then on the same circuit, the members 13, 14 are fully open and flow rates are distributed independently on each of the hydraulic motors 4, 4a according to their need which is variable and given by their speeds themselves imposed by cornering. All out in practice, according to Figure 5, as if the loops 3 and 3a were directly connected to one another by their sides HP and LP. The pumps 1, 1a flood then on a same line pressure which supplies the n set of hydraulic motors 4, 4a.

Figure 4 existing exposures also the transmission configuration mixing of the two possibilities. In this case, the turn is made by wheel steering controlled from the controller 27, on the one hand, and by supplementing obtained by a slip controlled by the differential variation of displacement volumes of the pumps 1, 1a and the simultaneous driving members 13, 14, on the other hand. Turning obtained by wheels pivot, plus the skid accomplished by varying the displacement volumes of the pumps 1, 1a (in principle in addition for the pump is connected to the outside of the bend and in less for the pump connected to the inside of the bend). The members 13, 14 are thus in intermediate position admitting a controlled flow rate, common to both circuits, allowing a pressure difference by partially throttling.

In all embodiments, the hydraulic motors 4, 4a may be high-speed motors, fixed or variable displacement, associated with means for speed reduction and torque multiplication disengageable such as 29, 29a or coupled together to form a system as 40, 41, 38, 39, 36, 46 (fig. 7). The drive system of the four front wheels of the vehicle of Figure 3, represented in Figure 7, constitutes a hydraulic clutch for wide range operation, for applications requiring high transmission ratios. The hydraulic motor 40, the hydraulic motor 41 disengageable by a clutch 39, provides a variable torque, proportional to its displacement varying itself; this torque, multiplied by the reduction ratio of a reduction gear 38, adds to the torque supplied by the hydraulic motor 41. All of these torques is transmitted to the wheels 35, 35a through reducing wheel 36, 36a. The wheels 35, 35a and reducing their integrated wheel 36, 36a are disengageable by a clutch 47.