Hydrostatic driving device for a motor vehicle and method for filling this driving device

(42) Date of commencement of the patent: 15. 9.1992 (45) Date of issue: 26. 4.1993

<td>(56) Documents:</td><td>(73) Patent owner:</td>

<td>WO-Al-87/01993 DE-OS 2551580 DE-OS 3514375 EP-A1 0025910 DE-OS 2221551</td><td>ECOMOBIL SOCIETY FOR ECOLOGICAL TECHNOLOGIES FOR VEHICLES, SOCIETY MBH A-1010 VIENNA (AT).</td>

<td></td><td>(72) Inventor:</td>

<td></td><td>THURNER JÖRG ING. VIENNA (AT).</td>

(54) HYDROSTATIC DRIVE DEVICE FOR A MOTOR VEHICLE AND METHOD FOR FILLING THIS DRIVE DEVICE

CQ (57) A drive device for a motor vehicle, wherein a hydrostatic hydraulic motor is provided for driving the wheels, the pump driven by an internal combustion engine, conveys the pressure fluid from a low pressure accumulator into a high pressure accumulator, is driven via the intermediate high-pressure accumulator with hydraulic fluid, wherein the braking energy occurring during braking of the vehicle is exploitable via the hydraulic motor acting as a pump for charging the high-pressure accumulator, is characterized the hydraulic motor (10) is equipped with an externally adjustable swivel disk and is in direct bidirectional connection with the high-pressure accumulator (8), the high-pressure side in the hydraulic motor (10) is always arranged at the same hydraulic connection of the hydraulic motor (10) both during acceleration and during braking of the motor vehicle, and that the low pressure accumulator (17) is tightly sealed on all sides and is under a relation to the atmospheric pressure slightly increased internal pressure.

AT 395 960

R 16 R

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AT395 960B

The invention relates to a hydrostatic drive device for a motor vehicle, wherein at least one hydrostatic hydraulic motor is provided for the drive of at least two wheels on at least one axis, that of at least one pump driven by means of an internal combustion engine and / or an electric motor, conveys the pressure fluid from a low pressure accumulator into a high pressure accumulator, is driven via the intermediate high-pressure accumulator with hydraulic fluid, wherein the braking energy accumulating during braking of the vehicle is exploitable via the hydraulic motor acting as a pump for charging the high-pressure accumulator and wherein the drive connection from the internal combustion engine and / or electric motor to the wheels of the motor vehicle takes place exclusively by hydraulic means. Such drive devices for a motor vehicle, by means of which, in particular in city traffic d. H. In the so-called STOP-GO operation, both the fuel consumption and the exhaust and noise can be drastically reduced, but the driving dynamics, d. H. the acceleration and braking capacity of the motor vehicle, should be the same as in previous motor vehicles or even improved against these are already described several times in the literature or been proposed. Despite the undeniable advantages of such drive devices, however, these have not yet been successful in practice.

This is partly due to the complicated structure of these known drive devices (see, for. B. DE-OS 35 14 375), in which, for example, the high pressure side of the hydraulic motor at the transition from accelerating to braking and vice versa must be switched by means of several valves, and on the other hand to the associated problems of cavitation. These cavitation problems are caused by the high pressures occurring in such pressure devices in the printing or Hydraulic fluid and the high flow velocities and amounts in connection with the air always contained in the hydraulic fluid (approx. 12 %) favors; Namely, this air forms especially on sharp edges, such as valves and sliders or sharp line creases, bubbles that implode due to the high pressure (autoignition), whereby material particles are torn away from these sharp edges and eventually malfunction occur after a relatively short time.

In the known from the aforementioned DE-OS 35 14 375 drive device is also different from the present invention to hydraulic motors with constant displacement, which are not driven by an intermediate high-pressure accumulator with hydraulic fluid.

From WO-Al-87/01993 drive devices for motor vehicles with heat engine and hydraulic drive with storage capability for the braking energy are known in which the hydraulic drive only has the character of an auxiliary drive, the drive shaft of the heat engine is constantly connected to the drive axle of the vehicle. Similarly, the vehicle drive known from DE-OS 25 51 580 is constructed, since the internal combustion engine is in mechanical communication with the drive axle via a Differentialsummiergetriebe These known drives do not allow the flexibility and efficiency of the initially defined drive, in which the drive connection from the internal combustion engine and / or electric motor to the wheels of the motor vehicle takes place exclusively by hydraulic means, fully exploit.

Furthermore, in the previously known drive means for maintaining a certain base pressure or feed pressure during braking operation, the hydraulic motor, a feed pump including the biasing valve must be connected in parallel.

The aim of the invention is an improvement of the known drive means to the effect that they are suitable for the rough everyday operation of a motor vehicle and less prone to failure u. primarily by saving on components that are particularly prone to cavitation.

This is achieved according to the invention by the combination of the following per se known features in the drive device described in more detail below: the hydraulic motor is equipped with an obliquely or hydraulically adjustable obliquely or externally Swivel disc equipped and communicates with the high-pressure accumulator in a direct bidirectional connection, the high pressure side is always arranged at the same hydraulic connection of the hydraulic motor both when accelerating and when Biemsen the motor vehicle, the low-pressure accumulator is tightly sealed on all sides and is under a relative to the atmospheric pressure something, z. B. by 2 to 5 bar, increased internal pressure and the high-pressure accumulator is arranged entirely inside the all-side tightly sealed low-pressure accumulator, wherein the useful for the pressurized fluid volume of the low-pressure accumulator equal to or greater, preferably by 10 to 20% greater than that usable for the hydraulic fluid Volume of the high-pressure accumulator is

It saves all changeover valves and also the feed pump including the preload valve, which results in a weight saving in addition to the reduction of the number of components susceptible to failure; by the increased internal pressure of the low-pressure accumulator or The bias in the system also reduces cavitation problems. Furthermore, a space saving is achieved, as well as lying between the individual elements of the high-pressure accumulator diabolo-shaped dead spaces are useless volume for the low-pressure accumulator usable. Furthermore, in the case of leaks in the high-pressure accumulator, the low-pressure accumulator can immediately serve as a collecting container for the leakage fluid. Finally, in this arrangement also still a highly desirable temperature or Heat balance between the high pressure and the low pressure accumulator instead. On average, namely, the actual pressure element of the high-pressure accumulator, which in z. B. by means of a flexible membrane trapped gas bubble, rather than it

-2AT395 960 B heats up, since the process of pressure reduction on average takes place in shorter time periods than that of the pressure build-up (hydraulic motor has much higher performance than the combustion or Primary motor). Since the pressure fluid in the low-pressure vessel usually flows back at a higher temperature, this excess heat can be delivered to the high-pressure vessel, whereby a pressure loss due to cooling in the same is avoided and cooling of the liquid flowing back into the low-pressure vessel can be at least partially eliminated.

A further development of the invention is characterized in that the high-pressure accumulator is completely surrounded by a tear-resistant arranged within the low-pressure accumulator, the hard parts of the high-speed accumulator being optionally restrained. Thus, in the case of bursting of the high-pressure accumulator, z. B. as a result of an accident involving the motor vehicle equipped with the drive device according to the invention, all hard parts of the high-pressure accumulator are retained.

The drive system according to the invention is particularly well suited for a motor vehicle with four-wheel drive, in which case a separate, associated hydraulic motor is provided for each of the vehicle wheels in a manner known per se, and wherein signals given by sensors or control elements per wheel are converted into correspondingly different signals by means of a computer , same inclinations of the individual swash plates can be implemented. With this configuration, both a traction control and an anti-lock braking system, and locking differentials front and / or rear and central differential lock can be realized in a simple and elegant way.

The invention also relates to a method for filling the drive device according to the invention with hydraulic fluid, which is characterized in that in a conventional manner to the first still unpressurized pressure or Hydraulic fluid is applied a vacuum to remove the air contained in the hydraulic fluid ', and that then, while avoiding access of air, this liquid is filled in the closed, previously filled with nitrogen drive means, optionally the low-pressure accumulator is connected to a nitrogen source under one opposite the atmospheric pressure something, z. B. around 2 to 5 bar, increased pressure. By removing the air from the hydraulic fluid and thus the required for the occurrence of cavitations (implosions) oxygen or Replacement of the same by the non-combustible nitrogen, the occurrence of harmful cavitations whose probability has already been greatly reduced by the pressure bias of the system, completely prevented.

Basically, the degassing of pressure or hydraulic fluid in a vacuum by EP-Al 0 025 910 and DE-OS 22 21 551 is known per se.

The invention will now be described in more detail with reference to the drawings; 1 shows a schematic circuit diagram for an exemplary embodiment of a drive device according to the invention for an axle of a motor vehicle, FIG. 2 shows a cross section through a combined high-low-pressure accumulator along the line II-II in FIG. 3 and FIG Longitudinal section through the same combined high-low pressure accumulator along the line (III-III) in Fig. 2nd

In the in Fig. 1 shown drive means drives by means of from the outside (gas or Brake pedal) hydraulically or electrically adjustable oblique or Swash plate control or variable hydrostatic hydraulic motor (10) arranged on an axis two driven wheels (R) in a conventional manner via a propeller shaft and a differential gear (16), with the π-shaped symbol in the hydraulic motor (10) to the differential gear (16) leading shaft is characterized a mechanical drive connection, which may have elastic or gimbal properties.

Between the combustion or primary engine (1) and driven by this (main) pump (2) for the hydraulic fluid or the hydraulic oil, an analog elastic or gimbal shaft is provided. It goes without saying that parallel to the (main) pump (2) further (secondary) pumps can be connected, which are driven by other (secondary) motors (eg a solar drive) (not shown).

It is assumed that the entire device filled with hydraulic oil is almost without pressure, d. H. To maintain this low pretensioning pressure, the low-pressure accumulator (17) can be connected to a pressure source (17 *) of 2 to 5 bar, which preferably contains nitrogen , It must therefore first the internal combustion engine (1) are started to promote hydraulic fluid from the low pressure accumulator (17) via the pump (2) and the check valve (5) in the high-pressure accumulator (8). The in the volume (8 ') of the high-pressure accumulator (8) funded hydraulic fluid presses of volume (8') by an elastic membrane, a piston od. like. separated gas volume (8) (z. B. Nitrogen), which through the closable opening (8 ') on or can be refilled together. As soon as the high-pressure accumulator (8), from whose outlet a safety valve (7) leads to the low-pressure accumulator (17), the required pressure, which is for example of the order of 200 to 400 bar, exhibiting the motor vehicle can be set in motion. For this purpose, the check valve (3) is magnetically unlocked when depressing the accelerator pedal of the motor vehicle and the hydraulic fluid released the way to the hydraulic motor (10).

The indicated by the arrow symbol in the hydraulic motor (10) adjustment of the inclined or swash plate of the hydraulic motor (10) is made by the accelerator pedal in the range of 0 to A for the acceleration phase depending on the required or desired torque on the wheels (R). For this purpose, a not shown, usual operative connection (electric, hydraulic, mechanical od. Like.) Between the accelerator pedal and the swash plate control is provided.

-3AT 395 960 B

Such an adjustable hydraulic motor (10) is also referred to as a hydrostatic hydraulic motor with secondary control. The check valve (9) is therefore provided to shut off the hydraulic fluid inlet leak-free when the vehicle is stationary

The pressurized fluid passing through the hydraulic motor (10) in the acceleration phase, the energy of which is converted into mechanical drive energy effective at the wheels (R), flows into the low-pressure accumulator (17), optionally through a cooler (not shown). However, as a result of the heat balance between these two accumulators, which can be achieved by nesting the high-pressure (8) and low-pressure accumulator (17), such a cooler can be saved in many cases.

Further, due to the biasing pressure (2 to 5 bar) in the low-pressure accumulator (17) and due to the withdrawal of the oxygen from the hydraulic fluid and replacement thereof by nitrogen according to the filling method of the hydraulic device according to the invention, the risk of cavitation occurrence is reduced to practically zero and it can Also provided in already proposed cases supply or biasing pumps parallel to the hydraulic motor (10) accounts.

In the freewheeling phase, the arrow symbol remains at the hydraulic motor (10) in the O position and, accordingly, the swash plate of the hydraulic motor (10) in its straight neutral position, so that the hydraulic motor (10) acts neither as a motor nor as a pump. The accelerator pedal of the motor vehicle is at rest and therefore the check valve (9) is closed and locked. There is no flow of hydraulic fluid in the hydraulic motor circuit.

In the deceleration phase, the swashplate of the hydraulic motor (10), which is operatively connected to the brake pedal of the motor vehicle in the adjustment range from 0 to B (see arrow symbol of the hydraulic motor), is adjusted in this way. the hydraulic motor (10) now acts as a pump for the hydraulic fluid driven by the wheels (R) of the motor vehicle which are driven in the same direction as before. which latter is sucked from the low-pressure accumulator (17) and fed back via the valve (9) into the high-pressure accumulator (8) until it is fully charged.

It should be noted that the high-pressure side of the hydraulic motor (10) is always arranged at the same hydraulic connection of the hydraulic motor (10), both during acceleration and during braking of the motor vehicle, so that any switching valves and complicated wiring omitted. Rather, the hydraulic motor (10) is in direct bidirectional connection with the high-pressure accumulator (8).

When the maximum accumulator pressure in the high pressure accumulator (8) is reached in the braking phase, the hydraulic fluid is returned via the safety valve (7) in the Niederdrucksp eicher (17), the braking or deceleration effect is fully maintained, since the now working as a pump hydraulic motor (10) must work against the maximum pressure of the high-pressure accumulator (8).

In this way, the kinetic energy of the motor vehicle is used to Auffullen the high-pressure accumulator (8) during each braking operation and fully exploited apart from the low friction and flow losses. This energy is then fully available, for example, for an acceleration process following the braking process, whereby u. a. the considerable fuel savings by the Ajntriebssystem invention gives; The latter also because the internal combustion engine (1) - if it is ever needed to fill the high-pressure accumulator (8) - is always operated at a constant speed and in the most favorable torque range.

In Fig. 2 is a cross section and in Fig. 3 a horizontal longitudinal section through a combined high-pressure accumulator, shown, in which the existing of three cylindrical containers high-pressure accumulator (8) is arranged entirely within the mutually tightly sealed, parallelepiped-shaped low-pressure accumulator (17). With (8 ') is again filled with hydraulic fluid volume of the high pressure accumulator (8), with (8) by an elastic membrane from the volume (8') separated gas volume and with (8 ') one with the gas volume (8) in combination standing closable opening referred

The high-pressure accumulator (8) is entirely surrounded by a tear-resistant net (18) arranged inside the low-pressure accumulator (17), which retains the hard parts of the high-pressure accumulator (8) in the event of the bursting of the high-pressure accumulator (8) during an accident.