FR2658259A1 - Hydromechanical vehicle transmission with independent regulation of the speed and of the torque of each wheel - Google Patents

Abstract

The transmission according to the invention is of the type comprising, between a heat engine (1) and driving wheels, a primary variable cylinder-capacity hydrostatic element (7) driven by the heat engine, at least two variable cylinder-capacity secondary hydrostatic elements (7) connected up in parallel with the primary hydrostatic element by a closed two-branch hydraulic circuit, each of the secondary elements being connected to one of the three components (9) of a planetary gear train, the second component (10) of which drives one of the wheels of the vehicle, and the third (8) is under the control of a mechanical shaft (5) capable of being immobilized by a brake (4) or of being driven by the heat engine when a clutch (3) is engaged. It is characterised in that a command and control system regulates each of the positive or negative cylinder capacities of the secondary hydrostatic elements, thus causing the torque and the speed of each of the wheels to vary independently of one another.

Description

Hydromechanical vehicle transmission with independent regulation of the speed and torque of each wheel
The present invention relates to a hydromechanical transmission for a vehicle comprising between a heat engine and driving wheels a primary hydrostatic element, rotating, with variable displacement, driven by the thermal engine, at least two secondary hydrostatic elements rotating with variable displacement connected to the element primary by a closed two-branch hydraulic circuit, the secondary elements all being connected in parallel to this circuit, each of these secondary elements being connected to one of the three components of a planetary train, the second component of which drives one of the wheels of the vehicle and the third is under the control of a suitable mechanical shaft
to be immobilized in rotation under the control of a brake or to be driven by the heat engine when engaging a clutch, applying the brake and disengaging the clutch allowing purely hydrostatic operation of the transmission during which the vehicle speed can reach a first predetermined limit value, while the release of the brake and clutch engagement allows hydromechanical operation of the transmission during which the vehicle speed can increase up to its maximum.

 Hydromechanical transmissions of this type have not made use of the many possibilities that their architecture allows and that modern electronic computers operating in an "intelligent system" (name that has become classic) are likely to provide.

 The present invention specifically proposes to remedy this shortcoming and, to do this, it relates to a hydromechanical transmission of the type mentioned above which is characterized in that each of the secondary hydrostatic elements is connected to a wheel (or to a group of two neighboring wheels) and in that monitoring and control means are provided for adjusting the displacement of each of these secondary elements thus varying the torque and the speed of each of these wheels, independently of one another, so as to during the acceleration, cornering, braking, respect the kinematic and dynamic laws that have been programmed in the control and command system which has for its object the automatic driving of the transmission.

 This set of provisions allows speed of evolution, agility in rapid maneuvers on the most difficult terrains, which considerably improve the mobility, performance and safety of the vehicle. The control and command system also acts on the injection of the engine and on the displacement of the primary hydrostatic element to obey the orders of the pilot while maintaining as much as possible the operation of the engine in the area of minimum consumption.

 During operation, whether in purely hydrostatic mode, i.e. brake on the tight mechanical shaft or in hydromechanical mode, ie when the third element of each of the planetary trains is driven by the heat engine, the torque provided by l 'one of the secondary hydrostatic elements is always in the same proportion with the torque on the wheel which corresponds to it. This is a property of planetary trains. This means that if the secondary hydrostatic element is likely to provide the wheel with the torque corresponding to the slip limit on the most gripping terrain, it will be able to provide whatever the speed. of the vehicle a braking torque corresponding to this adhesion limit provided that the pressure in the hydraulic circuit is the same.

 The transmission and its control and command system are then able to manage traction and braking at all vehicle speeds.

 In hydromechanical mode, that is to say when the third element of the planetary trains is connected to the motor, which will provide it with the torque necessary for traction. On the other hand, in the event of braking, the brake located on the mechanical shaft will intervene and its control will be modulated by the control and command system, so as to balance in the planetary trains the different braking forces regulated by the elements. hydrostatic.

The operation of the transmission and its control and command system will therefore be confirmed in the description below: -
The monitoring and control system is informed of the state of the engine transmission as well as the wishes of the pilot by at least the sensors detecting the values below
- accelerator position
- steering wheel position
- position of the fuel injection rack
- brake position
- pressure in the hydraulic circuit: P
- speed of wheel NO 1 and wheel NO 2 and
wheel NO 3 and wheel NO 4 etc.

- motor speed
- possibly in addition we may have an interest in
know the displacement of the hydraulic element
secondary on wheel NO 1, on wheel NO 2 etc.

to be able to control them in a closed loop,
me the displacement of the primary element
- the speed of the vehicle with respect to the ground, otherwise we can take as a reference the average wheel speed or the speed of the slowest in traction and the fastest in the event of braking.

The control and command system acts on different actuators to adjust to the minimum
- the displacement of the primary element
- the displacement of each of the secondary elements
- fuel injection into the engine
- the brake pressure of the mechanical brake
- the clutch
The operating laws to be introduced into the memories of the control and command system are at a minimum.

- The economic operating ranges of the engine
- The conditions for switching from hydrostatic mode to hydromechanical modes, which can be several if several speed ratios are given between the engine and the mechanical shaft.

 - The laws that govern the speed and acceleration of the vehicle depending on the position and movement of the accelerator.

- The laws which govern the deceleration of the vehicle according to the position (or the effort) awarded to the brake
- The value of the hydrostatic pressure P which can be constant whatever the speed of the vehicle or function of this speed.

 - Laws modifying the speed of each of the wheels according to the position of the steering wheel and possibly the speed of the vehicle.

 Possibly, this law can incorporate the fact that the vehicle drives at high speed only by steered wheels and at low speed and even when stopped by significant relative movement going as far as reversing the movement on the left and right wheels, causing a pivot similar to that of a track.

 - The laws relating to the evolution of the cubic capacity of the primary element within each of the operating modes, and that relating to the evolution of the cubic capacity of the secondary elements to respect on the one hand the difference in speed of the imposed wheels or prohibited whether in traction or in braking and on the other hand the available power.

 An embodiment of the present invention will be described below by way of nonlimiting example with reference to the appended figures which schematically represent a system according to the invention.

 Figure 1 shows a 4-wheel drive transmission (but they could be more numerous) equipped with various sensors and actuators connected to the control and command system which will advantageously contain one or more microprocessors and memories necessary for proper operation.

 Figure nO 2 represents the diagram of the hydraulic connections between the hydrostatic systems which are not on figure nO 1 so as not to overload it.

 FIG. 3 diagrammatically represents the control and command theme and more particularly the inputs and outputs of this system and in particular the steering wheel of the brake and accelerator pedals which are not in the other figures.

 A motor 1 drives on the one hand a static hydra system with variable flow 2 and on the other hand the primary of a clutch 3. The secondary of this clutch drives a mechanical shaft 5 either directly or via a gearbox. 6 speed multi-speed.

 This mechanical shaft 5 can be immobilized by a brake 4. The mechanical shaft 5 drives, for example by means of bevel gears 6 6'6 "ù6" ', the crowns 8 8'8' '' planetary trains of each wheel.

These are driven (directly or via reducers 11 11'11''11 '' ') by the satellite gates of these planetary trains.

The solar panels of these trains 9 9'9''9 '''are driven by the secondary hydrostatic systems 7 7'7''7'':
In Figure 2 there is shown the circuit of
hydraulic connection between hydrostatic elements
so as not to overload figure nO 1. This circuit of
connection advantageously has an accumulator 12 and
a discharge valve 13 which can be adjustable in two
positions corresponding to traction and braking.

The different sensors required for the function
the control and command system are shown
shown in Figures 1, 2 and 3.

In figure 1
in 13 the engine speed sensor
at 14 the fuel injection position sensor
at 15 the system displacement position sensor
primary hydrostatic
in 16 16'16''16 '''the cylinder position sensors
feed of each secondary hydrostatic system
in 17 17'17''17 '''the speed sensors of each
wheel
at 18 the pressure sensor P of the hydraulic circuit.

In figure 3
in 19 the vehicle speed sensor relative to the ground
at 20 the steering wheel position sensor
at 21 the position of the brake pedal or the pressure of the
brake system
in 22 the position of the accelerator
The different actuators receiving orders from
control and command system are shown in --- the figures.

In Figures 1 and 2 at 23 the regulating actuator
the displacement of the primary hydrostatic element
in 24 24'24''24 '''the actuators regulating the displacements
secondary hydrostatic elements
In Figure 1 at 25 the injection actuator
fuel
at 26 the metering valve regulating the brake pressure
of mechanical shaft.

at 27 the actuator enabling the clutch of the mechanical shaft to be actuated
In FIG. 2 at 28 an actuator capable of detaching the discharge 29 from the hydraulic circuit in the event of the vehicle braking. In fact, in the event of braking, the displacement of the primary hydrostatic element being reduced and the secondary hydrostatic elements being able to discharge at high pressure P; this will pass through the discharge which in traction is tarred to a slightly higher safety value. .

 An accumulator 12 participates in the stabilization of the pressure P or even can serve as an energy accumulator if it is large enough.

 We will now describe the operation of this system.

 1) Operation in purely hydrostatic mode.

 The transmission operates in purely hydrostatic mode when the brake 4 is applied and the clutch 3 disengaged.

In traction, the primary hydrostatic element acts as a variable flow pump and pressurizes the hydraulic circuit. The secondary hydraulic elements act as motors and drive the wheels through the planetary trains which, their crowns being stopped, are simple reducers
In a straight line, the control and command system must maintain the wheels at the same speed, if one of them slips due to lack of grip, the displacement of its hydraulic motor will be reduced,
When cornering the speeds required for the wheels inside and outside the corner will be different and will take into account the path traveled by these valleys on their trajectory.

 The system may also impose a wheel slip on the ground, laterally, in order to effect a pivot by reversing the displacements of the hydrostatic elements of the right wheels and of the left wheels, regardless of whether or not there will be steered wheels. If there are no steered wheels, the direction will be ensured by a speed difference imposed between the right and left wheels in the manner of a tracked machine.

 The system is applicable in accordance with the invention in the case where the wheels are replaced by track sprockets.

When braking, the primary hydrostatic element will have its cylinder capacity reduced, or even canceled if an engine brake is not sought. The secondary elements will become pumps and will flow according to the setting of their displacement through the discharge 29 slightly untied by the actuator 28.

 The also the wheel speed will be controlled and if one of them accelerates the displacement of the corresponding hydrostatic element will be reduced. The system therefore has an anti-slip action, also under braking.

In parallel with these regulations which characterize the transmission, the control and regulation system conventionally receives orders from the pilot who measures his speed and his acceleration by the so-called accelerator pedal and his deceleration by the brake pedal. He interprets his orders, compares them to the state of the moment and actuates the racks and displacements of the hydrostatic elements to place the engine preferably on its curve of lower consumption.

 In the case where the accumulator 12 is designed to receive and return energy in the form of a certain volume of oil under pressure, this can be filled during braking and add energy to that of engine 1 at during acceleration, emptying into the circuit.

 2) Operation in a hydromechanical mode.

The transmission operates in a hydromechanical mode when the brake 4 is released and the clutch 3 engaged.

The mechanical shaft is in rotation driven by the motor in a chosen ratio inside the gearbox 6.

The movements of this mechanical shaft and of each secondary hydrostatic element are added algebraically in the planetary trains to drive each wheel. Note that the speeds of the secondary hydrostatic elements can be positive or negative but that, as already noted, the torques on the wheels are always proportional to the displacements of these hydrostatic elements whether they are positive or negative, as long as the pressure P is constant.

 I1 nty therefore has no difference in principle in the management provided by the central and regulation system and it is a characteristic of the invention.

 At high vehicle speeds, the power passing through the hydrostatic branch may be small and even in some cases zero (secondary elements stopped, zero flow) the regulation will remain the same and the torque on each wheel and therefore its speed always controlled and controlled at through the displacements of each secondary hydrostatic element.

 However, unlike operating in purely hydraulic mode in the event of braking, part of the energy must be dissipated in brake 4 which will intervene, controlled by the actuator 26.

 The braking torque regulation will be obtained as in pure hydraulic operation, but the mechanical shaft no longer stopped by the brake 4 will tend to drive the motor 1 at high speed and it is obvious that the engine brake will not be sufficient . An engine speed law will therefore be imposed during this braking and this speed will be regulated by the value of the holding torque of the brake 4 thanks to the actuator 26, under the dependence of the control and regulation system.

The cornering operation also does not differ in principle from that in the purely hydraulic mode.
Different speeds will be imposed on the exterior and interior wheels when cornering. In the event of slipping and therefore a fall in grip, the torque on the faulty wheel will be automatically reduced by a drop in the displacement of its hydraulic element.

 The interest of the invention therefore appears on the one hand in the fact that the laws of regulation of the system remain practically the same whatever is the mode of operation in which it is found and on the other hand in the control of grip of the vehicle in all its evolutions from the same regulatory laws and the same means of action.

Claims (6)

 1. Hydromechanical transmission for vehicle, comprising between a heat engine (1) and drive wheels, a primary hydrostatic element with variable displacement (2) driven by this engine, at least two secondary hydrostatic elements with variable displacement (7) connected in parallel to the primary hydrostatic element by a closed two-branch hydraulic circuit, each secondary element rotating one of the three components (9) of a planetary gear, the second component (10) of which drives one of the vehicle wheels and the third ( 8) is under the control of a mechanical shaft (5) able to be immobilized in rotation under the control of a brake (4) or to be driven by the heat engine in one or different ratios during engagement dtun clutch (3), the brake application and disengagement of the clutch allowing a purely hydrostatic operation of the transmission during which the vehicle speed can reach reaching a first predetermined limit value, while the release of the brake and the engagement of the clutch allows one, or, thanks to a gearbox (6)> several hydromechanical operating modes of the transmission to be faster and faster, characterized in that each of the secondary hydrostatic elements 7 7 '7' '7' '' etc ... is assigned to a wheel and in that monitoring and control means are provided for adjusting the positive or negative displacement of each of these secondary elements thus varying the torque and the speed of each of the wheels independently of each other so as to respect, during acceleration, cornering, braking, the kinematic and dynamic laws programmed in the control and command system which has as its object the traction control of the wheels and the optimized automatic driving of the vehicle during all of its developments, this while maintaining a predetermined pressure P dan s one of the branches of the hydraulic circuit.  2. Transmission according to claim 1 characterized in that an accumulator 12 is capable of accumulating energy in the form of oil under pressure and of restoring it according to the laws of the command and regulation system.  3. Transmission according to one of claims 1 or 2 characterized in that the control and command system makes it possible to make pivots by imposing speeds opposite to the right and left wheels while retaining-steered wheels for cornering. faster vehicle speed.  4. Transmission according to one of claims 1 or 2 characterized in that the control and command system provides steering, without steered wheels, by imposing a difference in positive or negative speeds between the right and left wheels, in the manner of a tracked vehicle, at all vehicle speeds.  1 5. Transmission according to one of claims 1 or 2 characterized in that the transmission and the counter and control system provide the traction traction, braking and turning functions not on wheels but on sprockets of the track.  6. Transmission according to any one of claims 1 to 4 characterized in that each secondary hydrostatic element, associated with its planetary gear and the mechanical shaft, drives not a single wheel, but two neighboring wheels connected by common kinematics .