FR2709453A1 - Optimised hydraulic propulsion chain for an autonomous electric vehicle actuated by batteries - Google Patents

Abstract

The invention relates to an optimised hydraulic propulsion chain for an autonomous electric vehicle actuated by batteries. The said propulsion chain includes a reversible hydraulic transmission consisting of at least one hydraulic motor filled with pressurised oil via hydraulic lines by a variable output hydraulic pump driven by a constant- or non-constant-speed electric motor, the said motor being powered by the batteries via an electromechanical device. The said propulsion chain is optimised in terms of output at low power, noise level, and reversibility in that the pump is a pump with axial pistons including a ball bearing (1) and a needle thrust bearing (2) which are interposed between the pads (4) of the rotating pistons (4) and the swash plate (9) and in that the pads are made of a solid substance. This propulsion chamber, according to the invention, is particularly applicable to electric vehicles. It can make it possible to recover some of the energy of deceleration of the vehicle and send it back to the battery.

Description

TECHNICAL AREA - ECONOMIC ENVIRONMENT
The invention applies in the field of electric vehicles for the use of professionals or the general public. The invention advantageously replaces conventional solutions where the speed variation of the vehicle is electronic and / or mechanical and where the transmission of the rotational movement to the wheels is mechanical.

Transmission can be achieved by assembling modified hydraulic components. It benefits from the experience acquired in hydraulics applied in the agricultural field, public works and industrial machines. In fact, the elements selected respect the ISO9000 quality standard standard.

In addition, the range of components offered is very wide, which allows the invention to meet various needs. It can be used:
- in urban vehicles with low performance and very low cost
- on top of the range vehicles offering very good acceleration characteristics - on
utility vehicles (handling on private sites, transport vehicles for
public services, advertising vehicles, ...)
The process of converting and transmitting energy from the electricity source to the wheels allows continuous operation for a long time. Only the capacity of the on-board source limits the range, but this is not the subject of the invention and may develop independently of the propulsion chain.

A single command makes it possible to vary the speed and acceleration of the vehicle between 0 and the maximum speed, which brings its driving closer to that of a vehicle with an internal combustion engine with automatic gear change.

The economic environment of the invention is very competitive. The latter must allow to take a share of the market of vehicles with thermal engine already manufactured in very large series and it must offer a serious alternative to the traditional electric solution which turns out in 1993 still too expensive and too fragile.

 Thanks to the use of components already mass produced, the electric propulsion chain constructed using the invention costs at first assessment 50% of the price of the conventional electronic solution.

STATE OF THE PRIOR ART
Hydraulic or hydrostatic transmission systems exist in the fields of public works, agriculture and industry. They are also used for making mountain lifts. There are many publications on the subject in the form of bxvets concerning hydraulic components, documentation from manufacturers, press articles describing
The use of hydrostatic transmission for heavy vehicles on railways or public transport with diesel engines.

To our knowledge, there is no publication describing an autonomous light vehicle "with electric propulsion by source of energy inside the vehicle" whose transmission of energy to the wheels is hydrostatic and made up of hydraulic components, nor any work of optimization of the performance of a low-pressure, high-speed transmission enabling this objective to be achieved.

DISADVANTAGES OF THE PRIOR ART
The usual hydrostatic transmission systems transmit the rotation power of a diesel generator or of an electric motor coupled to the public electricity network.

In both cases the speed of rotation is adjustable and the current operating zone is located near the nominal power of the pump and the hydraulic motors. The yield is close to 90% for each element
However, some drawbacks exist:
I - When the operation of the transmission system leaves this optimal range, the
performance becomes very poor, as indicated in the documentation provided by the
hydraulic equipment manufacturers. But this does not represent a major drawback
and has so far not justified any optimization work.

2 - Current hydrostatic transmissions are not very reversible. Reversibility is not
moreover not useful if the power is supplied by a diesel engine.

3 - Hydraulic axial piston pumps have a high noise level, which is located in
the frequency range where the ear is most sensitive.

However, the operating regime at low pressure and high flow rate is precisely the most common for a vehicle. It comspozrd at the average stabilized speed on mute with very little or no slope. In the same way, reversibility allows the ricupRon of braking energy during decelerations of the electric vehicle or even downhill, to recharge the batteries.

PURPOSE OF THE INVENTORY
The invention describes a simple assembly of elements, reliable, efficient and inexpensive, making it possible to match the energy of an electric mouse with quasi constant voltage, generally a storage battery, in an antique rotation movement. variable speed applicable to any vehicle. This assembly includes a direct current electric motor, a variable flow hydraulic pump and one or more hydraulic motors.

The invention describes the complete propulsion system using the previous energy conversion and transmission applied to an electric vehicle.

The propulsion system described must also be reversible so that the electric vehicle which uses it has engine brake and that the energy of deceleration or deceleration is used to recharge the batteries.

It must allow the speed and acceleration of the vehicle to be varied between 0 and a maximum speed using a single m8caniclue command.

The invention is accompanied by a significant reduction in noise level compared to that of vehicles with an internal combustion engine.

ESSENTIAL MEANS CHARACTERISTICS OF THE INVENTION
Obtaining a hydrostatic transmission with improved efficiency at high flow and low pressure can be obtained by modification of a variable flow pump with axial pistons (fig 2).

The pistons (3) of the pump are housed in a barrel (7) between the axis (8) of the pump.

They rub on a tilting plate (5) not driven by the axis (8). The sliding is ensured by fluid bearing, that is to say that each piston pad (4) is drilled with a hole and dimensioned so that at the maximum pressure of the pump, a sufficient film of oil reduces the friction on the plate.

At low pressure, this process is insufficient. To remedy this, it is proposed to replace the friction movement with a bearing obtained using a needle stop (2) supporting the axial forces and a ball bearing (1) supporting the radial forces and plug the holes in the piston shoes, the fluid bearing no longer being necessary.

Other improvements can be made:
- surface treatment of the pistons and their housing to reduce friction due to their
reciprocating movement.

- replacement of the original auxiliary pump (6) ensuring low pressure boosting and
integrated into the main pump, by a high pressure pump of the same displacement offering
better performance and quieter.

 - choice of a very low oil viscosity.

The propulsion chain of FIG. 1 is obtained by coupling an electric motor (13) with direct current to a hydraulic pump (14) with variable flow supplying oil under pressure to one or more hydraulic motors (15) via hydraulic lines (10). Two hydraulic circuits are required:
- the high pressure circuit which transmits the mechanical power, and consisting of the pump
(14), conduits (10) and at least one motor (15).

- the low pressure circuit consisting of the booster auxiliary pump (17) with fixed flow from
filter (18) and a thermal radiator tank (19)
The low pressure circuit prevents any cavitation in the high pressure circuit, cools the oil and filters it.

The flow in the low pressure circuit must allow sufficient exchange between the two circuits through the pump to guarantee the cooling of the oil, therefore of the variable flow pump and the hydraulic motors.

When there are two hydraulic motors, an oil distributor device (16), inserted in the high pressure hydraulic circuit, makes it possible to put them in series, obtaining the maximum speed, or in parallel, obtaining the maximum torque.

If the engines drive two opposite wheels of a vehicle, the rotation speed may be different in the curves. In parallel, the oil flow is distributed automatically between the engines.

In series, the oil being an incompressible fluid, the aforesaid device (19) compensates for the differential effect by sura) umenting the most rapid motor and limiting the excess of oil on the other.

Said device (16) also makes it possible to obtain a neutral position enabling the vehicle to be coasted in the event of a failure of the propulsion chain. Indeed, in the absence of this neutral position, the hydraulic motors have a very high resistance to rotation. This neutral position can also be obtained using simple hydraulic valves.

The hydraulic pump (14) makes it possible to vary the oil flow and to reverse its direction which reverses the direction of rotation of the hydraulic motors and makes possible the forward and backward movement of the vehicle without additional device.

The electric motor runs at almost constant speed. The variations in speed are due to those of the supply voltage and the electrical power absorbed.

The pump unit can be made by an inseparable assembly of electrical and hydraulic element, in the sense that the axis of the pump and the electric motor is common. This arrangement limits the number of mechanical parts and simplifies assembly: bearing and rotation bearing in reduced number, coupling. deleted, automatic alignment and centering.

A hydraulic muffler can be installed in the high pressure line at the pump outlet. Its role is to absorb the flow fluctuations inherent in this type of pump, and to avoid their transmission throughout the hydraulic circuit, or even to the chassis of the vehicle.

An pneumatic accumulator can also be added as a bypass to the high pressure hydraulic circuit to recover part of the vehicle's deceleration energy and restore it at start-up.

The accompanying drawings illustrate the invention:
Figure I shows the general block diagram of the propulsion chain of an electric vehicle described in this patent.

FIG. 2 represents in section the characteristic modifications of the invention made on a hydraulic pump with variable displacement axial pistons.

Description of Figure 1:
Hydraulic propulsion chain optimized for electric vehicle
The battery (11) supplies the electric motor (13) via a protection and starting circuit (12). The electric motor obstructs the variable flow pump (14) at almost constant speed.

The pressurized oil is supplied to two motors (15) placed in parallel or in series by the oil distributor (16). The neutral position of (16) short-circuiting the flow of the motors and the pump is also shown.

The auxiliary circuit of the pump includes the auxiliary pump (17), the oil filter (18) and the radiator reservoir (19).

A configuration with only one motor is possible, in this case the parallel function! distributor series (16) is unnecessary. Only the neutral position can be useful to be able to push the vehicle without resistance from the hydraulic motor in the event of a breakdown.

The pressure relief valves (9) of the hydraulic pump (14) existing by construction are shown.

Description of figare2: optimistic hydranoqne pump for application to electric velucale
The drawing of Figure 2 is a section along the shaft (8) of a hydraulic variable speed pump with axial pistons. The pistons (4) driven by the rotating barrel (7) integral with the shaft (8) exerts pressure on the tilting plate (5) that pivots around the axis A but is not in rotation. The barrel drives the pistons, the pads of which roll on the needle stop (2) supporting the additional forces and held radially by the ball bearing (1).

 The auxiliary booster pump (6) is also shown.

Situation before modification:
The heads of the pistons (3) are made of bronze and mounted on a ball joint. They are pierced with a hole which opens into the body of the piston full of oil and on a knuckle cavity (4), the assembly dimensioned to behave as a fluid at high pressure, ie to reduce friction. by a thin film of oil between the bronze and the rectified cast iron track of the plate.

Modifications:
A bore is made in the plate so as to accommodate under the pads (4) of the pistons (3)
a ball bearing (1) supporting the radial forces and a needle bearing (2) supporting
axial efforts.

The low pressure gear pump (6) is replaced by a pump model
with external gear of the same displacement but high pressure, and also coupled to
the tree (8). This change is not shown.

DESCRIPTION OF SOME PARTICULAR EMBODIMENTS
The traction chain which is the subject of this patent is used on a small urban vehicle.

It consists of an electric motor coupled to a hydrostatic transmission made up
a pump and two hydraulic motors. It also has a circuit
low pressure hydraulics which ensures oil filling, cooling, filtering.

Hydraulic motors
Two hydraulic motors in parallel carry the rear wheels (propulsion). Using the hydraulic motor is a simple solution, allowing:
- A simplification of the assembly, the motors can carry the wheels, their name
current is then motor-wheel.

- Reduced costs, the many organs used by mechanical transmission
(rocket, bearings, universal joints, differential) being removed. Hydraulic hoses
therefore replace the meniscus gimbals, which makes it much freer, the location of the
pump unit than that of a mechanical system.

Hydraulic motors can be of fixed or variable displacement. Their mechanical coupling to the wheels is direct in the sense that they carry the wheels or can be done via any mechanical device (cardans, gearbox, etc ...)
The motors are supplied with pressurized oil by a pump unit, consisting of an electric motor and a pump.

The motor drives a hydraulic pump, with axial feet and tilting flap, at constant speed.

The oil flow is varied by tilting the plate more or less by means of a lever (with or without assistance), on which the pistons are based: the axial stroke of these determines the displacement of the pump, i.e. the oil flow at a given speed; and this stroke is all the greater as the plate is inclined.

This solution includes:
- a DC motor, uses at constant speed
- a variable flow plate pump, coupled to the motor
- a possible device stopping the electric motor when the vehicle is stopped
- a device for protecting and starting the electric motor
The protection and starting device can be electromechanical. n consists of a fuse disconnector at the battery outlet, a first so-called starter switch inserting between the battery and the electric motor a resistor having the effect of limiting the starting current of the motor when stopped and a second so-called contactor whose rise is delayed by a few seconds relative to the first and which short-circuits the resistance.

Said device can be electronic and consists of a semiconductor power switch controlled by a switching control circuit so as to obtain a progressive rise in the voltage across the terminals of the motor.

The variable flow pump can be obtained by judicious assembly and hydraulic switching of several fixed displacement pumps with gear for example. The pumps are all driven by the same axis coupled to the electric motor and each can deliver a short circuit on itself or in the high pressure circuit which supplies the hydraulic motor (s).

Claims (5)

CLAIMS 1 Hydraulic propulsion chain optimized for autonomous electric vehicle powered by battery characterized in that it comprises a set of elements made up of: - a hydraulic motor (15) providing mechanical torque on its axis at variable speed - a hydraulic pump variable speed (14) receiving mechanical torque on its axis with variable speed or not - hydraulic lines (10) connecting said hydraulic motor to said pump - an electric motor (13) powered by the battery (ll) via the protection and starting device (12) 2 Propulsion chain according to claim 1 characterized in that the hydraulic pump with said variable can be a hydraulic pump with axial pistons (14) comprising a ball bearing (1) and a stop needle (2) placed between the pads of the rotating pistons (4) and the tilting plate (5) and that the pistons pads have no holes. 3 propulsion chain according to claim I comprising an electric motor (13) which can be a direct current motor rotating at almost constant speed. 4 Propulsion chain according to claims I and 3 characterized in that the protection and starting device (12) can be electromechanical. 5 propulsion chain according to claim I characterized in that it can comprise several hydraulic motors (15) connected in parallel or in series 6 propulsion chain according to claims 1 and 2 characterized in that the auxiliary booster pump is a pump with high pressure gear coupled to the shaft (6). 7 propulsion screed according to claims I and 2 cararérisée in that it may include a low pressure ciuuit comprising an auxiliary pump (17), an oil tank (19) and a filter (18). 8 propulsion chain according to claim I characterized in that the variable flow pump consists of an assembly of several pumps with fixed displacement, and a hydraulic switching device for the wired debtor or not in parallel in the high circuit pressure that supplies the hydraulic motor (s).