RELATED APPLICATIONS

This application is related to, and claims the benefit of, Brazil patent application PI 1102937-4, entitled "SISTEMA DE TRANSMISSAO HIDRAULICO," filed on June 8, 2011, which is incorporated herein by reference in the entirety for all purposes.

BACKGROUND

The present invention relates to hydraulic transmission systems for vehicles. In particular, the present invention relates to a hydraulic circuit that can drive the wheels of a vehicle so it has torque and rotation compatible with a particular application, and still able to accumulate the energy from braking using it later when the need arises to accelerate the vehicle.

Hydraulic systems can match the power transmission in relation to transfer torque and rotation due to the characteristics of incompressibility of the hydraulic oil. These systems are widely used in special equipment to generate torque and rotate the wheels or other traction element (such as a vehicle track, for example). In general, these systems are used in industrial machinery, construction machinery, agricultural equipment and military vehicles.

Hydraulic circuits can be "open loop" or "closed loop" type. The "open loop" systems are those in which the hydraulic flow generator, such as a hydraulic pump, generates a flow of oil that is confined in a circuit, which is directed by control valves to the actuators, though the resistance to the operation of actuators will result in pressure increase of the system to working levels calculated for each project. These systems are not reversible and have specific pressure lines and oil return lines.

An example "closed loop circuit" is illustrated in Figure 1. It has a hydraulic flow generator, such as a hydraulic pump, which is a variable and reversible pump, and this device has the control of the circuit, managing the flow and the flow direction according the operator procedure. So it is not necessary to change the direction of rotation of the engine 100 that drives the pump 110. The principle of the "closed loop" is that the outlet of the pump is connected to the inlet of the motor and inlet of the pump is connected to the outlet of the motor. The main pump captures only the return of the actuator itself.

Since the pump 110 is connected directly to the actuator 160, which typically is a fixed displacement reversible hydraulic motor, the motor direction of rotation is switched when the oil flow is reversed by the pump 110. Therefore, the pump 110 is driven unidirectionally, which means only one direction of rotation of the driver. However, reversal of the pump 110 direction reverses the direction of the oil flow and causes the actuator 160 to reverse its direction of rotation. The pump 110 may be of a type of that varies the amount of oil displaced per revolution of the pump 110, which makes it possible for a single rotation of the pump 110 to provide a different number of rotations of the actuator 160. For this reason, the pump 110 has an internal booster pump 120 which receives hydraulic oil from a tank 130 and feeds continuously both lines of the loop, through a set of one-way flow control valves 140. In this type of hydraulic circuit, one of the lines connected to the pump 110 acts as a pressurized line the other acts as a return line. Thus, the auxiliary pump 120 is feeding the line that is functioning as part of return, keeping the circuit full of oil. In Figure 1, the dashed rectangle represents the pump 110 and all its components (including the auxiliary pump 120 and control valves 140).

The oil supply by an auxiliary pump 120 is necessary because both the main pump and the actuator allow leakages of the oil hydraulic circuit for internal controls and pressure lubrication. The oil used for this purpose returns to the tank 130 through a drain line 150, shown in Figure 1 by a dashed line that connects the actuator 160 to pump 110 and pump 110 to tank 130. The closed system is also called a "Circuit of Constant Torque," because as the torque of the system depends on the system pressure and the unit displacement of the actuator, then the same pressure will always have the same torque on the actuator, regardless of actuator rotation rate, which varies according to the flow delivered by the hydraulic pump.

The following formula describes the calculation of the torque as a function of displacement and pressure of the system: DisplacementUnitx Vr essure , where x is r =

2π the torque. For this reason, this system is widely used in machinery and vehicles that require a high and constant torque, which restricts their use in urban vehicles in general due to speed limitations and costs. They are also known from the prior art systems that store energy from braking a vehicle for later reuse of such energy when the need to accelerate the vehicle as described in document JP 07144617.

This document discloses a hydraulic pump coupled to the mechanical system of the vehicle through a gear that, when activated during braking, pumping fluid towards the batteries. This system, however, does not allow an efficient recovery of energy as it is connected to a mechanical shaft coupled to the drive wheels of the vehicle. This means that, besides the loss of efficiency inherent in the mechanical system of transmission, the system is applied in only one axis of the vehicle, only regenerating the braking energy from this axis. Consequently, it generated a low stored energy braking for future regeneration.

The implementation of the regeneration system in more than one axis of the vehicle would require a rather complex system of mechanical transmission, significantly increasing the weight and cost thereof.

OBJECTIVES OF THIS INVENTION

One of the objectives of the present invention to provide a hydraulic system capable of functioning as a vehicle transmission system, which replaces the traditional mechanical transmission system (mechanical axis). Another objective of the present invention is to provide a system capable of efficiently accumulating much of the braking energy for later regeneration when the need to accelerate the vehicle. SUMMARY

In order to achieve the above goals, the system of the present invention comprises: (i) a main circuit that includes a first hydraulic flow generator variable and reversible that feeds a closed circuit with at least a second middle actuator / generator hydraulic flow, while the latter is connected to at least one wheel of a vehicle, and a third means actuator / generator variable and reversible hydraulic flow in parallel with the first flow generator, and a regeneration circuit comprising a fourth means actuator / hydraulic flow generator that will work in the

regeneration of the brake system and at least one accumulator that stores hydraulic fluid under pressure for subsequent regeneration.

Therefore, the system of the present invention promotes, because it is hydraulic, excellent transmission efficiency and a huge mechanical simplification. This transmission system also provides an efficient recovery of braking energy

regeneration because it can be applied independently on each wheel of the vehicle. Consequently, this system provides a significant fuel economy, since it can move the vehicle, using the regeneration circuit for a certain time without the use of the engine. This is only effectively achieved by coupling two distinct hydraulic circuits. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a previously known closed hydraulic circuit.

Figure 2 illustrates the system of the present invention according to a preferred embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The following description includes a preferred embodiment of the invention, where the circuit described is applied to a vehicle with four wheel drive. As will be evident to anyone skilled in the art, however, the invention is not limited to this particular implementation, may be applied to vehicles with more or less traction wheels and can have different configurations of elements in the hydraulic circuits. Additionally, the media actuator / hydraulic flow generators will be directly presented as pumps and / or hydraulic motors. As can be seen in the preferred embodiment illustrated in Figure 2, the transmission system includes two circuits in parallel. The main circuit, which is a closed configuration, includes a main pump 1 and a variable displacement reversible flow, four-engines 4, in parallel, coupled to the wheels for traction and braking, and another third pump 3, also in parallel. The first pump 1 is powered by an internal combustion engine 2, for example.

The second circuit, the regeneration circuit includes a pump 5 hydraulically coupled to pump 3 which functions as the parallel port between the two circuits. Optionally, the coupling is mechanical. This second circuit, or regeneration circuit works as an energy accumulator when the pump 5 receives torque and rotation from the pump 3. Therefore, this circuit further comprises at least one hydraulic accumulator 8 for storing hydraulic fluid. The opening and closing line of the regeneration circuit can be made by a means of control, which may consist in the pump 5, a directional valve, and/or a proportional valve. In the preferred embodiment illustrated in Figure 2, are provided for four directional control valves 9, 10, 11, 14, and two proportional valves 12, 13.

The valve assembly has the functions to allow free flow when the vehicle is accelerating or moving uniformly, to converge to the flow accumulation of potential energy when braking, and to converge in the stream for reuse when regenerating. The regeneration circuit may further include at least one safety or relief valve 15 which opens in case of sudden increase of pressure in the regeneration circuit.

Just as the closed circuit of the prior art, the system of the present invention may include a drain line, illustrated in Figure 2 by a dashed line connecting the four engines 4 with pumps 1, 3 and a reservoir 7. The drain line optionally passes through a hydraulic oil cooling device which consists of a heat exchanger 6 in the example of Fig. 2, positioned immediately before returning to the reservoir 7.

The control system of the present invention can be done by an electronic module (not shown) that controls the system according to which receives two signals from the user, namely the accelerator pedal signal and brake pedal signal. In certain embodiments, these two signals are generated by potentiometers and sent to the electronic module to control the motor 2, the opening and closing of valves, and the direction and intensity of flow in hydraulic pumps and motors. The signal received from the brake pedal is still sent to the conventional braking system of the vehicle.

The details of an example embodiment of the system will now be described by the stages of operation of the vehicle and according to Figure 2. When it is given to start the vehicle, the engine 2 starts and transmits torque and rotation to a main pump 1 that begins in a neutral position, not providing hydraulic flow.

At the touch of the accelerator pedal, and/or in response to the accelerator pedal signal, the motor 2 is set for an acceleration rate and maximum torque of rotation, and the impetus for a pump flow is controlled so that, according to the second engine torque and displacement chosen, promotes a hydraulic flow that goes through the system to four hydraulic motors 4 to the wheels. Depending on the slope of the ground and rolling resistance, the system undergoes a pressure change due to reaction in the four wheel motors. In light of this response, the pump flow is adjusted with a pressure regulation system. At this stage, the pump 3, which acts as a parallel port between the main circuit and the regenerative circuit, is in neutral position (closed), and does not receive oil from the circuit, any pump, or any motor 4.

To achieve the optimal speed, the driver positions the throttle pedal to maintain a cruising speed, reducing the pressure of the system according to the required speed. In case of a slope, the driver tends to take off the foot from the accelerator and, thus, the main pump is placed in a neutral position and the pump 3 is opened to allow the free flow of oil, which now becomes driven by the four motors of the wheels. For the system to rotate freely, and once the pump 3 is coupled to pump 5 which moves the regeneration circuit, there are two directional valves 9 and 10, normally open, allowing all the oil flow generated by pump 5 to pass freely to a reservoir 7 and then return to the pump 5, so that the flow does not pass the line accumulators 8.

When braking the vehicle, the driver activates the brake pedal, which triggers both the regenerative system and the conventional brake (not shown). The braking system due to the regenerator operates the brake slightly before

conventional braking, functioning as a kind of engine braking. In this situation, the pumps 1 and 3 are immediately placed in neutral position (closed) and maximum throughput, respectively. The second pump 3, then starts to receive all the flow coming from the four wheel motors 4, which come to act as pumps, using the kinetic energy of the wheels to provide hydraulic flow in the loop.

The second pump 3, now acting as a motor, drives the pump 5 which is to provide hydraulic fluid into the regeneration circuit. The directional valves 9 and 10 are then closed in the line of free movement in order to force the flow generated by the hydraulic pump 5 for the oil accumulator. A proportional valve 12 between the pump 5 and the accumulator 8 is positioned for regulating the pressure at the pump outlet 5 regardless of the level of pressure in the accumulator 8, thus promoting a braking intensity compatible with the demand of the driver. Thus, the actions of the driver on the brake pedal is directly proportional to the pressure in the line 5 between the pump 5 and proportional valve 12.

At the end of braking, the driver stops pressing the brake pedal and, consequently, the system stops storing oil in the accumulator 8, reopening the directional valve 9 and 10 in line and closing movement of the directional valve 11 in line 8 accumulators. The system is now loaded with a certain pressure in the line of the accumulator 8 and the pump 5 is again in free flow.

With the system loaded, and with the touch of the accelerator pedal to move the vehicle again, the power demand from the pedal and the pressure on the accumulators 8 is compared and it will be decided whether to apply the

accumulated energy in the system. If the pressure is not enough, the pump 1 will be started to add work to the system, and when starting a new brake event, oil will again be accumulated through the regeneration circuit. If the pressure is

compatible with the demand for vehicle acceleration, the system goes into a regenerator action. The directional valve 14 is opened so as to direct the flow of hydraulic accumulators 8 for the regeneration circuit, passing through another proportional valve 13, which has the function of controlling the flow of oil in order to better harness the potential energy accumulated. This flow of oil goes to the pump 5, which starts to act as a hydraulic motor driving the pump 3 and hydraulic generating flow in the closed circuit to the wheel motors 4. When the pressure in the accumulator 8 is no longer sufficient to drive the vehicle, the regenerative system is stopped and pump 1 is to provide hydraulic flow to the engine 4.

When the vehicle is put into reverse, the flow from a pump in the main circuit is reversed and the hydraulic motors 4 rotate in the opposite direction. In this situation, the pump 3 receives no hydraulic flow and motor 2 does not need to change its direction of rotation, since the pump is reversible. This transmission system provides, besides the inherent advantages of a hydraulic transmission system, such as independent control of traction on each wheel, high performance, elimination of the need for drive axle, gearbox and system differential, and an increase in fuel economy because of accumulating and regenerating energy from braking.