Hydromechanical Transmission

Due to the limited supply of gasoline and its corresponding high cost, the importance of minimizing fuel waste in a car has taken new dimensions in recent years.

Presently cars waste fuel in several ways, some of which are:

1. During braking the car's kinetic energy is transformed to heat which is dissipated to the surroundings.

2. When moving in congested traffic, the engine operates very inefficiently and is running continuously even when the car is standing.

3. Present transmissions usually have a few fixed ratios vs. an infinitely variable transmission which can continuously provide an optimal ratio. Further, present day automatic transmissions introduce additional power losses in the torque converter and hydraulic pump areas.

An object of the present invention is to provide a transmission which will eliminate the above losses.

The advantages of regenerative braking, intermittent engine operation at an optimal carburetor opening and an infinitely variable transmission, as well as the value of these features to the fuel economy, are all known. However, to date, no system could be built that will provide these features without introducing undesirable and untolerable side effects of cost, complexity and bulk.

The present invention relates to a gearless hydrostatic split torque automotive power transmission which is adapted to incorporate regenerative braking and engine starting ability in one simple, compact, light and inexpensive hardware package.

The transmission is adapted to operate in several modes in order to maximize fuel economy in various driving modes: over the highway the transmission provides a direct mechanical drive (lock-up); when descending a long incline it operates in over-drive; in the city the transmission provides added hydrostatic torque; and in stop-and-go traffic the transmission is fully hydrostatic, enabling the engine to operate intermittently, charging an accumulator at an optimal carburetor's opening and shutting itself until the accumulator is almost depleted. At this point the transmission restarts the engine which recharges the accumulator.

During braking the transmission converts the vehicle's kinetic energy to pressurized fluid stored in the accumulator, to be reused for accelerating the vehicle later on.

While all the above features and their economical value is well established in the art, as mentioned previously, the unique aspect of the combination of the present invention is that is achieves all these goals without introducing unacceptable side effects of complexity, cost or bulk. On the contrary, it provides all these features with a system whose hardware is substantially simpler than present day automatic transmissions.

It can also be appreciated from the foregoing specification that the two pumps, which are combined in a unique way to form the transmission, are similar to conventional piston pumps. Thus, the present invention does not require any unproven or non-existing technology or manufacturing processes.

The control, whose specific construction is not within the scope of the present invention, can incorporate an electronic micro-processor to translate driver's inputs through the brake accelerator and gear shift levers to optimal setting of the transmission elements.

FIG. 1 is a side cross sectional view of a transmission according to the present invention, and

FIG. 2 is a cross sectional view along line 2--2 marked on FIG. 1.

FIGS. 1 and 2 show a hydrostatic transmission 10 adapted for a plurality of operational modes, comprising:

A first variable displacement pump 11 having a first section serving as a mechanical input member 9 of the transmission, a second section 13, an inlet port 14 and an outlet port 15.

The first section of the first pump comprises a shaft 16 rotatably supported by a housing 17 through a ball bearing 18. The shaft carries and rotates with a swash plate 19 which is pivotly inclined about an axis 20 (carried by the shaft) by a servo-actuator 21 (which also rotates with the shaft). The actuator is operated by pressurized fluid directed to its cavity 22 through a passage 23 and a slip ring 24. The shaft defines inlet and outlet passages 25 and 26 respectively, which communicate with the ports 14 and 15 via the slip ring.

The second section of the first pump comprises a drum 27 defining six cylinders 28 in which pistons 29 are slidably disposed. Each piston has a shoe 30 which slides against the swash plates.

A band brake 31 is actuated by a cylinder assembly 32 in response to pressurized fluid communicated to it by a conduit 33 from a control 47.

A second variable displacement pump motor 40, having a first portion 41 serving as a mechanical output member of the transmission, is coupled to the second section 13 by a one-way clutch 42 and a bearing 74. A second portion 43 of the second pump is anchored to the housing. Numerals 44 and 45 indicate suction and discharge points respectively.

A conventional accumulator 46 is adapted for storing pressurized fluid.

The control 47 is connected to ports 14, 15, 44, 45 and to the accumulator through conduits 48, 49, 50, 51 and 52 respectively. Mechanically, the control is connected to a brake pedal 70, an accelerator pedal 71 and a shift lever 72.

The first portion of the second pump comprises a drum 53 and pistons 54 similar to those in the first pump (each piston is urged outwardly by a spring 55, one shown). The drum 53 has a gear 56 affixed to it by a weld 75 and is supported by a ball bearing 57.

The second portion of the second pump comprises a center post 58 defining suction and discharge passages 59 and 60 respectively (similar to the inlet and outlet passage of the first pump) which communicate with the ports 44 and 45 respectively. A swash plate 61 is pivotally inclinable about an axis 62 by a cylinder assembly 63 which is controlled by pressurized fluid communicated to it by a conduit 64 from the control 47. The gear meshes with a ring gear 65 of a differential 66 which in turn drives right and left wheels (not shown) through axles 67 and 68 respectively.

An engine (not shown) drives the transmission mechanical input member, the shaft 16.

The present transmission is adapted to operate in a plurality of modes as a transmission, and in addition as a regenerative brake and as an engine starter. These various operational modes will be reviewed herein:

Direct lock-up mode is achieved by inclining the swash plate 19 and by the control 47 blocking the outlet port. This locks the two sections of the first pump one to the other, and in this mode the power is transmitted directly from the mechanical input member 16 through the first pump 11, through the one-way clutch 42 to the mechanical output member. This mode of operation is well suited for highway travel, etc. In the direct mode, 100% of the power is conveyed mechanically and the transmission's efficiency is close to 100%. The speed ratio and torque ratio are both 1 to 1.

Reduction mode is achieved by inclining both swash plates and connecting the outlet port 15 to the suction port 44. To analyze this mode, it will be assumed that the engine and the mechanical input member rotate 4000 RPM's and the mechanical output member rotates 2000 RPM's. That is a 2:1 speed reduction and somewhat less than 2:1 torque multiplication. It can be observed that the relative speed between the swash plate and the drum in both pumps is 2000 RPM's and since the pumps are in a series connection, this means that they are set in this speed ratio at equal displacements per revolution.

In this mode the power is split. The engine's full torque is conveyed mechanically from the mechanical input to the output member, exactly as in the direct mode. The relative rotation occurring in the first pump is translated to pressurized fluid flow which is translated to an additional torque of the mechanical output member by the second pump (motor).

With an increase of the volume per revolution of the second pump vs. the first pump, the tramsmission's speed ratio decreases and visa-versa. In all these ratios, the torque at the mechanical output member is the sum of the engine's torque, which is mechanically passed through the transmission exactly as in the direct mode, plus additional torque generated by the second pump (motor). The inefficiency that typifies hydrostatic transmission applies only to the power which is conveyed hydrostatically to generate this additional torque.

Thus, the overall efficiency of the transmission, especially when used in a passenger car which uses direct mode or ratio close to direct a substantial part of the time, can be very high.

Overdrive mode is achieved by inclining both swash plates and connecting the discharge port 45 to the outlet port 15. In this mode, part of the engine torque is passed mechanically through the first pump to the second pump to generate pressurized fluid which is used by the first pump to rotate both drums (which are coupled by the one-way clutch) over engine speed. Thus the torque is reduced and the speed is increased between the mechanical input and output members. In this mode, as in the reduction mode, the power is split with the hydrostatic inefficiency applicable only to the portion carried hydrostatically.

The importance of the over-drive mode is that it permits one to design the direct ratio to be in the middle of the ratio range which is in heaviest statistical use, thereby improving the overall efficiency of the transmission.

Regenerative braking is accomplished by connecting the discharge port 45 of the second pump (motor) 40 to the accumulator. The braking torque is increased or decreased by increasing or decreasing, respectively, the inclination of the swash plate of the second pump (motor). Thus, the kinetic energy of the vehicle is transformed to fluid under pressure in the accumulator, which can be reused to reaccelerate the car.

Engine starting is accomplished by connecting the charged accumulator to the inlet port 14 of the first pump 11 thus rotating the mechanical input member and the engine which is coupled to it.

Hydrostatic mode is accomplished by anchoring the drum of the first pump with the band brake 31 and by connecting the output port 15, the suction port 44 and the accumulator to one another. In this mode, the control causes the engine to work intermittently at a certain optimal carburetor opening, charging the accumulator. When the accumulator is fully charged, the control shuts off the engine and the car continues to move, accelerate, stop, etc. on power supplied from the accumulator.

When the accumulator is depleted to one quarter of its energy storing capacity, the control connects the input port 14 to it, causing the first pump to restart the engine and recharge the accumulator.

This mode of operation is most suitable for moving in heavy, stop-and-go traffic.

Reverse is achieved by setting the transmission as in the reduction mode, but reversing the connection of the ports of the second pump (motor). Further, in this mode the inclination of the swash plate of the second pump is set at a greater angle than the inclination of the swash plate of the first pump.

While the present invention has been illustrated with a single embodiment, it will be appreciated that modifications and substitutions can be made without departing from the spirit of the invention and the scope of the claims.