WO2016137604A1

WO2016137604A1 - Hydro-mechanical regenerative braking unit and transmission for electric and other vehicles

Info

Publication number: WO2016137604A1
Application number: PCT/US2016/013945
Authority: WO
Inventors: Robert H.F. LLOYD
Original assignee: Lloyd Robert H F
Priority date: 2015-02-26
Filing date: 2016-01-19
Publication date: 2016-09-01

Abstract

High surge currents associated with heavy braking and rapid acceleration of electric and hybrid electric vehicles result in reduced battery life and excessive heating of motors, generators and electronics. These can be reduced in two ways. 1. By the use of a speed changing transmission such that the motors and generators operate at higher speeds and therefore lower currents for the same power. 2. By providing an auxiliary regenerative braking means that can handle high power levels thereby reducing the load on the electric system. This invention describes a hydraulic device that can function as a speed changing transmission and/or a regenerative braking system that can handle very high power levels. It is implemented using fixed displacement pumps and motors to achieve low cost and high reliability.

Description

Continuation Non-Provisional Application

"Hydro-mechanical regenerative braking unit and transmission for electric and other vehicles."

This application is a Continuation Application that claims the benefits of copending Non-Provisional Application No. 14/086,503 filed 21 Nov. 2013 and entitled "Enhancements to High Efficiency Hydro-mechanical Vehicle

Transmission" (PCT/IB20141002962) and claims the benefit of provisional application # 62/121408 dated 26 Feb. 2015.

TECHNICAL FIELD

The present inventions relates a hydro-mechanical regenerative braking and transmissions for electric and other vehicles.

BACKGROUND OF THE INVENTION

Electric regenerative braking suffers from low efficiencies and difficulty handling both charge and discharge current surges. Dealing with these difficulties results in higher power batteries, motor/generators, and control electronics than would otherwise be required. A speed changing transmission can reduce the severity of these problems.

By adding hydraulic regenerative breaking to a vehicle with electric regenerative braking, the deficiencies of the electric regenerative system can be compensated for and the need for a transmission eliminated.

To date, most hydraulic schemes for vehicles are based on variable displacement pumps and motors. They usually result in very simple systems designs. However, compared to fixed displacement pumps and motors, variable displacement devices have many disadvantages. These undesirable features include:

• efficiency fall off at low displacement settings,

• low reliability due to high parts count and many reciprocating parts,

• high noise level,

• slow response times reduces overall vehicle performance ,

• awkward form factor that inhibit compact packaging, and

• high cost due to many parts.

An internal gear, crescent type pump or motor can consist as few as 2 moving parts (See Fig. 1).

For the above reasons, this disclosure describes a system built with only fixed displacement devices.

SUMMARY OF THE INVENTION

For the purposes of the below descriptions, a "pump/motor" will a fixed displacement hydraulic device that can function either as a hydraulic pump or a hydraulic motor for fluid flows in either direction; similar to that illustrated in Fig. 1.

Two or more fixed displacement hydraulic pump/motors are attached to the drive shaft of the electric or other vehicle either directly or thru gears. When acting as pumps, the pump/motors will cause the vehicle to slow down by pumping hydraulic fluid from a low pressure reservoir to a gas filled accumulator thereby storing the braking energy as high pressure gas. The braking energy is recovered by allowing the fluid to flow from the high pressure accumulator to the low pressure reservoir thru the pump/motors acting as motors and thereby turning the drive shaft and powering the vehicle. Valves are associated with each pump/motor which can cause the fluid to re-circulate within the device thereby de-activating it. In this manner, the degree of braking or accelerating can be controlled using combinations fixed displacement pump/motors. This avoids the many problems associated with variable displacement pump/motors. If the pump/motors are divided into two groups (designated input and output), they can be configured to provide soft-start and soft-stop characteristics by recirculating some of the fluid in either the output group of pump/motors or the input group of pump/motors. In this case one set of pump/motors is working in opposition to the other with the resulting torque being lower than possible with either separately.

3. In the case where this unit is used on an electric hybrid vehicle for example, the soft start and soft stop feature can also be accomplished by using the electric system to provide the low torque levels and the hydraulic unit to supply the high torque levels.

4. If configured as in 2, above, and a clutch is placed between the two groups of pump/motors, the unit can also function as a transmission. In this case the reservoir and accumulator would either be remove or shut off with a valve. The transmission function is accomplished by the input pump/motors functioning as pumps driving the output group as motors. Different transmission ratios are accomplished de-activating selected pump/motors in the input and output groups.

5. When operating as a transmission and the main power source is an internal combustion engine, a clutch would be required between the input shaft and the engine pumping losses won't subtract from the braking energy to be stored.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 describes a common fixed displacement hydraulic pump/motor.

Fig. 2 illustrates the basic hydraulic system in an electric vehicle.

Fig. 3 illustrates the arrangement necessary to implement soft start and soft braking. Fig. 4 illustrates how soft stop braking is accomplished. Fig. 5 illustrates how soft start is accomplished.

DESCRIPTION OF PREFERRED EMBODIMENT

In this description, the term "pump/motor" refers to hydraulic devices that can function either as a hydraulic pump or hydraulic motor with fluid flows in either direction. Fig. 1 illustrates such a pump/motor.

Fig.2 is the basic system diagram as it would appear on an electric vehicle. The battery 10 powered electric motor/generator 11 powers the wheels 8 through a drive shaft that is common to 4 pump/motors 1,2,3_/4. Each pump/motor has a valve 5 that controls whether the pumps pump fluid from the reservoir 9 to the accumulator 7 or causes the fluid to recirculate in the pump/motor, which in effect deselects the pump/motor. Valve 6 controls whether the unit is storing braking energy by "charging" the accumulator 7 or providing vehicle accelerating torque by allowing the accumulator to drive the pump/motors as motors.

One potential problem is that the minimum incremental step of braking or acceleration may be too large to satisfy harshness requirements. In Fig. 3 the valves 1 and 2 are such that they can cause on group of pump/motors to work in opposition to each other. If the various displacements are selected correctly, the difference in torque between the two groups can be small, thus allowing a small startup or stopping torque (i.e. soft start and soft stop).

In Fig 4 we have 8 pump/motors 1,2,3,4,5,6,7,8 which allows a much finer resolution of the torque level. Valve VI is in the position to cause the fluid in pump/motor 1 to recirculate within the pump/motor thereby in effect deselecting it from the system. Valve V4 is in the position to allow pump/motors 3 - 8 to pump fluid into the accumulator 9 from the reservoir 11 thereby affecting braking torque. Valve V3 is in the position to allow fluid to flow from the accumulator to the reservoir which will reduce the net braking torque to the low levels desired for the soft stop. V5 is shown to indicate that it is not necessary to make every pump/motor "selectable". The arrows marked as 14 illustrate the directions of the fluid flows and an approximation of the relative magnitudes for a typical example. A fluid pressure shock absorber A is required to absorb the shocks produce by the rapid switching of valves such as VI and V4. The gearing shown allows the pump/motors to operate at their rated rpm and facilitates compact mechanical packaging.

The chart in Fig. 4 is an example of how the system might work. Different displacements are shown with their associated peak torques. A "1" next to

Condition A indicates that that pump/motor is selected (i.e. not in recirculate mode). In Condition A the output pump/motors are supplying 200 N-m of braking torque while the input pump/motors are supplying 198 N-m of accelerating torque for a net braking torque of 2 N-m. The different gear ratios of the input and output pump/motors cause the torques shown not to be proportional to the displacements shown. Clutch 12 would be required if the unit was also to function as a transmission.

Valve V4 in Fig. 5 is in the position that the output pump/motors will inhibit initial acceleration and therefore subtract from the start-up torque supplied by the input pump/motors. As shown in the chart of Fig. 5, the net start-up torque will be 3 N-m and therefore provide a soft start.

Clutch 1 in Fig. 5 provides for the cases where it is necessary dis-engage the primary motor from the unit. For example, if it is desirable to prevent the pumping losses of an internal combustion engine from reducing the amount of braking energy stored in the accumulator.

This structure can also function as a transmission. In this case, clutch 2 would be disengaged so that the input pump/motors could function as pumps driving the output pump/motors as motors. The transmission ratio would be changed by selectively deactivating the input and output devices. Valve V5 would be closed.

Claims

CLAIMS For the purposes of the below claims, a pump/motor is defined as a fixed displacement hydraulic device that can function either as a hydraulic pump or a hydraulic motor for fluid flows in either direction.

1. A vehicle regenerative braking unit consisting of:

a, two or more pump/motors mounted on or connected by a gear to a common shaft and,

b, an accumulator and a reservoir and,

c, a valve associated with each pump/motor that can cause the fluid to either recirculate back into the pump/motor or to be piped to some other area in the system, and

d, pipes that connects corresponding outlets of all the pump/motors to an accumulator and the other outlets of all the pump/motors to a reservoir, and

e, valves connected such that they can change the fluid flow to and from the accumulator to flow to and from the reservoir and vice versa, and

f. with one end of the shaft designated as the input and the other as the output and, g. with or without a clutch attached to the input end of the shaft and,

h, for the purpose of performing the function of regenerative braking and or a transmission and,

2. The system of claim 1 where the pump/motors are divided into two groups and each group can be connected independently to the accumulator and reservoir to function either as a pump or a motor in opposition to each other such that the shaft experiences opposing torque from each group.

3. The system of claim 1 and 2 with a clutch located between the two groups of pump/motors and with or without an accumulator and reservoir and a valve to shut off the accumulator when present and with or without a clutch on the end of the input shaft so the unit can be used both as a transmission and regenerative braking unit.