TECHNICAL FIELD The present invention relates to motor vehicle drive trains generally and to self-propelled outdoor power equipment drive trains particularly. Outdoor power equipment such as golf course bunker rakes and amphibious vehicles may be required to operate at widely varying ground speeds and over a wide range of loads. The invention discloses a drive train adapted to operate over an unusually broad range of conditions.

BACKGROUND ART

The invention combines a variable-speed engine driving a hydrodynamic torque converter which, in turn, drives a hydraulic pump of any type, preferably a hydrostatic pump/motor set. Gear, piston, orbital, variable-displacement, single- stage, multiple-stage, and other types of pumps may be used to drive any type of hydraulic motor or servo. This arrangement permits automatic down-shifting when the load increases and automatic up-shifting when the load decreases if a multiple-stage pump is incorporated. It also allows the operator to avoid lugging the engine, an important consideration, particularly with air-cooled engines.

In the present embodiment, engine power is delivered to the pump by means of a torque converter, preferably a commercially available two-part torque converter assembly equipped with variable effective diameter split sheaves interconnected by a belt. In such torque converters, a rotational speed-responsive element is driven by the output shaft of a conventional internal combustion engine; a torque-responsive element is connected to a rotary load. The effective sheave diameter of the portion of the torque converter driven by the engine increases with increasing engine speed. The portion of the torque converter driven by the belt and which drives the hydraulic pump is equipped with a split sheave having an effective diameter that decreases with increasing rotational

speed. The torque converter output is delivered to a hydraulic pump (single or multiple stage) or to a variable displacement hydraulic pump through a shaft. The pump output is delivered to one or more hydraulic motors which may directly power the load (e.g. the drive wheels of a vehicle) or which may be connected directly or indirectly to the driven load by means including an intermediate shaft, transaxel, other gearing, sprockets or belts.

Compared to other drive train systems, this system offers numerous advantages. In particular, the system operates much more smoothly than conventional hydraulic, hydrostatic or gear transmission/friction clutch drives. This system yields smoother operation and uses components simpler than those required to produce a stepped-range, automatic-shifting, geared transmission having a similar range of input/output ratios. The benefits of smoother operation include, among other things, greater operator comfort and productivity, improved safety, lessened likelihood of damaging the turf or other surface on which the motor vehicle is being driven, and greater control over machine-mounted tools and implements. It is typical for hydraulic drive systems to have extremely fast response to operator control adjustments. The nearly instantaneous response can result in undesirable wheel slippage, and excessive mechanical stresses.

Another advantage of the invention disclosed herein is that it allows the motor vehicle engine to be operated at its optimum speed and efficiency at all times. This feature is particularly useful when it is necessary to accelerate under heavy load or when it is necessary to operate under varying conditions of load or terrain. By allowing the vehicle engine to operate at its optimum speed, it is possible to apply full power continually to the designated task, eliminate engine lugging, and reduce the likelihood of engine overheating. This advantage is important when the motor vehicle is powered by gasoline engines because such engines characteristically have low torque and low power when operated below the optimum speed. It is important when motor vehicles are required to change speeds frequently, particularly in diesel-powered vehicles which typically have poor acceleration characteristics. In addition, this drive system is particularly well- suited for applications where the working speed may vary widely and where it is desirable to move from one work site to another as quickly as practical.

A third advantage of the invention is that it reduces heat build-up within the hydraulic drive system compared to conventional systems. Because the torque converter permits the hydraulic pump to be stopped while the engine continues to run, the engine can be idled without forcing hydraulic fluid through the pump and controls. This characteristic also allows the engine to use less fuel at idle.

A fourth advantage of the present invention is that it operates more quietly than other systems. Conventional hydraulic or hydrostatic drive systems often become noisy when controls are set to halt machine movement. The problem is often most noticeable at high idle and may be avoided only by removing power from the pump which is impractical when other types of drive systems are used.

DISCLOSURE OF THE INVENTION The drive incorporates an interlock which prevents an operator from reversing the direction of rotation of the final drive motor(s) when the engine is supplying power to the hydraulic pump. When the pump sheave is turning, the faces spread apart allowing the belt to turn over a smaller radius. As the pump shaft slows, the faces of the sheave on the pump shaft move closer together and force the drive belt radially outward away from the pump shaft axis. A limiter rod, preferably having a curved or wear-reducing end portion, extends from a pivotable cross-shaft toward the belt. When the pump sheave forces the belt sufficiently far outward, the outer belt surface contacts the end of the limiter rod and raises it. As the end of the limiter rod is raised by the slowed belt, the cross-shaft is pivoted which thereby moves a stop away from the reversing control to permit the operator to reverse the direction of hydraulic motor rotation. As the engine speed is increased, the belt moves inward, out of contact with the end of the limiter rod.

The rod descends between the sheave faces and pivots the cross-shaft, moveing a stop to a position that prevents actuation of the pump-reversing control. By preventing reversal of pump output when the vehicle is moving, it is expected that damage to turf will be minimized. It is anticipated that this drive system would find its first application in golf course maintenance equipment including bunker rake machinery. This drive system is also suitable for use in a variety of landscape, agricultural, forestry, and industrial applications. It is suitable for use in all types of motor vehicles,

including golf carts, baggage carts, utility tractors, lawn and garden tractors, all- terrain vehicles, etc. It is also possible that this drive system could be used in material handling and lifting applications.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 shows a side elevation of a vehicle incorporating the invention. Fig. 2 is a perspective detail view of the drive train embodiment depicted in Fig. 1 showing the sheaves and interlock limiter rod when the engine is at low idle speed. Fig. 3 shows a plan view of the drive train detail shown in Fig. 2.

Fig. 4 shows an elevation view of the drive train detail shown in Fig. 2 depicting the belt, sheaves and interlock limiter rod when the engine is at full speed.

BEST MODE FOR CARRYING OUT THE INVENTION

Fig. 1 shows a vehicle 10 having a variable speed engine 1 2 having a conventional rotating output shaft 14. A conventional two-part torque converter 16 having a rotational speed responsive element 18, a belt 20 and a torque- responsive element 22 is interposed between the engine 1 2 and a hydraulic or hydrostatic, preferably a variable-displacement pump 24 as may be seen from the view depicted in Fig. 2. The speed responsive element 1 8 is adapted to increase the effective diameter of a split drive sheave as the speed of the engine 1 2 is increased. A belt 20 connects the speed responsive element 18 with the torque- responsive element 22 which is connected to the pump 24, preferably using a shaft 26 having bearings 28 to reduce mechanical stress on the pump 24 as is more clearly depicted in Fig. 3. It is to be understood that other types of torque converters may be incorporated without departing from the invention disclosed herein.

Hydraulic connections 29 of any suitable type convey power from the pump 24 to at least one hydraulic motor 30 which drives the wheels 32 of a vehicle 10.

A hydraulic control 34 may be used to regulate the speed and direction of rotation of the hydraulic motor 30 which may directly power a load such as the drive

wheels of a vehicle 32 or be connected to the driven load by means of an intermediate shaft, transaxel or other gearing.

An interlock assembly 36 is provided which allows reversing the direction of motor 30 only when the vehicle 10 is stopped or moving very slowly. The interlock 36 is comprised of a belt position actuated limiter rod 38 which descends between the sheave faces of the torque-responsive element 22 when the torque converter is at a working operating speed as is shown in Fig. 4. When limiter rod 38 descends, it causes cross-shaft 40 to pivot moving stop 42 into position where movement of a slotted plate 44 is restricted. The operator can move control link 46 to actuate valve link 48 for reversing direction of travel only when the belt position actuated limiter rod 38 is raised, as shown in Fig. 2. Raising the belt position actuated limiter rod can be accomplished when the drive train is in operation only when the speed of the engine 1 2 is at idle below a pre-determined idle speed and the hydraulic pump is either stopped as the result of the vehicle 10 being stopped or moving only very slowly.

Changes and modifications in the specifically described embodiments can be carried out without departing from the scope of the invention which is intended to be limited only by the scope of the appended claims.

INDUSTRIAL APPLICABILITY

The applicability of the invention to vehicles in industry is clear from the foregoing.