Patent Application
20140190284
Motor-driven vehicles generally include an engine with a transmission for driving the wheels of the engine. Often the engine has a significant excess of power available to drive auxiliary systems that are required to perform the vehicle's intended services. A power take-off (PTO) system typically delivers rotary power from the engine to auxiliary systems via a PTO shaft that allow the auxiliaries to draw power from the engine. In some cases, auxiliary systems, such as hydraulic systems for running non-drive components of industrial, agricultural and construction vehicles, require substantial amounts of power from the engine. In many instances, the space available within the engine compartment is limited, which creates a design challenge to implement a PTO system that can deliver enough power to drive auxiliary systems that require up to all the power of the engine.
PTO systems may be positioned so as to take power from the front end of the engine crankshaft (front drive PTO) or the rear end of the engine crankshaft (rear drive PTO). For front drive PTO, an integrated gear-driven or a chain-driven PTO system is often used to take power from the engine crankshaft. These systems, however, are usually bulky, integral parts of the engine that are difficult to fit into a vehicle that requires a compact engine configuration, such as a forklift. These PTO systems are also difficult to service, and deliver only a fraction of the power supplied from the associated engine.
Accordingly, the inventors have identified a need in the art for a more robust front drive PTO system for proving power to auxiliary systems in a compact environment.
Unless otherwise indicated herein, the foregoing description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
In one aspect, the invention is directed to a system for driving an auxiliary unit from the front end of an engine. The system includes a drive sprocket mounted on an engine crankshaft at the front end of the engine; an auxiliary shaft for driving the auxiliary unit, wherein the auxiliary unit is mounted on the engine and the shaft is spaced in parallel relation to the crankshaft; an auxiliary pulley mounted on the auxiliary shaft that is adapted for driving the auxiliary unit; a toothed drive belt interconnecting the drive sprocket and the auxiliary pulley to transmit power from the drive sprocket to the pulley; and a support structure that supports the crankshaft against a transverse load asserted by the drive belt. In particular embodiments, the toothed belt may be a synchronous belt. The system may also include a woodruff key associated with the crankshaft, wherein the woodruff key is configured to fit within a corresponding annular keyway in the drive sprocket. Also, the drive sprocket may be press fit on to the crankshaft.
In a further aspect, the invention is directed to a method for taking power off the front of an engine to power an auxiliary unit. The method includes mounting the auxiliary unit on the side of the engine, wherein an auxiliary power take-off shaft of the auxiliary unit is substantially parallel to an engine crankshaft; delivering substantially all of the power from the engine from a front end of the crankshaft to the auxiliary unit via a pulley and toothed belt system, wherein the pulley and toothed belt system comprises a pulley mounted on a power take-off (PTO) shaft, a sprocket mounted on the crankshaft, and a toothed belt rotatably connecting the pulley and the sprocket. In various aspects of the invention, one or both of the PTO shaft and the crankshaft are supported with a removable bracket. The toothed belt drive may be a synchronous belt.
Still further, the invention is directed to a method for minimizing space required for an engine in an engine compartment while delivering power to an auxiliary unit. The method includes mounting the auxiliary unit on the side of the engine, wherein an auxiliary power take-off shaft of the auxiliary unit is substantially parallel to an engine crankshaft; delivering substantially all of the power from the engine from a front end of the engine crankshaft to the auxiliary unit via a pulley and toothed belt system, wherein the pulley and toothed belt system comprises a pulley mounted on a power take-off (PTO) shaft, a sprocket mounted on the crankshaft, and a toothed belt rotatably connecting the pulley and the sprocket.
In these and other aspects of the invention, the system may be capable of transmitting substantially all the power from the engine to the auxiliary unit. The power requirement of the auxiliary unit may be over 50 horsepower and the auxiliary shaft may operate at greater than 2000 RPM. For example, the system is capable of delivering at least 80 kW at 3000 RPM of the auxiliary shaft. In addition, the lateral load on the crankshaft is at least 200 pounds, for example at least 360 pounds.
These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings.
Exemplary systems and methods are described herein. It should be understood that the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as “exemplary” or an “example” is not necessarily to be construed as preferred or advantageous over other embodiments or features. The exemplary embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.
Disclosed is a compact PTO unit and drive system suitable for front engine drive applications. The system allows substantially all of the engine torque and horsepower to be taken off the front of the engine for driving auxiliary components of a vehicle. Because the PTO unit can be mounted on the side of the engine, the unit is easily accessible and minimizes the space required for mounting the system in the engine compartment. Accordingly, the system is suitable, for example, for use with engines on vehicles with compact engine compartments. In addition, the PTO unit and drive system can be adopted on standard engine designs with space available on the crankshaft at the front of the engine such that the system does not require redesign of the vehicle drive system at the rear of the engine.
The maximum amount of power that can be delivered from an engine through the crankshaft to an auxiliary unit depends in part on the maximum power output of the engine. While the maximum power of engines used in industrial, agricultural and construction vehicles can vary widely, the auxiliary units typically require between 1 and 20 kW of power. Because it is desired that engines used in these vehicles have a compact design, smaller engines that deliver less power are often used. Also, the compact nature of the engine compartment in these vehicles limits the ability of the system to deliver power to an auxiliary unit. Accordingly, it is desirable that PTO systems on these small engines are able to transfer substantially all of the engine power to the PTO unit. Most engines used in these systems have power rating of between about 20 and 300 HP, which can span from about 40 to about 1000 ft/lbs of torque at 700 to 4000 RPM. As used herein, “substantially all the power from the engine” refers to the horsepower of the engine and torque provided by the crankshaft. In various embodiments, at least 70%, at least 80%, and least 90%, at least 95%, and at least 99% of the engine horsepower and crankshaft torque is transferred to the PTO unit.
The PTO system includes a PTO unit mounted on an engine body and a shaft extending from the PTO unit spaced generally parallel to the engine crankshaft. The PTO shaft cooperates with the portion of the crankshaft extending from the front of the engine via a pulley and toothed belt drive assembly. Accordingly, PTO unit can be mounted on the side of the engine yet derive power from the front of the engine body. Moreover, the system avoids truck/frame mounted output shafts that that are not suitable for the compact space requirements of most industrial, agricultural and construction vehicles.
In addition, a PTO system on the front of an engine must be compatible with timing belt driven engines. For example, the PTO system should not require modification to the host engine or require an oil galley. Also, the system should offer less complexity for use with overhead cam systems that are used on most modern internal combustion engines in which space and physical mounting locations for the PTO system may be very limited.
The engine 120 is typically, although not exclusively, an internal combustion engine that includes a block 122 housing a plurality of cylinders, pistons, and connecting rods, and a crankshaft 124 that turns the pistons' motion within the cylinders into circular motion. For example, the engine 120 can be any of a number of engines currently available, including inline, V, slant and boxer configurations, provided these designs provide for space on the crankshaft at the front of the engine for mounting a drive sprocket. The engine 120 may also drive a number of accessories, for example, an alternator, an air conditioner compressor, a water pump, and an air pump for emissions. While these accessories can use engine power, they do not typically require the substantial power load of an auxiliary unit described here. For instance, most accessories, even in combination with other accessories, use less than 50% of an engine's power. The engine 120 is usually the power source for both the accessories and any auxiliaries during vehicle operation.
The engine power is taken from the crankshaft 124 at the front of the engine, which is typically the weaker side of the crankshaft 124. In the example of
The output shaft 112 for the auxiliary unit extends from the PTO unit 113 in a direction generally parallel to the crankshaft and toward the front of the engine body 120. The pulley 114 is mounted and rotationally fixed to the output shaft 112. The drive sprocket 118 is mounted and rotationally fixed to the engine crankshaft 124. The drive belt 116 transfers power from the drive sprocket 118 to the pulley 114. Typically, the ratio between the drive sprocket 118 and the pulley 114 is between about 1:3 to about 3:1.
In one example embodiment, the drive sprocket 118 and the pulley 114 may each include a toothed edge and the first belt drive 116 may include corresponding teeth that mate with the toothed edge for more controlled movement of the first belt drive 116 on the drive sprocket 118 and the pulley 114. For instance, the drive belt 116 may be a synchronous drive belt having polyurethane construction with carbon fiber cords and nylon teeth, and that does not require lubrication and avoids the need for an oil galley. In one example, the drive belt is a POLY CHAIN® GT® Carbon™ belt drive (Gates, Inc., Denver Colo.), which has a carbon fibre tensile cord construction. Compared to a traditional Morse chain drive, the belt drive provides less vibration, can be operated at higher RPM, and results in less lateral load than the crankshaft. A tensioning system 122 may be used to provide the appropriate tension to the belt drive 116. Also, the tension of the belt can be addressed in the design of the framework 150 such that the distance between the crankshaft 124 and the output shaft 112 is correct for the particular belt used.
An accessory drive sprocket 119 may also be mounted to the crankshaft 124. The accessory drive sprocket 119 may be positioned adjacent to the auxiliary drive sprocket 118 to allow for a compact configuration. A second belt drive 117 may be positioned on an edge of the accessory drive sprocket 119 such that the rotation of the accessory drive sprocket 119 drives one or more accessories. For example, the second belt drive 117 may be positioned on or around various portions of one or more pulleys 160 such that the movement of the second belt drive 117 causes rotation of the plurality of the pulleys 160 that in turn run accessories off of the engine power. Some pulleys 160 may not run any accessories but may be tensioning pulleys that provide the proper tension in the second belt drive 117 as the belt moves. In one example embodiment, the accessory drive sprocket 119 may include a toothed edge and the second belt drive 117 may include corresponding teeth that mate with the toothed edge for more controlled movement of the second belt drive 117 on the accessory drive sprocket 119.
In one aspect, the system includes a structure to support either one or both of the crankshaft and the auxiliary shaft against the lateral load exerted by the belt drive. For example, the structure may include a bracket that receives the front end of the crankshaft, which can cooperate with a bearing (e.g., roller needle, ball, or journal bearing) associated with the bracket. Similarly, the structure may include a bracket that receives the auxiliary shaft, which can cooperate with a bearing (e.g., roller needle, ball, or journal bearing) associated with the bracket. For example,
Also, as show in the exemplary embodiment shown in
The drive sprocket 118 should be mounted to the crankshaft 124 in a manner that allows for a substantial load, for example nearly 100% of the engine power, to be transferred to the PTO unit. In a typical operation, the load can range from 20 to 1000 ft/lbs, which can result in a large stress on the crankshaft 124. In some embodiments, the drive sprocket 118 is press-fit on the crankshaft 124, which can cause additional stress on the crankshaft. In one embodiment, the crankshaft 124 may include a woodruff key that is received within an annular keyway in the drive sprocket 118. In a typical embodiment, the woodruff key is restrained in a curved keyway in the crankshaft 124. In some instances, the woodruff key may be press fit within the crankshaft keyway.
The system 100 of
In one aspect, the invention is directed to a method of minimizing the space needed in an engine compartment while taking power from the engine to run auxiliary units. The method includes mounting the auxiliary unit on the side of the engine, wherein the power take-off shaft of the auxiliary unit is substantially parallel to an engine crankshaft. The engine can then deliver substantially all of the power from the engine from a front end of the engine crankshaft to the auxiliary unit via a system that includes a pulley mounted on a power take-off (PTO) shaft, a sprocket mounted on the crankshaft, and a toothed belt connecting the pulley and the sprocket. In some embodiments, the toothed belt system uses a synchronous belt drive. A tensioning system as known to one of skill in the art can be used in conjunction with the belt drive.
As shown in
In comparison, a chain drive system mounted on a Nissan fuel-injected K21s engine, which produces 60.1 horsepower at 2,700 rpm and 118 pound-feet of torque at 2,000 rpm, can only provide about 35 kW of power at 3000 rpm of the pump. As shown in
Additionally, in the front PTO example represented in
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims
