EP3941185A1

EP3941185A1 - Electrically powered, universal accessory drive

Info

Publication number: EP3941185A1
Application number: EP20800321.0A
Authority: EP
Inventors: Louise STENEBRAND; Andreas HULTGREN
Original assignee: Husqvarna AB
Current assignee: Husqvarna AB
Priority date: 2020-03-04
Filing date: 2020-10-21
Publication date: 2022-01-26
Also published as: WO2021176266A1; SE543917C2; SE2050245A1

Abstract

A drive assembly for a vehicle including a power source, a hydraulic pump powered by the power source, and a motor assembly including a plurality of hydraulic motors that are operably coupled to the hydraulic pump and that include a first pair of hydraulic motors operably coupled to rear wheels of a vehicle associated with the drive assembly and a second pair of hydraulic motors operably coupled to front wheels of the vehicle. The drive assembly further includes a proportional flow control valve configured to control a swash flow through a bypass path formed to enable part of a total flow exiting the hydraulic pump to bypass one of the first pair of hydraulic motors or the second pair of hydraulic motors, and an ECU configured to control a position of the proportional flow control valve to provide differential speed control between the first and second pairs of hydraulic motors.

Description

ELECTRICALLY POWERED, UNIVERSAL ACCESSORY DRIVE

TECHNICAL FIELD

Example embodiments generally relate to yard maintenance vehicles and, more particularly, relate to a riding yard maintenance vehicle that employs differential speed control.

BACKGROUND

Lawn care tasks are commonly performed using various tools and/or machines that are configured for the performance of corresponding specific tasks. Certain tasks, like grass cutting, are typically performed by lawn mowers. Lawn mowers themselves may have many different configurations to support the needs and budgets of consumers. Walk-behind lawn mowers are typically compact, have comparatively small engines, and are relatively inexpensive. Meanwhile, at the other end of the spectrum, riding lawn mowers, such as lawn tractors and articulated riders, can be much larger. Riding lawn mowers can sometimes also be configured with various functional accessories (e.g., trailers, tillers, and/or the like) in addition to grass cutting components. Riding lawn mowers provide the convenience of a riding vehicle as well as a typically larger cutting deck as compared to a walk-behind model.

As can be appreciated from the description above, riding yard maintenance vehicles may come in many different sizes and may have wide variances in their capabilities. However, beyond mere changes in size and function, riding yard maintenance vehicles can also be produced with a great deal of variation in relation to the configurations via which various ones of the functions they can perform are provided. For example, some riding yard maintenance vehicles may have attachments that are rear mounted, front mounted, or even mounted between the front and back wheels. Moreover, some riding yard maintenance vehicles may be configured to operate with four-wheel drive (4WD) to facilitate operation in certain difficult operating environments.

However, this variation can also complicate the drive systems of some models. For example, articulated riders may be designed such that the rear wheels have a longer way to run than the front wheels when turning. The may occur if, for example, the steering axis is not centered right between the front and rear axles (i.e., non-centered articulated steering).

On a 4WD system, non-centered articulated steering may mean that the rear wheels need to spin faster than the front wheels when turning in order to avoid damaging the lawn during a turn. For some current 4WD riders, the propulsion system uses two transaxles. When turning the vehicle, a swash-linkage is used to act on one of the transaxles to either increase the displacement on the front axle to make it turn slower, or decrease the displacement on the rear axle to make it turn faster. The disadvantage of this type of system, which uses transaxles, is that it is space consuming and the control linkage wears out over time. The linkage also needs to be adjusted to keep the proper ratio between the front and rear axle.

A less space consuming driveline may be provided by using wheel motors instead of transaxles. In order to get the proper speed on both front and rear wheels under this design, all of the wheel motors could be connected in parallel. However, within systems that are connected in parallel, flow will always follow the path of least resistance. Thus, if one wheel loses traction, flow will tend to run through the wheel that has lost traction and the corresponding wheel will spin. Some parallel systems may include a differential lock valve that is intended to prevent the wheels from spinning. However, this creates an inefficient system. The wheel motors could also be connected in series to improve traction. However, this reverts the system design to the problem of different speeds during a turn, which results in leaving marks on the lawn, and it also makes the machine difficult to steer.

Accordingly, it may be desirable to develop a way to control steering in riding yard maintenance vehicles that balances the provision of good traction properties with having the proper speed on all wheels in order to avoid leaving marks in grass surfaces.

BRIEF SUMMARY OF SOME EXAMPLES

Some example embodiments may provide a hydraulic traction and speed controlling system that avoids the problems discussed above.

In an example embodiment, a riding yard maintenance vehicle is provided. The riding yard maintenance vehicle may include a frame to which front wheels and rear wheels of the riding yard maintenance vehicle are attachable, a steering assembly operably coupled to the front wheels or the rear wheels of the riding yard maintenance vehicle to provide steering inputs by an operator of the riding yard maintenance vehicle, and a drive assembly. The drive assembly may include a plurality of hydraulic motors and a proportional control valve controlled by an electronic control unit (ECU), the proportional control valve being configured to control a swash flow through a bypass path to enable differential speed control between the front wheels and the rear wheels based on the swash flow.

In another example embodiment, a drive assembly for a vehicle is provided. The drive assembly may include a power source, a hydraulic pump powered by the power source, and a motor assembly including a plurality of hydraulic motors that are operably coupled to the hydraulic pump and that include a first pair of hydraulic motors operably coupled to rear wheels of a vehicle associated with the drive assembly and a second pair of hydraulic motors operably coupled to front wheels of the vehicle. The drive assembly further includes a proportional flow control valve configured to control a swash flow through a bypass path formed to enable part of a total flow exiting the hydraulic pump to bypass one of the first pair of hydraulic motors or the second pair of hydraulic motors, and an ECU configured to control a position of the proportional flow control valve to provide differential speed control between the first and second pairs of hydraulic motors.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 illustrates a perspective view of a riding yard maintenance vehicle according to an example embodiment;

FIG. 2 illustrates a representation of steering geometries involved in a riding yard maintenance vehicle of an example embodiment;

FIG. 3 illustrates a block diagram of a drive assembly attached of the riding yard maintenance vehicle according to an example embodiment;

FIG. 4 illustrates a schematic view of various components of the drive assembly according to an example embodiment; and

FIG. 5 illustrates a swash flow curve for a ratio rear to front axle flows versus turning angle according to an example embodiment.

DETAILED DESCRIPTION

Some example embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all example embodiments are shown. Indeed, the examples described and pictured herein should not be construed as being limiting as to the scope, applicability or configuration of the present disclosure.

Rather, these example embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout. Furthermore, as used herein, the term “or” is to be interpreted as a logical operator that results in true whenever one or more of its operands are true. As used herein, operable coupling should be understood to relate to direct or indirect connection that, in either case, enables functional interconnection of components that are operably coupled to each other.

Some example embodiments may provide an improved speed and traction control system that avoids the problems discussed above. In this regard, example embodiments can improve speed and traction control on riding lawn care vehicles including those that employ articulated steering. Example embodiments may employ hydraulic motors that have flow controlled via a proportional flow control (or swash) valve that has swash properties that do not change over time (unlike the transaxle systems mentioned above), and that consume less space than transaxle systems. Example embodiments may have a swash flow curve that can be customized in order to optimize the desired traction properties of the system, and may have anti-slippage properties since it always drives on one rear wheel and one front wheel.

The system described herein is also energy efficient since only the swash flow runs through the proportional flow control valve.

FIG. 1 illustrates a riding yard maintenance vehicle 10 as one example of a host device that may employ a drive assembly according to an example embodiment. The particular model shown, which includes front mounted equipment and is an articulated rider, is not necessarily the only model of host device or vehicle to which example embodiments may be applicable. As such, other models, including models without front mounts and without articulated steering, could also be operated with the drive assembly as described herein.

In some embodiments, the riding yard maintenance vehicle 10 may include a seat 20 that may be disposed at a center, rear or front portion of the riding yard maintenance vehicle 10. The riding yard maintenance vehicle 10 may also include a steering assembly 30 (e.g., a steering wheel, handle bars, joystick(s) or the like) operably coupled to rear wheels 32 of the riding yard maintenance vehicle 10 to allow the operator to steer the riding yard maintenance vehicle 10 via steering inputs that are communicated to the rear wheels 32 (or front wheels 34). However, other steering arrangements are possible in other embodiments and the type of steering assembly 30 employed is not limiting to example embodiments.

In an example embodiment, the steering assembly 30 may include a steering wheel 36 and a steering column 37. The steering column 37 may operably connect to additional steering assembly components or, in other embodiments, to the front wheels 34. Moreover, in some embodiments, the steering column 37 may extend into a steering console 38, which may provide a cover to improve the aesthetic appearance of the riding yard maintenance vehicle 10 by obscuring the view of various mechanical components associated with the steering assembly 30. In some examples, the steering assembly 30 may include other equipment (e.g., steering levers or handlebars) instead of the steering wheel 36.

The operator may sit on the seat 20, which may be disposed to the rear of the steering assembly 30 to provide input for steering of the riding yard maintenance vehicle 10 via the steering assembly 30. The riding yard maintenance vehicle 10 may also include additional control related components that may be disposed at a control panel 40, which may be positioned proximate to the seat 20 to enable an operator to easily access various control related components located at the control panel 40. The control related components may include levers, switches and/or the like configured to provide control over certain functions or components such as a blade speed adjuster, a choke control, a cutting height adjuster and/or a cutting unit lifting controller.

In some cases, one or more additional controllers, may be provided in the form of foot pedals that may sit proximate to a footrest 46 (which may include a portion on both sides of the riding yard maintenance vehicle 10 (e.g., on opposite sides of the steering console 38)) to enable the operator to rest his or her feet thereon while seated in the seat 20. These foot pedals may provide speed control for forward and/or backward operation, breaking, cutting deck lifting or other functions. Other levers, operators or components are possible in other examples as well.

In some example embodiments, the steering assembly 30 may be embodied as an assembly of metallic or other rigid components that may be welded, fitted, bolted or otherwise operably coupled to each other and coupled to the wheels (e.g., rear wheels 32 and/or front wheels 34) of the riding yard maintenance vehicle 10 to which steering inputs are provided. For example, the steering assembly 30 may include or otherwise be coupled with a steering cable assembly or a system of mechanical linkages (e.g., pulleys, tie rods, cams, and/or other mechanical components) to translate rotational motion applied to the steering assembly 30 (and more particularly to the steering wheel 36) into directional inputs to orient the wheels accordingly. Other steering control systems may be employed in some alternative embodiments.

The riding yard maintenance vehicle 10 may also include, or be configured to support attachment of, a cutting deck 50 having at least one cutting blade mounted therein. The cutting deck 50 may be a removable attachment that may be positioned in front of the front wheels 34 in a position to enable the operator to cut grass using the cutting blades when the cutting blades are rotated below the cutting deck 50 and the cutting deck 50 is in a cutting position. When operating to cut grass, some example embodiments may provide that the grass clippings may be captured by a collection system, mulched, or expelled from the cutting deck 50 (e.g., via a discharge that may be directed to a side or rear of the cutting deck and/or riding yard maintenance vehicle 10). In some embodiments, the cutting deck 50 may be replaced by other working attachments to change the configuration of the riding yard maintenance vehicle 10 and correspondingly change the tasks that may be performed by the riding yard maintenance vehicle 10. Thus, for example, a plow blade or snow blower attachment may be provided to convert the riding yard maintenance vehicle 10 into a snow removal device. Alternatively, a tiller attachment may be provided to convert the riding yard maintenance vehicle 10 into a ride-on or remote control operable tiller. Other attachments and configurations are also possible such as a sweeper, brush cutter, or the like. In each case, the different type of attachment may be considered to be a respective different type of accessory that can be powered by the riding yard maintenance vehicle 10 (as one example host device).

In the pictured example embodiment of FIG. 1, an engine of the riding yard maintenance vehicle 10 is disposed in an engine compartment 60 that is behind a seated operator in a rear portion of the riding yard maintenance vehicle 10. However, in other example embodiments, the engine could be in different positions such as in front of or below the operator. In some embodiments, the engine may be operably coupled to one or more of the wheels of the riding yard maintenance vehicle 10 in order to provide drive power for the riding yard maintenance vehicle 10. In some embodiments, the engine may be capable of powering two wheels, while in others, the engine may power all four wheels of the riding yard maintenance vehicle 10. Moreover, in some cases, the engine may manually or automatically shift between powering either some wheels or all four wheels of the riding yard maintenance vehicle 10.

The engine, the steering assembly 30, the cutting deck 50, the seat 20 and other components of the riding yard maintenance vehicle 10 may be operably connected (directly or indirectly) to a frame of the riding yard maintenance vehicle 10. The frame may be a rigid structure configured to provide support, connectivity and interoperability functions for various ones of the components of the riding yard maintenance vehicle 10. In some embodiments, the frame may be split or articulated such that, for example, the front wheels 34 are disposed on an opposite portion of the frame than the portion of the frame on which the back wheels 32 are disposed with respect to an articulated joint 70 in the frame.

Due to the inclusion of the articulated joint 70, resultant steering geometries during a turn of the riding yard maintenance vehicle 10 are shown in FIG. 2. In this regard, FIG. 2 shows the steering geometries that may result in some cases. In this regard, FIG. 2 shows rear wheels 32 and front wheels 34 along with a turning radius at the center of the front axle and rear axle (shown as Φfront axle, and Φrear axle, respectively). The displacement from each of the front axle and rear axle to the steering axis is also shown in FIG. 2.

In order to provide improved performance for the riding yard maintenance vehicle 10, some example embodiments may employ a drive assembly 100 that provides hydraulic traction and speed control as described herein. In this regard, the drive assembly 100 (e.g., a hydrostatic drive assembly) of example embodiments may provide drive power to the front wheels 34 and the rear wheels 32 in a manner that provides both good traction and speed control by using hydraulic motors to drive each wheel, and a swash system with improved performance. FIG. 3 illustrates a block diagram of the drive assembly 100 according to an example embodiment. In this regard, as shown in FIG. 3, the drive assembly 100 may include a power source 110 (e.g., a petrol or gasoline engine, or an electric power source) that is operably coupled to and provides power for a hydraulic pump 120. The pump 120 may in turn be operably coupled to a proportional flow control valve 130 and a motor assembly 140. The motor assembly 140 may include individual motors for each of the front wheels 34 and the rear wheels 32, and the proportional flow control valve 130 may be operably coupled to the motor assembly 140 to provide swash properties that improve the performance of the system as described herein. In an example embodiment, the proportional flow control valve 130 may further be operably coupled to, and controlled by, an electronic control unit (ECU) 150 or other controller or processing circuitry of the riding yard maintenance vehicle 10.

The proportional flow control valve 130, which may be referred to as a swash valve, is configured to interact with the motor assembly 140 in order to control the speed of the rear wheels 32 and front wheels 34 in pairs. In particular, the total amount of flow that is produced by the pump 120 may be provided to the motor assembly 140 with the proportional flow control valve 130 being operable to provide a bypass path for some portion of the total amount of flow. The control of the proportional flow control valve 130 by the ECU 150, and therefore the bypass path, may be the method by which traction and speed control is provided by example embodiments.

In some cases, various sensor may be positioned within the system to monitor respective components and feed information to the ECU 150. Sensor 112 is an example of a sensor that may be disposed at the power source 110 (e.g., at an engine of the riding yard maintenance vehicle 10). Sensor 122 is an example of at least one sensor that may be disposed at the pump 120 to measure pump speed or pump angle. However, in some cases, two sensors may be provided at the pump 120 (e.g., one for pump speed and one for pump angle). One specific arrangement for instantiating the general structure described by FIG. 3 is shown in FIG. 4.

Referring to FIG. 4, the pump 120 is shown to be operably coupled to a plurality of hydraulic motors that form the motor assembly 140. These motors include a first motor 200 and second motor 202 that may be provided in parallel with each other to power the front axle (and therefore the front wheels 34). The motors of the motor assembly 140 may also include a third motor 204 and fourth motor 206, which are also provided in parallel with each other to power the rear axle (and therefore the rear wheels 32). Swash valve 220 is an example of the proportional flow control valve 130 described above and defines a bypass path 230 that enables part of the flow from the pump 120 to bypass the first and second motors 200 and 202.

As can be appreciated from FIG. 4, the bypass path 230 (e.g., when the riding yard maintenance vehicle 10 is turning) to bypass flow away from the front axle and the corresponding first and second motors 200 and 202. Using the bypass path 230 causes less flow to go to support turning of the front axle (by sending less flow to the first and second motors 200 and 202). Accordingly, the front wheels 34 turn slower than the rear wheels 32, since the third and fourth motors 204 and 206 that power the rear wheels 32 have a higher flow. Since the wheels within the axles are connected in parallel with each other, but the front and rear axles are powered series, the system tends to always drive one of the rear wheels 32 and one of the front wheels 34 if the wheels lose traction. Flow that runs through a hydraulic valve builds heat and therefore wastes energy. In the system shown in FIG. 4, most of the flow does not run through the swash valve 220. Thus, the efficiency of the system can remain high.

As noted above, the swash valve 220 (and example of the proportional flow control valve 130 of FIG. 3) may be controlled by the ECU 150. In an example embodiment, the ECU 150 may include processing circuitry that is configured to process various inputs to generate an output, which is used to control the position of the swash valve 220. For example, the ECU 150 may receive inputs including a steering angle 160 (e.g., measured by an angle sensor disposed proximate to the articulated joint 70 and therefore proximate to the steering axis). Another input the ECU 150 receives may include an indication of pump speed (in rpm). In some cases, the indication of pump speed may be provided to the ECU 150 via a sensor disposed at the pump 120 (e.g., sensor 122) or at the engine of the riding yard maintenance vehicle 10 (e.g., sensor 112). Thus, for example, the sensor may be a portable pilot unit (PPU) when disposed at the pump 120, or may be as sensor that is configured to detect signals directly from the engine of the riding yard maintenance vehicle 10. Pump angle may be a third input that may be provided to the ECU 150. The pump angle may be received from an angle sensor (e.g., sensor 122) disposed on a pump arm of the pump 120. The output provided by the ECU 150 based on the inputs received may, as noted above, control the position of the swash valve 220. In some cases, the swash valve 220 may be solenoid operated, and therefore the ECU 150 may be operably coupled to the solenoid of the swash valve 220 to control the position of the swash valve 220 and thereby also control the swash flow that passes through the bypass path 230.

In an example embodiment, the ECU 150 may be programmed to vary the swash flow based on vehicle speed and turning angle. Thus, if there is no vehicle speed and/or no turning angle, the swash flow may be zero (i.e., the swash valve 220 may be fully closed). The ECU 150 may be programmed to employ a multistep process (or calculation) to determine how to regulate the flow through the bypass path 230. In some cases, a first step in the process may be to calculate a ratio between parameters associated with the rear axle and the front axle.

The parameters may provide an indication of a ratio between the flows associated with each of the rear axle and the front axle, and may be provided using any of a number of different measurable parameters such as the driving distance, speed, or flow itself. Equation 1 below shows some examples of specific parameters that can be used, and it should be appreciated that the geometries associated with individual models of the riding yard maintenance vehicle 10 and the steering angle 160 may impact the calculations.

Equation 1 :

After the ratio is found, the swash flow may be calculated using Equation 4 below. In some cases, intermediate calculations show by Equations 2 and 3 may be necessary or helpful in relation to determining the swash flow.

Equation 2:

Equation 3 : Equation 4:

[0001] After calculation the swash flow, pump flow can be calculated using Equation 5 below:

Equation 5: in which is pump flow in liters/min,

D_p is pump displacement in cm³/rev (where 23.9 is the total displacement of the chosen piston pump and 15 is the maximum angle of the chosen piston pump arm, and a is the measured angle on the pump arm), n is pump speed in rpm, and n_v, is volumetric efficiency. Finally, the swash flow depends on steering angle in degrees (β), pump arm angle in degrees (α) and pump speed in rpm (n), which can be calculated in accordance with Equation 6 below:

Equation 6:

The swash flow formula, which is essentially used by the ECU 150 to provide control over the swash flow, and therefore the operation of the drive assembly 100, can also be customized by programming initiated by an operator in order to meet different requirements or priorities. For example, the swash flow formula could be customized to specific driving situations such as driving uphill, driving downhill, etc. The customization may result in different swash curves for corresponding different scenarios or situations. Moreover, in an example embodiment, the operator of the riding yard maintenance vehicle 10 may be enabled to select a scenario that applies to the current operational situation. By selecting the scenario, a corresponding swash curve that has been generated for the scenario may be loaded and the front and rear wheels 34 and 32 may be driven accordingly based on the corresponding swash curve. In the example of FIG. 3, a user input 170 (which may be provided via a user interface either at the control panel 40, or at another location) may provide the selection of the scenario (and/or the swash curve). The user input 170 may be provided via a button, lever, switch or the like that is dedicated to the corresponding function. However, the user input 170 could also be provided via a touch screen or other operator that is not dedicated to the corresponding function as well.

FIG. 5 illustrates a swash curve 300 showing how the ratio may change over a range of turning angles (from 0-61 degrees) in accordance with an example embodiment. The swash curve 300 is specific to the geometries demonstrated in the example of FIG. 2 for the respective distances from the front axle and rear axle to the articulated joint 70. The swash curve 30 may be determined from model-based calculations or from testing on actual products but, as noted above, changes for every model that has different geometries.

Some embodiments of the invention provide a drive assembly for a vehicle. The drive assembly may include a power source, a hydraulic pump powered by the power source, and a motor assembly including a plurality of hydraulic motors that are operably coupled to the hydraulic pump and that include a first pair of hydraulic motors operably coupled to rear wheels of a vehicle associated with the drive assembly and a second pair of hydraulic motors operably coupled to front wheels of the vehicle. The drive assembly further includes a proportional flow control valve configured to control a swash flow through a bypass path formed to enable part of a total flow exiting the hydraulic pump to bypass one of the first pair of hydraulic motors or the second pair of hydraulic motors, and an ECU configured to control a position of the proportional flow control valve to provide differential speed control between the first and second pairs of hydraulic motors. In some cases, the hydraulic motors may also be transaxles. For example, the hydraulic motors could be two transaxles connected in series, or one pair of wheel motors and a transaxle connected in series (e.g., two wheel motors in the front and one transaxle in the rear or the other way around).

In some embodiments, the drive assembly may include additional, optional features, and/or the features described above may be modified or augmented. Some examples of modifications, optional features and augmentations are described below. It should be appreciated that the modifications, optional features and augmentations may each be added alone, or they may be added cumulatively in any desirable combination. In an example embodiment, the ECU may be configured to receive input parameters including an indication of pump speed and pump angle of the hydraulic pump, along with a steering angle of the vehicle. The ECU may also be configured to determine a swash flow through the bypass path based on the input parameters. In an example embodiment, the swash flow may be determined at least in part based on a swash curve stored by the ECU, the swash curve defining a ratio of flows through the first and second pairs of hydraulic motors based on the steering angle of the vehicle. In some cases, the swash curve may be customizable by an operator. For example, the ECU may be configured to receive an input selecting a scenario or driving situation and select a corresponding swash curve associated with the scenario or driving situation. In an example embodiment, the vehicle may include an articulated joint separating a first part of the vehicle at which the rear wheels are disposed from a second part of the vehicle at which the front wheels of the vehicle are disposed. In some cases, the vehicle may employ non-centered articulated steering. In an example embodiment, the bypass path may divert the swash flow around the second pair of hydraulic motors. In some cases, the first pair of hydraulic motors may be in parallel with each other, and the second pair of hydraulic motors may be in parallel with each other. Drive power may be provided to one the hydraulic motors in each of the first and second pairs of hydraulic motors. In an example embodiment, the vehicle may be a riding lawn mower.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe exemplary embodiments in the context of certain exemplary combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. In cases where advantages, benefits or solutions to problems are described herein, it should be appreciated that such advantages, benefits and/or solutions may be applicable to some example embodiments, but not necessarily all example embodiments. Thus, any advantages, benefits or solutions described herein should not be thought of as being critical, required or essential to all embodiments or to that which is claimed herein. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

THAT WHICH IS CLAIMED:

1. A drive assembly comprising: a power source; a hydraulic pump powered by the power source; a motor assembly comprising a plurality of hydraulic motors that are operably coupled to the hydraulic pump, the motor assembly including a first pair of hydraulic motors operably coupled to rear wheels of a vehicle associated with the drive assembly and a second pair of hydraulic motors operably coupled to front wheels of the vehicle; a proportional flow control valve configured to control a swash flow through a bypass path formed to enable part of a total flow exiting the hydraulic pump to bypass one of the first pair of hydraulic motors or the second pair of hydraulic motors; and an electronic control unit (ECU) configured to control a position of the proportional flow control valve to provide differential speed control between the first and second pairs of hydraulic motors.

2. The drive assembly of claim 1, wherein the ECU is configured to receive input parameters comprising an indication of pump speed and pump angle of the hydraulic pump, along with a steering angle of the vehicle, and wherein the ECU is configured to determine a swash flow through the bypass path based on the input parameters.

3. The drive assembly of claim 2, wherein the swash flow is determined at least in part based on a swash curve stored by the ECU, the swash curve defining a ratio of flows through the first and second pairs of hydraulic motors based on the steering angle of the vehicle.

4. The drive assembly of claim 3, wherein the swash curve is customizable by an operator.

5. The drive assembly of claim 4, wherein the ECU is configured to receive an input selecting a scenario or driving situation and select a corresponding swash curve associated with the scenario or driving situation.

6. The drive assembly of claim 1, wherein the vehicle comprises an articulated joint separating a first part of the vehicle at which the rear wheels are disposed from a second part of the vehicle at which the front wheels of the vehicle are disposed.

7. The drive assembly of claim 6, wherein the vehicle employs non-centered articulated steering.

8. The drive assembly of claim 1, wherein the bypass path diverts the swash flow around the second pair of hydraulic motors.

9. The drive assembly of claim 8, wherein the first pair of hydraulic motors are in parallel with each other, and the second pair of hydraulic motors are in parallel with each other, and wherein drive power is provided to one the hydraulic motors in each of the first and second pairs of hydraulic motors.

10. The drive assembly of claim 1, wherein the vehicle is a riding lawn mower.

11. A riding yard maintenance vehicle comprising: a frame to which front wheels and rear wheels of the riding yard maintenance vehicle are attachable; a steering assembly operably coupled to the front wheels or the rear wheels of the riding yard maintenance vehicle to provide steering inputs by an operator of the riding yard maintenance vehicle; and a drive assembly comprising a plurality of hydraulic motors and a proportional control valve controlled by an electronic control unit (ECU), the proportional control valve being configured to control a swash flow through a bypass path to enable differential speed control between the front wheels and the rear wheels based on the swash flow.

12. The riding yard maintenance vehicle of claim 11, wherein the drive assembly comprises: a power source; a hydraulic pump powered by the power source; and a motor assembly comprising the hydraulic motors, the hydraulic motors being operably coupled to the hydraulic pump, the motor assembly including a first pair of hydraulic motors operably coupled to the rear wheels and a second pair of hydraulic motors operably coupled to the front wheels, wherein the bypass path is formed to enable part of a total flow exiting the hydraulic pump to bypass one of the first pair of hydraulic motors or the second pair of hydraulic motors, and wherein the ECU configured to provide the differential speed control between the first and second pairs of hydraulic motors.

13. The riding yard maintenance vehicle of claim 12, wherein the ECU is configured to receive input parameters comprising an indication of pump speed and pump angle of the hydraulic pump, along with a steering angle of the vehicle, and wherein the ECU is configured to determine a swash flow through the bypass path based on the input parameters.

14. The riding yard maintenance vehicle of claim 13, wherein the swash flow is determined at least in part based on a swash curve stored by the ECU, the swash curve defining a ratio of flows through the first and second pairs of hydraulic motors based on the steering angle of the vehicle.

15. The riding yard maintenance vehicle of claim 14, wherein the swash curve is customizable by an operator.

16. The riding yard maintenance vehicle of claim 15, wherein the ECU is configured to receive an input selecting a scenario or driving situation and select a corresponding swash curve associated with the scenario or driving situation.

17. The riding yard maintenance vehicle of claim 11, further comprising an articulated joint separating a first part of the riding yard maintenance vehicle at which the rear wheels are disposed from a second part of the riding yard maintenance vehicle at which the front wheels are disposed.

18. The riding yard maintenance vehicle of claim 17, wherein the vehicle employs non-centered articulated steering.

19. The riding yard maintenance vehicle of claim 12, wherein the bypass path diverts the swash flow around the second pair of hydraulic motors.

20. The riding yard maintenance vehicle of claim 19, wherein the first pair of hydraulic motors are in parallel with each other, and the second pair of hydraulic motors are in parallel with each other, and wherein drive power is provided to one the hydraulic motors in each of the first and second pairs of hydraulic motors.