GB2429048A

GB2429048A - Series parallel switchable fluid drive adjusts transmission ratio

Info

Publication number: GB2429048A
Application number: GB0516408A
Authority: GB
Inventors: Allan Keith Jackson
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-08-10
Filing date: 2005-08-10
Publication date: 2007-02-14
Also published as: GB0516408D0

Abstract

A vehicle drive arrangement has a single pump 2, two front wheel motors 14, 15 and two rear wheel motors 12, 13. The motors 12-15 can all be connected in parallel to give a low speed - high tractive effort range. They can be switched by control valve 5, during travel, to a high speed - low tractive effort range (figure 2) in which front 14, 15 and rear 12, 13 parallel pairs of motors are connected in series, thus doubling the vehicle speed for the same pump output. Flow dividing valve 16 can optionally be activated, to divide flow equally between left and right wheels, to ensure opposite wheels rotate at the same speed regardless of tractive effort produced.

Description

Fluid drive system for vehicles This invention relates to a fluid circuit

for providing a drive system for vehicles with variable speed and tractive effort using one variable output pump.

Conventional mechanical drive systems, using various combinations of mechanical linkages, gearbox, variable belt drive, shafts, rods and other standard automotive linkages, are traditionally used to provide power for vehicles. However, these moving-part systems are prone to physical damage, for example from common environmental contaminants, such as mud, sticks and small stones. This results in the need for maintenance to renew, repair or replace parts of the system.

The proposed invention's fluid system does not have external moving parts to be damaged by mud and sticks etc. thereby prolonging the service life of the vehicle.

Conventional fluid drives do exist. These can be combined with mechanical components such as shafts or rods, as described in the paragraph above, and have the same physical problems. Conventional fluid drives can be used to provide power directly, however, these drive circuits have a narrow range of tractive effort and speed. When using one variable output pump, existing fluid drive circuits require a choice to be made when selecting the range through which the circuit can be varied.

This choice is between a range with high tractive effort and low speed or a range with lower tractive effort and higher speed, this is then fixed. This is restrictive for applications which require the ability to provide both high tractive effort and high speed, though not necessarily at the same time.

To overcome the restrictive nature of existing fluid drive circuits this invention proposes a new fluid drive circuit which allows the tractive effortlspeed range to be altered easily. The circuit incorporates infinitely variable speed in set ranges to provide different speed/tractive effort ratios, the range can be changed during travel.

For example, starting in a high tractive effort, low speed range to accelerate but maintain tractive effort to climb a hill, switching to a lower tractive effort but higher speed range once back on the level to accelerate to a higher speed. The range can be switched using a simple hand lever, foot pedal, handle bar grip, remote electronic device or other standard control interface. The speed/tractive effort output of the system, within a set range, can also be altered using a variable output fluid pump which can be controlled by a simple hand lever, foot pedal, handle bar grip, remote electronic device or other standard control interface.

Conventional drive systems, both mechanical and fluid based suffer from wheel spin'. In a mechanical system, an axle pair, using a mechanical differential will suffer a loss of traction if one of the pair of wheels looses contact with the ground. The free wheel will spin, whilst the wheel on the ground does not move. In a fluid based system a similar loss of traction can occur due to the hydraulic circuit used.

The fluid circuit in the invention provides a proportional lock which ensures that the fluid is divided equally to each wheel using a gear or orbital flow divider which divides the flow by volume not pressure, this ensures both wheels maintain traction irrespective of the load applied, for example avoiding wheel spin on uneven ground.

2 of 5 In normal driving mode the circuit allows differential movement to ease steering, for example, when driving on a road. The proportional lock can be engaged on demand to assist with traction control, for example, when driving on uneven ground.

The invention operates in both forward and reverse directions.

The invention will now be described solely by way of example, with reference to the following accompanying drawings: Figure 1 Illustrates the fluid flow in forward direction with 4 wheel powered drive.

Figure 2 Illustrates the flow of fluid in forward direction with 2 wheel powered drive.

Figure 3 Illustrates the proportional lock system for each axle in forward direction on the rear axle.

Example 1: Fluid flow in the forward direction providing the maximum tractive effort range.

To provide maximum tractive effort the full fluid pressure is supplied to all the wheel motors, giving the vehicle the maximum tractive effort. In figure 1, the power source [I] drives a variable output pump [2] with the outlet of fluid at [3] split at tee junction [4]. The fluid then flows to both valve [5] port E and to valve [6]. From valve [6] the fluid flows to both rear wheel motors [12] and [13]. The return fluid from the rear wheel motors [12] and [13] combine at tee junction [11] and then flow to valve [5] at port B and out of valve [5] at port F. Fluid entering valve [5] at port E exits valve [5] at port A and flows to valve [7] and then to both the front wheel motors [14] and [15]. The return fluid from the front wheel motors [14] and [15] combine at tee junction [8] this then flows to tee junction [9].

The return flow from all four wheel motors combine at tee junction [9] and return to the pump [2] at inlet [10].

The vehicle speed is varied by altering the output of the variable output pump [2] using a standard control interface.

Parts Descriptions:

Pump [2] - variable output pump Valve [5] - spool valve Valve [6] - spool valve Valve [7] - spool valve Valve [16] - gear flow divider valve Example 2: Fluid flow in the forward direction providing lower tractive effort with increased speed.

To provide a range with increased speed, the full fluid pressure is supplied only to the rear wheels, this halves the tractive effort but doubles the forward speed. The return fluid from the rear wheel motors is fed through the front wheel motors to allow them to turn and keep cool.

3 of 5 In figure 2, the power source [I] drives a variable output pump [2] with the outlet of fluid at [3] flowing to tee junction [4]. The fluid from tee junction [4] is blocked at valve [5] port E, so all the pump output has to flow to valve [6]. From valve [6] the fluid flows to both rear wheel motors [12] and [13].

The return fluid from the rear wheel motors [12] and [13] combine at tee junction [11] and flows in to valve [5] at port B. The fluid flows through valve [5] in at port B and out at port D. The flow is then returned to valve [5], in at port C and out at port A. The flow then continues to valve [7] and both the front wheel motors [14] and [15].

The return fluid from the front wheel motors [14] and [15] combines at tee junction [8] and flows to tee junction [9] and flows back to the pump [2] at inlet [10].

Example 3: Proportional lock The combination of valves used provides a differential lock system for each axle, this is demonstrated using a description in forward direction on the rear axle.

In figure 3, the drive fluid from pump [2] directed towards valve [6] to power the rear wheels. The controls are adjusted to block the flow at valve [6] this forces the fluid to flow to valve [16] at port G. Equal volumes of fluid flow from valve [16] at ports H and J to tee junctions [17] and [18], and wheel motors [12] and [13] respectively. This ensures both rear wheel motors [12] and [13] turn at the same speed irrespective of tractive effort been produced.

Claims

4 of 5 CLAIMS

1. A fluid drive circuit used to power a vehicle, which allows the speed/tractive effort range to be altered easily during operation.

2. The circuit according to claim I allows the speed to be varied within the defined range.

3. The circuit according to claim 1, the speed/tractive effort range can be changed during travel.

4. The circuit according to claim, 1 incorporates a gear or orbital flow divider, which divides the flow by volume not pressure to ensure that both wheels maintain traction irrespective of the load applied.

5. According to claim 4, the flow divider is operated on demand to allow activation of this feature or not.

6. The circuit according to claim I uses a single variable output pump.

7. The circuit according to claim 1 will operate in both forward and reverse directions.

8. According to claim 3, the speed/tractive effort range can be changed using a simple hand lever, foot pedal, handle bar grip, remote electronic device or other control interface.

9. According to claim 2, the speed/tractjve effort output of the system, within the defined range, can be altered using a variable output fluid pump which can be controlled by a simple hand lever, foot pedal, handle bar grip, remote electronic device or other control interface.