Traction Control Using HTD10-40
Torque Divider
March, 2015
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HTD10-40
This 4-way 2-position valve halves the inlet pressure to balance torque between
series motors in a drive circuit.
Overview
Controlling traction in propel applications can be a slippery problem. Parallel circuits can send all your flow to a spinning wheel. Series circuits can lead to wheel scuffing or damaging cavitation.

Traditional solutions to this problem fall into two categories: inefficient and expensive.

The inefficient solutions use an orificed leak path between the wheel motors to allow the outside motors additional flow when cornering. This solution can allow unwanted slippage when traveling on slick terrain.
The expensive solutions involve sensors to determine when the flow needs of each wheel are different, valving to regulate the flow, and controllers to process the information. Not all applications can afford the added cost.

Applications such as turf care machines are particularly sensitive to wheel scuffing. Ice surfacing machines are highly susceptible to slippage. And there are non-propel applications where torque must be evenly distributed between motors in series.
steering geometry
Basic steering geometry: cornering vehicles must spin outside wheels faster.

Traditional Solutions
Series Circuits
We all know that oil in a hydraulic circuit follows the path of least resistance. In terms of traction control, this presents the need to equalize flow to multiple motors. Placing them in series is the easiest way to ensure they all receive the same flow.

Series circuits have some limitations, however: the first being that pressure is additive in a series circuit. The pressure available to the system must be shared by all motors in series. Motors in a series circuit must also be able to accommodate back pressure.
series circuit
Flow in series circuit is equal,
pressure is additive
The second limitation of series motor circuits is that flow through all motors is equal. Cornering vehicles need to spin the outside wheels faster than the inside ones. Failing to accommodate this fact leads to outside wheels scuffing the surface or worse, cavitating your motors.
Make-up Checks
Make-up checks can alleviate cavitation, but all the pressure is dropped by the first motor. The downstream wheel provides no tractive effort: it’s just along for the ride.
Makeup check
Makeup check allows extra flow (at charge pressure) to the second motor
Parallel Circuits
Parallel circuits require flow divider(s) to ensure all wheels spin, not just the one with no traction. This configuration has the same limitation: the outside motors require more flow when the vehicle turns. Flow dividers can be a strain on the system (pressure drop) in low speed conditions: a big disadvantage for machines with a creep mode.




Slip and Slop
A slip orifice allowing limited bypass from left to right solves the problem, but inefficiently. It can lead to unwanted wheel slip if one wheel loses traction: a problem made worse at very low speeds.
flow divider/combiner
Flow divider/combiner equalizes
flow to both motors

slip orifice
Slip orifice allows limited bypass
Bypass Valve/Differential Lock
A bypass valve or differential lock allows flow to bypass when cornering, but closes when driving straight. This requires some switching to close and open the valve at the appropriate time.
diff-lock
Diff-lock blocks flow through
slip orifice when activated
Steering Angle Feedback
The ideal system bypasses flow as needed while maintaining pressure. A system with a steering angle sensor and a proportional flow control can achieve this with the penalty of cost and complexity.





The Worst of Both Worlds
Cost-sensitive applications typically favor the sloppy solution. For some vehicles, operating in low-traction environments such as driving on ice, a little slip becomes a big problem.
steering angle
Steering angle bypass allows flow
proportional to steering angle. Supporting sensors and electronics are required.

The Torque Divider
HydraForce has a better option: the HTD10-40 torque divider. This unique valve lets you size your traction control system for performance in the curves and down the straightaways; without adding oversized components and complex electronics.

It’s a Pressure Control
Looking at traction control as a pressure control problem instead of a flow control problem led our application engineers to the solution. What is needed is a solution that allows necessary bypass without unwanted pressure drop.

The HTD10-40 does just that. It can bypass flow around either of two series motors without shunting. The internal pressure divider directs the balancing act. The flow through the valve is only the differential flow the cornering vehicle requires.
HTD10-40_valve

Operation
The HTD10-40 is a pressure reducing/relieving valve that adjusts its setting to half the pressure across 2 and 4. It allows flow from 3 to 4 or 2 to 3 as needed to balance the spool. The spool is balanced when pressure at 3 is half the pressure across 2 and 4.
Symbol
HTD10-40_symbol
Performance

HTD10-40_perf-chart
Application
Applied between two series motors, the valve balances the pressure drop across each motor. This achieves efficient torque division regardless of differing motor speeds. The valve is sized to accommodate the flow difference between the two motors.

Four Wheel Series-Parallel Drive Circuit with HTD10-40 Torque Dividers
series-parallel-drive_circuit


The series-parallel circuit is common in four-wheel drive applications: dividing the circuit into two parallel paths with series flow to opposite wheels. The two HTD10-40 torque dividers either divert or supply flow to the center point between the series motors while balancing the pressure to both. They are sized to accommodate the flow difference only. This approach requires no large flow dividers with associated pressure drop/heat buildup. Some extreme low-traction applications benefit from small flow regulators inline with the torque dividers.

The HTD10-40 is useful in any application where series motors require some limited variation in speed such as auger and conveyor/spinner, sweepers/brooms, drill motors in series, etc. New applications are popping up all the time.

Power Savings
Comparing two systems: one with traditional flow dividers, one using HydraForce HTD10-40 torque dividers, we can show a power savings of 3.3 kW at full system flow (100 lpm).

The traditional system achieves traction control by dividing the flow equally among all motors. Fluid passing through a flow divider exhibits a pressure drop that is converted to heat in the system. This pressure drop increases with flow.

HTD10-40_pressure-drop_chart
The system using torque dividers achieves traction control by dividing the pressure equally to all motors. Fluid only passes through the torque dividers when the wheels must turn at different speeds during cornering. Keeping all wheels at equal pressure ensures balanced torque without the losses and heat generation that flow controls exhibit.
Flow Divider Circuit

flow-divider_circuit
Torque Divider Circuit

torque-divider_circuit
Traction Performance
Both systems solve the primary traction control problem: flow favoring the wheel with the lowest traction. In the flow divider system, flow is equalized to all motors, but pressure (torque) can vary from wheel to wheel. The torque divider system outperforms the flow dividers because pressure is controlled, ensuring all wheels share the load (torque) of moving the vehicle forward.
Benefits
This is a new solution to an old problem. The benefits that make HTD10-40 the right choice for most applications are these:
All hydraulic solution—no sensors or controllers
No electronic development or fine-tuning
Simplified circuit—easy service and troubleshooting
Optimized flow rating—sized for the differiential only
Good in low-traction applications
Great for cost-sensitive applications—low valve count
Contact your HydraForce application engineer or technical service representative for information or application assistance with the HTD10-40 torque divider.

See catalog page
HTD10-40

Disclaimer: Nothing in this document constitutes an implied warranty of merchantability or of fitness for a particular purpose. The information contained in this document is provided for technical illustration purposes only and may not be used as a statement of suitability for use in any particular application. Each application is unique and prospective purchasers should conduct their own tests and studies to determine the fitness of HydraForce's products for their particular purposes and specific applications.