Hydraulic Motor Teardown and Study

Disclaimer

This study was conducted entirely in-house by ASI Engineering to demonstrate the capabilities of the xcPEP® platform. The product was independently procured by ASI. No proprietary or confidential information from any other party has been used. Results are not updated after publishing.

Introduction

Hydraulic motors are essential components in many heavy-duty applications, especially in off- highway vehicles like excavators, loaders, harvesters, and mining machines. These motors convert hydraulic pressure into mechanical energy, delivering torque and rotation to drive machinery.

What is a Hydraulic Motor?

A hydraulic motor is a mechanical actuator that converts hydraulic energy (fluid pressure and flow) into rotary mechanical energy (torque and rotation).

Types of Hydraulic Motors in Off-Highway Vehicles

Gear Motors (External and Internal)
Piston Motors (Axial and Radial)
Vane Motors
Gerotor/Geroler Motors

Product Used for Teardown Study

Type: Axial Piston Variable Motor
Used in: Excavators, loaders, skid steers, harvesters, and mining equipment.

Main Internal Components of Hydraulic Motor

Hydraulic Motor Housing

The housing encloses and protects all internal components from external contaminants and mechanical damage. It also provides structural support and acts as a reservoir for lubricating oil and return fluid.

Material: FG (Flake Graphite) Cast Iron

Cylinder Block

The cylinder block is a central rotating element that accommodates multiple axial pistons arranged in a circular configuration. It serves as the primary torque-transmitting member and interacts directly with the drive shaft to convert hydraulic energy into mechanical rotation or vice versa.

Material: Heat-Treated Steel

Axial Pistons

Pistons are precision-machined components that reciprocate axially within the cylinder block under the influence of hydraulic pressure. They perform the critical function of converting hydraulic energy into mechanical force and contribute to torque generation when acting upon the swash plate or rotating group.

Material: Hardened Steel.

Valve Control Housing

The valve plate is a stationary component that contains a series of ports and timing grooves designed to regulate the inflow and outflow of hydraulic fluid to and from the piston chambers. It ensures proper phasing of fluid distribution for efficient operation.

Material: FG (Flake Graphite) Cast Iron.

Drive Shaft

The drive shaft is mechanically coupled to the cylinder block and serves as the conduit for transmitting the mechanical load (in the case of a motor).

Material: Alloy Steel.

Bearings

Bearings support rotating elements such as the drive shaft and cylinder block, minimizing frictional losses and wear. They are critical to maintaining alignment and ensuring reliable, long-term performance under high load and speed conditions.

Types: Needle bearings, Ball bearings.

Working Principle – Hydraulic Motor

The bent-axis design separates the cylinder block and the drive shaft at an angle.
Pistons are arranged in a circle within a cylinder block.
As pressurized hydraulic fluid enters the motor, it pushes pistons, causing the cylinder block to rotate.
The angle between the shaft and cylinder block causes rotation of the shaft, producing torque.
The displacement is variable, meaning the swashplate angle can change, adjusting the output torque and speed.

Key Features of Hydraulic Motor

Variable displacement for flexible operation.
High pressure range (up to 450 bar continuous, 500 bar peak).
Bent-axis design for higher efficiency and power density.
Wide displacement range (28 to 1000 cm³).
Modular options for easy integration.
High-speed capability with optional flushing and boost pressure.

Applications of Hydraulic Motor

High Torque at Low Speed
Compact Size for Integration
Variable Displacement for Efficiency
Robust Design for Heavy-Duty Use
Reliable Performance in Harsh Environments

Bill of Material (BOM) of Hydraulic Motor

We conducted a detailed product teardown of the Rexroth hydraulic motor to study its internal components and system architecture. This teardown analysis involved examining data related to various part attributes, allowing for a comprehensive understanding of its design, construction, and operational functionality.

Following the hydraulic motor teardown, we developed a Multi-level BOM (Bill of Materials) structure, offering in-depth insights into the individual components.

The above image shows the Bill of Material of the Motor Casing of Hydraulic Motor in xcPEP software.

Manufacturing Category wise Weight vs Count Comparison

In the analysis of the components for a hydraulic motor assembly, it is critical to evaluate both the quantity and total weight of parts categorized by type. This data provides valuable insights into the design priorities and highlights the weight intensive contributors within the motor structure.

Weight vs. Quantity Insights:

The Casting category dominates the total weight at 25,130 g, despite comprising only 5 components, suggesting these are the primary structural elements of the hydraulic motor.
Fasteners are the most numerous, with 76 items, but their combined weight is only 1,331 g, indicating that they are small but essential for assembly integrity.

Category-specific Observations:

Forging components contribute 4,904 g across 12 items, likely representing key load-bearing or high-strength parts within the motor.
Bought-out Parts, though limited to just 3 items, weigh in at 3,226 g, suggesting the inclusion of dense or precision-engineered elements sourced externally.
Fabrication accounts for 711 g from 16 components, probably supporting structures or brackets in the motor.
Mouldings make up the smallest weight segment (90 g) across 10 items, possibly representing non-load bearing or insulation parts.

Hydraulic Motor Weight Pareto Analysis

As part of a detailed teardown, Bill of Materials (BOM), and should costing study of a hydraulic motor, we performed a comprehensive bill of material exercise to identify weight contributors across the assembly. The resulting Weight Pareto Analysis reveals that a small number of components contribute to a majority of the total weight, helping prioritize cost optimization efforts and alternative material evaluations. This chart forms a critical input for design-to-cost initiatives in off highway and industrial hydraulic applications.

Key Insights from the Weight Pareto Analysis:

The top 3 components—Motor Casing, Valve Control Housing, and Drive Shaft—contribute over
60% of the total assembly weight.
Drive Shaft and Cylinder Block, though smaller in number, are significant contributors and should be evaluated for alternate materials or hollow designs without compromising torque transmission.
Beyond the top 20 parts, over 100 components each contribute less than 0.5% to total weight—these include fasteners, dowel pins, springs, and seals, which have minimal impact on total mass but can influence part count and assembly time.

Should Costing of Hydraulic Motor

We have conducted a last-level teardown of the hydraulic motor, and the following are key outcomes from the study. In the costing analysis, data related to various part attributes were mapped and analysed to gain a detailed understanding of the entire hydraulic motor assembly.

Should Cost Drivers of Hydraulic Motor

A Comprehensive teardown, Bill of Material and Should Costing analysis of the hydraulic motor was carried out, resulting in a calculated manufacturing cost of INR 27,550.42. The following considerations were factored into the study:

The hydraulic motor is manufactured in Bengaluru, India
The production volume considered for the analysis was 2,500 units annually
The latest material rates and values required for MHR (Machine Hour Rate) calculations were based on Q4 FY24–25 data.

The above image shows the should-cost of the Motor Casing of Hydraulic Motor in xcPEP software.

Manufacturing Category wise Should Costing of Hydraulic Motor

In the teardown analysis of hydraulic motor components, it’s essential to examine not only the quantity of parts but also their corresponding should cost. This breakdown helps identify cost-intensive elements and guides value engineering efforts across manufacturing categories.

Cost vs. Quantity Insights:

The Bought-out Parts category contributes the highest total cost at ₹7,077, despite comprising only 3 components, indicating high-value, possibly precision or proprietary items sourced externally

Category-specific Observations:

Casting components account for a significant cost of ₹6,061 from just 5 items, suggesting they are major structural or machined parts within the hydraulic motor.
Fasteners are the most numerous, with 76 pieces, but their total cost is only ₹366, highlighting their low unit price yet essential role in assembly.
Forging components cost ₹1,486 across 12 items, indicating parts that are strength-critical or shaped for specific load-bearing functions.
Fabrication involves 16 parts at a total cost of ₹210, likely comprising minor brackets, supports, or non-complex welded structures.
Moulding parts have the lowest cost contribution at ₹155 for 10 items, potentially representing insulation covers or non-structural elements.